Single 130 watt panel on the Lynx
between a roof hatch and TV antenna.
Kyocera 130 watt panel before mounting
on the roof.
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.
Outback charge controller.
The heart of the system. It
can pass up to 60 amps DC
on to the batteries.
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 $17 150 watt inverter from Walmart.
Can charge the laptop, toothbrush and/or
camera batteries in the truck as we drive.
Mark installs the solar panel on the roof of
the Lynx on the northern California coast.
Not a bad place to do a job like this.
Factory installed custom battery box
Four battery boxes in forward
Looking up at the angle iron supporting
the batteries. The (red) batteries and
battery cables are exposed to the
elements beneath them.
Installing the solar panels on the roof of
Finally finished with the installation!
This time we did the installation in the
Cinder Hills area north of Flagstaff, AZ
Storms advance across the fields next to
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 the batteries when using
Exeltech 1100 watt true sine-wave inverter
Converts DC to AC when not connected to
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.
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!
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:
• 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.
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
Dual bulb DC light
Dual bulb fluorescent light
19" LCD TV
DVD / CD Player
15" MacBook laptop, on & running
15" MacBook, off and charging
Sonicare toothbrush charging
FM Radio w/ surround-sound
12' string of rope lights
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
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.
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/
• 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)
• 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). The charge controller deliberately reduces the
charge rate as the batteries approach full charge. 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
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.
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.
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
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:
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:
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.
Overcast, brighter midday
Ran the generator 4 hours, East/West orientation
Sunny, some clouds
Overcast, little sun
Ran generator 5 hours
Ran generator 3 hours
Overcast, tiny sun
Raining, fog, dark
Ran generator 2 hours
Clouds then sun
Travel day, many orientations for RV all day
Hazy then sunny
TV 3 hours
Sunny, late clouds
SOLSTICE, TV 1.5 hours
Sunny, then haze & clouds
Cloudy, some late sun
Rain, dark all day
Not home all day, did not use any power
Didn't charge much because wasn't discharged yesterday
Watched 1/2 hour of TV, not much other power use
Equalizing the batteries
Equalizing the batteries
Equalizing the batteries
MORE on TILTING BRACKETS and SERIES VS. PARALLEL WIRING
(Added March, 2009)
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 ( the likelihood that you will drive off with them still tilted up, and  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:
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.
One panel partly shaded
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
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.