Forget old-school remote controlled cars that drain your batteries -- alternate energy cars teach kids about the fuel sources of the future while ensuring you'll never need to buy a battery again. The simplest versions of these toys contain magnesium metal sheets. Sprinkle a few drops of saltwater into the car and it will run for hours without assistance. More advanced fuel cell cars, like the i-H2GO, come with all the pieces kids need to construct a hydrogen-powered car, then allow kids to connect the car to a smartphone, which acts as a wireless controller. Volta racers use built-in flexible sheets of solar panels to operate even in low levels of light. Like the i-H2GO, Volta racers comes in pieces, requiring kids to use their engineering skills to assemble the car before it's time to play.