There are many reservoirs scattered across Kagawa Prefecture, Japan. Given there is relatively less rainfall in the prefecture, many reservoirs have been built through the ages and used primarily for agriculture.

The number of reservoirs in the prefecture totals 14,619. This accounts for about 7% of all reservoirs across Japan and ranks third following Hyogo and Hiroshima prefectures. The ratio of reservoirs against the entire area of the prefecture is said to be the highest in Japan.

"Hiragioike" in Mikicho, Kida-gun near Takamatsu City, is one of such agricultural reservoirs. It was built in 1700 (Genroku 13).

The "Hiragioike Floating Solar Power Plant," a mega- (large-scale) solar power plant with an output of about 2.6MW, which makes use of the water surface, is about to start operation (Fig. 1).

Fig. 1: A floating mega-solar power plant with an output of about 2.6MW will shortly start operation on Hiragioike in Mikicho, Kida-gun, Kagawa Prefecture. (source: Nikkei BP)

Sumitomo Mitsui Construction Co Ltd started construction in May 2017 and plans to start power sale in November 2017 as the power producer. The construction of power generation facilities has already been completed, with pre-operation voluntary inspection currently ongoing.

Sumitomo Mitsui Construction also developed and operates another mega-solar power plant on the site of its plant (Mitagawa PC Factory) in Yoshinogaricho, Saga Prefecture. This plant is an on-ground-type one with an output of 1MW.

The project in Mikicho is the company's first floating type one that came after the facility in its plant site. Sumitomo Mitsui Construction adopted its own "floats" – devices to keep solar panels on the water.

Sumitomo Mitsui Construction's floats have been adopted at floating solar power plants both inside and outside of Japan. Starting from a 3.678MW-output plant (completed in March 2016) on a former eel farm in Kosai City, Shizuoka Prefecture, the company's floats have been adopted at a 1.8MW-output plant (completed in March 2017) in Toyoake City, Aichi Prefecture, and a 1.5MW-output plant (completed in June 2017) in Kagawa Prefecture and are slated for adoption at five other floating mega-power plants with a total output of about 10MW being developed in Japan.

Overseas, the adoption of Sumitomo Mitsui Construction's floats has been decided at plants with a total output of about 100MW in more than 10 countries.