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Power Generation

Electricity generation is the process of generating electrical power from other sources of primary 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. Other energy sources include solar photovoltaics and geothermal power.

History

Main article: Electrification

Central power stations became economically practical with the development of alternating current power transmission, using power transformers to transmit power at high voltage and with low loss. Electricity has been generated at central stations since 1882. The first power plants were run on water power[2] or coal,[3] and today we rely mainly on coal, nuclear, natural gas, hydroelectric, wind generators, and petroleum, with a small amount from solar energy, tidal power, and geothermal sources.

The use of power-lines and power-poles have been significantly important in the distribution of electricity.

Cogeneration

Main article: Cogeneration

Cogeneration is the practice of using exhaust or extracted steam from a turbine for heating purposes, such as drying paper, distilling petroleum in a refinery or for building heat. Before central power stations were widely introduced it was common for industries, large hotels and commercial buildings to generate their own power and use low pressure exhaust steam for heating.[4] This practice carried on for many years after central stations became common and is still in use in many industries.

Methods of generating electricity


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

  • Piezoelectric effect, from the mechanical strain of electrically anisotropic molecules or crystals. Researchers at the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a piezoelectric generator sufficient to operate a liquid crystal display using thin films of M13 bacteriophage.[7]

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% 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 is generated by:
  • 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.[9] 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"),[10] 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.

Economics of generation and production of electricity

The selection of electricity production modes and their economic viability varies in accordance with demand and region. Hydroelectric plants, nuclear power plants, thermal power plants and renewable sources have their own pros and cons, and selection is based upon the local power requirement and the fluctuations in demand.

All power grids have varying loads on them but the daily minimum is the base load, supplied by plants which run continuously. Nuclear, coal, oil and gas plants can supply base load, with the low-carbon option being nuclear.

Thermal energy is economical in areas of high industrial density, as the high demand cannot be met by renewable sources. The effect of pollution is also minimized as industries are usually located away from residential areas. These plants can also withstand variation in load and consumption by adding more units or temporarily decreasing the production of some units.

Nuclear power plants can produce a huge amount of power from a single unit. However, recent disasters in Japan have raised concerns over the safety of nuclear power, and the capital cost of nuclear plants is very high.

Hydroelectric power plants are located in areas where the potential energy from flowing water can be harnessed for moving turbines and the generation of power. It is not an economically viable source of production where the load varies too much during the annual production cycle and the ability to stop the flow of water is limited.

Renewable sources other than hydroelectricity (solar power, wind energy, tidal power, etc.) due to advancements in technology, and with mass production, their cost of production has come down and the energy is now in many cases cost-comparative with fossil fuels. Many governments around the world provide subsidies to offset the higher cost of any new power production, and to make the installation of renewable energy systems economically feasible. However, their use is frequently limited by their intermittent nature.

If natural gas prices are below $3 per million British Thermal Units, generating electricity from natural gas is cheaper than generating power by burning coal.[11]

Production

The production of electricity in 2009 was 20,053TWh. Sources of electricity were fossil fuels 67%, renewable energy 16% (mainly hydroelectric, wind, solar and biomass), and nuclear power 13%, and other sources were 3%. The majority of fossil fuel usage for the generation of electricity was coal and gas. Oil was 5.5%, as it is the most expensive common commodity used to produce electrical energy. 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 OECD 2011-12 Factbook (2009 data).[12]

Source of Electricity (World total year 2008)
- Coal Oil Natural
Gas
Nuclear Hydro other Total
Average electric power (TWh/year) 8,263 1,111 4,301 2,731 3,288 568 20,261
Average electric power (GW) 942.6 126.7 490.7 311.6 375.1 64.8 2311.4
Proportion 41% 5% 21% 13% 16% 3% 100%
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 (20,185 TWh), 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.[13]

Historical results of production of electricity

Production by country

Main article: World energy resources and consumption

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) and China: 3715 billion kWh (3715 TWh).

List of countries with source of electricity 2008

Data source of values (electric power generated) is IEA/OECD.[14]

Listed countries are top 20 by population or top 20 by GDP (PPP) and Saudi Arabia based on CIA World Factbook 2009.[15]

