RV Solar – How to Install Solar Power on an RV

This page describes two solar power installations we have had on our RV's, one for weekends / vacations and one for full-time RV living.

Single 130 watt panel on the Lynx

between a roof hatch and TV antenna.

At first we didn't mount the Kyocera 130 watt solar panel on the roof.

Kyocera 130 watt panel before mounting

on the roof.

A robust RV solar power solution: 4 solar panels, (1) 130 watt Kyocera solar panel and (3) 120 watt Mitsubishi solar panels on the roof of the RV

4 solar panels (490 watts total) in series

on the Hitchhiker.  The wire to and from

the basement runs through the fridge vent

on the left.

The Outback charge controller is the heart of our RV solar charging system.

Outback charge controller. 

The heart of the system.  It

can pass up to 60 amps DC

on to the batteries.

A 150 watt Radio Shack inverter can power our 19

150 watt Radio Shack inverter

Operates the 19" LCD TV, DVD & laptop.

Charges the cordless drill, camera

batteries, toothbrush & razor.

Not enough for vacuum, microwave,

toaster or coffee maker.

A 150 watt Walmart (Black and Decker) inverter provides AC power to appliances in the RV.

A $17 150 watt inverter from Walmart.

Can charge the laptop, toothbrush and/or

camera batteries in the truck as we drive.

Our RV solar panel installation was not difficult at all.  We did it while boondocking on the California Coast.

Mark installs the solar panel on the roof of

the Lynx on the northern California coast.

Every RV should have solar panels on the roof.

Not a bad place to do a job like this.

We have 4 6-volt golf cart batteries supplying 440 amp-hours of energy.

Factory installed custom battery box

vents

Our battery bank is four 6-volt Trojan 105 golf car batteries.

Four battery boxes in forward

compartment

Looking up at the angle iron supporting

the batteries.  The (red) batteries and

battery cables are exposed to the

elements beneath them.

Here the solar panels are being installed on the roof of the RV.

Installing the solar panels on the roof of

the Hitchhiker

Our RV solar panel installation is complete.

Finally finished with the installation!

This time we did the installation in the

Cinder Hills area north of Flagstaff, AZ

Solar panels provide charge even in shade, although they are greatly compromised.

Storms advance across the fields next to

the trailer

Outback charge controller shows 28.7 amps of charge going from the solar panels to the batteries in shade.

The Outback charge controller puts 28.7

amps into the batteries!

(2nd line, right side)

Atwood DC converter converts AC to DC when plugged into shore power; charges batteries when using shore power.

Atwood DC converter.

Converts AC to DC when plugged into shore

power. Charges the batteries when using

shore power.

Exeltech XP 1100 inverter converts DC to AC when not connected to shore power; true sine-wave inverter provides AC to every appliance in the RV.

Exeltech 1100 watt true sine-wave inverter

Converts DC to AC when not connected to

shore power.

RV Solar Installation: How to set up solar power on an RV

Thanks to solar power, we live completely off the grid in both our RV and sailboat.  This page describes both a high-end and a low-

end RV solar power installation.  Without doubt, our solar setups have given us more independence, freedom and fun as full-time

RVers than anything else in this lifestyle.  It has allowed us to go anywhere anytime.  If there is one area that RVers should spend

money, besides purchasing the rig itself, it is in getting set up to use the sun for electricity.  In this section I describe the two

systems we have had [June, 2012 prices]:

• A Modest (minimal) RV Solar installation for ~$750

• A Robust (all you need) RV Solar installation for ~$3,000

I also offer a little theory, discuss the installations and some of the discoveries we have made along the way.

For more info, please see our RV and Boat Solar Tutorial pages and Sailboat Solar Power Installation.

The biggest advantage of a solar charging system in an RV is that the system is working from dawn to dusk, silently and with no

smell or fuel cost, 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 til 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!

We have had two very different solar setups, a modest one on our Lynx travel trailer and a more robust one on our Hitchhiker

fifth wheel.  In both cases we camped without hookups 85% of the time or more, relying on our solar panels to provide all our

electrical needs.  We did purchase a Yamaha 2400i generator in January, 2008, but have used it only rarely since then: a few

times after many dark winter days to give the batteries a boost, and a few times to run the air conditioning in the summertime.

Other than that, we just lug it around and turn it on every 4-6 weeks to flush the gas through the lines.

After writing this post we installed an even more sophisticated solar power system

on our sailboat.  See our page, Sailboat Solar Power.

Our "modest" solar setup allowed us to use almost every appliance we own,

however, we had be conservative with our electrical use over the winter.  Our

"robust" system is like having full electrical hookups wherever we go.  No

conservation 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 the computer for 7 hours, made popcorn in the

microwave and ran several lights for 4 hours in the evening.  The next day the

batteries were fully charged by mid-afternoon.

BASIC ELEMENTS OF THE SYSTEM: BATTERY CHARGING and CURRENT CONVERSION

The basic components of each solar setup was the same, and is comprised of two major subsystems.  One subsystem charges the

batteries and includes:

• batteries

• solar panel(s)

• charge controller to protect the batteries from overcharging

The other subsystem converts the battery DC power to AC power so we can run our AC appliances like the TV and electric razor.

