Introducing distributed solar thermal power in small-scale district heating systems

District Heating Systems (DHS) connected to distributed solar collectors may contribute in reaching, especially in areas with high population density, the target of 50% of the heat demand for domestic hot water, space heating and cooling provided by renewable sources, which will be mandatory in Italy, from January 1, 2017, for new and deeply renovated buildings. By means of a software platform, developed by the Energy Efficiency Department of ENEA, a small-scale district heating system located in a suburb in the Municipality of Bologna (Italy) and including residential buildings, schools, public buildings and a commercial building and heated by gas boilers was simulated. The introduction, in the simulated DHS, of one or more solar thermal fields integrated on the roofs of the buildings was studied, and sensitivity analysis on the effect of the number and the size of the solar fields on the energy and economic performance of the DHS was carried out. The energy performance of the DHS integrated with the solar fields reaches its optimum in the configuration that maximizes the local self-consumption of the produced solar energy. Using the DHS as a vector to share solar energy, the increase in the thermal losses of the DHS can be considered acceptable in the configurations with a solar production equal to or lower than the domestic heat water loads plus the heat losses of the whole DHS in summer.