Life cycle performance comparison of the transcritical CO2 cycle and the organic Rankine cycle for power generation of hot dry rock

Hot dry rock (HDR) geothermal energy represents highly promising alternative clean energy. The organic Rankine cycle (ORC) and transcritical CO 2 power cycle dominate energy conversion schemes applied to hot dry rock power systems, yet few comparative investigations have systematically analyzed their respective generating characteristics. This paper establishes the numerical models of flow and thermal transfer in HDR reservoir, the ORC system, and the TCO 2 system with multi-stage pressurization with intercooling. Comparative analysis is conducted to reveal the impacts of injection parameters on dynamic output capacity and thermal performance across the entire operational lifespan. Results show that the outlet temperature of the production well of the ORC system drops rapidly and stabilizes in the early operation stage, while that of the TCO 2 system remains stable initially and then decreases gradually. The ORC system achieves higher thermal extraction capacity and net power output but suffers severe performance fluctuations in the early operation stage. The injection parameters have a minor effect on efficiency. The TCO 2 system exhibits higher energy conversion efficiency and stronger resistance to reservoir thermal depletion, which benefits long-term HDR development.