Dependable electricity generation, transmission and distribution became important when it became apparent that electricity was useful for providing heat light and power for human activities. Decentralised power generation became possible when it was recognised that alternating current electric power lines can transport electricity at low cost across great distances by taking advantage of the ability to transform the voltage using power transformers.
Electricity has been generated for the purpose of powering human technologies for at least 120 years from various sources of potential energy. The first power plants were run on wood, while today we rely mainly on oil, natural gas, coal, hydroelectric and nuclear power and a small amount from hydrogen, solar energy, tidal harnesses[?], and wind generators. The generation and distribution of electricity has mostly been in the hands of either privately owned or state owned public utilities. In recent years some governments have started to privatise or corporatise these utilities as part of a move to introduce market forces to monopolies. The New Zealand Electricity Market is a typical example.
The demand for electricity can be fed in two different ways. The primary method thus far has been for public utilities to construct large scale projects to generate and transmit the electricity required to fuel growing economies. Many of these projects have unpleasant environmental effects such as air or radiation pollution, vulnerability to terrorist attacks and the flooding of large areas of land.
Increasingly, distributed generation is seen as a new way to supply the electrical demand close to the users. Smaller, distributed projects can:
Turbines are usually rotated using using steam, water, wind or other fluid as an intermediate energy carrier.
Nuclear reactors use the energy created by the fission of radioactive plutonium or uranium to generate heat. They often use a primary and secondary steam circuit to add an additional layer of protection between the location of the nuclear fuel and the generator room.
Hydroelectric power plants use water flowing directly through the turbines to power the generators.
Tidal harnesses[?] use the force of the moon on bodies of water to spin a turbine.
Wind generators use wind to turn turbines that are hooked up to a generator.
Co-generation plants combine the generation of electricity and heat using solar power, fossil fuels, syngas, biomass, or biogas as a fuel source. Heated steam turns a turbine, and then excess heat is distributed through a district energy system[?] for space heating in buildings, industrial processes or green house heat.
These plants can achieve efficiencies as high as 80%, but many of these plants being built today only expect to achieve stated maximum 55% efficiencies.
The ability to achieve tri-generation[?] using fossil fuels or solar energy to generate heat, electricity and evaporative cooling exists. These combined power plants have the best energy conversion ratio after hydroelectric plants.
Small mobile generators are often driven by diesel engines, especially on ships, remote building sites or for emergency standby.
The world relies mainly on coal and natural gas for power. The high capital requirements of nuclear power and the fear of the dangers of nuclear power have prevented the ordering of any new nuclear power plants in North America since the 1970s.
Electricity reform around the world is de-coupling electricity generation from the regulated natural monopoly elements of transmission and electricity distribution (see for example New Zealand Electricity Market).
See also distributed generation.