Part of the show Naked Science Q & A and the World of Chemistry
Ken in Brenwood asked:
Can we crack water into it's components of oxygen and hydrogen and then burn the hydrogen using the oxygen to create a process to turn water into power?
Unfortunately it takes the same energy or more to split the water into hydrogen and oxygen than you could possibly get by burning the two back together again. So it will just cost you energy and not get you anywhere. There's no such thing as a free lunch in the world of physics! However, there are some fuel cells that use the energy from light to split the hydrogen and oxygen in water, and you can then use that to get power.