Kilojoule

The kilojoule (kJ) is equal to one thousand (103) joules. Nutritional food labels in certain countries express energy in standard kilojoules (kJ).

One kilojoule per second (1 kilowatt) is approximately the amount of solar radiation received by one square metre of the Earth in full daylight.

Megajoule

The megajoule (MJ) is equal to one million (106) joules, or approximately the kinetic energy of a one-ton vehicle moving at 160 km/h (100 mph).

Because 1 watt times one second equals one joule, 1 kilowatt-hour is 1000 watts times 3600 seconds, or 3.6 megajoules.

Gigajoule

The gigajoule (GJ) is equal to one billion (109) joules. Six gigajoules is about the amount of potential chemical energy in a barrel of oil, when combusted.

Terajoule

The terajoule (TJ) is equal to one trillion (1012) joules. About 63 terajoules were released by the atomic bomb that exploded over Hiroshima. The International Space Station, with a mass of approximately 450,000 kg and orbital velocity of 7.7 km/s, has a kinetic energy of roughly 13.34 terajoules.

Petajoule

The petajoule (PJ) is equal to one quadrillion (1015) joules. 210 PJ is equivalent to about 50 megatons of TNT. This is the amount of energy released by the Tsar Bomba, the largest man-made nuclear explosion ever.

Exajoule

The exajoule (EJ) is equal to one quintillion (1018) joules. The 2011 TÅhoku earthquake and tsunami in Japan had 1.41 EJ of energy according to its 9.0 on themoment magnitude scale. Energy in the United States used per year is roughly 94 EJ.

Zettajoule

The zettajoule (ZJ) is equal to one sextillion (1021) joules. Annual global energy consumption is approximately 0.5 ZJ.

Electricity is usually measured in Watts

Kilowatt

The kilowatt is equal to one thousand (103) watts, or one sthene-metre per second. This unit is typically used to express the output power of engines and the power of electric motors, tools, machines, and heaters. It is also a common unit used to express the electromagnetic power output of broadcast radio and television transmitters.

One kilowatt is approximately equal to 1.34 horsepower. A small electric heater with one heating element can use 1.0 kilowatt, which is equivalent to the power of a household in the United States averaged over the entire year.

Also, kilowatts of light power can be measured in the output pulses of some lasers.

A surface area of one square meter on Earth receives typically one kilowatt of sunlight from the sun (on a clear day at midday).

Megawatt

The megawatt is equal to one million (106) watts. Many events or machines produce or sustain the conversion of energy on this scale, including lightning strikes; large electric motors; large warships such as aircraft carriers, cruisers, and submarines; large server farms or data centers; and some scientific research equipment, such as supercolliders, and the output pulses of very large lasers. A large residential or commercial building may use several megawatts in electric power and heat. On railways, modern high-powered electric locomotives typically have a peak power output of 5 or 6 MW, although some produce much more. The Eurostar, for example, uses more than 12 MW, while heavy diesel-electric locomotives typically produce/use 3 to 5 MW. U.S. nuclear power plants have net summer capacities between about 500 and 1300 MW.[5]

The 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).

Gigawatt

The gigawatt is equal to one billion (109) watts or 1 gigawatt = 1000 megawatts. This unit is sometimes 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 and the installed capacity of wind power in Germany was 25.8 GW.The largest unit (out of four) of the Belgian Nuclear Plant Doel has a peak output of 1.04 GW. HVDC converters have been built with power ratings of up to 2 GW.The London Array, the world's largest offshore wind farm, is designed to produce a gigawatt of power.

Terawatt

The terawatt is equal to one trillion (1012) watts. The total power used by humans worldwide (about 16 TW in 2006) is commonly measured in this unit. 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 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 about 0.5 ps (5 × 10−13 s), giving a total energy of 600 J, or enough energy to power a 100 W light bulb for six seconds.

Based on the average total solar irradiance of 1.366 kW/m2, the total power of sunlight striking Earth's atmosphere is estimated at 174 PW (cf. Solar Constant).

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