One of the great technological challenges in 21st century is the development of renewable energy technologies due to serious problems related with the production and use of energy. A new promising area of research grows rapidly which is called Nanotechnologies are considered nowadays one of the most recommended choices to solve this problem. This review aims to introduce several significant applications of nanotechnology in renewable energy systems. Papers reviewed including theoretical and experimental works related with nanotechnology applications in solar, hydrogen, wind, biomass, geothermal and tidal energies. A lot of literature are reviewed and summarized carefully in a useful tables to give a panoramic overview about the role of nanotechnology in improving the various sources of renewable energies. We think that this paper can be considered as an important bridge between nanotechnology and all available kinds of renewable energies. From the other side, further researches are required to study the effect of nanotechnology to enhance the renewable energy industry especially in geothermal, wind and tidal energies, since the available papers in these fields are limited.