Compressed Air Underground Battery for Wind Farms

Wind energy may become even more important if the Iowa Association of Municipal Utilities succeeds in launching an innovative wind-powered compressed air energy storage (CAES) facility project they are working on. CAES technology uses off-peak wind turbine generated electricity to pump compressed air into an underground aquifer for use in later generation. The concept of using stored compressed-air energy to help generate electricity is more than 30 years old. Two plants currently exist—an 11-year-old plant in McIntosh, Ala., and a 23-year-old plant in Germany, both with the compressed air stored in caverns created by salt deposits. For you non-engineers, there's a step-by-step explanation after the fold. Caveat: from an environmental standpoint, CAES is not suitable for every wind farm. Saturating free-moving groundwater with pressurized air would change the redox state while the added carbon dioxide would dissolve calcite, with the combined effect of mobilizing metals. The result could be unfortunate for nearby well owners and would lessen energy efficiency. And CAES is definitely not something to try around a deep waste injection well that has previously accepted volatile hazardous wastes. CAES technology, in otherwords, is suitable for locations where natural underground vaults, essentially places where groundwater can be put under pressure and not flow outward due to that pressure, already exist and have not been contaminated. Having said that, this is a pretty cool innovation. For once Iowa beats Minnesota.CAES steps. This is essentially a peaking power design.

Wind turbines generate electricity which can flow directly to grid or, alternatively, power the site's air compressor bank.

Compressors run at "off peak" times when wind happens to be blowing strongly, but regional electricity demand is low, driving air down into a subterranean cavern of sorts.

Compressed air driven underground both dissolves in, and temporarily displaces, groundwater. The horizonatally displaced water is "contained" by surrounding aquitards, however, so the air remains under pressure for extended periods, ready to be let back up the pipes to the surface when needed. When air pressure is reduced, the previously displaced groundwater flows back toward the zone of lowered pressure, which is now under the "dome". This is the "battery-like" part of the design.

Air flowing back up the pipes, toward the non-wind turbines, is pre-heated by the combustion of natural gas...Our reading of the design narrative indicates this heating is from in-situ' combustion, not requiring a heat exchanger..., further increasing the air's pressure, prior to it's passing through the turbine blade chambers.

The hot compressed air turns the turbine blades just as would flowing water as it passes through a hydroelectric generator.

The turbines turn dynamos that generate electricity for the regional grid at peak demand periods.

"Rinse and repeat".