Hybrid Nanofluids for Renewable and Sustainable Energy

The urgent global demand for clean, reliable, and sustainable energy has accelerated the transition from fossil fuels toward renewable sources such as solar, wind, geothermal, and biomass. Despite their environmental and economic advantages, renewables face persistent challenges of intermittency, efficiency losses, and thermal management, which limit large-scale adoption. Hybrid nanofluids are engineered suspensions of two or more types of nanoparticles in a base fluid and have emerged as next-generation working fluids capable of overcoming these limitations. By combining superior thermal conductivity, enhanced specific heat capacity, tunable viscosity, and tailored optical properties, hybrid nanofluids significantly improve heat transfer, energy storage, and conversion efficiency in renewable energy systems. This chapter critically reviews the role of hybrid nanofluids in advancing renewable technologies, with emphasis on solar thermal collectors, concentrated solar power (CSP), photovoltaic/thermal (PV/T) systems, and energy storage units. Key thermophysical and chemical advantages, including improved convective heat transfer, greater dispersion stability, spectral selectivity, and multifunctional properties such as corrosion resistance and magnetic responsiveness, are analyzed alongside computational modeling approaches that predict performance enhancements. Practical considerations, such as pumping power requirements, long-term operational stability, and rheological behavior, are discussed with reference to experimental studies and pilot demonstrations worldwide. The chapter also addresses scalability, cost, environmental safety, and life cycle challenges, offering insights into the commercialization pathways of hybrid nanofluids. Emerging directions, including integration with phase change materials, adaptive smart fluids, and hybrid energy storage systems, highlight their transformative potential. By bridging materials science and renewable energy engineering, hybrid nanofluids are positioned as critical enablers of efficient, resilient, and sustainable energy technologies, directly contributing to global decarbonization and net-zero emission targets.