Earlier quoted context omitted.
Totally out of my depth here, but does cooling the gas down have the added benefit that it'll be heated by the earth whilst stored?
I'm guessing not. Earth's heat is way lower down. Think of a cave: always cold. I think what's going on is they're taking the heat out and storing it more efficiently than just dumping it down the ground, where (1) it would leak away, representing energy loss, and (2) as it leaks away, the air would lose pressure. (It would leak away b/c it's harder to insulate an entire mine, basically.) So, they pull it out ahead o…
(http://www.welshcoalmines.co.uk/forum/read.php?14,46717,4671...)
"...but other parts of the mine was very cold you made sure you had plenty to ware it depended where you worked"
(https://www.quora.com/Are-coal-mines-cold/answer/Keith-Scott...)
"Underground mines maintain a constant temperature, around 55 degrees Fahrenheit."
(https://www.quora.com/Are-coal-mines-cold/answer/Tom-Inghram)
«The temperature on average is in the 50s, but you still sweat an enormous amount when you start laboring.“ - Alan Bates, working in the coal mines of Letcher County, Kentucky.»
(https://www.quora.com/Whats-it-like-working-in-a-coal-mine/a...)
Yes, a 4000m gold mine is hot. I doubt that's where they're storing their compressed air.