Please create an account to participate in the Slashdot moderation system


Forgot your password?
Power EU Science

Underwater Pumped-Storage Hydroelectric Project Completes Its First Practical Test ( 238

What if you built massive concrete spheres -- 98 feet in diameter, with 10-foot walls -- under the ocean to help generate electricity during peak periods? Slashdot reader nachtkap reports that German researchers just finished testing their 1:10-scale prototype StEnSEA: It was retrieved from Lake Constance, where it was submerged at a depth of 100 meters [328-feet] since November. The system was developed by the Fraunhofer-Institut IWES in Kassel, Germany in collaboration with its inventors... The German Trade Department and Department of Education and Research as well as the German construction company Hochtief are also involved with the project.

The system's hollow concrete spheres are intended to be used in conjunction with off-shore wind-farms to serve as energy storage for peak hours. The spheres are ultimately supposed to be submerged near off-shore wind-farms and pumped free of water with excess energy. When additional energy is needed during peak hours the system goes into reverse and water rushes in, driving a turbine... At 700 meters the system has a capacity of 20MWh, with a linear capacity increase as depth increases.

This discussion has been archived. No new comments can be posted.

Underwater Pumped-Storage Hydroelectric Project Completes Its First Practical Test

Comments Filter:
  • by Anonymous Coward on Sunday March 05, 2017 @02:46PM (#53980691)

    When it implodes it goes MOOB!

    • by K. S. Kyosuke ( 729550 ) on Sunday March 05, 2017 @03:52PM (#53981017)
      It also takes some serious balls to try a system like this.
      • The pumps to remove water at that depth burn out quickly. Another made thingy that's always in the shop being repaired.

        • by gweihir ( 88907 )

          Nonsense. They are already in the state of practical tests at 100m (well, they just had complete success at those). You do not get there if you do not have very good indicators that this will work and there are only minor issues to address.

          • by HiThere ( 15173 )

            I'm not sure it's non-sense, but I think the answer might be "You need to choose pumps carefully designed to handle the job."

            I'm more worried about various frictional losses, storm damage, etc. There are some similar land-based systems where the geology is right, and I'm told that though they work well, it's best to combine the air flow with a gas flame that heats the air causing it to expand. Still worth-while, but then they didn't need to build the containment vessel.

            • by gweihir ( 88907 )

              I am not sure what you are getting at. To the best of my knowledge, they are pumping water not air and they are using the water rushing back in by outside pressure to recover the energy. As everything is done in the concrete-bubble at a target depth of 700m or so, there should be no problems with storms at all. I do admit I have no idea what details are in the story referenced here, I read the original German reporting.

    • by dohzer ( 867770 )


    • You're going to get all kinds of sea life growing on all those moving parts, turbine blades and such. Be nasty, expensive work trying to clean it all off. Maybe they can engineer around that??

  • by pla ( 258480 )
    In what ways is this better than simply pumping water uphill into a holding tank or artificial reservoir? It sounds a hell of a lot more complicated, so must have some offsetting feature that would shift the balance.

    Yes, I can see the obvious answer that the increased pressure means a higher energy density, but *so* much higher as to make it worth doing?
    • Re:Why? (Score:5, Informative)

      by religionofpeas ( 4511805 ) on Sunday March 05, 2017 @02:48PM (#53980713)

      In what ways is this better than simply pumping water uphill

      It's better if you don't have hills.

      • by davecb ( 6526 )

        You don't need a lot, and there's *lots* of hills near Lake Constance. Some positively pointy (;-))

        • Re:Why? (Score:5, Insightful)

          by religionofpeas ( 4511805 ) on Sunday March 05, 2017 @03:08PM (#53980831)

          Sure, but not everybody lives around Lake Constance. They have tested the system there, but the may want to use it near the coast, or at the bottom of the sea where the offshore wind farms are.

          • Re:Why? (Score:5, Insightful)

            by swb ( 14022 ) on Sunday March 05, 2017 @03:15PM (#53980863)

            This. Offshore wind farms have lots of water, but no hills and no place to pump water.

            Pumped hydro is great, if you have the water and the geography to impound the water.

