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.

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 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, 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 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

**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. 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"), 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)

1,111 41％

+ Source of Electricity (World total year 2008)
- !! Coal !! Oil !! Natural Gas !! Nuclear !! Hydro !! other !! Total
Electricity (TWｈ/year)	8,263	|	4,301	2,731	3,288	568	20,261
Proportion	|	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 (20,185TWｈ), 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.

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

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

4,301 21% 23 34 58 43 18 32 1.7 3.1 16 139 49 4.9 1.6 0.5 26 9.2 7.5 0.02 36 1.7 5.8 6.1 31 15 18 9.8 116 14 2.8 2.1

+ Composition of Electricity by Resource (TWh per year 2008)
rowspan="2" style="background-color: #ddf;"	Country	Fossil Fuel					Nuclear	rank	Renewable								Biomass, others					total	rank
Coal	Oil	Gas	subtotal	rank	Hydro	GeoThermal			SolarPV*	SolarThermal	Wind	Tide	subtotal	rank	Biomass	waste	other	subtotal	rank
! World total	8,263	1,111	|	13,675	-	2,731	-	3,288	65	12	0.9	219	0.5	3,584	-	198	69	4	271	-	20,261	-
Proportion	41%	5.5%	|	67%	-	13%	-	16%	0.3%	0.06%	0.004%	1.1%	0.003%	18%	-	1.0%	0.3%	0.02%	1.3%	-	100%	-
!	2,733	|	31	2,788	2	68	8	585	-	0.2	-	13	-	598	1	2.4	-	-	2.4	14	3,457	2
!	569	|	82	685	6	15	12	114	-	0.02	-	14	-	128	6	2.0	-	-	2.0	16	830	5
!	2,133	|	911	3,101	1	838	1	282	17	1.6	0.88	56	-	357	4	50	22	0.8	73	1	4,369	1
!	61	|	25	130	19	-	-	12	8.3	-	-	-	-	20	17	-	-	-	-	-	149	20
!	13	|	29	59	23	14	13	370	-	-	-	0.6	-	370	3	20	-	0.2	20	4	463	9
!	0.1	|	30	62	22	1.6	16	28	-	-	-	-	-	28	14	-	-	-	-	-	92	24
!	0.6	|	31	33	27	-	-	1.5	-	-	-	-	-	1.5	29	-	-	-	-	-	35	27
!	-	|	12	15	28	-	-	5.7	-	-	-	-	-	5.7	25	-	-	-	-	-	21	28
!	197	|	495	708	4	163	4	167	0.5	-	-	0.01	-	167	5	0.02	2.5	-	2.5	13	1,040	4
!	288	|	283	711	3	258	3	83	2.8	2.3	-	2.6	-	91	7	15	7.3	-	22	3	1,082	3
!	21	|	131	202	13	9.8	14	39	7.1	0.01	-	0.3	-	47	12	0.8	-	-	0.8	17	259	14
!	16	|	20	40	26	-	-	9.8	11	0.001	-	0.1	-	21	16	-	-	-	-	-	61	26
!	15	|	30	47	25	-	-	26	-	-	-	-	-	26	15	-	-	-	-	-	73	25
!	-	|	-	0.5	29	-	-	3.3	0.01	-	-	-	-	3.3	28	-	-	-	-	-	3.8	30
!	-	|	90	115	20	-	-	15	-	-	-	0.9	-	16	20	-	-	-	-	-	131	22
!	291	|	88	388	6	148	6	27	0.02	4.4	-	41	-	72	9	20	9.4	-	29	2	637	7
!	58	|	99	164	16	-	-	33	0.16	-	-	0.85	-	34	13	0.14	0.1	-	0.22	19	198	19
!	-	|	0.03	0.05	30	-	-	7.5	-	-	-	-	-	7.5	22	-	-	-	-	-	7.5	29
!	0.4	|	173	209	11	-	-	5.0	-	-	-	0.20	-	5.2	26	-	-	-	-	-	215	17
!	32	|	102	135	18	-	-	7.1	0.002	0.003	-	-	-	7.1	23	4.8	-	-	4.8	10	147	21
!	27	|	22	55	24	439	2	68	-	0.04	-	5.7	0.51	75	8	2.1	3.8	-	5.9	9	575	8
!	127	|	177	310	7	52	10	9.3	-	0.02	-	7.1	-	16	18	8.1	2.9	-	11	5	389	11
!	49	|	173	253	9	-	-	47	5.5	0.2	-	4.9	-	58	11	4.4	3.3	0.9	8.6	6	319	12
!	192	|	81	288	8	151	5	5.6	-	0.3	-	0.4	-	6.3	24	0.5	0.2	0.1	0.7	18	446	10
!	50	|	122	190	14	59	9	26	-	2.6	0.02	32	-	61	10	2.5	1.6	0.3	4.3	11	314	13
!	112	|	41	162	17	94	7	383	-	0.03	-	3.8	0.03	386	2	8.3	0.2	-	8.5	7	651	6
!	-	|	88	204	12	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	204	18
!	125	|	46	186	15	41	11	7.8	-	0.004	-	0.6	-	8.4	21	0.5	3.0	-	3.5	12	238	16
!	198	|	39	239	10	-	-	12	-	0.2	0.004	3.9	-	16	19	2.2	-	-	2.2	15	257	15
!	27	|	63	92	21	4.2	15	0.1	-	0.04	-	4.3	-	4.4	27	3.7	2.9	0.1	6.8	8	108	23
Country	Coal	Oil	Gas	subtotal	rank	Nuclear	rank	Hydro	GeoThermal	SolarPV	SolarThermal	Wind	Tide	subtotal	rank	Biomass	Waste	other	subtotal	rank	Total	rank

Solar PV* is Photovoltaics

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.

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

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. 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

External links

Electricity - A Visual Primer

Power Technologies Energy Data Book

NOW on PBS: Power Struggle

This Week in Energy (TWiEpodcast)

EURELECTRIC

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