Our daughter Lindsey, and grandkids Cameron and Sadie out for a walk at Baxter Conservation Area south of Ottawa, Ontario. Photo taken by Ruth October 26 2016.
Where are Kevin and Ruth right now? Osgoode, Ontario, Canada. Just south of Ottawa.

And where are they going next? We leave November 1st for a six week trip to Romania and Moldova.

Tuesday, August 9, 2016

Solar Panel Basics

When we were talking about 12 volt battery basics the other day, I had mentioned that it would be pretty easy to write an entire blog post about solar panel basics...so here it is!

We think that there is no better feeling than to be self sufficient for the electricity in your RV. No more having to worry about finding a place to plug in, no worries about whether it's stable source of electricity, and no need to buy surge protectors or voltage regulators.

Solar panels designed for RV use are rated in watts. You can buy single solar panels rated as low as 5 watts, or as high as 250 watts. Of course the 5 watt panel is very small, and the 250 watt panel is very large.

It is most common to find single RV solar panels rated between 80 watts and 150 watts. Simply due to size restrictions on roof space, these solar panels are the easiest to mount and make the most use of the roof space available.

The number of total watts that you will want will depend on two things.

1) How much battery capacity you have.

2) How much sunshine you have,

It is fairly standard, both from what I have read, and our own personal experience, that you want around 80 watts of solar power for every single deep cycle battery that you have. So, if you have two 6 volt deep cycle batteries, you will want approximately 160 watts worth of solar panels on your roof.

These numbers are not written in stone though. If you have lots of sunshine available, and you don't draw down your batteries very much in the evening then you can get by with less solar panel power. If you are a heavy user and/or have a lot of cloudy days then you may need more than 80 watts of solar per battery.

We have four deep cycle batteries but only three 80 watt panels. But we find this sufficient for our needs. On a sunny day, our batteries are usually fully charged again by noon the next day.

RV solar panels do not supply exactly 12 volts. In fact, most of them are rated to supply between 17 and 22 volts. So besides the solar panels, you also need a solar charge controller to electronically control the voltage and current being supplied to the batteries from the solar panels.

You can spend a lot of money on charge controllers! But, you don't need to.

We have a basic charge controller that is now 7 years old. It has done, and continues to do a good job. But not a great job. I have often thought of buying a better quality charge controller, but I can't justify the money for perhaps a 10% to 20% gain in efficiency.

Our charge controller.

The neat thing about RV solar panels is that you can start small and add panels as you need to. When we first bought our kit, it included two 80 watt panels and a 30 amp maximum charge controller. In full sunlight, each 80 watt panel will output about 5 amps. So we could have a total of six of these panels matched with that particular charge controller.

After using the system for a year, we decided that one more 80 watt panel would be better for our needs and usage, so we simply added another panel to the roof and ran another set of wires to the charge controller. 

RV solar panel kits have come way down in price since we bought ours. You can now buy a 100 watt starter kit including the mounting brackets, wiring, and charge controller for under $200 USD. For that kind of money, I don't understand why anybody wouldn't have one installed. Of course you still need to pay for installation, but if you are at all mechanically minded you could easily do it yourself.

For a beginner, this is the kit I would recommend...

As I said, the solar system can be added to over time. Simply buy another panel, or two, and wire them to the existing charge controller. If money is no object, you can even upgrade charge controllers to get one with a display or fancier electronics that charge your batteries more efficiently.


  1. Love ours wouldn't go with out one now

    1. I know, right? People who don't have solar don't realize how much more freedom it gives you.

  2. The rule of thumb we follow is one Watt for one Amp Hour of battery storage. We also add around 50-100 Watts of panel so there is NOT a need to tilt the panels. In our case we have 720 Watts for 660 Amp Hours. IMHO the controller is the brain of the system and worth the $ (batteries the heart). A MPPT controller (cost more $) allows for charging during low sunshine days if using 24+Volts to the controller on a 12V battery system. Solar is a lifestyle choice as a gen is cheaper in the long run.

    Your Tech post are excellent!

    rocmoc n AZ/Fld/Baja

    1. Thanks rocmoc.

      Yes, you are correct. You can spend lots of money on upgrades. However I was trying to stick to the basics for the beginner. And as I said, you can add on and upgrade over time if you feel the need to. For us, our fairly basic system suits our needs.

