Who would have thought it would work like that?

These guys have been starting their cars using Ultracapacitors.

It seems to work well and some of them are combining a small 17Ah battery with the Ultracapacitors to extend the time a car can sit in the driveway and so you can still run things like the radio for a while.

Adding a small 5 to 15W solar panel to the mix would be good, you could throw it in the back under the back window if your car allows that and it would keep the whole thing charged up to voltage every day even on cloudy days.

All the solar panel would have to do is bring the voltage up on the caps and overcome any small power drain the car might have such as a clock or alarm.

If you changed out the interior "dome light" to LED that would help too.

They are around $20+ each and you need 6 of them so it gets a little pricey but should last about 10 years maybe more so it might be worth it.

"High performance in all weather conditions from -40° to +65° C"  ---  "Durable and reliable with over a million cycles"

http://www.youtube.com/watch?v=GPJao1xLe7w
http://www.youtube.com/watch?v=GLVFqRa9tqY
http://www.youtube.com/watch?v=XCxS4SotOTo