This includes:

• inverter(s)

The difference between the systems is the overall capacity, that is, being able to run more appliances at once, being able to run

more appliances for a longer time at night, and being able to run larger appliances.

So, in a nutshell, the batteries, panels, charge controller and inverter(s) do the same job as plugging a generator into the shore

power connector on the side of the rig.  The panels and charge controllers charge the batteries.  The inverter makes it possible to

use AC appliances, though not necessarily via the AC plugs inside the trailer.  The cost of each setup was comparable to the cost

of a similar capacity generator, $970 for the modest setup (compare to a Honda 2000i) and $3,900 for the robust setup (compare

to an Onan 3.6 kW).  However, unlike a generator, there is no noise, no fuel cost, and no smell.

The solar panels are mounted on the roof.  In the Lynx we had just one panel, and

at first we didn't want to make holes in our perfectly watertight roof just to mount the

panel.  However, after loading it in and out of the trailer a bunch of times and

worrying about it getting damaged while traveling, Mark finally decided it was safer

on the roof.

Our panels  are mounted flat.  Some people mount them with tilting brackets so they

can be tilted towards the sun.  We were shown a persuasive graph indicating that

the difference in solar collection is just 11% between flat and perfect orientation

towards the sun, and if we absent-mindedly drove off with them tilted up they could

be destroyed in the wind.  The real deciding factor for us was that it would be a 6-

week wait for the store to order tilting brackets, and this way we don't ever have to

climb up on the roof to tilt our panels or even think about our solar charging system

at all once it was installed.

(See "A Winter's Tale" near the end of this page for what we learned about flat versus tilted panel performance in wintertime).

Cables run from the panels through the roof down to the charge controller which is mounted somewhere in a storage compartment

where you can see it.  Another wire run connects the charge controller to the batteries in the battery compartment.  The solar

panels send as much power to the charge controller as they can get from the sun.  The charge contoller monitors the power

coming from the panels and gives the batteries only what they can handle so they don't get fried.

The inverter(s) are installed separately.  These can either be portable units that plug

into cigarette lighters in the rig or larger units that are permanently wired to the

batteries.  When using a small inverter connected to a cigarette lighter, AC appliances

are then plugged into the 3-prong AC outlet on the inverter.  Turn the inverter on and

then the 3-prong outlets are "live" and you can run your appliance.  Alternatively, a

large inverter (to support a vacuum cleaner, microwave, hair dryer, toaster, coffee

maker, etc.) gets installed very close to the batteries and is wired direclty to them

permanently.  An extension cord can be run from the AC receptacle on the inverter

into the interior of the trailer.  Or the inverter can be wired into the AC wiring of the

trailer.  In either case, the inverter needs to be turned on in order to provide AC

power.  When we had the small charging system on the Lynx, we also kept a cheap

inverter in the truck that we could plug into the cigarette lighter to charge the laptop,

camera batteries or toothbrush as we drove around town.

When purchasing a solar setup, it helps to work with a knowledgeable solar power store and salesman.  We have seen huge

variations in what stores charge for solar equipment.

A MODEST RV SOLAR SOLUTION (~$750)

A fully functional, inexpensive solar setup, comparable in price and power output to to a portable Honda 2000i inverter generator

($700 or so in June 2012 prices) is simply:

• Two 6-volt batteries giving 220 amp-hours of capacity

• 130 watts of solar power

• A charge controller that can support 10 amps

• A portable inverter that can supply 150 watts of AC power

This is essentially the setup we had on the Lynx travel trailer.  It could power a 19" LCD TV and DVD player, radio or laptop as well

as charge camera batteries, razor, toothbrush, cordless drill, cell phone, etc.  It could not run the microwave, hair dryer, toaster,

coffee maker or vacuum.  For those, we simply installed a larger inverter connected directly to the batteries (not a portable

inverter).  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 middle of December when the days got short and the nights got long and cold.

Then we began to long for a bigger system.  On 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 on those winter 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 the following winter:  see the heater page).

I think every RV sold should have this kind of a charging system installed as standard equipment, as it is perfect for all part-time

campers who spend weekends and week-long vacations in their RVs during the summer months.

In 2007 we installed in the Lynx (prices as of June 2012 for comparable makes/models)

• Two Energizer (Sam's Club) 6-volt batteries giving us 220 amp-hours of capacity ($210)

• One Kyocera 130 watt solar panel ($300)

• A Morningstar Sunsaver charge controller that could support 10 amps ($85)

• A portable Radio Shack 150 watt inverter connected to a DC cigarette lighter in the trailer

[to run everything except the vacuum ($20)]

• A Pro One 800 watt inverter connected to the batteries with an extension cord run into the interior of the trailer

[to run the vacuum ($75)]

The total cost for this setup in June, 2012 would be about $750, including $50 for wire, connectors and mounting brackets.  We

were quoted $135-$350 for installationin June, 2007.  Mark is very handy, though not a Master Electrician, and the installation was

easy for him.

