Pumped storage hydropower, a late 19th century technology that was largely ignored by the markets for decades, is now emerging as pivotal to bringing balance and stability to Japan’s grid as the nation both reboots nuclear energy and moves to rely more on solar and wind generation.

Japan currently has three major pumped hydro projects in various stages of completion, including one serving Tokyo that will have the world’s third-largest pumped-storage power capacity when fully online. Utilities are also making investments in existing plants so they are more responsive to contemporary energy needs.

Japan already has the world’s second largest pumped hydro generating capacity and by far the largest per capita. In many countries, such as the U.S. which hasn’t developed a major pumped hydro plant since the 1990s, a lack of new, suitable sites has slowed or halted the expansion of this kind of energy storage over recent decades.

With reactors now coming back online and variable renewable energy (VREs) expanding, the once predictable recharge timetables for pumped hydro are becoming chaotic. Japan NRG looks at how pumped hydro capacity, a relatively simple energy storage method, is being developed, deployed and traded in new ways to meet Japan’s 21st century energy needs.