Analysis of an ultra-low temperature district heating and cooling as a storage system for renewable integration

Sector coupling is necessary for efficient renewable integration since almost all renewable energy sources depend on environmental parameter variations. This paper follows a research line that studies the application of ultralow temperature district heating and cooling systems, with working temperatures between 6 and 40 degrees C, to integrate renewable sources with a storage strategy, using the distribution network as a storage system. This work analyses the impact on the annual operation of the water volume, insulation characteristics, demand patterns, photovoltaic generation, design temperature limits and European climates. The optimal design of the district heating and cooling as a storage system will differ depending on the objective, to integrate the maximum amount of renewables excess or obtain maximum electricity savings. For the system located in Seville, hot Mediterranean climate, network insulation is almost negligible with water volumes below 30 m3; for greater values, the self-regulation temperature of the district heating and cooling system is relevant. Moreover, the maximum temperature increment in the distribution network is positive to minimise operational costs. Within the analyses performed in different European regions, the better results of grid consumption savings were obtained in hot Mediterranean areas, 33 %, meanwhile better renewable integration into the district system was obtained in the warm Mediterranean, with 65 % of the photovoltaic excess integrated.