SOME THEORY -

CHARGING & CONSUMPTION

Here is some theory to explain why the above system is "sufficient" but is not "robust."  When it comes to a

solar battery charging system, the concept of power charging and consumption is very simple.   The amount

you can use, or take out of the batteries, is essentially only as much as the amount you can charge or put

into the batteries.  If you use (or take out) more than you charge (or put in), 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.  Too often

we find people who want to add batteries to address their power shortages when what they really need to

do is add more solar panels.  Also, as a rule of thumb, you don't want to take out more than 1/3 to 1/2 of the total capacity of the

batteries in one night of watching TV and using the lights.

RV SOLAR POWER - AMPS and AMP-HOURS

Appliances use amps to run.  Another unit, the amp-hour, 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 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

15" MacBook laptop, on & running

5.5 amps

15" 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

Most DC appliances list their amp usage in the user manual or spec sheet.  Most AC appliances list their wattage instead of

amperage.  So for AC appliances you have to convert the wattage rating to get the amperage rating.  You can get a rough estimate

of the number of amps that an AC device will use simply by dividing the wattage by 10.

Technically:  Watts = Volts x Amps.  AC circuits run at 120 volts and DC circuits run at 12 volts, so on a DC circuit an appliance will

use 10 times as many amps as it will on an AC circuit.

To determine most precisely how many DC amps an AC appliance will use when running on an inverter, start by dividing the watts

by 12.  However, inverters are not 100% efficient.  Typically they are only about 85% efficient, losing a bunch of watts to heat as

the inverter runs.  So it takes more watts to get the required amps out of an inverter, the exact figure being 1 / 85%.  This means

you have to divide your DC amps (that watts / 12 figure you just obtained) by 0.85 to get the most accurate result.  This is messy.

Rather than dividing watts first by 12 and then by 0.85, you can simply divide the

watts by 10 and get a pretty close estimate.

Our 19" LCD TV is rated at 65 watts.  How many amps DC?  65/10 = 6.5.  We

measured the TV at 5.5 amps at the volume we like to hear it.  If we cranked the

volume the meter went up to 6.5 amps.  Likewise, the laptop is 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 6.5 amps.  Most of the numbers

were near 5.5 amps.  When we shut down the laptop and left it plugged in for

charging, the meter dropped to 1.6 amps.

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.  Upgrading to two 12-volt Group 24 batteries

(wired in parallel) will give you 140-170 Ah of capacity.   If, instead, you replace the single dealer-installed 12-volt battery with two

6-volt golf-cart batteries (wired in series) you will get 220-225 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 as little as 25 Ah of nighttime capacity if you keep the single 12-volt battery that came from the

dealership, or you can have as much as 75 Ah of nighttime capacity if you install two new 6-volt batteries.  You can always add

more batteries too, the only limit being where to put them.

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 Ah that the panel can store in a battery and its Watts rating

is not straight forward.  Suffice it to say that a 130 Watt panel produces 7.5 amps in maximum sunlight, and both of those numbers

are available in the specs for the panel.  What isn't stated is how many Ah a panel will produce in a given day.  We have found that

our 120 watt and 130 watt panels produce between about 8 Ah and 40 Ah per day depending on the season and the weather,

ranging from a dark winter day to a sunny summer day.  Latitude also plays a role (more sun to the south) and there are more fully

sunny days in the west than in the east.  However, in general our panels produce around 25-30 Ah per day each.

If you have the time and inclination, you must figure out how many Ah 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.  Luckily there are some rules-of-thumb.

NEVERMIND THE THEORY - HOW MUCH DO WE REALLY CONSUME?

We met a couple living on their 27' sailboat on its trailer in the desert (they were on their way to launch it in the Sea of Cortez), and

they were using just 6 amp-hours per day because they had a tiny solar panel.  In the Lynx we used about 25-35 amp-hours per

day.  In the Hitchhiker we use an average of 90-120 amp-hours per day.

In the Lynx, with its modest solar setup, we used just one light at a time and often used oil lamps, watched TV or DVDs for a few

hours a night some nights, listened to the radio or CD's for a few hours some days, charged the laptop and other appliances for a

few hours at a time.  On most winter mornings we woke up to find the batteries fairly well discharged (our simple 4-LED display

would have two or three LEDs lit, indicating partial discharge).  We did not use our microwave.  We could have if we'd installed a

slightly bigger inverter, but we rarely used one in our stick-built house, so we didn't bother in the trailer.  The Sunsaver charge

controller did not indicate how much charge was going to the batteries, but I would estimate it was typically anywhere from 1-6

amps per hour, or about 25 Ah per day in winter.

In the Hitchhiker, with its robust solar setup (described below), we often have two, three or more lights on at night, use the laptop

and 26" TV with a large surround-sound system for as many hours as we like, run the microwave once in a while, and even use the

hair dryer.  We never think about consumption but instead get a kick out of watching the charge controller as it pumps amps into

the battery -- or doesn't -- depending on how thirsty the batteries are.

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

• 6 Ah = living ultra-conservatively

• 25 Ah = live modestly in spring, summer, fall, but get very conservative in winter

• 120 Ah = live just about the way you do in your house

SOLAR SHOULD BE INSTALLED ON ALL RVs

It is strange to me that RV dealerships don't sell solar setups as a dealer add-on.  Many sell generators, but I haven't found any

that sell solar in an easy-to-purchase package.  With a little effort they could design three standard systems, modest, better and

deluxe, and give their customers something really valuable -- a trailer that is self-sufficient right there in the dealer lot, without

hookups.

