NIMS, the University of Tokyo and Hiroshima University jointly evaluated the economic efficiency of hydrogen production systems combining photovoltaic power generation and rechargeable batteries and estimated technology levels necessary for the systems to produce hydrogen at a globally competitive cost. The results obtained in this research may provide vital guidelines for pushing the intermittent renewable power generation systems as a main power source of the country.

The effort to increase renewable power generation has encountered some issues, such as unstable power generation and low annual capacity ratio. Specific examples include Japanese power companies suspending acceptance of applications from renewable energy suppliers in September 2014 and Kyushu Electric Power Company controlling output power suppression of solar power generations in October 2018. To address these issues, various organizations have been studying systems capable of storing excess electricity in rechargeable batteries and power-to-gas (P2G) systems capable of producing hydrogen using renewable electricity and storing and supplying produced hydrogen. However, most of these systems were found to be expensive to operate, undermining the effort to massively implement economically feasible power generation technology driven by domestic renewable energy.

The joint research team designed an integrated system (diagram below) capable of adjusting the amount of battery charge/discharge and the amount of electrolysis hydrogen production in relation to the amount of solar power generated. The team then evaluated the economic feasibility of the system. As a result, the team identified technology levels necessary for the system to produce hydrogen at low cost through a comprehensive analysis of various factors such as rechargeable battery and electrolyzer capacities, considering the future technological advancements. For example, rechargeable batteries that can discharge only at a low rate but can be produced economically are expected to become available by around 2030. The team estimated that integration of these batteries will enable the system operated in Japan to produce hydrogen at a globally competitive cost of 17 to 27 yen per cubic meter.

In future studies, the team plans to determine component technology levels required for proposed systems and set R&D target values to achieve these levels. The team will also investigate the system feasibility of renewable power generation systems even under output suppression control or restriction to electricity power grid connection in order to demonstrate a proto-type system of the proposed system.