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Encyclopedia > Kilowatt hour

The kilowatt hour, also written kilowatt-hour,[1] (symbol kW·h, kW h or kWh) is a unit of energy.[2] It is most commonly used to express amounts of energy delivered by electric utilities, and it appears on electric meters and bills in some countries.


The kilowatt hour is a measure of work, the watt is a measure of power. The amount of wattage times the amount of time is the amount of work done.


It is not used in the International System of Units (SI). The SI unit of energy is the joule (J), equal to one watt second. The kilowatt hour is commonly used, though, especially for measuring electric energy. Look up si, Si, SI in Wiktionary, the free dictionary. ... The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... This article is about the unit of time. ... Electricity (from New Latin Ä“lectricus, amberlike) is a general term for a variety of phenomena resulting from the presence and flow of electric charge. ...


One watt hour is equivalent to 3,600 joules (1 J/s × 3600 s), thus a kilowatt hour is 3,600,000 joules or 3.6 megajoules, and a kilowatt refers to the specific rate at which the amount of joules is used in a second (also known as power). As such, a kilowatt equals the production or usage of 1,000 joules of energy per second (that is, a definitive rate), and a kilowatt hour is the specific amount of energy produced, transmitted, distributed, or consumed in a 3,600-second time period, which is 3,600,000 joules as mentioned above. The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... The kilowatt (symbol: kW) is a unit for measuring power, equal to one thousand watts. ... In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time. ...

Contents

Definition

One watt hour is the amount of (usually electrical or natural gas) energy expended by a one-watt load (e.g., light bulb) drawing power for one hour.


Laymen and utilities tend to use watt hours to measure energy for reasons of convenience and intuition, rather than scientists, who use joules (J). For example, a light bulb draws power (units of watts) over a certain amount of time, resulting in a net amount of used energy; a watt has units of energy-per-time, and an hour is a convenient unit for measuring time, so when multiplied together they produce a unit of energy called the watt hour. The watt hour is derived from the multiplication of the SI unit of power (watt) and a non-SI unit of time (hour). In simple terms, it means the amount of power (watts) used for any given number of hours. A lightbulb that needs 50 J of energy per second to light up (50 watts) will consume 500 watt hours of energy if left on for 10 hours. The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... For delivered electrical power, see Electrical power industry. ... In physics, power (symbol: P) is the rate at which work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time. ... For other uses, see Watt (disambiguation). ... The hour (symbol: h) is a unit of time. ...


The kilowatt hour is commonly used for electrical energy and natural gas energy. Many electric utility companies use the kilowatt hour for billing. This is a convenient unit because the energy usage of a typical home in one month is several hundred kilowatt hours. In addition, the typical consumer can readily conceptualize the notion of "using a kilowatt for one hour”; common appliances that consume approximately 1 kW include hairdryers, microwave ovens, and vacuum cleaners. Megawatt hours are used for metering of larger amounts of electrical energy. Electrical energy can refer to several closely related things. ... For other uses, see Natural gas (disambiguation). ... 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. ...


Pricing for kilowatt hours

Power companies sell energy in units of kilowatt hours. In general, energy (E) is equivalent to power (P) multiplied by time (t). To determine E in kilowatt hours, P must be expressed in kilowatts and t must be expressed in hours. Suppose a 1.5 kW electric heater runs for 3 h. Then P = 1.5 kW and t = 3 h, so the energy E in kilowatt hours is: E = Pt = 1.5 kW × 3 h = 4.5 kW·h. If P and t are not specified in kilowatts and hours respectively, then they must be converted to those units before determining E in kilowatt hours. Consider the use of one 100 W light bulb (0.1 kW) used for 10 hours per day. This will consume 1 kilowatt hour per day (0.1 kW × 10 h). If a power company charges €0.10/kW·h, then this light bulb will cost €0.10 a day and €0.70 a week to operate (0.1 kW × 10 h × €0.10/kW·h × 7 d/week.) (See Units of measurement#Expressing a physical value in terms of another unit for more information). The former Weights and Measures office in Middlesex, England. ...


