RV solar power for keeping house batteries topped up....

You may find the info you want on the RV forum here in this PV forum website:
http://forum.solar-electric.com/forum

We use solar charging exclusively on our sail boat. To start with, you'll have to make some calculations to see what your energy needs are. Add up the amp hours of all the things that will be running off the batteries in your rv. You can use a current probe on a multimeter to check each circuit and measure amps. when on. Estimate how much use that circuit will get in a 24 hour period and multiply the amps measured times hours used. Add it all up, and make sure you have enough battery capacity to cover you when the sun isn't shining, without depleting the batteries too far. Then just make sure you install enough solar capacity to make up for what you use in a 24 hour period. Give yourself some leeway for days that don't produce much sun. If you don't want to measure things, see what other people are using on some of the rv or boat forums, and use that as a starting point.

When it comes to controllers, there's always the debate between using mppt and pwm contollers. pwm controllers will be quite a bit cheaper. I've always used one of the better pwm controllers, as I doubt I'd see a difference worth the added expense of an mppt controller, but that's just my opinion. Either way, cheapest does not usually equal good, whichever type you go with.

One tip I learned is that you can reduce your electrical needs quite a bit by switching all your interior lighting to LED. We did that, and also switched our mast light (used for overnight anchoring) to LED. You don't have to replace fixtures. You can usually find replacement LED bulbs to replace the incandescent 12v bulbs in the existing fixtures. Also, if you need additional lighting, the LED strip lights, I'll link to below, work really well under cabinets, recesses, etc. They can be cut to length as needed, and there's also a dimmer than can be bought separately...make great "mood" lighting. Just make sure you get the warm white color, not the cool white (same with your replacement bulbs).

http://www.amazon.com/LEDwholesalers-Flexible-SMD3528-Adhesive-2026WH/dp/B002Q8V8DM

LED are intrinsically DC, so I think the gain over incandescent or fluorescent would be even bigger in a 12V DC situation, than in a 120V AC house wiring, where the LED unit has an inverter built in to the base.

LED's typically are about 1.7-1.9vdc and multiple LED's in series frequently are used for a 12vdc bulb. Some lamps may have boost/buck circuitry to allow them to stay bright as battery voltage drops or to have multiple brightness levels. Amazing invention.

The last incandescent bulbs I swapped out for LED's, on our boat, were more than 20 watts. The LED replacements are 3.2 watts, so a pretty big improvement.

With an open area I would recommend trying out the harbor freight solar kit, it is built on the cheap side but it works: http://www.harborfreight.com/45-watt-solar-panel-kit-68751-8527.html

Use a 20% coupon or wait for a good sale and use the coupon and you can get it for a good price.

I check our local store for returns and have found some good deals.

Since you're not there using it much I don't see a bigger PV system being worth it.
Your generator & batteries can already give you what you need while you're there. If you only have some LEDs, propane furnace & propane fridge going, a good charge on the batteries can last quite a while.
What about when there's a foot of snow on your flat mount panels? Are you going to go up there after every storm to clean them off?
Why do you need CO & smoke alarms on when no-one is there to hear them & nothing is running?
How about a little 5 or 10 watt panel sitting inside on the dash trickle charging the batteries & just disconnect everything else when you leave?

There are SO many ways to do better $/W on solar panels than HF. The 220W panels on my roof were $0.78/W. At that cost $/W, the 45W HF kit should cost $35.10 Somehow, HF charges $3.38/W even with a 20% off coupon??

A host of 12V panels with aluminum frames can be found in the $1/W to $2/W range. I see some 90W and 60W panels for $1.6/W-$1.9/W. 50W panels for $1.8/W

For <100W panels eBay seems to have the best prices....amazon stinks.

To be honest, there is an advantage to shore-powering your camper since you have the opportunity, to prolong the life of your batteries. If you're not using the camper regularly, the cost of the electricity you use will be very low. And if you've got a dual-power fridge that can run on 110 VAC when available, it will save you a lot of propane.

Still, if you like being self-contained, especially if you use the camper elsewhere, the cost of a small solar setup like this is pretty reasonable these days.

mellow said:

With an open area I would recommend trying out the harbor freight solar kit, it is built on the cheap side but it works

Click to expand...

I'm not one of the anti-Harbor Freight folks, but their solar kits are a joke. I don't know why, but their solar panels are more expensive than other sources for a lower quality product.

Even Home Depot sells (by ordering and shipping, not in-store), better solar panels for a much lower cost per Watt:
http://www.homedepot.com/p/Grape-So...t-Systems-GS-Star-100W/204211365?N=5yc1vZbm18

You can get slightly better prices through Amazon, and I'm sure even better through Ebay, although I've always wondered about the quality of products coming from discount sellers on Ebay.

The above doesn't include the charge controller or wiring bits that the Harbor Freight kit has, but it's twice the rated output, and actually physically slightly smaller, for a lower price. Amorphous panels like Harbor Freight don't see their output decline quite as much in cloudy conditions as the polycrystalline panels that make up the majority of what gets sold these days, but polycrystalline also have lower performance degradation over time that will roughly make up for that. And the better pricing of non-HF panels more than makes up for the cloudy day performance.

If you can get a decent estimate of your daily usage, a couple of us can estimate how many Watts is appropriate. However, if you already know your existing batteries are enough to get you through a typical weekend, then a single 100 W seems like an acceptable start. Self discharge from both batteries should be less than 10 W-hr per day. A 100W panel should exceed that on even the darkest of cloudy days. Recharging after use for typical sun levels would take several weeks in the winter and several days in the summer. This is below the ideal charge rates, but as far as I know, that should only slightly reduce the life of the batteries.

It seems like there's lots of options for 30 Amp charge controllers, which will handle up to 3 similar size panels total.