EnergyVault gravitational energy storage

[voltsandjolts]

don't have the exact numbers, but the efficiency of a lake to store water is much better than a bunch of spheres..

Nope.
Read the post right above yours, the numbers are right there.

[Marco]

maintenance will be insane in the depth of 750m ... there is no such thing as "ok sending a technician down"... saturation diving takes time and is expensive.
pumped hydro you can drain the upper lake and the shafts and then use conventional technology for the maintenance , you take you everyday cranes, trucks, dudes in hard hats...

How reliable can you make machinery to make a sphere slightly boyant, decouple it from the mooring and winch it to the surface? If you can make that reliable enough at low enough cost, it becomes viable to do the only significant maintenance at the surface.

[AlbertL]

Here are a couple of surge tanks in action:

Meanwhile, here on earth :
https://de.wikipedia.org/wiki/L%C3%BCnerseewerk

Built 1958.
Head is nearly a kilometer. Water arrives downstairs with 100 bars, at a speed of 500km/h generating 230MW.
Very impressive.

The UK one, 288MW... https://www.electricmountain.co.uk/Dinorwig-Power-Station

I once went on the tour, but it didn't include the surge pond at the top of the vertical shaft. I bet that's a sight to see when they shut the valves!

[Gyro]

Impressive, thanks. 


P.S. I found a video showing just how fast the valves at Dinorwig actually open and close!...

[rob77]

maintenance will be insane in the depth of 750m ... there is no such thing as "ok sending a technician down"... saturation diving takes time and is expensive.
pumped hydro you can drain the upper lake and the shafts and then use conventional technology for the maintenance , you take you everyday cranes, trucks, dudes in hard hats...

How reliable can you make machinery to make a sphere slightly boyant, decouple it from the mooring and winch it to the surface? If you can make that reliable enough at low enough cost, it becomes viable to do the only significant maintenance at the surface.

ask the marine salvage companies how easy it is to lift and sink 25000 tons
and the biggest problem with your suggestion is that you hardly make a 25000 ton concrete ball buoyant when the inner volume is 12200 cubic meters , your math doesn't add up. whole point of that sphere is to stay put on the seabed without anchoring.

[rob77]

don't have the exact numbers, but the efficiency of a lake to store water is much better than a bunch of spheres..

Nope.
Read the post right above yours, the numbers are right there.

i was not talking about  the efficiency of energy  storage...  i was talking about the efficiency of concrete usage... the sphere is 25000 tons of concrete and stores 12200 tons of water... that 2:1 concrete to water by mass... when building a artificial lake you need far far less concrete than the mass of stored water.

[Marco]

ask the marine salvage companies how easy it is to lift and sink 25000 tons

Ships have a little more compromises against sturdiness. You can't just put a bubble of air in it and lift it up.

whole point of that sphere is to stay put on the seabed without anchoring.

It has to survive the pressure, nothing more. Mooring can stay down, mooring doesn't need maintenance.

Come to think of it though, how much maintenance does a concrete sphere even need? Will it really be so difficult to make a re-usable seat for the pump assembly which doesn't wear out any time soon? Just lift the pump assembly, do the maintenance and change the rubber seal at the surface and seat it on the sphere again when done?

[rob77]

ask the marine salvage companies how easy it is to lift and sink 25000 tons

Ships have a little more compromises against sturdiness. You can't just put a bubble of air in it and lift it up.

whole point of that sphere is to stay put on the seabed without anchoring.

It has to survive the pressure, nothing more. Mooring can stay down, mooring doesn't need maintenance.

Come to think of it though, how much maintenance does a concrete sphere even need? Will it really be so difficult to make a re-usable seat for the pump assembly which doesn't wear out any time soon? Just lift the pump assembly, do the maintenance and change the rubber seal at the surface and seat it on the sphere again when done?

you somehow ignored the point related to buoyancy of a 25000 ton  sphere with a 12200 cubic meter cavity... how exactly will you make it buoyant ? you would need to attach another cavity of 12800 cubic meters... or do you think you could inflate the concrete ball to make it buoyant ? 

"just lift the pump assembly" is in the same ballpark as "just make it buoyant" ... 750m water column vs vacuum , that's a serious force the pump assembly must cope with... do you think it's easy to dismantle something like that especially in a depth of 750meters and "just lift it" ? 

maintenance will be definitely needed, things break and wear out. 

[Marco]

Why would you leave it vacuum to lift the pump assembly? Just let it flood through a bypass.

[voltsandjolts]

you somehow ignored the point related to buoyancy of a 25000 ton  sphere with a 12200 cubic meter cavity... how exactly will you make it buoyant ?

Be sensible sir, of course you would not raise the concrete sphere for maintenance.

