Thermochemical energy storage for heating applications - An experimental study

The critical role of thermal energy storage (TES) in the net-zero energy transition future has been widely recognised, particularly for addressing challenges associated with variable renewable energy generation, waste heat utilisation, and energy supply and demand mismatches. There are mainly three types of TES technologies (sensible, latent and thermochemical), this work is concerned with thermochemical energy storage (TCES). The TCES is commonly regarded as a long-duration energy storage technology, but it can also be used for short-and medium-term applications. This work studies a packed bed-based TCES system, with a specific focus on district/domestic space and water heating applications. The work experimentally investigated the performance of a 7.5 kWh TCES system using both a pure sorbent (silica gel) and a salt hydrated based composite thermochemical material (CTCM) named BCES-CTCM-130. The temperature profiles at different locations in the system were monitored and the effects of charging/discharging flow rates and temperatures on the system performance were examined. The charging/discharging efficiency and system Coefficient of Performance (COP) are evaluated. The results showed a temperature lift of ~30 °C is achievable and the outlet temperature remained above 35 °C for more than 7 hours. Also, the CTCM has charging and discharging efficiencies of ~56% and ~71%, respectively, with an overall COP of 0.39. The COP would increase to 0.58 if the exhaust heat in the charging process could be utilised. Compared to pure thermochemical material, the BCES-CTCM-130 showed a higher temperature lift and a higher efficiency.