The kilowatt hour (symbol kW⋅h, kWh, or kW h) is a unit of energy equal to 3.6 megajoules. If energy is transmitted or used at a constant rate (power) over a period of time, the total energy in kilowatt hours is equal to the power in kilowatts multiplied by the time in hours. The kilowatt hour is commonly used as a billing unit for energy delivered to consumers by electric utilities.
Residential electricity meter located in Canada
|Unit system||Non-SI metric|
|1 kW⋅h in ...||... is equal to ...|
|SI units||3.6 MJ|
|CGS units||3.6×1013 erg|
|English Engineering units||≈ 2,655,224 ft⋅lbf|
|British Gravitational units||≈ 85,429,300 ft⋅pdl|
The kilowatt hour (symbolized kW⋅h as per SI) is a composite unit of energy equivalent to one kilowatt (1 kW) of power sustained for one hour. One watt is equal to 1 J/s. One kilowatt hour is 3.6 megajoules, which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour.
The derived unit of energy within the International System of Units (SI) is the joule. The hour is a unit of time "outside the SI", making the kilowatt hour a non-SI unit of energy. The kilowatt hour is not listed among the non-SI units accepted by the BIPM for use with the SI, although the hour, from which the kilowatt hour is derived, is.
An electric heater consuming 1000 watts (1 kilowatt), and operating for one hour uses one kilowatt hour of energy. A television consuming 100 watts operating for 10 hours continuously uses one kilowatt hour. A 40-watt electric appliance operating continuously for 25 hours uses one kilowatt hour. In terms of human power, a healthy adult male manual laborer will perform work equal to about half a kilowatt hour over an eight-hour day.
Electrical energy is typically sold to consumers in kilowatt hours. The cost of running an electric device is calculated by multiplying the device's power consumption in kilowatts by the running time in hours and then by the price per kilowatt hour. The unit price of electricity may depend upon the rate of consumption and the time of day. Prices vary considerably by locality. In the United States prices in different states can vary by a factor of three.
While smaller customer loads are usually billed only for energy, transmission services, and the rated capacity, larger consumers also pay for peak power consumption, the greatest power recorded in a fairly short time, such as 15 minutes. This compensates the power company for maintaining the infrastructure needed to provide peak power. These charges are billed as demand changes. Industrial users may also have extra charges according to the power factor of their load.
Major energy production or consumption is often expressed as terawatt hours (TW⋅h) for a given period that is often a calendar year or financial year. A 365-day year equals 8,760 hours, so over a period of one year, power of one gigawatt equates to 8.76 terawatt hours of energy. Conversely, one terawatt hour is equal to a sustained power of about 114 megawatts for a period of one year.
Other abbreviations and symbols may be encountered:
To convert a quantity measured in a unit in the left column to the units in the top row, multiply by the factor in the cell where the row and column intersect.
|joule||watt hour||kilowatt hour||electronvolt||calorie|
|1 J = 1 kg⋅m2⋅s−2 =||1||2.77778 × 10−4||2.77778 × 10−7||6.241 × 1018||0.239|
|1 W⋅h =||3.6 × 103||1||0.001||2.247 × 1022||859.8|
|1 kW⋅h =||3.6 × 106||1,000||1||2.247 × 1025||8.598 × 105|
|1 eV =||1.602 × 10−19||4.45 × 10−23||4.45 × 10−26||1||3.827 × 10−20|
|1 cal =||4.2||1.163 × 10−3||1.163 × 10−6||2.613 × 1019||1|
All the SI prefixes are commonly applied to the watt hour: a kilowatt hour is 1,000 W⋅h (symbols kW⋅h, kWh, or kW h); a megawatt hour is 1 million W⋅h (symbols MW⋅h, MWh, or MW h); a milliwatt hour is 1/1000 W⋅h (symbols mW⋅h, mWh, or mW h) and so on. The kilowatt hour is commonly used by electrical distribution providers for purposes of billing, since the monthly energy consumption of a typical residential customer ranges from a few hundred to a few thousand kilowatt hours. Megawatt hours (MW⋅h), gigawatt hours (GW⋅h), and terawatt hours (TW⋅h) are often used for metering larger amounts of electrical energy to industrial customers and in power generation. The terawatt hour and petawatt hour (PW⋅h) units are large enough to conveniently express the annual electricity generation for whole countries and the world energy consumption.
|10−3||mW⋅h||milliwatt hour||103||kW⋅h||kilowatt hour|
|10−6||µW⋅h||microwatt hour||106||MW⋅h||megawatt hour|
Petawatt hours can describe the output of nuclear power plants across decades. For example, the Gravelines Nuclear Power Station in France became in 2010 the first power plant to ever deliver a cumulative petawatt-hour of electricity.
