Wind Power… With no Wind!

As we all know, when the wind is blowing, the electricity is generating. When it’s not, it stops. The problem of storing wind-generated energy for the times when the wind isn’t blowing is one that occupies us as much as new wind turbine designs does.  But a revoloutionary approach from researchers at the world renowned Massechussetts Institute of Technology (MIT)  could go some way to solving the storage of wind-generated energy.

WindEnergyStorage 300x1951 Wind Power... With no Wind!

The idea is to place huge concrete spheres weighting thousands of tons on the seafloor under offshore “floating” wind turbines. These structures 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 extra power would be diverted to drive a pump attached to the underwater structure, pumping seawater from a 30-meter-diameter hollow sphere.  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. It’s a sort of wind/hydro-electric hybrid.

Is it practical? A 25-meter sphere in 400-meter-deep water could store up to 6 megawatt-hours of power, the MIT researchers have calculated; that means that 1,000 such spheres could supply as much power as a nuclear plant for several hours — enough to make them a reliable source of power. If you had 1,000 wind turbines anchored by the spheres, they would, on average, replace a conventional on-shore coal or nuclear plant. A further boon would be that, unlike nuclear or coal-fired plants, which take hours to gear up, this energy source could be made available within minutes and then taken offline just as quickly.

The system would be grid-connected, so the spheres could even be used to store energy from other sources, including solar arrays on the shore.

The people behind this concept are Alexander Slocum, the Pappalardo Professor of Mechanical Engineering at MIT and Brian Hodder, a researcher at the MIT Energy Initiative, plus three MIT alumni and a former high school student who worked on the project. There are some other issues to overcome before the project becomes feasible and practical. For one, a barge woukld beed to be constructed to take out the land-cast concrete spheres. No existing vessel exists that could be towed out to sea with this capacity.

The costs may at first look prohibitive. Just one such sphere could be built and deployed at a cost of about $12 million. But Hodder says costs will gradually come down with experience and economies of scale. This could yield an estimated storage cost of about 6 cents per kilowatt-hour — a evel considered viable by the utility industry. Hundreds of spheres could be deployed as part of a far-offshore installation of hundreds of floating wind turbines, the researchers say. To begin with the speheres and floating turbines would have to be seated in deeper water than most off-shore wind farms, but that has an advantage in that winds tend to blow stronger the further one goes from coastal waters.  The team calculated that the optimal depth for the spheres would be about 750 meters, though as costs are reduced over time they could become cost-effective in shallower water.

Slocum and some of his students built a 30-inch-diameter prototype in 2011, which functioned well through charging and discharging cycles, demonstrating the feasibility of the idea. The researchers estimate that an offshore wind farm paired with such storage spheres would use an amount of concrete comparable to that used to build the Hoover Dam — but would also supply a comparable amount of power.

Enemies of wind power will be quick to snipe and say that cement production is a major source of carbon-dioxide emissions. However the team calculated that the concrete for these spheres could be made, in part, using large quantities of fly ash from existing coal plants — material that would otherwise be a waste product — instead of cement. The researchers calculate that over the course of a decade of construction and deployment, the spheres could use much of the fly ash produced by U.S. coal plants and create enough capacity to supply one-third of U.S. electricity needs.