Study On Power Generation Systems With Dynamic Matching Geothermal-solar Hybrid Heat Source

China has huge reserves of Hot Dry Rocks.How to use Hot Dry Rock to generate electricity efficiently and sustainably is a key technical problem that needs to be solved at present.The heat transfer of Hot Dry Rock is almost pure conduction.Long-term uninterrupted mining will cause the local temperature of the thermal reservoir mining area to drop too quickly,and even cause“heat exhaustion”.In order to avoid this situation,a geothermal-solar hybrid heat source dynamic matching power generation system was constructed in this study to reduce the local“heat depletion”phenomenon of Hot Dry Rocks by coupling and utilizing solar energy and geothermal energy.The geothermal and solar heat sources in the hybrid system adopts a dynamic matching method,and the net power generation is maximized by adjusting the strategy or sequence of the working fluid entering the system.In the power generation system,the net power generation is kept constant,thereby avoiding frequent peak regulation of the power grid caused by load swings.In this study,the geothermal and solar resources in the Qinghai Gonghe region were used as the basic parameters,and the maximum amount of specific net power output of geowater per mass flow rate was used as the objective function.The operation parameters and operation strategies of power generation system with subcritical cycle and transcritical cycle was numerical simulated and optimized.The simulation considers different geowater temperatures and four organic working fluids(n-pentane,R245fa,R123,and isobutane)Under the given geothermal resource,the optimal evaporation temperature and evaporation pressure were obtained for subcritical and transcritical cycles,and the optimal production strategy under in time solar conditions is obtained.In the case of subcritical cycle,when the temperature of the geowater is 150°C,the parallel operation mode of the heat source is the best.When the temperature of the geowater is210°C and the DNI is greater than 825W/m~2,the heat source should adopt the series mode in which the solar source is first.When the geowater temperature is 240°C,and the DNI is less than 725W/m~2,the heat sources should use the parallel heating mode;when the DNI is more than 725W/m~2,the heat sources should use the strategy of series connection with solar first.In the case of transcritical cycle,when the geowater temperature is 185°C and the DNI is less than 675W/m~2,it is better to use the series strategy for the heat sources,when the DNI is higher than 700W/m~2,the heat sources should use the parallel operation mode;When the geowater temperature is 210°C,240°C,and 270°C,respectively,the optimal operation strategy is opposite to that when the temperature of the geowater is 185°C.In the economic evaluation,the LEC and PBP of the hybrid power plant with subcritical cycle were 0.8287CNY/k W·h and 19.83 years,respectively.In the case of transcritical cycle,when the equipment investment increase ratio is less than 1.38 the LEC of transcritical cycle is less than the subcritical cycle.when the equipment investment increase ratio is less than 1.46 the PBP of transcritical cycle is less than the subcritical cycle.When the price of standard coal is higher than 460 yuan/ton,the annual profit of the geothermal-solar hybrid power plant is better than that of conventional coal-fired power plants,and based on the current standard coal price,the payback period of hybrid power plant is shorter than the conventional coal-fired power plants.