Thermal energy storage

Heat storage is an essential ingredient in almost every energy conversion system. The batteries in automobiles, the reservoir in a hydroelectric plant, oil stored underground in porous formations, and the coal pile outside a fossil-fuel power plant are examples of storage which are taken for granted. Yet, when it comes to advanced and novel energy systems, people often regard storage as something to be put aside until after the main parts of the system have been studied in detail. Many researchers and scientists do not find storage as interesting or glamorous a topic as, for example, concentrating and collecting solar energy. But a closer examination shows that storage holds challenging problems which need successful solutions before an efficient energy system can be realized. An understanding of the requirements of a storage system, the alternative storage strategies available, and the operating characteristics of available storage systems are of importance to the energy system designer. This article focuses on those aspects of storage. First, a discussion in general terms of the need for storage points out the characteristics to look for in a candidate storage strategy and describes, in brief, the characteristics of currently available options for energy storage. Second, the techniquesmore » used in a specific class of storage devices, namely, heat storage devices, together with their operating characteristics are examined, concluding with a discussion of latent heat storage devices.« less