If in Fig. 1 the section labelled as Primary Fuels is added up and divided by Australia's population at that time, an amount of 196 GJ per annum is obtained. This is the average annual primary energy consumed by each individual in the country, allowing for the energy content of all goods and services and industrial production he/she purchases. It is a rough but useful measure of the invisible energy everybody consumes without being conscious of it and correlates well with standard of living in different countries expressed in annual income per head. It is rough, because it would not include the energy content of an imported car but would include that of an Australian product. It was increasing at the rate of 5.4 per cent p.a. in 1972 but had dropped to 4.1 per cent by 1980 and it has been suggested that there is an upper limit to it: which could mean zero energy growth of energy consumed per head early in the 21st century.

The concept of the energy content of a manufactured product or a structure is particularly useful in assessing the merit in energy terms of a renewable source of energy such as a solar installation. If it does not generate more energy in its lifetime than was used for its construction it cannot be classed as renewable.

Australian Academy of Technological Sciences and Engineering