The role of heat storages in facilitating the adaptation of district heating systems to large amount of variable renewable electricity

In the future energy system, it is likely that there is more variation in the electricity prices due to higher share of renewable energy sources in electricity production. In this paper, the effects of more variable electricity prices were analyzed in a district heating (DH) system that includes both combined heat and power (CHP) plant, fired mainly by biomass and heat only boilers. The most cost optimal dimensioning and combination of heat storages, heat pumps and solar collectors are searched in three future electricity price scenarios. When the impacts of different system components were analyzed separately, it was found that especially a larger heat storage (1% of annual DH energy) is economical. In addition, the results indicate that the most economical size for a heat pump is around 20% of peak heat demand. Yet, the most profitable solution was to include both a heat storage and a heat pump in the DH system. According to our results, solar collector was not a profitable investment in the studied DH system.