Achievements of Large Redox Flow Battery in Hokkaido (1)

2017/08/19 10:00
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Institute

The large storage battery system validation project by Hokkaido Electric Power Co Inc (HEPCO) at the Minami-Hayakita Substation is getting into full swing.

The redox flow battery manufactured by Sumitomo Electric Industries Ltd (SEI), which was installed at the substation, features an output of 15MW and a capacity of 60MWh. It is one of the largest redox flow batteries currently operating in the world.

The results of the validation project will be utilized to increase the framework for new grid connection for wind power, under the condition that storage batteries are attached to the facilities, for example, aiming to expand the introduction of fluctuating renewable energies.

Hometown of famous racehorses becoming the Mecca of large storage batteries

Abira Town in Hokkaido, which is known for the cheese and melons it produces, is also known as a town of racehorses; the famous racehorse "Deep Impact" was raised there. The town is now seeing a concentration of advanced energy facilities.

The "Softbank Tomatoh Abira Solar Park," a 111MW mega (large-scale) solar power plant, started operation in December 2015. It is the second largest among the power stations currently operating in Japan. At present, a mega solar power plant attached with a 64MW storage battery is under construction on a site adjacent to the solar park. A huge storage battery with 17.5MWh capacity and 34MW output will be operated to smooth output fluctuations from the mega solar power plants. The storage battery is expected to be the largest in Japan among storage batteries attached to mega solar power plants.

A huge storage battery, which is about three times the capacity of the one mentioned above, is actually in operation in Abira Town. It is the facility for the large storage battery system validation project, which was started in December 2016 at the HEPCO Minami-Hayakita Substation by HEPCO and SEI (Fig. 1 & 2).

Fig. 1: The building accommodates the redox flow battery installed at the Minami-Hayakita Substation. (source: Nikkei BP)

Fig. 2: Model of the storage battery building (source: Nikkei BP)

The "redox flow battery" manufactured by SEI was used. The battery, featuring 15MW output and 60MWh capacity, is the largest-scale redox flow battery in operation in the world.

The battery is used for validation, aiming for the stable operation of power grids throughout Hokkaido. HEPCO will validate the performance of the battery to control fluctuations in the output of wind power and solar power facilities and develop optimum control technology by conducting the validation for about three years.

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)

13 banks consisting of 65 modules

Each module of the battery includes two electrolyte tanks (cathode/anode), eight cell stacks (aggregates of membrane electrode composites), pipes for circulating electrolytic solution between the tanks and stacks, and heat exchangers. Five modules form one bank, and each bank is equipped with a PV inverter that controls charge and discharge (Fig. 5).

Fig. 5: Redox flow battery system and configuration of one module (source: HEPCO)

The cell is divided into cathode and anode by an ion exchange membrane that permeates hydrogen ions only, and charging and discharging are done by the exchange of electrolyte (vanadium ions) and electrons between the cathode and anode.

Thirteen banks (65 modules) are housed in the building. The DC power output from the cell stack is converted to AC power of 6.9kV by 13 PV inverters, and the power is boosted to 66kV by a transformer and is transmitted to a 66kV bus bar (extra-high-voltage transmission line) in the substation.

The "Tank-5-E-Cathode" indication on the tank near the entrance denotes the "cathode tank for the E module in the 5th bank."

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