Suitable mounting for PV cells

Gentlemen

I have ordered 100off, 6" 6" PV cells and plan to assemble 72 of them on a single panel which will be mounted between the bows of an electric motorised catamaran, not a task for the faint hearted, but this fool is going to have a go anyway. I would appreciate suggestions as to suitable laminates to produce a light but adequately durable installation.

My thanks in anticipation.

Geoff V

Normally you would use 3-4 mm hardened glass and L shape anodised aluminium profiles. On the backside you cover the cells with EVA foil or encapsulate with uv resistant non expanding potting epoxy from a brand like dow corning.
Check youtube, there are tons of videos on DIY solar panels.
http://www.youtube.com/user/GREENPOWERSCIENCE for example has a lot of videos about the subject (and also other cool stuff too).

on the other hand...you want to make all the effort? solar panel prices are at an all time low these days. Im pretty sure they offer a lot more sealing quality also.

Monstarr

Thank you for going to the trouble of replying.

Traditional solar panels are not quite what I had in mind due to the weight of the glass and because none that I have found so far fit the dimensions that I need. To fit between the hulls at the bow I need to arrange the cells 9 across and 8 rows, my currnet thoughts are to laminate a panel of honeycomb or end grain balsa with GRP cloth, onto which the cells would be mounted. On top of the cells I visualise a thin plastic sheet, possibly self adhesive or a thin sheet of polycarbonate and finally the edges would be protected by an aluminium U section.

My problem is finding a suitable, transparent, plastic material for the upper surface.

Geoff V

I had pretty much the same problem when fitting solar panels to my electric boat. My first attempt was to buy some raw cells so that I could do as you intend, fit the tiling pattern to the shape of the fore and aft decks. I did several experiments and none were very successful, as it is fairly difficult to get good results without using a vacuum system, I found.

I can tell you what doesn't work, which may help.

- laying the cells on glass cloth and encapsulating with clear epoxy, of the sort used for casting, produced a tolerable result at first but the cells cracked from the difference in expansion coefficients (this is important, I found, as the cells will easily reach 50 to 60 deg C in bright sun).

- Laying the cells face down on clear polycarbonate, then encapsulating the rear with Dow Corning two part silicone produced a panel that worked well, was slightly flexible and the cells didn't crack. The downsides were all the air bubbles between the cell faces and polycarbonate and the poor light transmissivity of polycarbonate, which reduced power a fair bit.

- laying cells face down on acrylic sheet (Perspex) and encapsulating with the clear Dow Corning stuff worked the same as the polycarbonate, but gave much better performance. It still looks unsightly, though, with all the air bubbles.

If I were tempted to do this again then I'd opt to use acrylic sheet, the Dow Corning resin and try and rig a way to put it under vacuum to get the air bubbles out. You'd need to maintain the vacuum for several hours, as the resin sets very slowly, and it would help if you had a way to hold the cells face down to the acrylic, as they tend to float up in the resin I found. I was tempted to try embedding a piece of woven glass cloth on the rear, as I believe that might add strength and help protect the rear of the cells better. The Dow Corning resin is expensive, but I don't believe there is anything else that is really usable for DIY use. It remains slightly soft, even when fully cured, and so allows for the differential expansion that's inevitable with the different materials used.

I ended up fitting a canopy to my boat to which I installed four 50 W flexible panels from Sunflex. Not as cheap as DIY. I believe Sunflex may make custom shaped panels, certainly they asked me what shape I wanted mine and where I wanted the terminal box located, so they might be worth contacting. They laminate the cells inside a layer of EVA, with a thin aluminium back plate and a tough plastic top surface (which may be acrylic I believe).

Jeremy

Thank you for the benefit of your experiences.

I am starting to think I may finish up with proprietry panels! but as I have a vacuum pump to hand I will try your final suggestion and see how I get on. I'm not clear at this stage how I will 'bag it', your idea of a glass woven rovings sounds good and may behave like a 'peel ply'.

Geoff V

I'm dreaming of the same - cat with PV battery. No experience at all in this sphere. So ideas only.

The PV battery back plate should be very light and hard enough to withstand wave and weight loads.
I've made an experiment - took three equal pieces of cellular polycarbonate and glued them
together. Two outer sheets have the same orientation, while the middle one is rotated by 90 degrees.
I received a kind of plywood. It is very hard and extremely light - has density about 150 kg/cu.m. I will
make my first tries with solar battery using this material.

I did a test with glass cloth in EVA and it was just as flexible as the EVA alone. Fiberglass cloth adds nothing to any rubbery resin.

For baking my EVA sheet, what I want to test first is a flat sheet of metal. Lay a sheet of thin Lexan/polycarb followed by a sheet of EVA, then the cells already wired, then EVA sheet backing. Hopefully the EVA adheres to the Lexan during the baking process. If not, then I simply bake the cells in the front/back sheets of EVA to waterproof the cells, and do that on a flat surface. Then use a thin coating of liquid EVA or a thinned silicone, whichever adheres better in testing, as no a bubble adhesive between the protective lexan face and the softer EVA. For backside support I plan to use a nice thick epoxy/fiberglass rigid backing. I'm unclear how to adhere that to the back. I've thought about imbedding some plastic pieces in the EVA layer on the back for a good mechanical bond when doing the glass work. If I can do that without much risk of losing a waterproof seal.

That's for a no-walking area top portion of the nacelle of a cat. No way I'd put it as a support piece between the hulls out front. There's just too much pounding and flexing for absolute the waterproofing necessary for a solar panel.

John

Is the top cover like glass or EVA or polycarbonate or some other sheet or film really nesessary?
If we promise ourselves not to step to the panel, why not glue cells to a base and cover them with epoxy (is it UV-resistant?) or this Dow Corning two part silicone or any non-colored varnish?

After much deliberation I finally made a start on my proposed PV panels.
Non of the tradition methods of construction seemed best suited to my needs being either too heavy or to expensive so I'm trying a different approach, for better or for worse!
I purchase two pieces of polycarbonate laminated roof material, the type typically used on conservatory roofs, 16mm thick in three layers with diagonal webbing. I soldered the tabbing wire to the underside of the cells first and then attached them to the support sheet using double sided foam tape 12mm wide by 1mm thick (used for attaching number plates to cars). Next the tabbing wire is soldered to the top surface of the cells and connected by bus wire to complete the circuit. The panels are 1500mm x 690mm each and carry 36 cells in a 9 x 4 pattern to give 18v each (36v total for a 24v system). To protect the cells and avoid the need to encapsulate them, the edges of each support panel have a strip of 3mm thick double sided foam tape onto which a sheet of 2mm thick UV resistant polycarbonte is attached, with a strip of waterproof gaffer tape for extra security. The weight of the bare panel is 2.8Kg plus a further 2.6Kg for the protective 2mm thick cover, so 5.4Kg total ( may try 1mm thick cover sheet to reduce the weight by 1.3Kg).


I have no idea as yet as to the durability of the technique but will report later in the Summer, assuming we get one this year!

GeoffV