Tuesday, April 30, 2013

Clever MIT floating wind turbines can store power for when the wind doesn't blow

by , Michael Graham Richard
Taming the ocean windWind and solar are growing rapidly worldwide, but because the sun doesn't always shine and the wind doesn't always blow, we need to find more ways to store energy. That's a huge challenge, and we'll probably end up using a mix of technologies to reach that goal (for example, grid-scale liquid-metal batteries look promising). A clever new way to do that was invented by MIT researchers, combining both the production of clean energy and - when needed - its storage.
At first glance, their system might look like a regular offshore wind farm. But what happens beneath the surface is what makes all the difference. When the wind is blowing and there is demand for electricity in the grid, the turbines act just as any offshore wind turbines would. But when the wind is blowing and there's not enough demand for electricity on the grid to soak up that power, or when there's demand but no wind, that's when things get interesting:
The key to this concept is the placement of huge concrete spheres on the seafloor under the wind turbines. These structures, weighing thousands of tons apiece, could serve both as anchors to moor the floating turbines and as a means of storing the energy they produce.
Whenever the wind turbines produce more power than is needed, that power would be diverted to drive a pump attached to the underwater structure, pumping seawater from a 30-meter-diameter hollow sphere. (For comparison, the tank’s diameter is about that of MIT’s Great Dome, or of the dome atop the U.S. Capitol.) Later, when power is needed, water would be allowed to flow back into the sphere through a turbine attached to a generator, and the resulting electricity sent back to shore. (source)
A single 25-meter sphere at a depth of 400 meters could store up to 6 megawatt-hours of power, so a large offshore wind farm with hundreds or even thousands of those could become a giant on-demand battery, potentially producing as much power as large power plants (it all depends on how far you scale up the idea). These anchor/storage spheres could be built on land and then brought out to sea. No need for too much super-expensive deep sea construction.
Preliminary estimates indicate that one such sphere could be built and deployed at a cost of about $12 million, Hodder says, with costs gradually coming down with experience. This could yield an estimated storage cost of about 6 cents per kilowatt-hour — a level considered viable by the utility industry.
And since the wind farm has to be connected to the grid anyway, you could use power from other surplus sources to pump water, such as solar.
Update: This is similar to a Canadian concept that Lloyd wrote about a couple years ago, check it out: How To Store Wind Power: Pump It Into A Big Underwater Balloon. These balloons couldn't act as anchors for floating turbines, but in some other situations (wind farms in shallower waters, for example), they might actually be much more cost-effective.