Power for when the wind won't blow

TXU’s power generation business, Luminant, is teaming up with Royal Dutch Shell’s wind business to build a new 3,000 megawatt wind turbine project in the Texas Panhandle.
The size of the project alone is noteworthy because it’s almost equal to the 3,352 megawatts of wind capacity the state currently has. But it’s also going to try to use a technology that could answer one of the biggest shortcomings of wind power, namely the variability of output, or the fact wind doesn’t always blow when you need the power the most.
As Luminant put it in the press release:

Shell and Luminant will also explore the use of compressed air storage, in which excess power could be used to pump air underground for later use in generating electricity. This technology will further improve reliability and grid usage and becomes more economical with large-scale projects, such as proposed for Briscoe County.

caes2 Ridge Energy has an animation of this picture on its web site under the “CAES Technology” tab on the left side of the screen.

A report done for the Texas State Energy Conservation Office by Ridge Energy Storage & Grid Services , a Houston company developing the technology, explains it this way:

Off-peak or excess electricity is used to “pre-compress” air, which is held for storage in an underground cavern, typically a salt cavern. When the CAES plant regenerates the power, the compressed air is released from the cavern and heated through a recuperator before being mixed with fuel (natural gas) and expanded through a turbine to generate electricity.
Because the turbine’s output no longer needs to be used to drive an air compressor, the turbine can generate almost three times as much electricity as the same size turbine in a simple cycle configuration, using far less fuel per MWh produced. The stored compressed air takes the place of gas that would otherwise have been burned in the generation cycle and used for compression power.

By the way, Shell said last week it will be moving its wind business under the gas and power business unit, a move that essentially mainstreams alternative energy.