Assessment of Combined Heat and Power Utilization for a Super-Long Gravity Heat Pipe Geothermal System

The super-long gravity heat pipe (SLGHP) geothermal system provides a viable approach for utilizing geothermal energy from hot dry rocks. This study investigates two SLGHP-based cogeneration configurations, namely a heat–power independent system and a heat–power coupled system. Thermodynamic and economic models are developed to evaluate the energy conversion, exergy performance, and economic characteristics of both configurations. The performance of the coupled system is systematically compared with that of the independent system. The results show that the heat–power coupled system achieves higher net power output and exergy efficiency, together with a shorter payback period. For both configurations, major exergy destruction occurs in the expander and condenser, while drilling and SLGHP components account for more than 90% of the total investment cost. In addition, the heat–power independent system exhibits significantly higher exergy destruction during hot water production. The results indicate that system scaling and multi-well deployment are effective measures to improve economic performance. Overall, this work provides a quantitative basis for configuration selection and performance optimization of SLGHP-based geothermal cogeneration systems.