            • Re:Why? (Score:5, Funny)

              by DontBeAMoran ( 4843879 ) on Sunday March 05, 2017 @04:07PM (#53981089)

              What if - and stay with me here for a second, but what if we pumped the water into the clouds? It works for data, surely it would work with water.

              • by slew ( 2918 )

                What if - and stay with me here for a second, but what if we pumped the water into the clouds? It works for data, surely it would work with water.

                I believe we have a pump for that: the sun (not to be confused with sun microsystems). The problem with that is a bunch of environmentalists won't let us build turbines to recover that energy, so we are stuck with these balls...

                • by swb ( 14022 )

                  It makes me wonder if anyone has considered a turbine generation system for storm water runoff.

                  My back of the envelope math says that our local stormwater system handles something like 40,000 acre-feet of water per year, which is the current flow rate of the Mississippi river at St Paul for a month.

                  That's potentially a lot of water flow that hasn't been tapped, and a lot of it is all downhill with no pumping (because it goes into the river itself).

                  • Re:Why? (Score:5, Informative)

                    by thebigmacd ( 545973 ) on Sunday March 05, 2017 @08:08PM (#53982077)

                    You've just reinvented hydroelectric power stations ;)

                    The practical problem to extracting a useful amount of energy from water is that you have to restrict its flow. You'd end up with a giant lake like every other hydroelectric system, except it would flood the city.

                    There's no getting around the fact that extracting kinetic energy from water makes it slow down. When it slows down it backs up. Its level raises as upstream flow is converted to gravitational potential energy in the form of increased head height while it is "waiting" to flow through the restriction.

                    If you want to allow the water to flow mostly unimpeded, you could only extract a fraction of a percent of the available kinetic energy.

            • by rtb61 ( 674572 )

              To make it more economical, simply mount the windmill on an upright concrete cylinder and when the windmill is not required to generate electricity for consumption it empties that cylinder of water. The cylinder also can provide a mounting surface for vertical axis water current generator around it's periphery and to a serviceable depth. Although near the surface it would be better to make use of wave energy, cyclic rising and falling water. So one structure achieves many purposes, generating much more capi

          • Re:Why? (Score:5, Insightful)

            by HiThere ( 15173 ) <{ten.knilhtrae} {ta} {nsxihselrahc}> on Sunday March 05, 2017 @08:32PM (#53982203)

            If they plan to use it in salt water, they should be testing it in salt water. The problems aren't the same. It may still be a good idea, but testing it in fresh water worries me. Of course, this may be an early prototype...but they damn well better be testing the pilot in salt water...if it were near where I live I'd say they also need to be testing it in winter storms, but perhaps they're planning on using it in a sheltered area.

        • You don't need a lot, and there's *lots* of hills near Lake Constance. Some positively pointy (;-))

          I have relatives in that area. It's a pretty and expensive part of Germany, so being able to put the pumped storage offshore is a neat idea and would probably save money.

          I have always wondered: for land-based wind turbines, has anyone thought of building a flywheel storage unit into the base of each tower, just under the ground surface for safety? This would add up to a lot of storable power for a large windfield.

        • You *do* in fact need to store a *lot* of water up hill if you want to have energy when the weather isn't cooperating for a few days at a time, and power electric cars, etc. To provide for all of our energy needs, replacing petrol, heating oil, etc, we need three times as much electricity as we have now.

          I did the geographic modeling for the US. Obviously Germany has different geography, but this will give you a general sense to scale. To have three days of pumped storage sufficient to provide for the ener

      • It's better if you don't have hills.

        Lake Constance has a few hills . . . they're called the Alps. But rich folks like to live on the shores of the lake, so the "Kape Kod Kennedy" rule applies here: Rich folks don't like ugly-ass power generation structures spoiling their view. The solution? Put them under water!

        Actually the real purpose of this engineering feat is given away in the first line of TFS: "massive concrete spheres -- 98 feet in diameter, with 10-foot walls." And Germany's Angela Merkel will be visiting Trump next week!

        Obviously, she is going to attempt to patch up German-US relations by offering to build Trump a wall of massive concrete spheres.

