> To do this, you need a lot of energy, it is essentially charging a battery. If this was really feasible wouldn't we be using solar panels to separate water in

> To do this, you need a lot of energy, it is essentially charging a battery. If this was really feasible wouldn't we be using solar panels to separate water into hydrogen on Earth? We do. If you buy commercial hydrogen, it was probably extracted by water by that process (although other processes are possible), using energy from the grid of which some percent is solar. So what exactly is your point anyway? The needs in space are far different than on Earth. Solar energy is abundant and available 24/7, but stored energy is needed by rocket engines in large amounts and all at once.