The issues inhibiting, the future commercialization of the Hot Dry Rock (I-IDR) or Enhanced Geothermal System (EGS) technologies are both technical and economic. The costs of drilling wells and the pumping and supply of water are still the major cost barriers to commercializing HDIUEGS technologies. Since drilling costs are related both to the geological formations and to well depth, power plants, which can effectively use lower temperature fluids Ä-om shallower wells can reduce power production costs. In addition power plants which do not consume any water, regardless of fluid temperatures, and which are insensitive to water chemistry, are desirable for HDIUEGS applications. ORMATís Organic Rankine Cycle (ORC) binary based technology allows for the effective utilization of air cooled condensers with EGS produced fluid temperatures Ä-om 100?C to 315?C. The basic binary cycle system operates with the produced fluid continuously under high pressure and in contact only with the power plant piping and the heat exchanger tubes. Thus there is no loss of water circulating in the EGS system, no corrosion and no scaling of the plant or well bore. The use of modular power units allows for increasing the plant size as more EGS fluid production is developed. This presentation describes tbe binary and steadbinary geothermal combined cycle systems, and presents case histones of operating plants successfully employing these technologies.

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