    • by fisted ( 2295862 )

      Wouldn't greater depth also imply requiring more energy to pump the containers empty?

    • Re:Why? (Score:5, Insightful)

      by AnotherBlackHat ( 265897 ) on Sunday March 05, 2017 @03:04PM (#53980817) Homepage

      Advantages that I can see;
      More places they can go, and the places they go (off the coast) are usually closer to places that want the electricity.
      If it works, you can scale it by building more spheres.
      A change in height of 700m is easy to obtain in the ocean. On land, not so much.
      Out of sight, out of mind - Since fewer people will see it, fewer will complain about it.
      If a sphere fails, it's far less catastrophic than a dam failing.

    • Direct injection into peak "Rocket" turbine power systems, that's how.
      Saving some 13% of the energy lost to pressurizing coal or increasing burn temperature for Natural Gas, absent a smokestack which also steals power.
    • With a hill the water is stored at the top and taken out through a turbine at the bottom. So you have to store water in two places, the top and the bottom. The water is exposed to sunlight so it will grow crap in it. And you battle evaporation. the whole apparatus will take miles of pipe. finally there's friction losses as the water moves down the miles of pipe. And there's the modest potential of flooding if you scale this up. It takes up useful and expensive mountain top land or destroys wilderness.

    • Re:Why? (Score:4, Interesting)

      by gurps_npc ( 621217 ) on Sunday March 05, 2017 @03:35PM (#53980939) Homepage

      First, that pressure is extremely important. As per Mythbusters episode, it can take a human and crush it inside an underwater pressurized suit when the suit breaks.

      More important, water pumped up hill has multiple issues you are not considering. Evaporation, rain, land use areas, pollution, danger of dams breaking, are all major issues.

      But the most important issue is simple power transmission is expensive. We lose more power moving it around than you would believe.

      If you are inland, with natural hills, then pumping water up hill makes sense.

      But if you are near a shore line, where beach front property is prime real estate, then finding a way to store energy OFFSHORE makes a lot more sense, as all the land near the ocean is to valuable.

    • If a sphere cracks, you don't flood dozens or hundreds of houses.

    • by gweihir ( 88907 )

      It is a bit hard to get that 700m hill next to the wind-farm in the sea...

      That thing with the hill is being done already (for almost 100 years now) where conditions are right. Next to a off-shore wind-farm they are not.

    • Well for openers you don't need to dig out a reservoir and flood a hilltop. This would have a much smaller overall environment footprint than say something like this:

      Also, if there's a breach in the system there will be a muffled crump and that's about it. Hilltop reservoir bursts? Well that same picture above looked like this in December 2005.


    • With the difficulties regarding maintenance in an underwater environment and the limited number of places this could be applied, I second your question. Pumping water uphill is one option but there is also the option of compressing gas by pumping (clean) water into pressure tanks. Compressing gas should support the same energy density without the difference in height.
    • by AHuxley ( 892839 )
      Export potential for Germany.
      For Germany this is about perfecting a product they can sell to the world and then sell spare parts and support.
      Nations might have built all the easy hydro with loans back in the 1950-70's.
      Or they need power near the coast and hydro is far away or all the hydro is been used, exported.
      Nations upgrade from coal to gas, hydro, wind farms, solar, why not sell them on German underwater tech as the next clean upgrade?
      Take out a nice loan and pay it back. Germany gets export jobs
    • >In what ways is this better than simply pumping water uphill into a holding tank or artificial reservoir?
      It can be done in places where there are no handy hills to pump up. Potential energy storage by height is directly determined by just how high you go - and the volume you store - the higher you can make the water fall - the more acceleration you get, and the faster your turbine can be turned). You can only get a little storage from a tank on a tower (at least one built at reasonable cost). Such syste

  • Pumps are very inefficient. I wonder why they wouldn't just use the excess energy to drive a motor/generator to pull an empty sphere towards the bottom with a cable and then generate energy in reverse as it rises up?
    • by religionofpeas ( 4511805 ) on Sunday March 05, 2017 @02:55PM (#53980769)

      Sounds like that would create more moving parts in an environment that's not kind to them.

