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The '''kilowatt hour''', or ''kilowatt-hour'', (symbol '''kW·h''', '''kWh''') is a unit of [[energy]] equal to 1000 watt hours or 3.6&nbsp;[[mega]][[joule]]s.<ref name="taylor1995">Taylor, Barry N. (1995). [http://physics.nist.gov/Document/sp811.pdf ''Guide for the Use of the International System of Units (SI)''] (Special publication 811). Gaithersburg, MD: [[National Institute of Standards and Technology]]. 31.</ref><ref name="taylor2001">"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.) [http://physics.nist.gov/Pubs/SP330/sp330.pdf ''The International System of Units.''] (Special publication 330). Gaithersburg, MD: [[National Institute of Standards and Technology]]. 20</ref>
Energy in watt hours is the [[Product (mathematics)|multiplication]] of [[Power (physics)|power]] in [[watt]]s and time in hours.
The kilowatt hour is most commonly known as a billing unit for energy delivered to consumers by electric utilities.
==Definition==
The standard unit of energy in the [[International System of Units]] (SI) is the [[joule]] (J), equal to one [[watt]] [[second]]. Inversely, one watt is equal to 1 J/s. One kilowatt hour is 3.6&nbsp;[[mega-|mega]]joules, which is the amount of energy [[wiktionary:expend|expended]] (or [[wiktionary:dissipate|dissipated]]) if work is done at a constant rate of one thousand watts for one hour.
==Examples==
A heater, rated at 1000 watts (1 kilowatt), operating for one hour uses one kilowatt hour (equivalent to 3,600 kilojoules) of energy.
Using a 60 watt light bulb for one hour consumes 0.06 kilowatt hours of electricity. Using a 60 watt light bulb for one thousand hours consumes 60 kilowatt hours of electricity.
If a 100 watt light bulb is on for one hour per day for 30 days, the energy used is
100 W &times; 30 h = 3000 W·h = 3 kW·h or 10.8 million [[joules]].
==Symbol and abbreviation for kilowatt hour==
The brochure for [[SI]]<ref>[http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf The International System of Units (SI)]. (2006, 8th ed.) Paris: [[International Bureau of Weights and Measures]]. 130.</ref> and a voluntary standard<ref>''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 Conshohocken, PA: [[Institute of Electrical and Electronics Engineers]] and [[ASTM]]. 15.</ref> 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<ref>''Chicago Manual of Style''. (14th ed., 1993) University of Chicago Press. 482.</ref> 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".<ref> Taylor, Barry N. (1995). 13</ref> Nonetheless, it is commonly used in commercial, educational, scientific and media publications.<ref>See for example: [http://www.windpower.org/en/stat/unitsene.htm ''Wind Energy Reference Manual Part 2: Energy and Power Definitions''] Danish Wind Energy Association. Retrieved 9 January 2008; [http://www.businessdictionary.com/definition/Kilowatt-Hour-kWh.html "Kilowatt-Hour (kWh)"] BusinessDictionary.com. Retrieved 9 January 2008; [http://www.world-nuclear.org/info/inf41.html "US Nuclear Power Industry"] www.world-nuclear.org. Retrieved 9 January 2008; [http://eeru.open.ac.uk/natta/energy.html#4"Energy. A Beginners Guide: Making Sense of Units"] ''Renew On Line (UK)''. The [[Open University]]. Retrieved 9 January 2008.</ref>
==References==
{{Reflist}}
==External links==
* [http://tcip.mste.illinois.edu/applet1.php Power and Energy in the Home]: The [http://tcip.mste.illinois.edu/ Trustworthy Cyber Infrastructure for the Power Grid (TCIP)] group at the [http://illinois.edu 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.
* [http://www.batteryhippo.com/pages/Capacity-Conversion.html Battery Capacity: ampere hour to watt hour conversion]
* [http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html Prices per kilowatt hour in the USA, Energy Information Administration]

Revision as of 16:50, 22 January 2010


The kilowatt hour, or kilowatt-hour, (symbol kW·h, kWh) is a unit of energy equal to 1000 watt hours or 3.6 megajoules.[1][2]

Energy in watt hours is the multiplication of power in watts and time in hours.

The kilowatt hour is most commonly known as a billing unit for energy delivered to consumers by electric utilities.

Definition

The standard unit of energy in the International System of Units (SI) is the joule (J), equal to one watt second. Inversely, one watt is equal to 1 J/s. One kilowatt hour is 3.6 megajoules, which is the amount of energy expended (or dissipated) if work is done at a constant rate of one thousand watts for one hour.

Examples

A heater, rated at 1000 watts (1 kilowatt), operating for one hour uses one kilowatt hour (equivalent to 3,600 kilojoules) of energy.

Using a 60 watt light bulb for one hour consumes 0.06 kilowatt hours of electricity. Using a 60 watt light bulb for one thousand hours consumes 60 kilowatt hours of electricity.

If a 100 watt light bulb is on for one hour per day for 30 days, the energy used is

100 W × 30 h = 3000 W·h = 3 kW·h or 10.8 million joules.

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]

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 Conshohocken, 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.


External links

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