Abstract
Geothermal energy at low-temperature levels (100–220 °C) is abundant in the nature, and it can be used for clean and sustainable power supply. This study analyzes the transcritical CO 2 (T-CO 2 ) cycle and the organic Rankine cycles (ORCs) with 90–150 °C hot water as the heat source and ambient temperature at 20–10 °C to simulate possible geothermal sources. R245fa and R601a are selected as the working fluid for the ORCs. Numerical parametric optimization and comparative study have been conducted via MATLAB and NIST REFPROP. The main performance indicators are net power output and heat recovery efficiency of the cycle. The results show that, as heat source temperature increases, the net power output and heat recovery efficiency of the ORCs increase more rapidly than the T-CO 2 cycle. On the other hand, as ambient temperature rises, the net power output of the T-CO 2 decreases more significantly than the ORCs. The heat recovery efficiencies of all the cycles are slightly affected by the ambient temperature change. In general, based on the assumptions made in this study, the T-CO 2 cycle is more recommended in lower-temperature environment due to its dominant advantages in both net power output and heat recovery efficiency, while the R245fa ORC is more preferable in higher-temperature environment.