A compressed-air energy storage (CAES) unit in the U. S

Soyland Power Cooperative, Inc., a Decatur, Illinois-based co-op, could get reasonably priced baseload power from neighboring utilities' coal and nuclear plants, and even had one coal plant of its own planned for the near future, as well as a share in a nuclear plant; but peaking power, generated by costly oil and gas to instantly meet sudden surges in demand, was another story. CAES splits the two basic stages of a conventional gas turbine, making the most of baseload power, while using the least peaking or intermediate fuel. During off-peak periods, inexpensive baseload electricity from coal-fired or nuclear power plants runs a combination motor-generator in a motor mode, which in turn operates a compressor. Air is compressed, cooled, and pumped into an underground storage reservoir hundreds of thousands of cubic yards in volume and about two thousand feet ( about610m) below the surface. There the air remains, at pressures up to about 60 atm (6.1 MPa), until peaking or intermediate power is required. Then, the air is released into a combustor at a controlled rate, heated by oil or gas, and expanded through a turbine. The turbine drives the motor-generator in a generator mode, thereby supplying peaking or intermediate powermore » to the grid.« less