Modeling and Simulations of Solar Bidirectional Substation

Decentralized surplus feed-in of solar heat into a District Heating Network (DHN) is here addressed. The heat collected from solar panels located on rooftops of DHN connected buildings may either be used locally for domestic hot water and space heating or fed into the DHN. Two-way substations able to transfer heat from and into the network seem then to be required utilities. The present paper presents the specifications (60kW capacity, return-to-supply connection) and promising architectures of such two-way substation based on a previous analysis. A first-of-a-kind Modelica-based dynamic model of the substation together with the consumer and the solar field connected to it is then detailed. Two-day simulations considering real operating conditions of DHN were then performed. The results highlighted i) the good match between the periods of solar heat reinjection with the periods of low supply temperature and differential pressure and ii) the decisive benefit of the reinjection to increase the part of useful solar energy.