Hello, I had good luck getting set straight on a seemingly good but inherently flawed idea a few months ago on this site. I have another seemingly (to me) good idea and am hoping for helpful input.
The idea is essentially to sink compressed air in deep water, release it at depth and use the energy of its bouyancy, the trip back up, to make electricity. The catch is how to overcome the energy cost of compressing the air in the first place:
Imagine-
-a floating platform over deep water
-a very long length of bicycle style chain (how long it needs to be is an essential question)
-a generator unit on top of the platform
-the chain draped over the platform, threaded through alternator and free cogs on either side of platform.
-equally-weighted underwater cages attached to either end of the chain. Cages have large bags on top, open at the bottom to catch bubbles released from below by compressed air tanks. Cages also could/should have lots of extra weight, (rubble or something).
-alternator plus batteries runs compressor and tank exchange system at top.
Start:
-cage 1 is down(chain fully out below platform on cage 1 side), cage 2 is up. Both have empty bags.
-Tank in cage 1 releases air to fill bag. Cage 1 begins to rise while cage 2 descends, turning generator.
-When cage 1 nears surface platform, valve on bag opens and releases air.
-At the same time, valve on tank in cage 2 opens to release air, filling bag on cage 2.
-When tanks near empty, they are replaced with full ones at the top by a robotic arm/some kind of shuttling device. Empty tanks are refilled by compressor.
The crux: (Assuming the basic concept doesn't have anything major wrong with it.)
-How long of an ascent/descent does it take to overcome the energy cost of compressing the air. If it is too long, then the air at depth will not be buoyant enough to lift the lowered cage. I imagine that would have to be very deep indeed, so hope that it will work, at least in principle. Great depth could also make it unfeasible because of distance from points of use. It would be fantastic, although unlikely, if it worked at a small enough depth to be feasibly used in large man-made tanks/deep pits/lakes.
Right, there's my idea, thanks for reading and thinking about it.