Warm air takes up more space. If you cool it before pumping it into the ground you will not waste time/energy. If you pump warm air down it will lose heat into the ground and shrink and you would lose capacity - pumping that last x% the tanks will be fuller until they cool down.

You warm up the air on the way out to expand it and you get more air to spin the turbine. More bang for your buck.

I believe is the thinking.

> Warm air takes up more space. If you cool it before pumping it into the ground you will not waste time/energy.

The real masterstroke here might then be to put this system in an area with large diurnal temp changes like the desert, then charge this system with cool night air, and then reheat it and generate electricity during the day with warm daytime air. Heat pumps could be used to nudge the temp on either end into it's optimal range.

It then becomes a solar thermal hybrid compressed air energy storage.

This could pair well with renewables that are more available at night like onshore wind.

Many years ago I was doing shrooms in the Nevada desert -- and the epiphany I had was that the desert, and the caves all around and throughout the deserts served as "the lungs of the earth" -- they would heat and cool and would suck air in and out based on this...

I was 17 at the time, and I have been into some of the most incredible caves - the best in Ganung Mulu National Park in Borneo Malaysia...

As the rains flowed out and carried the guano from 5 million bats into the forest to fertilize it...

And then I realized it wasnt just the desert - it was the caves...

Caves (giant ones) are really important for planet health.

Air pressure is strongly correlated to temperature. Cooling the air after compression reduces pumping effort during storage, reheating it increases turbine head pressure during generation.

In other words: gas compression storage suffers from temperature losses. The compressed gas is hot, the heat dissipates from storage and that energy won't be coming back.

But if you extract that heat during compression you can put in a separate storage, one that is much easier to insulate than the compression tanks, and "mix it back in" during recompression, avoiding a large part of those losses.

> In other words: gas compression storage suffers from temperature losses.

Yes, and you can also compress air further when it's cooled (this is why there is an intercooler on turbocharged cars, as an example), this means your density per volume of storage is higher at a given pressure.

The reality though is that this is likely less efficient than many other storage mechanisms. Additionally, this may require some sort of additional energy input for reheating if the heat storage is not capable of holding long enough to fully reheat the air on release to get the highest turbine efficiency.