Thermodynamic and economic performance of super-long gravity heat pipe geothermal power plant

Hot dry rock energy has the potential to be a solution for both energy shortage and carbon-emission reduction. The novel technical scheme based on the super-long gravity heat pipe system in a single well has aroused great interest in the geothermal research and industry community; however, there is yet very few investigations on its power generation performance. Unlike other hot dry rock energy exploitation technologies, super-long gravity heat pipe produces saturated vapor, which can directly drive a steam turbine to generate electricity in a similar fashion to thermal power plants. This study comprehensively analyzes and compares the performance of the super-long gravity heat pipe system with the traditional single-well downhole heat exchanger system from the perspective of technology and economy. The acquired knowledge gives in-depth information about the super-long gravity heat pipe geothermal power generation system. The analysis and comparison are based on a novel thermodynamic and economic model specially developed in this study. Both systems consider the same geothermal conditions and the working fluid of both systems is optimized to maximize their power output. Thermodynamic results show that the super-long gravity heat pipe system has higher efficiency compared to that of the downhole heat exchanger system. The economic analysis indicates that the downhole heat exchanger system involves slightly lower costs than those of the super-long gravity heat pipe system, while the levelized cost of energy of downhole heat exchanger system is, much higher than that of the super-long gravity heat pipe system. For the baseline cases investigated, the energy efficiency of the super-long gravity heat pipe system is 10.92%, which is 1.37 times that of the downhole heat exchanger system; having a larger scale power station by increasing the number of wells from 1 to 10 makes the levelized cost of energy decrease from 0.30 $/kWh to 0.18 $/kWh for the super-long gravity heat pipe system, and from 0.74 $/kWh to 0.43 $/kWh for the downhole heat exchanger system.