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Scientists Splash into Underwater Energy Storage

Like flooding a submarine: a novel use of water pressure

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Ingenious scientists have come up with a novel method of storing energy – the use of water pressure to keep it at the bottom of the sea until needed.

The idea came from a German engineer and expert in aerospace technology called Rainer Schramm, “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 utilise,” explained Schramm, inventor and founder of the company Subhydro AS. “Many people have launched the idea of storing energy by exploiting the pressure at the seabed, but we are the first in the world to apply a specific patent-pending technology to make this possible,” he added.

In partnership with Norwegian research organisation SINTEF, a group of scientists have developed an underwater pumped storage concept. Pumped storage is nothing new – off-peak electricity is used to pump water uphill; when needed it is then allowed to cascade down through turbines, just like a normal hydroelectric power station. See this article for details of the largest UK pumped storage plant

Seabed Pumped Storage

To use the water pressure at the sea bed in practice, the mechanical energy is converted by a reversible pump turbine, as in a normal pumped storage hydroelectric plant. Credit: Knut Gangåssæter/Doghouse

To use the water pressure at the sea bed in practice, the mechanical energy is converted by a reversible pump turbine, as in a normal pumped storage hydroelectric plant. Credit: Knut Gangåssæter/Doghouse

 In this pumped storage power plant the turbine will be connected to a tank on the seabed at a depth of 400-800 metres. The turbine is fitted with a valve, and when this is opened, water flows in and starts turning the turbine. The turbine drives a generator to produce electricity. As many tanks as necessary can be connected. More water tanks mean more electricity storage, and therefore that increases the duration the plant can generate electricity, before the energy storage capacity is exhausted.

Schramm calculates that there is an energy efficiency of 80% for this type of storage. If this is correct then it would be a valuable addition to the various types of electricity storage methods needed. As more renewables are added to the grid, the variability will mean that innovative technologies will be needed for storage. This concept looks promising.

The deeper the better

In addition to the number of tanks, the sea depth also determines the effectiveness of the plant: the deeper the equipment is located, the greater is the pressure difference between the sea surface and the seabed, and the more energy is stored in a single tank.

“This is part of the reason why we want to try out the technology in Norway,” says Rainer Schramm. In his native country Germany the sea is too shallow for the system to be profitable, but there are many parts of the world where great water depths are located close inshore, such as the marine areas around Italy, Portugal and Spain, as well as North and South America.

This is an interesting development and it clearly has potential if its costs make it justifiable as a storage technology.

Links:

http://subhydro.com/

http://www.sintef.no/

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