|Named after||James Watt|
|1 W in ...||... is equal to ...|
|SI base units||1 kg ⋅ m 2⋅ s −3|
|CGS units||107 erg⋅s −1|
|English Engineering Units||0.7375621 ft⋅lbf/s = 0.001341022 hp|
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor of James Watt (1736–1819), an 18th-century Scottish inventor, mechanical engineer, and chemist who improved the Newcomen engine with his own steam engine in 1776. Watt's invention was fundamental for the Industrial Revolution.
When an object's velocity is held constant at one meter per second against a constant opposing force of one newton, the rate at which work is done is one watt.
In terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V), meaning the watt is equivalent to the volt-ampere (the latter unit, however, is used for a different quantity from the real power of an electrical circuit).
Two additional unit conversions for watt can be found using the above equation and Ohm's law.
where ohm () is the SI derived unit of electrical resistance.
The watt is named after the Scottish inventor James Watt.The unit name was proposed initially by C. William Siemens in August 1882 in his President's Address to the Fifty-Second Congress of the British Association for the Advancement of Science. Noting that units in the practical system of units were named after leading physicists, Siemens proposed that watt might be an appropriate name for a unit of power. Siemens defined the unit consistently within the then-existing system of practical units as "the power conveyed by a current of an Ampère through the difference of potential of a Volt".
In October 1908, at the International Conference on Electric Units and Standards in London, A2 × 1 Ω.) The watt was defined as equal to 107 units of power in the "practical system" of units. The "international units" were dominant from 1909 until 1948. After the 9th General Conference on Weights and Measures in 1948, the "international" watt was redefined from practical units to absolute units (i.e., using only length, mass, and time). Concretely, this meant that 1 watt was now defined as the quantity of energy transferred in a unit of time, namely 1 J/s. In this new definition, 1 "absolute" watt = 1.00019 "international" watts. Texts written before 1948 are likely to be using the "international" watt, which implies caution when comparing numerical values from this period with the post-1948 watt. In 1960, the 11th General Conference on Weights and Measures adopted the "absolute" watt into the International System of Units (SI) as the unit of power.so-called "international" definitions were established for practical electrical units. Siemens' definition was adopted as the "international" watt. (Also used: 1
|Value||SI symbol||Name||Value||SI symbol||Name|
|10−1 W||dW||deciwatt||101 W||daW||decawatt|
|10−2 W||cW||centiwatt||102 W||hW||hectowatt|
|10−3 W||mW||milliwatt||103 W||kW||kilowatt|
|10−6 W||µW||microwatt||106 W||MW||megawatt|
|10−9 W||nW||nanowatt||109 W||GW||gigawatt|
|10−12 W||pW||picowatt||1012 W||TW||terawatt|
|10−15 W||fW||femtowatt||1015 W||PW||petawatt|
|10−18 W||aW||attowatt||1018 W||EW||exawatt|
|10−21 W||zW||zeptowatt||1021 W||ZW||zettawatt|
|10−24 W||yW||yoctowatt||1024 W||YW||yottawatt|
|10−27 W||rW||rontowatt||1027 W||RW||ronnawatt|
|10−30 W||qW||quectowatt||1030 W||QW||quettawatt|
|Common multiples are in bold face|
In the electric power industry, megawatt electrical (MWe MWt (i.e. heat), which creates steam to drive a turbine, which generates 648 MWe (i.e. electricity). (See Betz's law for the associated efficiency.) Other SI prefixes are sometimes used, for example gigawatt electrical (GWe). The International Bureau of Weights and Measures, which maintains the SI-standard, states that further information about a quantity should not be attached to the unit symbol but instead to the quantity symbol (i.e., Pthermal = 270 W rather than P = 270 Wth) and so these units are non-SI. In compliance with SI, the energy company Ørsted A/S uses the unit megawatt for produced electrical power and the equivalent unit megajoule per second for delivered heating power in a combined heat and power station such as Avedøre Power Station.or MWe) refers by convention to the electric power produced by a generator, while megawatt thermal or thermal megawatt (MWt, MWt, or MWth, MWth) refers to thermal power produced by the plant. For example, the Embalse nuclear power plant in Argentina uses a fission reactor to generate 2109
When describing alternating current (AC) electricity, another distinction is made between the watt and the volt-ampere. While these units are equivalent for simple resistive circuits, they differ when loads exhibit electrical reactance.
Radio stations usually report the power of their transmitters in units of watts, referring to the effective radiated power. This refers to the power that a half-wave dipole antenna would need to radiate to match the intensity of the transmitter's main lobe.
The terms power and energy are closely related but distinct physical quantities. Power is the rate at which energy is generated or consumed and hence is measured in units (e.g. watts) that represent energy per unit time.
For example, when a light bulb with a power rating of 100W is turned on for one hour, the energy used is 100 watt hours (W·h), 0.1 kilowatt hour, or 360 kJ. This same amount of energy would light a 40-watt bulb for 2.5 hours, or a 50-watt bulb for 2 hours.
Power stations are rated using units of power, typically megawatts or gigawatts (for example, the Three Gorges Dam in China, is rated at approximately 22 gigawatts). This reflects the maximum power output it can achieve at any point in time. A power station's annual energy output, however, would be recorded using units of energy (not power), typically gigawatt hours. Major energy production or consumption is often expressed as terawatt hours for a given period; often a calendar year or financial year. One terawatt hour of energy is equal to a sustained power delivery of one terawatt for one hour, or approximately 114 megawatts for a period of one year:
equivalent to approximately 114 megawatts of constant power output.
