Yeah, compressed air is a very viable and promising solution. It does have efficiency trade-offs as you mention though. And typical compressed air designs still

Yeah, compressed air is a very viable and promising solution. It does have efficiency trade-offs as you mention though. And typical compressed air designs still use fossil fuels in the compression process. There are some new designs I've seen that get around using fossil fuels. One of the most prominent new startups out there exploring advanced compressed air is hydrostor. Note that they also dig underground :) https://www.hydrostor.ca/technology/ https://www.hydrostor.ca/technology/