> The efficiency over an entire storage cycle is slightly lower than that of a conventional pumped storage power plant, at 75 to 80 percent. This calculation is based on a storage park with six spheres, a total power capacity of 30 megawatts, and a capacity of 120 megawatt-hours, with 520 storage cycles per year. StEnSea spherical storage is particularly suitable for two business models: for arbitrage, i.e., buying electricity at low and selling at high market prices, and for providing ancillary services to stabilize power grids.

So it's workable, it's 10 percentage points or so less efficient than land based pumped hydro, it works optimally at around 600m-800m of water depth. It's main function is arbitrage and time shifting for stability of service. Which means, coupled to wind sources, or solar, where for some reason land batteries or land pumped hydro in dams is not feasible.

Land based pumped hydro is somewhat invasive. It has big upfront costs. This rig may be more expensive per unit energy but is less intrusive and has incremental deployment capabilities.

Nothing under water is easy. Maintenance of any pumping component underwater is a burden. And, the life down there is also probably adversely affected although this may be less than the alternatives.

I was disappointed manufactured giant sea-vent tubes with wind turbines up top didn't happen at scale. Felt mechanistically much less burdensome, exploits the tidal energy we have. The kind of thing you can do anywhere with consistent tide patterns and a cliff face. Maybe this system can couple with it.