The company uses four gas engine cogeneration units (Fig. 6). The outputs are 7MW, 1.252MW, 550kW and 55kW, respectively. The systems are introduced under a 15-year energy service contract with Tokyo Gas Engineering Solutions Corp (TGES) of Minato-ku, Tokyo, and the power and steam are purchased. The systems contribute significantly to CO2 reduction because the waste heat can also be used.
In gas cogeneration, the efficiency is the highest when the engine continues to turn at the maximum output, contributing to reducing environmental loads. For this reason, the systems are operated on weekdays from Monday to Friday at the maximum output by weekly start-stop (WSS) continuous operation, and the operation is stopped on weekends and consecutive holidays.
Gas engine generators need to be stopped for about one month every several tens of thousands of hours for a full overhaul, in addition to the need for routine oil replacement and plug replacement. Because the output is high, the power received from the TEPCO group increases than usual during the inspection. Periodic inspections are performed by arranging them in advance to avoid consumption of power exceeding the amount agreed with TEPCO.
The VOC generator features an output of 300kW and uses waste gasoline as the fuel (Fig. 7). The VOC generator and the solar power generation systems are owned by the company. The basic design of the VOC generator was prepared by the Japan Aerospace Exploration Agency (JAXA), and the generator was manufactured by IHI Power Systems Co Ltd. It was introduced in 2003 and is currently in operation.
The power consumed at the center is purchased and supplied from the four power generation and storage systems, as well as the TEPCO power grid.
The on-site smart grid is constructed via the Community Energy Management System (CEMS), which combines the systems and optimally controls and manages them. High-efficiency and stable energy consumption is realized by the CEMS (Fig. 8).
All electricity at the center is centrally controlled, starting from power generation to storage in batteries and reception of power from the grid. The energy consumed by each of 10,000 to 20,000 lights and power supplies to the equipment in all buildings is measured.