Integration of decentralized solar collectors into a district heating system

Abstract

• Development of the prototype of the prosumer heat substation with solar collectors. • Experimentally validated TRNSYS model of the prosumer heat substation. • Key factors influencing stability of the feed-in temperature from the solar collectors. • Proposals for DH operators for integration of prosumers with solar collectors. This study focuses on the integration of small capacity prosumers in district heating networks. The challenge for installations with solar collectors lies in the fact that fluctuations in cloud cover and pressure drops in the network are unpredictable. Therefore, it is more difficult to ensure a stable feed-in temperature that meets the technical requirements of the district heating network. For this, an experimental prototype with flat plate and vacuum thermal collectors was developed and the TRNSYS simulation model was created. The model has been validated using data from the test facility. Multiple simulations have been performed to analyse various options for improving the stability of the feed-in temperature. An analysis of the change in the temperature of the heat carrier on sunny and cloudy days in three control modes was carried out. It showed that the temperature fluctuation depends both on weather conditions and "idling" and "rotating" time intervals of the three-way valve. Results of the study show that the cloud cover has a strong influence on the stability of the collector outlet temperature. Fluctuations in the feed-in temperature need to be compensated for by changing the flow rate and different strategies for operating the three-way valve, which become a challenge in real-life conditions with fluctuating differential pressure in the district heating network.