I went to the PHEV Symposium in Washington we mentioned yesterday. I talked to Bob Bruninga about his solar powered Prius. Bob's pitch is solar power is perfect for electric cars and hybrids because that's where you get the payback. Solar power for your house makes less sense says Bob because your house has easy access to cheaper electricity. You can watch Bob talk about the logic of using solar power on electric cars below the fold.
I asked Bob how much of an improvement he got in the electric-only range of the solar Prius. Bob said the batteries are doubled but he gets more than a double in electric-only range. How? You would not know this unless you looked at your Prius battery indicator constantly but: The Prius battery never goes below about 60 percent charge. At some point around 80 percent charge, the Prius software starts to do things to make sure the battery never goes dead.
So if you increase the capacity of the battery, you could get larger than expected improvements in electric-only range because the point at which the Prius pretends the battery is dead is much higher. Logically, Bob should get four miles on electric power only but Bob says he can get 6. Before you run off to hack your Prius software to increase your mileage and save a lot of money on gas, remember that Toyota has set the software to increase the life of the battery.