Is RV Solar Affordable? 3 Solar Solutions for RVs and Boats

Is RV solar power affordable or is installing a solar power system on a motorhome or trailer — or even on a sailboat — just too darn expensive to be cost effective? We never thought this question would be hard to answer untpil recently.

This article describes everything you need to install a solar power system on your RV in three different levels:

1. A Small, Expandable Rooftop Solar Power Solution
2. A Portable Solar Power Solution
3. A Big Rooftop Solar Power Solution

Solar panels on a fifth wheel trailer

Can a solar power installation on an RV or sailboat pay for itself?

Ever since we installed our first (very small) solar power system on our first full-time RV nearly ten years ago, we’ve been excitedly telling people it is a very affordable do-it-yourself project for anyone with some mechanical and electrical knowledge. And for those who can’t turn a wrench, it shouldn’t be that much more.

Our first 130 watt solar power system cost us about twice as much as the same system would today, but even at that high price, we felt it was dollar-for-dollar an equal value to buying a Yamaha or Honda 1000 generator. Best of all, once a little system like that was installed, it was a whole lot less noisy, expensive to operate and complicated to use than a generator would be.

At today’s super cheap solar prices, that little solar power system is even more valuable compared to one of those nice Japanese portable gas generators than it was 10 years ago!

Installing solar panels on a motorhome RV

Installing solar power can be a DIY project if you’re handy.

Recently, however, we’ve heard some crazy prices being quoted for installing solar power systems on RVs. We met one couple with a gorgeous brand new DRV Suites fifth wheel who were quoted $13,000 for a solar power installation. Not long after that, we read an article in a popular RV magazine describing a $12,000 solar power installation on a fifth wheel.

Yikes!! These are outrageous prices!!

We sure hope no one is finding they have to spend that kind of crazy money to get a solar power system installed on their trailer or motorhome or sailboat.

We’ve got oodles of articles on this website that go into the nitty gritty details of things to consider when designing and installing a solar power system on an RV or a boat (located HERE). However, all that theory aside, it’s not all that complicated.

Here are three solar power “packages” — with approximate prices — that will do the trick whether you’re a part-timer or full-time RVer.

Although it is possible to buy “pre-packaged RV solar power kits” online, we suggest hand selecting the components you want so that just in case any individual item has a problem it can be returned easily.

We’ve heard of cases where people bought a pre-packaged solar power kit online and then had problems returning a broken part because they had to return the entire kit — solar panels, charge controller, cables and all — just because the one item wasn’t working right.

 

SMALL ROOFTOP RV SOLAR POWER SYSTEM – 150 WATT SYSTEM

Affordable solar panel with a popup tent trailer

For part-time RVers, installing solar on the roof isn’t a requirement.

The following is essentially what we put on our roof and what we camped with off the grid every night for a year when we started.

The brands are not exactly the same, but these components are highly rated and will do the trick for anyone that wants a roof-mounted solar power system on their motorhome or trailer.

This kit includes both a solar battery charging component and an 110 volt AC power component provided by an inverter. If you don’t understand the distinction, please see our post: RV Solar Power Made Simple.

The simplest inverter installation is to connect the inverter to the batteries using heavy duty cables and then to run an ordinary (but long) power strip (or two) from the inverter to somewhere convenient inside the rig.

Rather than using the wall outlets in the rig, just plug the AC appliances into the power strip as needed, taking care not to operate too many things at once and overload the inverter.

Prices always change, so check the links to see the current prices.

The nice thing about this kit is that it is easily expandable. If a second or third solar panel is eventually desired (to double or triple the size of the system to 300 or 450 watts, for another $200 or $400), those panels can be purchased at a later date. At that point the solar charge controller can also be replaced with a bigger and more sophisticated charge controller (for $600).

 

PORTABLE FOLDING SOLAR POWER KIT SUITCASE – 120 WATT SYSTEM

Portable folding solar panel suitcase for RV and motorhome use

A portable solar power kit that folds up and can be carried like a suitcase is an awesome solution for weekenders, vacationers and seasonal RVers.

A really nifty alternative for anyone that isn’t super skilled with tools or that’s a bit spooked by electrical things, is a portable solar power kit that folds into a suitcase. These come with two matching solar panels, battery cables with alligator clips, and a panel-mounted solar charge controller. The solar panels are hinged together and can be folded towards each other. A handle on the side of one of them makes the whole thing easy to carry and store like a suitcase.

These portable folding suitcase solar panel kits come in all sizes. A good size is anywhere from 120 to 200 watts:

The advantage of a portable suitcase solar kit like this is that it is self-contained. If you think you might upgrade to a different RV soon, then there’s no loss in investment when one RV is sold and another is purchased. Also, if you decide to install a roof-mounted system at a later date, the suitcase solar panel kit can be sold to another RVer.

As for the inverter, heavy duty cables and power strip, they are included here just to round out the package so you have AC power in the rig as well as the ability to charge the batteries just like the “small solar power kit” described above.

 

Affordable solar power on a motorhome

Installing solar panels on tilting brackets is popular, but only necessary in mid-winter. We’ve never done it.

With a big RV solar power installation, it is likely that the RV’s house battery bank will need to be upgraded or replaced too, so this package includes a “replacement” AGM battery bank.

The Magnum inverter is an inverter/charger that has a built in transfer switch, making it very straight forward to wire the inverter into the house AC wiring system so you can use the standard wall outlets in the rig rather than plugging things into a power strip.

We’ve been living exclusively on solar power since we started this crazy traveling lifestyle in 2007, and this system is larger than any system we’ve ever had on a boat or trailer. So it ought to work just fine for anyone who wants to RV full-time and do a lot of boondocking.

 

INSTALLATION COSTS

If you are not a DIY RVer, you’ll need to budget for the installation labor too. As a very rough estimate, I would allow for $500-$1,000 for a small system installation and $1,500-$2,500 for a big system installation. The variations in labor costs will depend on how difficult it is to work in your rig, how hard it is to mount the various components and run the wires from roof to basement, and whether or not you choose to have the batteries upgraded or replaced.

 

RETURN ON INVESTMENT

RV park and campground prices are all over the map, but assuming that the average cost is $25 per night for a site with hookups if you don’t take advantage of monthly discounts or $15 per night if you do, these systems can pay for themselves in anywhere from 18 camping days to 14 months, depending on what size system you buy, whether or not you do the installation yourself, and how you typically camp. Of course, this assumes the rig is equipped with a refrigerator that can run on propane and that if air conditioning is needed an alternative power source like a generator is used.

As with everything in the RVing world, starting small and cheap is the best way to go.

 

BIG and COMPLEX SOLAR POWER INSTALLATIONS

Solar panel arch with solar panels on sailboat transom

Installing solar power on a sailboat has its own set of challenges.

We have installed three different RV solar power systems and one solar power system on a sailboat.

We published an article in the February 2017 issue of Cruising World Magazine (one of the top magazines in the sailing industry) describing the solar power system we installed on our sailboat Groovy back in 2010. This system gave us all the power we needed to “anchor out” in bays and coves away from electrical hookups in marinas for 750 nights during our cruise of Mexico.

Cruising World has posted the article online here:

Sunny Disposition – Adding Solar Power – Cruising World Magazine, February, 2017

Installing solar power on a sailboat is very similar to installing it in an RV, but there is an added complexity because there isn’t a big flat roof to lay the panels on. Instead, we had to construct a stainless steel arch to support the panels. Fortunately, our boat, a 2008 Hunter 44DS, had a factory installed stainless steel arch over the cockpit already. So, we hired a brilliant Mexican metal fabricator named Alejandro Ulloa, to create our solar panel arch in Ensenada, Mexico.

Solar power installation on sailboat Hunter 44

We turned to Alejandro Ulloa of Ensenada, Mexico, for our solar panel arch
He can be contracted the=rough Baja Naval.

Solar panel arch installation on Hunter 44 sailboat

Alejandro is an artist. He wrapped the arch in plastic to prevent scratches until it was permanently mounted on our boat!

Solar panel arch on sailboat Hunter 44

The arch went back to Alejandro’s workshop for tweaking after this measuring session.

Solar panel arch on sailboat Hunter 44 installed by Alejandro Ulloa

Dimensions now perfect, Alejandro mounts the arch permanently.

Getting the 185 watt 24 volt solar panels up onto the arch was a challenge. Getting solar panels up onto an RV roof is tricky too!

Affordable marine Solar panel installation on sailboat Hunter 44

Getting the solar panels onto the roof of an RV or up onto this arch takes two people (at least!)

Installing solar panels on an arch on sailboat (Hunter 44) with Alejandro Ulloa Baja Naval Ensenada Mexico

The second of the three panels gets installed.

The solar panel arch was going to double as a “dinghy davit” system with telescoping rods that extended out over the transom. These davits supported a pulley system to hoist the dinghy up out of the water. So once the solar panels were mounted on the arch, we had to be sure it could handle the weight of the dinghy.

Our dinghy weighed a lot less than the combined weight of Mark and Alejandro!

Strong solar panel arch and dinghy davit extension

Alejandro and Mark test the arch to be sure it can support the dinghy (which weighed half what they do).

The solar panels were wired in parallel because they would be subjected to shade constantly shifting on and off the panels at certain times of the day as the boat swung at anchor.

Wiring solar panels on a sailboat (Hunter 44) marine solar power installation

Mark wires up the panels in parallel.

Affordable solar panel installation on a sailboat

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Solar panel arch with dinghy davit extension supporting affordable solar power on sailboat

A beautiful, clean installation with wire loom covering the exposed cabling and the rest snaked down inside the tubes of the Hunter arch. The davit extensions for hoisting the dinghy are clearly visible under the panels.

Solar panels installed on arch on Hunter 44 sailboat

Nice!

Down below the cockpit inside a huge locker in the transom, Mark mounted a combiner box that brought three cables in from the three panels and then sent out one cable to the solar charge controller.

Emily and Mark Fagan aboard sailboat Groovy

The transom locker in our Hunter 44DS sailboat was very large!

Combiner box for solar panel parallel wiring on a sailboat

A combiner box brings the wires from the three panels together before a single run goes to the solar charge controller (this is optional and not at all necessary).

The solar charge controller was installed in the cabin inside a hanging locker in the master stateroom.

Xantrex solar charge controller installed in sailboat locker

We have an Outback FlexMax charge controller on our trailer but chose a Xantrex controller for our boat because there were no moving parts. We compare the two HERE.

The solar charge controller was located about 8 feet from the near end of the battery bank which spanned a ~14 foot distance under the floorboards in the bilge.

Two 4D AGM batteries in bilge of sailboat

We had four 160 amp-hour 4D AGM batteries for the house bank and a Group 27 AGM start battery installed under the floorboards in the bilge.
One 4D house battery and the Group 27 start battery are seen here

This 555 watt solar power system, which charged a 640 amp-hour house bank of 4D AGM batteries, supplied all of our electrical needs, including powering our under-counter electric refrigerator.

Usually our engine alternator provided backup battery charging whenever we ran the engine. However, at one point our alternator died, and we were without it for 10 straight weeks while we waited for a replacement alternator.

Why such a long wait for a simple replacement part? Getting boat parts in Mexico requires either paying exorbitant shipping fees and import taxes or waiting for a friend to bring the part with them in their backpack when they fly from the US to Mexico.

During that long wait our solar power system supplied all our electricity without a backup while we were anchored in a beautiful bay. Diesel engines don’t require an alternator to run, so we moved the boat around and went sailing etc., and lived our normal lives during our wait.

Solar panel arch and dinghy davit extension with solar panels installed on sailboat

View from the water — cool!

The dinghy davit extensions on the solar panel arch made it easy to raise and lower the dinghy from the water and also to raise and lower the 6 horsepower outboard engine.

Solar panel arch and dinghy davit extension on sailboat

A pulley system on the davit extensions made hoisting the outboard and dinghy a cinch for either of us to do singlehandedly.

Solar panel arch and solar panels on sailboat transom

For 7 months we left our boat at the dock in Chiapas, unplugged from shorepower, and let the solar panels keep the batteries topped off. Everyday during that time they put 19 amp-hours into the batteries which was essentially the power required to operate the solar charge controller!

At anchor, sometimes the solar panels were in full sun all day long if the current and wind and the pattern of the sun crossing the sky allowed the boat to move around without the sun coming forward of the beam of the boat.

However, whenever the sun was forward of the beam, the shadow of the mast and the radome fell on the panels. We could watch the current production from the panels go from full on, to two-thirds, to one-third and back again as the shadow crossed one panel and then two at once, and then one and then none, etc, as the boat swung back and forth at anchor.

Mast and radome cast shade on solar panels on sailboat

RV solar installations have to avoid shade from air conditions and open vent hatches.
On boats the shade from the mast and radome is often unavoidable.

Mast and radome cast shade on pair of sailboat solar panels

When the shadow fell across two 185 watt panels at once, it knocked both of them out of the system so only one of the three solar panels was actually producing power.

The coolest and most unexpected benefit of having our solar panels mounted on an arch over the cockpit was the shade that they provided. The sun in Mexico is very intense, especially out on the water, and it was wonderful to have two huge forward facing jump seats at the back of the cockpit that fully shade as we sailed!

Under the shade of solar panels and a solar panel arch on a sailboat

Made in the shade — What a life that was!!

We have more solar power related articles at these links:

SOLAR POWER OVERVIEW and TUTORIAL

BATTERIES and BATTERY CHARGING SYSTEMS

LIVING ON 12 VOLTS

Our technical articles in Cruising World magazine can be found here:

Do We Miss Our Boat “Groovy” and Sailing?

We describe our thrilling — and heart wrenching — first and last days on our wonderful sailboat in the following posts. It is very true that the happiest days of a boater’s life are the day the boat is bought and the day it’s sold!

Our most recent posts:

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RV Solar Panels – Flexible or Rigid? 12 or 24 volt? Mono or Poly? Yikes!

There are a lot of decisions to make when you install solar panels on an RV or boat. Some of the most basic are: what size solar panels to buy, whether to go with flexible solar panels or aluminum framed rigid panels, whether the solar cells should be monocrystalline or polycrystalline, and whether to install nominal 12 volt or 24 volt panels.

We have done several RV and marine solar panel installations, and we have used not only 12 volt and 24 volt panels of various sizes but we have also used both aluminum framed rigid solar panels and the newer semi-flexible solar panels. We have also worked with both monocrystalline and polycrystalline solar panels. This article outlines the pros and cons of the various types and sizes of solar panels and offers some things to think about when you are deciding which solar panels to buy for your RV or boat.

RV solar panel selection

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Our article RV Solar Power Made Simple explains how to determine the overall wattage for an RV solar power installation. In general, a weekend / vacation RV can get by with 200 watts or less while a full-time solar power system is best with 500 watts or more.

SOLAR PANEL SIZE and PLACEMENT

Once you decide on overall capacity for your solar panel array, the next thing to think about is solar panel placement and wiring. The panels should be a matched set of identical or nearly identical panels. If you have a lot of real estate on the RV roof, then you can get a few big panels. If you have a truck camper or your RV roof is cluttered with a lot of things on it already (hatches, vents, antennas, etc.), then you may need to go with smaller panels that can be squeezed in and around everything else.

Solar panel installation on a ffith wheel RV

Our fifth wheel trailer is powered by four 120 & 130 watt 12 volt rigid polycrystalline solar panels wired in series

WHAT VOLTAGE IS THAT SOLAR PANEL?

Solar panels are constructed internally with DC wiring, and they are sized to work on 12 or 24 volt circuits. So, they are commonly referred to as 12 or 24 volt solar panels. What’s confusing is that while the nominal voltage of a solar panel may be 12 or 24 volts, the open circuit voltage is higher. So, for a nominal 12 volt solar panel that is 100 watts, the open circuit voltage (“Voc“) will be 17 or 18 volts. Likewise, for a nominal 24 volt panel, the Voc will be 34 to 36 volts.

Also, smaller solar panels (both physically and in terms of watts) are typically nominal 12 volt panels while larger panels are typically 24 volts. Solar panels under about 150 watts in size are usually 12 volt panels. Solar panels over about 150 watts are usually 24 volt panels.

Solar panel installation on a sailboat

For nearly four years, we sailed our boat on Mexico’s coast relying on three 185 watt 24 volt
polycrystalline rigid solar panels, wired in parallel, for all our electrical needs.

Solar panels work best when they are a matched set. The electrical characteristics of all the solar panels in the array need to be very similar, preferably identical. When upgrading a solar power array this can make things complicated as you try to mix and match old small panels with new big ones.

One technique for upgrading is to wire two 12 volt solar panels in series to work on a 24 volt circuit. For instance, if you have two 100 watt 12 volt panels and you are buying a 200 watt 24 volt panel, you can wire the two 100 watt panels in series and then wire that pair in parallel with the new 200 watt solar panel.

This will work as long as the electrical characteristics of the pair of solar panels in series match the electrical characteristics of the single panel that is wired in parallel with them.

THE EFFECT OF SHADE ON SOLAR PANELS

Shade is the biggest enemy of any solar power installation. Unbelievable as it seems, a tiny bit of shade will effectively shut down a solar panel. The impact is dramatic: a few square inches of shade can drop a solar panels current production down from 8 amps to 2 amps. A few more square inches of shade can drop the current production to 0.

