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this post was submitted on 11 May 2025
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I’m pretty skeptical about this- wouldn’t a 30m sphere be incredibly buoyant when empty? I get its concrete, but it’s displacing huge amounts of water. So you’d need some massive anchoring, maybe that’s not a big deal. Second, I don’t know what depths we’re talking about here, but I feel like the stress from cycling these things daily would be insane- in high pressure salt water no less. I also wonder what the efficiency of this system would be compared to other similar batteries, like pumped hydro storage. It seems to me pumping out water to near vacuum while under crushing outside water pressure would be a significant power hog.
From the article:
Thanks, I missed that on my read through - 1000 feet of water is pretty serious pressure.
The more pressure the more "equivalent head" power discharge potential. Separate "vacuum pump" (instead of bidirectional) could also have several stages to improve efficiency.
Well, yeah. That's the point. It's a battery. Whatever energy you put in to pump the water out, you get some percentage (probably in the 50-70% range) of it back when you let the water back in. The point of these is to store energy from renewables whenever they are providing more power than the grid demands - otherwise the power would be wasted.
Edit: The paper claims 72% efficiency which is pretty good if I understand things correctly
Yeah don't get me wrong- I get it’s a battery. But a battery that’s 5% efficient isn’t great. Now 72? That’s pretty incredible, I’d like to see that in action.
The most pressure it would experience would be the difference in internal vs external pressure. At 1000ft of depth there’s a pressure of 440psi. Assuming the sphere somehow managed a perfect vacuum that’s still well below the 6000psi compressive strength of high strength concrete, hell they would still have more flexural strength. The spheres themselves definitely wouldn’t be the weak link.