Wind Power Without Wind

Diagram of the phere (Creditt: Alexander Slocum MIT)
In recent years more an more offshore wind farm projects have been emerging all over the world. Although many of them are capable of producing large amounts of power, depending on the wind can be tricky and unreliable at times. A new method developed by researchers at MIT could help alleviate that problem, by storing large amounts of power which can be used, on demand, whenever it’s needed.
Researchers from MIT developed a revolutionary new method that could make offshore wind farms much more practical sources of large scale clean energy. Although several projects currently in existence (like the British London Array offshore wind farm) as well as many planned projects (such as the Fukushima wind farm) can produce Giga watts of clean power using dozens (and even hundreds) of giant turbines, they are still prone to wind changes which can dramatically reduce the output of the farm.  
 
Countries looking to make substantial investments in off shore wind farms as energy sources face the problem that they will not be able to meet demand at all times, therefore backup (usually polluting, costly gas or coal power stations need to be built to back up and supplement wind farms). I there was a way to insure a continuous flow of electricity from the offshore farm to the costumers onshore at all times, more countries might be willing to invest in this form of green technology.
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The new method developed at MIT involves the placement of large concrete spheres on the seafloor, just under the wind turbine. The spheres, weighing thousands of tons each, will be used as both anchors to for the floating turbines, as well as a means of storing the energy they produce.
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The way the spheres function is quite simple. Each time the turbines produce more energy than needed (for instance during off-peak hours), the power would be diverted to a pump that will push away water from a 30-meter-diameter (98 feet) hollow sphere. When the energy will be needed again, the water would be allowed to flow back into the sphere operating a turbine on the way which will be attached to a generator that will produce energy.
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The researchers calculated that a single sphere in 400-meter (1300 feet) deep water could store up to 6 megawatt-hours of power. Having 1,000 spheres on the seafloor might ensure an uninterrupted power supply equal to that of a nuclear plant for several hours which should be enough to make the entire system much more reliable according to the researchers.
 
Another important advantage of the spheres is that they can be used almost immediately when needed, unlike a nuclear or coal energy plants which require hours until they can be turned on (and they can also be turned off just as quickly). The researchers also suggested that the sphere system will be grid-connected, so that it could also be used to store energy from other power sources as well such as solar arrays on shore which operate most efficiently at steady levels. This combination could potentially reduce the dependence on peak-power plants, which are typically considered to be less efficient and more polluting.
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Cost estimates conducted by the research team estimates that each sphere will cost about 12 million dollars and that a backup array of 1000 spheres will run at just over one billion dollars (far less that the cost of a comparable coal or nuclear power plant).
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The MIT team already tested a small scale model of the sphere and is looking to expend the testing into larger models whenever funding will become available.
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More information on the sphere system can be found on the MIT website as well as on the following detailed paper (paid PDF).