Glencore sank a shaft 8,530 feet under Ontario from the bottom of a mine it closed in 2009, and put five lithium-ion locomotives and 23 battery machines down there so it would not have to pump cooled air a mile and a half to keep the crews working //

So why do batteries win underground while they’re still fighting for every point of market share up here? Run a diesel engine in a closed parking garage and you’ll have your answer inside a minute. A mine is that garage stretched over miles of tunnel, with warm rock on every side. Every diesel machine down there’s a heater with an exhaust pipe, and the mine has to push enough fresh air past it to keep people alive and cool enough to work. //

Push air down a shaft and it compresses, and compressed air heats up, at roughly 29 degrees Fahrenheit for every mile of depth (10 degrees Celsius per kilometer) in engineering studies of deep mines in Northern Ontario. At Onaping’s depth, the intake air shows up dozens of degrees warmer than it left the surface, before the rock or a single machine adds anything.