Watching the Tour de France on TV, we noticed that most of the RVs lining the roads had solar panels.  Sadly, that is not true on

this side of the Atlantic.  Also, most trailers in the US are sold with one 12-volt Group 24 battery.  That is inadequate for anything

more than stopping at a rest area for lunch!  12-volt "marine" batteries are hybrid batteries.  They are designed to be both "starter"

batteries to start a marine engine, and to be "house" batteries to provide power to lights and appliances.  6-volt golf-cart style

batteries are strictly "house" batteries designed only for deep cycle use, not for engine starting.  Trailer batteries aren't used to

start any engines, so those 6-volt golf-cart batteries are really superior for powering the lights and appliances in an RV.  It doesn't

make sense for dealers to sell trailers for tens of thousands of dollars with one measely, insufficient 12-volt Group 24 battery

instead of two 6-volt golf-cart batteries, when the cost difference is just $65.

GET YOUR HANDS DIRTY!

It is hard to play with solar until you actually take the leap and buy a panel, charge controller and cables and hook it all up.

However, you can definitely get the hang of how inverters work without a huge financial outlay.

Here is a sampling of inverters along with current prices, specs and reviews.  They are 175 watt, 400w, 700w, 1200w, a true-sine

1500w (explained below) and a generator.  The inverters we bought aren't the more well-known brands, whereas the ones shown

here are.  If you are curious about all this and haven't used an inverter before, pick up the cheapest one and try it in your car to

see how it works.  You can charge your cell phone or laptop or run a small TV just as you would in your RV.

This will help give you a hands-on feeling for the "how to run AC appliances from a DC battery" half of the equation.  The other half

is the solar panel and charge controller, of course, and since it involves purchasing cable and connectors, is not easy to

experiment with until you take the plunge.

The Yamaha generator rounds out the list to a nicely formatted 6 items but is also here because it is the one we have.  As

mentioned above, we do not use it to charge the batteries, but we do use it to run the 15,000 BTU air conditioning unit about 5-10

nights a year.

BATTERY TYPES

The factory standard 12-volt Group 24 battery found in most RVs will give you 70-85 amp-hours of capacity -- not enough.  It would

make so much more sense for the dealers to sell standard (or sell an upgrade kit for) two 6-volt batteries, giving you 220 amp-

hours of capacity (upgrading to two 12-volt Group 24 batteries gives you only 140-170 amp-hours of capacity).  The 6-volt batteries

will also give you true deep cycle batteries rather than hybrids.  Cheap dealer-quality 6-volt batteries cost about the same as cheap

dealer-quality 12-volt batteries.  So why bother installing an upgrade to two 12-volt batteries?  We bought our Lynx with two 12-volt

batteries, not knowing the difference.  By winter we had upgraded to two 6-volt batteries, giving us much more capacity to run our

lights and appliances for more hours at night and on consecutive cloudy days when the batteries didn't get fully recharged.

I have heard the very bizarre argument that it is better to have two 12-volt batteries in parallel instead of two 6-volt batteries in

series, because if one battery fails in the 12-volt pair you will still have a working battery, whereas if one fails in the 6-volt pair you

will have nothing.  If you have a solar charging system and you pay attention to your power consumption you will never have a total

battery failure.  Check your batteries every so often to make sure the water level is topped off -- and add enough distilled water to

bring any low cells up to the bottom of the neck of the cell.  A single battery of a pair will never just up and fail if it is charged daily

and you take care of it.  However, if the battery gods are just dead set against you and one does fail, you will be without power only

for the length of time it takes to go to a hardware store and get another.  Worst case, you can place the new battery on the ground

outside the trailer and hook it up temporarily to get the water pump (or lights or TV or whatever appliance you absolutely have to

have) working again until you sort out your longer term battery solution.

6-volt batteries have the same footprint as 12-volt Group 24 batteries, however the 6's are about 3 inches taller.  So, before

upgrading, you have to check the height in your battery compartment.  Our Lynx travel trailer had enough room in the battery

compartment on the hitch to fit the larger 6-volt batteries.  The Hitchhiker fifth wheel required quite a bit of retrofitting, both at the

factory and at the dealer.  The NuWa factory custom installed four vented battery boxes for us, but they were for 12-volt Group 24

batteries.  The dealer cut the bottoms off the battery boxes and ran some angle iron along the bottoms so the batteries could be

recessed, sitting on the angle iron, and still fit their vented tops in the basement compartment of the trailer.  NuWa now offers four

factory installed 6-volt battery boxes that are properly sized with their 2009 models.

Batteries are racist and ageist.  They like to be surrounded by other batteries of the same age, make and model.  Don't mix and

match 6- and 12-volt batteries or old batteries with new ones.  Batteries are very altruistic, and the strong ones will spend all their

energy charging the weak ones and trying to help them keep up.  So if you are upgrading, consider just replacing the batteries that

you have with a new matched set.

A ROBUST RV SOLAR POWER SYSTEM (~$3,000)

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

• 360 or more watts of solar power

• A charge controller that can support 30 amps or more

• An inverter that can supply at least 1000 watts of AC power

That is a very big system and is comparable in cost and power output to a 3,500 watt or larger onboard Onan diesel or propane

generator -- $3,500 or so.  It will power everything except the air conditioner, regardless of weather or season.

