As Yoshida did not specifically mention what is the reason of outage, it could be due to building maintenance or a compulsory power cut issued by the Japanese government.

Power demand is being monitored daily and forecast-ed, and monitored by the Japanese government. As Japan's nuclear power plants are still shut down, at times the demand may be taxing (especially summer) and thus the government will ask companies and households to cut usage by a certain percentage. It could be just a request or it could be a compulsory order by the government.