Compressed air energy-storage (CAES) is a concept for electric utility application which stores energy generated during periods of low demand and releases that energy during peak demand periods. Air is compressed during low demand periods by motor-driven compressors and stored in large underground reservoirs. When power is required, the air is heated by burning fuel in combustion chambers, and expanded in turbines to drive electric generators. CAES technology appears to be one of the most attractive near-term energy storage options for utilities. This is reflected in the currently operating CAES plant in West Germany and the present American CAES technology and demonstration programs.
Compressed air energy storage (CAES) is a concept for electric utility application which stores energy generated during periods of low demand and releases that energy during peak demand periods. Air is compressed during low demand periods by motor-driven compressors and stored in large underground reservoirs. When power is required, the air is heated by burning fuel in combustion chambers, and expanded through gas turbines to drive electric generators (Fig. 1). CAES technology appears to be one of the most attractive near-term energy storage options for utilities. This is reflected in the current CAES plant experience in West Germany (Herbst, Hoffeins, and Stys, 1979) and the present American CAES technology and demonstration programs. As an energy storage technology, CAES provides load management (as mentioned above) and a degree of flexibility and control in system operation, e.g., frequency stabilization, along with other advantages. It is essentially a spinning reserve because it can be started rapidly to provide supplemental generation in emergencies. Replacement of gas turbine peaking plants by CAES plants in the United States could result in annual savings of more than 100,000,000 barrels of oil. CAES plants are not limited by the siting difficulties faced by conventional pumped hydro plants. A CAES system for an individual utility requires an appropriate geological formation for the underground storage of compressed air. Three broad classes of rock are reservoir candidates: hard rock, rock salt, and porous rock. Investigations are underway to establish stability criteria for long-term operation of reservoirs in these media without unacceptable degradation. A key question about the future of CAES plants is their dependence on petroleum fuels, a dependence which could become a barrier to large scale utility use. Studies in progress examine advanced CAES concepts requiring little or no petroleum fuels. This paper is based on CAES programs sponsored by the United States Department of Energy. First, preliminary reservoir stability criteria are presented. Second, analyses of several advanced (no-petroleum),concepts are examined. Turbomachinery for CAES plants is not an issue, because manufacturers are willing to provide this equipment with standard guarantees. CAES RESERVOIRS Integral to the CAES concept is a large underground cavern for pressurized air. Air at pressures between 5 MPa (50 atm) and 10 MPa (100 atm) is to be stored and cycled on a daily basis.' As a result, the reservoirs undergo daily pressure, temperature, and humidity fluctuations.
