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A voltage is potential energy. A transformer transforms voltage yes but is also a storage of potential energy via a magnetic field.
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No, that's not even wrong. But there's very little waste in modern power grids--excess capacity is simply shut down/taken offline, so there's little point in blowing millions of dollars on mining gear which will only mine a fraction of the time (as it becomes obsolete). Here's a pic:

Well, that's what I meant. They know the current draw at peak and non peak times and would either slow their fuel feed or bring generators offline.
I think you'd be hard pressed to find a power company storing energy in batteries.