ENERGY CONVERSION

the transformation of energy from forms provided by nature to forms that can be used by humans. Over the centuries a wide array of devices and systems has been developed for this purpose. Some of these energy converters are quite simple. The early windmills, for example, transformed the kinetic energy of wind into mechanical energy for pumping water and grinding grain. Other energy-conversion systems are decidedly more complex, particularly those that take raw energy from fossil fuels and nuclear fuels to generate electrical power. Systems of this kind require multiple steps or processes in which energy undergoes a whole series of transformations through various intermediate forms. Many of the energy converters widely used today involve the transformation of thermal energy into electrical energy. The efficiency of such systems is, however, subject to fundamental limitations, as dictated by the laws of thermodynamics and other scientific principles. In recent years, considerable attention has been devoted to certain direct energy-conversion devices, notably solar cells and fuel cells, that bypass the intermediate step of conversion to heat energy in electrical power generation. This article traces the development of energy-conversion technology, highlighting not only conventional systems but also alternative and experimental converters with considerable potential. It delineates their distinctive features, basic principles of operation, major types, and key applications. For a discussion of the laws of thermodynamics and their impact on system design and performance, see thermodynamics. Additional reading The concept of energy General introductions are provided by Richard P. Feynman, Robert B. Leighton, and Matthew Sands, The Feynman Lectures on Physics, 3 vol. (196365; vol. 1 and 2 have been reprinted, 1977); Mitchell Wilson, Energy, rev. ed. (1970); Energy: Readings from Scientific American, with introductions by S. Fred Singer (1979); and Janet Ramage, Energy: A Guidebook (1983). History of energy-conversion technology Historical developments are outlined in Charles Singer et al. (eds.), A History of Technology, 8 vol. (195484); Maurice Daumas (ed.), Histoire gnral des techniques, 5 vol. (196279)the first 3 vol. have been translated as A History of Technology and Invention: Progress Through the Ages (196979); and Melvin Kranzberg and Carroll W. Pursell, Jr. (eds.), Technology in Western Civilization, 2 vol. (1967). The Editors of the Encyclopdia Britannica