Comments by "Bo McGillacutty" (@Mrbfgray) on "Europe’s deepest mine transformed into a GIANT underground battery" video.

  1.  @boballen9095  Friction should be very low, on the order of a couple %, just a cable over a sheave. Losses will be from motor/generators and electrical which might be on the order of 10% round trip. A lot better than pumping water uphill or compressing air in a cavern. So it's down to initial costs and maintenance, mainly capital upfront. Could be viable at first glance, no blatant deal breakers.
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  2. Exactly. A closed in 1990's, "upside down mine" (enter at 8200ft. side of granite mountain, up to 1100 inside) only had to cap the bottom tunnel, back up flowing ground water, plus small high pressure turbine, high psi tunnel plug the main investment. Guessing enough to run a couple dozen homes. (not international news) Maybe 1500 to 2k ft max head at small flow rate--say enough to fill a 1 by 2ft ditch flowing several mph. Plug back pressure on the ground water is 'reclamation' of sorts, possibly crucial for some natural springs or whatever...not crucial to overall landscape, it all ends up as crystal clear cold creek water in a mile anyway. (((high Sierra's E. Central Cali))) IF I had a point--some leftovers have low impact or even positive impact w productive potential.
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