Help designing a 500 - 600 watt RV 12 volt system

Travlin5vr · March 2016

Hi all

I'm attempting to build/design a system for a 27-5 Arctic Fox 5th wheel. I would appreciate your comments and advice on the following.

First off, It appears that I've made the common mistake of buying equipment before considering needs. However, due to space limitations, I'm going to go with 4 - 6 volt batteries, which came with the RV (Canadian Energy, GC2s, 232 ah). Obviously, I'm trying to design the most efficient system with the equipment I've already purchased from NAWS. We travel to the US regularly and even with the currency exchange, it's much cheaper to bring it back a little at a time.

Here's what I currently have:

Xantrex - 2000 Prowatt SW, with the compatible on/off remote and separate 15 amp transfer switch
Morningstar - Tristar 45 Amp MPPT controller with the temperature sensor and remote digital meter
Yamaha 2400 iSHC generator

Now on our next trip, I need to get some solar panels. I have enough room on the roof for 2 or even 3 - 265 watt Kyocera's. However, they would have to be on both sides of a roof vent and within 2 to 3 inches. From what I gather this would present a problem with shading; as 1 panel would always be shaded unless the sun was directly overhead. Therefore, my problem appears to be that I need to go with narrower panels. I'm looking at the Topoint 190 watt 24 volt panels which are 32" wide. I could easily fit 3 or 4 of those on the roof. But I am concerned about their quality and whether they would be reliable and durable enough for an RV.

My other option is to go with 4 - 12 volt, 140 or 145 watt Kyocera's, but I understand if I run 2 strings in series, I'ld be back to the shading issue. It's hard to tell, but I may have a 20 foot wire run from the most distant panel to the controller; if I go with all the panels in parallel.

l see that Solartech has 130 watt, 24 volt panels that may also be an option.

I would appreciate your responses and advice. The batteries are in a separate compartment, right alongside the basement storage compartment, where I intend to install the controller, inverter and breaker panel. So long wire runs shouldn't be a problem there.

Thanks in advance.

westbranch · March 2016

Was there a reason for a 2 Kw inverter? Microwave?

Travlin5vr · March 2016

Toaster and coffee pot for me. Hair dryer and CPAP for the wife. We boondock and dry camp exclusively. The RV contains a convection microwave for which I would fire up the generator if needed. I try to avoid it though. It's for those cloudy days with endless rain.

vtmaps · March 2016

Let's design a system. Usually the first step is define loads, second step is to choose battery, third step is buy enough panels to keep battery happy.   In your situation, the battery will define the system.   Your inverter is 12 volts, so that is another constraint (unless you want to go 24 volts, and buy a different inverter).

Under normal circumstances (no shading) we have rules of thumb... for a first approximation you want to be able to put a 10% charge rate into the batteries.   You have 464 ah so a charge rate of 46 amps would be a good start. 46 amps at 14.4 volts is 662 watts going into the batteries. Under normal (panels are hot, aimed at sun, no shading) circumstances about 77% of the panel rating goes into the battery. That includes controller losses. Therefore your battery would like to have 662 watts ÷ 77% = 860 watts of solar panels. with no shading.

Given your high energy usage and your limited space for solar panels, don't forget to bring the generator.

To optimize the use of your roof space, consider the use of multiple controllers. That way you can have panels with different sizes and different specs.   There's getting to be a trend towards electronics for each panel (microinverters, DC optimizers).   There's no reason you can't have a mix of PWM and MPPT controllers.

If you choose your panels and then choose a controller for them (the normal thing to do), you will be making some compromises. You probably won't get the 77% mentioned above. You might find that for less than the cost of one panel, you could buy another controller and get more than one panel's worth of additional energy harvested.

So my advice is to look for high efficiency panels in whatever shapes give you the most watts on the roof. Then see how many controllers you need to handle their various specs.   Price it out and see what it looks like. Maybe it will look like a good value compared to the alternatives. Or maybe not.

--vtMaps

Travlin5vr · March 2016

Wow. And I thought I was narrowing down my choices.

Without going to many more smaller panels, I'm pretty well limited to 4 panels under 35 inches in width. I understand it would still be undersized, but if I was to go with 4 of the Topoints would the 45 amp controller be able to handle it? Using the calculations provided, I get 40.6 amps (4 x 190 watts) x 77% / 14.4 volts. I may be able to exchange the controller for a 60 amp.

Damn if I need 860 watts of panel, I'm going to have to go without toast. You know the wife's not going without her hair dryer.

Thanks. Your response was certainly helpful and something I should have picked up on.

zoneblue · March 2016

VT has it spot on. Try to get that 0.1C, its not just about a charge rate that the battery likes, but dictates how often you need to pull the genset out. Look at the sunpowers, they are smaller, if more expensive. And your TS45MMPT will do just fine. MPPT controllers dont max out and blow up like PWM controllers usually do.

scrubjaysnest · March 2016

Two thoughts, one you can take the route I went and have both roof mounted and portable panels. There is more flexibility but more messing around with camp set up.
2nd thought and I really hate to direct you away from NAWS on this as they are great to deal with, but AMSolar.com has specially designed narrow width panels for RV's. This may help the roof situation.
A 3rd thought just occurred, CPAP, look into to the 12 volt LI battery ones I hear they good for about a week between recharges.

grizzzman · May 2016

I built mounts that put the panels 6" off the roof. This really reduced the vents shading issues.

Help designing a 500 - 600 watt RV 12 volt system

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