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. Major energy production or consumption is often expressed as terawatt-hours (TWh) for a given period that is often a calendar year or financial year. Industrial users may also have extra charges according to the power factor of their load. These charges are billed as demand changes. This compensates the power company for maintaining the infrastructure needed to provide peak power. 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. In the United States prices in different states can vary by a factor of three. The unit price of electricity charged by utility companies may depend on the customer's consumption profile over time. The cost of running an electrical device is calculated by multiplying the device's power consumption in kilowatts by the operating time in hours, and by the price per kilowatt-hour. A 40-watt electric appliance operating continuously for 25 hours uses one kilowatt-hour.Įlectrical energy is typically sold to consumers in kilowatt-hours. A television consuming 100 watts operating continuously for 10 hours uses one kilowatt-hour. Īn electric heater consuming 1,000 watts (1 kilowatt), and operating for one hour uses one kilowatt-hour of energy.
Its combination with the kilowatt, a standard SI unit, is therefore permitted within the standard. The hour is a unit of time listed among the non-SI units accepted by the International Bureau of Weights and Measures for use with the SI. The notation "kW/h" for the kilowatt-hour is incorrect, as it denotes kilowatt per hour.Variations in capitalization are sometimes encountered: KWh, KWH, kwh, etc., which are inconsistent with the International System of Units.The United States official fuel-economy window sticker for electric vehicles uses the abbreviation "kW-hrs".One guide published by NIST specifically recommends against "kWh" "to avoid possible confusion". However, the IEEE/ASTM standard allows "kWh" (but does not mention other multiples of the watt-hour). The SI brochure states that in forming a compound unit symbol, "Multiplication must be indicated by a space or a half-high (centred) dot (⋅), since otherwise some prefixes could be misinterpreted as a unit symbol." This is supported by a voluntary standard issued jointly by an international ( IEEE) and national ( ASTM) organization, and by a major style guide. "kW⋅h" and "kW h" are less commonly used, but they are consistent with the SI.
Other representations of the unit may be encountered: This common representation, however, does not comply with the style guide of the International System of Units (SI).
It is also the usual unit representation in electrical power engineering. It is commonly used in billing for delivered energy to consumers by electric utility companies, and in commercial, educational, and scientific publications, and in the media. Unit representations Ī widely used representation of the kilowatt-hour is "kWh", derived from its component units, kilowatt and hour. Expressed in the standard unit of energy in the International System of Units (SI), the joule (symbol J), it is equal to 3,600 kilojoules or 3.6 MJ. The kilowatt-hour is a composite unit of energy equal to one kilowatt (kW) sustained for (multiplied by) one hour. Metric prefixes are used for multiples and submultiples of the basic unit, the watt-hour (3.6 kJ). Kilowatt-hours are a common billing unit for electrical energy supplied by electric utilities. Residential electricity meter located in CanadaĪ kilowatt-hour ( unit symbol: kW⋅h or kW h commonly written as kWh) 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.
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