Sustainable development
The concept of sustainable development originates in the 1987 United Nations report “Our Common Future”. It describes development that meets our present needs without compromising the ability of future generations to meet theirs.
The limit of sustainable production
Every geothermal field has a limit known as the maximum sustainable production. Below it, production can be maintained for a very long time; above it, production cannot be sustained in the long run. The limit depends on the production technology used and can therefore change over time.
Determining whether use is sustainable requires a time horizon; for geothermal energy a span of one to three centuries has been considered reasonable. Experience and research show that geothermal systems can recover their former state if they are rested after periods of aggressive production.
Examples
The Laugarnes field in Reykjavík is a good example of a geothermal system that has reached reasonable equilibrium under substantial production. The Geysers field in California, by contrast, is an example of unsustainable production: installed capacity reached about 2000 MW around 1985 and output had to be cut back sharply.