    • Hang two of them on a pulley and motor set up so when one sphere is full you raise it to the surface while dropping an empty sphere. all you are lifting is the water as the spheres are equal. Once the empty sphere is on the bottom and the full sphere is swinging in the breeze, you drain the full one using gravity...
      • I always wondered if you couldn't do essentially the same thing on dry land with raised masses. Use excess generation capacity raise a series of masses and when the power is needed let gravity lower the masses, dumping the power into flywheel(s) attached to generators.

        The masses could be sized so that rather than raising one very large mass, a series of smaller masses would be raised allowing relatively small excess generation amounts to captured over time.

    • Pumps are very inefficient. I wonder why they wouldn't just use the excess energy to drive a motor/generator to pull an empty sphere towards the bottom with a cable and then generate energy in reverse as it rises up?

      My guess would be: fewer moving parts and/or less complexity with a pump.

      • The advantage of the pump system becomes even greater when you scale up the storage capacity, as that only requires adding more empty storage spheres, and not more pumps.

        • I was envisioning a system of anchored pulleys with locking brakes below each sphere with cables going all the way back to a floating motor/generation unit on the surface. Nothing would be under water but spheres, pulleys, and cables. The motor generation unit could have many spheres tied to a single shaft with an ability to control whether the shaft is actually engaged with each sphere's cable individually (or the cable is locked at the bottom pulley when the generator is not engaged). A sphere near the bo
          • by fgouget ( 925644 )

            The system described in the article uses the pressure difference between the inside of the sphere (low pressure to near vacuum) and the water outside. What's interesting is that the deeper you get the higher the pressure difference and thus the more potential energy you get.

            In contrast your mechanism only relies on the density difference between your spheres and the water so that no matter what depth they're at the force they exert on the cable is the same. If you place your spheres at a depth of 700m, to

    • Pumps are very inefficient. I wonder why they wouldn't just use the excess energy to drive a motor/generator to pull an empty sphere towards the bottom with a cable and then generate energy in reverse as it rises up?

      Conventional pumped storage systems have about 75-80% round trip efficiency, which is not that bad. One reason for the loss is evaporation from the upper reservoir, which would not be a problem for this system, so round trip efficiency in the 80+% range is realistic. That is not to bad if you have free electricity to begin with.

    • by hey! ( 33014 )

      Because gearing is also really inefficient, and you'd need to gear up the motion of the buoys as the rise in the water column so it's fast enough to spin a generator.

      In contrast with this scheme you can retrieve the energy using a perfectly conventional (and highly efficient) hydroelectric turbine. The net efficiency is (presumably) greater.

      In any case physical efficiency isn't quite as big a deal with renewables as it is with fossil fuels. Renewables capture energy that you're not paying for in the first

    • I don't think that the solid spheres would be very buoyant. They are made of very thick concrete to withstand the pressure, which has a density several times that of water. By my calculation, the shell uses 27% of the total volume, so these things would barely float.

      If you made the spheres out of thin material like a balloon instead, the air inside would compress as you pulled it down and you would get thermodynamic losses like a heat engine.

      • At 700m where they are experiencing ~70 atmospheres of pressure, the story becomes different. I bet that one of the hardest problems they will have is reliably keeping these things anchored to the bottom when they pump the water out.
        • I don't see how the pressure will affect buoyancy. Since water is almost incompressible, its density will be the nearly the same at 700m as at the surface. The force pulling the empty sphere upwards will be about the same as near the surface; my math says it's about 4700 tons of force either way.

          Given that the sphere would already comprise about 10,000 tons of concrete, it wouldn't be too hard to weigh it down a little more so it doesn't even float.

  • I have a cottage outside of Marmora, who has a lovely pumped-storage kit in the form of a large mine (see the picture at []) that's well above the Crow river. A good modern pump/turbine could do a sparkling job of storing wind-/solar-power until night.

    • by c ( 8461 )

      A good modern pump/turbine could do a sparkling job of storing wind-/solar-power until night.

      It's a heck of a lot better than previous plans for the mine, such as filling it with Toronto's garbage...

