Another Advance for Renewable Energy
|March 29, 2007||Posted by Staff under Progress Report, The Progress Report|
Another Advance for Renewable Energy
Saving Wind Energy for Calm Days
Here are excerpts of an article appearing recently in the Star Tribune (Minneapolis, Minnesota, U.S.).
How do you store the wind?
by Mike Meyers
Wind power is clean and renewable. Now a group of utilities in Iowa, Minnesota and the Dakotas has a plan to make it reliable.
Using existing technology, backers plan to spend $200 million for a “wind storage” project that would be under construction in 2009 and in service in 2011.
“It really gives wind energy a much greater value. It’s essentially a ‘battery’ for wind energy,” said Bob Haug, executive director of the Iowa Association of Municipal Utilities.
While Xcel Energy and the federal government also are experimenting with ways to “store” wind power in the form of hydrogen, the Iowa Stored Energy Park would employ a far simpler strategy. Wind parks in Iowa, Minnesota and the Dakotas would ship energy over the power grid to a rural site outside Des Moines, about 230 miles south of the Twin Cities.
Three thousand feet below the surface outside Des Moines, a sandstone aquifer (caverns that now hold water) will be injected with pressurized air, with the air temporarily displacing some of the water. The electricity from wind turbines will power the compressors. A pipe will deliver underground air compressed to 900 to 1,000 pounds per square inch. The compression of millions of cubic feet of air will be scheduled for nights and weekends, when wind power often sells for next to nothing.
Wind parks pay for themselves when demand and electricity rates are higher — during weekdays and on hot summer days. But when electricity is most needed, sometimes the wind isn’t blowing.
The stored energy park would get around that problem by slowly releasing the pressurized air from the aquifer to provide most of the energy needed to turn the blades of a generator otherwise powered by natural gas. Metered valves would control the release of the pressurized air. Similar operations already are used to store natural gas underground across the nation.
The cavern complex would produce 268 megawatts of electricity to be sold to Midwest utilities on the grid. That’s enough to turn on the lights in 268,000 homes.
Kent Holst, development director of the stored energy park, said the plan could transform the economics of wind power.
With the storage park option, the utility owners will be able to store and produce energy at a price equivalent to 6.5 cents per kilowatt hour, then sell the energy at peak times for 8 to 10 cents a kilowatt hour.
“That’s where we make our money,” Holst said.
Similar plants already are operating in Alabama and Germany.
Planners surveyed more than 100 sites to find an aquifer with exactly the right geological characteristics — porous rock capped by shale or some other hard stone, before leasing the Iowa site from the owners of the land 3,000 feet above the aquifer.
The aquifer that would be affected in the caverns is so deep that no one uses its water. What’s more, as air is stored in the caverns, the water seeps into sandstone nearby, they said. When the air pressure falls, the water returns, so there is no permanent disruption to the aquifer.
“We expect [the project] to produce the lowest-cost energy to serve the intermediate loads of our citizen-owners,” Haug said. “It will do so in an environmentally friendly way that reduces emissions of greenhouse gases and adds to the value of wind energy.”
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