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Sea Eggs

Could “sea eggs” solve our energy storage problem?

According to Rebecca Harrington in Tech Science European countries have added so much renewable energy generation that they are undermining electricity grids that were designed for large-scale fossil fuel generation:

“Since renewable energies like wind and solar can’t provide energy 24/7, battery storage captures it for when the wind’s not blowing and the sun’s not shining.  Countries need to update their electricity grids and add more storage before they will be able to fully capture all the renewable energy they can now generate.”

Adding even more renewables at this stage just means more wind turbines standing idle on windy days when there is surplus capacity. Until some means of mass storage can be developed, we are in something of a bind.  The problem is that battery storage is currently too expensive, inefficient and dependent upon scarce materials to provide a solution.  However, looking to batteries to solve our problems may be further evidence of what critics refer to as “techno-utopianism” – the belief that advanced technology is always the answer to our problems.  In fact, the most effective “batteries” are already in use.  They are the large artificial lakes built in mountainous areas to provide hydroelectric power when demand spikes.  They work by using excess electricity to pump water into the mountain lake during times when demand is low; then releasing the water through turbines to generate electricity when demand peaks.

Unfortunately, there are only so many mountain valleys that we can flood.  And since most also contain people’s homes and businesses, flooding them might not be the most popular course of action.  For this reason, energy planners have tended to look elsewhere for solutions to the storage problem.  But there is a place where nobody lives, where there are massive mountains, where we could deploy this kind of large scale hydroelectric storage.  It is called the seabed.

Obviously the seabed is already full of water.  That’s the point, according to scientists on the German StEnSea (Storing Energy at Sea) project.  Their idea is to use “sea eggs” – hollow concrete spheres, 30 meters in diameter– anchored to the sea bed:

“The sphere is flooded whenever electrical power is needed. As the water streams in it drives a turbine that produces electricity which is fed into the grid. If there is an energy surplus in the grid, the water is pumped out of the sphere and the energy is stored until it is released again the next time the sphere is filled.  In a model, 200 such spheres each drive a turbine. The individual spheres achieve 20 megawatts each. This means that a park with 200 spheres on the seabed would make four gigawatts available within a few hours for storage or equalisation.”

Much will depend upon the cost of building and deploying the spheres together with the amount of energy that can be recovered when needed.  Nevertheless, it is one of those low-tech ideas, based on readily available materials that may well have a part to play in a low-carbon future.

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