Other expressions of the watt hour

Another derived unit that is sometimes used for household purposes is the kW·h/yr., usually considered in annual energy consumption calculations, but with the dimensions of power, with 1 kW·h/yr. = 0.114 W. Note that this unit uses three units of time in one unit, namely second, hour and year, of which only the first is an SI unit. This article is about the unit of time. ... The hour (symbol: h) is a unit of time. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ...


The Board of Trade unit or B.O.T.U. is an obsolete UK synonym for kilowatt hour. The term derives from the name of the Board of Trade that regulated the electricity industry. The B.O.T.U. should not be confused with the British thermal unit or BTU, which is a much smaller quantity of thermal energy. The Board of Trade circa 1808. ... The British thermal unit (BTU or Btu) is a unit of energy used in the Power, Steam Generation and Heating and Air Conditioning industry globally. ...


Burnup of nuclear fuel is normally quoted in megawatt days per ton (MWd/MTU), where ton refers to a metric ton of uranium metal or its equivalent, and megawatt refers to the entire thermal output, not the fraction which is recovered as electricity. In nuclear power technology, burnup is a measure of the neutron irradiation of the fuel. ... Nuclear Fuel Process A graph comparing nucleon number against binding energy Nuclear fuel is any material that can be consumed to derive nuclear energy, by analogy to chemical fuel that is burned to derive energy. ...


Multiples

SI multiples for watt hour (W·h)
Submultiples Multiples
Value Symbol Name Value Symbol Name
10–1 W·h dW·h deciwatt hour 101 W·h daW·h decawatt hour
10–2 W·h cW·h centiwatt hour 102 W·h hW·h hectowatt hour
10–3 W·h mW·h milliwatt hour 103 W·h kW·h kilowatt hour
10–6 W·h µW·h microwatt hour 106 W·h MW·h megawatt hour
10–9 W·h nW·h nanowatt hour 109 W·h GW·h gigawatt hour
10–12 W·h pW·h picowatt hour 1012 W·h TW·h terawatt hour
10–15 W·h fW·h femtowatt hour 1015 W·h PW·h petawatt hour
10–18 W·h aW·h attowatt hour 1018 W·h EW·h exawatt hour
10–21 W·h zW·h zeptowatt hour 1021 W·h ZW·h zettawatt hour
10–24 W·h yW·h yoctowatt hour 1024 W·h YW·h yottawatt hour
Common multiples are in bold face

Symbol and abbreviation for kilowatt hour

The brochure for SI[3] and a voluntary standard[4] issued jointly by an international (IEEE) and national (ASTM) organization state that when compound unit symbols are formed by multiplication, the individual symbols should be separated by a half-high dot or a space (for example, "kW·h" or "kW h"). However, at least one major usage guide[5] and the IEEE/ASTM standard allow kWh (but do not mention other multiples of the watt hour). One guide published by NIST specifically recommends avoiding "kWh" "to avoid possible confusion".[6] Nonetheless, it is commonly used in commercial, educational, scientific and media publications.[7] Look up si, Si, SI in Wiktionary, the free dictionary. ... The Institute of Electrical and Electronics Engineers or IEEE (pronounced as eye-triple-ee) is an international non-profit, professional organization incorporated in the State of New York, United States. ... ASTM International is an international voluntary standards organization that develops and produces technical standards for materials, products, systems and services. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ...


Conversions

from / to joule watt hour electronvolt calorie
1 J = 1 kg m2 s-2 = 1 0.278 × 10−3 6.241 × 1018 0.239
1 W·h = 3600 1 2.247 × 1022 859.8
1 eV = 1.602 × 10−19 4.45 × 10−23 1 3.827 × 10−20
1 cal = 4.1868 1.163 × 10−3 2.613 × 1019 1

The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... The electronvolt (symbol eV) is a unit of energy. ... Etymology: French calorie, from Latin calor (heat), from calere (to be warm). ...