Before deciding on the size of the panels, it is worthwhile to take some time to study the various things that might cast shade across them once they are in place. A closed hatch may cause little shade, but when it is open on a hot day, depending on where the sun is in the sky, it might cast a big shadow across a nearby solar panel. Satellite dishes, air conditioners and even holding tank vents can cast sizable shadows as well.

We put a book in one corner of a 120 watt 12 volt panel and discovered that even though it was a small percentage of the surface area of the panel, that 8.5″ x 11″ book was enough to knock down the current production of a 120 watt solar panel by 80%. Rather than producing 7 amps, it produced a measly 1.4 amps. Egads!

Shade on one corner of solar panel

Just 8.5″ x 11″ of shade from this book reduced current production by 80%!

Similarly, shade wreaked havoc on our three185 watt 24 volt panels on our sailboat. The shade from our mast traveled across the panels as the boat swung at anchor, and the current production dropped by 1/3 and then by 2/3 as the shade first crossed one of the three panels and then straddled two of them. It did this over and over, with the current rising and falling repeatedly, as the boat slowly swung back and forth at anchor.

Effect of shade on solar panels installed on sailboat

A line of shade from the mast on our sailboat reduced our solar panel array to 65% and then 35% of its capacity as it traveled across the panels and occasionally straddled two of them.

Shade is a huge concern in the solar power industry, and there are several white papers (here’e one) about the impact of shade on commercial solar panel installations. The gist is the importance of spacing the rows of commercial solar panel arrays in such a way that one row of panels doesn’t accidentally shade the bottom inch or so of the next row behind it when the sun is low in the sky.

If it does, the second row of panels shuts down. If there are rows and rows of solar panels spaced like this, none of the panels except the ones in the first row can function until the sun rises a little higher in the sky.

Solar panels are most sensitive to shade along the longest part of the panel, so in the case of our sailboat, when the sun was over our bow, the mast would shade the panels in a strip that had a maximum impact on current production (as you can see in the above photo)!

For RVers, besides rooftop obstructions, shade comes into play primarily if you park near a building or trees. Snowbirds boondocking in the southwest deserts of Arizona and California during the wintertime have little concern with shade from trees and buildings. But summertime RV travelers who boondock in wooded areas need to be cognizant of where the shade from the trees will fall during the course of the day.

WIRING SOLAR PANELS IN PARALLEL vs. IN SERIES

One of the big decisions for a solar power installation on an RV or boat is whether to wire the solar panels in series or in parallel. There are several things to consider when making this decision.

When the solar panels are wired in series, then the developed voltage across all the panels is additive while the current remains constant from panel to panel. That is, if there were four 120 watt 12 volt panels producing 7 amps each, then the developed voltage across all the panels would be 48 volts (12 x 4) while the current would be just 7 amps.

In contrast, when the solar panels are wired in parallel, then the voltage of the panels remains constant through the circuit while the current is additive from panel to panel. For instance, for those same four panels, the developed voltage across them would be 12 volts but the current would be 28 amps (7 x 4).

The solar charge controller takes care of balancing everything out by ensuring the circuit between it and the batteries is 12 volts. In the case of the above solar panels wired in series, the solar charge controller steps down the voltage from 48 volts to 12 volts (if they are 12 volt batteries). The current then increases from 7 amps to 28 amps in the wire run going between the solar charge controller and the batteries.

In the case of the above solar panels wired in parallel, the voltage is already 12 volts, so the solar charge controller does not need to step it down for the batteries.

SHADE EFFECTS on SOLAR PANELS WIRED IN SERIES vs. WIRED IN PARALLEL

When solar panels are wired in series, if shade hits one panel and shuts it down (caused by that solar panel’s internal circuitry building up a massive amount of resistance), then the entire string of solar panels shuts down. For instance, if a tree shaded 1/3 of one solar panel in the string of four panels given above, wired in series, the current production of the entire array of four panels would be reduced to to 0 amps, even though the three other solar panels were in full sun.

In contrast, if the panels are wired in parallel, when shade knocks one panel out, the other panels are unaffected. So, even if 1/3 of one solar panel were shaded, reducing it to 0 amps of current production, the other three would be working just fine. The total current production would be 3/4 of what it could be if that one panel were in full sun (in this case, 21 amps), rather than 0 amps.

So, it would seem that the best way to wire solar panels is in parallel.

Unfortunately, it’s not that easy, and here’s why:

CURRENT and WIRE SIZE in a SOLAR PANEL INSTALLATION

The more amps of current there are flowing in a circuit, the thicker the wire needs to be to ensure that no energy is lost to heat. Unfortunately, thicker, heavier gauge wire is a pain to work with. It’s stiff and doesn’t bend around corners easily. It is hard to tighten down in the solar charge controller connections and it’s hard to crimp ring terminals onto. It is also more expensive per foot.

So, when the solar panels are wired in series, a thinner gauge wire can be used for a given distance than when they are wired in parallel.

Of course, the thickness of the wire is also dependent on the length of the wire. The longer a wire is, the more energy is lost along its length. So, if you are installing the solar panels high on an arch off the aft end of a 50′ sailboat and the batteries are located at the bottom of the hull over the keel, the wire must be a lot heavier gauge than if you are installing the panels on an RV roof directly above the battery compartment.

What is the price difference in the cable? We like to use Ancor Marine Cable because it is tinned and it is very supple (the copper is fine stranded). Here are the price differences for 25′ of 2 gauge wire as compared to 25′ of 10 gauge wire.

Ultimately, there is a dilemma: Is it better to go for thinner, cheaper wire and an easier installation, and wire the panels in series, risking that the whole array will shut down whenever a corner of one panel is shaded by a nearby tree? Or is it better to pay the extra bucks for heavier gauge wire and endure a more challenging installation but have a system that will be more tolerant of partial shade?

What to do?

SOLAR PANEL VOLTAGE and WIRE SIZE

Luckily, there is another option: higher voltage solar panels can be wired with thinner gauge wire. Remember, Watts = Current x Voltage. So, for the same number of watts in a panel, a higher voltage panel will produce a smaller amount of current.

Rather than using four 120 watt 12 volt panels wired in parallel that would produce 28 amps at 12 volts, you can use two 240 watt 24 volt panels wired in parallel that produce 14 amps at 24 volts. The net effect on the battery bank will be the same, but the bigger panels can be wired with smaller gauge wire.

As mentioned above, the wiring that is most affected by these solar panel choices is the wiring that runs from the solar panels to the solar charge controller. The wiring from the solar charge controller to the batteries is the same in either configuration, as the same amount of current will be flowing in that wire regardless of how the solar panels are wired. In the case of solar panels wired in parallel, the voltage will be stepped down in the solar charge controller. So, in our example, the solar charge controller will step down the voltage from 48 volts to 12 volts, ensuring that the circuitry between the solar charge controller and the batteries is at operating at 12 volts.

CHOOSING THE OPTIMAL WIRE GAUGE

The thickness of the wire, or wire gauge, depends entirely on how long the wire is going to be. That is, the wire gauge is determined by how far apart the solar panels and the solar charge controller and the batteries are.

Why is this? The more current that flows in a wire, the more the conductor in the wire will warm up. The more it warms up, the more energy is lost to heat. Eventually, this becomes measurable as a voltage loss between the two end points.

When wiring solar power circuits, you can choose how much voltage loss you are willing to have. Somewhere between 2.5% and 5% is typically considered okay. There are voltage loss tables that will help you decide on the proper wire gauge size for the distance you are spanning between the solar panels and the solar charge controller and between there and the batteries. Here’s a good one:

AWG Voltage Loss Table

An Example: 480 watts of solar power located 27′ from the batteries

  • Say we have four 120 watt 12 volt panels wired in series. If the distance is going to be 27′, then by looking at the third chart at the above link (the 12 volt chart) and going to the line for 8 amps flowing in the wire, it shows a wire run of up to 27′ can be done with 10 gauge wire.
  • Now, imagine putting those same panels in parallel. 32 amps will flow at 12 volts. For that same 27′ distance you’ll need 2 gauge wire.
  • Lastly, instead of using four 120 watt 12 volt panels, use two 240 watt 24 volt panels wired in parallel. For this you use the 2nd chart down (24 volt chart). There will be 16 amps flowing in the wire at 24 volts. You will be able use 8 gauge wire.

Of course, due to the nature of multi-stage battery charging and the changing position (and angle) of the sun in the sky, the solar panels will be operating at full tilt for a very short time each day. They may produce max current for 30 minutes near noon as they wrap up the Bulk Stage, however, as the Absorb stage takes over and continues in the afternoon, the solar charge controller will gradually hold the panels back so they produce far less than max current.

With less than peak current flowing in the wires, less energy will be lost to heat.

If this is confusing, see our articles:
RV and Marine Battery Charging Basics
How Solar Charge Controllers Work

So, although it may seem dire that you’re wiring is on the hairy edge size-wise, it is only that way for a little while each day. Depending on the overall size of the solar power array, the size of the battery bank, and the state of discharge when the batteries wake up in the morning, your system may not even hit the theoretical maximum current production or even come close.

MULTIPLE SOLAR CHARGE CONTROLLERS

Another method of keeping the wire size down is to install more than one big solar charge controller. For instance, you might install several smaller charge controllers for each pair of panels wired in series, or perhaps even one for each panel. Of course, this adds complexity and expense, and you will probably buy less sophisticated solar charge controllers that have fewer programming options than a single big one.

You must run more wires between the RV roof and the location in the coach where the solar charge controllers are installed (preferably next to the batteries), and so you must not only pay for additional solar charge controllers, but you must buy more wire and install it all. However, this design option does deserve mention and consideration.

TILTING THE SOLAR PANELS

Solar panels perform a whole lot better in the summer than in the winter. This is because the sun rides much higher in the sky and its rays hit the panels at a nearly perpendicular angle in the summertime. The days are also a whole lot longer. In the winter, the sun’s rays hit the panels at an angle and the sun is only out for a short while.

Solar panels on a fifth wheel RV roof

Tilting solar panels in winter can improve current production by 30%
Or…install more panels and save yourself from climbing up and down the RV ladder!

To get around this, rather than using ordinary Z-brackets to mount their solar panels on the roof, many RVers use tilting brackets. By tilting the panels towards the sun at about a 45 degree angle (technically, at the angle of your latitude), then the sun’s rays hit the panels at a nice 90 degree angle if they are oriented to face south. This can increase the overall power production by about 30% on a sunny winter day.

The only problem is that you have to climb up on the roof to tilt the panels each time you set up camp and then climb up again later to lay them flat when you are packing up before you drive away. We’ve seen many a winter snowbird driving their RV around with the solar panels still raised.

An alternative is simply to install more solar panels and to keep them lying flat all the time. This is easy for a big RV that has a huge roof but is not so easy for a little trailer with a small roof. We have not installed tilting brackets on our trailers.

MONOCRYSTALLINE vs. POLYCRYSTALLINE SOLAR CELLS

Monocrystalline solar panel

Monocrystalline
solar panel

There are lots of different kinds of solar panels on the market today. There are two primary types of solar cells used in the manufacture of solar panels: monocrystalline and polycrystalline.

Monocrystalline solar panels are more efficient and more expensive, but they are also extremely intolerant of shade. Polycrystalline panels are slightly less efficient and less expensive, but they handle partial shade just a smidge better.

The way to tell if a solar panel is monocrystalline or polycrystalline is to look at the pattern of rectangles on the panel itself.

If the circuitry between the rectangles has large silver diamond shapes, it is monocrystalline. If the pattern of rectangles is just intersecting lines, it is polycrystalline.

Polycrystalline solar panel

Polycrystalline
solar panel

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Examples of popular polycrystalline solar panels are here:

RIGID ALUMINUM FRAMED SOLAR PANELS vs. SEMI-FLEXIBLE SOLAR PANELS

Flexible solar panel

Flexible solar panel

Solar panels can also be rigid or flexible.

Rigid panels are built with an aluminum frame surrounding tempered glass that covers the solar cells.

Flexible solar panels are built with the solar collecting material impregnated into a thin mylar film that is affixed to an aluminum substrate.

Flexible solar panels are not flimsy, they are simply bendable up to about 30 degrees.

 

There are a number of manufacturers selling flexible solar panels:

FLEXIBLE SOLAR PANEL ADVANTAGES

Flexible solar panels have several advantages over rigid panels. They are a little lighter than framed solar panels and you can glue them onto an RV roof using Dicor Lap Sealant, or something similar. This saves you from the complexity of drilling holes into a perfectly watertight roof and risking creating leaks. This is especially helpful with a fiberglass roof. It takes just a few minutes with a caulk gun to attach these panels to the RV roof.

Another nice feature is that on a rounded roof, like an Airstream travel trailer or Casita travel trailer, the panels can bend to follow the contour of the roof.

Installing solar panels on a motorhome roof

Mark uses Dicor Lap Sealant to affix flexible solar panels to a friend’s fiberglass roof.

One of the most important things for solar panels to work well is heat dissipation. Rigid aluminum framed solar panels stand up off the roof of the RV by about an inch, allowing air to flow underneath and for heat to dissipate. Air can’t flow underneath flexible solar panels. The aluminum substrate serves to dissipate the heat instead. This may or may not be as efficient a method of heat dissipation, and I have heard of a case where all the flexible solar panels on a sailboat had to be replaced after two years because they did not dissipate the heat sufficiently in the tropics and the panels self-destructed.

FLEXIBLE SOLAR PANEL CONSTRUCTION and INSTALLATION

Our RVing friends Dick & Katie asked us to install six 100 watt 12 volt flexible solar panels made by Eco-Worthy on the roof of their motorhome, along with all the other projects involved in an RV solar power installation. Ironically, the hardest part of the entire installation was removing the plastic protection from the aluminum substrate of each panel (it kept ripping!). We all ended up working on this together.

Flexible solar panel installation on an RV

We had a tough time getting the plastic off the back of the Eco-Worthy flexible solar panels

Removing plastic from flexible solar panel

With all of us working together, we got the job done!

Once we got up on the roof, and got past a cute warning from Winnebego, the installation was straight forward.

Warning slippery roof on RV

Hmmm…I wonder what sage advice the manual suggests for this problem?

Solar panel installation on a motorhome RV

Flexible solar panels are lighter than their rigid counterparts

The plastic protection needed to be removed from the face of the panels as well. Interestingly, at one point Mark found himself picking at the corner of the mylar that has the solar collection circuitry embedded in it and almost began to peel that whole layer off the aluminum substrate! But once he got a hold of just the most superficial layer of plastic, it came off easily.

Removing plastic from flexible solar panel

Mark removes the plastic from the face of the flexible solar panels

He used Dicor Lap Sealant to tack down the corners of the panels and then ran a bead around each side of each panel.

FLEXIBLE SOLAR PANEL DISADVANTAGES

Flexible solar panels are less efficient than rigid aluminum framed solar panels, which means you may want to get a few more total watts of solar panels than you would if you were buying framed panels. Bendable panels also can’t be installed on tilting brackets. So, again, buying more total watts may be the best solution.

Flexible solar panels are not as rugged as rigid aluminum framed solar panels built with tempered glass. Overhanging branches can scratch them. This is important for anyone that will be boondocking or dry camping a lot on public lands and in rustic public campgrounds, as it is often impossible to get in or out of a site without ducking under some low lying tree branches.

Some RVers have found that flexible solar panels installed on flat motorhome roofs tend to pool water when it rains. This can lead to debris building up and taking root and damaging the panels.

Perhaps for all these reasons, flexible solar panels are sold with a much shorter warranty than rigid solar panels. Whereas many solar panel manufacturers warranty their tempered glass aluminum framed rigid solar panels for 25 or 30 years, bendable solar panel manufacturers generally warranty their panels for 5 years or less.

This may or may not be relevant for RVers, as the fine print in almost every solar panel manufacturer’s warranty states that their solar panels are not warrantied for use on mobile vehicles.

Also, there has been a huge problem across the entire solar power industry with rigid solar panels failing prematurely in large numbers in big commercial installations (see a May 2013 NY Times article here). Apparently, just because those lovely rigid solar panels are warrantied for decades doesn’t mean they will last that long. We have already had a failure of one of our framed solar panels that was warrantied for 25 years, and we discovered the manufacturer’s warranty did not apply to RV installations.

However, as a general rule, when manufacturers warranty a product for 5 years versus 30 years, it says something about how they think their product will hold up over time.

Flexible solar panels installed on a motorhome RV roof

Nice job! (but don’t fall off that roof!)

CONCLUSION

There are many ways to go about installing solar power on an RV roof, and the solar panels that work best in one installation may not be the same as those that are best for another. Not only is every RV roof different, but every RVer’s needs are different.

If you have loads of space on a big motorhome roof or fifth wheel trailer roof, and you are setting it up for full-time use, you may be best off with three or four 200+ watt 24 volt rigid solar panels wired in parallel. If you have a little tear drop camper you use on weekends and store in the garage, a single flexible 100 watt 12 volt panel may be just the ticket for you.

