Solar panel for van camping - RV-Dreams Community Forum

natbr · RV-Dreams Community Member

Solar panel for van camping

Jack Mayer · RV-Dreams Family Member

Well, in "theory" a 45 watt appliance can be "run" with a 45 watt panel. In practice, of course, it does not work that way. So having the battery bank "buffer" is critical. You do not want to run your batteries lower than 50% of their capacity -they will not last long if you routinely use more than 50%. So your usable capacity is at most 50% of your total capacity. That is assuming that you have deep cycle house batteries, not regular automotive starting batteries.

Since solar panel cost is pretty cheap these days, I would put on the largest single panel that you can. If money is not a major object then a high voltage panel with an MPPT controller (that can utilize the higher voltage) is what I would do. Panel form factor (shape) will be a major consideration. Look on wholesalesolar.com at panels that are high voltage (over 21 volts Vmp). Or, if you wnat to stick to "12-volt" panels look for panels 21 volts Vmp or under - these will not require an MPPT controller (which costs more than a PWM controller). Then, look at the Imp for your panel - that is the number of amps it outputs in max sun....and size your controller for that.....except always put in more controller than required, you may want to add a panel.

If I was doing it I'd put in probably something around 200+ watts, high voltage, and add a Morningstar MPPT45 amp controller. That would handle all your future needs and easily keep the batteries up in sun. But it is a higher-end solution. That is just one suggestion....more info could result in a different solution. Also, it is wise to put in a battery monitor if you are gong to come near the capacity of your battery bank. I like a Trimetric 2025RV. But it does add to cost.

Bill and Linda · RV-Dreams Family Member

Hello Nat, welcome to the forum.

Well, I had typed up a response saying what Jack said and also recommend 200+ watt panels, closer to 300, IMO if you can make them fit, because you probably use 12 volt lights in the van at night. Also, on some days you can't get that many hours of good charging and you need more "collectors" to get all the sun you can.

Anyway, Jack beat me to the post. Good for you. You really need this stuff he outlined to make this work well. Might need a very small generator as well but that's another discussion.

What Jack left out is the following:

Highly recommended reading to help with your questions more fully than space here permits:

http://www.jackdanmayer.com/rv_electrical_and_solar.htm

Bill

natbr · RV-Dreams Community Member

GREAT. Thanks for your input guys. Do most solar panel controllers (PWM and MPPT) come with a anti-back charging diode that prevents a generator, the vehicle's alternator or shore power from sending current through the solar panel when those systems are operating?

Thanks for your thoughts on sizing the system. I had done the math and was thinking around a 200w system but will think about upgrading that. Given that we don't (or at least haven't yet) done long term boondocking I was initially thinking about a PWM controller, but I do fine that even on shore power (Intelipower 9160A battery charger) it takes quite a while to recharge the battery bank from 50% (as in more than overnight). Perhaps a higher volatage MPPT-based system would allow it to recover quicker.

I do have a Trimetric battery monitor that I use for the batteries and they will give me a good idea of where I am in terms of full charge or not.

-- Nat

Bill and Linda · RV-Dreams Family Member

Nat:

If you want it to do the best possible job in the limited physical space you have, I would suggest you need a MPPT charger, such as the model jack recommended, I have one, and some ~22+ volt or so panels. Best physical size vs. output naturally in your situation. That’s why the MPPT is so important as are higher voltage panels. PWM chargers can work, but are probably not going to cut it in your situation.

With this charger you don’t have to worry about the generator “charging” the panels. No “diodes” required.

You will probably need a small gas generator at times to supplement the panels. Just reality IMO 30-45 minutes with a generator and a high current (smart) charger can do a lot of initial bulk charging and then the solar can finish the last ~25% in the absorption mode. On some days you may not need the generator at all. Naturally, “it depends.”

Jack has a lot of links on his website I gave you the link to which can provide a source. AM Solar is a good place for one-stop shopping with reasonable prices IMO. They have “packages” that can save you a few dollars.

www.Amsolar.com

Bill