[mikeash]

There just isn't enough surface area. A Model S has a roof area of around 9m^2. The sun provides about 1000W/m^2 on a clear day at high noon when directly overhead, so with 100% efficient solar cells on a perfect day, you'd get around 9kW of electricity. A Model S goes about 4 miles per kWh when it's doing well, so in this ideal situation you'd top out at around 36MPH. In the real world, the sun isn't directly overhead, and real solar cells have more like 20% efficiency, so cut that number down by a factor of ten or more.

The best way to build a solar-powered car would be to have a battery-powered car that gets recharged from solar energy. Basically, a Model S and a home solar generating system.

[baddox]

That illustrates the advantage of electric cars, even if the electricity is currently generated by fossil fuels.

[ctdonath]

I recently ballparked the cost of a home solar charger for my Leaf EV. Came out around half the price of the car ... not cheap, but feasible for someone serious about it.

I do have a propane-powered electrical generator for emergency/backup home power. Some day I'll try charging the Leaf with it.

[mikeash]

Have you ever worked out your approximate cost per kWh for the generator? I imagine it's painful compared to what you get from the power company, but I'd be curious to know just how painful.

[ctdonath]

About $1.23/kWh.

Ad verbiage for the allegedly 3250 running watts generator states "engine run time of 10 hours at 50% on a common 20Lb (gas grill type) cylinder". So that's under $2 for 1.625kWh, which is roughly the power draw for recharging the Nissan Leaf in question, which takes 20 hours - costing upwards of $40. More to your point, that's about $1.23/kWh. Not cheap, but a 10x markup is appropriate and acceptable for emergency needs.

[mikeash]

Thanks. That sounds pretty reasonable for a generator, considering.

[SupremumLimit]

You probably mean 0.9m^2. 9m^2 is a decent size bedroom.

[mikeash]

I shouldn't have said "roof," I meant the whole vertical-facing area of the car.