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.

The electrical utility industry is a major provider of energy in most countries. An electric utility is a company (often a public utility) that engages in the generation, transmission, and distribution of electricity for sale generally in a regulated market..

World electricity generation by source. Gwh=gigawatt-hours. Source: International Energy AgencyThere are two broad categories of electricity generation. In a thermal power station, the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine that drives an electrical generator.  The source of the heat is typically provided by the combustion of a fossil fuel (oil, natural gas, coal), a biofuel (wood), or municipal solid waste. Primary sources of electricity refer to power generated by energy sources that undergo no prior human-made conversions or transformations. Wind, solar, and hydropower are examples of primary sources of electricity.

History

Until the many practical applications of electricity that became available in the late 19th century, no single energy source could provide light, heat, and power. Electricity's versatility made it an enabling technology that allowed people in all walks of life—including architects, designers, homemakers, industrialists, doctors, and farmers—to do new things.

The phenomenon of electricity had remained a curiosity since classical times, when static electricity was known but scarcely investigated. Practical applications were only possible in the 19th century and after. Few scientists focused attention on it until after the invention of the Leyden jar (1746), which facilitated a century of experiments that prepared the way for practical applications. Charles Coulomb, Michael Cavendish, Benjamin Franklin, Luigi Galvani, Alessandro Volta, Humphrey Davy, and Andre Ampere developed a rich store of observation and theory that made possible Faraday's studies of electromagnetic induction, which in turn made possible the dynamo (1831).

On September 4, 1882, the first commercial power station in the U.S., located on Pearl Street in lower Manhattan, went into operation providing light and electricity power to customers in a one square mile area.

Methods of generating electricity

There are a variety fundamental methods of  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 and thermopiles
• 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 generates about 80 percent of the electric power in the world using a variety of heat sources. 

Environmental impacts

All forms of electricity generation have impacts on the environment. For example, fossil fuel power plants release air pollution, require large amounts of cooling water, and can disturb large areas of land during the mining process. Nuclear power plants are generating and accumulating large quantities of high level radioactive waste. Even renewable energy facilities such as wind turbines and solar cells can affect wildlife (fish and birds), involve hazardous wastes, or require cooling water.

Air impacts

• Climate change: The use of fossil fuels to generate electricity is the single largest source of greenhouse gas emissions from human activity.  Primary sources of electricity (solar, wind, nuclear, hydropower) release far smaller amount of greenhouse gases compared to thermal power generation from fossil fuels.
• Acid rain: The burning of fossil fuels generates air pollution that is the major cause of acid rain. Power plants, along with factories and vehicles that also burn fossil fuels, all emit sulfur dioxide (SO₂) and oxides of nitrogen (NO_x). When combined with moisture in the atmosphere, these pollutants are returned to the earth as acids. This process is known as "deposition" and occurs when it rains or snows, but it can also occur when dust settles out of the atmosphere during dry periods.
• Ozone (smog) and fine particulates: Tropospheric ozone is harmful to human health and the environment as it becomes a major pollutant when created at ground level. Ozone is not emitted directly into the environment. It is produced by a complex chemical reaction when nitrogen oxides (NO_x) and volatile organic compounds (VOCs) react in the presence of sunlight. NO_x is produced when cars and trucks, electric power plants and industrial processes burn fossil fuels. VOC's are unstable and easily-evaporated organic compounds present in vehicle exhaust, paint fumes, and industrial process waste. The interaction between these two chemicals create ozone pollution, the primary harmful ingredient in urban smog.
• Air toxics (mercury): Toxic air pollutants are substances released into the air that can cause cancer or other serious health effects. They may also damage ecosystems. These pollutants can come from natural sources, as is the case with radon gas. However, they are predominately generated by factory smokestacks, electric power plants and motor vehicles. Mercury has been the focus of regulatory activity because of its documented carcinogenic effect, as well as its persistent prevalence in the environment.

Water impacts

• Consumption of water resources. Thermal electric generating facilities make electricity by converting water into high-pressure steam that drives turbines. Once water has gone through this cycle, it is cooled and condensed back to water and then reheated to drive the turbines again. The process of condensation requires a separate cooling water body to absorb the heat of the steam. These condenser systems typically consist of banks of thousands of one-inch diameter tubes, through which cooling water is run, and over which the hot steam and water is circulated. The amount of water used for power plant cooling also varies by each specific power plant's electricity generating technology and size. For example, nuclear reactors require the most water for cooling, and baseload fossil fuel power plants come in second.  Most renewable energy technologies require little or no water for cooling.
  
