International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

This article analyses the factors affecting the cost of electricity from geothermal power plants. Geothermal power is a capital – intensive technology and the installation costs are highly site sensitive. The costs of geothermal electricity are influenced by the thermal properties of the reservoir, the costs of site exploration and wells drilling, the number and depth of the wells, the power plant type. The choice of the power plant type depends on the properties of the geothermal resource, its temperature, quantity and quality. Being site- and technology-dependent, the installation costs for geothermal power may be as low as 2000 US$/kW and as high as 7000 US$/kW, with the global weighted average at 4000 US$/kW. This wide range of installation costs translates into levelized cost of electricity (LCOE) between 40 US$/MWh for upgrade and expansion projects and 170 US$/MWh for greenfield projects. The global weighted average LCOE is estimated at 70 US$/MWh. Further costs reductions may be accomplished through the research and development of more innovative and low-cost techniques for site exploration and drilling as well as with advanced exploitation methods for geothermal reservoirs.

This article presents the thermodynamic analysis of a 17.5 MW gross electric geothermal power plant based on binary cycle technology with isobutane. The geothermal power plant comprises two separate closed loops: the geothermal fluid flows in one loop and the Organic Rankine Cycle (ORC) fluid flows in the second loop. The geothermal fluid is extracted from a depth of 2500-3000 m with a temperature of 170 °C and a pressure of 25 bar. Two production wells supply geothermal fluid (brine and steam) with a high fraction of noncondensable gases (NCG). A separator extracts NCG from the geothermal fluid. Isobutane is preheated and evaporated before entering the ORC turbine with a temperature of 133 °C and a pressure of 28 bar, where expands to the condenser pressure of 4 bar. Electricity is generated by a 17.5 MW axial ORC turbine and additionally by a 1.5 MW NCG turbine. The analysis revealed that the configuration without NCG turbine achieves a net efficiency of 12.73% and a net electric power of 13.68 MW while the configuration with NCG turbine achieves a net efficiency of 14.04% and a net electric power of 15.16 MW but with much higher CO2 emissions into the atmosphere.