In 2008 we installed on our Hitchhiker fifth wheel the following (prices shown are approx June 2012 prices for comparable makes/

models):

• 4 Trojan 105 6-volt batteries (2 in parallel to make two 12-volt batteries, and those 2 pairs in series with each other) ($420)

• 3 120-watt Mitsubishi solar panels and 1 130-watt Kyocera panel, for a total of 490 watts of solar power ($1,200)

• 1 Outback MX-60 60 amp charge controller ($515)

• 1 Exceltech XP 1100 watt true-sine wave inverter ($560)

The cost for all of this in 2012 would be $2,845, including $150 for wire, connectors and mounting brackets.  Mark did the

installation.  My rough guess is that the installation might have cost $500 if done by someone else.  We would have bought 3

Kyocera 130 watt panels to complement our existing one, but they did not manufacture one that was easy to connect.  Mitsubishi's

120 watt panels could connect to our Kyocera more easily and were about $25 less per panel, so we chose those instead.  Our

batteries are fully charged by the end of each day, rain or shine, and we typically use anywhere from 75 to 120 amp-hours of

battery power per day.  The charge rate varies greatly, but it is typically anywhere between 4 and 25 amps per hour, depending

predominantly on the state of charge of the batteries (moreso than on the weather).  As the batteries approach full charge,

they demand less and less current.  We have seen charge rates of 10

amps per hour in driving rain storms and in full shade.  That is more than our Yamaha

2400i generator could produce; it charges at just 8 amps per hour!

The solar panels are mounted on the roof in series with 10 gauge wire running

between them. (See section at end of this page about Series versus Parallel wiring).

The wire comes up to the panels from a ground location on the trailer frame in the

basement compartment and it returns to charge controller in the basement.  The two

wires running to and from the basement are housed in a 6' piece of 1" PVC pipe that

we placed behind the refrigerator, and the wires run from the top of the fridge vent out

onto the roof.  Because the panels are in series, only 7.5 amps of current runs

through these wires.

Down in the basement, more 10 gauge wire runs from the charge controller to the

batteries.  This section of the wire sometimes carries 25 amps or so, as the charge

controller delivers as many amps to the batteries as they can take, and at times they

want a lot.  In hindsight I'm not sure it was any easier running the wiring through the

fridge vent down the back of the fridge than it would have been to drill a hole in the

roof above a closet and run the wire down the inside of the closet through a hole

drilled in the floor to the basement compartment.  Mark did the closet method in the

Lynx, but we learned later most installers use the fridge vent, so he tried it on the

Hitchhiker.

Our inverter is wired in a manner that is ideal for us but would be greeted with jeers

and dire warnings by Master Electricians.  It works well for us because we never get

electrical hookups.  If you switch a lot between hookups and boondocking, then this

method would not be a good idea.

First we unplugged two appliances that use a lot of AC power when they sense AC power on the line.  We did not want the inverter

to be taxing the batteries in order to run AC appliances we did not need or that could run from some other energy source.

The first appliance we took out of the AC circuitry was the fridge.  We simply unplugged its AC plug in the back, effectively forcing it

to use propane gas to run all the time.  Ours is a model where you can push a "Gas" button on the front to force it to gas, but by

unplugging it from the AC outlet it can never switch by mistake.

The second appliance we removed was the DC converter box.  This box is provided so the trailer can run its DC appliances when it

is plugged into shore (AC) power without having to use the batteries.  It takes a lot of AC power to run, and it turns on as soon as it

senses AC power on the line.  When we boondock we want to run our DC appliances from our batteries, so the DC converter

needs to be shut down.  We simply unplugged its AC connector from its outlet.  When first learning about this stuff, I found the

terms "inverter" and "converter" very confusing and did not understand the difference between them.  If you are a little puzzled too,

check my notes about these two components at the bottom of this page.

Next, we wired -- no, Mark wired -- the inverter directly to the batteries.  Then he took a 3-prong

extension cord and cut off the female end.  He purchased a male connector and wired it to where

the female end had been, effectively making a male-male extension cord.  He plugged one end

into the inverter and the other end into the AC outlet where the DC converter had been plugged in

(this just happened to be a handy AC outlet near where he had installed the inverter).  Bingo!

When the inverter was turned on we had AC power to all the outlets in the trailer.

The huge caveat about cheating like this -- and it is cheating -- is that the shore power outlet on

the outside of the trailer is LIVE.  Don't stick your finger in there.  Actually, don't stick your finger in

any outlet...  More importantly, don't try to plug something into the shore power outlet on the trailer

(either electrical hookups OR a generator) when the inverter is turned on -- things will blow up.

This is the reason that you don't want to have this kind of quasi-wiring if you frequently switch

between shore power and boondocking.

If you are going to be switching between shore power and inverter power frequently, you need to

wire the inverter into the AC wiring via a subpanel connected to your AC distribution panel, and

other websites describe this process in beautiful detail.

RV SOLAR POWER OPERATION - AN IMPRESSIVE MOMENT

We have seen some remarkable numbers on the Outback charge controller, showing how many amps are currently going into the

batteries or how many amp-hours have been collected for a given day.  I wanted to get a photo of the display for this web page.

