The Spanish developer will install the array on a 40-hectare unused golf course in the town of Daigo, Ibaraki prefecture.
It will sell the electricity — enough to supply roughly 10,000 homes — to regional utility Tokyo Electric Power (Tepco).
It secured a ¥11.1bn ($109.6m) non-recourse loan with Deutsche Bank to finance construction of the plant. Gestamp Solar chief executive Jorge Barredo said the company would probably strike similar arrangements with Deutsche Bank in Japan in the future.
