How viable is hydrogen as an energy storage medium? It would be extremely easy to split water into hydrogen and oxygen . It also has high energy content so relatively a large amount of energy can be stored with a small amount of hydrogen. How efficient would be hydrogen for storing energy?
Hydrogen has some issues for energy storage. The biggest one is density. It isn't very dense compared to hydrocarbon fuels and compressing it costs you money. So you either have a huge tank or compressors that use up a lot of the energy your system is harvesting. It also embrittles a lot of metals so you have pipes and tanks breaking after a while. It also leaks really easily (small molecules) so pipe fitup has to be really good.
How bad is the density problem? At 700 atmospheres, hydrogen only has 1/3 the energy density of gasoline. And getting stuff compressed to that pressure is going to be costly.