[rob77]

you somehow ignored the point related to buoyancy of a 25000 ton  sphere with a 12200 cubic meter cavity... how exactly will you make it buoyant ?

Be sensible sir, of course you would not raise the concrete sphere for maintenance.

yes exactly that was my point ! you can't lift the concrete sphere for maintenance and you can't dive to 750m for maintenance either ! but the tech submerged to 750 meters needs to be maintained to keep it running.

[rob77]

Why would you leave it vacuum to lift the pump assembly? Just let it flood through a bypass.

either you don't understand or trolling....
you have assembly which must withstand vacuum against the pressure of 750m water column. it means it must be sealed and fastened well... all clear right ? hope you follow me.

now imagine how would you remove such a assembly from the concrete ball in a depth of 750m.

a) you can't fish it out with a hook... "plop" and it's out like cork from a bottle... doesn't work like that , it's has those seals and fasteners.
b) you can't dangle a wrench on a 750m rope and release the fasteners with your tongue at the right angle... doesn't work that way.
c) you could send down saturation divers - it takes roughly a week do to down and week to come back up, probably even longer. divers live in a steel tank/submarine in the depth and breathing helium-oxygen... expensive as hell to have anything done by saturation divers. and as far as i know 700m is the current depth record for such a work.
d) you could develop and build some specialized robot submarines controlled through cables from barges/ships above (wireless doesn't work under water except very long waves) - also expensive as hell and doable only during calm seas.

i know that you have a solution for every impractical idea some startup comes up with , but real life is a bit more complicated

 

[Marco]

The pump assembly will weigh a couple tons and the moment you pull vacuum a 10 m2 lid will get forced down with around 10 extra ton. I don't think it's all that natural to assume you need pre-strain on the seal to hold back the water, I assumed simple guide pins would be enough. With some robot to clean the seal seat.

[voltsandjolts]

Why would you leave it vacuum to lift the pump assembly? Just let it flood through a bypass.

either you don't understand or trolling....
you have assembly which must withstand vacuum against the pressure of 750m water column. it means it must be sealed and fastened well... all clear right ? hope you follow me.

now imagine how would you remove such a assembly from the concrete ball in a depth of 750m.

a) you can't fish it out with a hook... "plop" and it's out like cork from a bottle... doesn't work like that , it's has those seals and fasteners.
b) you can't dangle a wrench on a 750m rope and release the fasteners with your tongue at the right angle... doesn't work that way.
c) you could send down saturation divers - it takes roughly a week do to down and week to come back up, probably even longer. divers live in a steel tank/submarine in the depth and breathing helium-oxygen... expensive as hell to have anything done by saturation divers. and as far as i know 700m is the current depth record for such a work.
d) you could develop and build some specialized robot submarines controlled through cables from barges/ships above (wireless doesn't work under water except very long waves) - also expensive as hell and doable only during calm seas.

i know that you have a solution for every impractical idea some startup comes up with , but real life is a bit more complicated

either you don't understand or your trolling....

I played a very small part in a project which placed a multi-megawatt electrically driven turbine compressor at a water depth of >200m and it’s been down there, running since 2016. In comparison, pumping water out of these concrete bell jars is child’s play. Of course, you would not go this route if geology allowed other means of pumped storage. Maybe the volume of concrete is abhorrent. Maybe the numbers won't add up in reality. But to dismiss it out of hand because of these nonsense maintenance issues (which are solvable BTW) is short sighted and lacks the imagination required for creating new technologies.

[rob77]

Why would you leave it vacuum to lift the pump assembly? Just let it flood through a bypass.

either you don't understand or trolling....
you have assembly which must withstand vacuum against the pressure of 750m water column. it means it must be sealed and fastened well... all clear right ? hope you follow me.

now imagine how would you remove such a assembly from the concrete ball in a depth of 750m.

a) you can't fish it out with a hook... "plop" and it's out like cork from a bottle... doesn't work like that , it's has those seals and fasteners.
b) you can't dangle a wrench on a 750m rope and release the fasteners with your tongue at the right angle... doesn't work that way.
c) you could send down saturation divers - it takes roughly a week do to down and week to come back up, probably even longer. divers live in a steel tank/submarine in the depth and breathing helium-oxygen... expensive as hell to have anything done by saturation divers. and as far as i know 700m is the current depth record for such a work.
d) you could develop and build some specialized robot submarines controlled through cables from barges/ships above (wireless doesn't work under water except very long waves) - also expensive as hell and doable only during calm seas.

i know that you have a solution for every impractical idea some startup comes up with , but real life is a bit more complicated

either you don't understand or your trolling....

