In this work, we will discuss the applications of nanomaterials in some important renewable energy technologies such as photovoltaic solar cells, photocatalytic production of hydrogen, fuel cells and new technologies for energy conversion. We will particularly discuss their application in the field of energy storage such as lithium-ion batteries, sodium-ion batteries, supercapacitors, and battery technology. Some important examples of nanostructured materials include metal oxides, carbon nanotubes, graphene, quantum dots, transition-metal dichalcogenides, and perovskite nanomaterials which help in increasing the conductivity, energy density, rate of charging and cycling stability. In the field of energy generation from renewable sources, nanomaterials will help in increasing the light absorption efficiency, charge separation, catalysis, and conversion efficiency. There are still some problems which need to be addressed in the field of large scale production, stability of the materials, cost, environmental effects, toxicity, and longevity. Thus, future research needs to focus on sustainable synthesis approaches, multifunctional nanocomposite development, scalable manufacturing, and life-cycle assessment.