If you want flexible solar cells take a look here:
EV-Power | Solar Panel GWL/Sunny Flexible Mono 60 Wp (MPPT 18V)
That would do
A liter contains about 9 kWh of raw power, but the engine typically wastes more than 75% in heat. So a liter yields 2 kWh, tops. Need to convert that to electricity, another loss. Electric power from the engine costs almost an euro per kWh in Europe.
You may actually regain the investment by feeding the battery with solar power... but I think it is best to feed a piggyback battery, like I described. And you can charge that from the mains before you leave in the morning, so you use the battery capacity to the max.
(I want to do a high-voltage parallel pack to boost the hybrid pack, but the 12V setup may be a safer testing ground)
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2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut.
lifetime FE over 0.2 Gigameter or 0.13 Megamile.
For confirmation go to people just like you.
For education go to people unlike yourself.