Green energy solutions?

Why don't companies selling solar energy utilization solutions use electrolysis of the water for energy accumulation?

• That should be much cheaper and more "green" than using traditional lithium accumulators. With electrolysis it is possible to save almost unlimited amounts of energy.

• Answer:

  Here are a few technical challenges.  Not necessarily insurmountable, but difficult enough that we don't have cheap enough options yet. Hydrogen doesn't store well.  Most materials will get http://en.wikipedia.org/wiki/Hydrogen_damage when storing the stuff.  You'd have to replace the canisters pretty often.  Steel (the usual material for gas canisters) is subject to http://en.wikipedia.org/wiki/Hydrogen_embrittlement. from http://sirius.mtm.kuleuven.be/Research/corr-o-scope/hcindex2/tutor2.htm Hydrogen also doesn't give you very good energy density, even when compared to batteries, when you consider the conversion efficiency -- the fact that while the hydrogen technically has more energy, you can't come anywhere close to converting 100% of it back to electricity. See:  http://stormthecastles.blogspot.com/2009/02/hydrogen-vs-batteries.html This is considering efficiency all around -- energy in vs hydrogen out, then hydrogen in vs electricity out. Hydrogen looks a little better if you consider only hydrogen in vs electricity out, and a lot better if you consider only the energy available in hydrogen without considering what it takes to generate and store the gas and then convert it back to electricity.