Solar radiation is abundantly available across the globe but the intermittent is challenging. Phase change materials (PCMs) are used for thermal energy storage and can absorb/release heat, but they face the problem of poor thermal conductivity. To enhance the thermal conductivity of the PCMs nanofluids are integrated into it. PCMs heat transfer efficiency is increased by taking advantage of the special thermal properties of nanofluids, which are colloidal suspensions of nanoparticles inside a base fluid, resulting in more effective energy storage and recovery. The hybrid nanofluid-PCM systems have better thermal stability, reduced supercooling, and accelerated phase transition kinetics compared to traditional PCMs. In this chapter application of nanofluid in PCM for thermal conductivity enhancement is discussed and further their various applications in solar collectors, PV systems, and cooling purposes in building and industrial uses are discussed.