[chrismeller]

I was actually wondering why the whole thing needed the complexity of being underwater and felt like I was just an idiot, so thanks.

From the article it sounds like the only reason to deal with the hassle of the water is so you can put these somewhere no one ever sees?

[credit_guy]

I think when you lift a cubic meter of water by one meter at a depth of 500 meters, it is like lifting an entire column of 500 cubic meters. It's a huge multiplier effect.

[LorenPechtel]

They specifically talk about putting them deep. There's only one thing to be gained by going deep: pressure.

It sounds like this is simply compressed air storage, except using seawater to contain it so you don't need a pressure vessel.

[stubish]

There is no air involved. They are pumping water out, creating a vacuum. Water rushing back in generates power. No need to compress air or have a hose to the surface.

[yummypaint]

Making a big hollow object that can withstand crushing is much cheaper than something that can contain high pressure. Achieving the same pressure difference on the surface wouldn't be possible with concrete alone.