[paulgato]

Most of the time the vehicle is not in motion, so most of the charging will happen while parked up. My guess is that heat from the sun while parked is likely to heat the panels more than heat from the engine while driving, as when driving you have the wind blowing over them.

I've looked into these flexible panels in the past and always decided they are good but too expensive for any reasonable output. Car body panels are compound curves, so I would also want to know whether they can bend in two planes at once. The fact that they are (some of them) long and thin does mean that rows of them could deal with compound curves OK.

One problem with mounting potentially expensive kit on your roof is that someone might come along and try to steal it. Flexible panels could be bonded down, but there still may be a tempatation to try, and when thieves are frustrated they can get aggressive (and break things in revenge for someone making their job harder than they thought it was going to be.) That's one reason I thought that actually building the cells into the body panel - into the paint layer in effect - might be the best way to go, as it would then be 100% obvious that they couldn't be removed.

A bonnet, in that case, might be preferable, as one could get a spare bonnet (hood) panel from a breakers' yard and build the solar panel into it indoors, and then when it's complete, swap it over with the original bonnet panel. That's a bit more difficult to achieve on a roof panel, although one could perhaps make a thin (3mm?) fibreglass 'mould' of the roof shape, build the cells onto the 'mould' indoors and then attach the roof-shaped solar panel when it's done. All the electronics and so on can be mounted just below the roof, out of the windstream. I think solar cells can bend a tiny bit (even a cracker will bend a bit) but even if they had to be mounted dead flat, one could sand multiple flat areas on a slightly curved fibreglass panel to mount the individual cells onto. Water-clear resin over the top, smoothed and polished.

Raw solar cells can be arranged on a gentle compound curve quite easily, covering the area optimally, therefore maximising wattage on any given panel area. The cells themselves are very cheap.