The conversion efficiency of a solar battery for home use is between 10% and 20%. Two university professors developed technologies to increase the conversion efficiency of a solar battery dramatically. Susumu Noda of Kyoto University changed sunlight of a wide range of wavelength to sunlight of a specific wavelength easily usable for photovoltaic generation. His research team developed a new material by combining a semiconductor that emits only light of a specific wavelength if heated with the photonic crystal that locks in and amplifies light. Only light suitable for solar battery can be taken out if the new material is heated by sunlight collected by a lens, and the energy conversion efficiency is estimated to grow higher than 40%. The research results were reported to the Nature Photonics.
Taku Saiki from Kansai University developed a crystal that can convert sunlight to laser. The generated laser is used to irradiate a particle of oxidative products of iron or aluminum, making it possible to create a metallic particle without oxygen at a temperature higher than 4,700 degrees centigrade. This metallic particle generates hydrogen when it reacts with water, and the hydrogen can be used as a fuel. Because the efficiency of conversion from sunlight to laser is about 60%, it will supposedly have higher conversion efficiency than the existing solar battery even though the process to generate hydrogen from laser is taken into consideration.