|Clean electricity makers
Fuel cells have also been around for a while. They create electricity from the reaction between oxygen and hydrogen fuel - the only waste product is clean water.
The main problem with fuel cells is size. Nanotechnology is helping to squeeze a large number of reactions into a very small space as well as improving the catalysts they need to work.
And scientists are now looking beyond non-renewable natural gas to water as a possible alternative source of hydrogen fuel.
|Fuel cells create electricity from the reaction between oxygen and hydrogen fuel and the only waste product is clean water.|
Image: VW Press Archive