Well... heres the interesting part...Audi/Volkswagen sell solar battery "tenders" for their cars,since they are so electrically dependent.If you let one sit for a month(say its your sunny afternoon cruiser)You will find a dead battery waiting for you to charge it back up.A fully loaded Audi A-6 or A-8 will need to go back to the dealer if the battery goes dead,since they have to reset the keep alive memory in 8 to 10 different computers to allow them to start and run not to mention all the other electrical doohickies.I dont know how much the solar things put out but they are rather large,say 10X16 inches from the ones I have seen.Dont know how well they work either but...Thats all I got to say about that.
the problem is.... if you had enough money/status for the audi/vw that was fancy enough to require the solar cell... not a rabbit or bug....wouldn't you park it in the garage, NOT in the sun??? for the actual working of such a devise... a 10x16 pad of cells should be more than more than enough. a properly designed (the are German right??) volatile memory circuit should require almost NO current, only a voltage... realistically, it would probably pull 1mA per hour. so the only problem with the devise is where the cars they are put on are parked. i wouldn't want to wait for it to recharge the entire battery though.