The purpose of this work was to investigate heat transfer in a KNO3-NaNO3-based PCM heat storage for concentrated solar power applications. This was done by appling a CFD tool and a numerical approach. The work was done in three stages, covering quasi-1D, 2D and finally 3D. Results were based on evaluation of two models with graphite and steel fins, respectively. Each model was simulated for 3, 10, 30 and 60 minutes. The conclusion of this work was that the choice of the fin material was of less importance during discharge mode, as PCM solidifies on the heating surfaces, which acts as a thermal insulator. This results in reduced heat transfer through the heating surface. Furthermore, it was discovered that natural convection in the liquid PCM was of great importance to the heat transfer.