In the present work, a focused analysis of the cost-components distribution of a low-enthalpy Rankine cycle using supercritical carbon dioxide (sCO₂) as the working fluid is made. This investigation aims to evaluate the cost distribution of the main sCO₂ components and identify the most cost-intensive elements to support future techno-economic assessments of low-enthalpy power plants. More specifically, the present work explores the utilization of a low-enthalpy geothermal field located in the Sidirokastro area, in Serres region in Greece, for approximately 250 kW of power generation, with a maximum geothermal water source temperature of 78 °C. To estimate the thermodynamic performance of this specific geothermal field, a thermodynamic model was developed, modelling a transcritical Rankine cycle using sCO₂ as the working fluid. The thermodynamic model was developed using the Cape Open to Cape Open (COCO) simulator and incorporated the most recent available data describing the geothermal source properties and typical performance characteristics of the main thermodynamic cycle components. Furthermore, the Peng-Robinson equation of state was used, to estimate the thermophysical properties of sCO₂. For the calculation of the low-enthalpy power plant, a preliminary assessment of the purchase cost of the main components of the geothermal power plant was performed, based on the most updated correlations from international literature. These correlations connect the equipment purchase cost to the key operational parameters, such as the power output and the UA value (the product of the overall heat transfer coefficient and the heat exchanger surface area). To improve the accuracy of the calculation of the UA parameter in the power plant heat exchangers, detailed sub-models for the geothermal heat exchanger and the water condenser were used. These models allow to properly capture the effect of the CO₂ thermophysical properties variations to the calculation of the logarithmic mean temperature difference and thus, to the UA parameter value. The analysis of the results led to the identification of the most important components of the geothermal power plant from a cost-intensive point of view. More specifically, the condenser and the geothermal heat exchanger, accounted for over 55% of the total cost, with the water condenser cost corresponding to 32.44% and the one of the geothermal heat exchanger to 23.05%. These findings provide valuable insights for future techno-economic analyses aiming at the evaluation and optimization of the performance of low-enthalpy geothermal power plants.

Low enthalpy geothermal plant, heat exchangers, component cost, cost function