Environment

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

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

19 comments
19 comments
Jeff J Carlson
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 ...
Jon A.
You can exploit potential energy anywhere. Why in the world would you want to have to build something on the bottom of the sea?
Slowburn
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.
Craig Jennings
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 :(
Robert Smithers
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.
Adruna
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:
www.youtube.com/watch?v=NgvLvZHzJrE
youtu.be/ktup6CAvfGo
Slowburn
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.
Synchro
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.
MQ
@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...
bergamot69
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.