The metric unit for energy is the joule (1J).
For power, or energy use per unit time, the unit is the watt (1W).
The metric time unit is the second (1 s) so
1 J = 1 W * 1 s
It also helps to be familiar with the standard metric prefixes for large numbers, since we'll be dealing with some very large numbers here. Each of these is 1000 times larger than the previous:
|G||giga-||10^9 (1 billion)|
|T||tera-||10^12 (1 trillion)|
|P||peta-||10^15 (1 quadrillion)|
Many other energy and time units are frequently used in reporting energy industry data:
|1 Btu||British thermal unit||1055 J|
|1 kWh||kilowatt-hour||3.6 MJ (megajoule)|
|1 kWh||kilowatt-hour||3412 Btu|
|1 bboe||barrel of oil equivalent||5.8 million Btu|
|1 bboe||barrel of oil equivalent||6.12 GJ (gigajoule)|
|1 bboe||barrel of oil equivalent||1700 kWh|
|1 toe||(metric) ton of oil equivalent||39.7 million Btu|
|1 toe||(metric) ton of oil equivalent||41.9 GJ|
|1 tce||(metric) ton of coal equivalent||27.8 million Btu|
|1 tce||(metric) ton of coal equivalent||29.3 GJ|
|1 short ton coal||2000 lb of coal equivalent||25 million Btu|
Note that coal has only about 70% the energy content of oil, for the same
The following units are on the scale of yearly world energy consumption (1 year = 8766 hours or 31.5 million seconds):
|1 TWh||terawatt-hour||1 billion kWh|
|1 TWy||terawatt-year||8766 TWh|
|1 TWy||terawatt-year||31.5 EJ (exajoule)|
|1 quad||quadrillion (10^15) Btu||1.055 EJ|
|1 quad||quadrillion Btu||293 TWh|
|1 TWy||terawatt-year||29.9 quad|
|1 quad||quadrillion Btu||172 million bboe|
Very roughly, 1 quad is about the same as 1 EJ, 1 TW or 1000 1 GW power plants generate 30 quads of energy in a year (but see the next paragraph on the issue of heat rate), and a billion barrels of oil can yield about 6 quads of energy.
An additional important number is the heat to power ratio (or "heat rate") for an electricity production system; the number of kWh (thermal) or Btu of fuel burning required to produce 1 kWhe (electric). For comparison between different types of energy source in electric power production, a common heat rate of about 3 kWh/kWhe, or 10,400 Btu/kWhe, typical of fossil fuel steam generators, is useful. At a heat rate of 3 kWh/kWhe, 1 bboe is just under 600 kWhe, ie. you get about 600 kWh of useful electric energy from burning 1 barrel of oil. See this EIA table for actual numbers from a range of power sources.