Experimental and numerical analyses were carried out to obtain essential data for a thermal energy storage system for off-peak electric power utilization. Cross-linked polymer rods were packed in the column as a latent heat storage material, and ethylene glycol was used as a heat transfer medium. In the experiments, the transient response of the outlet temperature of the heat transfer medium was measured with changes in the operating conditions. The operating conditions include the initial temperature in the column, the inlet temperature, the mass how rate of the heat transfer medium, and the length of the thermal energy storage material. In the numerical analyses, the transient outlet temperature of the heat transfer medium is calculated by means of a finite difference method using the empirical formula of polymer rods-to-fluid heat transfer coefficient: obtained from separate experiments. The numerical results exhibit good agreement with the experimental results.