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RVers Jason and Nikki Wynn have written about the condition of their flexible solar panels after a year of use HERE

Wet Cell vs. AGM Batteries & Wiring Tips for Installation on an RV or Boat!

There is a world of difference between wet cell batteries (also called flooded batteries) and AGM batteries for use in an RV or marine battery bank, because AGM batteries are totally sealed, maintenance free and keep the user from coming into contact with battery acid (electrolyte). In a nutshell, the advantages of AGM batteries over wet cell batteries are the following:

  • AGM batteries are maintenance free, which means:
    • They don’t need periodic equalizing to clean the internal plates and never need the electrolyte topped off with distilled water.
    • They do not release gasses during charging, so they don’t need special venting in the battery compartment.
    • Since gasses are not released, the terminals and battery cables do not corrode over time and don’t need to be cleaned.
  • AGM batteries discharge more slowly than wet cells, so an RV or boat can be stored for a few months without charging the batteries.
  • AGM batteries charge more quickly than flooded batteries because they can accept a higher current during the Bulk charging phase.
  • AGM batteries can be installed in any orientation, which is helpful if installation space is limited.
  • AGM batteries can’t spill battery acid if they are tipped over. This is especially important when a boat heels excessively or capsizes. (Not that you’d be too concerned about spilling electrolyte if your boat were upside down!)
RV battery upgrade from 6 volt wet cell batteries to AGM batteries

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OUR ORIGINAL BATTERY INSTALLATION

We used Trojan T-105 wet cell (flooded) batteries for nearly six years in our fifth wheel trailer, and they worked great. They were installed in our basement compartment, all lined up in a row. This was a custom installation that was done by H&K Camper Sales in Chanute, Kansas, when we purchased our trailer new from the NuWa factory in 2008.

Fifth wheel RV battery boxes in basement

Four 6 volt golf cart batteries installed in our fifth wheel basement

The original battery compartment was designed at the NuWa factory to hold two 12 volt Group 24 batteries. Group 24 batteries have the same footprint as 6 volt golf cart batteries but are about an inch shorter. We had 2″ angle iron bolted onto our fifth wheel frame so the four batteries could stand side by side in battery boxes.

Angle iron supports under an RV fifth wheel battery bank

2″ angle iron is bolted onto the fifth wheel frame
to support the batteries.

There were four venting flex hoses that ran from the battery boxes to four individual louvered vents on the front of the basement on either side of the hatch door.

RV 5th wheel basement with 6 volt battery boxes

Each battery box is vented to the outside with flex hose going to a louvered vent cover.

These batteries worked well, but because we put our RV in covered storage for 4 to 20 months at a time during the four years we cruised Mexico’s Pacific coast on our sailboat, we were not actively present to take care of the the battery charging and maintenance duties. Despite our best efforts to have someone do this while we were gone, when we moved off of our boat and back into our fifth wheel, we found our four Trojan wet cell batteries were completely dead and unrecoverable.

We replaced these batteries with four inexpensive 6 volt golf cart flooded batteries from Costco. These new batteries did not last. Within 18 months, the internal plates had sulfated badly, they took forever to charge, and they discharged extremely quickly.

6 volt wet cell batteries in fifth wheel RV basement

Upgrade time! We removed the old wet cell batteries and replaced them with AGMs.

In April, 2015, while staying in beautiful Sarasota, Florida, we replaced our wet cell batteries with four fabulous new Trojan Reliant T105-AGM batteries that Trojan had just begun manufacturing and selling. We replaced all the wiring as well.

CORROSION CAUSED BY WET CELL BATTERIES

One of the biggest problems with wet cell, or flooded, batteries is that the battery terminals and ring terminals on the battery cables get corroded easily due to the gassing that goes on when the batteries are being charged. When Mark removed the battery cables from our old batteries, he measured as much as 20 ohms of resistance from the end of each cable to its ring terminal.

Corrosion on battery cable

We measured 20 ohms of resistance between the end of the cable
and the end of the ring terminal.

Flooded batteries need to be held at 14.5 or more volts during the Absorption charging stage (depending on the battery), and at this voltage the electrolyte in the batteries begins to release gasses into the air. These gases are both explosive and corrosive, and venting them protects everything around them. However, inside the battery box these gases can corrode the battery terminals and wiring.

The best way to clean off the corrosion is with a solution of baking soda and distilled water. Put it in a disposable cup and then use a cheap paintbrush to paint it on and smooth it around the terminals and cable ends. Let it sit for a few minutes and then pour a little distilled water over it to rinse the baking soda and crud off. Dry it with paper towels.

Also, while driving down the road, the electrolyte can splash around inside the battery cells and drip out the vent holes. Dust can settle on the spilled electrolyte and can cause a minute trickle discharge across the top of the battery. So, it is important to wipe down the tops of the batteries regularly and keep them clean.

It’s a good idea to wear rubber gloves for all of this too!

6 volt wet cell RV house batteries

These batteries did not hold up well and corroded badly every few weeks.

Watch out for drops of liquid settling on your clothes when messing with the batteries. It’s nearly impossible to avoid, and Mark has holes in some of his jeans from drops of battery acid landing on his pants while he either checked the state of charge of the batteries with a hydrometer or poured distilled water into the battery terminals or cleaned the corrosion from the battery terminals and cable connections.

Battery hydrometer not used with AGM batteries

Now that we have nifty new AGM batteries, we no longer need the hydrometer!

OUR NEW RV BATTERY INSTALLTION

We chose the new Trojan Reliant T105-AGM batteries to replace our old flooded batteries because these are a completely redesigned battery from one of the top battery manufacturers, Trojan Battery. Rather than being dual purpose batteries, like othe AGM batteries on the market, the new Trojan Reliant AGM batteries are single purpose deep cycle batteries.

Trojan Reliant AGM 6 volt RV batteries

Our new Trojan Reliant T105-AGM batteries ready to go.

TRUE “DEEP CYCLE” – START BATTERIES vs. HOUSE BATTERIES

Large RV and marine batteries can be used both to start big engines and to run household appliances. However, these functions are polar opposites of each other! A start battery gives a big but short blast of current to get an engine started and then does nothing. In contrast, a house battery provides a steady stream of current to power lights and household appliances for hours on end.

Most deep cycle AGM batteries on the market today are actually dual purpose start and deep cycle batteries, largely due to the history of how batteries have developed and what they have been used for. The new-to-market (in 2015) Trojan Reliant AGM batteries were engineered from the ground up to be strictly deep cycle batteries, and the design is not compromised with start battery characteristics.

Installing Trojan 6 volt Reliant AGM battery in RV fifth wheel

Mark installs the new batteries in the old plastic battery boxes.

12 volt batteries come in many sizes: Group 24, Group 27, Group 31, 4D, 8D and more. As the battery sizes increase, they provide more and more amp-hour capacity. 6 volt batteries come in various sizes too, and the golf cart size is one of several.

The Trojan Reliant T105-AGM 6 volt golf cart style batteries (68 lbs. each) are rated to have a capacity of 217 amp-hours when two of them are wired in series to create a 12 volt battery bank. In comparison, our sailboat came with three Mastervolt 12 volt 4D AGM batteries (93 lbs. each), and we added a fourth. These batteries were rated to have a capacity of 160 amp-hours each.

The advantage of using two 6 volt golf cart batteries instead of enormous 4D or 8D 12 volt batteries is that they are smaller, lighter and easier to carry around and to put in place during the installation and easier to remove in the event of a failure.

BATTERY WIRING

We wired our four new 6 volt batteries in series and in parallel. We wired two pairs of batteries in series to create two virtual 12 volt battery banks. Then we wired those two 12 volt banks in parallel with each other.

Four 6 volt batteries wired in series and in parallel

Four 6 volt batteries: two pairs wired in series to make virtual 12 volt batteries.
Those pairs are wired in parallel with each other (red / lavender circles explained below).

Trojan Battery recommended the following wire sizes for this battery configuration:

  • 4 gauge wire between the batteries that are wired in series
  • 2 gauge wire between the pairs of 12 volt battery banks wired in parallel

This is thicker wire than many RVers and sailors typically select for their battery banks.

Because we were wiring batteries that would be physically lined up in a row, we drew out a wiring diagram to be sure we got it right.

Four 6 volt batteries in a row wired in series and in parallel

Same wiring but with the batteries lined up in a row (red and lavender circles explained below).

WIRING THE BATTERY CHARGERS and INVERTER

Because AGM batteries have a lower internal resistance, they can accept a higher bulk charging current than wet cell batteries.

Trojan Reliant AGM batteries can accept a bulk charge current of 20% of their 20 hour amp-hour rating. For the T105-AGM batteries, the 20 hour amp-hour rating is 217 amps per pair of batteries wired in series. So the max current the batteries can accept is 20% of 217 amps, or 43 amps, per pair. The wiring for each charging system should be sized for a max current flow of 43 amps.

In contrast, Trojan’s wet cell batteries can accept only 10%-13% of their 20 hour amp-hour rating. For the T105 battery, the 20 hour amp-hour rating is 220 amps per pair of batteries wired in series. So the max current the batteries can accept is 13% of 220 amps, or 28 amps.

It is important when wiring both the battery charging systems and inverter systems into the battery bank (that is, the solar charge controller, the engine alternator on boats and motorhomes, the inverter/charger or the individual DC converter and inverter), to ensure that the wiring going to those devices is connected across the entire battery bank and not to just one 12 volt battery (or 6 volt pair) in the bank.

If the charging systems are connected to the battery terminals of just one 12 volt battery, whether it’s an individual Group 24 or 4D battery or is a pair of 6 volt golf cart batteries wired in series, then the batteries in the system will not charge equally. Likewise, if only one battery of the parallel bank is wired to the DC side of the inverter, the batteries will not discharge equally.

In the above drawings, the two optimal connection points for the charging and inverter systems are shown in red and in lavender. Either pair of terminals works equally well.

We found that with individual devices for our converter, our inverter and our solar charge controller, there were a lot of ring terminals getting piled up on two of the battery terminals. So we chose the inner pair of battery terminals for the inverter and the outer pair for the converter and solar charge controller.

Since we dry camp 100% of the time and rarely use our converter except when we have to pull out our generator after days of storms or to run our air conditioning, this division means that our primary charging system spans the batteries one way while the inverter driving the AC household systems that discharge the batteries span the batteries the other way.

NOT ALL BATTERY CABLE IS CREATED EQUAL

We chose Ancor marine wire for our battery cables because it is very high quality cable. The individual strands of wire inside the casing are thin, which makes this cable very supple, despite being thick overall. It is easy to work with and to snake around tricky areas. The individual strands inside the cable are tinned as well.

This is expensive wire, but after all the wiring projects we have done on our RVs and on our sailboat, we felt it was well worth the extra cost.

We also used Ancor marine tin plated lugs made of high-grade copper with flared ends for our ring terminals (available here).

Ring terminal on battery cable

Mark slips a ring terminal onto the new battery cable.

It was critical to get a good solid connection between the ring terminals and the 2 gauge and 4 gauge wire we were using.

We don’t own a crimper of that size, but West Marine Stores often have a crimper for heavy gauge wire that customers can use, and we got an excellent crimp from a workbench mounted crimper.

Crimping ring terminal on battery cable

Crimping 2 and 4 gauge wire requires a large crimper.

With Mark hanging onto the ring terminal and me hanging onto the wire, we both pulled with all our might and we couldn’t pull the lug off the wire.

Good crimp on battery cable

A good, solid crimp.

As these projects always go, we needed to return to West Marine for crimping a few days later when we wired in our solar charge controller. We went to a closer West Marine store this time, and they had a different crimper that wasn’t quite as nice.

Using a hand crimper to crimp ring terminal onto battery cable

This wire is so thick you need a huge wire cutter!

Mark wasn’t as confident that these crimps were as good electrically as the ones made with the first crimper, even though we couldn’t pull the lugs off the wire. So he fluxed the wire and used a propane torch to flow solder into the connection. This way we had not only a solid physical connection but an excellent electrical connection as well.

Soldering ring terminal crimp on battery cable

Mark flows solder into the connector to make a superior electrical connection.

Then he slipped shrink tubing over the connection and used a heat gun to shrink it in place.

Heat gun shrink wrap over ring terminal on battery cable

Shrink tube covers the whole connection, and a heat gun tightens it up.

After our installation, we discovered that Camco makes 2 and 4 gauge battery cable and you can get them here.

Back at the RV, Mark wired the batteries up. He placed the batteries in the battery box bottoms to keep them from sliding around and put the battery box tops on as well so that if anything fell over in the basement while we were driving, it wouldn’t accidentally land on the battery terminals and short something out. We keep that area clear, but you never know when you’ll hit a huge bump and things will go flying.

Trojan Reliant AGM 6 volt batteries in fifth wheel basement

The batteries are ready for their battery box tops.

The AGM batteries do not need to be vented, so he removed all the vent flex hoses. This gave us much better access into the fifth wheel basement from the front hatch door.

Trojan Reliant AGM 6 volt batteries in fifth wheel RV battery compartment

The new batteries are installed, wired and labeled.

Without any flex hose behind the louvered vents, dust and road grime could now flow into the basement, so Mark removed the vent covers and placed a piece of solid plastic behind each one.

Replacing battery vents on fifth wheel RV

The louvered vents are open to the basement in the back and will let dust in.

RV battery vent

Mark puts a thin plastic sheet behind each louvered vent to keep dust out.

We then went on to wire in our new converter, inverter and solar charge controller (installations to be shown in future blog posts).

HOW DO THE NEW TROJAN RELIANT AGM BATTERIES WORK?

The performance of these new batteries is nothing short of outstanding. We are floored everyday by how quickly they get charged, and not one bit of corrosion has appeared anywhere.

Mark is happy not to have to check the electrolyte levels in the batteries any more or to remember to equalize them every month. The new AGM batteries are winners all around.

RV battery boxes in 5th wheel basement

Even though AGM batteries don’t have to be installed in battery boxes,
ours are because our basement is large and open and we want to protect them from falling objects!

WHY WOULD ANYONE USE FLOODED BATTERIES?

Our Trojan T-105 wet cell batteries worked just fine for us for years, and flooded are actually advantageous over AGM batteries in two significant ways:

  1. Flooded batteries are much cheaper than AGM batteries.
  2. Well maintained wet call batteries can be cycled more times than AGM batteries

Flooded batteries cost 30% to 40% less than AGM batteries. This can add up to a savings of hundreds of dollars. Depending on the value of the RV or boat, it just may not make sense to have a huge investment in batteries on board.

Also, perfectly maintained wet cell batteries can be cycled more times than AGMs. “Perfectly maintained” means staying on top of equalizing the batteries to keep the battery plates clean and also checking each cell in each battery regularly to ensure that the electrolyte is completely topped off with distilled water at all times.

Under these ideal conditions in the laboratories at Trojan Battery, the Trojan T105 flooded batteries can survive 1,200 cycles where they are discharged to 50% (12.06 volts) and then fully recharged. The Trojan Reliant T105-AGM batteries can survive only 1,000 cycles.

Of course, battery cycling in real world conditions is very different than in laboratory conditions. The degree to which RV and boat batteries are discharged and recharged day to day is far from regular (partial discharging and partial recharging are common). Also, batteries on RVs and boats that are left in storage for any period of time can be difficult to maintain and may degrade despite good intentions (like ours did).

So, the ultimate performance and value of flooded versus AGM batteries is going to vary widely from one RVer or sailor to the next. However, for us, we will not be going back to wet cell batteries any time soon!

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Solar Tutorial Part IV – Solar Panel Selection and Wiring

<- Solar Tutorial Part III – Full-timer Kits                                                         Solar Tutorial Part V – Battery & Inverter Selection ->

The two sample systems described in Part III of our Solar Power Tutorial series are essentially the same systems we have installed on our RV and sailboat.  The RV system is pretty standard for full-time RVers (four 120-140 watt 12-volt panels and 440 amp-hour battery bank).  The sailboat system is bigger than many cruisers carry (three 185 watt 24-volt panels and 710 amp-hour battery bank).

Cruisers often install less solar power and rely on additional charging methods via engine alternator, and wind/gas/diesel generators.  However, we have found our solar power alone is sufficient to live an ordinary house-like lifestyle on our boat (if we don’t use our standalone DC freezer).  We lived for 10 mid-winter weeks in southern Mexico on solar power alone, without using the alternator once (it was broken), and still used two laptops, the TV/DVD, stereo, microwave, chartplotter, autopilot, anchor windlass and vacuum as much as we wanted.

Our rationale for having enough solar power to live comfortably without alternative charging methods was:  we didn’t want to store a lot of gasoline to power a gas generator; we had found that boats with wind generators often suffered from the whirring noise and vibration; and we didn’t want the added cost, installation work and maintenance of an inboard diesel generator.  Solar power has been a great solution for us on both the boat and the fifth wheel.

Part III described these two basic full-timer systems with just a cursory comparison of the solar panel choices.  This page goes into more detail about the various options for sizing solar panels and suggests different ways to wire them.

Wiring in Series versus in Parallel and Wire Gauge Size

There are quite a few choices for solar panel configurations, each with its own pros and cons.  But before choosing a panel configuration it’s worthwhile to consider how to deal with the large current that will be flowing through the wires.  As much as 35 amps or more might be flowing from the panels to the charge controller and then from the charge controller into the batteries.  This requires heavier gauge wire which is more difficult to work with and is expensive.  However, there are several ways to reduce the amount of current in the wires.

