I'll keep this updated throughout the day.
Two generators were set up outside of Tokyo Dome for use during night games (each capable of generating about 280kW). Neither was needed on for tonight's game because the air conditioning system wasn't used as much due to the cool weather.
Daily Sports adds that according to the Giants, power usage for May games last season topped out at about 4,600kW; during the summer, usages peaked at about 6,000kW.
The Giants are also planning on renting out an additional three generators beginning in mid-June.