Storing it as heat is several orders of magnitude easier and cheaper than storing it in a battery. Beyond some very esoteric/fragile/expensive vehicles like a Sunraycer, putting solar on a vehicle does a few things for you: 1) Increases drag 2) Increases weight 3) Tempts you to park it in the sun. Parking vehicle in the sun = hotter vehicle, shorter battery life 4) Gets you a little power. 20-30 watts for a scooter, 200-500 watts for a vehicle. From experiments a lot of people have done, putting solar on a mainstream vehicle reduces its range overall, and makes it less effective as a vehicle. (Not to say you can't try it but I suspect you will end up learning the same thing.) All that sounds great, but again, you don't need a solar heating system if the sun is already coming in the window and hitting the wall. You've got one already. A friend of mine did that and can grow tomatoes year-round now. It's San Diego, granted, and we only have about a dozen freezes a year, but she still sees a 20-30F gain at night. Why? In most places, go down a few feet and the soil never freezes. It's a good way to "back up" solar heat if you run into a cloudy spell.