Comparison of distributed and centralised integration of solar heat in a district heating system

Ambitious greenhouse gas emission reduction targets set by EU pose a significant challenge for the member countries. District heating as an efficient solution for heat supply and distribution can play a major part in meeting these targets. One key issue concerning district heating is the integration of renewables. The current study focuses on solar assisted district heating systems.Centralised and distributed solar collectors in an existing district heating system are investigated. The effects of reducing supply temperature are studied in two scenarios. Outdoor dependent supply temperature level (115-80 °C) and low supply temperature level (65 °C) are considered. Both distributed and centralised systems are defined with same investment costs, but different capacities due to differences in unit costs (€/kW). The aim is to study cost-efficient solutions for integrating solar heating an existing district heating system.Heat demand consisting of space heating and domestic hot water consumption, solar collectors and district heating network itself are all modelled by dedicated models in order to provide realistic input for a techno-economic analysis.Investigation is based on a case study of a local district heating system in Finland with an annual heat consumption of 1.2 GWh and a heat demand density of 0.74 MWh/m.