Thermal efficiency and heat rate are frequently utilized to evaluate the thermodynamic quality of fossil fuel-fired power plants.² Evaluation of geothermal systems using similar definitions of thermal efficiency and heat rate is inappropriate, except for plants which operate on a cycle, such as binary plants. A utilization factor, defined as the ratio of net work output to the ideal work available from the geofluid, provides a more equitable basis for evaluation of the thermodynamic excellence of geothermal systems.

1.1 This guide covers power plant performance terms and criteria for use in evaluation and comparison of geothermal energy conversion and power generation systems. The special nature of these geothermal systems makes performance criteria commonly used to evaluate conventional fossil fuel-fired systems of limited value. This guide identifies the limitations of the less useful criteria and defines an equitable basis for measuring the quality of differing thermal cycles and plant equipment for geothermal resources.

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.