The watt-second is a unit of energy, equal to the joule. One kilowatt hour is 3,600,000 watt seconds.
While a watt per hour is a unit of rate of change of power with time,it is not correct to refer to a watt (or watt-hour) as a "watt per hour".
The joule is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).
Geothermal energy is thermal energy in the Earth's crust. It combines energy from the formation of the planet and from radioactive decay. Geothermal energy has been exploited as a source of heat and/or electric power for millennia.
A kilowatt-hour is a non-SI unit of energy equal to 3.6 megajoules (MJ) in SI units which is the energy delivered by one kilowatt of power for one hour. Kilowatt-hours are a common billing unit for electrical energy supplied by electric utilities. Metric prefixes are used for multiples and submultiples of the basic unit, the watt-hour.
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid.
The Manitoba Hydro-Electric Board, operating as Manitoba Hydro, is the electric power and natural gas utility in the province of Manitoba, Canada. Founded in 1961, it is a provincial Crown Corporation, governed by the Manitoba Hydro-Electric Board and the Manitoba Hydro Act. Today the company operates 16 interconnected generating stations. It has more than 527,000 electric power customers and more than 263,000 natural gas customers. Since most of the electrical energy is provided by hydroelectric power, the utility has low electricity rates. Stations in Northern Manitoba are connected by a HVDC system, the Nelson River Bipole, to customers in the south. The internal staff are members of the Canadian Union of Public Employees Local 998 while the outside workers are members of the International Brotherhood of Electrical Workers Local 2034.
Peaking power plants, also known as peaker plants, and occasionally just "peakers", are power plants that generally run only when there is a high demand, known as peak demand, for electricity. Because they supply power only occasionally, the power supplied commands a much higher price per kilowatt hour than base load power. Peak load power plants are dispatched in combination with base load power plants, which supply a dependable and consistent amount of electricity, to meet the minimum demand.
In the United States, the efficiency of air conditioners is often rated by the seasonal energy efficiency ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute, a trade association, in its 2008 standard AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment. A similar standard is the European seasonal energy efficiency ratio (ESEER).
Nevada Solar One is a concentrated solar power plant, with a nominal capacity of 64 MW and maximum steam turbine power output up to 72 MW net (75 MW gross), spread over an area of 400 acres (160 ha). The projected CO2 emissions avoided is equivalent to taking approximately 20,000 cars off the road. The project required an investment of $266 million USD, and the project officially went into operation in June 2007. Electricity production is estimated to be 134 GWh (gigawatt hours) per year.
Electric power is the transfer of electrical energy within a circuit. Its SI unit is the watt, the general unit of power, defined as one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions of watts are called kilowatts, megawatts and gigawatts respectively.
Many countries and territories have installed significant solar power capacity into their electrical grids to supplement or provide an alternative to conventional energy sources. Solar power plants use one of two technologies:
Energy conversion efficiency (η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radiation), or heat. The resulting value, η (eta), ranges between 0 and 1.
The Nellis Solar Power Plant is a 14-megawatt (MW) photovoltaic power station located within Nellis Air Force Base in Clark County, Nevada, northeast of Las Vegas. The power plant was inaugurated in a ceremony on December 17, 2007, with Nevada Governor Jim Gibbons activating its full operation. On average, it has since generated 32 gigawatt-hours of electricity annually and supplied more than 25% of the power used at the base.
A grid-tie inverter converts direct current (DC) into an alternating current (AC) suitable for injecting into an electrical power grid, normally 120 V RMS at 60 Hz or 240 V RMS at 50 Hz. Grid-tie inverters are used between local electrical power generators: solar panel, wind turbine, hydro-electric, and the grid.
A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and convert sunlight into electricity, a solar inverter to convert the output from direct to alternating current, as well as mounting, cabling, and other electrical accessories to set up a working system. It may also use a solar tracking system to improve the system's overall performance and include an integrated battery.
Nominal power is the nameplate capacity of photovoltaic (PV) devices, such as solar cells, modules and systems. It is determined by measuring the electric current and voltage in a circuit, while varying the resistance under precisely defined conditions. The nominal power is important for designing an installation in order to correctly dimension its cabling and converters.
Between 1992 and 2022, the worldwide usage of photovoltaics (PV) increased exponentially. During this period, it evolved from a niche market of small-scale applications to a mainstream electricity source. From 2016-2022 it has seen an annual capacity and production growth rate of around 26%- doubling approximately every three years.
Solar power has been growing rapidly in the U.S. state of California because of high insolation, community support, declining solar costs, and a renewable portfolio standard which requires that 60% of California's electricity come from renewable resources by 2030, with 100% by 2045. Much of this is expected to come from solar power via photovoltaic facilities or concentrated solar power facilities.
The electricity sector in Switzerland relies mainly on hydroelectricity, since the Alps cover almost two-thirds of the country's land mass, providing many large mountain lakes and artificial reservoirs suited for hydro power. In addition, the water masses drained from the Swiss Alps are intensively used by run-of-the-river hydroelectricity (ROR). With 9,052 kWh per person in 2008, the country's electricity consumption is relatively high and was 22% above the European Union's average.
Solar power in Switzerland has been growing rapidly in recent years due to declining system costs and a feed-in tariff instituted by the Swiss government. In 2013, cumulative capacity increased by 69% to 730 megawatts (MW) and contributed 544 GWh or 0.8% of the countries net-electricity production.
Zagtouli Solar Power Station is an operational 33 MW (44,000 hp) solar power plant in Burkina Faso. At the time of its commissioning, in November 2017, it was one of the largest grid-connected solar power stations in West Africa.