How sunny is it where you live? What kind of driving do you do?
Since I drive around town slow a lot I've thought of building a big solar panel over the top of the Prius. One that goes from bumper to bumper and side to side. It would double as a portable shade. It's very sunny here and aerodynamics wouldn't be hurt that much since the town speed limit is 25mph. If I add a boat tail I might be able to make it as big as 2kW if I could angle it towards the sun. That's not enough to satisfy the Prius A/C at full blast, but would be enough once it's cooled the interior down some.
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