DIY Panels - Backing?

[Harry459]

I am planning to relocate eventually to the desert-southwest US. I want to play with solar power at that future location.  

A lot of comments are negative on the subject but from what I have seen, it's still possible to make solar panels for about 50% of what one could buy the same capacity panels for.

I have read a bit about the efforts of others to do home-made panels and the main problems seem to be condensation and mildew, but in a desert I doubt I'll see either of those issues. What I'm curious about is if there's ever usually any other reason to be able to open up the panels.

The fronts would be tempered glass with aluminum edging glued on with silicone sealant. The backing is what is undecided.

I have seen the sheets of Tedlar on eBay and have read how they are applied but cannot find the same material (polyvinyl fluoride) anywhere else. The Tedlar sheets are only available in one size and I don't know what size of glass I'll be using.... And I don't have an oven big enough to hold a 3' x 5' panel anyway. Can this stuff be worked with a heat gun? Or is there any other suitable substitute that can (would need to be UV resist, ~200-250F melting, colored white or clear)....

I've never seen a commercial panel up close and am curious as to if the Tedlar sticks well to the glass. In other projects I've done, I've not seen any thermoplastic that would do that. All the stuff I've worked with was horribly sticky when hot, but after it cooled, it would pop cleanly right off glass or metal. It only stayed stuck to porous stuff like wood or fabric.

Alternately I though of using three sheets of 6mm "coroplast" sheet (corrugated PVC) as backing. The top sheet would have holes cut for the cells, the next sheet would have crossways holes for the tabbing runs between cells, and the final sheet would be solid to close in the back. Screws in the aluminum edging would hold it all in, they wouldn't be glued at all. Coroplast comes in different colors (so I could get white) and I'm not sure about the long-term UV resistance but the top sheet could be painted to add even more UV barrier if need be.

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Also,,, I was assuming I'd wire them in series runs of 50 cells, giving an open voltage of around 25 volts. I was planning to use them to run a Peltier-based cooling system (that I could wire to suit any supply voltage) but I want them to be enough to easily run a 12V battery charger. Would 25V open be enough for that?

[fini]

[DanG]

Peltier devices are designed to fail - out of safety the matrix of active junctions are made to eventually open up instead of welding into a short. IF you are talking surplus elements one can't tell how they were sorted or why they are surplussed. 600-800 operating hours is a very long lifetime for a peltier chip - but only a couple of months of sunshine.

Opps, you blinked... We just entered the trade secret realm - proprietary knowledge zone ... I earnestly forward to you reverse-engineering 100,000+ man-hours of trial and error done by Universities and Government Research Centers is not going to save any money for a aspiring basement DIY panel maker.

Can't say I know any of the following more than intuitive extrapolation from a lot of reading...

Roughly a panel is Glass - EVA - Cells - EVA - Tedlar.

There is a 'tackifier' coating to the EVA laminate sheet that touches the glass in mass production that promote adhesion to the glass - on the other side it has another coating that helps weld EVA-EVA together when heated and subjected to vacuum clamping.

EVA is close to the original hot-glue sticks composition, sticks being a cruder resin. base. Dupont has all the materials you need - but they want to sell you 5-ton rolls.

"Etching" from water can occur without visible moisture, a hermetic seal is vital - then there are mosses, lichen and algae and things like soot and pollen that would rapidly take the performance down.

Glass is to be iron-free, iron gives glass edges a green tint & absorbs energetic wavelengths.

Your PVC sheet most likely has too large of a coefficient of expansion to be used - freezing to 140°F should be expected and the heave and shrink of polycarbonate is too active to be adhering to fragile PV cells or trapped tightly in an alloy frame; plus the vibration resonance on impacted by hail or debris might expand any flaws present or help lift tabs etc...

An oven can be a recirculating loop of forced air that a heat-gun adds heat into to keep the heat evenly distributed over a cycle period, the return air duct monitored for temperature along with a non-contact IR thermometer spot checking surface temps area - drywall or cement tile backer board with plenty of fiberglass insulation comes to mind as oven shell material.

I've seen silicon wafer strings layed out face down directly on tempered glass in aluminum frames that were immersed in a vat of nitrogen gas and silicone sealant poured in as encapsulation then heated to set the silicone - that is old style marine navigation arrays.

-------- oops, chores calling... I will continue later ------

[DanG]

Actually I think the Silicone pour was UV activated hardening...

I've seen a style of panel construction that has the wafers arrayed on top of a sturdy plate, encapsulated and then a metal mask placed over that so it is a raised epoxy bump that is shielding the wafers and sheet metal shielding the tab wiring.

I've asked US Composites if they could recommend a resin to use and they steered me toward their surfboard resin (while qualifying that they had no idea but....) and that is a good possibility if the initial shrinkage or 500 thermal expansion cycles don't grind the wafers into sand. An epoxy or resin that suffers from the surface discoloring may not be that bad - yearly refreshing is not that difficult.

If I were going to invest the time and energy in making my own panels I would use a modular rack system with only six or eight PV cells per pane of glass, then slide fifty of glass-PV panelettes (framless) into a larger warp-free holding frame and use a bus bar arrangement to tap power out.

If, no, when one of the small strings failed it would be easier to replace just that module, reclaim the glass or repair the panelette and just keep going. If you can get a bulk order of tempered glass the price drops dramatically, especially if you can avoid crating and transportation charges by dealing direct or getting the glass people interested in your project...

So. To review. Just invest in pre-made panels with a 5 or 7 year general warranty and 25 or 30 year power warranty. Take your time shopping and network or try to group-buy a pallet quantity.

[howlet]

Industry Standard for the backing of mono and poly crystalline cells is PVF, better known as Tedlar. A sound vacuum system combined with an evenly distributed heat source has produced quality modules for me.

The main problems that I encountered came from poor climate control. Ambient temperature and humidity levels should be monitored and recorded. A sound method of removing ALL the air pockets from within the module must be developed.

Primed surfaces and tackifiers may help adhesion but I have read studies published by the NREL that suggest otherwise. EVA composition and age appear to have the largest impact on proper adhesion.

Finally, Cleanliness is next to Godliness when producing an encapsulated solar module.

"Water White" low iron glass is the industry standard but standard tempered glass has produced better than expected results for me. If you have the money for the low iron, go for it. I have fabricated 90 to 100 watt panels useing (36) 5" pseudo square monocrystal cells and tempered glass purchased from a window framing company. I have no idea what the actual composition of the glass is but you can see a light green shade when looking at the edge. JB