Are these good panels to start with?

TexOil

I have a chance to barter for 6 MEMC P275AMA panels. According to the person I'm getting them from they've never been energized or used. I know nothing about solar panels but plan on learning. I was hoping to get advice on these panels. I'm hoping to totally power a fifth wheel, I don't think I'll need all 6 to do that but not sure how many it might take. Thanks in advance 

Photowhit

Might well take more, if you expect to run air conditioning!


RV's are tough, they tend to have a lot of things going on, on the roof that could shade solar panels. I would think you are money ahead if you would further discuss what you want to do and measure the panels and see what area you have for panel placement. These panels would require either an MPPT type charge controller or running a 24 volt system. MPPT charge controller to run all 6 in a 12 volt system would run $550+.

I wouldn't expect to pay more than 30 cents a watt from a 2nd party. There are panels available in that neighborhood new (+ shipping). So realistically $20 cents a watt would be the approx. value for working panels.

TexOil

Thank you for the reply. I deal in tools and he deals in solar panels. He said these were valued at $275 apiece and we talked about $100 credit for every solar panel. So I'm not sure if I'm getting a good deal at $100 each panel. I was hoping to run the entire rv on solar including the AC, it wouldn't have to supply the rv 24/7 but I was hoping to at least see a great reduction in my light bill with these.

As far as the roof I'll have to crawl up there and take some measurements, He said the measurements on the panels were roughly 78x39 so I don't think I'll be able to fit more than six up there due to the ac, sky lights and vents but I'll take some measurements today. 

I'll start looking into an MPPT type charge controller today. I was wondering where you might suggest going for solar panel supplies?

mcgivor

These panels could be used with a PWM or MPPT  controller running a 24V nominal system or only a MPPT for 12V nominal, gives some flexibility, PWM is less expensive, MPPT slightly more efficient in some/most applications, if by bartering means you'll give up something you don't need for something you do, that's always a good deal.

Photowhit

Using the solar panels for 'some' of the load really doesn't make a lot of sense, since it still requires having a 'shore line' or generator. Flat mounted panels are less efficient than those angled toward the sun.

I had a similarly sized system running a window air in a cabin. I had serious advantages over a camp. 6" thick well insulated walls and the cabin was in the shade while the properly angled solar panels gave maximum power through out the day. The window air was @440 watts running. I think good roof air conditioners run 800 watts on campers. I was only able to run the window air about 4-6 hours a night off the 4 golf cart batteries. I ran a 24 volt system to maximize the system efficiency and did run the air during the day once the batteries were recharged.

Math works out to 4 - 6v 220ah batteries have 6 volts x 220 ah = 1320 watt hours x 4(batteries) or roughly 5000 watt hours of storage. Even recharging quickly/the next day. You really don't want to discharge a standard lead acid battery bank more than 50%. You should be able to see the 800 watt load would be a strain on the system. Batteries are rated at a drain of 1/20th of capacity, if they are drained at a higher capacity they will have a lower effective capacity. In addition a 12 volt system will see a larger voltage sag and may trigger a low voltage disconnect on your inverter!

Something else you may not be aware of is the panels, while rated at 275 watts, will typically produce only 75% of that, in addition there are other system losses. The inverter will only be 90-93% efficient and charging the batteries about 80% efficient.

As to 'value' he can value these at what ever he wants. Solar panels are available at 35-50 cents a watt new. Valuing these at $100 each toward your full value tools, would not be too bad, assuming you have reasonable markup on the tools.

Photowhit

Our sponser carries a full line of solar equipment and have knowledgably sales people. You may find cheaper prices elsewhere but hard to beat knowledge when dealing with solar. They also may have the best pricing on Midnite equipment, makers of some nice combiner boxes and power centers. They make a great charge controller too, but I would recommend one with out a fan for an RV installation.

Something I didn't mention before is charge controllers are rated on output amperage. A 1625 watt array will max out a 100 amp controller (Magnum PT100(?)) on a 12 volt system, but fit on a 60 amp charge controller in a 24 volt system (Morning star MPPT 60)

TexOil

Thanks for the helpful input. I think I'll pass on these and look into having it done. I can't thank yall enough for the information