Solar Panel Prototypes

The design I was looking for needed to be weatherproof. I checked the spec sheets on a few professional panels. As best as I can tell, UL certification means being able to withstand 50lb/ft2, which translates to something around 125mph winds. It also required surviving a hailstorm with 1 inch hailstones at 52mph. A worthy goal for a home-made panel, but quite probably not one that could be acheived. But I could try to get close.

Polycarbonate (generic Lexan) seemed to be a good choice for the front. It offered very high shatter resistance and overall strength, but it was also easily worked with, allowing for cutting with a bandsaw, something you just can't do with glass. Plus, the tempered glass that the big companies use has a few layers of some kind of plastic over it for additional shatter-resistance.

For the backing, I wanted something that was not only light and resistant to weathering, but could act as a heatsink. Aluminum was about the best thing I could come up with. Main problem with it though is that it's not exactly the cheapest thing to get. As of this writing, I'm hoping to come up with some other backing (something cheap) that can absorb and dissipate at least some heat, as well as provide good structural stability.

The sides would have aluminum framing - a C-channel, running around the entire perimeter. These were to be held in place with epoxy. Late in the design process, I came across polyurethane foam spray cans in a hardware store; the can said waterproof and airtight - exactly what I needed.

I also needed to get as much moisture out of the panel as I could - it might cause corrosion over a period of years, but it would also obscure some sunlight. How to remove it? Flush it out and seal the panel. Helium seemed like the best option - easily available, fairly cheap, as only a small amount is needed per panel, and completely inert.


Prototype Back Reinforcement
There's a shot at the reinforcements on the back of the panel. They are rectangular aluminum tubes, epoxied in place. I found that welding aluminum is quite difficult. I also read that airplane manufacturers use epoxy between the layers of aluminum in the fuselage. While I'm sure that they use something of slightly higher grade than the stuff found at a hardware store, standard 2-ton 2-part epoxy seems to work quite well. 		Prototype Aluminum Side, Test Fit
Yes, the picture is blurry. Either the macro mode on my digital camera (Kodak DC3400) is just really touchy about its focal distance, or else I just haven't figured out what the optimal distance is. At any rate, this was a quick test fit of the aluminum framing over the backing and the polycarbonate. 		Prototype Aluminum Side, Test Fit With Bottle Cap
There's the sophisticated piece of technology I used for the test fitting. It was exactly the right height. The framing fit on very snugly, so I measured the thickness there, and sought a more reasonable solution for the final panel.



Prototype Dowel Fittings
The thickness of the bottlecap was just a bit more than a quarter of an inch - I came out to a figure of 0.6825cm (.2687 inches), based on calculations using the dimensions of the aluminum and polycarbonate sheets. I needed something that ran the entire length of the edges of the panel - a dowel would have been perfect. But they only come in standardized widths; increments in the thousandths of an inch just aren't feasible to make. So, I found some aluminum roof flashing I'd bought for a computer project some years back, and wrapped it around various lengths of dowel, and used Goop to secure it in place. There are multiple pieces here because one edge has three gaps in it - one for the helium inlet, two for wires; one other edge has a gap for the air to exit as helium is pumped in. 		Prototype Dowel Fittings, Attached
This is what one augmented, cut dowel looked like once it was Gooped to the aluminum backing. The white squares at the bottom are laser-printed scans of the 4 solar cells that were to go in the prototype. I only wanted to make a small panel, so as to minimize the amount of materials needed, meaning less of a loss should the prototype fail. The printed scans were there as a placement guide for the perimeter components. 		Prototype, Epoxy Solidifying
All the perimeter supports are attached here, as are the solar cells. The various chunks of metal in the two corners are holding down the bus wires while the epoxy holding them down solidifies. The thing is sitting on top of a wood pellet stove, and is enjoying temperatures of over 70oC - heat helps epoxy cure faster.



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