Mounting Flexible Solar Panels

There's more than enough content for a good book on the topic of solar panel mounting, and more opinions on the subject than there are fish in the sea (approximately), so the following is more of a selection of ideas and points to consider than a final and expert opinion. None of it constitutes a recommendation so, at best, take it as a summary of what I have seen working, and a few pointers on what might cause a problem. We'll assume you are mounting on a caravan, although similar thoughts apply for mounting on boats, boxes, campers etc

• Flexible solar panels, generally a 3-5mm bank of solar cells on some form of flexible backing material, are only partially flexible. They can be carefully fitted with the right adhesives around very gentle curves. They can't be bent round sharp curves and they can't withstand pressure on unsupported areas. If you pick one up by one end to put it on your caravan roof, it'll probably make a gentle cracking sound and be completely useless. This isn't a warranty issue, it's careless handling, so pick them up really carefully and make sure that no areas of the panel are put under any form of bending strain other than VERY gentle curving when they are being adhered to a surface.
• The panel must be firmly glued down. If it can get air under it when you are driving at 90kmh then you can bet that it will bend, flex, wobble and crack. End of panel.
• These panels tend to be dark in colour and get very warm (even very hot) in full sun. Remember that if the panel is producing power and the batteries are full then the power has to go somewhere and the best place is radiated heat from the panel (out to the air and down into your caravan via the roof) and radiated heat through the cables - yes, cables can get VERY hot, especially if they are the wrong size. Speaker cable is not suitable, ever.
• The heating and cooling will cause the panel to expand and contract and, as your caravan roof isn't made of the same material, the coefficient of expansion will be different and the panel is flimsier than the roof so the panel will get pulled and pushed in all directions and will probably crack.
• It is very useful to have ventilation below a panel so that the panel stays cool(er) and so that less heat passes into the roof of the caravan. Ventilation underneath it? Firmly glued down? This sounds like a contradiciton. Read on.
• The best system that I have seen, so far, in terms of longevity and cooling, is to mount each panel on top of a sheet of 3mm aluminium composite sandwich (ie typically thin aluminium sheets with a layer of polyethylene or similar between them). The glue between the panel and the aluminium sandwich would usually be a marine grade adhesive (available in large DIY warehouses). This unit was then be laid on a twin wall polycarbonate roofing product with about an 8mm airgap, and that is then glued to the roof of the caravan, using, in both the latter joints, an adhesive suitable for the polycarbonate (many standard adhesives eat into the poly making it brittle). This seems to weigh around 6kg for a typical 120w panel, or around 50% of the weight of a glass and aluminium rigid panel of the same output. The sandwich construction seems to keep the expansion differences down to a much lower level, and the use of two sandwich separators seems to work better than just using one. The roof inside the van is now cooler below the panels than it is where there is no panel covering (which was not the case when panels were adhered directly to the roof), the panels are getting cooled underneath, so their efficiency is kept at peak, they are more rigid and less susceptible to damage/cracking/flexing/bending. So far so good.

Now all of the above is experimental. Several people with a reasonable scientific background have been involved in the design of this solution, and it seems to be working, but panels are a long term play, so we might not know this year, or next, if this is a good solution. The panel construction is also a bit of a work in progress. The latest panels have a covering called ETFE, which has been used on things like the Beijing Olympic Swimming Centre, and it is reckoned to make the panels more durable. We'll know if it does, with the benefit of hindsight. My guess is that it will, and thus it will also be worth the small extra cost that is needed. Nobody is going to wait 20 years to see if it works before they buy the panels for their caravan. Human nature isn't like that, so our demand for the latest and greatest also makes us all guinea pigs for the testing programme.

I haven't talked about wiring, regulators, fuses, batteries etc. If in doubt, ask someone that does this for a living because they will have a lot more practical experience than someone who has done it once on their own vehicle, however handy they happen to be. If you haven't got a fuse on the batteries, if you are in doubt about the use of diodes to prevent backflow, or if you aren't sure what cable to use, get help. It's too important to risk something failing or, worse, a fire when cables burn through their protective sheath and short out. Does that happen? You bet!

Just a reminder. These are observations and ideas. It's your choice how you install your panels, and my ponderings don't constitute advice!