Mitsui Home and Tokyo Gas have revealed plans to deploy Japan’s first combined on-site and virtual solar power purchase agreement (PPA), cutting factory emissions and maximizing rooftop energy use.
November 28, 2025
Brian Publicover
Image: Asanagi, Wikimedia Commons, CC0 1.0
Mitsui Home and Tokyo Gas have agreed to deploy Japan’s first combined on-site and virtual power purchase agreement (PPA) using thin, lightweight solar panels at Mitsui Home’s factory in Saitama prefecture.
Tokyo Gas said in an online statement that it will install a 1 MW system across the plant’s full roof surface, enabled by panels that weigh about 40% less than conventional modules.
The on-site PPA will supply the factory directly, while surplus generation will be sold to the market with its environmental value transferred to Mitsui Home’s Chiba and Kansai factories through a virtual PPA.
The project is expected to deliver about 1,170 MWh of renewable electricity annually and cut Mitsui Home’s domestic factory emissions by roughly 506 metric tons, equal to a 44% reduction across its Saitama, Chiba, Kansai and Kyushu sites.
The companies described the arrangement as a model for addressing rooftop load limits and surplus-power constraints as Japan seeks to expand solar capacity under the Seventh Strategic Energy Plan amid a shortage of suitable land.
The initiative also complements other ongoing innovation across Japan’s renewable and energy storage sectors.
In January, for example, Japan reinforced its lead in solid-state batteries, backing four major R&D projects by Toyota, Idemitsu, Mitsui Kinzoku, and TK Works with over $660 million in subsidies to support commercialization by around 2030.
In July, PXP Inc and Tokyo Gas began developing lightweight chalcopyrite solar cells for low-load industrial roofs, while a consortium including Toshiba and YKK AP started a perovskite window pilot at Tokyo’s Telecom Center Building.
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