Composition of Electricity by Resource (TWh per year 2008)
Country Fossil Fuel Nuclear rank Renewable Bio
other*
total rank
Coal Oil Gas sub
total
rank Hydroe Geo
Thermal
Solar
PV*
Solar
Thermal
Wind Tide sub
total
rank
World total 8,263 1,111 4,301 13,675 - 2,731 - 3,288 65 12 0.9 219 0.5 3,584 - 271 20,261 -
Proportion 41% 5.5% 21% 67% - 13% - 16% 0.3% 0.06% 0.004% 1.1% 0.003% 18% - 1.3% 100% -
 China 2,733 23 31 2,788 2 68 8 585 - 0.2 - 13 - 598 1 2.4 3,457 2
 India 569 34 82 685 5 15 6 114 - 0.02 - 14 - 128.02 6 2.0 830 5
 USA 2,133 58 911 3,101 1 838 1 282 17 1.6 0.88 56 - 357 4 73 4,369 1
 Indonesia 61 43 25 130 19 - - 12 8.3 - - - - 20 17 - 149 20
 Brazil 13 18 29 59 23 14 13 370 - - - 0.6 - 370 3 20 463 9
 Pakistan 0.1 32 30 62 22 1.6 16 28 - - - - - 28 14 - 92 24
 Bangladesh 0.6 1.7 31 33 27 - - 1.5 - - - - - 1.5 29 - 35 27
 Nigeria - 3.1 12 15 28 - - 5.7 - - - - - 5.7 25 - 21 28
 Russia 197 16 495 708 4 163 4 167 0.5 - - 0.01 - 167 5 2.5 1,040 4
 Japan 288 139 283 711 3 258 3 83 2.8 2.3 - 2.6 - 91 7 22 1,082 3
 Mexico 21 49 131 202 13 9.8 14 39 7.1 0.01 - 0.3 - 47 12 0.8 259 14
 Philippines 16 4.9 20 40 26 - - 9.8 11 0.001 - 0.1 - 21 16 - 61 26
 Vietnam 15 1.6 30 47 25 - - 26 - - - - - 26 15 - 73 25
 Ethiopia - 0.5 - 0.5 29 - - 3.3 0.01 - - - - 3.3 28 - 3.8 30
 Egypt - 26 90 115 20 - - 15 - - - 0.9 - 16 20 - 131 22
 Germany 291 9.2 88 388 6 148 5 27 0.02 4.4 - 41 - 72 9 29 637 7
 Turkey 58 7.5 99 164 16 - - 33 0.16 - - 0.85 - 34 13 0.22 198 19
 DR Congo - 0.02 0.03 0.05 30 - - 7.5 - - - - - 7.5 22 - 7.5 29
 Iran 0.4 36 173 209 11 - - 5.0 - - - 0.20 - 5.2 26 - 215 17
 Thailand 32 1.7 102 135 18 - - 7.1 0.002 0.003 - - - 7.1 23 4.8 147 21
 France 27 5.8 22 55 24 439 2 68 - 0.04 - 5.7 0.51 75 8 5.9 575 8
 UK 127 6.1 177 310 7 52 10 9.3 - 0.02 - 7.1 - 16 18 11 389 11
 Italy 49 31 173 253 9 - - 47 5.5 0.2 - 4.9 - 58 11 8.6 319 12
 South Korea 192 15 81 288 8 151 5 5.6 - 0.3 - 0.4 - 6.3 24 0.7 446 10
 Spain 50 18 122 190 14 59 9 26 - 2.6 0.02 32 - 61 10 4.3 314 13
 Canada 112 9.8 41 162 17 94 7 383 - 0.03 - 3.8 0.03 386 2 8.5 651 6
 Saudi Arabia - 116 88 204 12 - - - - - - - - - - - 204 18
 Taiwan 125 14 46 186 15 41 11 7.8 - 0.004 - 0.6 - 8.4 21 3.5 238 16
 Australia 198 2.8 39 239 10 - - 12 - 0.2 0.004 3.9 - 16 19 2.2 257 15
 Netherlands 27 2.1 63 92 21 4.2 15 0.1 - 0.04 - 4.3 - 4.4 27 6.8 108 23
Country Coal Oil Gas sub
total
rank Nuclear rank Hydro Geo
Thermal
Solar
PV
Solar
Thermal
Wind Tide sub
total
rank Bio
other
Total rank

Solar PV* is Photovoltaics

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

Environmental concerns

Main articles: Global warming and Coal phase out

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% of emissions, the largest of any source. Transportation emissions are close behind, contributing about one-third of U.S. production of carbon dioxide.[16]

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.[17] Electricity generation is the fourth highest combined source of NOx, carbon monoxide, and particulate matter in the US.[18]

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".[19]

Though Solar PV generation is positioned as environmentally friendly, fabrication of PV cells utilizes substantial amounts of water in addition to toxic chemicals such as phosphorus and arsenic. These are often overlooked 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, which produces approximately half the world's PV panels.

Lifecycle greenhouse gas emissions by electricity source.[20]
Technology Description 50th percentile
(g CO2/kWhe)
Hydroelectric reservoir 4
Wind onshore 12
Nuclear various generation II reactor types 16
Biomass various 18
Solar thermal parabolic trough 22
Geothermal hot dry rock 45
Solar PV Polycrystaline silicon 46
Natural gas various combined cycle turbines without scrubbing 469
Coal various generator types without scrubbing 1001

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.[21] 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

Energy portal

References

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
  • Carboun

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