Dynamic exergy and economic assessment of the implementation of seasonal underground thermal energy storage in existing solar district heating

In this paper, an exergoeconomic approach is proposed to assess the impact of the integration of a Borehole Thermal Energy Storage (BTES) in the existing district heating of the city of Chateaubriant in France. To do so, a dynamic simulation is run over ten years of operation. The model includes a new approach for cost calculation of short-term thermal storage, which is extended to seasonal BTES. The analysis of the system operation at yearly and daily scales revealed several issues. Hence, without redesigning the existing installation, it was found that a non-comprehensive control strategy results in an increase of fossil fuel share by 1.2%. At the BTES scale, from an exergoeconomic point of view, the charging stage is found particularly sensitive to the dynamic. For example, charging the BTES at low temperature increases of the specific cost of the heat stored. Hence, it is shown that some exergoeconomic indicators, like the specific cost of stored heat, could be relevant for designing and operating heating systems with borehole thermal energy storage.

Automated summary

This paper proposes an exergoeconomic approach to assess the impact of integrating BTES into the existing district heating system in Chateaubriant, France. Through a ten-year dynamic simulation, it is shown that control strategies and charging temperature of BTES greatly affect the system operation and cost of heat storage.