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?
Says on the wiki 2.7 meters thick
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.
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.
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.
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.
Decoy spheres.
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
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.
It seems to me pumping out water to near vacuum while under crushing outside water pressure would be a significant power hog
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.
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.
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.
… you’d need some massive …
from the srticle :
… a sphere nine metres in diameter and weighing 400 tonnes will be submerged …Can you calculate the weight of a sphere of 9 m of displaced water ?
No ? Well, it is 382 tons.
So, the concrete sphere is already massive by itself. “You” don’t need any complicated anchoring.
Same goes with the rest of your mechanical engineering intuitions : you did not work in this domain or study it, did you 😆 ?
Also, stress cycling is bad on most material, yes. But here it is compressive stress and the geometry is symmetric. Without further study, i want to believe this thing has good potential and my intuitions tells me it looks nice. Time will tell 😁 !Can you calculate the weight of a sphere of 9 m of displaced water ?
No ? Well, it is 382 tons.Metric strikes again.
I bet you didn’t even have to convert through football fields, elephants, or olympic sized swimming pools!indeed i made a very simplified calculation not taking into account increase density of salted water nor increased density because of compressibility of water at 500 m deep. Basically i took 1m³(water) is 1 (metric) ton.
Thanks for the insight, I’m not a mechanical engineer, I’m a software engineer :) The walls on these spheres have got to be pretty thick- 400 tonnes is no joke. 3/4 of a meter if I had to guess.
Perfect guess ! (afaik) ρ(concrete) ≈ 2.5 tons/m³
so full sphere ≈ (2.5 x 382) tons = 955 tons
they have 400 t so the cavity removes :
955 - 400 = 555 t … so 7.51m diam. cavity
… so, yes 3/4m thick wall 😌👍 !That’s exactly the way I would have calculated it, glad someone beat me to it though. Thanks!
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
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.
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.
Now imagine this 27 foot wide ball shooting water out of its bottom while on the sea floor and tell me there’s still no silt being stirred up. Or algae. Or mineral buildup.
That’s why I said siphon it from the bottom, a siphon tube going from the bottom to the top would eject the water up and away while still sucking out most of the sediment that had gotten in and settled on the floor of the ball.
The sediment that gets pushed out into the surrounding water. That gets pulled up with the ball as it creates negative pressure behind it as it rises.
Bro, the ocean is FILTHY. Like, crazy filled with stuff. Like, you could take a coffee filter and pull stuff out filthy. Like the water has so many living organisms in itself it’s basically alive.
And let’s talk about the salt. Corrosive af salt.
This isn’t impossible, but the people trying to point out why this is CRAZY difficult are right. This will not be a set it and forget it scenario by far. It will need regular maintenance. The issue is whether that maintenance is easier or harder than a dam or stationary tank.
Like, why can’t we build these in giant freshwater reservoirs? Stick them a pool. Or why does it need to float? Wouldn’t a tank at the bottom of a pool with a pump do the same thing? Or two tanks at different heights with a conection between them and a pump? This is just mechanical energy being stored for later. Do the work when it’s cheap and reclaim it later.
They don’t float, they’re fixed in place at depth. They use the pressure of the surrounding water to spin a turbine as its pumped in and out, the only moving parts are the turbine and its associated components. And seeing as how the water is pumped in and out, most of the silt/detritus pulled in during filling, would be pumped out during draining assuming a siphon tube is used to draw the water from the bottom of the sphere (where all the debris settles) to the pump.
Yes salt water is corrosive, but that problem is already solved, there are currently concrete oil platforms built in the 70s and still in service today. We have formulas for concrete that are proven to be seawater resistant.
Building storage tanks on land wouldn’t be as efficient due to the greater pressure differential at 500m underwater vs on land. Dams are one of the most expensive structures to build and are very damaging to the surrounding environment. They also have a much larger problem with silt deposition as there is a constant flow of it, every time it rains there’s another surge of silt making its way downstream to be trapped by the dam.
Overall this project would be considerably cheaper, more friendly to the environment, and most likely more efficient than any pumped storage on land. And its not like the sea floor is lacking for real estate, unlike any feasable locations for dams here on land.
Did they say it was intended to be on the seafloor? I didn’t see that but assumed it would be moored deep enough for water pressure to turbo boost the turbines, but well clear of silt from the sea floor. That would also be a key benefit if you can moor it at the most useful depth but in any depth of water
The article say about 500/600 meters deep. No mention if on the sea floor or not.
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.
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.
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.
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.
You need specialized equipment also if you send down people to do the job that deep. And given you need to use many more specialized people (not everyone can work at these depths and they are not cheap) with all the associated support infrastructures like decompression chanbers and so on. I doubt that the cost will be lower that simply hauling the whole thing out of water.
My point is that whether you send down divers or haul 400+ tons of concrete and equipment up from the bottom of the ocean, it’s going to be expensive to maintain either way, especially if things don’t go according to plan and they have to perform maintenance more than once every 20 years or whatever.
And my point is that, given how deep these things seems to be, it is cheaper to haul them on the surface than sending a diver down, even if you need to do some unscheduled maintenance, especially because sending down a commercial diver (the only that can hope to work this deep) is not an easy feat in itself.
Obviously it will be expensive either way, I was only pointing out that sending down commercial divers a lot of additional levels of complexity (decompression periods measured in days or weeks, need to hire many more highly specialized people and from a way smaller pool and so on) that will drive up the price.
I’d assume they’d put these pretty close to the surface, lowers the water pressure and makes it more accessible
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.
Why not submerge a tank with a hole at the bottom and blow air in the tank via a hose to store energy?
They need to pair this with Tidal power
Tidal power probably needs shallow water while these would be great in deep water
https://en.m.wikipedia.org/wiki/Wave_power
They can do wave power deep sea buoys then :)
