Electricity generation

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

The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday. His basic method is still used today: electricity is generated by the movement of a loop of wire, or disc of copper between the poles of a magnet.^[1]

For electric utilities, it is the first process in the delivery of electricity to consumers. The other processes, electric power transmission, electricity distribution, and electrical power storage and recovery using pumped storage methods are normally carried out by the electrical power industry.

Electricity is most often generated at a power station by electromechanical generators, primarily driven by heat engines fueled by chemical combustion or nuclear fission 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 such as solar photovoltaics and geothermal power.

Sources of electricity in the U.S. in 2009^[2] fossil fuel generation (mainly coal) was the largest source.

History

Sources of electricity in France in 2006;^[3] nuclear power was the main source.

Centralised power generation became possible when it was recognised 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 at central stations since 1881. The first power plants were run on water power^[4] or coal,^[5] 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, thermopiles, and Thermionic converters.
• 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

Large dams such as Three Gorges Dam in China can provide large amounts of hydroelectric power; it will have a 22.5 GW capability.

Susquehanna Steam Electric Station, a nuclear power plant.

A combined cycle natural gas power plant near Orem, Utah.

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.

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.^[6]

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.^[7] 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

Wind-powered turbines usually provide electrical generation in conjunction with other methods of producing power.

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 (e.g. deltas, ...)

Electrochemical electricity generation is also important in portable and mobile applications. Currently, most electrochemical power comes from closed electrochemical cells ("batteries") ^[8], 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.

Cost of generating electricity

Production by country

Electricity output in 2005

The United States has long been the largest producer and consumer of electricity, with a global share in 2005 of at least 25%, followed by China, Japan and Russia.

As of Jan-2010, total electricity generation for the 2 largest generators were as follows:

USA: 3992 billion KWh

China: 3715 billion KWh

Environmental Concerns

Most scientists agree that emissions of pollutants and greenhouse gases from fossil fuel-based 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^[9] .

In the United States, fossil fuel combustion for electric power generation is responsible for 65% of all emissions of sulfur dioxide, the main component of acid rain^[10]. Electricity generation is the fourth highest combined source of NOx, carbon monoxide, and particulate matter in the US ^[11].

See also

References

Large dams such as Hoover Dam can provide large amounts of hydroelectric power; it has a 2.07 gigawatt capability.

1. ↑ 'The Institution of Engineering & Technology: Michael Faraday'
2. ↑ http://www.eia.doe.gov/cneaf/electricity/epm/table1_1.html
3. ↑ (French) DGEMP / Observatoire de l'énergie (April 2007). "L’Electricité en France en 2006 : une analyse statistique." (PDF). http://www.industrie.gouv.fr/energie/statisti/pdf/elec-analyse-stat.pdf. Retrieved 2007-05-23. 
4. ↑ In 1881, under the leadership of Jacob Schoellkopf, the first hydroelectric generating station was built on Niagara Falls.
5. ↑ Pearl Street Station: The Dawn of Commercial Electric Power
6. ↑ Reuters News Service (2005-12-30). "Mohave Power Plant in Nevada to Close as Expected". Planet Ark. http://www.planetark.com/dailynewsstory.cfm/newsid/34265/story.htm. Retrieved 2007-07-16. 
7. ↑ New World Record Achieved in Solar Cell Technology (press release, 2006-12-05), U.S. Department of Energy.
8. ↑ 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."
9. ↑ Borenstein, Seth (2007-06-03). "Carbon-emissions culprit? Coal". The Seattle Times. http://seattletimes.nwsource.com/html/nationworld/2003732690_carbon03.html. 
10. ↑ http://www.epa.gov/air/sulfurdioxide/
11. ↑ http://www.epa.gov/cgi-bin/broker?_service=airdata&_program=progs.webprogs.emcatbar.scl&_debug=2&geotype=us&geocode=USA&geoname=United+States&epol=CO+NOX+VOC+SO2+PM25+PM10&years=2002&mapsize=zsc&reqtype=viewmap

External links

• Power Technologies Energy Data Book
• [1] NOW on PBS: Power Struggle
• This Week in Energy (TWiEpodcast)