I played a very small part in a project which placed a multi-megawatt electrically driven turbine compressor at a water depth of >200m and it’s been down there, running since 2016. In comparison, pumping water out of these concrete bell jars is child’s play. Of course, you would not go this route if geology allowed other means of pumped storage. Maybe the volume of concrete is abhorrent. Maybe the numbers won't add up in reality. But to dismiss it out of hand because of these nonsense maintenance issues (which are solvable BTW) is short sighted and lacks the imagination required for creating new technologies.

cool project and amazing reliability! , but compressing natural gas can't be compared to pumping sea water at 75atmospheres of pressure.
what was the cost of the pump assembly ? it sure makes economical sense when pumping natural gas, but let's be realistic.. we're talking about 5MW of pumped hydro with similar cost for the pump assembly (of course manufacturing at large scale would bring the cost down a bit).

btw.. the numbers from that reality you linked are terrifying...

lifetime 20 years... what ?? why ? concrete lasts much longer ! why only 20 years then probably the maintenance issues i'm talking about are the reason of the short lifetime ?
so we'll end up with concrete spheres on seabed everywhere ? are we creating "new technology" to be cleaner while leaving crap behind ? manufacturing concrete creates a lots of CO2, abandoning concrete structures is definitely not "green".
furthermore all calculations are based on assumption of having 2 cycles per day ? i don't think we have lows on the grid 12 hours apart long enough to charge a pumped hydro twice a day...  so probably we should double the cost per kWh in their calculations.

[voltsandjolts]

compressing natural gas can't be compared to pumping sea water at 75atmospheres of pressure.

Correct, it can't. Subsea natural gas compression is much more complex.

Hydrocarbon reservoirs don't produce nice clean gas ready to pipe to consumers. If you’re lucky it's a condensate mix with minimal hydrogen sulphide, so hydrogen metal embrittlement isn't a big problem over the long term. Regardless, the multi-phase flow needs to be separated into gas and liquid before the compressors. The gas passes through the turbine compressor while the liquid goes through a centrifugal pump. Then they are mixed again into the export line. All these pressure and temperature changes means hydrate formation can spoil the fun, so mitigations for that need to be designed in. Then throw in some magnetically levitated bearings because you’re aiming for decades long operational life in harsh media. So, yeah, pumping some sea water is much simpler.

what was the cost of the pump assembly ?

Subsea gas compression is a relatively new technology with only a handful in actual operation. The complexity and costs are high.

it sure makes economical sense when pumping natural gas, but let's be realistic.. we're talking about 5MW of pumped hydro with similar cost for the pump assembly (of course manufacturing at large scale would bring the cost down a bit).

The cost of a water turbine, relatively well understood technology would be much less. Is it economically viable? Neither you nor I know at this time.

btw.. the numbers from that reality you linked are terrifying...

Ah, your terrified. That explains the lack of logical thought

lifetime 20 years... what ?? why ? concrete lasts much longer ! why only 20 years then probably the maintenance issues i'm talking about are the reason of the short lifetime ?

Calm down and think logically. The document did not say 20 year life for the concrete. You're right, concrete can and does last many decades in sea water, particularly in benign seabed conditions.
The pump/generator and controls package would likely need replaced several times in that timespan.

concrete structures is definitely not "green".

Humans have produced a horrific amount of concrete, and with it a horrific climate-changing amount of carbon dioxide. The question is whether the CO2 required for the production of these spheres is less than they save over their lifetime. Demand for concrete globally will continue and likely increase, so hopefully we can find new ways to produce it more sustainably.

I am just making the point that your responses are generally emotive with little to no effort in the understanding of technical detail. Please use reddit for such shallow discussions, not an engineering forum. Subsea pumped hydro may or may not be a viable solution for grid energy balancing. There may be better solutions, but it has enough merit to warrant investigation.

[rob77]

btw.. the numbers from that reality you linked are terrifying...

Ah, your terrified. That explains the lack of logical thought

yes i'm illogical irrational so we must support this impractical startup and let the governments waste taxpayer money. abandoning investment after 20 years and creating negative impact is terrifying...

lifetime 20 years... what ?? why ? concrete lasts much longer ! why only 20 years then probably the maintenance issues i'm talking about are the reason of the short lifetime ?

Calm down and think logically. The document did not say 20 year life for the concrete. You're right, concrete can and does last many decades in sea water, particularly in benign seabed conditions.
The pump/generator and controls package would likely need replaced several times in that timespan.

and we're again back to the impractical and expensive (probably even impossible) maintenance the very point everyone is fighting against... i was thinking logically and logic says either needs to be maintained (back to the initial problem) or abandoned after 20 years.

concrete structures is definitely not "green".

Humans have produced a horrific amount of concrete, and with it a horrific climate-changing amount of carbon dioxide. The question is whether the CO2 required for the production of these spheres is less than they save over their lifetime. Demand for concrete globally will continue and likely increase, so hopefully we can find new ways to produce it more sustainably.

