20-year maintenance intervals for something pumping seawater? Impressive. Way better than a chemical battery.

This seems like a workable idea but just electric cranes lifting and lowering weights seems like a simpler approach and I think that has already been proposed.

My guess is there are many ways to balance the grid and the biggest is the utilities not wanting pay.

One thing to consider is the America power grid is in poor shape already and utilities are aiming to avoid modernizing. IE, adding storage to the grid would involve the double of cost of the actual balance equipment and the fixing the old equipment that needs fixing anyway. And utilities are looking avoid both cost.

> In 2026, a sphere nine metres in diameter and weighing 400 tonnes will be submerged off the coast of California at a depth of 500 to 600 metres. It will have a storage capacity of 0.4 megawatt hours (400 kWh), enough energy to power an average household for several weeks.

What is this going to cost? From a quick search, Tesla Megapacks are now about $250/KWh. With battery costs still falling steadily, those might be considerably cheaper by the time the first 9m sphere hits the water.

And with all the recent anchor-dragging incidents, how many countries would be eager to have their energy storage located far off-shore?

Is there any reason to need a concrete sphere? Couldn't a robust, durable flexible bag do the trick?

My hydroflask, when compressed, will push water out :)

I'm curious why pumping the water out, creating a vacuum for water to rush in, is better than pumping air in for water to displace.

I had assumed it would be cheaper to have large underwater balloon connected by a hose to a pontoon, and use air. Rather than install and maintain at depth the pumps and a giant concrete sphere able to withstand that sort of pressure.

Have I got the economics wrong? Or is there an efficiency gain from dealing with a liquid rather than compressible gas?