If the panels are wired in parallel, the amps produced by each panel are additive while the volts remain constant (Ohm’s law).  Therefore, the cable leading from the connection point of all the panels to the charge controller and then on to the batteries will carry the full current load, or potentially as much as 35 or 40 amps at 12 volts DC.  Heavier gauge wire must be installed to handle this large current load throughout the system.

If there is too much current on a cable, then it will get warm (or hot), and lose some of its precious amperage to heat.  In other words, if the wire gauge is too small, not all the power produced by the panels will make it to the batteries.  It will dissipate as heat loss along the way.  And at the extreme, there’s the risk of melting the shielding off the cable (highly unlikely).

Larger wire is more expensive and is more difficult to handle because it is stiffer.  “Larger” generally means 6 or 8 gauge wire and “smaller” is generally 10 gauge.  The size is dependent on the current flowing through the wire and the length of the wiring run.  A detailed chart for selecting wire gauge is given here.  Note that some charge controllers can’t accommodate wire heavier than 4 or 6 gauge.

If the panels are wired in series, the amps produced by each panel stay constant while the voltage is additive (also Ohm’s law).  Therefore, the cable leading from the connection point of the panels to the charge controller will carry just the amperage produced by a single panel (7-9 amps) at 48 volts DC (if four 12 volt panels are installed in series), rather than the 25-35 amps at 12 volts DC that would flow when wired in parallel.  Because there is less current, thinner gauge wire can be used throughout the system.

In practical terms, most solar power systems on RVs and boats never reach their full potential current load.  During the morning hours, before the sun gets high and powerful in the sky, the batteries get quite a bit of charge.  Usually, by the time the sun is really cranking out maximum energy at noon — the time when the system could be producing max amps — the batteries have already gotten pretty well charged and are starting to ask for less and less current.  So the charge controller has already begun to throttle the panels back a bit and less current is flowing through the system.

Also, solar panels are rated for operating with the sun perpendicular to their surface, and anything other than a perpendicular orientation reduces their output significantly.  In all months except May-July, the sun doesn’t ride all that high in the sky.  We have rarely seen much more than 25-30 amps on either of our full-timer systems, although they are capable of 30 and 36 amps respectively.

Another important consideration is that when a small fraction of a solar panel is shaded — as little as a 4 square inch area on a 2′ x 5′ panel — the entire panel stops producing power.  That is because internally the panel is “wired” in series.  When there is resistance, caused by shade, in just one portion of it the panel’s internal circuitry, current can’t flow through any of it.

By extension, if the panels are all wired in series, when one panel shuts down due to a palm-sized bit of shade, then the entire array of panels shuts down.  A tree branch or part of a boat’s standing rigging or mast/boom can cause the entire array to shut down if it is wired in series.

marine solar panels on hunter 44ds sailboat

Shade from the mast and shrouds on our three 185 watt panels.

If the panels are all wired in parallel, a small amount of shade on one panel will only shut down that individual panel.  Current will still flow through the rest of the panels and then through the rest of the system.

We were persuaded by our solar panel vendor to wire our trailer’s panels in series so we could use small gauge wire throughout the system.  We have experimented with shading a small corner of one of the four panels and were stunned to see the entire array quit working!  However, almost everywhere we boondock we are in full sun.  So, in the end, it doesn’t matter for us. Wiring our RV’s solar panels in series has worked out just fine.   If, however, you anticipate camping under trees on a regular basis and you want to maximize the panels’ chances of getting access to the sun, wire the panels in parallel and use heavier gauge wire.

On a boat, this series versus parallel decision is much more critical than on the roof of an RV.  The mast, boom and shrouds often shade portions of the panels as the boat swings at anchor.  Under sail the shading can be even worse.  So the best wiring option on a boat is to wire the panels in parallel.  However, the cable runs in a boat can be much longer than in a comparably sized RV.  On our sailboat the wiring running from one end of the system to the other — panels-controller-batteries — is 45′.  Why so long?  The panels are high in the air on an arch at the back end of the boat, the batteries are at the bottom of the hull in the middle of the boat, and the all the wiring is routed so as not to be seen.

12 volt versus 24 volt panels

Another way to tackle this issue of having a lot of current flowing through the system is to use 24 volt solar panels instead of 12 volt panels.  When the voltage is doubled like this (24 versus 12 volts), the current is halved.  So the current produced by 24 volt panels is half that of equivalent wattage 12 volt panels (the watts don’t change whether the panels are 12 volts or 24 volts).  We chose to go this route on our sailboat, using three 185 watt 24 volt panels wired in parallel.

Since the batteries are 12 volt batteries, the input side of the charge controller coming from the solar panels is 24 volts while the output side going to the batteries is 12 volts.  Most large capacity charge controllers allow this kind of configuration.  This means that the current flowing between the panels and the charge controller is half that flowing between the charge controller and the batteries.  So, while the panels may be producing 14 amps at 24 volts, and those 14 amps may be flowing from the panels to the charge controller, the current will double to 28 amps at 12 volts when it flows from the charge controller to the battieries.

While the wiring run between the panels and the charge controller can be smaller gauge (less current flows in that portion of the system), the last wire run between the charge controller and the batteries needs to be as short as possible and wired with heavier gauge wire to accommodate the larger amount of current.

We made the mistake of placing the charge controller 25′ from the batteries at first and using 10 gauge wire (I suspect we didn’t explain our situation to the salesmen at the solar panel store well enough when we asked him for guidelines).  When the panels were running at full power we lost about 10-15% of the power they were producing.  Once we moved the charge controller to within 10′ of the batteries and replaced the 10 gauge wire with 8 gauge wire, we lost just 1.5% of the power between the charge controller and the batteries, which is considered acceptable.

Tilting Brackets

Tilting brackets make a lot of sense on an RV because an RV is parked in a stationary position.  In wintertime it is possible to tilt the panels towards the sun (tilt them about 45 degrees).  Most folks align the panels with the length of the RV and tilt them on their sides.  This means that either the driver side or passenger side of the RV will be situated to face due south and the panels will be tilted in that direction.  In most boondocking locations we find we can orient the rig any way we want to because there is so much space around us.

In experiments one December with RVing neighbors who had tilting brackets, we found that their solar power system produced about 40% more amp-hours throughout the day.  Their system was fully charged and their batteries were floating in the afternoon, while ours never reached the Float stage.  Some of that may have had to do with their batteries being better charged to begin with in the morning (we have no idea if they were or weren’t), but it is a pretty dramatic difference nonetheless.

RV solar panels on fifth wheel trailer

Four 120-130 watt panels on our fifth wheel’s roof

However, to get the advantage of tilting brackets, you have to get on the roof to tilt each panel every time you set up camp, and then remember to return them to their flat position before breaking camp and driving off. 

An alternative is to keep the panels flat in all but the most dire circumstances (a week of cloudy winter days), but have one more panel in your system than necessary.  Or don’t even bother installing tilting brackets at all. The trade-off is a few hundred dollars for an extra panel versus climbing up and down your RV ladder and fussing with the panels, as well as the risk that you might drive off with them raised up (we’ve seen plenty of people do that).

Tilting brackets don’t make much sense on a boat because boats move around so much at anchor.  Ours swings back and forth in a 90 degree arc.  Also, the tilting mechanism for a lot of boats introduces shade across the panels at certain angles.  On a boat, it is best to mount the panels as far from the mast and boom as possible and to focus on keeping the shade off the panels as much as possible by forcing the boom off to one side or the other while at anchor.  A fixed, flat mounting position works best.

 For more information about how to select the best solar panels for your installations, see this article:

Which Solar Panels To Buy – Flexible or Rigid? 12 or 24 volt? Monocrystalline or Polycrystalline?

 

Most of the components for an RV or marine solar power installation can be purchased at Amazon.

Shown here is a complete full-timer's kit (far left), a big charge controller (middle) and a big inverter (right). More comprehensive listings of each component type can be found at the following links:

Purchases at any of our Amazon links help cover our out-of-pocket costs for operating this site -- thanks!

 

This is the end of our solar power tutorial series.
We have lots of other info about solar power on this website. See the pages listed below to learn more.

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FURTHER READING and RELATED ARTICLES

SOLAR POWER OVERVIEW and TUTORIAL

BATTERIES and BATTERY CHARGING SYSTEMS

LIVING ON 12 VOLTS

 

Our most recent posts:

More of our Latest Posts are in the MENU.
New to this site? Visit RVers Start Here to find where we keep all the good stuff!!

Solar Tutorial Part III – Full-time RV & Cruising Solar Systems

<– Solar Tutorial Part II – Starter Kit
Solar Tutorial Part IV – Panels & Wiring –>

This page outlines the parts needed for two different solar power systems to be used for full-time “off the grid” living in a moveable home: one for an RV and one for a sailboat

If you are going to live in your RV full-time, year-round, you will need a much bigger system than the one described on the previous page.  You will likely be using your computer a lot, you’ll keep the lights on for many evening hours in the winter, you’ll be using the TV and stereo quite a bit, and you will want to use your microwave, hair dryer, vacuum and toaster on a regular basis. 

Compared to the small-medium sized systems described in our Solar Power Tutorial Part II, this will require more total wattage in the solar panels, a bigger and more sophisticated charge controller, more total amp-hours in the batteries and a better quality inverter that is wired into the RV’s AC wiring system.  At the very least, a full-timer’s system should have 400 watts of solar panels, a 40 amp charge controller, 400 amp-hours of battery capacity and a 1000 watt inverter.

Full-time RVers Solar Power System – 12 Volt

A sample full-time RVer’s solar power system consists of the following:

4 150 watt (12 volt) solar panels ($900)
1 Outback FlexMax FM60 MPPT charge controller ($550)
10 gauge wire rated for outdoor use (or 8 guage) ($100)
4 6-volt golf-cart style batteries ($650)
1 Go Power 2000 watt pure sine wave inverter ($850)

Total parts cost:  ~$3,600

Wild guess at an installer’s fee:  ~$1,500

* Additional parts may include MC4 connectors and transfer switch and Cable and DC circuit breaker for the inverter

Full-time RV solar panel installation

The 12-volt 120- to 130-watt panels are sized about right to fit between the many little things that stick up on our fifth wheel’s roof.

This system is rated to produce 600 watts at 12 volts and has a 440 amp-hour battery bank.  It is a little bit larger than the system that we have on our fifth wheel trailer. Ae have three 120 watt panels and one 130 watt panel (for a total of 490 watts), and our system cost a whole lot more back in 2008!

We can get as much as 170 amp-hours per day in summer, although more typically it is about 120 amp-hours.  There have been summer days/nights when we watched our 26″ TV for 15 hours (the Olympics), and there have been days/nights when we ran two laptops for 10 hours and then watched a movie (such couch potatoes!!).

In the dead of winter, around the winter Solstice (December 21), this system can produce about 80-100 amp-hours per day.  The only limitation in winter is when storms cloud the skies for three or more consecutive days.  Three cloudy winter days in a row where we get just 40-60 amp-hours makes us start thinking about supplemental charging or cutting back on our power use.

Our weird choices for solar panel sizes were due to what we already owned from our first solar panel installation (a 130 watt panel) and what was available in the store at the time of purchase (120 watt panels).  If we were buying today, we would have purchased four 150 watt panels as shown above.

This system will allow you to run everything inside your rig but the air conditioner and big power tools.  We have even used it to run a small compressor to change a flat tire on the rig (on four different occasions, ugh!).

 

RV Full-timer’s System Installation

Installation follows the same guidelines as the smaller systems described in our Solar Power Tutorial Part II, but is just a little more complicated.  An outline of the installation follows.

(1) Install the solar panels on the roof

We wired ours in series, but wiring in parallel may be preferable.  A discussion about the pros and cons of wiring the panels in parallel versus series comes on the next page of this tutorial along with a discussion of wire gauge sizes.  Run the wires down through the refrigerator vent to the battery compartment. If the fridge is in a slide-out, run the wires down the outside of the gray or black water vent pipe

(2) Install the batteries in the battery compartment

Not many RV’s have enough battery boxes for four 6-volt batteries, especially trailers.  Often the battery boxes are too short as well, since 6-volt batteries have the same footprint but are taller than the typical 12-volt Group 24 batteries that are shipped with RVs from the factory.  Here are example 6 volt battery boxes and Group 24 12 volt battery boxes.

If you haven’t purchased your RV yet, you may be able to get the manufacturer or dealer to modify the battery boxes for you as part of the deal (that’s what we did with NuWa on our fifth wheel).  Wire two pairs of the batteries in series to form two 12-volt batteries, and wire those two pairs in parallel.

RV Solar Panel Installation Outback Charge Controller

Outback 60 amp charge controller

(3) Install the solar charge controller near the battery compartment

Connect the wires that come from the solar panels to one side of the charge controller and wire the batteries to the other side.  It is best to crimp eyes on the ends of the cables.

(4) Install the inverter near the battery compartment

Wiring the inverter to the AC wiring system in the RV is complex.  The proper way to wire it is to place the inverter as close to the batteries as possible. Protect the DC side with a big fuse, and wire it to a transfer switch. We are not master electricians, and we took a short cut on our system that not everyone would be comfortable with but that works very well for us.

We positioned the inverter next to the DC to AC converter in the basement of the fifth wheel and wired it directly to the batteries.  The converter is located next to an AC outlet that it uses for power to run (the converter uses the AC power to charge the batteries). 

When we use shore power, we plug the converter into the AC outlet to allow the converter to do its normal job of charging the batteries.  However, we use shore power only a few nights a year, at most.

When we dry camp, which we do virtually 100% of the time, we unplug the converter from the AC outlet so it is totally dormant and not in use, and then we plug the inverter into the AC outlet instead.

The inverter and converter are never “on” at the same time.

The inverter draws its power from the batteries and converts that DC power into AC power. That is, it generates AC power which it supplies to the rig backwards through the AC outlet it is plugged into.

This is very non-standard and would be frowned upon by master electricians.  What would concern them is that when the rig is in this configuration, the shore power outlet on the outside of the trailer is live, with power coming out. Accidentally plugging the shore power cable into the shore power outlet on the outside of the RV while the inverter is turned on would be disastrous. However, because we almost never use our shore power cable and we rarely change our setup to switch between dry camping and hooking up (since we dry camp almost exclusively), this method has worked fine for us for over seven years.

This is not a recommended strategy if you plan to switch between dry camping and using electrical hookups frequently.

We also connect the two 50 amp AC legs of our 50 amp coach by plugging a modified extension cord with a male connector on each end into one outlet on each leg. We have two outlets next to each other in the bedroom, one on each of the 50 amp legs in the trailer, that are ideal for this purpose. We plug the “cheater” cord into each outlet, effectively connecting the two 50 amp halves of the RV together at that point.

It is handy to wire the inverter to a simple toggle switch located somewhere inside the RV so you can turn the inverter on and off from inside the rig without having to go outside to the battery compartment each time you want to turn on your AC power.

Liveaboard Cruiser’s Solar Power System – 24 Volt Solar Panels

Marine sailboat solar panel installation

A large arch installed off the back end makes it possible to use very big panels. Note the shade on the panels from the mast and shrouds. The panels are producing about 50% of their potential power right now!

A system like the above would work fine on a sailboat.  However, another style of design — which we ended up using — is the following.  Of course, this system could be used on an RV as well.

3 250 watt (24-volt) solar panels ($1200)
1 Outback FlexMax 80 MPPT charge controller ($650)
10 gauge wire rated for outdoor use ($200)
4 AGM 4D 12 volt batteries ($2,000)
1 Combiner Box & breakers ($180)
Go Power 3000 watt pure sine wave inverter ($550)

Total parts cost:  ~$4,800

Solar Panel Arch:  ~$2,000-$8,000

Wild guess at an installer’s fee:  ~$1,500-2,500

This system is rated to produce 750 watts at 24 volts and has a 650 amp-hour battery bank.

System Comparison – How do these two full-timer/liveaboard systems differ?”

The system we installed on our sailboat was bigger and more robust than the one we installed on our trailer. If we were to install a solar power system on our RV today, it would be what we put on our boat. Here are the differences between the two:

AGM versus Wet Cell Batteries

One basic difference between the sailboat design and the RV design is the use of AGM batteries rather than wet cell batteries. AGM batteries are not only maintenance free but they can be operated while lying on their sides, whereas wet cells prefer to be upright. They also charge up faster and discharge more slowly.

There is less need for expensive AGM batteries in an RV than on a sailboat since an RV never lies on its side the way a sailboat does while sailing. However, that said, gazillions of cruising boats have sailed around the world with wet cell batteries, through all kinds of storms and mayhem, with no problem, so AGM batteries are by no means required on sailboats. On the other hand, if you have the money and don’t want to be hassled with battery maintenance on your RV, go for AGM instead of wet cell!

