Question on Number of Solar Panels

[Ductape_Dave]

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

[Ed_Gee]

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.

[Almot]

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.

[msmith1_wa]

Since your trailer is basically being used as a cabin. Why not build a ground mount where the sun is all year.

[Almot]

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.

[pianotuna]

Consider a tilting installation that would allow sunlight to bounce off snow.

[Ductape_Dave]

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.

[scrubjaysnest]

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]

Just the info I was looking for, thank you everyone, appreciate it!
And HAPPY HOLIDAYS TO ALL!!!

[pianotuna]

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.

[Almot]

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.

[BFL13]

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"

[MEXICOWANDERER]

Ductape Dave,

IMHO Good Thinking!

[Ductape_Dave]

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]

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.