      • Hey, if you don't fill the mine with our garbage, we'll have to resort to "Plan B": []

        • by c ( 8461 )

          I think in this case "Plan B" was shipping the garbage to Michigan. Although many people would be okay shipping Toronto there too.

      • by davecb ( 6526 )

        Thats a different mine: this one is utterly prohibited for use as a dump: our dump is miles away in different terrain.

    • by hey! ( 33014 )

      Well, I think this is an example of how engineering is about the intersection of economics and technology.

      The basic physical principle here is quite mature: pump water against gravity to store energy. Retrieve that energy later by allowing water to flow with gravity. Back it the 60s they built a system [] to store off-peak power from the Vermont Yankee nuclear plant by pumping water into a reservoir, and then retrieving that power during peak demand by running it through a conventional hydro plant.

      This is the

      • by Cyberax ( 705495 )
        Pumped hydro is widely used around the world. It's nothing unusual. However, this particular project is ridiculously impractical - it's quite literally cheaper to buy lithium batteries than to build big structures underwater.
        • by hey! ( 33014 )

          Ridiculously impractical compared to what? The only answer I can think of is building the storage facility elsewhere.

          • by Cyberax ( 705495 )
            Pretty much everything else, including buying power from neighbors with nuclear power stations. Even batteries are cheaper and easier to scale.

            Seriously, think about it - 1kWh of energy at 100m depth requires storage for around 3600 liters of water at 100m depth. At this depth the only viable option for construction are robots, humans need many hours of decompression and if you go deeper it's even worse.

            3600 liters is a lot - one third of a cubic meter. If you need to store something like 200MWh then y
            • by hey! ( 33014 )

              That assumes you build the concrete structures underwater, which I agree would be insane. But that's not how civil engineers do that kind of stuff. For example when they build an immersed-tube tunnel they build the concrete sections onshore, seal the ends, then tow the floating sections out and sink them in place.

              You can always find an impractical way to build anything, even something as well-understood as a wire suspension bridge. The question is can you find a workable way to build it.

              People here always

              • by Cyberax ( 705495 )
                They are still going to be assembled and maintained underwater, at the edge of feasible human diving range (technical divers are not certified for more than 100m). There's no question at all if we can build it - we totally can, just look at Transbay Tube in San-Francisco, the question is the price of doing it. It'll be literally billions of euros for very modest gains.

                People here always assume that companies just throw hundreds of millions of dollars into a project like this without actually having actual engineers figure out the construction and operation costs first.

                Oh, this very thing happens all the time in Europe. Sometimes on purpose (e.g. initial subsidies to drive down the price of renewables) and s

        • Why would they build it underwater? It could be built at the water's surface or even on dry land and floated to the location. All they would need to do is sink it then anchor it to the bottom or whatever depth they wish to keep it.

          Although a slightly different set of complexities, it wouldn't be much different than building a boat or submarine.

          • by Cyberax ( 705495 )
            These structures will be VERY big and quite thick to withstand 10 atmospheres of static pressure and they'll still have to be connected with all the piping. They can certainly use multiple smaller structures, but that'll increase the cost of piping and connections. And all of these for energy storage that simply makes no sense in a pan-European energy grid.
            • It's concrete. They will not pour it all at once. Damns aren't even made that way because it would never harden correctly. The hoover dam for instance is 726 feet high with tubing behind and through it.

              But we are talking the depths of several orders deeper. It's more like 69-70 atmospheres at 700 meters. This isn't virgin territory though. We have DSVs or Deep-submergence vehicles capable of going deeper with humans on board too.

              A simple way to build this would be to set some barges up, use them to float it

              • by Cyberax ( 705495 )
                We don't have any large-scale structures at 700m - this is a completely new realm for engineering. I don't even think it'll be technically possible to design large-scale structures that can withstand regular 70 atm. pressure changes. And never mind that they'll be servicable _only_ by using robots. And all that to store some power (not even enough to compensate for multi-day lows in renewables)?
  • It's going to take some pretty big balls to pull something like this off.

