It'd take far too many solar cells to power a car's air conditioner. Remember, 1 horsepower = 746 watts of electricity. That's a physical constant and not a matter for debate. In the real world where friction and mechanical inefficiency rules, a good rule of thumb is that it'll take closer to a kilowatt of electricity to produce 1 horsepower.

Take note some time how much your car's RPM and gas mileage drops when you turn on the AC. It takes a substancial amount of power to spin an AC compressor. Solar arrays big enough to power the AC compressor would have too much aerodynamic drag and weight. You'd end up wasting a lot more gas with that approach than you'd ever save, to say nothing about the expense.

The Honda DualNote is a cool car. It combines high performance, 400 HP, and still gets 42 MPG. Unfortunately, the one thing not discussed in the article is price. Something tells me this won't be something average people could afford even if it were put into production.