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A German engineer is patenting a device that can store energy on the seabed.
The device works in a similar way to a pumped storage hydroelectric plant. The pressure of the deep sea pushes water into tanks that sit on the seabed at 400-800m below the surface. The influx of water drives a turbine, which in turn drives a generator to produce electricity.
Once the tanks are full, electricity is used to run the turbine in reverse so that it pumps water out of the tanks. Although more energy is used to pump the water out of the system than is recovered from flooding it, calculations suggest that the efficiency of the system is around 80%. This is in line with conventional pumped storage plants.
Rainer Schramm, inventor and founder of the company Subhydro, is working with Scandinavian research organisation Sintef to develop the concept.
Schramm said: “We envisage that this type of storage plant will function well in conjunction with windfarms. At strong wind conditions, excess electricity is sent subsea to pump water out of the storage tanks. In periods with little wind, energy can be obtained from this underwater plant instead.”
He added that it could also work with solar installations to provide constant electricity at night when the sun is not shining.
The depth of the device will dictate how much energy it can generate. The deeper it sits on the sea floor the greater the pressure of the water and so the more energy it can store in a single tank.
But one of the challenges of turning the concept into reality is developing a type of concrete that can be used to cast the water tanks and that is strong enough to withstand the pressure.
Tor Arne Martius-Hammer, from Sintef Building and Infrastructure, said: “The challenge is to find the optimal balance between strength and cost. 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%.
“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.”
One option being investigated is to reinforce the concrete with thin steel fibres.
Trials of the device are slated to take place in Norway.