Common property constructed in Edo Period

Kanancho, the town of Kanan, in the southeast of Osaka Prefecture, Japan, boasts abundant nature and history with many ancient tombs and ruins. To the east of the town border are the mountains leading to Mt Katsuragi, and at the foot of the mountain spreading to the west are terraced hills. For this reason, the policymakers in the Edo Period made the people construct reservoirs for farming in preparation for water shortages, thus increasing the amount of rice production.

"Imandoike" is such a reservoir that has been managed as common property since it was constructed in 1672. Expanded using a national subsidy during the period between 1948 and 1950, the reservoir was placed under the joint management of the town of Kanancho and Imando district. The reservoir is in the shape of a rectangle measuring about 130m x 80m, and the surface area is about 10,400m2 when it is filled with water.

In September 2015, a floating solar power plant with an output of 504kW was completed and started operation on this reservoir (Fig. 1). A total of 2,016 solar panels were set up on plastic float mounting systems. The panels account for roughly 6,000m2 of the entire surface area. PV inverters were set up on the embankment adjacent to the reservoir.

Fig. 1: Floating solar power plant completed on Imandoike in September 2015 (source: Kanancho)

The power producer is West Energy Solution Inc (Hiroshima City), a subsidiary of West Holdings Corp (West HD) which is widely engaged in solar power generation business. The company set up the power generation facilities after agreeing to rent the water surface from Kanancho. Generated power is sold to an electric power company for 20 years using the feed-in tariff (FIT) scheme. The annual power generation amount is estimated to be 575,000kWh for the first year.

Pioneer of floating solar plants

This project began with West Energy Solution's proposal to Kanancho. The company has set up solar panels on the water and roofs of public facilities by proposing the ideas to and collaborating with local governments. The collaboration with Kanancho was one of such approaches. Kanancho, as a municipality, started to positively consider the floating solar plant after the proposal by West Energy Solution in 2013.

When it came to leasing the surface of the reservoir to a solar power producer, however, Kanancho found both benefits and challenges as it specifically verified the project from the perspective of an entity that manages the reservoir and uses its water.

The biggest benefit was the rent earned by leasing the water surface, which would offset part of the cost for maintaining and managing the facility borne by the district that managed the reservoir. In addition, blue-green and other kinds of algae and waterweeds that interfere with reservoir management were likely to be kept from growing as the sunshine would be blocked by float mounting systems and panels. The power producer was also expected to be responsible for weeding around the embankment and water surface cleaning as part of maintenance and management of the solar power generator (Fig. 2).

Fig. 2: Power producer weeds around embankment and cleans water surface. (source: Kanancho)