Effect of PV Coverings on Electric Output

[Tom in NH]

Volvofarmer made an interesting remark a few posts down about how low-e glass cut output on his solar cells by 20%. What was meant by output? Was it o.c. voltage? s.c. current? Or some other measurement? How thick was the glass?

I had one of my panels apart  for repairs and I measured current produced in full direct sun, both with and without the 5/32 inch plexiglas covering I use. I found the plexiglas of this thickness cuts my short circuit current by 9%. This was obtained by measuring the difference in current between with-covering and without-covering, and dividing by without-covering current. My panel without-covering produced 6.6 amps. With-covering it produced 6.0 amps.

I also learned that a clean covering was not measureably greater than a covering that had accumulated the normal film of pollen and pollutants that accumulates here. So I guess I don't have to feel guilty about not washing my panels all the time (yay!). I didn't have a piece of glass or other materials to try over my panel, but maybe some of you other panel builders have some firsthand data like Volvofarmer that you'd be willing to share. --Tom

[Volvo farmer]

My measurement was short circuit amps, and 20% is a very round figure, it was several months ago and I mostly only remember that low-e glass was unsuitable for solar panels.

I do know that regular tempered glass cuts down on output somewhat, perhaps 5%, but I had to cover them with something and that's just a loss I have to live with so I never measured it. Sorry I don't have the exact figure but I'm pretty sure glass is better than plexi for covering solar cells if you want to minimize losses. My panels are now sealed up so I can't check them without the glass on.

[Experimental]

        E- glass, filters out ultriviolet rays, that will definitely affect the panels !!    But, any glass, plastic or other, will filter out some rays and my panels have nothing over them ..

        I know, some folks have had serious problems with broken panels, etc..And some types are much more durable than others -- some can even be walked on !!

        Can,t tell you much, except mine have been up for over two years, and I haven,t even cleaned them  (maybe I should)  Mine are BP, 65 watt and came with an aluminum frame -- other than that -- they work great !!   Wishing you good luck, Bill H......

[wooferhound]

 I have a solar panel covered with 1/4 plexiglas that has been out in the weather for more than 10 years. I have taken it down at this time to rebuild it with glass instead of plexi. The plexi was clear and new when I origionally made the panal, but had become fairly cloudy / milky and output had dropped below 12 volts full sun. I don't have any measurement from when it was new. Here is a picture taken just before I took it down.

[Tom in NH]

Hey Woof,

Before you put your panel back up would you measure the short circuit current to the nearest 1/10th amp with the old covering, the new covering, and with nothing at all?

I think I finally figured out that picture that you include with each of your posts. It's of you holding the ends of your inverter output cables, right?

--tom