Nice idea but mines are full of holes, seriously. We drill into everything, there are slips and fractures, we even have a mildly angery fault line in my mine....
Hydrogen also because the Atoms are so small naturaly slips threw holes other heavier gases can't so the tanks and joints have to rated for it.
Making hydrogen is also wasteful you loose a lot of energy in heat. It might be more feasable and cost effective to use wind farms to supliment our grid electricity.
I remember read about a thermal method of extracting hydrogen form water that used Carbon + Heat from a solar collector to produce C0 + H2 ( endothermic reaction ). But I can't rememeber how they regenerated the carbon to free the oxygen. And I don't know how efficient it was comapred to other solar power systems.
Doug