 To learn more about AGM versus Wet Cell Batteries, see this article:

Wet Cell vs. AGM Batteries ~plus~ Wiring Tips

Physical Panel Size

The primary difference between the two systems is the size of the solar panels.  An RV has things sticking out of the roof that may hamper the installation of very big solar panels (hatches, fridge vents, air conditioning units, TV antenna, domes, etc.).  So the slightly smaller 150 watt panels may be easier to position on the roof than the big 250 watt panels. Going even smaller (120 watt or 100 watt) may be advantageous.

Finding a place for solar panels on a sailboat is challenging, but the best solution is often to build an arch over the back of the boat, as far behind the end of the boom as possible.  This arch can be designed to support large panels.  See our Sailboat Solar page for more details about our arch and panel installation.  If you are a west coast sailor, consider going to Baja Naval in Ensenada, Mexico, and having Alejandro Ulloa install your arch.  His stainless steel fabrication is by far the highest quality and most beautiful we have seen in all of the US West Coast and Mexico.

24-volt versus 12-volt

This sailboat system differs slightly from the first RV system shown above in that rather than being a strictly 12-volt system, one part of the circuitry is 24-volt (the portion between the panels and the charge controller), and one part of the circuitry is 12-volt (the portion between the charge controller and the batteries). 

Marine sailboat RV Solar Panel installation combiner box

The combiner box contains a breaker for each panel and combines the 3 wires from the panels into 1 for the charge controller.

The charge controller steps down the voltage from 24-volt to 12-volt (and correspondingly doubles the current).  Large panels aren’t available in 12-volt configurations.  Also, the wiring for 24-volt panels can be slightly thinner gauge, which is advantageous (discussed in more detail on the next page of this tutorial).

Combiner Box and breakers

The other difference is that this system uses a combiner box and circuit breakers.  This makes for a more professional installation and can be used on any/all solar power installations that use more than one panel in parallel.  The combiner box sits between the panels and the charge controller.  One of its purposes is to combine the three wires coming from the three panels into one wire that goes to the charge controller.  The other purpose is to provide a breaker for each solar panel so that if something goes wrong the panel can be shut down easily or will trip the breaker automatically.

Liveaboard Cruiser’s System Installation

Installation of a solar power system on a sailboat is more complicated that on an RV simply because the panels are flying out there on some crazy scaffolding in the sky and the batteries are scattered about the bilge of the boat somewhere. The solar panels and batteries are often separated from each other by a big distance.  Finding space for batteries, installing them so they will stay in place even if the boat flips upside down, and snaking wires down the inside of stainless steel tubing in an arch is not all that easy.

The things to keep in mind are simply:

– Install the panels so they get shaded as little as possible by the mast and boom
– Make the wire runs as short and direct as possible
– Install the charge controller as close to the batteries as possible

Our Experience on Our Sailboat

The system outlined here is basically the system we have on our sailboat, except we have three 185 watt panels instead of three 250 watt panels (we weren’t sure if the bigger panels would be physically too big.  In hindsight they would have probably fit fine).

We have anchored out over 750 nights, usually for months at a time.  In a typical day we use two laptop computers for about 4-8 hours and watch a movie on our 22″ TV/DVD (with power hogging sub-woofer & surround-sound) at night.

We get about 220 amp-hours (at 12 volts) per day in the summertime and about 165 amp-hours per day in the wintertime, provided the panels are unshaded all day.  We have found that the winter prevailing winds on the Pacific Mexican coast usually position the boat so the mast shades the panels for a few hours each afternoon, dropping our typical daily total to 150 amp-hours.

We have found that if we run both our DC refrigerator and our separate DC freezer (both of which both cycle on and off 24/7 — a very different load than a few hours of continuous computer or TV use — we come up a little short charging the batteries each day in winter. 

However, if we turn off the freezer (which uses about 50-70 amp-hours every 24 hours all by itself!), our batteries are fully charged and in “float” mode by mid-afternoon each day throughout the winter.  So — provided we can live without frozen meat and ice cubes (gasp!) — we can sit at anchor indefinitely without ever going into a marina or running the engine for supplemental charging from the alternator.  This is a good thing, because our fancy Balmar smart charger/alternator combo gave up the ghost in Huatulco, and we waited eight weeks at anchor for a replacement to come down with a friend from the US.  We don’t have any kind of generator on the boat.

Further Discussion

These two solar power systems have worked well for us in their different settings.  I’ve described them here without any background theory because they will do the job for most full-time RVers and cruisers just as they are.  However, there are lots of things to think about when choosing the different components that make up these two systems.  There is a more detailed discussion of those issues on the next page: 

Solar Tutorial Part IV – Panels & Wiring ->

Most of the components for an RV or marine solar power installation can be purchased at Amazon.

Shown here is a complete full-timer's kit (far left), a big charge controller (middle) and a big inverter (right). More comprehensive listings of each component type can be found at the following links:

Purchases at any of our Amazon links help cover our out-of-pocket costs for operating this site -- thanks!

 

Subscribe
Never miss a post — it’s free!

FURTHER READING – RELATED ARTICLES

SOLAR POWER OVERVIEW and TUTORIAL

BATTERIES and BATTERY CHARGING SYSTEMS

LIVING ON 12 VOLTS

Our most recent posts:

More of our Latest Posts are in the MENU.
New to this site? Visit RVers Start Here to find where we keep all the good stuff!!

Solar Tutorial Part II – A small, upgradeable system for simple summertime living

<– Solar Tutorial Part I – Basic Concepts
Solar Tutorial Part III – Full-timer Kits –>

Designing a solar power system for your RV depends entirely on how you plan to use your RV.  Are you RVing in summer or winter, or both?  Are you staying in it for a week or two at a time or for several months at a time?  Do you want to use a laptop for an hour or so a day, or do you need to camp out on it for 4-8 hours at a time?  Do you hit the sack after an hour or so of watching TV or do you want to plunk down in front of it with a cocktail and stay planted there until after midnight?

RV solar panel on the ground

We didn’t install the panel on the roof at first. Silliness! Install it on the roof so you don’t have to think about it!

As a general rule, more solar power is better.  It is really awesome to have so much power that you never need to think about it.  If you are planning to live in your RV for extended periods of time, want to use big appliances a lot and don’t want to be dependent on electrical hookups, get a big full-timer’s system right off the bat.

However, if you are just weekending, vacationing, and living largely outdoors, get a small system.  You’ll quickly learn what you can and can’t do.  It is very easy to upgrade if you find you need more.  Upgrading is mostly a matter of adding more and bigger parts.  Not too many parts have to be swapped out.

RV solar panel installation - wiring the panel's junction box

Mark connected the cable to the panel’s junction box before hoisting the panel onto the roof.

This page describes a “starter solar setup” which is good enough for heading off into the woods for a month or two of simple living in the summer.  We used a system of this size for a full year, boondocking (dry camping) for months on end.  We typically used the laptop or TV or stereo just 1-2 hours a day.  We went to bed 2-3 hours after sunset.

In the summer it was fully adequate for those kinds of light electrical needs.  In the winter there was so little sun that we had to be very conservative.  We used oil lamps at night, and we supplied extra charging for laptop, toothbrush, camera batteries etc. by charging them in the truck while driving around, using a portable inverter plugged into the cigarette lighter in the truck.

A Small Solar Setup:  150 watts of solar power with portable 150 & 300 watt inverters

If you are going to dry camp in your RV in the summer, you don’t need an big solar power system.  You will be busy around the campfire at night rather than watching hours and hours of TV.  You will be using your RV when there is abundant sunshine, and you probably won’t spend too many hours on your computer.  Here is a very simple solution that will be sufficient for as much as a few months of simple living in summertime:

1 150 watt solar panel ($220)
1 Morningstar 10 amp charge controller ($60)
1 Portable 150-300 watt modified sign wave inverter ($30)
10 gauge wire that is rated for outdoor use ($150)
2 12-volt batteries wired in parallel ($150 for that second battery, as your RV should have a battery already)

Total cost:  ~$650
Wild guess at an installer’s fee:  ~$400

Installation

RV solar panel installation on a fifth wheel

Cardboard covers the panels (shown here on our big full-timer’s installation) so they aren’t live

Installation isn’t too difficult if you are willing to scramble around on the roof a bit:

(1)  Install the solar panel on the roof.

While working with the panel, keep it covered so it isn’t producing electricity.  One easy way to cover it is to cut part of its cardboard packaging to size and tape it on.

Mark drilled holes in the roof and used anchors for the screws in places where the panel couldn’t be screwed into a roof truss.  He jammed Dicor lap sealant into the holes before putting the anchors in, then ran the wire and then put more Dicor on the whole works after it was screwed down.

RV solar panel installation on a travel trailer

Mark used lots of Dicor roofing lap sealant

If there is a chance you might eventually want to use your RV in winter, install the panel on tilting brackets so you can tilt the panel towards the sun.  It isn’t necessary to tilt the panel in the summertime, but it can be a huge help in the winter when the sun rides very low in the sky and doesn’t shine down on the panel but actually shines kind of across it from just above the horizon.  Tilting the panel towards the sun might give you an extra 25% of total charge for the day in the wintertime.

When you have tilting brackets, you have to climb up on the roof to tilt the panel each time you set up camp — and you have to remember to climb back up again to lower it down before you drive off.  If you don’t think you want to do all that scrambling around on the roof, skip the brackets (and consider getting two panels instead, described in Part III of this tutorial).

(2)  Install the charge controller inside a hatch near the battery compartment.

(3)  Run the wires from the panel to the charge controller

Connect one end of the wire to the panel (there are screws in the junction box on the panel that you screw the wire to).  You can use duplex wire or two runs of single conductor wire for the positive and negative leads. If the refrigerator is not in a slide-out, run the wire down through the refrigerator vent to the battery compartment.  Otherwise, run the wire down along the outside of the grey or black water vent pipe.

Taping the wire to a metal snake and snaking it down behind the fridge really helps.  We snaked ours down inside a piece of PVC pipe that we used as a kind of conduit to keep the wire away from the back of the fridge.  If you do that, make sure the PVC pipe is quite a bit bigger than the thickness of the wire so you can get it through easily.

RV solar panel installation crawling on the roof

Our lightweight Lynx trailer did not have a “walk-on” roof, but Mark used a telescoping ladder and crawled around to install the panel

You can also use the MC4 connectors in the solar panel’s junction box and use solar power cable that has MC4 connectors pre-installed

At the charge controller, connect the wire coming down from the solar panel to the input side.  Run a second wire from the output side of the charge controller to the batteries.  It is best to crimp eyes on the ends of the cables.

(4)  Remove the cardboard from the panel.

 

You should see an LED light on the charge controller turn green to indicate that it is charging.

300 watt inverter for an RV solar panel installation

Use small, portable inverters plugged into the RV’s cigarette lighters for the TV, laptop, etc.

Now your panel will start charging your batteries all day every day.  It might even start charging them before you get out of bed in the morning!  They will charge faster if you are in full sun.  Just a little shade on the panel (like a single tree branch across one corner) will cause them to charge much more slowly.

(5)  Use your AC appliances

Plug your portable inverters into whatever available cigarette lighter outlets there are inside the RV.

Whenever you want to watch TV, DVD’s or use your laptop or charge your camera batteries or toothbrush or whatever, plug the appliance into an inverter, turn the inverter on, and use the appliance as you would at home!!

RV solar panel installation on a travel trailer - completed

A successful morning’s work – the panel is permanently installed!

(6)  Add a second 12-volt battery to your battery box (this could also be Step 1, it doesn’t matter). 

The battery is your energy storehouse.  You add energy to it when you charge the batteries and you remove energy from it when you use your appliances and lights.  Think of your batteries as being a big kitchen sink.  You fill the sink with water (charge the batteries) by turning on the faucet.  You drain the sink (when you use your appliances and lights) by removing the drain plug.  The goal is to keep the sink at least 2/3 full all the time.  After a day of sunshine, as the sun is setting, your sink should be full.  After an evening of watching TV and computer work, your sink should not be less than 2/3 full (batteries don’t like to be drained until they are empty).

Group 24 deep cycle 12 volt battery for use in an RV solar power system

Add a second Group 24 12-volt battery in parallel

So you have to balance the size of your faucet (the total wattage of the solar panels), the size of your sink (the total amp-hour capacity of your batteries) and your appliance usage (how often and for how long you remove the drain plug) to make sure you don’t drain out more than you can fill up on a sunny day.

Most RVs come with a single Group 24 12-volt battery.  These typically store about 70 amp-hours of energy.  Adding a second Group 24 12-volt battery will double the size of your “sink” to about 140 amp-hours of energy.  As a very general rule of thumb, the total watts of your solar panels should be comparable to the total amp-hour capacity of your batteries.  With 140 watts of solar panels in this system, it makes sense to have two 12-volt batteries to give you 140 amp-hours of battery capacity.

Make sure there is room in the battery compartment for a second battery, as some RVs don’t have room for one.  When shopping for an RV, if you plan to dry camp a lot, make sure the battery box can hold two 12-volt batteries.  Wire the two batteries together in parallel.

 To learn more about batteries and battery charging, read this article:

RV and Marine Battery Charging Basics

And that’s it for this whole system.  Very very simple.  The only limitation to this system is that you need to keep your TV/laptop usage fairly light and you cannot use your microwave, toaster, hair dryer, vacuum or air conditioning unit.  However, it is a great starter setup to get your feet wet and learn to live in a solar driven home on the road.

Monitoring Your Batteries

Fluke snap-on multimeter voltmeter

A multimeter can help you monitor the batteries

The easiest way to see how your batteries are faring is to use a multimeter and measure the voltage.  We use a Sperry clamp-on meter that has jaws that can wrap around wire so you can measure the amperage flowing through the wires, if need be. The Fluke meter is an even better unit because it is true RMS.

Monitoring the battery voltage with a multimeter is not scientifically accurate, because batteries have personalities and memories and only tell the truth about themselves when they have not been under load for a long time and have been cleaned of their surface charge.  However, checking your batteries’ health with a multimeter can still give you a good indication of how they are doing.

Early in the morning, before the sun has gotten over the horizon, measure the voltage between the battery terminals.  If it is 12.3 or higher, you’re okay.  If it is lower than that, go outside and play and leave the indoor appliances alone for a day or two (and hope for sunshine).  If that’s not possible, start thinking about finding a place to plug in.

Likewise, check out the voltage sometime right after sunset before you get the TV or laptop going.  If it is 12.6 or more, you are golden.  If not, then rethink your evening’s activities a bit.

A Portable Solution with NO INSTALLATION NEEDED!!

Folding RV 12 volt solar panel suitcase for_

Portable solar panel kit that folds into a hard shell suitcase!

One very slick option for adding a small solar power system to your RV without going through the trouble of installing the panels on the roof is to get a folding portable solar panel kit. These wonderful kits are pairs of panels that are hinged together on the long side, and they fold together to form a hard shell suitcase that has a handle for easy carrying.

The beauty is that the panels are naturally protected when you store them away, and they have built-in stands that support the panels at a tilted angle when they are set up, so you can aim them south for maximum efficiency.

They come with a small solar charge controller so the batteries don’t get overcharged, and they have alligator clips that make it easy to clip the leads onto the battery terminals.

This is not an upgradeable system, but if you are simply looking to enjoy some dry camping and boondocking in your RV and want a little solar boost for your batteries, this is an all-in-one 120 watt system that will get the job done!

Most portable suitcase kits don’t come with an inverter, so remember to buy that too!

Most of the components for an RV or marine solar power installation can be purchased at Amazon.

Shown here is a complete "weekender/vacationer" kit (far left), a small charge controller (middle) and a small inverter (right). More comprehensive listings of each component type can be found at the following links:

Purchases at any of our Amazon links help keep us going. But don't buy anything yet. Finish the tutorial first!

 

Part III of this tutorial describes ways this starter system can be upgraded to get a little more power. Return to Part I here.

Solar Tutorial Part III – Full-timer Systems –>

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FURTHER READING – RELATED ARTICLES

SOLAR POWER OVERVIEW and TUTORIAL

BATTERIES and BATTERY CHARGING SYSTEMS

LIVING ON 12 VOLTS

 

Our most recent posts:

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Solar Tutorial Part I – Understanding the Basics of Boat & RV Solar Power

This page is the first in a series of four posts that explain the nitty gritty details of RV (and sailboat) solar power. The intention is to demystify the subject of marine and RV solar power and make it understandable for all, regardless of how technical you are or how much you know about electricity. The pages are linked together with arrows at the bottom of each page.

Since we started traveling full-time in 2007, we have been living almost exclusively on solar power, first in a travel trailer, then a fifth wheel trailer and also in a sailboat.  We don’t stay in RV parks or campgrounds or marinas, and on the rare occasions that we do, we don’t hook up to shore power.  As of May, 2017, we’ve spent over 3,200 nights living off the grid without electrical hookups in our rolling and floating homes.

A solar power installation in an RV gives you the freedom to have full electrical power anywhere and at any time: at a rest area, in a parking lot, or at a National Forest campground.  Likewise on a boat, you can anchor out for an unlimited time in bays and coves.  Solar power runs without using any gas, is silent, doesn’t smell, and doesn’t require any setup (those shore power cords are mighty ungainly).  Although we do have a gas generator in our trailer, we use it only when we want to run our 15,000 btu air conditioner, not for charging the batteries.  It is a Yamaha 2400i.

