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Large-Scale Electricity Storage Could Come from Offshore Pumped Hydroelectric Plants

Efficient grid-scale storage and energy conversion solutions are key components to a smarter and more robust grid, especially with more renewable energy sources entering the market.

Almost all (99%) large-scale electricity energy storage in the world uses pumped hydro technology, and a recent design for offshore energy storage from MIT takes that model and puts it at the bottom of the ocean. And now it looks like there’s another contender for energy storage solutions exploiting the pressure differential at the seabed, this time from Subhydro in Norway.

“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” – Rainer Schramm, inventor and founder of Subhydro AS

Instead of pumping water uphill to store energy potential, this type of storage device would let water flow into underwater tanks under its own pressure, spinning a turbine and generator as it fills. Once the tanks are full, the turbine can be reversed in order to remove the water to begin the cycle again. In essence, pumping the tanks empty “charges” the device, and opening the feed mechanism and letting the water flow in generates the electricity.

“We envisage that this type of storage plant will function well in conjunction with, for example, wind farms. 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. The same applies to solar generation: the pumped storage power station can contribute to constant electricity production at night time when there is no sunshine to run a solar power plant.” – Schramm

According to Subhydro, their system (at between 400 and 800 m deep) has an electric storage efficiency of about 80% round-trip, which is comparable to conventional onshore installations (pumping out the water from these undersea tanks consumes a little more energy than can be recovered through filling them).

This offshore pumped hydro system can be sized up to meet greater electrical demand or storage needs, through adding more tanks to the system for higher capacity, and through installing them at greater depths under the ocean (where there is a higher pressure differential). Subhydro says their system is patent-pending, and are currently working to develop a type of concrete that is strong enough to handle the pressures, while also remaining cost-effective.

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