Revised 24 May 2019

Figure 8 shows an example of growth in energy storage and supply with a large and newly discovered oil field. 

Figure 8: Growth in energy storage and supply with a large and newly discovered oil field.

A limited energy source is where the source itself controls the energy flow. An example is sunlight falling upon Earth. Photosynthesis depends on this incoming flow of energy. Once this incoming energy has been used to the fullest, growth either declines - a situation in which outflows exceeds inflows and storages are decreasing - or the system maintains a steady state where the inflows of energy just keep up with depreciation and losses as shown in Figure 9. 

Figure 9: Growth to steady state using solar energy.

Figure 10 shows the process of decline. An example would be termites feeding off a log until the energy source is completely eaten away.

Figure 10: Process of decline. (Odum & Odum, 1976, p72)

Growth of quantity (Q) accelerates at first until the source (T) begins to run out. The quantity of stored order (Q) then gradually declines as depreciation (D) and outflow of feedback (F) exceed production (P).

Most systems are able to tap into a steady source of energy and during their period of rapid growth they have been able to tap into a temporary energy source as well. Figure 11 shows a surge of growth and then a return to steady state.

Figure 11: Surge growth to steady state (Odum & Odum, 1976, p73)