Wrapping your brain around solar power for a rolling or floating home can be confusing, but it is actually quite straight forward.  Here’s the whole thing in a nutshell (wherever it says “RV” you can also think “sailboat,” as the principles are the same).

RV Solar power instalation on a fifth wheel trailer

Mark finishes three days of installing our fifth wheel’s solar power system while boondocked in Flagstaff, AZ.

There are 2 functions that your rig needs to have if you want to live without electrical hookups:  

  •  A system to charge the batteries
  •  A system to create AC power for the rig so you can watch TV and use a vacuum

There are 3 components (or “parts”) used in an RV solar power installation to accomplish the two objectives listed above:

Now put it all together…

  1. To charge the batteries you need:  Solar Panels and a Charge Controller
  2. To use your batteries to generate AC power for your TV, computer, etc., you need:  An Inverter

That’s it!!   Very simple.  To flush it all out a little, here it is in more depth:

Solar Power Function #1 – Charging the Batteries

When an RV comes from the dealership, it usually has either a Converter or an Inverter/Charger in it so it can charge the batteries when it is plugged into shore power (via “hookups” or gas generator).  Converters are cheaper and are factory installed on most trailers.  Inverter/Chargers are expensive (because they are dual-purpose, see below) and are factory installed on higher-end motorhomes.

These appliances take the AC power coming in from the external source (hookups/generator) and use it to charge the batteries.  They usually have a 3-stage charge cycle that charges the batteries quickly at first and then drops to a trickle charge once the batteries are close to fully charged.

morningstar sunsaver 10 charge controller

A $45 charge controller for a small solar power installation

How do you charge the batteries when you don’t have shore power?  That is where solar power comes in.

When you install a solar power system in an RV, you add two things:  Solar Panels and a Charge Controller.  The solar panels are installed on the roof and they gather energy from the sun and pump it down to the charge controller.  The charge controller keeps an eye on the batteries and takes only as much power coming from the solar panels as the batteries can handle.

Outback Flex 60 MPPT Charge Controller

A $500 charge controller for a big solar power installation

Early in the day, the batteries are hungry and the charge controller passes everything it can to the batteries.  As the day wears on, the batteries become more fully charged and require less and less power.  By afternoon, if the system is sized right for the way the RV is being used, the batteries throw up their hands and say, “No More!!” and the charge controller puts them into “Float” mode, a fancy term for a trickle charge.

None of this has anything to do with running your TV or computer.  It is only about charging the batteries up after they become depleted from use the night before.

The solar panels will charge the batteries no matter where your RV is parked.  If you are out hiking, or shopping at Walmart, or taking a nap inside, the batteries will be getting charged all day long.  If you are at an RV park or marina with metered electricity, you can save a few dollars by not plugging in!!

If you park under a tree, and the panels are shaded, you will get dramatically less power from the sun.  A tiny bit of shade results in a huge decrease in how much the charge the batteries can get.  We always park in full sun.

Sailboats have a terrible time with unwanted shade from the mast and boom.  When at anchor, pulling the boom over with the traveler and forcing it further out with a preventer helps a lot, but the mast is always a problem when the sun comes from forward of the beam.  If you are sailing and heeled away from the sun or the panels are shaded by the sails, too bad!!  So, on a sailboat, install more solar panels (more total watts) than you think you’ll need!

100 watt portable inverter from Walmart

A 100 watt portable inverter ($15). Plugs into a cigarette lighter and has one AC outlet

Solar Power Function #2 — Generating AC Power to run the TV

When an RV comes from the dealership, it usually has a shore power cable so you can plug the rig into electrical hookups or into a gas generator.  The shore power cable takes the AC power from the source (“hookups” or generator) and passes it straight through to your AC outlets. 

In other words, when the rig is plugged in like this, all the AC outlets, including “built-ins” like the microwave, become “live,” and you can run your AC appliances like the TV, computer, toothbrush charger, electric razor, hair dryer, vacuum, etc.

If you want to have AC power without plugging into shore power, you have to have an Inverter.  An Inverter converts the DC power that is stored in the batteries into AC power so you can run your AC appliances like the TV and computer. 

However, the Inverter is not technically part of the RV solar power installation.  That is, it doesn’t connect to the solar panels in any way.  You can use an inverter and not have any solar panels installed.  However, unless you plug into shore power, your batteries will get run down by watching all that TV!  That is why Inverters are lumped into the overall notion of RV solar power installations.  They are a vital component if you want to dry camp.

You can buy small, portable inverters for under $25 that will run your laptop from a cigarette lighter.  These work on the cigarette lighters inside an RV just the same as they work on the cigarette lighter in a car.  No difference.  If you are puzzled by all this, get a little power inverter and try it out.  I was totally enlightened the first time I turned on a small inverter in a car and saw the “charging” light on my laptop light up.

300 watt portable inverter

A 300 watt portable inverter ($20) with cigarette lighter plug and 2 AC outlets

A small 300 watt portable Inverters can run small 19″ LED TV too.  Anywhere from 300-500 watts is fine for pretty much everything in an RV except the microwave, hair dryer, vacuum and air conditioner.  You need an inverter of 1000 watts or more to run a small microwave, hair dryer or vacuum.  You can’t run an air conditioning unit from an inverter unless you have a boatload of batteries, something that few RVs can support because of the weight. To run our air conditioning, we use a Yamaha 2400i generator.

A 2000 watt inverter is fine for most things you might use.  You just can’t run the big appliances (microwave, vacuum and hair dryer) simultaneously.  If you are content using these appliances one at a time, don’t bother with an inverter larger than 2000 watts.  We power everything on the boat except the microwave with a 600 watt inverter.  We power everything in the fifth wheel, including the microwave, with a 2000 watt inverter.

Some higher end motorhomes come with an Inverter/Charger (see above), so they don’t need to have an Inverter installed – they already have one.  Turn on the Inverter/Charger, and shazam – all the AC outlets in the rig are “live.”

Atwood converter

A converter – this was factory installed on our fifth wheel

Most trailers do not come with an Inverter/Charger.  They come with a Converter instead.  So if you have a trailer, you will need to get an Inverter to watch TV.

This terminology is unfortunate, as “Inverter” and “Converter” sound so much the same.  However, they are almost the opposite of each other.

  • A Converter charges the batteries, i.e., it takes AC power from an external source — hookups or generator — and puts that energy into the DC batteries to charge them up.
  •  

  • An Inverter takes the DC power from the batteries and creates AC power so you can watch TV.

 

 

Wait, what was all that, again??

So, to recap:  when you install Solar Power in your RV, you are tackling two problems:  ( 1 ) Charging the batteries, and ( 2 ) Generating AC power from your DC batteries so you can watch TV, surf the internet, and charge your camera batteries.

You need three types of components or “parts” to do all this:

  •  An Inverter to create AC power out of the DC power that is stored in your batteries so you can use the TV and computer.  You can use little portable ones that plug into cigarette lighter outlets and/or you can install a big one.

If your rig came with an Inverter/Charger, you are halfway there and need only to add the components for charging the batteries (Solar Panels and Charge Controller).

Next Up: What you need for a small RV solar installation that’s good enough for summer weekends, vacations, and simple living on an extended tour.

Solar Tutorial Part II – A “Starter” Installation –>

FURTHER READING and RELATED ARTICLES

SOLAR POWER OVERVIEW and TUTORIAL

BATTERIES and BATTERY CHARGING SYSTEMS

LIVING ON 12 VOLTS

 

Most of the components for an RV or marine solar power installation can be purchased at Amazon.

Shown here is a complete "weekender/vacationer" kit (far left), a small charge controller (middle) and a small inverter (right). More comprehensive listings of each component type can be found at the following links:

Purchases at any of our Amazon links help keep us going. But don't buy anything yet. Finish the tutorial first!

 

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RV Solar Power Made Simple

Thanks to solar power, we have lived completely off the grid in two trailers and a sailboat full-time since May 2007. Without doubt, our solar power installations have given us more independence and freedom as full-time RVers and sailors than anything else in these lifestyles. It has allowed us to go anywhere at anytime, and has revolutionized our lives.

On this page I describe the two systems we have had on our trailers. These were installed in 2007 and 2008 respectively. Prices for solar power equipment have dropped every year since then, however the prices listed throughout this page are from August 2014:

  • A Small (minimal) RV Solar installation for ~$800 that we used full-time for a year of boondocking in 2007
  • A Full-timer (all you need) RV Solar installation for ~$2,500 that we have used for full-time boondocking since 2008

I also offer a little theory and reveal some of the discoveries we have made along the way. For more info, please see our Solar Power Tutorial pages and our Sailboat Solar Power Installation page.

Links to all of our articles about solar power can be found on our Solar Power For RVs and Boats page.

You can navigate to different parts of this article by using these links:

This page was first published in the fall of 2008 but was completely revised and rewritten in the summer of 2014.

WHY BOTHER WITH A SOLAR POWER INSTALLATION ON AN RV?

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The biggest advantage of a solar power system in an RV is that the system works from dawn to dusk, silently, odor free and without requiring any fuel or maintenance, no matter where you are or what you are doing. Towing, parked at the grocery store, or camped, the batteries are being charged. They start getting charged before you finish breakfast, keep charging while you hike or go sightseeing, and continue all day, rain or shine. They don’t quit charging until nightfall. You never have to think about the batteries getting charged. It just happens. In our current rig, I feel like we have electrical hookups all the time — and we never get hookups any more!

Traveling full-time since 2007, we have connected to electrical hookups for a total of about 25 days, and that was during our first 18 months on the road. The last time we got electrical hookups was in October, 2008. Since we began our full-time travels in 2007, as of May 2017, we have boondocked in our RV over 2,400 nights. We also lived on solar power on our sailboat for over 900 nights during our sailing cruise of Mexico.

We do carry a Yamaha 2400i generator, but use it only a few days each year, either after a long period of winter storms to give the batteries a boost, or on hot summer days to run our 15,000 BTU air conditioner. We have used it a total of about 20 times since we purchased it in December 2007. We run it every six months or so to flush the gas through the lines. Little as we have used it, we have found the Yamaha to be a fabulous generator. It has always started on the first pull, even after it sat in storage for 20 months when we first moved onto our sailboat!

Our first solar power installation that we used for a year in 2007 was a “small” system that allowed us to use almost every appliance we owned, that is, laptop, TV, hair dryer, vacuum, two-way radio charger, power drill, etc. However, we had to be very conservative with our electrical use during the winter months. A similar “small” RV solar power kit can be found here.

Our second “full-timer” solar power system that we have been using since 2008 is like having full electrical hookups wherever we go. Very little conservation is necessary! On our biggest electrical use day to date, we watched our 26″ LCD TV with its huge surround-sound system and sub-woofer for 15 hours (it was the Olympics!) and ran two 13″ laptops for 7 hours, made popcorn in the microwave and ran several lights for 4 hours in the evening. It was July, and the next day was very sunny and the batteries were fully charged by mid-afternoon. A similar “full-time” RV solar power kit can be found here.

BASIC ELEMENTS OF A SOLAR POWER INSTALLATION

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BATTERY CHARGING and AC POWER
The basic components of all solar power installations is the same, and is comprised of two major subsystems: BATTERY CHARGING to get the batteries charged up and AC (120v) POWER for appliances that can’t be run on DC (12v) power (i.e., TV, computer, vacuum, hair dryer, etc.).

The BATTERY CHARGING subsystem includes these components:

  • Batteries
  • Solar panel(s)
  • Charge controller to protect the batteries from getting overcharged

The AC POWER subsystem includes this component:

  • Inverter(s) to convert the batteries’ 12 volt DC power to 120v AC power

GET YOUR HANDS DIRTY!

300 watt inverter for an RV solar panel installation

A 350 watt portable inverter
Plug it into a cigarette lighter

It is hard to “play with” the battery charging subsystem of a solar power installation to get a feel for how it works until you actually take the leap and buy a solar panel, charge controller and cables and hook it all up to the batteries. One great option if you don’t want to do any wiring but want some hands on experience is to get a portable solar panel kit. You can sell it later if you want to upgrade to a rooftop system.

You can get the hang of how the AC power subsystem works very easily. Simply run down to Walmart or any auto parts store and pick up a $15-$20 inverter that plugs into a cigarette lighter. Plug it into the lighter in your car, turn it on, and then plug your laptop into it or your electric razor or any other small appliance. Now your 12 volt car battery is operating your 120 volt appliance.

Big inverters that can run the microwave, toaster, blender and vacuum cleaner work on exactly the same principal, the difference is just the amount of power the inverter can produce. Big inverters are also wired directly to the batteries rather than plugging into a cigarette lighter.

IS SOLAR POWER EXPENSIVE? SMALL SYSTEMS VERSUS BIG SYSTEMS

The difference between the “small” system we used for one year on our little Lynx travel trailer and our “full-timer” system we have now on our big Hitchhiker fifth wheel is simply the overall capacity of each of the components. That is, the capacity of the battery charging system (solar panels, batteries and charge controller) and of the AC power system (the inverter).

In functional terms this means that the difference between the “small” and “full-timer” systems is threefold:

1) the ability to run more appliances at once (i.e., have two laptops running while the TV and blender are going)
2) the ability to run larger appliances (i.e., using a VitaMix versus a small blender)
3) the ability to run more appliances for a longer time at night without discharging the batteries too much.

So, in a nutshell, the two subsystems — battery charging (batteries + panels + charge controller) and AC power (inverter(s)) — combine to do the same job as plugging a generator into the shore power connector on the side of the rig. The panels and charge controller charge the batteries. The inverter makes it possible to use AC appliances.

The cost of the parts for these installations is:

Small: $800 – Comparable to having a Yamaha 1000i generator
Full-timer: $2,500 – Comparable to having a built-in Onan 4KW generator

With solar power there is no noise, no fuel cost, no maintenance and no smell, unlike a generator. However, it is not possible to run the air conditioning in the summertime on solar power, unless you have a massive system with several hundred pounds of batteries and a roof absolutely loaded with panels. As mentioned before, we use our Yamaha 2400i generator to run our 15,000 BTU air conditioner.

 

OUR “SMALL” RV SOLAR POWER SYSTEM (~$800 in parts)

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This setup is a fully functional, inexpensive solar power installation, and is what we used for a 350 nights in our first year in our Lynx travel trailer. It could power a 19″ LCD TV and DVD player, radio, laptop and vacuum as well as charge camera batteries, razor, toothbrush, cordless drill, cell phone, etc.

  • Two 6-volt batteries (wired in series) giving 220 amp-hours of capacity $220

    Ours were Energizers from Sam’s Club

  • 140 watts of solar power $285

    Ours was a Kyocera 130 watt DC panel. Today Kyocera sells the 140 watt panel instead.

  • A charge controller that can support at least 10 amps $60

    Ours was a Morningstar Sunsaver 10 amp charge controller (consider a Sunsaver 20)

  • A portable inverter that can supply 1000 watts of AC power $120

    Ours was a Pro One 800 watt inverter

  • Cables, connectors and mounting brackets $100

This system is the smallest size system I would consider for an RV if you want to drycamp or boondock for more than a night or two and be comfortable. This setup worked great in the spring, summer and fall when the sun was high in the sky and the days were long. We never thought too much about our power use until the wintertime when the days got short and the nights got long and cold. Then we began to wish for a bigger system.

RV solar panel installation - wiring the panel's junction box

Mark installs our first solar panel on the roof.
He chose a nice spot by the ocean to do it!

On those long cold winter nights we had to conserve our use of lights and the TV to make sure our furnace (which used a lot of battery power) could still run. We used oil lamps a lot in the evenings. If we had stayed in that trailer longer, we would have installed a vent-free propane heater that did not use any battery power (we eventually did that in our bigger trailer the following winter: see our Vent-Free Propane Heater Installation page).

I think every RV should have this kind of a charging system installed as standard equipment, as it is useful even for the most short-term camping, like weekends and week-long vacations during the summer months.

When we installed this “small” system in our little Lynx trailer in June 2007, we were quoted $135-$350 for installation. Mark is very handy (although he is not a Master Electrician), and he found the installation was not difficult at all and completed it in one day.

SOME THEORY – SIZING THE SYSTEM

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CHARGING & CONSUMPTION

Here is some theory to explain why the above system is “sufficient” but is not great for “full-time” use. When it comes to a solar battery charging system, the concept of power charging and consumption is very simple. The amount of power you can use, or take out of the batteries, is essentially only as much as the amount you can put into the batteries. If you use (or take out) more power than you replace (or charge them with), sooner or later your batteries will be discharged and dead. The batteries are just a temporary storage place for electricity. They act as a flow-through area for the power you are going to use.

The most important part of any solar setup is the amount of charging going on (i.e., the total size, or capacity, of the solar panels), and you want that to be greater than the amount of electricity you use. More must go into the batteries than comes out. You can have an infinite number of batteries and eventually discharge them all completely if you repeatedly use more electricity than your solar panels put in.

We often find people want to add batteries to address their power shortages when what they really need to do is add more solar panels. As a rule of thumb, don’t use more than 1/3 to 1/2 of the total capacity of the batteries in one night. More important, though, is that the bigger the solar power panel array, the better. And lastly, Keep the size and age of all the batteries in the system fairly similar so the strong ones don’t waste their energy helping the weak ones keep up.

