The project company, Tomakomai Yufutsu Mega Solar, operates a 29.8 MW solar array on a 48-hectare plot of land in the city of Tomakomai, on the island of Hokkaido.
SB Energy did not disclose the financial terms of the deal.
Tokyo-based Marubeni finished building the project in October 2015. The array generates enough electricity to cater to the needs of roughly 9,000 homes, according to an online statement.
SB Energy — a unit of Japanese telecoms service provider SoftBank — is primarily a renewables developer, although it is increasingly acquiring operational PV assets.
It owned 274.1 MW of solar capacity in Japan by the end of November 2016, according to company documents.
Its largest operational projects are a 111 MW array in the town of Abira, Hokkaido, and a 42.9 MW installation in the western city of Yonago, Tottori prefecture.
It recently completed a 43.4 MW project in Hamamatsu, Shizuoka prefecture.
The company has an additional 360.2 MW of solar in varying stages of development.
This year, it will finish building a 32.3 MW array in the southern town of Yusui, Kagoshima prefecture, in cooperation with Mitsubishi UFJ Lease & Finance.
Although SB Energy has thus far primarily focused on developing renewables projects in Japan — aside from investments in Mongolian wind farms — its parent company jumped into the Indian PV market in 2015 with a $20 billion investment, in cooperation with Bharti Enterprises and Taiwan’s Foxconn Technology.