Primary energy measures the amount of energy available, in the form it is first accessed from natural sources. Consumer energy measures energy in the form in which it is finally used. (Figures in both graphs are rounded.)

Electricity, for example, can be generated using coal, oil, natural gas and water, geothermal energy and other renewable sources. When primary energy is measured, each type of energy is counted in its original form. When consumer energy is measured, the natural gas, coal, oil and geothermal energy used for generation are counted as electricity.

Coal, for example, was 9.2% of New Zealand's primary energy supply in 2007. Some of the coal was burnt to create electricity, and some of it was used by industry or in homes. Primary energy measures the energy in coal, no matter what will be done with it, as coal. Consumer energy measures the energy in coal according to the final form of energy it is used in. The portion used for generation is counted as electricity. The portion used as coal is counted as coal.

Some energy is lost during transmission to end users. Lost energy isn’t included in consumer energy. It is only counted as part of New Zealand’s primary energy supply.