I am just making the point that your responses are generally emotive with little to no effort in the understanding of technical detail. Please use reddit for such shallow discussions, not an engineering forum. Subsea pumped hydro may or may not be a viable solution for grid energy balancing. There may be better solutions, but it has enough merit to warrant investigation.

i said "abandoning concrete structures is definitely not green" - you excluded 1 word and literally changed the whole meaning.... so you're reacting to your fabricated sentence while pretending it's mine ? ... i think you should move over to reddit  

[voltsandjolts]

impractical and expensive (probably even impossible) maintenance

So, your main argument against this idea is difficulty of maintenance. I suppose I can forgive that, as my judgement is based on a career which for the most part has been in subsea and subterranean engineering. You perhaps don't have the benefit of that, I mean, seeing the difficult engineering challenges that can be overcome when the finances are viable. Sure, there are challenges in fitting a subsea turbine in a retrievable package, for maintenance or replacement from a vessel. But I've seen similar challenges end successfully. So I don't see it as unsurmountable. You do.

i said "abandoning concrete structures is definitely not green" - you excluded 1 word and literally changed the whole meaning....

That was not an intentional miss quote, in fact I don't think it means much.
Neither creating or abandoning concrete structures (in the way we manufacture cement today) is sustainable.
But the point is that with maintenance of the turbine package, the concrete structure is not abandoned.

[rob77]

impractical and expensive (probably even impossible) maintenance

So, your main argument against this idea is difficulty of maintenance. I suppose I can forgive that, as my judgement is based on a career which for the most part has been in subsea and subterranean engineering. You perhaps don't have the benefit of that, I mean, seeing the difficult engineering challenges that can be overcome when the finances are viable. Sure, there are challenges in fitting a subsea turbine in a retrievable package, for maintenance or replacement from a vessel. But I've seen similar challenges end successfully. So I don't see it as unsurmountable. You do.

i said "abandoning concrete structures is definitely not green" - you excluded 1 word and literally changed the whole meaning....

That was not an intentional miss quote, in fact I don't think it means much.
Neither creating or abandoning concrete structures (in the way we manufacture cement today) is sustainable.
But the point is that with maintenance of the turbine package, the concrete structure is not abandoned.

i'm not saying it's impossible - i said "impractical, expensive and probably even impossible maintenance"... and the fact they're presenting the solution with a lifetime of only 20years and don't mention anything about maintenance is very trange

for the maintenance you would need high accuracy in a depth of 750m. you say you have experience in sub-sea stuff... then you know you need expensive ROVs (or divers) to aid the operations.. expensive sea-cranes , insurance, weather must be good to perform such a lift. so it's definitely expensive.
you say it's not a problem, so try to get a quote for such a operation and share the results    releasing ~ 20 bolts  in a depth of 750m and lifting a several ton assembly from that depth , then lowering it back down 750m while placing it accurately into the hole and fasten those bolts. and let's not forget the electrical connections as well. ( 18-20 bolts is what seems they have on the prototype, final might be even more)

i just hope the representatives of the governments considering this solution will ask the questions about maintenance and lifespan before investing into it.

[voltsandjolts]

you need expensive ROVs (or divers) to aid the operations.. expensive sea-cranes , insurance, weather must be good to perform such a lift. so it's definitely expensive. you say it's not a problem, so try to get a quote for such a operation and share the results

OK, it's your turn for a misquote, I said I don't see it as an unsurmountable problem.
Of course, like all grid-scale engineering, it's expensive. Like a 700km subsea interconnector or a £9Bn offshore windfarm.

i just hope the representatives of the governments considering this solution will ask the questions about maintenance and lifespan before investing into it.

I am sure they will since the real question is the economic viability and that takes time to assess. Not a job for a 10min rant on eevblog like batteriser was.

[f4eru]

Come to think of it though, how much maintenance does a concrete sphere even need?

A concrete structure needs regular maintenance, especially when subjected to salt water.
Under extreme pressure salt water, the salt and water will penetrate deeply and quickly.

[voltsandjolts]

https://newscenter.lbl.gov/2013/06/04/roman-concrete/

The chemical secrets of a concrete Roman breakwater that has spent the last 2,000 years submerged in the Mediterranean Sea have been uncovered by an international team of researchers led by Paulo Monteiro of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), a professor of civil and environmental engineering at the University of California, Berkeley.

Analysis of samples provided by team member Marie Jackson pinpointed why the best Roman concrete was superior to most modern concrete in durability, why its manufacture was less environmentally damaging – and how these improvements could be adopted in the modern world.

“It’s not that modern concrete isn’t good – it’s so good we use 19 billion tons of it a year,” says Monteiro. “The problem is that manufacturing Portland cement accounts for seven percent of the carbon dioxide that industry puts into the air.”