Computational comparison of a novel decentralized photovoltaic district heating system against three optimized solar district systems

Abstract Climate change is one of the biggest challenges at the present time, and to tackle such issue, solar energy and efficient buildings, in general, can be used. The goal is to design and optimize photovoltaic based decentralized district heating system and later compare it—economically and technically—against three different optimized typologies of solar district heating system in Nordic conditions. The photovoltaic based decentralized system consists of one centralized low temperature tank charged by photovoltaic and air-water heat pumps and a borehole thermal energy storage, while the decentralized high temperature tank charged by an individual water-water heat pump in each house. The centralized warm tank charges the borehole thermal energy storage. The other three systems are photovoltaic based centralized, roof-mounted solar thermal based centralized and roof-mounted solar thermal based decentralized district heating systems. In solar thermal based systems, collectors are used to directly charge the short-term storage tanks instead of the photovoltaics/heat pump combination. The proposed system is simulated using TRNSYS software. Lastly, purchased electricity and life cycle costs of the system are minimized using multi-objective optimization and the genetic algorithm. The results indicated that the decentralized photovoltaic based system outdoes all the other systems in terms of techno-economic performance. The purchased electricity can be reduced by 22% while at the same time life cycle cost can be reduced up to 40%, compared to the worst optimized system (solar thermal based centralized system). Moreover, the decentralized photovoltaic based energy system has a payback period of 9–27 years, compared to the solar thermal based system and the conventional single building-heat pump system, i.e. around 17–58 years and 15 years, respectively. The highest renewable energy fraction for heating can be close to 99% for this system. The decentralization and electrical based district systems are better in terms of life cycle cost, payback period and in terms of technical performance, compared to traditional single house and solar thermal based district heating systems.