On March 2011, the Great East Japan Earthquake and the accident at the Fukushima Nuclear Power Plant occurred, which added weight to arguments that Japan’s power system has significant problems. These include: (i) The reliability of nuclear power plants, which had been regarded as a major source of energy in the future, was significantly reduced. The accident at the Fukushima Nuclear Power Plant forced the Japanese government to suspend the operations of the existing nuclear power plants and reconsider its policy for Japan’s energy mix, especially taking into account the necessity of increasing the market share of renewable energy;