Forget Better Batteries, Nothing That Exists Or is in Development Can Store Energy as Well, And as Cheaply, as Compressed Air (theconversation.com)

An anonymous reader shares a report: The concept seems simple: you just suck in some air from the atmosphere, compress it using electrically-driven compressors and store the energy in the form of pressurised air. When you need that energy you just let the air out and pass it through a machine that takes the energy from the air and turns an electrical generator. Compressed air energy storage (or CAES), to give it its full name, can involve storing air in steel tanks or in much less expensive containments deep underwater. In some cases, high pressure air can be stored in caverns deep underground, either excavated directly out of hard rock or formed in large salt deposits by so-called "solution mining", where water is pumped in and salty water comes out. Such salt caverns are often used to store natural gas. Compressed air could easily deliver the required scale of storage, but it remains grossly undervalued by policymakers, funding bodies and the energy industry itself. This has stunted the development of the technology and means it is likely that much more expensive and less effective solutions will instead be adopted.

Comments

I was curious

[Jfetjunky]

I was curious about the energy density of this proposed solution. I dug in the comments and found a reply from the author of the study. Kinda interesting.

There is no “minimum storage pressure” but the economics are poor for anything lower than 50bar. For CAES with tanks, the economics push you towards pressures of 200 - 250 bar. In caverns, the pressure you can use depends on the cavern depth. 120bar is not unusual. For a cavern with 120bar storage pressure that was allowed to swing down to (say) 70bar when “discharged”, you would be storing ~23MJ in each cubic meter of cavern. Thus for 1GWh (3.6 million MJ), you would need 156,000 cubic metres of cavern. That is actually a relatively small salt cavern! If it was a sphere, it would have radius of 33.4m. Surprising as it may seem, most salt caverns in existence are bigger than that!

Re:Is it air tight

[lgw]

You're talking about a liquid under pressure. Pressurize liquids store very little energy, because they are largely uncompressable.

You might find it informative to read about the biggest presses. The 1500 HP motors don't make nearly enough power to operate the press directly: they accumulate the energy in pressure accumulator bottles until there's enough in storage to operate the press once. it's a "hydro-pneumatic" system.

It's the only example I can think of where energy is routinely stored and discharged at thousands of PSI, and safely. Scuba tanks store air at a reasonable fraction of that pressure, but they aren't used for power (so limited fill/discharge rate) and they do blow up from time to time.