Okay, but now you just have some steam and heat floating around. It's gonna dissipate pretty quickly, not a great way to store power for the medium-long term.

Okay, but now you just have some steam and heat floating around. It's gonna dissipate pretty quickly, not a great way to store power for the medium-long term. Hydrogen separated from Oxygen is where the useful potential energy difference is. The idea behind hydrogen fuel cell batteries is that you spend your cheap clean renewable energy to split H2O slowly when energy is available, and burn the hydrogen when you need bursts of power. If you burn the hydrogen right away, you're just un-doing the water-splitting reaction and you won't have anything to use for power when the cheap clean renewable energy is not available, like during the night for solar power. I think that the usual way to get energy back out of the hydrogen is just to burn it and let the hot pressurized gas power a steam turbine, but don't quote me on that. Or try it at home; scalding and flash burns are good things to avoid.