This work presents a 1-D numerical model of a passive sensible thermal energy storage (TES) system using high-temperature concrete as storage medium. It is successfully validated against experimental data obtained from a pilot-scale concrete storage module. A specific Nusselt number correlation is developed providing better accuracy for the specific heat transfer fluid (Therminol VP1) and observed Reynolds numbers, than conventional general purpose heat transfer correlations for forced convection inside tubes. Then, the model is up-scaled to a commercial-sized thermal capacity of 504 MWh, providing grid-independent solutions and cyclic-steady-state initialization values for further use in a general purpose CSP model library. The proposed implementation in Modelica provides a flexible and intuitive simulation tool, which is not limited to a single simulation platform. Next, the presented model of the concrete TES system is used to compare its transient response with that of a conventional active indirect two-tank heat storage system. Whilst the concrete TES system shows lower maximum rates of change in HTF outlet temperature right after the switching of operating modes, the conventional two-tank TES system has the important advantage of steady-state operation, providing constant HTF outlet temperature, which is very favorable considering steam cycle efficiency and thermal fatigue management. (C) 2017 Elsevier Ltd. All rights reserved.