Webster's International DictiThe earliest citing of the megawatt in the Oxford English Dictionary (OED) is a reference in the 1900 Webster's International Dictionary of English Language. The OED also states that megawatt appeared in a 28 November 1947 article in the journal Science (506:2).
The gigawatt (GW) is equal to one billion (109) watts or 1 gigawatt = 1000 megawatts. This unit is often used for large power plants or power grids. For example, by the end of 2010 power shortages in China's Shanxi province were expected to increase to 5–6 GW[18] and the installed capacity of wind power in Germany was 25.8 GW.[19] The largest unit (out of four) of the Belgian Doel Nuclear Power Station has a peak output of 1.04 GW.[20] HVDC converters have been built with power ratings of up to 2 GW.[21]
Terawatt
The terawatt (TW) is equal to one trillion (1012) watts. The total power used by humans worldwide is commonly measured in terawatts. The most powerful lasers from the mid-1960s to the mid-1990s produced power in terawatts, but only for nanosecond time frames. The average lightning strike peaks at 1 terawatt, but these strikes only last for 30 microseconds.
Petawatt
The petawatt (PW) is equal to one quadrillion (1015) watts and can be produced by the current generation of lasers for time scales on the order of picoseconds (10−12 s). One such laser is the Lawrence Livermore's Nova laser, which achieved a power output of 1.25 PW (1.25×1015 W) by a process called chirped pulse amplification. The duration of the pulse was roughly 0.5 ps (5×10−13 s), giving a total energy of 600 J.[22] Another example is the Laser for Fast Ignition Experiments (LFEX) at the Institute of Laser Engineering (ILE), Osaka University, which achieved a power output of 2 PW for a duration of approximately 1 ps.[23][24]
Based on the average total solar irradiance[25] of 1.366 kW/m2, the total power of sunlight
Based on the average total solar irradiance[25] of 1.366 kW/m2, the total power of sunlight striking Earth's atmosphere is estimated at 174 PW.
In the electric power industry, megawatt electrical (MWe[26] or MWe[27]) refers by convention to the electric power produced by a generator, while megawatt thermal or thermal megawatt[28] (MWt, MWt, or MWth, MWth) refers to thermal power produced by the plant. For example, the Embalse nuclear power plant in Argentina uses a fission reactor to generate 2109 MWt (i.e. heat), which creates steam to drive a turbine, which generates 648 MWe (i.e. electricity). Other SI prefixes are sometimes used, for example gigawatt electrical (GWe). The International Bureau of Weights and Measures, which maintains the SI-standard, states that further information about a quantity should not be attached to the unit symbol but instead to the quantity symbol (i.e., Pthermal = 270 W rather than P = 270 Wth) and so these units are non-SI.[29] In compliance with SI the energy company Ørsted A/S uses the unit megawatt for produced electrical power and the equivalent unit megajoule per second for delivered heating power in a combined heat and power station such as Avedøre Power Station.[30]
When describing alternating current (AC) electricity, another distinction is made between the watt and the volt-ampere. While these units are equivalent for simple resistive circuits, they differ when loads exhibit electrical reactance.
<When describing alternating current (AC) electricity, another distinction is made between the watt and the volt-ampere. While these units are equivalent for simple resistive circuits, they differ when loads exhibit electrical reactance.
Radio stations usually report the power of their transmitters in units of watts, referring to the effective radiated power. This refers to the power that a half-wave dipole antenna would need to radiate to match the intensity of the transmitter's main lobe.
Distinction between watts and watt-hours
The terms power and power and energy are frequently[when?] confused.[by whom?] Power is the rate at which energy is generated or consumed and hence is measured in units (e.g. watts) that represent energy per unit time.
For example, when a light bulb with a power rating of 100W is turned on for one hour, the energy used is 100 watt hours (W·h), 0.1 kilowatt hour, or 360 kJ. This same amou
For example, when a light bulb with a power rating of 100W is turned on for one hour, the energy used is 100 watt hours (W·h), 0.1 kilowatt hour, or 360 kJ. This same amount of energy would light a 40-watt bulb for 2.5 hours, or a 50-watt bulb for 2 hours.
Power stations are rated using units of power, typically megawatts or gigawatts (for example, the Three Gorges Dam in China, is rated at approximately 22 gigawatts). This reflects the maximum power output it can achieve at any point in time. A power station's annual energy output, however, would be recorded using units of energy (not power), typically gigawatt hours. Major energy production or consumption is often expressed as terawatt hours for a given period; often a calendar year or financial year. One terawatt hour of energy is equal to a sustained power delivery of one terawatt for one hour, or approximately 114 megawatts for a period of one year:
equivalent to approximately 114 megawatts of constant power output.
The watt second is a unit of energy, equal to the joule.
One kil
The watt second is a unit of energy, equal to the joule.
One kilowatt hour is 3,600,000 watt seconds.
While a watt per hour exists in principle (as a unit of rate of change of power with time[iii]), it is not correct to refer to a watt (or watt hour) as a "watt per hour".[31]
