Optimal incorporation of a thermally integrated Carnot battery into a renewable energy community

Energy storage systems (ESS) are crucial to support Europe’s energy transition, allowing efficient integration of renewable energy sources by balancing supply and demand. In the buildings sector specifically, ESS provides the potential to enhance energy self-sufficiency, reduce grid dependency, and lower emissions, playing a vital role in the shift toward carbon-neutral energy systems. In this context, this work presents an optimal framework for the synthesis, design, and operation of a Renewable Energy Community (REC) supported by a thermally integrated Carnot Battery (TICB) system. TICB systems offer higher roundtrip efficiency, compared to non-TICB systems, by utilizing a heat source at a temperature above ambient and a surplus of photovoltaic (PV) electricity. The aim of this work is to evaluate the role that TICB systems can play in reducing electric grid dependency and promoting renewable energy source expansion on a REC. The REC considered in this study relies primarily on solar energy to meet its electricity and heating needs and comprises a District Heating Network (DHN) connecting nine third sector buildings in the northeast of Italy. The REC framework includes a building-level superstructure composed of solar technologies (PV and solar thermal ST panels), heat pumps, thermal storage, and auxiliary boilers. The REC is supported by a central unit, which incorporates a seasonal thermal storage, large PV and ST plants, and a TICB for eventually storing the PV electricity surplus. Additionally, peer-to-peer electricity sharing among EC members is enabled through a local electricity grid, prior to engaging in electricity exchange with the main grid. The superstructure is optimized using a mixed-integer linear programming (MILP) model, which permits the minimization of the total annual REC costs. The impact of the TICB on the optimal solution for the REC is evaluated through two scenarios. The first one regards the reference case in which the REC operates without a TICB, relying solely on thermal storage in the final solution (no electricity storage). The second scenario incorporates not only thermal storage devices but also a TICB system to the central unit. The results showed that the presence of a TICB not only promotes the high level of electricity production from PV panels but also leads to a 60% increase in the installed capacity of the solar thermal plant. Such an increase improved the overall thermal integration of the community and reduced the reliance on gas-powered auxiliary boilers by approximately 23%.