Constant Pressure Compressed Air Storage

Reader Paul Blais sends us an interesting idea:

“I’ve been following your website for years and I like it very much. I’ve been reading your article from 2018 about off-grid compressed air energy storage and I’ve been thinking about a possible solution regarding the varying pressure problem which you mention about small scale, low pressure vessels.

What about using a constant pressure reservoir? My idea is to use a long airtight bag stored in a trench and covered with sand, that would inflate and deflate pushing the sand up and down. The height of the sand column would determine the inside pressure of the bag, which would remain constant across it’s whole inflation range. The sand would also act as a thermal mass, taking and restoring heat to the air.

I’ve read that similar storage ideas exist [1] but involve putting the bags deep underwater, which is not practical for off-grid purposes. Unlike a deep-water reservoir, a bag put under sand would not try to float, so there would be no need for complex anchors at the bottom.”