See also

Energy Portal

Image File history File links Crystal_128_energy. ... An ampere-hour (abbreviated as Ah or A-h) is a unit of electric charge. ... This article or section does not cite any references or sources. ... For other uses, see Watt (disambiguation). ...

References

  1. ^ Taylor, Barry N. (1995). Guide for the Use of the International System of Units (SI) (Special publication 811). Gaithersburg, MD: National Institute of Standards and Technology. 31.
  2. ^ "Half-high dots or spaces are used to express a derived unit formed from two or more other units by multiplication." Barry N. Taylor. (2001 ed.) The International System of Units. (Special publication 330). Gaithersburg, MD: National Institute of Standards and Technology. 20.
  3. ^ The International System of Units (SI). (2006, 8th ed.) Paris: International Bureau of Weights and Measures. 130.
  4. ^ Standard for the Use of the International System of Units (SI): The Modern Metric System. (1997). (IEEE/ASTM SI 10-1997). New York and West Conshohoken, PA: Institute of Electrical and Electronics Engineers and ASTM. 15.
  5. ^ Chicago Manual of Style. (14th ed., 1993) University of Chicago Press. 482.
  6. ^ Taylor, Barry N. (1995). 13
  7. ^ See for example: Wind Energy Reference Manual Part 2: Energy and Power Definitions Danish Wind Energy Association. Retrieved 9 January 2008; "Kilowatt-Hour (kWh)" BusinessDictionary.com. Retrieved 9 January 2008; "US Nuclear Power Industry" www.world-nuclear.org. Retrieved 9 January 2008; "Energy. A Beginners Guide: Making Sense of Units" Renew On Line (UK). The Open University. Retrieved 9 January 2008.

NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ... NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ... The International Bureau of Weights and Measures is the English name of the Bureau international des poids et mesures (BIPM, often written in English Bureau International des Poids et Mesures), a standards organisation, one of the three organizations established to maintain the International System of Units (SI) under the terms... Not to be confused with the Institution of Electrical Engineers (IEE). ... ASTM International is an international voluntary standards organization that develops and produces technical standards for materials, products, systems and services. ... is the 9th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 9th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 9th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... Affiliations Alliance of Non-Aligned Universities, Association of Commonwealth Universities, European Association of Distance Teaching Universities, Middle States Association of Colleges and Schools Website http://www. ... is the 9th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ...

External links

  • Power and Energy in the Home - The Trustworthy Cyber Infrastructure for the Power Grid (TCIP) group at the University of Illinois at Urbana-Champaign has developed an applet which illustrates the consumption and cost of energy in the home, and allows the user to see the effects of manipulating the flow of electricity to various household appliances.

  Results from FactBites:
 
WEST VIRGINIA CODE (818 words)
(C) The total kilowatt hours of electricity generated at the generating unit exempted from tax during the period by subsection (b), section two-n [§ 11-13-2n] of this article.
For the purposes of this subdivision, net kilowatt hours of electricity generated or produced in this state by the taxpayer includes the taxpayer's pro rata share of electricity generated or produced in this state by a partnership or limited liability company of which the taxpayer is a partner or member.
The provisions of this subdivision (2) shall not apply to those kilowatt hours exempt under subsection (b), section two-n [§ 11-13-2n] of this article.
The Gas (Metrication) Regulations 1992 (0 words)
A is the number of cubic metres of gas supplied to the customer during the relevant charge period, and B is the relevant calorific value in megajoules per cubic metre, of the gas supplied to the customer during such period.
(b) with effect from 1st January 2000, in the definition of "a relevant supplier", for the word "therms" there shall be substituted the words "kilowatt hours".
(b) with effect from 1st January 2000, in paragraph (a), for the word "therms" there shall be substituted the words "kilowatt hours".
  More results at FactBites »

 
 

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