Sounds interesting, but considering how thick hydroelectric dams need to be to hold back a mere lake, how thick are these spheres going to be to hold back an entire ocean?
this post was submitted on 11 May 2025
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High social acceptability: Installed far from inhabited areas, these facilities arouse less opposition.
Actually, being very close to inhabited areas, but 0 impact, including nonsensical nuissance arguments, means short power transmission. It's also very easy to pair with offshore wind.
Wow, someone invented upside down pumped storage.
I would like to know what is the % of loss when storing power as any energy conversion is not lossless.
Regular pumped hydro has an overall efficiency of about 80%. I would guess these sphere things would be similar, assuming you can put them near a high-voltage line, since the underlying technology (pump and turbine) is the same.
Cheap storage is more important than conversion ratio. Enough renewables leads to periods of negative prices without matching storage capacity. Storage can mean 1-2c/kwh charging costs, and even 50% efficiency makes discharged power 2-4c/kwh.
if 0.5m thick sphere, 30m diameter is 1413 m^3 of concrete. $300k to $400k in materials. Stores 150mwh power. About $2-$3/kwh
Each sphere has an estimated lifespan of between 50 and 60 years, with partial replacement of components every 20 years or so.
The concept is fascinating, but what I'm most curious about is how they achieve that longevity in seawater. Benthic life really loves to settle and build on hard surfaces.
Every time I see these “We’ll do X in/around the ocean” projects I think, “These people have not spent a lot of time near the ocean.”
There are 2000 year old Roman concrete piers that are still just hanging out in sea water. So it's possible if you find the right mix.
The concrete isn’t the problem. Like mentioned above, the sealife growth is. Also, metal and moving mechanicals are savaged by seawater (and the sealife growth). Keeping things working on the surface of the water is difficult and expensive. Water pressure makes that even worse. Maintenance requires divers which are likewise very expensive.
I think the sea has a huge potential of energy production that is totally untapped because of that.
There are tons of ways to produce energy with sea water but as soon as you put any moving parts in water it gets corroded and covered with benthic life (I've learned a word today). Every project of ocean energy production dies because of that.
Would it particularly affect the performance if the sphere ends up covered in barnacles or coral? It's what's inside that matters (it's just a big hollow tank).
If you fill and empty with raw seawater on the regular then you will have plenty of opportunity for growth on the inside and a constant supply of new water with fresh nutrients meaning everything is going to want to grow into the water inlet and clog it.
Maybe they will sink a giant bladder of sterile water together with the hollow sphere, and then figure out a way to make the bladder not fail for 20 years?
I envision issues with turbulent flow over surfaces that work best with laminar flow. It sounds like a turbine or pump system is used for these spheres.
Benthic Life needs to be band/album/movie title.
Unfortunately, you can't see BENTHIC live.
They don't have a tour planned.
https://lifeforcerecords.com/archives/artists/benthic/
Of course they’re not touring. They’re sessile.
Narrated by Sir Attenborough.
Decoy spheres.
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.
I don’t know what depths we’re talking about here,
From the article:
The idea is relatively simple: hollow concrete spheres are installed at a depth of several hundred metres.
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Interesting concept, but not very scalable. It's basically a reversed dam - when it's full, there's 0m head of water. Then with excess energy, you lower the level inside, storing the energy in the water outside. E.g -2m head. Water then flows in to equalise head, and doing so, regenerates electricity. Adding depth to supercharge pressure differentials is a good idea, although I wonder how they limit the flow rate, or otherwise prevent cavitation shocks each cycle.
Could be useful as a private industrial battery, but a dam would still be better on an infrastructural level.
Dams do have their own significant challenges with habitat destruction and displacing people and silt buildup
Dams have issues around silt buildup over time and to the best of my understanding the US is already dammed to the max (within reason).
I'm keen to see how it pans out. Seems like a very interesting concept.
damned to the max
Silt did not magically disappear because your dam is spherical, and there is a lot of it on the sea floor. They need to install some kind of filtering system anyway.
Also, the lifetime of a sphere is estimated to be 60 years, while the traditional dam is engineered for 100+ years of service.
The main advantage is that the sea floor is unused and unregulated like the dry land , but then you could as well build an actual scuba diving underwater base with a hydro dam instead of a sphere, it will also be easier to clean and repair, but I guess that would be too much evil moustache twirling to get funded.
I don't see silt being as big of a problem here, if the intake is located at the top of the sphere that puts it well away from the seabed. The only silt it could suck in is what's dispersed in the water already, and at 500+ meters there's very little current to stir it up. And if they put the intake on top and siphoned the output from the bottom it would even be relatively self-cleaning.
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Plus the places most suited for dams also tend to be natural wonders. Rip Glen Canyon and Hetch Hetchy
Or places which are already heavily inhabited/productively used. Inland river valleys are some of the most desirable real estate, in human habitation terms.
Major river dams are often only feasible in countries which either have lots of sparsely populated wilderness (like North America), or which don't have a problem with displacing hundreds of thousands of people and destroying whole communities (like China). Takes it off the menu for a lot of the world.
Like a battery, it’s not scalable as a one off, but it may be as a modular mass produced item.
Or maybe like a wind turbine. You’d have a field of them comprising a power plant. If you lose some individuals, who cares. If you need to do maintenance you can take one offline or entirely replace it without really impacting the power plants output
An easy manufacturing method would be to 3d print in plastic a double walled shell, with fill holes for concrete, and mounting chanels for motors. Plastic "lining" would provide salt water protection for the concrete.
... 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.
Add to this: The chemical process of creating concrete is itself a significant contributor to CO2 emissions. So assuming the goal is to reduce CO2eq, that also needs to be accounted for.
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.
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