We were outside Bryce Canyon, Utah, in early August and it was around noon -- a very favorable location, season and time of day

for solar collection.  However, this particular day was extremely gloomy.  There were no visible shadows on the ground, and storms

were advancing towards us in the distance.

I took a photo of the black sky over the field next to our trailer.  Then I turned around and looked at the Outback.  it was putting 25

amps into the batteries!  As I stood there the sky around us lightened a little -- still no visible shadows, but everything lightened just

a bit.  I looked at the Outback and it was now putting over 28 amps into the batteries.  I took a photo.  Soon the sky darkened again

and the Outback fell first to 19 amps, then 15, and eventually to 10 as it started to pour.

INVERTER and CONVERTER CONFUSION

If you are like me, the terms "inverter" and "converter" sound so similar it seems they might be one and the same thing.  They are

actually two very different components with very different missions in an RV.

Inverters

The AC inverter takes the DC battery power and uses it to make AC power so you can run things like TVs and DVDs and charge

things like your camera batteries.  You turn on the inverter, plug an AC appliance like an electric razor or TV into it, and poof, the

razor or TV works.

Inverters can be "true sine wave," meaning the AC power signal coming out of the inverter is identical to the power signal of a wall

outlet in a house, or they can be "modified sine wave." meaning the waveform is clipped at the top and bottom and is stair-stepped

in between rather than being a smooth sine wave.  True sine wave inverters start at about $400 for the smallest ones whereas

modified sine wave inverters top out at about $400 for the largest ones.  We purchased a true sine wave inverter for our "robust"

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.  Ironically, some RV parks have unstable AC power that can damage AC appliances in an RV; our

inverter power is cleaner and more reliable!  Desktop computers, laser printers, TV and stereo equipment are the most likely

appliances to have trouble with modified sine wave inverters.  However, we never had a problem with any of our appliances using

those inverters with our modest solar setup on the Lynx.  Modified sine wave inverters often have loud fans, and Mark did have to

put WD40 on our Radio Shack inverter twice when the fan quit working unexpectedly.

Inverters come in two flavors:  plain inverters and inverter/chargers.  An inverter/charger can be a very efficient battery charger

when you are plugged into shore power.  However if your solar charging system is effective and you aren't going to plug into shore

power very often, there is no need to pay the extra money for an inverter/charger rather than a plain inverter.

Converters

The DC 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.

The DC converter is not involved in the solar setup.  In our "robust" solar setup the DC converter is actually unplugged because our

inverter powers all the AC outlets in the rig.  By design, if it were plugged in, the DC converter would automatically impose a huge

demand on our batteries whenever we turned on the inverter.

RV SOLAR POWER - A WINTER'S TALE - To Tilt or Not To Tilt ??

(Added January, 2009)

When I first wrote this page, we hadn't yet experienced a winter with our new solar setup.  Now, in January, we are some three

weeks past the winter solstice, and we have all kinds of data to report.

We didn't pay any attention to our charging capabilities until about November 15th.  At that point we were in Yuma, Arizona, about

as far south in the western US that you can go, and I noticed that the charge controller wasn't reaching "float" mode by the end of

the day.  So we started turning off the inverter when we went to bed at night.  Then all was well again (the inverter uses about 2

amps per hour, even when nothing is running, so that conserved an easy 40 amps per day).

Around December 1st we moved to Quartzsite, Arizona, and set up camp next to our friends Bob and Donna Lea Jensen, veteran

RV boondockers who have been wintering in the Arizona desert for over 20 years.  We compared notes on our solar setups and

discovered some interesting results.  The Jensen's setup includes 3 Kyocera 120 watt solar panels in parallel and a Heliotrope

charge controller.

Their panels are mounted on tilting brackets, and they oriented their rig to maximize their southern exposure.  Each of their panels

was a perfect 45 degrees toward the sky facing due south.  We were nearby, oriented to maximize the sun coming in our windows

in the morning.  By this season, the sun was rising in the southeast, skimming along above the horizons, and setting in the

southwest.  Our panels follow the roof line of our trailer, so in our current orientation two of our panels were tilted about 5 degrees

to the northeast, one faced directlly upwards, and one faced about 10 degrees to the southwest.

In general, as we compared our charging pattern with the Jensens, we found that our charge controller would work all day to

achieve a full charge, which it generally did by about 4:45 in the afternoon (at which point it could no longer get anything from the

sun).  The Jensens were fully charged by 1:00 p.m., and their charge controller quit trying to put anything into the batteries after

that (our charge controller always puts 5-7 amps into the batteries, even when they are "fully charged" and "floating."

One day we decided to keep closer tabs on each other.  We had watched two DVDs the night before, and they had watched TV a

bit less, so the two battery banks were probably not equally discharged.  They have a 23" flat screen HDTV with no surround-

sound, whereas we have a 26" flat screen TV with surround-sound and a large subwoofer, so we had probably drained our

batteries a bit more.  However, I was shocked at how much more efficient their system was because of the tilted panels.  It was

clear to me that if you want to operate your panels to their full potential during the worst winter weeks (December 1 to January 20),

it is important to have tilted mounting brackets and to orient your RV so the panels face due south.  The mere "11% difference"

between flush-mounted and tilted panels that Wind & Sun had alluded to last summer must have been the average difference over

the course of a year.  The difference in the weeks around the solstice is more like 50%.  Also, few RVs have flat roofs; most flush-

mounted panels on RVs will have a 5-10% tilt in some direction.