Power is measured in watts or joules per second. Energy is measured in watt seconds, or joules.
A common household battery contains energy. When the battery delivers its energy, it does so at a certain power level, that is, the rate of delivery of the energy. The higher the power level, the quicker the battery's stored energy is delivered. If the power is higher, the battery's stored energy will be depleted in a shorter time period.
For a given period of time, a higher level of power causes more energy to be used. For a given power level, a longer run period causes more energy to be used. For a given amount of energy, a higher level of power causes that energy to be used in less time.
Power units measure the rate of energy per unit time. Many compound units for rates explicitly mention units of time, for example, miles per hour, kilometers per hour, dollars per hour. Kilowatt hours are a product of power and time, not a rate of change of power with time. Watts per hour (W/h) is a unit of a change of power per hour. It might be used to characterize the ramp-up behavior of power plants. For example, a power plant that reaches a power output of 1 MW from 0 MW in 15 minutes has a ramp-up rate of 4 MW/h. Hydroelectric power plants have a very high ramp-up rate, which makes them particularly useful in peak load and emergency situations.
The proper use of terms such as watts per hour is uncommon, so misuse may be widespread.
Several other units are commonly used to indicate power or energy capacity or use in specific application areas.
Average annual power production or consumption can be expressed in kilowatt hours per year; for example, when comparing the energy efficiency of household appliances whose power consumption varies with time or the season of the year, or the energy produced by a distributed power source. One kilowatt hour per year equals about 114.08 milliwatts applied constantly during one year.
The energy content of a battery is usually expressed indirectly by its capacity in ampere-hours; to convert ampere-hour (A⋅h) to watt hours (W⋅h), the ampere-hour value must be multiplied by the voltage of the power source. This value is approximate, since the battery voltage is not constant during its discharge, and because higher discharge rates reduce the total amount of energy that the battery can provide. In the case of devices that output a different voltage than the battery, it is the battery voltage (typically 3.7 V for Li-ion) that must be used to calculate rather than the device output (for example, usually 5.0 V for USB portable chargers). This results in a 500 mA USB device running for about 3.7 hours on a 2500 mAh battery, not five hours.
The Board of Trade unit (BOTU) is an obsolete UK synonym for kilowatt hour. The term derives from the name of the Board of Trade which regulated the electricity industry until 1942 when the Ministry of Power took over.
The British thermal unit or BTU (not to be confused with BOTU), is a unit of thermal energy with several definitions, all of which are about 1055 joules or 0.293 watt hour. The quad, short for quadrillion BTU, or 1015 BTU, is sometimes used in national-scale energy discussions in the United States. One quad is approximately 293 TW⋅h or 1.055 exajoule (EJ).
Burnup of nuclear fuel is normally quoted in megawatt days per tonne (MW⋅d/MTU), where tonne refers to a metric ton of uranium metal or its equivalent, and megawatt refers to the entire thermal output, not the fraction which is converted to electricity.
Reference [4: ISO 31-0] suggests that if a space is used to indicate units formed by multiplication, the space may be omitted if it does not cause confusion. This possibility is reflected in the common practice of using the symbol kWh rather than kW ⋅ h or kW h for the kilowatt hour. Nevertheless, this Guide takes the position that a half-high dot or a space should always be used to avoid possible confusion;
The six-unit Gravelines nuclear power plant near Dunkerque in northern France has become the first nuclear plant in the world to deliver 1000 billion kilowatt-hours (one petawatt-hour) of electricity.
Burgos Wind Farm is a wind farm in Burgos, Ilocos Norte, Philippines. It is the second wind farm built in the province of Ilocos Norte and the largest project of its kind in the Philippines. The estimated cost for the construction of the wind farm was US$450 million. The wind farm was commissioned in November 9, 2014 and upon its completion it became the largest wind farm in the country and in Southeast Asia, covering 600 hectares and three barangays of Burgos, namely Saoit, Poblacion and Nagsurot. The project was the first one to be nominated by the Department of Energy as eligible for the department's feed-in tariff scheme.Under the Renewable Energy Act of 2008, the Philippine Energy Regulatory Commission can "(guarantee) fixed rate per kilowatt-hour – the FIT rates – for power producers harnessing renewable energy under the FIT system." In February 2015, the ERC agreed to give a FIT rate of P8.53 per kilowatt hour for 20 years to the Burgos Wind Farm of the Energy Development Corporation.Collie Power Station
Collie Power Station is a power station in Collie, Western Australia. It is coal powered with one steam turbine that generates a total capacity of 300 megawatts of electricity. The coal is mined locally from the Collie Sub-basin and is transported to the power plant by overland conveyor.
