A novel design approach for Carnot Batteries thermal energy storage tank

The ongoing energy transition is reshaping geopolitical strategies and accelerating the integration of variable renewable energy sources into power grids. However, their intermittent nature poses significant challenges to grid stability, emphasising the need for efficient energy storage solutions. Among available technologies, Carnot batteries – and in particular Integrated Thermal Energy Storage Systems (I-ESS) – have emerged as promising options for sustainable and large-scale energy storage. A core element of I-ESS is the sensible heat thermal energy storage (SH-TES) unit, implemented as a packed bed filled with solid materials. Despite growing interest in TES systems, the literature still lacks standardised methodologies for optimal design, especially regarding tank sizing. This study proposes an iterative MATLAB-based sizing approach to determine both the optimal TES volume and the I-ESS design power within a Virtual Power Plant (VPP) integrating a photovoltaic (PV) plant, user demand, and the electrical grid. The method accounts for PV generation, dynamic electricity pricing, and load profiles under two management strategies: (1) PV-only charging and (2) mixed charging (PV plus grid electricity). Results show that the optimal SH-TES volume is 155 m³, enabling storage of all surplus PV production in the highest-generation month (July). Under typical operating conditions, mixed charging strategy extends the discharge period to cover more high-price hours, yielding July revenues of about €550/day, while December operational costs range from €230 to €330/day depending on the strategy. These findings highlight the importance of accurate TES sizing and flexible management to maximise both technical and economic performance.