power, electric: Sources of Electrical Energy

Electrical energy occurs naturally, but seldom in forms that can be used. For example, although the energy dissipated as lightning exceeds the world's demand for electricity by a large factor, lightning has not been put to practical use because of its unpredictability and other problems. Generally, practical electric-power-generating systems convert the mechanical energy of moving parts into electrical energy (see generator). While systems that operate without a mechanical step do exist, they are at present either excessively inefficient or expensive because of a dependence on elaborate technology. While some electric plants derive mechanical energy from moving water (hydroelectric power), the vast majority derive it from heat engines in which the working substance is steam. Roughly 89% of power in the United States is generated this way. The steam is generated with heat from combustion of fossil fuels or from nuclear fission (see nuclear energy; nuclear reactor).

Sections in this article:

• Introduction
• Reactive Power
• Transmission of Electrical Energy
• Alternative Energy Sources
• Environmental Concerns
• Steam as an Energy Source
• Sources of Electrical Energy
• Bibliography

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