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Europe joins race to store energy at the bottom of the ocean


May 20, 2013

By exploiting pressure at the seabed, researchers hope to create stores of energy at the ocean floor (Photo: Andrew Jalbert/Shutterstock)

By exploiting pressure at the seabed, researchers hope to create stores of energy at the ocean floor (Photo: Andrew Jalbert/Shutterstock)

"Imagine opening a hatch in a submarine under water. The water will flow into the submarine with enormous force. It is precisely this energy potential we want to utilize." This is how German engineer Rainer Schramm describes his idea for storing energy under the sea. By using surplus energy to pump water out of a tank at the seabed, the water is simply let back in again when there's an energy shortfall, driving turbines as it rushes in. The deeper the tank, the more power is generated.

The technology is being developed by Schramm's company, Subhydro AS. Based in Olso, Norway for access to deeper water, the company claims to be the "first in the world to apply a specific patent-pending technology to make this possible." In fact the energy storage principle is identical to MIT's underwater hollow concrete spheres which could store surplus energy from offshore wind turbines. Subhydro also positions its tanks as a logical counterpart to offshore wind, but like MIT's technology, it could also be used to store energy from the grid.

Really, the idea is very similar to that behind above-ground pumped-storage hydroelectric power stations which pump water from a low reservoir to a high one when energy is cheap or plentiful, and allow it to flow back down through turbines when more energy is required. As with this new underwater technology, less energy is gained from the drop than is used to create the store of potential. The idea is simply to have potential energy reserved for when it's needed – half-time of major televised sporting events being a classic example. Schramm calculates the "round-trip" efficiency of the system to be 80 percent, which is in the same ballpark as conventional pumped-storage hydro.

Subhydro AS is working with Norwegian research organization SINTEF to develop the technology, which is designed for depths of between 400 and 800 m (1,300 and 2,600 ft). Subhydro claims that a plant of "normal size" would supply 300 MW of power for 7 or 8 hours at a time, though how many tanks that would require, or how big the individual tanks would be, is unclear.

Like MIT, Subhydro and SINTEF are looking at concrete as the material of choice. "The challenge is to find the optimal balance between strength and cost," explains SINTEF's Tor Arne Martius-Hammer. "If we achieve the goal of creating a concrete which will withstand at least five times as high loading as ordinary concrete, we can reduce the wall thickness by 75 per cent. This is a critical factor. We need to reach production and installation costs which make storage of energy economical in relation to the price of electrical energy."

MIT's technology is also patent pending, so gauging which team's plans are the more advanced is difficult.

Sources: Subhydro AS, press release

About the Author
James Holloway James lives in East London where he punctuates endless tea drinking with freelance writing and meteorological angst. Unlocking Every Extend Extra Extreme’s “Master of Extreme” achievement was the fourth proudest moment of his life. All articles by James Holloway

Someone already has ideas to solve lots of these problems. Look for "Seamus Garvey" and "Energy bag" on youtube. He is working on this since before 2009:




other than to store excess offshore wind power why would anyone look at this technology ? onshore pumped hydro is currently buildable technology ... looks like they are grant fishing ...

build more nat gas power plants and you can spin up power production in minutes to meet peak power needs with NO storage losses ...

Jeffrey Carlson

You can exploit potential energy anywhere. Why in the world would you want to have to build something on the bottom of the sea?

Jon A.

The harder the shell material and the more perfect the sphere the less shell to volume you need, but you will then need extra ballast or a stronger anchor to keep it down. However having the container buoyant is not all bad having it float to the surface for maintenance would be convenient.


a buoyant chamber is an excellent idea Slowburn :) only just buoyant and just tether her off to the seabed. the pumping losses with this sort of idea must be rather impressive though :(

Craig Jennings

Pumping losses are completely irrelevant if your power source is excess night time wind power. This allows you to save wind power that might otherwise be lost and sell at times of greatest demand and price, sure you have some pumping loss but the utility gain is far greater.

Robert Smithers

re; Jeffrey J Carlson

Some generating systems when running at maximum efficiency are efficient enough to pay for the storage loss and still be more efficient than the Natural Gas plants that spin up in minutes. Then there is government mandated randomly intermittent power generation. (wind and solar)

re; Craig Jennings

The hydroelectric plant is simpler and more efficient. Plus your tether is going to wear out rapidly.

re; Adruna

I like pneumatic energy storage but Hydraulic is more efficient and the tank can sit on the bottom under its own weight the airbags have to be tethered. Also the storage vessels are compatible with storing compressed gas at equivalent pressure. If the gas is C02 the energy storage is impressive but pumping heat in will be necessary.


Heavy concrete is a bit over twice as dense as water, so as long as your volume of air is about the same as the volume of concrete, the chamber will sink and can thus sit nicely on the bottom without tethers. That does impose a volume/cost limit, but I can see concrete chambers holding an enormous amount of pressure, so J/m^3 could be pretty high.

Pumped storage requires that you have somewhere to pump the water to - if you're somewhere flat and coastal with lots of wind power, like say the Netherlands, this seems like an appropriate solution.

Coupling the storage with generation, i.e. storage tanks near turbines should minimise transmission loss.


@Slowburn... You said about hydraulic storage with the last MIT story...

The only reason there is a return of energy is because of the lower density of air... As most hydraulic fluids are mostly water, there will be no return of energy using an under water system such as this.... Remember that the pressure is only there because of a tall column of water above the seabed, if a fluid as dense as water (or nearly) is used, the net pressure at the surface is zero... And this sort of system can only be used by venting it to the atmosphere (or any handy vacuum).. Air just happens to be the most abundant gas to use.

