[user104658]

Originally Posted by Rudolphthebellendnosedreindeer

How much hydrogen is there available on earth?

I don't know if this is a serious question or not so I'll just answer as though it is;

There's two elements in water, Oxygen and Hydrogen, and they're easy to split (electrolysis - you probably did it at least once a school science class). So ... the answer is "a lot", infinitely more than could ever be used.

One could argue I suppose though, that a true permanently sustainable energy source hasn't been discovered until you can both contain the reaction AND generate the energy required to split hydrogen from water - I suspect, though, that that energy requirement is tiny compared to the fusion process. You can do electrolysis with a 9 volt battery in your kitchen, containing fusion reactions involves extremely high-powered laser technology.