ADVANCED POWER PLANTS FOR USE WITH HOT DRY ROCK (HDR) AND ENHANCED GEOTHERMAL TECHNOLOGY

1. ABSTRACT The future commercialization of the Hot Dry Rock (HDR) or Enhanced Geothermal System (EGS) technologies will be dependent on solving both technical and economic issues. The major identified barriers to commercialization of these technologies are the costs of drilling the wells, the supply of water and the pumping of the HDR produced brine. Drilling costs are related to the geological formations and well depth, and thus power plants, which effectively utilize lower temperature fluids from shallower wells can reduce power production costs. Power plants which do not consume any water in the conversion process regardless of fluid temperatures, and are insensitive to water chemistry, can optimize HDR/EGS commercial power projects. Organic Rankine Cycle (ORC) binary based power conversion technology effectively utilizes air cooled condensers with no consumption of geothermal fluid. Such closed loop power plants generate electricity with EGS produced fluid with temperatures from 95 o C to 315 o C without loss of water in the power plant, and with no corrosion or scaling of the plant components. In addition, modular power units may be used to increase power plant capacity as more EGS fluid production is developed. This presentation describes advanced geothermal power conversion systems and along with case histories of operating power plants employing these conversion systems. 2. BACKGROUND The greatest potential for the utilization of geothermal energy to generate electrical power may well be in the utilization of heat from geological formations that lack natural water. This heat utilization process is known as Hot Dry Rock (HDR) technology, also referred to as Enhanced Geothermal Systems (EGS) technology. As HDR geothermal technology advances, a significant portion of the world's needs may be met from the widely distributed HDR resources. The costs of drilling injection and production wells and the pumping and supply of water are currently the major cost barriers to commercializing HDR/EGS technology. With drilling costs related both to the geological formations and to well depth, power plants which can effectively make use of lower temperature fluids from shallower wells will reduce power production costs and overcome these barriers. Power plants which do not consume any water, regardless of HDR fluid temperatures, and which are insensitive to water chemistry, will be the most desirable for HDR/EGS applications, since even the anticipated loss of 5 to 10% of the water injected into the geological structure of an HDR system imposes a serious requirement for make up water. The field proven (over 600 MW) advanced ORMAT ORC technology power plants will optimize the effectiveness of future HDR/EGS systems over the widest range of fluid temperatures and characteristics.