Design and off-design optimization procedure for low-temperature geothermal organic Rankine cycles

In this paper, a two-step optimization methodology for the design and off-design optimization of low-temperature (110-150°C) geothermal organic Rankine cycles (ORCs) is proposed. For the investigated conditions-which are based on the Belgian situation-we have found that the optimal ORC design is obtained for design parameter values for the environment temperature and for the electricity price which are both higher than the respective yearly-averaged values. However, the net present value is negative (-12.62MEUR) which indicates that the low-temperature (130°C) geothermal electric power plant is not economically attractive for the investigated case. Nevertheless, and demonstrated by the results of a detailed sensitivity analysis, a low-temperature geothermal power plant might be economically feasible for geological sites with a higher brine temperature or in a country with a more favorable economic situation; e.g., with higher electricity prices (~70EUR/MWh). The novelty of our paper is the development of a thermoeconomic design optimization strategy for low-temperature geothermal ORCs, accounting for the off-design behavior already in the design stage. The generic methodology is valid for low-temperature geothermal ORCs (with MW scale power output) and includes detailed thermodynamic and geometric component models, is based on hourly data rather than monthly-averaged data and accounts for economics.