In a rice farming district in Kato City in the center of Hyogo Prefecture, Japan, solar panels are laid out on three ponds (Fig. 1). The ponds are for agricultural use and supply water to rice fields in the Yado District of Kato City.

Fig. 1: Solar panels float on three ponds in Kato City, Hyogo Prefecture. The solar panels on the pond in the top right of the picture are on-water panels of the "Kato City Yado Solar Power Plant." The panels on the two ponds at the center are for the "Kato City Yado Oike Solar Power Plant." (Source: Nippon Comsys Corp)

The on-water solar power generation system is developed and operated by the Nippon Comsys Group, which is engaged in the communication infrastructure business. There are two mega (large-scale) solar power plants in the area. Of the two plants that comprise the solar power system, in the 2MW plant, all the panels are installed on water. In another plant, which has a capacity of 1.3MW, panels are installed on the ground and water; the panels on the water have a capacity of 71.5kW (See related article).

Floats manufactured by Takiron Engineering Co Ltd of Kita-ku, Osaka City, are used for floating the solar panels on water. Takiron Engineering is a 100% subsidiary of synthetic resin manufacturer Takiron Co Ltd and offers engineering services mainly to public facilities such as water supply and sewerage facilities. The company's water supply and sewerage business led to the chance to develop the floats for on-water solar panels. The development was started before the enforcement of the feed-in tariff (FIT) scheme for renewable energies.

"Coverings" are used at water supply and sewerage facilities. They are used to cover water treatment facilities to prevent the entry of foreign substances and excessive growth of algae, aiming to ensure safety and health. They are also used at sewerage facilities to prevent the spread of smells.

When coverings began to be used widely by water supply and sewerage facilities throughout Japan, some local governments introduced "coverings mounted with solar panels." The Yokohama Waterworks Bureau introduced such coverings to settling tanks in water treatment facilities.

The solar panel-mounted coverings adopted by the Yokohama Waterworks Bureau were supplied by Takiron Engineering. Two types of products were supplied. One is a type that moves along rails on concrete roads to travel to and from the area above the filtration pond. The other is a float type.

The products introduced by the Yokohama Waterworks Bureau began to be known among power producers and companies that offer EPC (engineering, procurement and construction) services after the enforcement of the FIT scheme. They began to look into developing or constructing solar power plants on water in reservoirs, and the company received inquiries regarding the development and production of floats.