The station was commissioned in 1999 with a single 300 megawatts steam turbine. Power generated by the station supplies the south-west of Australia through the South West Interconnected System (SWIS) operated by Western Power.In the financial year of 2008/2009, the station consumed approximately 1 million tonnes (2.2 billion pounds) of coal. Carbon Monitoring for Action estimates that, in 2009, Collie Power Station emitted 2.59 million tonnes (5.7 billion pounds) of CO2 to generate 2.3 terawatt-hours (8.3 petajoules) of electricity.In household consumer terms, this equates to 1.13 kilograms (2.5 lb) of CO2 emitted for each one kilowatt-hour (kWh), or 3.6 megajoules, of electricity produced and fed into the electricity grid. That is, Collie Power Station emits slightly less CO2 per kilowatt-hour of electricity produced than nearby closing Muja Power Station (1.14 kilograms or 2.5 pounds) but more than also nearby Bluewaters Power Station (0.825 kilograms or 1.82 pounds) based on estimates for the same year.Cost of electricity by source
The distinct ways of electricity generation can incur significantly different costs. Calculations of these costs can be made at the point of connection to a load or to the electricity grid. The cost is typically given per kilowatt-hour or megawatt-hour. It includes the initial capital, discount rate, as well as the costs of continuous operation, fuel, and maintenance. This type of calculation assists policymakers, researchers and others to guide discussions and decision making.
The levelized cost of energy (LCOE) is a measure of a power source that allows comparison of different methods of electricity generation on a consistent basis. It is an economic assessment of the average total cost to build and operate a power-generating asset over its lifetime divided by the total energy output of the asset over that lifetime. The LCOE can also be regarded as the average minimum price at which electricity must be sold in order to break-even over the lifetime of the project.Electric power
Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second.
Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries. It is usually supplied to businesses and homes (as domestic mains electricity) by the electric power industry through an electric power grid. Electric energy is usually sold by the kilowatt hour (1 kW·h = 3.6 MJ) which is the product of the power in kilowatts multiplied by running time in hours. Electric utilities measure power using an electricity meter, which keeps a running total of the electric energy delivered to a customer.
Electrical power provides a low entropy form of energy and can be carried long distances and converted into other forms of energy such as motion, light or heat with high energy efficiency.Electrical efficiency
The efficiency of an entity (a device, component, or system) in electronics and electrical engineering is defined as useful power output divided by the total electrical power consumed (a fractional expression), typically denoted by the Greek small letter eta (η – ήτα).
If energy output and input are expressed in the same units, efficiency is a dimensionless number. Where it is not customary or convenient to represent input and output energy in the same units, efficiency-like quantities have units associated with them. For example, the heat rate of a fossil-fuel power plant may be expressed in BTU per kilowatt-hour. Luminous efficacy of a light source expresses the amount of visible light for a certain amount of power transfer and has the units of lumens per watt.Electricity meter
An electricity meter, electric meter, electrical meter, or energy meter is a device that measures the amount of electric energy consumed by a residence, a business, or an electrically powered device.
Electric utilities use electric meters installed at customers' premises for billing purposes. They are typically calibrated in billing units, the most common one being the kilowatt hour (kWh). They are usually read once each billing period.
When energy savings during certain periods are desired, some meters may measure demand, the maximum use of power in some interval. "Time of day" metering allows electric rates to be changed during a day, to record usage during peak high-cost periods and off-peak, lower-cost, periods. Also, in some areas meters have relays for demand response load shedding during peak load periods.Energy in Hawaii
Energy in Hawaii is complicated by the state's isolated location and lack of fossil fuel resources. The state relies heavily on imports of petroleum and coal for power although renewable energy is increasing. Hawaii is the state with the highest share of petroleum use in the United States, with about 62% of electricity coming from oil in 2017. As of 2016, 26.6% of electricity was from renewable sources, including solar, wind, hydro and geothermal.Hawaii has the highest electricity prices in the United States. As of 2016 the average cost of electricity was $0.24 per kilowatt-hour, followed by Alaska at $0.19. The U.S. average was $0.10.Geothermal power in Germany
Geothermal power in Germany is expected to grow, mainly because of a law that benefits the production of geothermal electricity and guarantees a feed-in tariff. Less than 0.4 percent of Germany's total primary energy supply came from geothermal sources in 2004. But after a renewable energy law that introduced a tariff scheme of EU €0.15 [US $0.23] per kilowatt-hour (kWh) for electricity produced from geothermal sources came into effect that year, a construction boom was sparked and the new power plants are now starting to come online.Joule
The joule (/dʒuːl/; symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m). 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).
