The transition to sustainable energy highlights the importance of thermal energy storage (TES) systems, particularly in concentrated solar power plants. While Portland cement has shown potential in TES applications, its high CO₂ emissions limit its sustainability. Therefore, this research examines alternative cementitious materials, specifically alkali-activated (AAM) and hybrid alkaline materials (HM), which use blast furnace slag as a binder and incorporate recycled aggregates such as glass waste and electric arc furnace slag. These alternatives not only demonstrate enhanced thermal and mechanical stability up to 500 °C but also exhibit improved energy efficiency. Finite Element Method simulations indicate that these alternatives can reduce TES system volume and improve heat transfer efficiency. Additionally, Life Cycle Assessment highlights significant reductions in carbon and water footprints. This study provides insights into the use of AAM and HM mortars as viable, lower-impact alternatives that align with sustainability goals in renewable energy applications.