I believe two things can be easily solar and light powered. First off your cell phone could easily have sensors on it to help power it in the same vain as a calculator does. It could also be plugged in when needed by mainly run off solar power, it already has sensors on the iPhone to make the screen darker or brighter according to how bright it is in the area. A car could also be powered by sun-powered, battery powered, and gas powered. Use the first two sources first and only use gas when needed. Thus cuts down on the amount of times you have to fill up and pollute the environment.