Electricity generation is the process of converting some form of energy into electricity. For electric utilities, it is the first process in the delivery of electricity to consumers. The other processes are electric power transmission and electricity distribution which are normally carried out by the electrical power industry. Electricity is most often generated by electro-mechanical generators, primarily driven by fuel combustion but also by other means such as the kinetic energy of flowing water and wind. There are many other technologies that can be and are used to generate electricity though, with solar photovoltaics being the most significant alternative currently.
Contents |
History
Centralized power generation became possible when it was recognized that alternating current power lines can transport electricity at very low costs across great distances by taking advantage of the ability to raise and lower the voltage using power transformers. Electricity has been generated for the purpose of powering human technologies since 1881, over 120 years, from various sources of energy. The first power plants were run on water power or coal,[3] and today we rely mainly on coal, nuclear, natural gas, hydroelectric, and petroleum with a small amount from solar energy, tidal harnesses, wind generators, and geothermal sources.
Electricity demand
![Coal fired power plants provide more than 50% of consumed electricity in the United States. Cleaner burning technologies continue to make coal fired power one of the cheapest ways to generate electricity[1]. This is the Castle Gate Plant near Helper, Utah.](http://wiki.bookrags.com/thumb/1/19/Grand_Junction_Trip_92007_098.JPG/180px-Grand_Junction_Trip_92007_098.JPG)
The demand for electricity can be met in two different ways. The primary method thus far has been for public or private utilities to construct large scale centralized projects to generate and transmit the electricity required to fuel economies. Many of these projects have caused unpleasant environmental effects such as air or radiation pollution and the flooding of large areas of land. Distributed generation creates power on a smaller scale at locations throughout the electricity network. Often these sites generate electricity as a by-product of other industrial processes such as using gas from landfills to drive turbines.
Methods of generating electricity
Turbines
Rotating turbines attached to electrical generators produce most commercially available electricity. Turbines are driven by a fluid which acts as an intermediate energy carrier. The fluids typically used are:
- Steam - Water is boiled by nuclear fission or the burning of fossil fuels (coal, natural gas, or petroleum). Some newer plants use the sun as the heat source: solar parabolic troughs and solar power towers concentrate sunlight to heat a heat transfer fluid, which is then used to produce steam. Another renewable source of heat used to drive a turbine is Geothermal power. Either steam under pressure emerges from the ground and drives a turbine or hot water evaporates a low boiling liquid to create vapour to drive a turbine.
- Water (hydroelectric) - Turbine blades are acted upon by flowing water, produced by hydroelectric dams or tidal forces,
- Wind - Most wind turbines generate electricity from naturally occurring wind. Solar updraft towers use wind that is artificially produced inside the chimney by heating it with sunlight.
- Hot gas (gas turbine) - Turbines are driven directly by gases produced by the combustion of natural gas or oil.
Combined cycle gas turbine plants are driven by both steam and gas. They generate power by burning natural gas in a gas turbine and use residual heat to generate additional electricity from steam. These plants offer efficiencies of up to 60%.
Reciprocating engines
Small electricity generators are often powered by reciprocating engines burning diesel, biogas or natural gas. Diesel engines are often used for back up generation, usually at low voltages. Biogas is often combusted where it is produced, such as a landfill or wastewater treatment plant, with a reciprocating engine or a microturbine, which is a small gas turbine.
Photovoltaic panels
Unlike the solar heat concentrators mentioned above, photovoltaic panels convert sunlight directly to electricity. Although sunlight is free and abundant, solar electricity is still usually more expensive to produce than large-scale mechanically generated power due to the cost of the panels. Low-efficiency silicon solar cells have been decreasing in cost though, and multijunction cells with close to 30% conversion efficiency are now commercially available. Over 40% efficiency has been demonstrated in experimental systems.[5] Until recently, photovoltaics were most commonly used in remote sites where there is no access to a commercial power grid, or as a supplemental electricity source for individual homes and businesses. Recent advances in manufacturing efficiency and photovoltaic technology, combined with subsidies driven by environmental concerns, have dramatically accelerated the deployment of solar panels. Installed capacity is growing by 40% per year led by increases in Germany, Japan, California and New Jersey.
Other generation methods
Various other technologies have been studied and developed for power generation. Solid-state generation (without moving parts) is of particular interest in portable applications. This area is largely dominated by thermoelectric (TE) devices, though thermionic (TI) and thermophotovoltaic (TPV) systems have been developed as well. Typically, TE devices are used at lower temperatures than TI and TPV systems. Piezoelectric devices are used for power generation from mechanical strain, particularly in power harvesting. Betavoltaics are another type of solid-state power generator which produces electricity from radioactive decay. Fluid-based magnetohydrodynamic (MHD) power generation has been studied as a method for extracting electrical power from nuclear reactors and also from more conventional fuel combustion systems. Electrochemical electricity generation is also important in portable and mobile applications. Currently, most electrochemical power comes from closed electrochemical cells ("batteries") [6], which are arguably utilized more as storage systems than generation systems, but open electrochemical systems, known as fuel cells, have been undergoing a great deal of research and development in the last few years. Fuel cells can be used to extract power either from natural fuels or from synthesized fuels (mainly electrolytic hydrogen) and so can be viewed as either generation systems or storage systems depending on their use.
Producers
In 2005, USA continued to remain as the top producer of electricity with a global share of at least 25% followed by China, Japan and Russia.
See also
| Energy Portal |
| Sustainable development Portal |
- Distributed generation
- Emissions & Generation Resource Integrated Database (eGRID)
- Electric power transmission
- Electric utility
- Electricity distribution
- Electricity retailing
- Energy development
- Environmental concerns with electricity generation
- Eugene Green Energy Standard
- Lineman
- Load profile
- Mains electricity
- Power quality
- Vehicle-to-grid
- Virtual power plant
- Voltage drop
- World energy resources and consumption
References
- ^ Net Generation by Energy Source by Type of Producer, (c. 2006), accessed 2007-04-26, Washington: U.S. Dept. of Energy, Energy Information Administration.
- ^ (French) DGEMP / Observatoire de l'énergie (April 2007). L’Electricité en France en 2006 : une analyse statistique.. Retrieved on 2007-05-23.
- ^ Pearl Street Station: The Dawn of Commercial Electric Power
- ^ Reuters News Service. "Mohave Power Plant in Nevada to Close as Expected", Planet Ark, December 30, 2005. Retrieved on 2007-07-16.
- ^ New World Record Achieved in Solar Cell Technology (press release, 2006-12-05), U.S. Department of Energy.
- ^ World's Largest Utility Battery System Installed in Alaska (press release, 2003-09-24), U.S. Department of Energy. "13,670 nickel-cadmium battery cells to generate up to 40 megawatts of power for about 7 minutes, or 27 megawatts of power for 15 minutes."
