Sustainable management of geothermal resources

Abstract

Sustainable development involves meeting the needs of the present without compromising the ability of future generations to meet their needs. The Earth’s enormous geothermal resources have the potential to contribute significantly to sustainable energy use worldwide and to help mitigate climate change. Experience from the use of geothermal systems worldwide, lasting several decades, demonstrates that by maintaining production below a certain limit the systems reach a semibalance between net energy discharge and recharge that may be maintained for a long time. Therefore, a sustainability time-scale of 100 to 300 years has been proposed. Studies furthermore indicate that the effect of heavy utilization is often reversible on a time-scale comparable to the period of utilization. Sustainable management basically involves setting up and maintaining a specific long-term production scheme. It also involves the basic ingredients of successful geothermal resource management, i.e. reinjection, monitoring and modelling. The most ideal way to utilize a geothermal resource in a sustainable manner is through a step-wise increase in production, even though other sustainable utilization schemes can be envisioned.

The long production histories that are available for geothermal systems worldwide provide the most valuable data available for studying sustainable geothermal utilization, and reservoir modelling is the most powerful tool available for this purpose. The paper reviews long utilization experiences from e.g. Iceland, New Zealand, El Salvador and China and presents sustainability modelling studies for a few geothermal systems in these countries. Distinction needs to be made between sustainable production from a particular geothermal resource and the more general sustainable geothermal utilization, which involves integrated economic, social and environmental development. A sustainability policy is based on general sustainability goals and includes specific sustainability indicators to measure the degree of sustainability of a given geothermal operation.