The use of alternative energy sources in various areas of industry and in everyday life is becoming increasingly important. This is due to the depletion of the sources of hydrocarbon raw materials and, at the same time, the use of fossil fuel leads to environmental degradation and environmental pollution. Among the various possible sources of renewable energy, solar and hydrogen energies are considered the most promising. The main obstacle to widespread use and distribution of them is the lack of materials, which can effectively convert the energy of Sun and hydrogen into electricity and heat. The main requirements for such materials are the high-energy capacity, structural stability, and low price. These properties are inherent in nanocrystalline materials and, therefore, many studies of recent decades have been devoted to them. In this review, a special attention is focused on the three types of nanocrystalline objects of greatest interest for power engineering, namely, solar cells, lithium-ion batteries and solid-state hydrogen storage. Their structural features, manufacturing techniques as well as the relationship between structure and energy capacity are considered. The state and prospects of application of nanocrystalline structures in renewable energy are analysed.