This page outlines the parts needed for two different solar power systems for full-time “off the grid” living in a moveable home: one for an RV and one for a sailboat. There are lots of things to consider when planning a larger system like this, and a full discussion of these issues can be found on the next page of this tutorial.
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:
4 140 watt (12 volt) solar panels ($1,200)
1 Outback FlexMax FM60 MPPT charge controller ($550)
10 (or 8) gauge wire rated for outdoor use ($300)
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
This system is rated to produce 560 watts at 12 volts and has a 440 amp-hour battery bank. It is essentially the system that we have on our fifth wheel trailer, except that we have three 120 watt panels and one 130 watt panel (for a total of 490 watts).
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 Solistice (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 140 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 Kit 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 a 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. 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.
(3) Install the 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 and the to wire it into a sub panel. 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 factory-installed 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 supply DC power to the rig). So, when we use shore power, we plug the converter into the AC outlet to allow the converter to do its normal job. However, we use shore power only one or two nights a year, at most. When we dry camp, which we do virtually 100% of the time, we unplug the converter and plug the inverter into the AC outlet instead, using a modified extension cord that has a male connector on each end.
The inverter then draws its power from the batteries and generates AC power which it supplies to the rig backwards through the AC outlet. This is very non-standard and would be frowned upon by master electricians. The concern 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 that outlet 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 six years. This is not a recommended strategy if you plan to switch between dry camping and using electrical hookups frequently.
It is handy to wire the inverter to a simple toggle switch located somewhere inside the RV so you can turn it 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
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.
3 220 watt (24-volt) panels ($885)
1 Outback FlexMax 80 MPPT charge controller ($560)
10 (or 8) gauge wire rated for outdoor use ($400)
4 AGM 4D 12 volt batteries ($2,000)
1 Combiner Box & breakers ($180)
1 Go Power 2000 watt pure sine wave inverter ($550)
Total parts cost: ~$4,500
Solar Panel Arch: ~$2,000-$8,000
Wild guess at an installer’s fee: ~$1,500-2,500
This system is rated to produce 660 watts at 24 volts and has a 650 amp-hour battery bank.
System Comparison – How do these two full-timer/liveaboard systems differ?
Physical Panel Size
One of the basic reasons for using one of these systems versus the other is the size of the panels. An RV has things sticking out of the roof that may hamper the installation of very big panels (hatches, fridge vents, air conditioning units, TV antenna, domes, etc.). So the slightly smaller 140 watt panels may be easier to position on the roof than the big 220 watt panels.
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.
AGM versus Wet Cell Batteries
The other basic reason for using one of these designs versus the other is that AGM batteries are not only maintenance free but they can be operated while lying on their sides, whereas wet cells prefer to be upright. So there is less need for expensive AGM batteries on 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!
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). 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).
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, often separated from each other by a big distance. Finding space for another battery, installing it so it 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 220 watt panels (we weren’t sure if the bigger panels would be physically too big. In hindsight they would have fit perfectly).
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. I’m not sure if the additional 105 watts of solar panel capacity from the slightly bigger panels would have made up the difference, but it would have helped.
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.
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 Power Tutorial Part IV.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:
- RV Solar Power Kits (all sizes)
- Outback Charge Controllers (for "full-timer" installations)
- Pure Sine Wave Inverters (for "full-timer" installations)
We have MANY MORE PAGES about SOLAR POWER on this website!
See: SOLAR POWER under TECH TIPS in the MENUS at the top of this page.
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