Insolating, UV tolerant, Machinable Material

[deLight]

I am building a solar cockpit cover for my '33. I built a stainless steel frame an made 160X160X3mm modules with a 156X156mm solar cell, terminal block and Schottky diode mounted on 3mm foamed PVC.

After I made 100+ modules and installed them in the frame, I discovered that the foamed PVC warped (de-stretched) badly when exposed to hot sun for a period of time.

I need to make a whole new set of modules. Any suggestions on an appropriate backing material?

[deLight]

Additional photo.

[Soggy Paws]

I am not familiar with 'foamed PVC'.  We built a cockpit cover for our CSY44 WT about 15 years ago from .5" Expanded PVC.  I did not get to paint it for about 4 years, but during that time there was no UV impact.  One advantage of Expanded PVC is that you can paint it with any paint.  Another is that you can use common PVC cement on it.  A third is that you can work it with common plywood tools.  It is still on the boat and doing fine, but now has two coats of polyurethane paint on it.  See details of our cockpit cover construction here:  http://www.svsoggypaws.com/CSY/cockpit.htm

[deLight]

A web search indicates that expanded PVC and foamed PVC are the same product just different names/manufacturers. It is great stuff. I use it a lot by laminating a couple of layers of fiberglass cloth with epoxy on both sides . That makes it stiff and strong and still thin and lightweight for drawers, panels, etc.

Thinking about the differences with your success and my failure. You used a 12mm sheet and I am using 3mm. You have a white reflective surface. I laminated a solar cell onto mine. The solar cells job is to absorb sunlight and gets very hot in bright sunlight. I am in Tunisia (North Africa) and it is well known that suppliers with poor quality products who cannot sell to Europe or the US send their goods to Africa.

After the fact, I read that plastic will de-stretch when exposed to heat and UV. I take that to mean that the plastic is manufactured in thick sheets, then rolled into thinner sheets as needed. So what I think happened is the cell (glass) gets hot and transfers the heat to the thin foamed PVC which shrinks causing the module to deform convexly. The modules still worked even severely deformed until the polycarbonate sheet I used to cover the modules cooled down at night and shrank crushing the deformed modules.

I had always had such good success with the foamed/expanded PVC that I did not think to build one module and test it long term in bright sunlight.  I will not make that mistake again.

Any ideas what to do with 100 solar modules that your cannot put in the sun?

[Soggy Paws]

We have mounted 800 watts of solar in 4 panels on top of our cockpit cover.  One important solar panel mounting requirement is that the cells be mounted in such a way that there be good ventilation both above and below the cells.  So we have the cells mounted in an aluminum frame positioned about 2" above the fiberglass cockpit cover.  Maybe that would solve your problem.  Try mounting your cells above your PVC top.
 Dave

[deLight]

I consider owning and living aboard deLight an enforced hobby. Salt air and UV eats anything man-made so fixing things is a continual task. There are the things that I want to do to make the experience better. Originally, deLight had a fabric dodger and an awning over the cockpit. The visibility from the helm was abysmal leading to docking by braille occasionally. The awning was functional but less than ideal. I needed an alternate power source to charge my batteries and power the boat.

I decided to combine all of these into a major project. Fortunately, since Tunisia  lacks exports to generate foreign exchange, they fix everything. I have latched onto a machinist, welder, artisan to help with my projects. We built a windscreen with complete cockpit cover from stainless steel and polycarbonate. The cover of the windscreen and cockpit was constructed as a hollow structure with provisions to install the solar modules. I am happy with the result and helm visibility is fantastic.

So, it is all built and wired for the planned modules - my current snag. Needless to say, starting over with a different design is something I would not care to do. Also, commercial panels are glass covered and I would hate to face a disaster with glass shards in the cockpit. (I do not want any glass on the boat during a crossing.)

I will continue with my testing. Theoretically, the Schotkty diodes will isolate the broken cells and I will  be able to verify my wiring and test the charge controllers.  And at least, I can test the effectiveness of my weather proofing by blasting the cockpit cover with a pressure washer without worrying  about damaging the cells.

I will construct some test modules of various materials and rigorously test them before building 100+ of them. I make mistakes but generally learn from them.

Max