In terms firstly of base SI units and then in terms of other SI units:
where kg is the kilogram, m is the metre, s is the second, N is the newton, Pa is the pascal, W is the watt, C is the coulomb, and V is the volt.
One joule can also be defined as:Köthen Solar Park
The Köthen Solar Park is a photovoltaic power station in Köthen, Germany. It has a capacity of 45 megawatts (MW) and an expected annual electricity generation of 42 gigawatt-hours. The solar park was developed and built by RGE Energy.The PV project is built on a former military airfield in Köthen on 116 hectares (290 acres). In 2009, the project was the largest solar power plant in Saxony-Anhalt and the world's largest system using string inverters. The project is equipped with 205,000 solar module made of crystalline silicon by BP Solar. Total investment in the project was around €133 million. The solar park was connected to the grid in 2009. Payment was fixed to 35.49 Euro-cents per kilowatt-hour for 20 years.Muja Power Station
Muja Power Station is a power station 22 km (14 mi) east of Collie, Western Australia. It has eight steam turbines served by coal-fired boilers that together generate a total capacity of 854 megawatts of electricity. The coal is mined in the nearby Collie Sub-basin.
The station was first commissioned on 21 April 1966. Currently four of the eight turbines are running (units 5 through to 8). Muja has four 60 megawatts units (stages A and B), two 200 megawatts units (stage C) and two 227 megawatts units (stage D). The four smallest and least efficient units, stages A and B, were closed in April 2007. In June 2008 it was announced that these older generator units would be recommissioned, due to a statewide natural gas shortage.According to the National Pollutant Inventory (NPI), Muja Power Station is one of the biggest emitters of air pollution in Australia, including high emissions of beryllium, fluoride and particulate matter. Carbon Monitoring for Action estimates that, in 2009, Muja Power Station emitted 5.75 million tonnes (12.7 billion pounds) of CO2 to generate 5.05 terawatt-hours (18.2 petajoules) of electricity.In household consumer terms, this equates to 1.14 kilograms (2.5 lb) of CO2 emitted for each one kilowatt-hour (kWh), or 3.6 megajoules, of electricity produced and fed into the electricity grid. That is, Muja Power Station emits slightly more CO2 per kilowatt-hour of electricity produced than nearby Collie Power Station (1.13 kilograms or 2.5 pounds) and much more than Bluewaters Power Station (0.825 kilograms or 1.82 pounds) based on estimates for the same year.Namugoga Solar Power Station
Namugoga Solar Power Station is a proposed 50 megawatt solar power plant in Uganda.Perovo Solar Park
The Perovo Solar Park is a 100 MWp photovoltaic power station located at Perovo, Simferopol Raion, Crimea. As of July 2012 it is the world's fourth-largest solar farm, and is made up of 440,000 solar panels. It is owned by Activ Solar, and the final 20 MW stage was completed on December 29, 2011.
In 2009, Ukraine established a feed-in tariff of €0.46 per kilowatt hour until 2030, one of the highest.Reckahn Solar Park
Reckahn Solar Park is a photovoltaic power station in Reckahn, Southwest of Berlin, Germany. It has a capacity of 37.7 megawatt (MW) and was constructed in three phases. Reckahn I was 22.661 MW covering 56 hectares (140 acres) and was built by Beck Energy GmbH (Belectric) using 292,000 First Solar thin-film CdTe-panels, and was expected to produce about 22 gigawatt-hours per year. Reckahn II added 13.3 MW, using 172,000 modules on a 35 hectares (86 acres) site. Reckahn III, completed in 2011, added 1.8 MW, bringing the total to 37.7 MW. The FIT is 21.1 Euro cents per kilowatt-hour.Solar power in Illinois
Solar power in Illinois has been increasing, as the cost of photovoltaics has decreased. Illinois adopted a net metering rule which allows customers generating up to 40 kW to use net metering, with the kilowatt hour surplus rolled over each month, and lost at the end of either April or October, as selected by the customer. In 2011, the limit was raised to 2 MW, but is not net metering, as the term is commonly known, as it uses two meters for systems larger than 40 kW.Illinois ranks 26th nationally in cumulative installed solar capacity. There is enough solar energy installed in the state to power 9,500 homes.A 2012 estimate suggests that a typical 5 kW system will pay for itself in about nine years. Additionally, a 5 kW system could end up adding around $10,000 to the value of your home. Reports have also shown that a home with a solar panel system will end up selling approximately 15% faster than a home without. Illinois also offers up to a $10,000 tax credit for a solar installation.In 2002, Illinois' largest solar array was the 99.4 kW array on the roof of the Field Museum of Natural History, in Chicago.In 2010 the country's largest urban solar array, 10 MW, was installed in West Pullman, on