I know those tiny compressed air cars have fairly small tanks, but they operate at very high pressure.  Much easier to build a small strong tank than a huge one.

People are looking at large scale battery systems, giant flywheels etc.  but the old reliable is pumping water uphill for later use.  

There are also potentials for constructing versions of hydro facilities ...

Could use wind to make hydrogen (already occurring in limited cases) ... flywheel storage ... etc ...

Lots of potential storage options ... challenge is to move from the potential to cost-effective large-scale implementation.

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