Electricity generation

Turbo generator

Electricity generation is the process of generating electric 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. 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 and electrochemical batteries.

History

Main article: Electrification

Diagram of an electric power system, generation system in red

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 or coal, and today, 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.

Methods of generating electricity

U.S. 2014 Electricity Generation By Type.

Sources of electricity in France in 2006; nuclear power was the main source.

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 the most used form for generating electricity and is based on Faraday's law. It can be experimented by simply rotating a magnet within closed loops 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
• Photovoltaic effect, the transformation of light into electrical energy, as in solar cells
• Thermoelectric effect, the 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. 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.
• 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% 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 has a 22.5 GW capability.

Almost all electrical power on Earth is generated with a turbine of some type. Turbines are commonly driven by wind, water, steam or burning gas. The turbine drives an electric generator. Power sources include:

• Steam
  • Water is boiled by coal burned in a thermal power plant, about 40% of all electricity is generated this way.
  • Nuclear fission heat created in a nuclear reactor creates steam. Less than 15% of electricity is generated this way.
  • Renewables. The steam is 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 vapor to drive a turbine.

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

• Gas Natural gas is burned in a gas turbine, turbines are driven directly by gases produced by combustion. Combined cycle 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 steam. At least 20% of the worlds electricity is generated by natural gas.
• Water Energy is captured from the movement of water. From falling water (dam), the rise and fall of tides or ocean thermal currents. Each driving a water turbine to produce approximately 16% of the worlds electricity.
• Wind The windmill was a very early wind turbine. In a solar updraft tower wind is artificially produced. Before 2010 less than 2% of the worlds electricity was produced from wind.

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.

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, and the United States.

Electrochemical

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

Primary cells, such as the common zinc-carbon batteries, act as power sources directly, but many types of cells are used as storage systems rather than primary generation systems.

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.

Other generation methods

Wind 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 fresh water merges (e.g. deltas, ...)

Economics of generation and production of electricity

See also: Cost of electricity by source

The selection of electricity production modes and their economic viability varies in accordance with demand and region. The economics vary considerably around the world, resulting in widespread selling prices, e.g. the price in Venezuela is 3 cents per kWh while in Denmark it is 40 cents per kWh. 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.

Thermal energy is economical in areas of high industrial density, as the high demand cannot be met by renewable sources. The effect of localized 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 falling 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 store the flow of water is limited.

Due to advancements in technology, and with mass production, renewable sources other than hydroelectricity (solar power, wind energy, tidal power, etc.) experienced decreases in cost of production, 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.

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).

Source of Electricity (World total year 2008)

-	Coal	Oil	Natural Gas	Nuclear	Renewables	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

Energy Flow of Power Plant

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.

Historical results of production of electricity

Production by country

Main article: World energy resources and consumption

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

Composition of Electricity by Resource (TWh per year 2008)

Country's electricity sector	Fossil Fuel					Nuclear	rank	Renewable								Bio other*	total	rank
	Coal	Oil	Gas	sub total	rank			Hydro	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	12	114	-	0.02	-	14	-	128.02	6	2.0	830	5
USA	2,133	58	1011	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	6	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)

Cogeneration

Main article: Cogeneration

See also: Electrification

Co-generation 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. This practice carried on for many years after central stations became common and is still in use in many industries.

Environmental concerns

Main article: Environmental impact of electricity generation

See also: Global warming and Coal phase out

Variations between countries generating electrical power affect concerns about the environment. In France only 10% of electricity is generated from fossil fuels, the US is higher at 70% and China is at 80%. The cleanliness of electricity depends on its source. 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. 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. 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".

Main article: Life-cycle greenhouse-gas emissions of energy sources

Lifecycle greenhouse gas emissions by electricity source.

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	Polycrystalline 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. 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

• Cost of electricity by source
• Directive on Electricity Production from Renewable Energy Sources
• Distributed generation
• Electrification
• Emissions & Generation Resource Integrated Database
• Droop speed control
• Electric power transmission
• Electric utility
• Eurelectric
• Electric power distribution
• Electricity retailing
• Energy development
• Environmental concerns with electricity generation
• Eugene Green Energy Standard
• Generating Availability Data System
• Load profile
• List of countries by electricity production
• List of countries by electricity production from renewable sources
• Mains electricity
• Parallel generation
• Power quality
• Virtual power plant
• Voltage drop
• World energy consumption

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
• The Power Sector in Lebanon via Carboun