Norwegian research scientists will contribute to realizing the concept of storing electricity at the bottom of the sea. The energy will be stored with the help of high water pressure. The idea of an underwater pumped hydroelectric power plant may sound like Jules Verne fiction, but then it was hatched by a German engineer who has spent much of his professional life working in aerospace technology.
“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,” explains Rainer Schramm, inventor and founder of the company Subhydro AS to Gemini.no. He has joined forces with Scandanavian research institute SINTEF in order to realize the concept.
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. In this pumped storage power plant, a turbine will be connected to a tank on the seabed at a depth of 400-800 meters. 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. One can connect as many tanks as one wishes. In other words, it is the number of water tanks that decides how long the plant can generate electricity, before the energy storage capacity is exhausted.
When the water tanks are full, the water must be removed from the tanks. This is achieved by running the turbine in reverse, so that it functions as a pump. The process consumes energy from the power grid, just as when one charges an ordinary battery. Although a bit more energy is used to empty the water tanks than can be recovered from flooding them, the degree of efficiency of this type of power plant is just as high as that of a conventional, onshore plant. Calculations indicate an electric storage efficiency of approximately 80 per cent round-trip.
One of the challenges faced by the SINTEF research scientists is to develop a type of concrete that can be used to cast the water tanks that are placed on the seabed. One of the solutions SINTEF will work on is reinforcing the concrete with thin steel fibers instead of the normal steel rebar. This will result in a significant simplification of the production process.