Engineering Ocean

Concrete Balls Store Wind Energy Power

The idea is brilliant: Why not to save energy in huge, hollow concrete balls at the bottom of the sea? If this works be tested soon in Lake Constance. If the concrete balls to withstand and proven technology, offshore wind farms could be equipped with balls that can store 20 MWh per piece.

The buffer system, engineers of the Essen construction Hochtief Group and Fraunhofer Institute for wind energy and energy system technology in Kassel have concocted, consists of hollow concrete spheres with a diameter of 30 meters. You have three-meter thick concrete walls and should be anchored on the sea floor right next to offshore wind farms.

Store Wind Energy Power
The concrete balls are empty, water can be taken, which drives a turbine. With excess electricity, the water can be pumped out again. Photo: Hochtief solutions

Each ball weighs around 10,000 tons

Is on land power, opens a valve at the top of the balls. Sea water shoots an enormous pressure in the cavity.

Because the balls are part of the wind farms, energy via the connection cables can be transported to the Mainland. Excess electricity is produced, for example, in the night, then used the concrete ball empty to pump again.

20 mega watt hour capacity per ball

System, and thus the energy of incoming water works best if the balls at a water depth of 500 meters and more be positioned, because the water pressure with increasing depth. With today’s technology pump allowing to set it up on 700 meters maximum. A 30-meter ball can store up to 20 megawatt per hours.

Vacuum Store Wind Energy Power
The concrete balls are empty, water can be taken, which drives a turbine. With excess electricity, the water can be pumped out again. Photo: Hochtief solutions

The advantages of this technology are enormous: the pumped storage power plants rely on the infrastructure of the wind farms and they are deep on the seabed, without disturbing. Conventional pumped storage power plants need large areas, landscape consumption by upper and lower Lakes would be enormous to cover only a portion of storage needs.

Vacuum Wind Energy Power
To pour the concrete balls, Hochtief has developed an inner casing tubes, which can be later removed through the opening at the top of the ball and use it again.

The concrete balls, however, may be on the ocean floor and can store excess electricity volumes of wind farms without great losses. Hochtief and Fraunhofer engineers speak of a to the 85 percent efficiency. To serve as a buffer of offshore wind farms would have to be installed between 80 and 200 bullets. That would be a capacity between 1600 and 4000 megawatt-hours.

Wind farm should have 80 to 200 balls anchored

If the technique works, Hochtief and Fraunhofer want to test in the fall at Lake Constance on a scale of 1:10. A concrete sphere with a diameter of three meters and a weight of 20 tonnes already poured Hochtief engineering in Frankfurt am Main.

It is stationed in the autumn in the Bodensee at Überlingen in a water depth of 100 meters, to test the system named Stensea (stored energy in the SEA, so energy storage in the sea). The test run is to take four weeks. The project is funded by the Federal Government within the framework of the energy revolution.

Also with concrete balls under water, researchers at the Massachusetts follow a similar concept, Institute of technology in Cambridge in the United States. Researchers of the Canadian company hydro store want to use instead of the concrete ball huge underwater balloons, which are pumped up and emptied. Even Belgian engineers have devised an unusual concept. An artificial island with a large hole want to shower on off the coast in the middle. They want to save so excess offshore energy by changing water levels.