Expectations are high for storage batteries in various aspects such as ensuring quality of electric power in response to the growing supply of renewable energy via grid connection, attaining efficient operation of electric power, and offering solutions in time of outage. Sumitomo Electric has been developing redox flow batteries, which are large storage batteries characterized by their safety and long service life. Recently, Sumitomo Electric and the New Energy and Industrial Technology Development Organization (NEDO) have started an electric power bidding and trading demonstration project in the wholesale power market in California, U.S. using redox flow batteries to verify the most profitable operation techniques.

California has set ambitious targets for the introduction of renewable energy. Senate Bill 100 (SB 100) was enacted to make the state’s electric power completely free of greenhouse gas emissions by 2045. These developments have been accompanied by emerging problems including rapid fluctuations in demand during morning and evening hours and declining power quality due to the shift to photovoltaic power generation. As it is imperative to manage these fluctuations, the state law requires electric power companies to introduce power storage equipment. Thus, a new program has been designed for the wholesale power market to ensure adequate revenues from the storage batteries.

In this demonstration, electric power bidding and trading started in the wholesale power market established by California Independent System Operator using redox flow battery equipment set up in California. To cope with the growing amount of renewable energy, this market requires regulation capabilities to offer short-term output (in kW) such as frequency regulation and supply capabilities to offer long-term electric energy (in kWh) such as energy supply time-shift. The operation of redox flow batteries is free from restrictions in terms of the depth of charge and discharge and the number of charge and discharge cycles. This implies that the redox flow batteries are suited to meeting the charge and discharge requirements in both short-term output and long-term electric energy. Thus, redox flow batteries are expected to attain multi-purpose and flexible operation by outputting power to concurrently meet both short- and long-term fluctuations.

This demonstration aims to flexibly combine multiple trading markets, such as the ancillary service market to procure short-term supply capability and the wholesale power trading market to procure long-term supply capability, to maintain the quality of electric power, verify the most profitable operation techniques depending on the season or specific hours, and increase the economic value of redox flow batteries.