This converts electricity to hydrogen. There are very few situations where that is desirable - electricity is almost always more useful.

So this has value only in that you can store the hydrogen or use it somehow. You can also store electricity, so they question boils down to: Which is easier to store: Hydrogen or Electricity?

Water simply never enters into the question.

Storing hydrogen is hard enough that it's pointless to even talk about. Storing electricity can only be done in small quantities.

That's why I said methane: The best thing to do is grab some carbon and make methane with your hydrogen, methane you can store.

This is not really a solution for anything though, round trip efficiency of solar cell->electricity->hydrogen->methane->electricity would be quite low.

Much better is heat+coal+water = methane (you can thermalize water with heat). You can use a solar collector or nuclear power.