Originally Posted by thommy

it is quite hard to get a huge part of the energy back to use that you need to compress it.
but it makes sense to use free clean energy for that (like sun energy) that does not have really costs or emissions.

there is a way to get more out of it and I am thinking already 10 years on a theory that I could never approve yet because I am not a really tech-guy and handworker.

once I found one who can build my idea we will see if it will work.
but compressed air is in fact the cheapest thing to keep. it will not need any battery
with a limited lifetime and compression is still compression if you keep it for 50 years
somewhere. aluminium tanks have a near to unlimited lifetime.