Progress in solar thermal applications in Japan.

The use of solar energy will be important among various energy sources if we consider the possible shortage of fossil fuels. Solar energy is abundant in quantity, free from pollution and safety. At present, it is considered that solar systems are inferior to other energy systems such as conventional fossil fuel and nuclear plants and have disadvantages in respect to the density of energy flux and energy cost.Solar energy mainly has been used in two fields which are solar thermal applications and photovoltaic power systems. The progress in solar thermal applications, such as solar heating and cooling systems for building, advanced heat process systems, solar thermal electric power systems, and hybrid photovoltaic/thermal systems in Japan is described.