130 huge tanks

The Minami-Hayakita Substation lowers the power transmitted from thermal power plants, including the Tomakomai Power Plant and the Tomatoh Atsuma Power Plant, as well as the Hidaka Hydropower Plant, which is far from the substation, at a high voltage exceeding 180kV to 66kV for supply to Sapporo City, Obihiro City and other areas. The substation plays an important role in supporting the center of the economy in Hokkaido.

When you approach the substation, a number of steel towers are seen along the horizon. When you enter the site and walk past the transmission lines, you see a huge white building as magnificent as the steel towers. The building is 120m in length, 35m in width and 20m in height, and the size is about four times that of a gym at elementary schools and junior high schools.

The "redox flow battery" with a capacity of 60MWh is installed in this building. Huge electrolyte tanks, 3m in diameter and 7m in height, are standing side by side in the building. The total number of tanks is 1,300. The tanks are wrapped in silver insulation sheets and are shining, reflecting the surrounding lights (Fig. 3).

Fig. 3: Electrolyte tanks stand side by side (source: Nikkei BP)

The tank near the entrance has a seal on which is written "Tank-5-E-Cathode Deleterious substance - Vanadium sulfate" (Fig. 4). Vanadium sulfate solution is used for both the positive and negative electrodes of redox flow batteries, and charging and discharging are done by vanadium ion valence modification.

Fig. 4: Vanadium sulfate solution flows between the tanks and cell stacks. (source: Nikkei BP)