Latent thermal energy storage (LTES) can play a key role in a sustainable energy future in the EU. At the moment there is no general design method for LTES heat exchangers, comparable to e.g. the effectiveness - number of transfer units method for steady state heat exchangers. This is due to the transient behaviour of these systems, corresponding with different melting regimes taking place during the melting process. This project proposes a new approach for the characterization of heat transfer in solid-liquid phase change, which provides the basis for a new design method of LTES systems. The novel approach describes the heat transfer as a function of stored energy or liquid fraction, instead of as a function of time. The effect of the different melting regimes is taken into account by determining the liquid fractions at the transitions between the different melting regimes. These are determined based on experimental and numerical data sets. With these transition liquid fractions, melting regime maps are constructed and correlations are developed for the heat transfer rate as a function of liquid fraction, for each melting regime. In a second part of the project, the above method to characterize the heat transfer in LTES heat exchangers is expanded to enclosures with extended surfaces.