Continued from Achievements of Large Redox Flow Battery in Hokkaido (1)
System efficiency higher than 70%
The redox battery (60MWh, 15MW) used at the Minami-Hayakita Substation was selected for the Large-Scale Storage System of the Ministry of Economy, Trade and Industry (METI) and was adopted (Fig. 6).
Under the demonstration project, a NAS (sodium-sulfur) battery (300MWh, 50MW) installed at the Buzen Power plant operated by Kyushu Electric Power Co Inc (Kyuden) and a Li-ion battery (40MWh, 40MW) installed at the Minami-Soma Substation operated by Tohoku Electric Power Co Inc are in operation (See related article 1, 2).
When the properties of the three types of storage batteries are compared, all of them feature high charge/discharge response speed and are effective as measures for both short-cycle fluctuations and long-cycle fluctuations. Large capacity batteries are also possible. As for system efficiency, however, Li-ion batteries have the highest efficiency at about 80%, followed by NAS batteries and redox flow batteries, which are the lowest at about 70%.
When the equipment costs are compared, Li-ion batteries are the highest at 200,000 yen per 1kWh. NAS batteries are the lowest and redox flow batteries are about midway between the two. As for Li-ion batteries, the unit cost per 1kW is the lowest because the type features the highest response among the three. In addition, it is often said that "NAS batteries are also the lowest in kWh-based cost because manufacturers in Korea and others are lowering the cost by mass production."