http://www.engadget.com/2009/09/18/ja-solar-and-innovalight-team-up-to-commercialize-silicon-ink/

In the comments, one person comments that he can’t wait to see when the printable solar cell technology can be used for cars.

He really doesn’t understand the energy involved in cars. At work we have 80-watt panels that are just huge. I think you could probably squeeze 8-10 of them on my car, for a total of about 800 watts power generation on a good, sunny day. Assuming that they are 9% efficient and the new solar cells are 18% efficient, that gives you 1.6 kilowatts.

Car engines are generally measured in Horsepower in the US. My car outputs 131 horsepower, which equals around 97 kilowatts (Rounding down to give solar the benefit of the doubt. 1HP is about 745 watts.)

That’s over 50x as much power.

The engine on the ultra-efficient VW car that they’ve been showing off recently http://www.huffingtonpost.com/2009/09/18/vw-l1-hybrid-most-efficie_n_291257.html , has an engine that outputs 39 horsepower. Its backup hybrid electric motor is 14 horsepower. That’s 29 and 10 kw respectively. (Link Dead) Even with the larger surface area of a big car, you couldn’t run the electric motors of a tiny cigar shaped coffin car off solar yet. 

About all you could do with it is let it sit for 8 hours in the parking lot at work in the sun and charge up your batteries for your 30 minute drive home… Which in itself could be a workable thing, but even 100% efficient solar cells are probably never going to drive a car directly and maintain anything near the performance of an underpowered econobox.

A house is a different matter. You probably never exceed 6kw in the average house, and you have a much higher surface area to work with.