Sustainability evaluation and sensitivity analysis of district heating systems coupled to geothermal and solar resources

District heating systems assisted by renewable energy harness local energy sources, save fossil fuels, and reduce greenhouse gas emissions. Here, geothermal and solar resources are integrated into district heating through a geothermal heat pump and an absorption heat pump by employing vapor-compressor and absorption cycles, respectively. A quantitative sustainability assessment model was constructed for the resulting hybrid district heating systems. Indicators on energy, environment, economic, and societal aspects were used to evaluate the composite sustainability index of hybrid systems with information entropy method. The results demonstrate that a district heating system coupled to compound parabolic concentrator-photovoltaic/thermal solar collector system with 100% photovoltaic coverage ratio is the ideal system for the case study when the annual cost saving ratio is given the highest impact in the composite sustainability index. A detailed analysis on the annual cost saving ratio shows that a higher ambient temperature, solar beam irradiance and grid electricity price would have a positive impact on the annual cost saving ratio. It can be concluded that the quantitative sustainability evaluation approach proposed helps to select the ideal hybrid system.