  3. I am new to all this, can you recommend a specific deep cycle battery please

    1. Simply go back a couple of days to previous posts. We just finished writing a 3 part series about 12 volt batteries...


  4. Solar panel voltage is also VERY important. Beginners should make sure any panels they buy are "12 volt" panels that put out the 17-22 volts Kevin mentioned.

    The lowest cost panels are intended for the home/business market, and are usually rated 24-36 volts. These require a more expensive MPPT charge controller to prevent damage to 12-volt RV electronics.

  5. We have had our 130 watt panel and good controller for 9 years now and works wonderful, but going to add another 100 watt panel to our controller and 2 six volt batteries, just so that they will charge faster, the two batteries work fine for what we use them for.

    1. Yep, another 100 watts should do you just fine George.

  6. Dugg
    you're absolutely right. But however
    if you take one 240. Panel 24 V system along with an MPPT controller you could instead of three panels on the roof you'd only have one to do the same job
    On top of that with the MPPT controller You could adjusted to 13.6 Where most standard controllers are fixed

  7. I need to make a correction that's 14.2 - 14.6 on bulk and 13.4 - 13.6 on Float. Sorry

  8. Mister Ed, at 65x39" it would be a challenge fitting a 240W panel on most RV roofs, whereas 41x27" for three 100W should be easier. A single 240W panel does not quite do the work of three 100W, even with an MPPT controller. So cost per watt, the two systems are comparable. I do think 24V panels make sense for higher wattage systems---especially since you can find these panels under $1/W---but the beginner should probably stick with 12V panels.

  9. Dugg, I can think of a couple of instances where a single 240W panel with a MPPT controller would put the same/more amps into a battery bank. All that is needed is an improvement over 25%. MPPT controllers at low irradiance, cool temperatures and arrays over 170 Watts show a gain over PWM. The wiring from the array to controller at the higher voltage also has a lower loss. A user may also have a 300W array but a 15 amp controller where the excess wattage could be lost. In low load instances, and high temperature environments the MPPT is not worth the extra cost. Add to it, as you pointed out, the challenge for the placement of the very large panels.

  10. Interesting topic, in that we're thinking of getting into the RV lifestyle, along with some boon docking at times. Being in this situation though, we'd obviously have no idea (as of yet) what our 'needs' will be, for the need of power. Sure, one's fridge, and water pump are the two culprits of need the most, but we haven't gotten to need television (or how long one can watch it) yet, or the few other current needs. Still being fairly active, our thinking is that we'd be out hiking/biking etc. thus not home for chunks of time...no pets to stay cool during the day, or other needs of electricity. There again, as we get older that may change....but this 'beginner' part makes for a healthy dream of getting out and meeting others doing the same!

    1. Not knowing your needs is why starting off with a basic system and then adding to it is the best way go. Not only that but it also isn't a big drain on the pocketbook all at once either.

      Actually the fridge and the water pump aren't huge draws on electricity. If the fridge is on propane the only electricity needed is to run the electronics which is very minimal. Having a residential fridge or wanting to run a two way fridge on electric is a whole other story. The water pump again doesn't use much unless you are constantly running it non-stop. We don't have a TV to watch so can't really say how much power it would use but I believe most appliances tell you what the power usage is per hour. We also spend a lot of time outdoors and have no pets so our 240 watts in solar and our 4 - 6 volt batteries serve us well. Perhaps that would be a good starting point for you.

  11. Peter, I ran the calculations and concluded that the 240W single panel still underperforms the 3x100W under typical conditions. At these low currents I²R wire losses don't really play a significant role in either system as long as prudent wire size choices are made. And while I agree wholeheartedly that MPPT shines under cold, low light conditions, RVers can easily save the extra $100-300 by simply choosing generally warmer, sunnier locations.

    Another major issue with large (over 200W) panels is the fact that they cannot be shipped using UPS or FedEx Ground. It makes very little economic sense for a single 240W panel to be shipped freight. This is not the case when multiple 240W panels are trucked. Indeed, here their sub $1/W cost alone can offset the cost of an MPPT controller.

    1. Agree. Just trying to make the point that sometimes just having more Watts does not mean it will all be harvested.

      Recently saw some panels available to the consumer at 38 cents a Watt. The 320 Watt Panel, almost 80X40 were $119 with a shipping charge of $250 for a single. Now what is going to be the price when they start to use Perovskite solar cells?


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