  The use of water to generate power at hydropower facilities has significant, ecological impacts. The diversion of water out of the river removes water for healthy in-stream ecosystems. Fluctuations in water flow from peaking operations create a "tidal effect," disrupting the downstream riparian community that supports its unique ecosystem. A dam's impoundment slows water flows, which hinders natural downstream migration of many fish species. By slowing river flows, dams also allow silt to collect on river and reservoir bottoms and bury fish spawning habitat. Silt trapped above dams accumulates heavy metals and other pollutants. Disrupting the natural flow of sediments in rivers also leads to erosion of riverbeds downstream of the dam and increases risks of floods. The impoundment of water by hydropower facilities fundamentally reshapes the physical habitat from a riverine to an artificial pond community. This often eliminates native populations of fish and other wildlife. Dams also impede the upstream and downstream movement of fish and other wildlife, and prevent the flow of plants and nutrients. This impact is most significant on migratory fish, which are born in the river and must migrate downstream early in life to the ocean and then migrate upstream again to lay their eggs (or "spawn").
   
• Pollution of water bodies.  The construction and continued operation of power plants, particularly those fueled by fossil or nuclear fuels, are among the human activities that can have the most profound and wide ranging negative impacts on water quality. This waste stream results from periodic purging of the impurities that become concentrated in steam boiler systems. These pollutants include metals such as copper, iron and nickel, as well as chemicals added to prevent scaling and corrosion of steam generator components.
  • Coal pile run-off: This waste stream is created when water comes in contact with coal storage piles maintained on the power plant site. While most piles are kept covered, active piles used to meet the power plants immediate needs are often open to the elements. Metals and other naturally occurring contaminants contained in coal leach out with the rainfall and are deposited in nearby water bodies.
  • Cooling process wastes: Water used for power plant cooling is chemically altered for purposes of extending the useful life of equipment and to ensure efficient operation. Demineralized regenerants and rinses are chemicals employed to purify waters used as makeup water for the plant's cooling system. Cooling tower blowdown contains chemicals added to prevent biological growth in the towers and to prevent corrosion in condensers.
  • Boiler cleaning wastes: These wastes derive from the chemical additives intended to remove scale and other byproducts of combustion.
  • Thermal pollution: Thermal plants create or use steam in the process of creating electricity require water for cooling. This water typically comes from adjacent water bodies or groundwater sources and is discharged back into the water body at significantly higher temperatures. By altering the temperature in the "mixing zone," the discharge of thermal wastewater can both negative and positive effects on aquatic life. On the plus side, the warmer temperature water may create more favorable feeding and breeding conditions for certain species located near the power plant's water source. However, when the power plant is suddenly shut down for routine maintenance or unplanned outage, the resulting wide swing to colder temperatures can be lethal to sensitive fish populations. Hydropower dams can also alter the natural temperature of the water.

Land impacts

• On-site land impacts.  Large central-station, electric generating facilities that provide the vast bulk of the world's electricity can occupy acres upon acres of land just for the power plant components alone. These power plants also require on-site fuel storage facilities as well as structures for connecting to the transmission grid, which requires additional land. Depending on the fuel burned at any one power plant, electricity generators can permanently disrupt the landscape. Construction of hydropower dams floods riverside lands, permanently eliminating riparian and upland habitat. Solar and wind facilities require much larger land areas per unit of electricity generated compared to a fossil or nuclear facility.  However, they generate far fewer wastes and tend to to disrupt the land to a lesser extent then their fossil and nuclear counterparts.
• Off-site land impacts.  Most generating facilities also produce solid waste by-products of combustion that can be toxic. Solid wastes from power plants are typically landfilled, another way in which a generating facility impacts land as it extends its environmental footprint beyond the boundaries of the power plant site. In this case, the waste will likely remain at the landfill forever. Mining, collecting and transporting the natural gas, coal, oil, and nuclear fuel necessary to generate electricity can also impact land in much the same way by precluding other uses and leaving permanent alterations.

Sources

• Kydes, Andy (Lead Author); Cutler J. Cleveland (Topic Editor). 2007. "Primary energy." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth June 1, 2006; Last revised August 13, 2007; Retrieved March 25, 2010]. <http://www.eoearth.org/article/Primary_energy>
• Nye, David E. Electricity Use, History of, In: Cutler J. Cleveland, Editor(s)-in-Chief, Encyclopedia of Energy, Elsevier, New York, 2004, Pages 177-190.
• Pace Energy and Climate Center, Pace University School of Law, Power Scorecard, Accessed 25 March 2010.
• Wikipedia contributors, Electricity generation, Wikipedia, Accessed 25 March 2010.