December 8th was a very bright sunny day with perfectly clear skies.  It was 13 days before the solstice (which occurs on

December 21).  Here are the readings from the two systems:

Time

Jensens

Us

360 watts

490 watts

Perfect tilt

Random tilt

8:30

9.0 amps

4.2 amps

9:40

14.5

10.0

11:30

(doing errands)

15.8

1:00

20.1

15.8

1:30

(full charge)

15.0

2:30

(full charge)

11.0

3:30

(full charge)

6.5

4:45

(full charge)

(snoozing)

However, tilting panels offer no advantage on cloudy days, and the tendency in winter is to get 3-5 overcast days in a row as

storms pass through.  The value of our extra wattage, and possibly our sophisticated charged controller which excels in low light

conditions, was apparent two days later.  On December 10th we had a grey day with no sign of the sun and not a shadow to be

seen.  It made no difference which way the panels faced, as the light was very uniform in all directions.  We did just one check of

the two systems in the morning:

10:30

1.5 amps

3.7 amps

In the weeks following this experiment, we also found that the real limiting factor in the wintertime isn't so much the efficiency of the

system on a bright sunny day, but the fact that overcase, miserable, cold, grey days tend to come in groups when it is stormy.  Our

very worst day for solar collection was a scant 14 amps, and on two other days we got 24 amps and 28 amps.

At this point we pulled out the generator that we had patiently carried all over the country for the past 12 months.  We had turned it

on faithfully every 4-6 weeks to flush the lines, and we had actually used it three times in Las Vegas in September so we could run

the air conditioning.  Boy, were we glad we had that beast with us now.  We ran the generator for 3-6 hours three days in a row,

and happily used all our appliances as we had grown used to doing.  Without the generator, we would have had to conserve to the

utmost during the storm until the sun finally came out a few days later.  Instead, we hunkered down and watched some movies,

read, listened to the radio, and let the generator keep the batteries topped off.

Is a generator necessary?  We've used ours 6 times in a year -- 3 times for air conditioning and 3 times to supplement the

batteries.  However, as fulltimers, we were very grateful to have it on those six occasions.  Otherwise we would have had to swelter

in 90 degree heat inside the trailer or we would have had to go to bed very early and resort to non-power-using methods to

entertain ourselves during a winter storm.  So it depends on what level of comfort you require.  In general, our generator just takes

up space in the back of the pickup.

During the shortest days of 2008-09 I kept a log of the total amp-hours collected each day.  During this time we were parked

predominantly in Buckeye, Arizona (outside Phoenix) with two panels tilted slightly south, one facing the sky, and one facing slightly

north.  A preferred orientation would have been for the slightly tilted panels to be east and west, as I think the one that was facing

slightly north was not contributing much at all.  So perhaps these numbers might have been higher by 10% or so.

Date

Collected

Weather

Comments

12/12/08

33

Overcast, brighter midday

Ran the generator 4 hours, East/West orientation

12/13/08

65

Sunny, some clouds

12/14/08

57

Overcast, little sun

Ran generator 5 hours

12/15/08

26

Totally overcast

Ran generator 3 hours

12/16/08

41

Overcast, tiny sun

12/17/08

14

Raining, fog, dark

Ran generator 2 hours

12/18/08

52

Clouds then sun

12/19/08

91

Sunny

Travel day, many orientations for RV all day

12/20/08

77

Hazy then sunny

TV 3 hours

12/21/08

68

Sunny, late clouds

SOLSTICE, TV 1.5 hours

12/22/08

40

Cloudy

No TV

12/23/08

68

Sunny, then haze & clouds

12/24/08

58

Cloudy, some late sun

12/25/08

Rain, dark all day

Not home all day, did not use any power

12/26/08

24

Sunny

Didn't charge much because wasn't discharged yesterday

12/27/08

43

Sunny

Watched 1/2 hour of TV, not much other power use

12/28/08

73

Sunny

Equalizing the batteries

12/29/08

78

Sunny

Equalizing the batteries

12/30/08

80

Sunny

Equalizing the batteries

MORE on TILTING BRACKETS and SERIES VS. PARALLEL WIRING

(Added March, 2009)

Tilting Brackets

When deciding whether or not to install tilting brackets on an RV setup, there is one other consideration besides the two I have

mentioned so far ([1] the likelihood that you will drive off with them still tilted up, and [2] the inferior performance without brackets

during the 12 weeks around the Winter Solistice).

The third consideration is that it is impossible to clean the roof under the panels if they are flush-mounted and fixed on the rooftop.

While staying in Florida for six weeks in February and March, our roof began to suffer the consequences of the lush, moist, warm

environment, and little mold spores began taking root.  Cleaning the roof was a snap -- except under the solar panels...

Series vs. Parallel - High amps vs. Low amps in the wire

Another vital consideration is whether to wire the panels in series or in parallel.  The advantage of wiring the panels in series is that

there is very little amperage (and correspondingly high voltage) running along the wires on the rooftop and interior of the trailer.

