Dual-objective optimization of large-scale solar heating systems integrated with water-to-water heat pumps for improved techno-economic performance

•The dual-objective optimization model based on NSGA-Ⅱ is proposed for concentrated solar district heating system.•The optimized system can increase the solar fraction from 53.26 to 74.17 %.•The increments of solar fraction can reach 16.2 % after Water-to-water heat pump intervention.•Whether Water-to-water heat pump can improve system economy is related to guaranteed heat source’s efficiency and energy price.