Abstract: Latent heat thermal energy storage (LHTES) is an attractive method enhancing the functionality and availability of renewable energy sources, and it is extensively used to support concentrated solar power technologies. The main feature of every LHTES system is a phase change material (PCM), i.e., a substance used to absorb/release energy upon cyclic melting/solidification. This study investigates the potential of ferro-alloys as high-performance PCM candidates, targeting energy storage capacities exceeding 1 MWh·m^–3, and operational temperatures above 1000°C. A thermodynamic assessment of binary and ternary Fe-based systems, alloyed with Si, B, Cr, V, and Ti, was conducted to identify compositions with optimal phase transition characteristics and heat storage potential. The results highlight the significant potential of the Fe–Si–B system, where boron’s exceptionally high latent heat enhances energy storage capacity despite challenges posed by its high melting point and cost. The Fe–Si–Cr system revealed promising alloys, such as Fe–34Si–38Cr and Fe–34Si–43Cr, offering excellent energy storage density and favorable phase transition temperatures. In the Fe–Si–V system, vanadium additions produced alloys like Fe–30Si–16V, Fe–32Si–10V, and Fe–36Si–14V, which meet energy storage criteria, although the high melting points of some Si–V phases may restrict their practical applicability. The Fe–Si–Ti system showed standout compositions, including Fe–38Si–20Ti and Si–48Ti, achieving energy storage capacities of approximately 1.5 MWh·m^–3. This study compares ferro-alloy PCMs against state-of-the-art metallic PCMs, highlighting the performance of certain ferro-alloys.