Chicago's south side. In 2012, IKEA installed solar PV on its two stores in Bolingbrook and Schaumburg totaling almost 2 MW. Also in 2012, the 20 MW Grand Ridge Solar Plant in LaSalle County was completed. The University of Illinois built a 5.87 MW solar farm in 2015 which will provide 2% of the university's electricity.The first experimental solar power plant was in 1902, in Olney, Illinois, by H.E. Willsie and John Boyle, and was based on a design by Charles Tellier. In 1904 they set up the Willsie Sun company in St. Louis, and built a 6-horsepower motor.In November 2016, ComEd (one of the state's utility) attempted to add additional fees to the bills of only residential solar users, commonly called demand charges, in the text of a wider energy bill. They were eventually pulled out of the bill, which passed in December 2016 without them (the bill also did not repeal net-metering, the practice of compensating solar customers at the retail rate for any excess electricity they produce and export to the grid).Solar power in Ohio
Solar power in Ohio has been increasing, as the cost of photovoltaics has decreased. Ohio installed 10 MW of solar in 2015. Ohio adopted a net metering rule which allows any customer generating up to 25 kW to use net metering, with the kilowatt hour surplus rolled over each month, and paid by the utility once a year at the generation rate upon request. For hospitals there is no limit on size, but two meters are required, one for generation, the other for utility supplied power.In 2010, the 12 MW solar farm in Upper Sandusky, Ohio was the largest solar farm in the state. The 20MW DG AMP Solar Bowling Green was completed in January 2017.The First Solar factory in Perrysburg, Ohio can make almost 600 MW of panels per years.Costs have decreased to the point that the average consumer may save approximately $17,527 over a 20-year period by installing solar panels. Euclid's City Hall and library installed solar panels and expects to save $25,000 over the next 15 years. The panels were installed at no cost to the city by Ohio Cooperative Solar, which is leasing the rooftops.Solaren
Solaren, Inc. is a Southern California startup corporation created to utilize solar energy for terrestrial electricity usage. In 2009, the company had a contract under negotiation with Pacific Gas and Electric Company of California to deliver 200 megawatts of power for at least 15 years., starting in 2016 The cost of the contracted activities has been reported as "slightly more" than California's projected energy cost in 2016 of 12.9 cents per kilowatt hour. As of 2014, the planned delivery date has been moved back to the end of the decade.Solaren plans to provide this electrical power to PG&E's customers from solar panels mounted on satellites placed in Earth's orbit. The satellite would convert this energy into radio waves and send it to a receiving station in Fresno County, California. The plan is to provide 200 megawatts of continuous power, estimated as the average usage of 150,000 homes.
If successful, this project would be the first implementation of space-based solar power (SBSP). The concept was first dreamed up in 1941 by science fiction author Isaac Asimov in his short story "Reason", and was later described scientifically by Peter Glaser in 1968.SunShot Initiative
The SunShot Initiative is a federal government program run by the US Department of Energy's Solar Energy Technologies Office. It bills itself as a national effort to support solar energy adoption in order to make solar energy affordable for all Americans. The initiative is a collaboration of private companies, universities, state and local governments, and nonprofits, as well as national laboratories.Wind power in Utah
Wind power in Utah is in the early stages of development. As of 2016 Utah had 391 MW of wind generation capacity, responsible for 2.6% of in-state electricity generation. Wind thus plays a small role in the state's renewable portfolio standard goals.A 2009 Utah Renewable Energy Zone Taskforce estimated that the state could produce over 9,000 megawatts of wind power. As about 80% of Utah’s population is concentrated along the foot of the Wasatch Front mountain range, reliable and predictable canyon winds offer opportunities for wind power generation and efficient wind energy distribution without long-distance transmission.Utah Power, now PacifiCorp, launched the Blue Sky Program in 2000 to give customers an opportunity to purchase imported wind power, giving customers the option of purchasing 100-kilowatt hour (kWh) "blocks" of renewable energy for a monthly fee through their electricity bills. In the spring 2003, radio station KZMU began operating solely on wind power. Kinkos also participates.
PacifiCorp, the major provider in Utah, imports much of it renewable energy in the state and does not intend to build facilities within it until at least 2024.The first utility scale wind farm was built at Spanish Fork in 2008.