How much energy does it take to separate the oxygen and hydrogen, vs how much is produces when it it burned?

But the idea is a good one: The big problem with hydrogen is the transports and storage, which would be solved by a fuel-cell like sealed system ( or one with only water as the input/output)

But why is this method so great? What is wrong with electrolysis? THat seems to work with just two wires and a power source.