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

MEXICOWANDERER
Explorer
Dec 24, 2015
HARD EARNED TIP

Insulation panels with highly reflective laminate on one side can be used to amplify lighting. Four by eight panels can be used. Not recommended for high wind areas. And use of amplification in full sunlight can damage cells. Position the reflective panels to shine as best as possible on mounted solar panels. This can DOUBLE the amperage output.
Ductape_Dave
Explorer
Dec 24, 2015
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.
MEXICOWANDERER
Explorer
Dec 24, 2015
Ductape Dave,

IMHO Good Thinking!
BFL13
Explorer II
Dec 24, 2015
Your batts need to get to 100% every so often or they will be ruined by sulfation. You can't get them to 100% using the generator--not enough time.

That leaves taking them back and forth with you during the winter visits, keeping them above 50% while there using the generator and a portable charger.

After you get home use the charger to get them up and then use a battery "maintainer" to keep them fully charged.

In the other half of the year, you could use "some solar" at the location, if you find the winter routine is a bother to do it all year.

If there is a security from theft risk at the location, you could do the whole thing with portable everything--solar, charger, batteries. Some folks have it all in a utility trailer they tow back and forth. Just plug the "cabin" into the utility trailer "power set"
Almot
Explorer III
Dec 24, 2015
Ductape Dave wrote:
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.

This is about the only thing that solar will be able to do, in your location - maintain batteries when not in use. And it very well might be that during winter and in the mountain shadow a 400W will put exactly "an amp hour" out, compared to 300W. Like in "one amp hour". I don't understand the hesitations about 400W over 300W. Controller will control the charging - this is what it is for. It will prevent the overcharging if it ever comes to this.

BLF is correct - it's a pain always getting a full charge with a generator. Solar is perfect for the last slow finishing stage. You come there once a while, run a generator for an hour or so daily while you're there, and go home. Solar will complete the charging and will maintain it in your absence. 400W will do this better than 300W.
pianotuna
Nomad III
Dec 24, 2015
Hi,

If the rv is in 'storage mode' then, 400 watts, even with indirect light may be enough to balance the 6% self discharge that high antonym deep cycle batteries exhibit.

In my previous RV I had 30 watts which maintained 250 amp-hours of twelve volt Walmart jars. By accident I had wired them in a balanced manner. Every trip started with the battery bank fully charged. They lasted for 9 years until the next owner plugged in the Magnatek charger full time. That toasted them pdq.
Ductape_Dave
Explorer
Dec 25, 2015
Just the info I was looking for, thank you everyone, appreciate it!
And HAPPY HOLIDAYS TO ALL!!!
scrubjaysnest
Explorer
Dec 25, 2015
Ed_Gee wrote:
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.

+1 you'll do good to get 10% of panel rated.
Ductape_Dave
Explorer
Dec 25, 2015
I have overestimated my use of amp hours, after rechecking the figures I am closer to 35 to 50 amp hours per day, so I am going to install the 400 watt kit which will give me about 2.2 amps during indirect sunlight and use my sears battery charger off the generator when needed.
If the winters are rough I will just bring the batteries home for the winter and keep them on the battery tender, being I won't be able to get up there when its that bad.
pianotuna
Nomad III
Dec 25, 2015
Consider a tilting installation that would allow sunlight to bounce off snow.