Latent thermal storage (LTS) technologies are taking over the sensible heat type storages due to the former's higher energy storage densities, which are better suitable for demand response (DR) applications in distribution grids for capacity relief, or on the electricity market for balancing. However, the existing energy models are not capable of representing the rate of energy exchange inside the storage tank due to interdependencies of heat transfer coefficient and temperature difference between heat transfer fluid and phase change material (PCM), which is an important factor for finding the energy stored and transferred at any given point of time. This work presents detailed modelling of average and discretized methods for PCM based storage systems. The proposed models can capture the heat system dynamics which are necessary for modelling and enhancing energy flexibility. The simulation model is validated with an actual system to evaluate the potentiality of the concept, and the achieved results were noteworthy.