Also the others, this can be used for storing energy in flat countries or like most places, those without adequate mountains near the coast....

Transmission and pumping losses in pumped hydro are significant, in Australia for instance the only viable pumped hydro systems are in the Snowies and Tasmania, sending the power from Sydney to the Snowies for storage and back again, loses something like 30% of the power..... but then burning it off in resistor banks loses all of it... Sending the power from Perth would probably result in a net loss.... BUT Perth could store energy at the bottom of the ocean... (remember there are no mountains on the west coast (Ok, they may call some mountains, but not really... that's just to make the WA residents feel they aren't without a landscape. (haters, just trolling, don't respond.) (Oh maybe I meant Bahrain) oops to many words...


How do you mitigate against damage to sea floor and close-to-sea floor fauna and flora? I mean obviously you can have filters to stop foreign objects from being sucked in, but it isn't going to do sea life any favours being mashed up against a sieve every time there is a peak in energy demand.


surplus power can now be used to make steel ,instead of using coal see this as a way to level electric demand.

Stewart Mitchell

one of the biggest problems is that you are pumping air into the chamber to displace the water. While it sounds good, it is only efficient if the air is insulated, if not, as you compress the air it heats up and then it will cool and loose energy. Maybe using buoyancy would work better, but I agree with previous comments that better to pump water up into a reservoir then air into an underwater chamber.

Rodger Evans

why not use bell's law and fill balloons at the bottom of seabed and then raise them slowly capturing the power from the gas expansion instead? just asking

science ninja

@ Rodger

My understanding of the MIT system (and the one in the article) is that there is an air line to the surface that maintains the pressure inside the structure at atmospheric pressure and allows the air to move in and out passively. The water is allowed to flow into the structure through a turbine displacing the air (air moving up the air line at atmospheric pressure). Then to store power the water is pumped out of the structure and air moves down the air line to replace the water that is pumped out. The air should only be compressed or expanded slightly due to the dynamics/air line sizing of the system but not compressed to force the air out. So in essence this system is the same as pumped hydro not compressed air energy storage.


Not only would this be bad for sea life, I can't imagine that the sea life would be good for it. Fish, crabs, algae, coral, barnacles, clams - not to mention the "who knows what" from the deep sea ... no, I'm not sure the ocean is such a good place for this.

Charles Bosse

re; MD

Hydro power is an open cycle hydraulic system. Hydraulic fluid is oil because the molecules are bigger and thus it is easier to keep them from escaping. I suggested having the wind turbines operate pumps (liquid or gas) instead of driving an electrical generator because it solves sever of the problems of wind energy. because water can be lifted by vacuum only a trivial distance the pump to empty the storage vessel has to be at depth so the hydraulic power generated by the wind turbine drive a pump on the tank. I would use seawater as my working fluid to reduce the pipe and friction by half but I am also creating a thermal differential and I suggest using it. If the wind turbine is compressing air and displacing the water in the storage vessel I pointed out that the energy contained in the compressed air can be tapped as well increasing the total energy stored. For WA it does not take a huge drop to effectively store energy 10m will work but it will take a correspondingly larger amount of working fluid for the same amount of energy storage.

re; Rodger Evans

Yes it is true that when you compress air you get heat. Use the heat as generated and then when you get the cold on the expansion of the gas use the cold. The same Stirling Cycle engine will do both.

re; Charles Bosse

The surface instillation provides habitat for much sea life and the footprint on the rest of the habitat is quit minimal. There is very little life at depth and the noise of the plant operating should keep the mobile away. and again the footprint is quit small. The viability of energy storage systems is based on that they boost total efficiency if you are concerned about the impact you should probably live in a mud hut without electricity.


Most of the planet is covered in ocean. Why not develop this technology?

Seth Miesters

Fluid is good... IT MAY TURN OUT that electrolysis at that depth and pressure and temp may more easily displace water than just pumping in air /pumping out water ? Plus you would get the added benefit of Hydrogen (H) and Oxygen (O) which are valuable as fuel and fuel additive (H burns with O very well , in fact it can explode if not metered properly). It would be worth a look see.


While fluid is good , it also requires a separate ($$) turbine; if Windpower is being used, and you have a land base site, why not simply use a motor/generator to LIFT A HUGE SOLID (or solid/liquid) WEIGHT (IE a huge tank of water could be lifted empty, then filled with water)...NOT to use the water as a stream but simply as a potential energy" weight to be lowered using system of gears to run motor/gen to create electricity, seems inefficient until you think about cots of turbines but you already have a motor/gen set anyway, so now you can use excess electricity to LIFT the weight (perhaps a thousands of tons weight) to as high as you can, then lower it and kick in the generator to create more electricity to meet peak demand intervals. In fact the very rain itself could be captured in the already high tank to be used later. Could lightning bolts (LB) be captured to help the "weight system", well maybe a little bit but probably too expensive to maintain and build the motor, (one moderate LB is about 1 Billion Joules , but since a 100 watt light bulb uses 100 joules for 1 second, a 1 B joule LB would only run a 100 watt bulb for about 120 days. Advantages, its on dry land (easy maintenance, can be used anywhere, takes advantage of bad as well as good weather (wind, and solar), can use either solid or fluid or combination weight, can almost instantly rise to the occasion to meet peak energy needs, and then also instantly go back to "collection mode", because of gearing, it "could" be more efficient than turnbine methods and definitely less expenssive, can "potentially" lift very big huge weights such as abandoned skyscrapers? (yeah sounds crazy but..... so was flying in 1800)

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