Renewable energy sources fluctuations demand for novel large-scale energy storage solutions. Ultra-High Temperature Latent Heat Thermal Energy Storage (UHT-LHTES) systems are candidates to efficiently store and convert energy at temperatures above 1000°C. They can capture solar energy and UHT waste heat and convert them back into heat or electricity when needed, supporting grid stability. Due to high energy density, they have compact designs, good for decentralized storage. Operating at UHT poses two engineering challenges : (i) the development of a suitable LHTES material ; (ii) the durability and reactivity of the housing materials. As LHTES materials, state-of-the-art Si alloys contain much boron, which is quite expensive and poses supply problems. It is proposed to replace them by new compositions that meet the specifications at a lower cost. For housing materials, Ceramic Matrix Composites
(CMC) are ideal candidates due to their exceptional UHT stability, fracture toughness, corrosion & thermal shock resistance, and low density. The LaTESt-CUT project will propose a modular compact design of a UHT-LHTES prototype (TRL4) utilizing cost-effective CMC-based solutions and advanced pressure-less joining methods. The interaction and thermochemical compatibility of Si-alloys with the CMC materials proposed will be tested in the expected application environment up to 1300°C under thermocycling conditions. The prototype will be tested in a specific setup in these conditions.