Water Use and Geothermal Power Plants

Abstract

With significant opportunity for growth of geothermal electricity generation through the development of enhanced geothermal systems (EGS), it is important to understand the potential environmental impacts of geothermal development. Argonne National Laboratory conducted a life cycle analysis of geothermal electric power generation systems that assessed the water requirements of these systems and potential impacts of geothermal waters on the environment. Four power plant scenarios were evaluated: a 20-MW EGS plant, a 50-MW EGS plant, a 10-MW binary plant, and a 50-MW flash plant. Over the life cycle of a geothermal power plant for the scenarios evaluated, plant operations is where the vast majority of water consumption occurs. Although the makeup water requirements are less for a hydrothermal flash plant than for a hydrothermal binary or EGS plant, the long-term sustainability of the reservoir is less certain for hydrothermal flash due to evaporative losses of produced geofluid at operating flash plants. The chemical composition of geofluid has important implications for plant operations and the environment. Geofluid composition was found to vary significantly both among and within geothermal fields. By comparing geofluid composition with U.S. drinking water standards, geofluids were found to present a potential risk to drinking water, if released, due to high concentrations of antimony, arsenic, lead, and mercury. The risk to drinking water can be mitigated through proper design and engineering controls. The concentration and impact of noncondensible gases (NCG) dissolved in the geofluid was also evaluated. The majority of NCG was either nitrogen or carbon dioxide, but a small number of geofluids contain potentially recoverable concentrations of hydrogen or methane. This is part of a larger effort to compare the life cycle impacts of large-scale geothermal electricity generation with other power generation technologies.