AMPS and AMP-HOURS

Appliances use amps to run. Another unit, the amp-hour (abbreviated as “Ah“), refers to the number of amps an appliance uses when it is run for an hour. For instance, an appliance that uses three amps to run will use up three amp-hours when it runs for an hour. These amp-hours will be drawn from the batteries, and the batteries, in turn, will look to the solar panels to recharge the amp-hours they have forked over to the appliance. It is for this reason that you need to know how many amp-hours you will use in a typical day. Ultimately those amp-hours must be replaced by the solar panels, so the size and number of panels you purchase will be determined by how many amp-hours you use in a day.

To estimate how many amp-hours you might use in a day, estimate how many hours each appliance will run and multiply that by the number of amps the appliance uses. We have measured some of the appliances in our trailer, and this is how many amps they use:

Single bulb DC light — 1.5 amps
Dual bulb DC light — 3.0 amps
Dual bulb fluorescent light — 1.5 amps
19″ LCD TV — 5.5 amps
DVD / CD Player — 0.5 amps
13″ MacBook laptop, on & running — 6-8 amps
13″ MacBook, off and charging — 1.6 amps
Sonicare toothbrush charging — 0.1 amps
FM Radio w/ surround-sound — 3.0 amps
12′ string of rope lights — 3.3 amps

We find that we typically use anywhere from 50 to 150 amp-hours per day, most commonly in the 70-90 range.

HOW MANY AMP-HOURS DOES MY FAVORITE GIZMO USE?

Since RV solar power systems are DC battery based, it is helpful to know how many amps (in DC) various appliances use. Multiplying that value by the number of hours the appliance is used each day then reveals how many amp-hours the appliance will require from the battery in the course of a day.

Most DC appliances list their amp usage in the user manual or spec sheet. In contrast, most AC appliances list their wattage in the user manual instead of amperage. So, for AC appliances that are run on an inverter you have to do some math to get their equivalent DC amperage rating.

You can get a rough estimate of the number of amps that an AC device will use on an inverter simply by dividing the wattage by 10.

Why is that?

Here’s one way to look at it: Technically, Watts = Volts x Amps. AC circuits run at ~120 volts. DC circuits run at 12 volts. An AC appliance will use the same number of watts whether running on a DC or AC. On a DC circuit (using an inverter so it can run), that AC appliance will use 10 times as many amps as it will on an AC circuit (that is, 120/12 = 10).

Here’s another way to look at it: Watts / Volts = Amps. So, to determine most precisely how many DC amps an AC appliance will use when running on an inverter, start by dividing the number of watts it uses by 12 volts to get its Amps DC. HOWEVER, keep in mind that inverters are not 100% efficient. Typically they are only about 85% efficient. That is, an inverter loses a bunch of watts to heat as it runs — about 15% of the watts it needs to run get dissipated into heat. So, it takes more watts to get the required amps out of the inverter, the exact figure being 1 / 85%. This means that after you divide the appliance’s Watts by its Volts (Watts / 12, as I mentioned above), then you have to divide that result by 0.85. This is messy.

Rather than dividing watts first by 12 and then again by 0.85, you can simply divide the watts by 10 and get a pretty close estimate. (That is, (1/12)/0.85 = 0.1)

Our AC 19″ LCD TV is rated at 65 watts. How many amps is that DC? 65/10 = 6.5 amps DC. We measured the TV at the volume we like to hear it and it was using 5.5 amps. If we cranked up the volume, the meter went up to 6.5 amps.

Likewise, our old white MacBook Pro laptop was rated for 65 watts. As we opened and closed files and started and stopped various programs, the meter zoomed all over the place between 3 amps and 8 amps. When we ran Adobe Lightroom, which is very disk and memory intensive, the readings hovered in the 7-8 amp range. So on average you could say it uses about 6.5 amps DC.

When we shut down the laptop and left it plugged in and charging, the meter dropped to 1.6 amps. This is important if you are trying to conserve electricity! Run your laptop on its own battery until the battery is depleted. Then turn it off and let it charge from the inverter while you do something else!

HOW DO YOU MEASURE THE POWER USAGE OF A DEVICE?

If you have nothing running in the rig (no computers running, no TV, no vacuum or toaster, etc.), you can measure the current a device is drawing from the batteries using a clamp-on meter around one of the battery cables. To measure the AC current of a small device, you can use a Kill-a-Watt meter. Simply plug it into an AC outlet and plug your device into it.

WHERE DO THE BATTERIES FIT IN?

Battery storage capacity is measured in amp-hours (Ah), and more is better. As a starting point, most new RVs come equipped with one 12-volt Group 24 battery which will give you about 70-85 Ah of capacity. Assuming the sun has charged the batteries completely by nightfall, and sticking to the rule of using only 1/3 of your total battery capacity each night, you will have only 25 Ah available each evening. That isn’t very much!

What is the best upgrade strategy?

Upgrading to two 12-volt Group 24 batteries (wired in parallel) will give you 140-170 Ah of capacity.

However, a 6-volt golf cart style battery has the same footprint as a Group 24 12-volt battery (although it is about 3″ taller), and a pair of them wired in series will give you about 210-240 Ah of capacity.

So, rather than buying a second 12-volt Group 24 batteries and getting just 140-170 Ah of capacity out of the pair, why not sell the 12 volt battery and buy to two 6-volt golf cart style batteries for 210-240 Ah of capacity? That’s what we did on our first trailer. Just make sure that you have enough height in the battery compartment for the taller golf cart batteries.

WHAT ABOUT BATTERY MAINTENANCE?

So far I’ve been talking about wet cell batteries, and these kinds of batteries need to be maintained. Wet cell batteries are made with thick metal plates and liquid between them. Over time the liquid evaporates and needs to be replaced with distilled water. Also, over time, sulphite builds up on the plates and needs to be removed by “equalizing” the batteries.

Hydrometer Reading on Battery

Use a hydrometer to check each battery cell.

Before we upgraded to AGM batteries, Once a month Mark would check the liquid levels in each cell of each battery and pours in a little distilled water wherever needed. He also checked the condition of each battery cell using a hydrometer. This little device indicates whether a cell is functioning at full capacity. Then he equalizes the batteries by programming our charge controller to raise the voltage on them to one volt higher than their normal charging voltage for five hours. Last of all, he re-checks the liquid level in each battery cell and adds distilled water as needed and re-checks each cell with the hydrometer. Usually any cells that had a poor reading before equalizing now give a good reading.

This maintenance stuff can be avoided by buying AGM batteries which are maintenance free. However, AGM batteries are really expensive. One big advantage of AGM batteries for sailors and for people with tight battery compartments is that they operate fine in any position, that is, they can be installed on their sides and will operate when a sailboat is heeling. We had them on our sailboat.

On our trailers, we initially opted for wet cell batteries. We had Trojan 105 wet cell batteries for the first five years on our fifth wheel. Then we replaced them with cheaper Costco batteries from Interstate (Johnson Controls).

The Trojans worked very well, but replacing them with cheapo batteries was a mistake. The cheap batteries failed completely within 14 months.

We now have four Trojan T-105 Reliant AGM batteries which are truly awesome. They are a little more money than the T-105 wet cell batteries, but they are superior and, in our minds, worth the extra little bit of cash.

To learn more about our new batteries, why we chose them, and how we upgraded the power plant on our trailer in April 2015, visit:

Wet Cell vs. AGM Batteries – Why We Upgraded to AGM Batteries PLUS Wiring Tips!
RV Electrical System Overhaul

To learn more about batteries and what “single-stage” and “multi-stage” battery charging is all about, visit:

RV and Marine Battery Charging Basics

AND HOW ABOUT THE SOLAR PANELS?

Battery capacity is only part of the story. The ultimate limiting factor is how many amp-hours the solar panels can put into the batteries during the day. If the solar panels are sized too small to charge the batteries sufficiently each day, you will eventually discharge the batteries over a series of days and they will be dead.

Solar panels are rated in terms of Watts. The relationship between the amp-hours that the panel can store in a battery and the panel’s watts rating is not straight forward. Suffice it to say that a 130 Watt panel produces 7.5 amps in maximum sunlight when the panel is exactly perpendicular to the sun, and both of those numbers are available in the specs for the panel. What isn’t stated, however, is how many amp-hours a panel will produce in a given day. That is because it varies by what latitude you are at, what angle the sun is to the panel (which changes all day long), how brightly the sun shines, how many clouds go by, etc.

We have found that each of our 120 watt and 130 watt panels typically produces between about 8 Ah and 40 Ah per day depending on the season, weather, latitude, battery demands, etc. Most commonly, they produce around 25-30 Ah per day each.

If you have the time and inclination (who’s got that stuff?), you can figure out how many amp-hours you use each night. Make sure that that number is less than 1/3 of your total battery capacity AND make sure your panels can provide that many amp-hours of charging each day.

But all that sounds very difficult.

To learn more about SOLAR PANELS, see our detailed review of the many different types of panels available today:

Solar Panel Selection – Flexible or Rigid? 12 volt or 24 volt? Monocrystalline or Polycrystalline?

NEVERMIND THE THEORY – JUST TELL ME WHAT SIZE STUFF I NEED!

As I have mentioned before, we changed how we lived when we had a small solar power installation and again when we got a big one. You can opt to live with very little electricity or not.

We met a couple living on their 27′ sailboat on its trailer in the desert in Quartzsite, Arizona (they were on their way to launch it in the Sea of Cortez). They were using just 6 amp-hours per day because they had a tiny solar panel. Lord knows, I never saw their lights on at night! In our little Lynx travel trailer we used about 25-35 amp-hours per day. In our Hitchhiker fifth wheel we use an average of 60-120 amp-hours per day.

So as a rule of thumb, here is the number of amp-hours you might consume per day:

• 6 Ah = living ultra-conservatively
• 35 Ah = living very modestly
• 120 Ah = living much the way you do in your house

The amp-hour capacity of your battery bank should be three (to four) times your typical daily amp-hour usage.

A popular rule of thumb is to match (roughly) the amp-hour capacity of the batteries to the watts capacity of the solar panels. So, 140 Ah of battery capacity “goes with” 140 watts of solar power. 440 Ah of batteries “goes with” 440 watts of solar power.

However, having more solar capacity than that is not a problem, as it gives you much more flexibility in case you have cloudy days, the panels aren’t oriented well towards the sun, or you have periodic shading during the day from buildings or trees.

 

OUR “FULL-TIMER” RV SOLAR POWER SYSTEM (~$2,500 in parts)

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Fifth wheel trailer solar power 681

In a nutshell, in order to run your RV with the same level of comfort as a house, using all of your appliances whenever you feel like it without thinking about conserving at all, you will need at least the following:

  • Four or more 6-volt batteries giving you at least 440 amp-hours of capacity

    We have four 6-volt batteries (2 pairs of batteries in series to make two 12-volt equivalent batteries, and then those 2 twelve volt equivalent batteries placed in parallel with each other). We had Trojan 105’s for the first five years, and after that we’ve had batteries from Costco, ~$480, which we soon replaced with Trojan T-105 AGM Reliant batteries, $1,200 (see note below).

  • 500 or more watts of solar power (preferably 600-800 watts)

    We have three 120-watt Mitsubishi panels and one 130-watt Kyocera panel, for a total of 490 watts of solar power, `$1,140

  • A charge controller that can support 40 amps or more (preferably 60 or 80 amps)

    We have an Outback FlexMax 60 60 amp charge controller (consider the FlexMax 80) $565
    For more info see our page: Solar Charge Controllers – Optimizing RV Battery Charging

  • A true sine wave inverter that can supply at least 1000 watts of AC power (preferably 2000 or 3000 watts)

    For 7 years we had an Exceltech XP 1100 watt true sine wave inverter $600.

PLEASE NOTE: In April, 2015, we upgraded to Trojan 105 Reliant AGM batteries ($1,200) and an Exeltech XP 2000 watt true sine wave inverter ($1,700). See our post RV Electrical Power System Overhaul to learn more.

This system will power everything except the air conditioner, regardless of weather or season. My notes indicating “preferably” larger sizes for everything reflects the fact that our installation is now quite old and component parts costs are half what they were when we were buying. More is definitely better.

I’ve never heard anyone say they wished they had less solar power!

Mark did the installation of this solar power system on our Hitchhiker fifth wheel. My rough guess is that the installation might have cost $700-$1,500 if done by an experienced installer. It took him three partial days, largely because we were boondocked in the woods about 15 miles from Home Depot, and I had to keep running back and forth to get little things for him!

NOTES and LESSONS LEARNED

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More and more solar power equipment manufacturers are selling complete kits for RVs, boats and cabins. Here is an example full-timer kit from Go Power, and a slightly smaller full-timer system from Renogy. Here is a small solar power kit from Go Power for “weekender/vacation” use and another small solar kit using Renogy panels.

Also, if you don’t want the hassle of doing an installation, here’s a nifty portable solar panel kit that folds into an easy-to-carry suitcase!!

 

INVERTER and CONVERTER CONFUSION

If you are like me, the terms “inverter” and “converter” are confusing. They sound so similar it seems they must be one and the same thing. They are actually two very different components with very different missions in an RV.

CONVERTERS

A converter takes the AC power coming in from the shore power cord (via electrical hookups or a generator) and gives power to all the DC appliances in the rig so the batteries can take a break. It essentially does what the batteries do, but does it only when there is shore power.

The DC converter in an RV also charges the batteries while connected to shore power. Some converters have sophisticated multi-stage charging mechanisms, and others simply provide a trickle charge.

For more about single-stage versus multi-stage charging, click here.

The DC converter is not involved in the solar power system. In our “full-time” solar setup, the DC converter is actually unplugged because our inverter powers all the AC outlets in the rig. Because of our converter’s design, when it is plugged in it senses when there is AC power available and automatically turns on. This would impose a huge demand on our batteries whenever we turned on the inverter.

Once in a while, when the skies have been overcast or stormy for a few days, we fire up our trusty Yamaha 2400i generator to bring the batteries up to full charge. We plug our shore power cord into the generator, unplug the inverter and plug in the converter. Now the converter is charging the batteries.

The converter that came with our rig was a single-stage trickle charge Atwood 55 amp converter. This was very inefficient for use with the generator because it charges at such a slow rate that we had to run the generator for hours and hours to get the batteries charged up.

In April, 2015, we replaced that converter with a slick new Iota DLS-90 / IQ4 converter. This converter can put as much as 90 amps into the batteries and has a true multi-stage charging algorithm. To see our introductory post about our big electrical system upgrade, see this post: RV Electrical Power System Overhaul

For more about converters, visit: RV Converters, Inverter/Chargers & Engine Alternator Battery Charging Systems

Almost all trailers and many smaller motorhomes have a converter installed at the factory.

INVERTERS

An inverter takes the DC power from the batteries and converts it to AC power so you can run things like TVs, computers, vacuum cleaners, hair dryers, toasters, etc., and also charge things like your phone and camera batteries. Turn on the inverter, plug an AC appliance like an electric razor or TV into it, and poof, the razor or TV works.

Inverters come in two flavors:

True Sine Wave (or Pure Sine Wave) which means the AC power signal coming out of the inverter is identical to the power signal of a wall outlet in a house (a smooth sine wave).

Modified Sine Wave which means the waveform is clipped at the top and bottom and is stair-stepped in between rather than being a smooth sine wave.

It is easier to convert DC power to a square-type wave than a smooth sine wave, so modified sine wave inverters are much cheaper. However, some sensitive AC appliances don’t work with a modified sine wave inverter.

We purchased a high-end true sine wave inverter for our “full-time” solar setup, because it matched the quality of the system and our particular unit was noted for its ruggedness (we run it 15 hours a day, sometimes 24). Our Exeltech true sine-wave inverter is designed to operate medical equipment, so it provides exceptionally clean and stable AC power.

See our story “How Much Inverter Is Enough?” to learn about what happened to us when we accidentally “blew up” our fancy Exeltech true sine wave inverter and had to live on a tiny cheapo 350 watt modified sine wave inverter while waiting for the parts to fix it!

Ironically, some RV parks have unstable AC power that can damage AC appliances in an RV. Our inverter power from our Exeltech is cleaner and more reliable (Exeltech inverters are designed to power sensitive medical equipment)! Desktop computers, laser printers, TV and stereo equipment and Sonicare toothbrushes are the most likely appliances to have trouble with modified sine wave inverters. However, when we used modified sine wave inverters exclusively with our small solar power setup on our Lynx travel trailer, we never had a problem with any of our appliances. Modified sine wave inverters often have loud fans, and Mark did have to put some WD40 on our Radio Shack inverter twice when the fan quit working unexpectedly.

INVERTER/CHARGERS

To add to the confusion about inverters and converters, some inverters combine a little of the functionality of both an inverter and a converter. These are called inverter/chargers and have two independent functions: (1) convert the batteries’ DC power to AC (inverter), and (2) use the AC power from the shore power cord (connected to electrical hookups or generator) and charge the batteries.

