... 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) ...

i will try a rough calculations : suppose we can have concrete at $100 per ton, then it's a minimum investment of $40,000. Also suppose electricity is stored with a large added value of 10 cents per kilowatt hour, so, for every cycle a rough gain of $40. By these numbers, 1,000 cycles would pay for the concrete ... so, it may look good considering they plan a life of about 50 years for such devices.
On the other hand if competitive battery storage cost only one cents per kilowatt hour (temporary in and out storage) and if concrete and fabrication goes up 10 times to $1,000 per ton then it is not economically viable anymore.

A good calculation of profitability would need to take into account the less than 100% energy efficiency of batteries cycling and of hydraulic energy cycling, ... and so many more parameters which have to be studied.

[–] Libra@lemmy.ml 7 points 2 days ago (2 children)

They describe these as giant concrete spheres, but there are (obviously) pumps and turbines involved too, and that those are aimed at a 20-year partial part-replacement lifespan. There's no indication as to how much these pumps/turbines will cost but I'm gonna guess probably more than the cost of the concrete since it's relatively cheap in comparison, and that's before you consider that the major wearing components (which is to say, the expensive stuff) will have to be replaced twice within the intended lifespan. And that's not accounting for things that break and need to be replaced, inside of a giant concrete sphere on the bottom of the ocean where maintenance will be absurdly expensive. Needless to say I'm pretty skeptical of the economic viability of this project. I'd be happy to be proven wrong, but I'm not holding my breath.

[–] A_A@lemmy.world 2 points 2 days ago (1 children)

i agree with all of this except, you know, when they will have to do maintenance ... i guess they will be (they would be) more simply hauling the whole thing out to work at the surface of the sea ... in this scenario the mechanical components would be at the top of the sphere and out of the water.

[–] Libra@lemmy.ml 4 points 2 days ago (6 children)

Yeah, so instead of sending down divers with equipment you're hauling hundreds of tons of concrete out of the sea, which means aside from a ship and crew which you'd need anyway you're still going to need specialized equipment (some big honkin' chains and winches at a minimum) and tools and such, and that stuff isn't cheap either. Also they're aiming at a 20 year partial replacement cycle for parts that are going to be submerged in or otherwise exposed to sea water which is notoriously corrosive, some of which will be at fairly high pressure (otherwise the turbines will be less efficient), that seems optimistic at best, even if nothing breaks before the scheduled replacement time, and you certainly can't count on that.

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[–] tiddy@sh.itjust.works 0 points 2 days ago (1 children)

I'd assume they'd put these pretty close to the surface, lowers the water pressure and makes it more accessible

[–] Libra@lemmy.ml 4 points 2 days ago

If you read the article it includes this line:

The idea is relatively simple: hollow concrete spheres are installed at a depth of several hundred metres.

The pressure is needed to drive the turbine, cause just gently-flowing water isn't going to cut it.

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[–] JennyLaFae@lemmy.blahaj.zone 7 points 2 days ago (1 children)

They need to pair this with Tidal power

https://en.m.wikipedia.org/wiki/Tidal_power

[–] AA5B@lemmy.world 3 points 2 days ago (1 children)

Tidal power probably needs shallow water while these would be great in deep water

[–] JennyLaFae@lemmy.blahaj.zone 4 points 2 days ago

https://en.m.wikipedia.org/wiki/Wave_power

They can do wave power deep sea buoys then :)

[–] MonkderVierte@lemmy.ml 5 points 2 days ago* (last edited 2 days ago) (1 children)

Why not submerge a tank with a hole at the bottom and blow air in the tank via a hose to store energy?

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