Electricity generation

Electricity generation is the process of generating electric energy 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, electricity transmission, distribution, and electrical power storage and recovery using pumped storage methods are normally carried out by the electric 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.

History

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, this is most used form for generating electricity, it is based on Faraday's law, can be experimented by simply rotating a magnet within closed loop of a conducting material (e.g Copper wire)
• 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. Charge carriers are separated and physically transported to a position of increased 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 potential 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) currently 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
    • Solar thermal energy (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.
    • Ocean thermal energy conversion (OTEC ): uses the small difference between cooler deep and warmer surface ocean waters to run a heat engine (usually 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.^[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

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

The production of electricity in 2008 was 20,261TWh, which was 11% of the solar energy the earth receives in one hour (174,000TWh). Sources of electricity were fossil fuels 67%, renewable energy 18%, and nuclear power 13%. The majority of fossil fuel usage for the generation of electricity was of coal and gas. Oil was only 5.5%. Ninety-two percent of renewable energy was hydroelectric followed by wind at 6% and geothermal at 1.8%. Solar photovoltaic was 0.06%, and solar thermal was 0.004%. Data are from IEA/OECD (2008)^[9]

data source IEA/OECD

Total energy consumed at all power plants for the generation of electricity was 4,398,768 ktoe (kilo ton of oil equivalent) which was 36% of the total for primary energy sources (TPES) of 2008.
Electricity output (gross) was 1,735,579 ktoe (20,185TWｈ), efficiency was 39%, and the balance of 61% was generated heat. A small part(145,141 ktoe, which was 3% of the input total) of the heat was utilized at co-generation heat and power plants. The in-house consumption of electricity and power transmission losses were 289,681 ktoe.

The amount supplied to the final consumer was 1,445,285 ktoe (16,430 TWh) which was 33% of the total energy consumed at power plants and heat and power co-generation (CHP) plants.^[10]

Historical results of production of electricity

Production by country

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, Russia, and India.

As of Jan-2010, total electricity generation for the 2 largest generators was as follows: USA: 3992 billion kWh (3992 TWh) China: 3715 billion kWh (3715 TWh)

List of countries with source of electricity 2008

Data source of values (electric power generated) is IEA/OECD^[11]

Listed countries are top 20 by population or top 20 by GDP (PPP) and Saudi Arabia based on CIA World Factbook 2009.^[12]

Solar PV* is Photovoltaics

Bio other* = 198TWh (Biomass) + 69TWh (Waste) + 4TWh (other)

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.^[13]

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.^[14] Electricity generation is the fourth highest combined source of NOx, carbon monoxide, and particulate matter in the US.^[15]

In July 2011, the UK parliament tabled a motion that "levels of (carbon) emissions from nuclear power were approximately three times lower per kilowatt hour than those of solar, four times lower than clean coal and 36 times lower than conventional coal".^[16]

Though PV generation is positioned as environmentally friendly, fabrication of PV cells utilizes substantial amounts of water in addition to toxic chemicals such as phosphorous and arsenic. These are often over-looked when promoting PV. Because of strict environmental regulations in the United States, for example, PV fabrication is often performed in countries with lower standards, such as China.

Water consumption

Most large scale thermoelectric power stations consume considerable amounts of water for cooling purposes and boiler water make up - 1 L/kWh for once through (e.g. river cooling), and 1.7 L/kWh for cooling tower cooling.^[17] Water abstraction for cooling water accounts for about 40% of European total water abstraction, although most of this water is returned to its source, albeit slightly warmer. Different cooling systems have different consumption vs. abstraction characteristics. Cooling towers withdraw a small amount of water from the environment and evaporate most of it. Once-through systems withdraw a large amount but return it to the environment immediately, at a higher temperature.

See also

References

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. ^ IEA/OECD IEA Statistics/Electricity and Heat by country
10. ^ International Energy Agency, "2008 Energy Balance for World", 2011.
11. ^ IEA Statistics and Balances retrieved 2011-5-8
12. ^ CIA World Factbook 2009 retrieved 2011-5-8
13. ^ Borenstein, Seth (2007-06-03). "Carbon-emissions culprit? Coal". The Seattle Times. http://seattletimes.nwsource.com/html/nationworld/2003732690_carbon03.html. 
14. ^ "Sulfur Dioxide". US Environmental Protection Agency. http://www.epa.gov/air/sulfurdioxide/. 
15. ^ "AirData". US Environmental Protection Agency. 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. 
16. ^ http://www.parliament.uk/edm/2010-12/2061
17. ^ AAAS Annual Meeting 17 - 21 Feb 2011, Washington DC. Sustainable or Not? Impacts and Uncertainties of Low-Carbon Energy Technologies on Water.Evangelos Tzimas , European Commission, JRC Institute for Energy, Petten, Netherlands

External links

• Electricity - A Visual Primer
• Power Technologies Energy Data Book
• NOW on PBS: Power Struggle
• This Week in Energy (TWiEpodcast)
• Electricity: From Table-top to Powerplant