These are pricey pieces of equipment and many higher end motorhomes come with them. Our sailboat came with both a 600 watt pure sine wave inverter (which we used for everything on the boat except the microwave) and a 2500 watt modified sine wave inverter/charger (which powered the microwave and charged the batteries when we plugged into shore power).

NOW THAT IT’S ALL CLEAR, THE MANUFACTURERS MESS US UP!

The distinction between inverters and converters is pretty easy, isn’t it? However, recently when I was in an auto parts store I noticed a box labeled “POWER CONVERTER” and the picture and description were very clearly that of an INVERTER! So, maybe the distinction is going to get all muddied up after all.

For more about inverter/chargers, visit: RV Converters, Inverter/Chargers & Engine Alternator Battery Charging Systems

AN IMPORTANT NOTE ON RV REFRIGERATORS

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Because conventional propane RV refrigerators are inefficient and are (shockingly) expected to fail within ten years of service (see our blog post about that here), the current trend in full-time RVs is to manufacture them with residential AC refrigerators. These RVs are built with an inverter large enough to power the refrigerator while the RV is in transit. This is great for folks that are going to plug into electrical hookups 100% of the time. However, the electricity required to run a refrigerator, whether AC or DC, and no matter how Energy Star Efficient it is rated to be, is astronomical.

A typical 10 to 12 cubic foot Energy Star refrigerator will use over 300 kilowatts per year, or 822 watts per day. There is some energy lost when running on an inverter, so this will be roughly 822 Watts / 10 Volts = 82 amp-hours per day. To keep this fridge operating during the short days of winter when the sun is low in the sky, you will need 400+ watts of solar panels and 200+ amp-hours of battery capacity in addition to whatever you will need to run the rest of the household.

If you plan to boondock a lot, and you don’t want to run your generator 24/7, be prepared to outfit your rig with over 1,000 watts of solar panels and close to 1,000 amp-hours of battery capacity to power a residential refrigerator.

Non-Energy Star compliant DC electric refrigerators are even worse. Our sailboat had a 3.5 cubic foot DC refrigerator (“counter height” or “dorm size”) that was built for RV use. It did not have a freezer compartment. We had 710 amp-hours of AGM batteries and 555 watts of solar power. Granted, we were living in the tropics and the ambient cabin temperature was generally 85 degrees. The refrigerator compressor ran about 50% of the time and our solar power system was pushed to the max to keep the batteries topped off every day.

We had a separate standalone 2.5 cubic foot DC freezer on our sailboat. If we turned the freezer on, the solar panels could not keep the batteries charged without supplemental charging from the engine alternator every third or fourth day.

Residential refrigerators have vastly improved in recent years, running on a mere 25% of the electricity they used to use in 1986, and they are only getting better. For more information about refrigerator energy use and energy saving tips, see this resource: How Much Electricity Does My Refrigerator Use?

I have corresponded at length with a reader who has been boondocking 95% of the time for 6 months in a 40′ Tiffin Phaeton motorhome. He has a Whirlpool 22 cubic foot residential refrigerator, 1,140 watts of solar panels on his roof and 940 amp-hours of battery capacity in his basement. His fridge is powered with a dedicated Xantrex pure sine wave 2,000 watt inverter that is wired through a transfer switch to both his shorepower line and his generator, just in case the inverter fails (he had a 1,500 watt modified sine wave inverter that literally burnt up and started smoking).

So it can be done, but it will be easier in a motorhome that has a big payload capacity than in a fifth wheel or travel trailer that has a smaller payload capacity due to the weight of the batteries required. Even though we had to replace our RV refrigerator in its 8th year of service, we do not want double our battery bank and solar panel array just to power a residential fridge. I would rather put that extra 275 lbs into other things we need in our mobile lifestyle.

PHEW! THAT WAS A LOT OF INFO. WHAT NOW?

Still confused about the components and operation of an RV solar power system? See our four part RV SOLAR POWER TUTORIAL series where these concepts are re-introduced and discussed in greater detail:

Learn more about the different kinds of solar panels on the market:

Solar Panel Selection – Flexible vs. Rigid, 12 volt vs. 24 volt, Monocrystalline vs. Polycrystalline – PLUS Wiring Tips!!

Get the quick-and-dirty shopping list of things to buy for your solar power installation:

Three RV Solar Power Solutions: Small, Portable, and Big!

Want to learn more about BATTERIES and understand how battery charging works at a deeper level? Our Intro to Battery Types and our four-part tutorial series covers all the details involved in charging RV and marine batteries and takes a close look at a variety of specific charging systems, from converters to inverter/chargers to engine alternators to solar charge controllers. It also reveals how these systems work together:

Curious about the solar power installation we did on our sailboat? See our page: SAILBOAT SOLAR POWER INSTALLATION.

In April, 2015, we overhauled our electrical power plant on our trailer. See the introductory post about this upgrade here:
RV ELECTRIC POWER SYSTEM OVERHAUL

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Where do you buy solar panels, charge controllers, inverters and such? Surprisingly, Amazon offers solar power kits and more. Click the following links for a wider selection of:

If you click through to Amazon from anywhere on this website, anything you put in your shopping cart or wish list immediately after that results in a small commission to us at no cost to you, no matter what you search for and no matter when you finalize the purchase. This is a wonderful way that you can "help us help you" with detailed and carefully researched articles. Thank you!

 

We offer all the information on our website free of charge in hopes of helping help our fellow RVers and cruisers. We have been alarmed and saddened to find portions of the copyrighted material on this page plagiarized in ebooks that are sold for profit, but so it goes. Imitation is the sincerest form of flattery. Good luck with your solar power installation — we hope our articles on this website are useful to you!

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How much inverter is enough?

Living totally off the grid on battery power in an RV or sailboat requires a good sized inverter to power the AC appliances like TVs, laptops, microwave, camera and cell phone chargers, hair dryers and vacuum cleaner.

But what is “good sized?”  How much is too much — or not enough?  What happens if you go over the limit? A recent mishap when we first returned to living in our trailer a few months ago sent us back to the basics and reminded us about limits, living skinny and living large while boondocking and living on a small inverter.

Exeltech XP1100 Power Inverter in the basement

Our Exeltech XP 1100 watt pure sine wave inverter lives in the
fifth wheel basement.

Figuring out the math behind the theory — the amps, volts, watts and conversions between them — and doing that for each appliance while guessing how much time each one will be used every day is downright daunting.

What’s worse — for people like I once was who are dealing with this stuff for the first time when they contemplate full-timing — just the terms “inverter,” “converter,” and “inverter/charger” leave us scratching our heads in bewilderment.  Techie phrases like “modified sine wave” and “pure sine wave” made my head spin when we first started out.

If that is the case for you too, have a look at our multi-part Solar Power Tutorial series where those terms (and many more) are explained in plain words.

As for inverter capacity, it is given in watts, and after living on several different sized inverters and inverter/chargers for almost seven years in two trailers and a sailboat, we have gotten a pretty good feel for what our moveable household of two people requires.  But that doesn’t mean we are immune to slipping up!

When we bought our full-time fifth wheel trailer in 2008, like most trailers, it did not have a factory installed inverter.  It had a 55 watt converter, and that was it.  (Most motorhomes have a factory installed inverter/charger that is wired to the AC outlets instead of a converter.)  So, we installed a pure sine wave Exeltech XP 1100 watt inverter

This is a top quality inverter that is built to such high standards that it can run very sensitive medical equipment off the grid. Exeltech inverters are used on the International Space Station to provide AC power to both the American and Russian sides of the station!

Sinergex Pure Sine Wave 600 watt inverter

This 600 watt pure sine wave inverter powered almost all
of our activities on the boat.

We chose that size because there was a huge increase in pure sine wave inverter prices once you got over about 1100 watts, and we had no single appliance on board that required more than that.  (In 2014 prices, the XP1100 inverter is ~$600 while the XP2000 inverter is ~$1,300).

The trailer’s microwave is 900 watts, and everything else we use (except the air conditioning which requires a generator anyways) is much less than that.  As long as we used only one big appliance at a time, all would be well.

The only real conflict that ever came up was when we used the microwave.  We had to be sure the TV was off and the laptops were running on battery power for the few minutes we used the microwave.  No big deal.

The sailboat we bought and moved aboard a few years after the trailer came with two factory installed inverters: a 2500 watt Xantrex Freedom 25 modified sine wave inverter/charger and Sinergex 600 watt pure sine wave inverter. The big inverter/charger was wired to all the AC outlets on the boat.  However, the little 600 watt pure sine wave inverter had been installed exclusively for the entertainment system: the two AC outlets on the inverter had two ordinary extension cords that went directly to the TV and the Bose 3-2-1 surround sound system.  This little inverter was independent of the boat’s AC wiring system.

The big modified sine wave Freedom 25 2500 watt inverter powered the microwave and vacuum.

The big modified sine wave Freedom 25 2500 watt inverter
powered the microwave and vacuum.

Because we had used a pure sine wave inverter in our trailer for a few years (and liked the idea of feeding our expensive computers a good quality signal), and because we assumed the big Xantrex inverter/charger would use a fair bit of power just to run in a “no load” state, we decided to rearrange the extension cords on the small pure sine wave inverter and use it as our primary inverter instead, running our laptops and charging up all our small appliances on it.

So, effectively, the only time we ever turned on the Xantrex inverter/charger was to use the boat’s 500 watt microwave that the factory had wired into the AC system, and to use our little dirt devil vacuum cleaner.  Everything else — 22″ LED TV, 13″ MacBook laptops, cameras, portable GPS/VHF radio, GMRS walkie/talkie radios, toothbrush, etc. — got plugged into a power strip coming from the 600 watt pure sine wave inverter’s AC connector.

Mark inspects inverter

Mark inspects the Exeltech inverter

This worked really well for us for the 3.5 years we lived off the grid on the boat.

However, when we moved back into our trailer, we were still living in the mindset we’d had on the boat, which made us careless with the microwave.  Whereas, on the boat, the 500 watt microwave was on a very big standalone inverter and we could use it without thinking, in the trailer, our 900 watt microwave shares the 1100 watt pure sine wave inverter with everything else on board.

One day, shortly after we moved back into the trailer, Mark popped some potatoes into the microwave for a few minutes.  We were deep in conversation as he puttered around the kitchen and I messed around with photos on my laptop.

I thought it was odd when I noticed the charging light on my laptop go out, and he thought it was odd when he went to hit the button on the microwave for the next round of potato-cooking to find that none of the buttons on the microwave worked.

What the heck?

Exeltech Exeltech XP 1100 inverter opened up

Well, at least nothing is visibly smoking!

We checked the usual things, and then went outside and around to the basement to see what the inverter was up to.  Eventually, we realized that the inverter had just died.

Yikes!!  This little black box is our life blood!  And it would be a pricey devil to replace.

After a rather solemn dinner with almost-cooked potatos, Mark removed the inverter from the basement and opened it up to have a look inside.

Ouch.  All four slow-blow fuses had blown.  But thank heavens the rest of it was fully intact and there were no charred marks or burnt looking things anywhere.

The trailer repair gods were definitely smiling on us.  We called Exeltech the next day to find out the fuse sizes (there were no sizes printed or etched on the blown fuses), and they were kind enough to put a few sets of fuses in the mail for us (free of charge!) to replace the four dead ones and to give us some spares in case of future mess-ups!

08 Exeltech XP1100 inverter slow blow fuses 451

Wait, what’s up with the four “slow blow” fuses?

However, we had a five day wait until the replacement fuses arrived.  It turns out that the size of these things is unique (35 amp slow blow). A sweep of the local auto parts stores turned up a few 30 amp slow blow fuses, which Exeltech said would work in a pinch, but Mark didn’t want to do the repair twice.

We liked our boondocking spot and didn’t feel like moving just to get electrical hookups, so, for the next five days we lived on a 350 watt modified sine wave inverter.

Sound crazy?  Well, it CAN be done!  We didn’t have to sacrifice too much.  We just had to pay attention.

We aren’t big TV watchers unless the Olympics or Tour de France is on, but we use our two laptops for hours every day.

In the good old days of 2007, this little inverter of ours could power our white 13″ MacBook without a hitch, no matter what application we ran or how discharged the laptop was.

Slow blow 35 amp slow blog fuses

All four “slow blow” 35 amp fuses are blown

However, we soon discovered that today’s 13″ MacBook Pro’s (2011 and 2012 vintage, non-retina display) — and today’s software (2014 vintage) — all use a lot more power.  Plus, we now have two laptops instead of one, which is more than the 350 watt inverter can handle.  So, we had to devise a sharing scheme.

There are a few tricks to this.

The power required to charge a laptop varies depending on the laptop’s state of charge and the way in which it is being used:

  • A laptop that has discharged batteries (nearly dead) requires more power to get charged up than one that’s 90% charged already.
  • A laptop in use, especially if it is running disk-access intensive programs (like photo manipulation software), requires more power to charge than one running something tiny like a plain text editor (think Mac TextEdit or Windows Notepad).
  • A sleeping laptop requires less power to charge than one that is in use
  • A laptop that is completely shut down requires the least power of all to charge

I don’t have any firm numbers, but my hunch numbers are that it takes about 5-10 times more power to charge a laptop that is nearly discharged and is humming away on a bunch of really big photo manipulation programs (or moving lots of files around on disk) than it does to charge a laptop that is near full charge already, is shut down and is simply plugged into AC power.

With all these things in mind — and since our laptop use was our biggest power use in the trailer (we didn’t even try running our 26″ TV with surround sound on the 350 watt inverter) — this was our daily strategy:

350 Watt Inverver

This 7-year-old 350 watt modified sine wave inverter powered our lives for five days.

First thing in the morning, we would run the laptops from their own internal batteries until they were about 50% discharged (about an hour or two). If we weren’t done on the computers at that point, one of us would connect to the little inverter while the other continued on battery power.

After an hour or so, we would usually want to get outdoors. We would turn both laptops off and connect the most discharged on to the inverter to get charged up.

We’d return home later and either begin charging the other laptop up, or, if we both wanted to get back on our computers, we would alternate use of the inverter and go through the cycle again.

As for the Exeltech XP1100 inverter repair, as soon as we got the replacement fuses, Mark popped them into the inverter, installed it back in its home in the basement, and life was good and AC power was abundant in our home once again.

Boondocking in North Phoenix Arizona 521

We were in a good spot. Why leave if we could make things work
for a while with a small inverter?

What did we learn from all this?

We can live simply when we need to!

Also, I’m really glad I asked the NuWa factory to install a cigarette lighter style DC outlet in the living room part of our trailer behind the TV (it came with one in the bedroom already).  This makes it easy to use a small portable inverter in a pinch.  In all honesty, I had questioned my sanity in asking the factory for this upgrade until this episode!

Then — on our next trailer (not that we’re getting a new one, but it’s always nice to think about that dreamy “next one”) — we will get a bigger inverter.  There is nothing wrong with 1100 watts, as long as we think for a moment before flipping the switch on the microwave.  However, in the next installation, we will be much more willing to spend double to get Exeltech’s 2000 watt pure sine wave inverter instead of their 1100 watt version.  A bigger inverter will also allow us to use our Vita-Mix (1600 watts) which has been waiting in storage until we finish this crazy off-the-grid traveling lifestyle (which isn’t happening any time soon!).

Lastly… we learned that the Exeltech XP1100 inverter is well protected from absent-minded users with four wonderfully precious slow blow fuses. Very fortunately for me, it was an easy fix for Mark to do. But it seems that it is a fix that anyone who dares open the inverter case could accomplish. They were inline buss fuses and they didn’t even require a fuse puller — just a screwdriver to lift them out.

Note: We installed an Exeltech XP 2000 inverter in April, 2015, and what an incredibly worthwhile upgrade that has been.

Learn more at our page: RV Electrical Power Overhual: New Batteries, Inverter and Converter

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Kyocera Solar Features Our Sailboat Groovy on their Website!!

Groovy Boat Solar Panel Installation

Groovy’s solar panel installation

Kyocera, the solar panel manufacturer, took notice of our sailboat Groovys solar power setup and has featured our story on the Kyocera Solar website.  We were very surprised and pleased when they contacted us (out of the blue) to say they wanted to feature us.

We’ve been using Kyocera solar panels since May, 2007, when we installed a single 130 watt solar panel on our first full-time RV, a 27′ Fleetwood Lynx travel trailer.  We have been living on solar power full-time in our moveable homes since then.

That first solar installation, like our first trailer, was a little small.  After a year of skinny solar living, we upgraded to 490 watts of solar power on a 36′ Hitchhiker fifth wheel trailer (which included some Mitsubishi panels because the store was out of Kyoceras in the size we wanted!), and we posted a page describing the two RV solar installations.  A few years later, with even more solar experience under our belts, we installed solar power on our sailboat Groovy.  And of course, we keep learning.  Our NEXT solar panel installation will be even snazzier!!

The gist of the story is the value of anticipating your needs before installing a system.  In general, from what we’ve learned over the years, more and bigger is always the best way to go!!

To learn more about solar power on RVs and boats, see our article, RV (and Marine) Solar Power Made Simple as well as our Solar Tutorial Series:

There are loads more solar power and battery charging articles on this site here:

 

Solar Power for RVs and Boats – Components, Design and Installation Tips

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