Advanced materials for Hybrid Solar–Geothermal (HSG) systems in sustainable buildings: A review

The urgent need to reduce global greenhouse gas emissions has positioned the building sector as a critical arena for advancing sustainable energy technologies. Hybrid solar–geothermal systems, which combine solar thermal collection with shallow or deep geothermal heat exchange, offer a reliable and renewable pathway to achieving net-zero energy performance in buildings. This review evaluates the role of advanced materials in enhancing the efficiency, durability, and environmental sustainability of hybrid systems. Emphasis is placed on materials used in solar collectors, geothermal piping, heat exchangers, and thermal energy storage, highlighting their thermal conductivity, mechanical resilience, corrosion resistance, and life-cycle impacts. Special attention is given to emerging bio-based and recyclable options, as well as to material optimization strategies tailored to diverse climatic conditions. Case studies demonstrate that the integration of innovative materials leads to measurable improvements in system performance, energy savings, and long-term durability. The review concludes by identifying research gaps in cost reduction, sustainable material development, and interdisciplinary integration, underscoring that advanced materials are not only enablers but key drivers of hybrid solar–geothermal adoption in sustainable buildings.