Steve, I love these articles and updates!

Not trying to go all engineer on you or anything (and I haven't read the linked article - it may mention this already), but one efficient way to store energy for peak is to use it to pump water into human-made retention ponds/lakes of hydroelectric facilities. Pump it at night when power is cheap and then release it to the generators at peak.

I didn't think of this, I heard it on a tour of Kerr Reservoir (Buggs Island Lake) years ago and thought it was a cool idea... at least until gravity runs out.

:{> Andy