  • by gweihir ( 88907 ) on Sunday March 05, 2017 @04:21PM (#53981163)

    No bullshit grab-for-the-stars (and never get them) waste of money and time, but practical, pragmatic and addressed at real problems. Of course, this will take another 10 years or so to practical deployment, but it is highly likely to work and be both reliable and cost-effective. Things like these drive progress.

    • No bullshit grab-for-the-stars (and never get them) waste of money and time, but practical, pragmatic and addressed at real problems.

      Are you referring to the various attempts at fusion energy?

  • Seriously.... a major death trap.... you're going to pump a giant underwater sphere free of water?

    Then when you release it, or if something breaks,
    That will be some SERIOUS... Delta-P []
    Imagine all the potential energy build-up, and the impact of the sudden release on anything living happening to be anywhere near the input pipes.

    • The pipes are underwater at the same depth too. Can't remember the principle that causes it, but water can't be "pulled" uphill through a pipe more than 30ish feet. The turbines for this have to be at the bottom with only the electricity running uphill.
    • by belthize ( 990217 ) on Sunday March 05, 2017 @07:18PM (#53981905)

      Death trap for whom ?

      By death trap do you mean 'non-zero' risk similar to the people who live below a hydroelectric dam, or near a nuclear power plant, or who mine coal, or who live downwind from a dirty coal plant ? I suspect the human risk is pretty low comparably.

      if you mean the critters living nearby, we eat around 100M tons of fish / year, so that might be a better place to focus in terms of 'death trap'.

  • If you're working with offshore wind farms, this makes a great deal of sense - as part of the construction you add as many of these as appropriate and use them to stabilize the power output from the farm.

    Methods of storing power to be delivered when needed have always been the goal, what's changed more in recent years is more focus on the efficiency and cleanliness of the storage and delivery methods. If you change your thinking from "coal/oil/gas is a fuel" to "coal/oil/gas are energy storage mediums" it c
  • by Anonymous Coward on Sunday March 05, 2017 @05:44PM (#53981543)

    Have these people ever lived by the sea? There is no way a pump is going to sit at depth without needing to be taken out and cleaned every few weeks. There is no way the generator turbine is going to sit at depth without getting furred up. There is no way the influx and drain pipes will remain clear. Even the sphere itself will slowly fill.

    The sea is not just salty water. It's a soup of animals, plants and minerals in suspension. The test might work in a fresh water lake for a few months but the sea is far more active at destroying machinery. Otherwise we'd just build big turbines and let the tides generate all of our electricity.

    • by swb ( 14022 ) on Sunday March 05, 2017 @07:02PM (#53981847)

      I'm sure they're considering all the usual options, including filtration on the turbine ingress and egress, biocidal coatings, zinc plating and probably active cathodes (since they have electricity to begin with). And some of the active cathodic systems can use copper anodes to act as biocides, too.

      It's not going to be maintenance free, for sure, but we've managed to put giant iron ships in the water for over 100 years, I'd suspect managing the ocean here is no worse and maybe even easier because the objects are stationary.

  • by silentcoder ( 1241496 ) on Monday March 06, 2017 @04:33AM (#53983497)

    Normal hydro-storage depends on pumping water uphill - and that means you can only use it where there are hills or mountains nearby. But this only requires pressure, which is available in many places where drops aren't. It could certainly add to the options for large-scale storage.

    It's big and expensive to build of course - but I'm not sure it's actually bigger and more expensive than a coal or solar plant. So it may still be a win.

  • by FeelGood314 ( 2516288 ) on Monday March 06, 2017 @10:08AM (#53984681)
    The killer to these projects is you have to recoup your cost before the system wears out while also covering maintenance costs. We do this on land pumping water up hills and doesn't make economic sense. The systems require to much maintenance. In North America the ones that are already build are used as insurance. Utilities pay for the ability to draw several MW from these systems while they wait for a coal system to come on line. Coal takes a while, while hydro is close to instant. The utilities pay for this insurance every month whether they use the electricity or not and when they do use the electricity they pay in the multiple dollars per KWh. The system in the article will be charged with unwanted electricity, cost 0, but will sell the electricity only at peak and shoulder prices. It's not going to viable.

To write good code is a worthy challenge, and a source of civilized delight. -- stolen and paraphrased from William Safire