Condensation easier than you think.

[Paulm]

I got some moisture already in my test panel. Sealed with average air inside the house. I put the panel in the sun resting up against a snow bank at the right angle to the sun. Got 14v at 2.75a into a battery for 4 hours. At dusk I picked up the panel and took it in the house. Looking thru the glass on the back I could see moisture in three or four small areas. Especially where small bits of snow had stayed. So - to check your panels get them warm in the sun then cold with snow or ice on the glass for 30 minutes or so. Move the ice away and see where ice was for condensation. Let me know what you get. The panel should be kinda warm first then make the temp extreme difference with the snow or ice.

[tcrenshaw]

I took a different route. I was going to shoot inert gas into my panels at first but then opted for just putting a small hole through the back at the very bottom. I did the same at the top. The panel heats up and the heat rises, pulling cooler air in the bottom while the heat goes out the top. This so far has worked well. I don't get snow though so that may be different. I plan to wait until a really hot day, get the panels hot and then plug the holes to see if that makes a difference.

[Volvo farmer]

I haven't tested mine for hours like that yet. The aluminum box piece between my glass is filled with dessicant though, I can hear it slide around in there. If you're only getting a little moisture, I bet dessicant would take care of it. Those guys who build double pane windows don't put dessicant in there for nothing.

<img src=http://www.frontier.net/~bobwenn/toys/panel4.jpg

[Paulm]

Why did you post that picture?

[Tom in NH]

Hi Todd,

You might be better off waiting for a really cold day to seal your holes. Cold air holds less vapor than warm air does. If you trap warm air with a relative humidity of 50%, it will have considerably more moisture in it than cold air with the same relative humidity. Of course if the materials of your panels are not completely vapor-proof, hermetically sealed and all that, the inside of the panel will seek its own humidity anyway, and sealing the hole will have little effect (or a negative effect if water gets in and can't get out!).

After watching my open-air panels for several months now, I'm happy to see that in my damp climate, good ventilation is better than trying to seal them up. In the morning there is often a small amount of dew or frost under the plexiglas, but by midday, even when the sun doesn't shine, its gone. --Tom

[Volvo farmer]

It shows the aluminum piece that goes between the glass in double pane windows. See the little holes in it? that's how the moisture can get absorbed by the dessicant inside the aluminum box piece.

[Jeff7]

I intend to torture my prototype panel, once I build it. It's going in the sun, in front of a stove, submersed in water, and maybe I'll throw ice chunks at it (hailstorm test). I want to be sure that the good panels are going to be working in a few years; kind of useless to save money on cheap panels when they're only going to last a few months, right?

I'm hoping for:

• Aluminum backing to aid in cooling
  
• Solar cells mounted with thermal epoxy in the middle, and some small thermal pads to keep them from shorting out on the aluminum backing. The thermal epoxy is just some silicone heatsink compound, mixed either with 2-part epoxy or maybe with Goop. Epoxy mixes more uniformly than the Goop does, but the Goop makes a stronger bond...of course, once the sun bakes the cells, the epoxy should strengthen.
  
• Aluminum structural channel around the outside, possibly sealed with silicone, chaulking strips, and/or polyurethane foam.
  
• Aluminum square tubes on the back for structural support. UL-listed panels are rated for 120mph winds. I want these to be close to that spec.
  
• A price that's still lower than store-bought panels.
  
• Considering helium filler for the panel. A canister at Walmart is less than $20, and is labeled as containing 8.9 cubic feet (.25 cubic meters, or 15,379.2 cubic inches) of helium. I'll have to calculate how many full-sized panels that could fill, but I like the number.
  
  

Quick estimate for the volume of a full-size panel is....huh, only 472 cubic inches. Cool. Pretty decent number of panels for a $20 canister of helium, even assuming lots of losses from unskilled application.

Thus far, I've got the plans ready, and most of the supplies on hand. I just need the time now to do the cutting and assembly. Then I can assault the prototype. And do a cost analysis.

[Jeff7]

What about the possibility of either insects using the panels for housing, or else buildup of mold? Also, what of corrosion? Especially if you use copper, I think that stuff will begin to turn green once it starts to oxidize. I don't know what happens to lead and tin in the solder.

[Tom in NH]

Those are good questions, Jeff. I know that insects, particularly small wasps like little tiny holes. I don't know if the big ventilation slots I provided will be affected by bugs. It might get too hot inside the panel for insects to live.

So far I haven't seen any corrosion, but it has only been 3 months. Over the course of the next year, I should have some better answers. --Tom

[ghurd]

Stinging bugs seem to love living on the back side.

G-