Therefore, with less current in the wires, it is somewhat safer in the event of a failure, it doesn't require very large guage wire, and

there is very little voltage loss over the wires.  In our case, in full sun, there is about 7.4 amps and 48 volts in the wire run between

the solar panels on the roof and the charge controller in the basement.  Our charge controller steps down the voltage from 48 volts

to 12 volts, which is what the batteries can accept (our batteries are actually charged by our controller at 13.8 to 14.8 volts).

When the panels are wired in parallel, there is a huge amount of current flowing through the wires between the solar panels and

the charge controller, and correspondingly little voltage.  If our same solar panels were wired in parallel, there would be 30 amps

flowing at 12 volts in the wires on the roof and in the walls of the trailer.

The high amperage system requires larger guage wire to handle the higher amperage flowing through it.  We have 10 guage wire

on the roof, which is more than plenty in that location for our 7.4 amps.  However, in the run between the charge controller and our

batteries, the amperage can be as high as 30 amps for 1-2 hours when the batteries are getting a maximum charge from the

panels and controller in full sun in mid-summer.  We have 10 guage wire there as well, but the run is just 8 feet across the

basement from the charge controller to the batteries.  That short run of wire gets warm to the touch when 30 amps flows through it.

We rarely have that much amperage in that section; more typical is 15-21 amps, and in that case the wire is always cold.  If we had

wired our panels in parallel, we likely would have used 8 guage wire on the roof and along the inside of the trailer.

Impact of Shade on Series-wired Solar Panels, see also:

Sailboat Solar Power

Besides the danger and guage of wire, the most critical aspect of choosing a series versus a parallel panel installation is the

behavior of the panels themselves.  When a panel is shaded it becomes an enormous resistor electrically.  This blocks all current

flow, and the panel is effectively "turned off" or knocked out of the system.  If four panels are wired in series, and one gets shaded,

the resistance will affect all four panels, blocking the current flow in the circuit entirely.  If, however, the same four panels are wired

in parallel, and one gets shaded, the current will still flow from the other three to the charge controller.

I had a hunch about this theoretically, but it really got driven home to me when we compared notes with our friends the Jensens

once again.  Since our last experiment with them to check the tilting versus non-tilting panel setup, they had added one more 130

watt Kyocera panel to their system.  The new panel was wired in parallel with their other three (parallel-wired) panels and went into

a Heliotrope charge controller.  So, other than our different charge controllers and different wiring, we had the identical setup:

three 120 watt panels and one 130-watt panel, for a total of 490 watts.  In addition, they left their panels flush to the roof rather

than tilting them up.  We were both parked in full sun in the Arizona desert with no trees or tall buildings anywhere in sight.  Perfect

conditions.  It was about 10:00 in the morning in late January.

Bob and I each checked our charge controllers, and we were getting identical readings.  Then we each climbed up on the roof of

our trailers and stood in front of one panel to cast a partial shadow across it.  The shadow covered the mid-section of the panel

and covered about 1/4 of the total surface of the one panel.  The rest of the panels were still in full sun.  Our obliging spouses

checked the charge controller readings inside our trailers.

We were all stunned by the results.  We repeated the experiment a few times just to make sure we were getting accurate readings.

So we cast our shadows across the one panel and then stepped back to allow it full sun several times in a row.  The results were

100% repeatable every time.

The Jensens

Us

(parallel wiring)

(series wiring)

Full sun

12.8 amps

12.8 amps

One panel partly shaded

10.0 amps

1.6 amps

Stunning!!!  Yikes!!!  We generally park in full sun, so we have never really felt a negative impact from this dramatic limitation in our

system.  However, if we frequently parked in places where a tree branch might shade part of the roof, or if we were putting the

panels on a sailboat where the mast, boom, radar mount and sails might shade one or more panels at times during the day, then

the series wiring would be extremely inferior to a parallel setup.

The reason we originally went with a series-wired setup was because there is less voltage loss over the wiring between the panels

and the charge controller than there is with a parallel setup (assuming full sun exposure).  So the charging capability of the series

system is slightly more efficient than with a parallel wired system.  Also, the wire size could be smaller and therefore easier to

handle during the installation.  However, I don't think the minute gain in charging efficiency and slightly easier (and cheaper) wire

used during installation outweighs the huge disadvantage of losing almost all charging capability when one panel is partly shaded.

Our system has provided us with all the electricity we can ever use, all the time, except for a few stormy days in midwinter.  So it is

not worth changing the wiring.  However, for a new installation, the selection of a wiring plans is an important point to consider in

your design.

For more info and lessons learned, check out our Solar Power System installed on our Hunter 44DS sailboat.

Also see our multi-part RV and Boat Solar Power Tutorial pages.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Need help with your RV solar installation? Check in with the experienced installers at RV Mobile Solar !!

 

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:

Solar power kits
Outback charge controllers
Pure sine wave inverters

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New to this site?  Check out RVing Lifestyle and Tech Tips at the top of the page for detailed info about installing a vent-free propane heater, living the full-time RV lifestyle, how to go boondocking, the costs of full-time RVing and more.  Please visit our Home page and Welcome page for RVers to learn more about us and discover all the other good stuff available to you on this blog.

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