Toshiba and Chubu Electric Power have opened a demonstration plant in a paper mill in Shimada, Shizuoka Prefecture, that converts electricity from renewable energy sources into heat and stores it in rocks. They plan to scale up the project in Okazaki and conduct a feasibility study by the end of FY2026.
Toshiba and Chubu Electric Power opened to the press a demonstration plant at the Shin-Tokai Paper Mill operated by Tokushu Tokai Paper in Shimada, Shizuoka Prefecture. The plant is designed to convert electricity from renewable energy sources into heat and store it in rocks, with the aim of testing a new way to use renewable energy, whose power output fluctuates with weather conditions.
The plant's container is 4 meters high, 9 meters wide and 4 meters deep. The rocks inside are heated and used for thermal storage at temperatures of up to 700°C. The heat is used in the paper-drying process, supplying drying steam and thermal energy through a steam generator and heaters.
The thermal storage capacity is approximately 10 megawatt-hours in electricity-equivalent terms, corresponding to one day's electricity consumption for approximately 880 households. It is the largest rock thermal storage plant in Japan, and its use in a factory in combination with an energy management system is said to be rare worldwide.
The plant uses 70 tonnes of rock sourced in Shizuoka Prefecture and is expected to complement the stable operation of renewable energy facilities. The rocks are described as having a long service life and offering the benefits of lower costs than batteries and the use of local resources.
A larger-scale plant is now being planned in Okazaki. In March 2025, Toshiba Energy Systems & Solutions, Chubu Electric Power and the city are scheduled to sign an implementation agreement. The plan is to conduct a feasibility study toward developing one of Japan's largest rock thermal storage plants, with a capacity of several tens of megawatt-hours, by the end of FY2026.