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Abstract:

An increasing share of intermittent renewable energy sources calls for more flexible energy systems. This flexibility - the capability of shifting energy use in time and/or magnitude - can be obtained, amongst others, by integration of thermal energy storage in district heating systems. Adequate control of storage systems allows increasing intermittent renewable energy supply and/or decreasing curtailment. In a district heating network, many different thermal energy storage systems are available, each with their own characteristics and dynamics. To facilitate an optimal selection and combination of these different storage systems, a flexibility characterization method was defined by IEA-EBC Annex 67. This paper applies this characterization method to evaluate the energy flexibility provided by two sources inherently present in a district heating network, being the water thermal mass in the network pipes and the thermal inertia of the buildings connected to the network. The paper evaluates multiple scenarios, comparing different streets and districts and combinations of dwelling types. The obtained energy flexibility characteristics shows that the contribution of the network pipes is limited compared to that of the buildings’ thermal inertia. Furthermore, results show that the non-linear characteristics of the district heating network, such as congestion, could complicate the aggregation of the flexibility characteristics.