Ee4fire wrote..

Long term energy storage of electricity is the use of batteries.

That is only really feasible for very small-scale storage, and, from what I understand, they are looking at energy, not electricity, storage

What is generally being considered/proposed (already used in numerous smaller-scale installations) is the use of pumps to lift water up to a reservoir during periods of excess power availability and then to let the falling water drive turbines to generate electricity at night or for other periods of lower power production during cloudy and/or windless weather.

In theory, the principle is sound, but there are hellacious energy losses involved, that would require huge overbuilding of wind and/or solar farms to provide the excess power for the pumping of adequate amounts of water to accommodate the sunless/windless periods. I haven't seen the numbers they are using to justify the proposals, but, at a gut level, I believe that the cost/effort to actually make that work on a large (i.e., regional or state-wide) scale would be prohibitive.

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