Kilowatt hour Totally Explained

Everything about Board Of Trade Unit totally explained

   The kilowatt hour, also written kilowatt-hour, (symbol kW·h, kW h or kWh) is a unit of energy. 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 isn't 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.
   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.

Definition

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 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.

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).

Other expressions of the watt hour

Another derived unit that's 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.
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. shouldn't be confused with the British thermal unit or BTU, which is a much smaller quantity of thermal energy. 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.

Multiples

Symbol and abbreviation for kilowatt hour

The brochure for SI and a voluntary standard 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 and the IEEE/ASTM standard allow kWh (but don't mention other multiples of the watt hour). One guide published by NIST specifically recommends avoiding "kWh" "to avoid possible confusion". Nonetheless, it's commonly used in commercial, educational, scientific and media publications.

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

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