Compressed-air-energy storage (CAES) is a way to store energy for later use using compressed air. At a utility scale, energy generated during periods of low demand can be released during peak load periods. The first utility-scale CAES project was in the Huntorf power plant in Elsfleth, Germany, and is still operational as of. Compression of air creates heat; the air is warmer after compression. Expansion removes heat. If no extra heat is added, the air will be much colder after expansion. If the heat generated during compression can be stored and used. CAES systems are often considered an environmentally friendly alternative to other large-scale energy storage technologies due to their reliance on naturally occurring resources, such as for air storage and ambient air as the working medium. Unlike Citywide compressed air energy systems for delivering mechanical power directly via compressed air have been built since 1870. Cities such as, France;, England;,, and, Germany; and,. In order to achieve a near- so that most of the energy is saved in the system and can be retrieved, and losses are kept negligible, a near-reversible or an is desired. Compression can be done with electrically-powered and expansion with or driving to produce electricity. Air storage vessels vary in the thermodynamic conditions of the storage and on the technology used: 1. Constant volume storage ( caverns, above-ground vessels, aquifers, automotive applications, etc.)2. Constant pressure. In 2009, the awarded $24.9 million in matching funds for phase one of a 300 MW, $356 million installation using a saline porous rock formation being developed near in.
