'Storing solar power underground' - what if it's in a pressurized and compressed form that's easily transported and has a high mass to energy ratio? Brilliant!
I think you're describing methane, the primary component of natural gas. Methane production from electricity is ~60% efficient, according to a 6.3MW plant that Audi and SolarFuel cobuilt in Germany. And then converting methane into electricity or movement will only be ~50% efficient, for total roundtrip efficiency of 30%. That may make sense for electrical storage if the price swings from low to high are 3x or more.
Well I think thebmax is joking about how all fossil fuels are effectively dense, underground storage of solar energy. ;)
(But your information on methane is interesting. I somehow didn't realize it was the biggest component in natural gas; I guess I had assumed it was a more complex hydrocarbon and not considered it further.)
That was what I was getting at ;). I had an old boss who used to call hydrocarbons 'Mother Nature's Battery'. Its almost a miracle when you think of it. Millions of years of solar energy stored in solid, liquid, and gas forms, available for the ingenuity of man to extract and use to power the marvels of the modern world.
For all the hate that hydrocarbons get they are probably the main reason most of us aren't still living a very primitive existence.