I have a 24'stationary travel trailer that I want to install solar on. I plan on using 2 GC-2 batteries (230ah)in series to provide 12 volts with 230 AH, which I know only 40-50% of that is usable. Being up against a mountain I do not receive direct sunlight from November to Mid-March so I wanted to know which kit would be better to install. I have the option to install either a 300 watt kit (3 panels) or a 400 watt kit (4 panels), but wasn't sure if the 400 watt kit would be overkill or be better for the indirect sunlight months. My average use is about 75-90 amp hours per day.Thanks in advance!Dave

No solar is going to work with sunlight being blocked by a mountain.

There's no overkill; a charge controller will just cut back production when the batteries get full.However, 90 Ah per day is about 1080 watt hours. You would need to make close to 1200 watt hours to replace that taking loses into account. Given the conditions you describe I don't think 400 watts will be enough.

You need to figure out how long you have to charge the batteries before losing high sun. A typical 120WATT solar panel will produce around 5-6AMPS DC current so you need to figure out how long 5-6AMPS DC will recharge a battery. Two panels will produce 10-12AMPS. It is a known fact that 14.4VDC with 17-20AMPS DC Current capacity will re-charge a 50% depleted battery back up to its 90% charge state in a three hour time period. That would need to be four panels in high sun for a good 3-4 hours time for one battery.You can probably get around 6 hours of high sun here on the East side of the US and alot more on the West Side of the US.For me here on the east side I would have to run my 2KW generator for the first hour to get past my 50-53AMPS battery demand when first hit with 14.4VDC and then perhaps I can allow the remaining time I have in the high sun using four solar panels to finish my re-charge when the batteries are being hit with 13.6VDC before the high sun goes away.If you never deplete your batteries down to their 50% charge state then you won't need as much re-charge time to get them back up to their 90% charge state. The batteries will perform very well with only a 90% charge state on them. If you cannot get to the 90% charge state then the batteries will start falling off rather quickly when you use them. This will eventually harm your batteries.I think you have to plan using something like this to get there...I am just now starting to think Solar Panels after doing alot of camping off the power grid since 2009 with my 255AH battery bank which works out great for us running down our batteries to their 50% charge state by 8AM each morning and then running my trailer off my 2KW generator for three hours re-charging the battery bank back up to its 90% charge state so we can do all of this all over again the next day/night run off the batteries.For me the solar panels would work great after I got past the initial 53AMP DC Current demand using the generator first.Others get by ok with less charge time because they never run the batteries down to the 50% charge state over night...Roy Ken

2OLDMAN is the only one that got it right. With NO sun shining directly on your panels for months at a time, even 400W of solar panels will not come close to replenishing your daily use of 75-90 AH per day.

Roy has good advice.One thing I will add, with good quality 6V batteries you can discharge them down to 70 or 80 DOD (20-30%SOC) hundreds of times before they will loose noticeable capacity. I've done that for a decade or more on them, hundreds of discharges. That's what they are rated for and designed for.,Now, below 20% SOC life drops drastically. So if your going to use that capacity, you do need a good way to actually determine SOC. Trimetric or something similar.Course discharged that deep they will take a long time to charge, but at least that's an option when you end up with many cloudy days in a row and don't want to fire the generator etc. And you do need to get them back up to 90% or so within a reasonable period of time (Days??)

Question on Number of Solar Panels | Good Sam Community

Almot
Explorer III
Dec 25, 2015
Don't mount them flat. They should be tilted at least 4-5 degrees to shed water and snow. Higher tilt, like 30-45 degrees "could" help with output, but under gray skies and in the mountain shadow this won't help much, and will create more wind loads. Reflection from snow is an interesting idea, but... New Jersey isn't exactly Alaska, and with weather globally screwed up there might be no snow at all.
msmith1_wa
Explorer
Dec 25, 2015
Since your trailer is basically being used as a cabin. Why not build a ground mount where the sun is all year.
Almot
Explorer III
Dec 25, 2015
msmith1.wa wrote:
Since your trailer is basically being used as a cabin. Why not build a ground mount where the sun is all year.

He said it has to be moved 500ft away to clear the shadow.

As a maintenance charging, there is a good chance that 400W will work in the shade. People telling that "solar panels don't work in the shade" don't understand the physics. Full soft shade - when all the panel is in the shade but it's not pitch dark either - is better than partial hard shade. The output (in the former scenario) will drop proportionally to the amount of light that panel is getting. If on a cloudy day in winter behind the mountain it is (for example) 20 times darker than in direct sunshine in summer, then the current will be 20 times less, ex. 1A at noon instead of 20. Plus, shorter daylight.
Ed_Gee
Explorer II
Dec 27, 2015
Ductape Dave wrote:
I forgot to add that I also have a Yamaha 3000iseb generator so charging them would not be a problem during the winter months when they come up short. I don't go too often in the winter and usually just for long weekends.

Just thought the 400 watts(over the 300 watts) would put out an extra amp or so to keep the batteries maintained when I am not there.

I am right up against the side of a mountain and would have to go out 500 feet to get sun, but it returns on my side from mid-March to mid-November.

I think most of us were assuming you wanted the 400W of shaded solar panels to maintain your battery while camping in the RV. If all you want is a maintenance charge to keep the battery up with very little current draw being done during the Winter months....and you are not using the RV .... then yes, I would expect 400W of panels in full shade but exposed to the sky would get enough light to at least maintain your batteries. Even one amp or two would probably be sufficient.

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