Heating accounts for approximately 50 % of all final energy consumption worldwide. To decarbonise heating, renewable energy sources must be employed. To account for intermittency of renewable energy sources and provide operational flexibility, low cost and versatile thermal energy storage unit integrated systems are required. Rock-based high temperature thermal energy storage (up to 600 °C) integrated with high temperature solar thermal collectors provide a solution to reduce natural gas consumptions in steam boilers for medium temperature (100 °C–250 °C) industrial processes. This study develops and validates a two-dimensional model of an existing vertical flow 1 MWh high temperature thermal storage unit using experimental data. A parametric study is performed to evaluate the key design parameters and their effect on the temperature profile and charge efficiency. The charge efficiency was found to be in the range of 77–94 %. This pilot scale model is upscaled in the numerical model to an industrial level 330 MWh storage where the output temperature and flowrate are presented for a constant power output, taking into consideration the residual input heat from the solar thermal collectors.