Barometric energy generator

This is just a crazy concept for renewable energy that i came across, I'm not saying that it will work, I'm saying it could work.

Basically, this is a scheme of sorts to generate energy by abusing the pressure differences on this planet. What we need is a decently deep body of water and a gas medium preferably denser than water. A flexible "bag" of gas is dropped from a factory down a pipeline into the depths, where the gas becomes pressurized. A simple mechanism at the bottom of the lake transfers the gas from the flexible container to a rigid one. The rigid container is large and takes several bags to fill, once it becomes filled to capacity with pressurized air, it is brought up to a surface generation plant where the pressurized gas is either packaged and sold or used to power gas turbines for power.