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The '''kilowatt hour''' (symbol '''kWh''' or '''kW·h''') is a unit of [[energy]] equal to 1000 [[watt]] hours or 3.6 [[SI#prefixes|mega]][[joule]]s. Energy in kilowatt hours is the multiplication of [[Power (physics)|power]] in [[SI#prefixes|kilo]][[watt]]s and time in hours. The kilowatt hour is most commonly known as a billing unit for electrical energy delivered to consumers by electric service providers.


The '''kilowatt hour'''(symbol '''kWh''' or '''kW·h''') 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>
==Definition==
 
Energy in kilowatt hours is the multiplication of [[Power (physics)|power]] in [[kilowatt]]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 and thus one kilowatt hour is 3.6 × 10<sup>6</sup> joules or 3.6 [[SI#prefixes|mega]][[joule]]s, which is the amount of energy expended if [[work]] is done at a constant rate of one thousand watts for one hour.
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==
==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.
*A heater, rated at 1000 watts (1 kilowatt), operating for one hour uses one kilowatt hour (equivalent to 3.6  megajoules) of energy.


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


100 W &times; 30 h = 3000 W·h = 3 kW·h or 10.8 million [[joules]].
*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 Wh = 3 kWh (equivalent to 10.8 megajoules).  


==Symbol and abbreviation for kilowatt hour==
==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>
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>
<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>


==References==
==References==

Revision as of 17:29, 22 January 2010

The kilowatt hour (symbol kWh or kW·h) is a unit of energy equal to 1000 watt hours or 3.6 megajoules. Energy in kilowatt hours is the multiplication of power in kilowatts and time in hours. The kilowatt hour is most commonly known as a billing unit for electrical energy delivered to consumers by electric service providers.

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 and thus one kilowatt hour is 3.6 × 106 joules or 3.6 megajoules, which is the amount of energy expended 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 3.6 megajoules) 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 Wh = 3 kWh (equivalent to 10.8 megajoules).

Symbol and abbreviation for kilowatt hour

The brochure for SI[1] and a voluntary standard[2] 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[3] 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".[4] Nonetheless, it is commonly used in commercial, educational, scientific and media publications.[5]

[6][7]

References

  1. ↑ The International System of Units (SI). (2006, 8th ed.) Paris: International Bureau of Weights and Measures. 130.
  2. ↑ 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.
  3. ↑ Chicago Manual of Style. (14th ed., 1993) University of Chicago Press. 482.
  4. ↑ Taylor, Barry N. (1995). 13
  5. ↑ 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.
  6. ↑ 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.
  7. ↑ "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


External links

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