Although Si and Si-B alloys seem to be perfect candidates as high temperature PCMs (phase change materials) (in terms of their high melting points and latent heat values), a number of scientific/technical challenges have to be faced before introducing them into real Latent heat thermal energy storage (LHTES) devices. A special attention should be paid to a proper selection of reliable refractories for building the PCM container. For this purpose, the involved teams from the Foundry Research Institute in Krakow (FRI) and Norwegian University of Science and Technology (NTNU), have agreed to explore two distinctly different approaches: (i) “Non-wetting + negligible reactivity concept” and (ii) “Self-crucible concept”, respectively. In the former attempt, it has been assumed that the selected refractory material will be inert towards the contacting PCMs, i.e. the system will be characterized by non-wetting behaviour and a lack of significant dissolution of the refractory in molten PCM as well as no new reactively formed products. On the contrary, the principles of the latter approach include a reactive formation of continuous interfacial product layer at initial stages of PCM/refractory interaction. The reactively formed layer should play a role of barrier coating, and thus forms a “self-crucible” inside the PCM vessel. In order to accomplish the Project’s goals, Si and Si-B alloys were fabricated by using various metallurgical routes (including an induction melting or an electric arc melting). After that, their high temperature solid/liquid state interaction with refractories selected in accordance to both proposed approaches, was examined. Additionally, a proper thermodynamic assessment of phase equilibria was performed in order to support obtained experimental data.