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    Electricity Generation Background Information

    Definition

    Electricity generation is the process of creating electricity from other forms of energy.

    Basics

    Electricity generation 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.

    History

    Centralized power generation became possible when it was recognized that alternating current electric power lines can transport electricity at low costs 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 energy. Power plants are run on coal, nuclear, natural gas, hydroelectric, and petroleum power and a small amount from solar energy, tidal harnesses, wind generators, and geothermal sources.

    Electricity demand

    The demand for electricity can be met in two different ways. The main method is to build large centralized projects to generate and transmit the electricity required. 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 on the electricity network. These sites often generate electricity as a byproduct of other industry such as using gas from landfills to power 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.
    • water - 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 gases - 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 panels are expensive to produce and have only a 10-20% conversion efficiency. 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 solar capacity is growing by 30% per year in several regions including Germany, Japan, California and New Jersey.

    Topics of Interest

    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.

    History

    Centralized power generation became possible when it was recognized that alternating current power lines can transport electricity at 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, 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.

    Methods of generating electricity

    There are seven fundamental methods of directly transforming other forms of energy into electrical energy:

    • Static electricity, from the physical separation and transport of charge (examples: triboelectric effect and lightning)
    • Electromagnetic induction, where an electrical generator, dynamo or alternator transforms kinetic energy (energy of motion) into electricity
    • Electrochemistry, the direct transformation of chemical energy into electricity, as in a battery, fuel cell or nerve impulse
    • Photoelectric effect, the transformation of light into electrical energy, as in solar cells
    • Thermoelectric effect, direct conversion of temperature differences to electricity, as in thermocouples and thermopiles
    • Piezoelectric effect, from the mechanical strain of electrically anisotropic molecules or crystals
    • Nuclear transformation, the creation and acceleration of charged particles (examples: betavoltaics or alpha particle emission)

    Static electricity was the first form discovered and investigated, and the electrostatic generator is still used even in modern devices such as the Van de Graaff generator and MHD generators. Electrons are mechanically separated and transported to increase their electric potential.

    Almost all commercial electrical generation is done using electromagnetic induction, in which mechanical energy forces an electrical generator to rotate. There are many different methods of developing the mechanical energy, including heat engines, hydro, wind and tidal power.

    The direct conversion of nuclear energy to electricity by beta decay is used only on a small scale. In a full-size nuclear power plant, the heat of a nuclear reaction is used to run a heat engine. This drives a generator, which converts mechanical energy into electricity by magnetic induction.

    Most electric generation is driven by heat engines. The combustion of fossil fuels supplies most of the heat to these engines, with a significant fraction from nuclear fission and some from renewable sources. The modern steam turbine invented by Sir Charles Parsons in 1884 - today generates about 80 percent of the electric power in the world using a variety of heat sources.

    Turbines

    All turbines are driven by a fluid acting as an intermediate energy carrier. Many of the heat engines just mentioned are turbines. Other types of turbines can be driven by wind or falling water.

    Sources include:

    Steam - Water is boiled by:

    • Nuclear fission,
    • The burning of fossil fuels (coal, natural gas, or petroleum). In 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 natural 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%.
    • Renewables. The steam generated by:
      • Biomass
      • 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.
      • 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.
  • Other renewable sources:
    • 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, and are more properly seen as forms of solar thermal energy.

    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. However most large power grids also use Diesel generators, originally provided as emergency back up for a specific facility such as a hospital, to feed power into the grid during certain circumstances. 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 and multijunction cells with close to 30% conversion efficiency are now commercially available. Over 40% efficiency has been demonstrated in experimental systems. 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 Jersy.

    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. Osmotic power finally is another possibility at places where salt and sweet water merges (eg deltas, ...)

    Electrochemical electricity generation is also important in portable and mobile applications. Currently, most electrochemical power comes from closed electrochemical cells ("batteries"), 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.

    Environmental Concerns

    Most scientists agree that emissions of pollutants and greenhouse gases from electricity generation account for a significant portion of world greenhouse gas emissions; in the United States, electricity generation accounts for nearly 40 percent of emissions, the largest of any source. Transportation emissions are close behind, contributing about one-third of U.S. production of carbon dioxide.

    Did you know that...

    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.

    Large Dams such as Hoover Dam are able to provide large amounts of hydroelectric power; it has a 2.07 gigawatt capability.

    A coal-fired power plant in Laughlin, Nevada U.S.A. Owners of this plant ceased operations after declining to invest in pollution control equipment to comply with pollution regulations.

    Wind powered turbines provide reliable sources of electrical generation in conjunction with other methods of producing power.

    Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)

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