Solar panels spread even faster than before in Japan, especially after the Tohoku earthquake in 2011. As the government is giving a subsidy for solar power generation systems, there will be even more reasons for people to buy them. Since Japan faces the growing possibility of radiation leaks from the Fukushima nuclear power plant which was damaged by the earthquake on March 11, 2011. It abandoned a nuclear power plant in eastern Japan. There is only one nuclear power plant in western Japan. We need actively to promote the spread of the technology throughout society.