Box 19A Energy definitions

The official SI units for energy measurement are Joules (J) and Watt hours (Wh) and their metric multiples (1kWh = 3600 kJ). However, the tonne of oil equivalent (toe) is widely used to help visualise the quantities involved (1 Mtoe = 41.86 PJ, where P (peta) is 1015), 1 GWh = 86 Mtoe, and 1 TWh=1000 GWh. This chapter uses mostly million toe (Mtoe).

Energy may be broadly divided into two categories:

  1. Primary energy sources include non-renewable fossil fuels (mainly solid fuels, crude oil, natural gas), nuclear power and renewables such as hydropower, geothermal, biomass and solar energy. Combined together, they provide a measure of primary energy production. Primary sources may be divided into two further categories in respect of their impact on global warming: carbon-intensive (solid fuels, oil, gas) and low- or zero-carbon (wind, solar, biomass, hydropower, geothermal and nuclear).
  2. Derived energy sources are produced from the primary energy sources by converting them into other forms of energy for end use consumption. Examples are electricity, petroleum products and heat.

The main convention used for energy data is to refer to the actual energy content of each energy source at each stage. In particular, this means that the amount of electricity generated by hydropower and by wind power is considered directly as primary energy production.

For nuclear power, the amount of heat supplied for the generation of electricity is the primary energy input. Given the average thermal efficiency of a nuclear power station, the amount of heat supplied is about three times the amount of electricity generated. The amount of electricity produced in a conventional thermal power station may also be as little as one third of the amount of fossil fuel inputs, correctly reflecting the efficiency of traditional power stations (CEC, 1988).