Your analysis is way too conservative. An analysis by Tesla Motors some time ago calculated that if you drive the Roadster an average of 35 miles a day, you need about 105ft^2 of solar panels to produce all the electricity for it, assuming 18%-efficient solar panels. [1]
The Tesla Roadster has an area, when viewed from the top, of 72ft^2. [2] That means if you were able to cover it with solar panels that were 27% efficient, you could power it just from the power it produced.
As far as your last point, I agree: I'd rather put the solar panels on the garage roof, where I can somewhat control how much sunlight it gathers, than on the car.
Good numbers in the Tesla Roadster wikipedia introduction.
wikipedia: The tesla roadster use 490 kiljoules per kilometer.
compute: Our 30 megajoules above will take us 38 miles.
Of course I'm still using mythical 100% efficient solar cells on a biggish flat roof and all sunny days, and Tesla used mythical shape hugging solar cells on all of their exposed surfaces.
I still think the best solution for a solar powered car is to place your solar cells the south western deserts near LA and pull what power you need from the grid. That way you get a lot more power delivered from your cells.
The Tesla Roadster has an area, when viewed from the top, of 72ft^2. [2] That means if you were able to cover it with solar panels that were 27% efficient, you could power it just from the power it produced.
As far as your last point, I agree: I'd rather put the solar panels on the garage roof, where I can somewhat control how much sunlight it gathers, than on the car.
1. http://www.teslamotors.com/blog/electric-cars-and-photovolta...
2. http://www.netcarshow.com/tesla/2008-roadster/