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## PowerPedia:Watt

Lasted edited by Andrew Munsey, updated on June 15, 2016 at 2:08 am.

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The watt (symbol: W) is the `There was an error working with the wiki: Code[4]` of Power (physics), equal to one `There was an error working with the wiki: Code[5]` lightbulb uses 40 to 100 watts.

The watt-hour (symbol W·h) is a unit of `There was an error working with the wiki: Code[6]` Energy.

#### Definition

One watt is one `There was an error working with the wiki: Code[7]`. That is, if 1 volt of potential difference is applied to a resistive load, and a current of 1 ampere flows, then 1 watt of power is dissipated.

One watt-hour (abbreviated Whr) is the amount of (usually electrical) Energy expended by a one-watt load (e.g. light bulb) drawing power for one hour.

Humans tend to use watt-hours to measure energy rather than `There was an error working with the wiki: Code[8]`, because of intuitive reasons: 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 unit of time, so when multiplied together they produce a unit of energy called the watt-hour.

Power companies produce energy - a good - which is often purchased by the customer in units of kilowatt-hours. Consider a setup with two 50W light bulbs (100W total) left on for 10 hours per day. The setup will consume 1kilowatt-hour per day. If a power company charges US\$0.10 / kilowatt-hour, then those two light bulbs will cost US\$0.70 over the course of a week. (See `There was an error working with the wiki: Code[9]` for more information.)

1 watt-hour is equivalent to 3,600&nbsp`There was an error working with the wiki: Code[13]`s, the joule being the SI unit of energy. (Thus a kilowatt-hour is 3,600,000&nbspjoules or 3.6&nbspmegajoules.)

#### Origin

The watt is named after `There was an error working with the wiki: Code[14]` for his contributions to the development of the Steam engine, and was adopted by the Second Congress of the British Association for the Advancement of Science in 1889 and by the 11th `There was an error working with the wiki: Code[15]` in 1960.

#### SI multiples

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#### Derived and qualified units for power distribution

The watt-hour is derived from the multiplication of the SI unit of Power (physics) (`There was an error working with the wiki: Code[10]` and Natural gas energy. Many `There was an error working with the wiki: Code[16]` 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." Megawatt-hours are used for metering of larger amounts of electrical energy. For example, a Power plant's daily output is likely to be measured in megawatt-hours.

Some sources mistakenly refer to watt-hours as "power." A similar confusion can arise when describing daily energy use. For example, a Solar cell array might have a peak power output of 100 watts, but in order to give an indication of its useable output as a function of time-varying conditions (such as the apparent daily solar motion, or dust collection on the surface), its typical output might be described as “1200 watt-hours per day". Different writers may disagree as to whether this is a measure of power or energy usage.

Another derived unit that is sometimes used for household purposes is the kWh/yr, usually considered in annual energy consumption calculations, but with the dimensions of power, with 1 kWh/yr = 0.114 W. Note that this unit uses three units of time in one unit, namely `There was an error working with the wiki: Code[17]`, `There was an error working with the wiki: Code[18]` and `There was an error working with the wiki: Code[19]`, of which only the first is an SI unit.

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 `There was an error working with the wiki: Code[20]` that regulated the electricity industry. The B.O.T.U. should not be confused with the `There was an error working with the wiki: Code[21]` or BTU, which is a much smaller quantity of thermal energy.

as the energy goes the more kw to get per hour

##### Megawatt

The megawatt (symbol: MW) is equal to one `There was an error working with the wiki: Code[22]` (106) watts.

Many things can sustain the transfer or consumption of energy on this scale some of these events or entities include: `There was an error working with the wiki: Code[23]` strikes, large electric motors, naval craft (such as `There was an error working with the wiki: Code[24]`s and `There was an error working with the wiki: Code[25]`s), engineering hardware, and some scientific research equipment (such as the `There was an error working with the wiki: Code[26]` and large `There was an error working with the wiki: Code[27]`s). A large residential or retail building may consume several megawatts in electric power and heating energy.

The productive capacity of `There was an error working with the wiki: Code[11]` is often measured in MW. Modern high-powered `There was an error working with the wiki: Code[28]` railroad `There was an error working with the wiki: Code[29]`s typically have a peak power output of (3 to 5) MW, whereas a typical modern `There was an error working with the wiki: Code[30]` produces a peak output on the order of 500 to 2000 MW.

According to the `There was an error working with the wiki: Code[31]`, the earliest citing for "megawatt" is a reference in the 1900 `There was an error working with the wiki: Code[32]` International Dictionary of English Language. The OED also says "megawatt" appeared in a `There was an error working with the wiki: Code[33]`, `There was an error working with the wiki: Code[34]`, article in `There was an error working with the wiki: Code[35]` (506:2).

##### Watts electrical and thermal

Watt electrical (abbreviation: We) is a term that refers to power produced as electricity. `There was an error working with the wiki: Code[12]` versus the (larger) thermal output. For example, the `There was an error working with the wiki: Code[36]` in Argentina uses a `There was an error working with the wiki: Code[37]` to generate 2109 MWt of heat, which creates steam to drive a turbine, which generates 648 MWe of electricity.

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#### Related

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`There was an error working with the wiki: Code[42]` (RMS)

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`There was an error working with the wiki: Code[45]` (power plants)

Nelson, Robert A., "The International System of Units Its History and Use in Science and Industry". Via Satellite, February 2000.

http://ebtx.com/mech/ampvolt.htm

`There was an error working with the wiki: Code[1]`, Wikipedia: The Free Encyclopedia. Wikimedia Foundation.

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