Japan’s First Floating Solar System with Microinverters Installed on an Irrigation Reservoir

Japan’s First Floating Solar System with Microinverters Installed on an Irrigation Reservoir

On a farming reservoir in Fukuoka City, Fukuoka prefecture, 1,200 photovoltaic (PV) modules cover the water surface to generate electricity and additional revenues for the city. Many floating solar systems have been developed in Japan, but this 300-kW system, which became operational this July, is a bit different. This is the nation’s first floating solar system equipped with microinverters.

Due to the steep topography, rivers are short in Japan; water flows out rather quickly to the sea. For this reason, a great number of reservoirs have been created for farming irrigation, specifically for rice paddies. It is estimated that there are over 190,000 reservoirs throughout Japan. Fukuoka city is not an exception. The city located on the island of Kyushu, the most southwesterly of Japan’s four main islands, has over 300 irrigation reservoirs.

floating solarPhoto: Japan’s first floating solar system with microinverters debuted in Fukuoka city, Credit: The Fukuoka City’s Department of Agriculture, Forestry, and Fisheries

Local governments maintain and operate these reservoirs, and they have been finding a way to reduce the cost of managing reservoirs. Floating solar systems can provide a viable solution: local governments can generate extra revenue by leasing the surface of reservoirs.

According to a city official at the Fukuoka City’s Department of Agriculture, Forestry, and Fisheries, last July the city issued a proposal for reuse options and a lease for a city-owned reservoir as part of a plan for effective utilization of the city’s assets.

Power Max, a local solar EPC company, won a contract to develop and operate the solar system on a reservoir called “Rengeji-ike” with a surface area of over 14,000 square meters. The floating system can provide better efficiency in power generation than land-based PV systems because the module temperature of floating solar systems is lower than that of land-based systems.

Besides being on the water, this system provides a few more advantages. Microinverters installed behind each 1,200 PV module were provided by another local company called NEP Microinverter, Inc. The company claims that the system performance is increased by about 10 percent because microinverters convert DC power into AC power for each panel individually. Furthermore, since microinverters connect PV modules with lower voltage (200 V) DC wires, compared to 600-1,000 V for string inverters, it can reduce the risk of electrical shock if the electrical wires touch water.

The floating solar platforms are developed and provided by a France-based company Ciel et Terre, which is also involved in a 13.4-MW floating solar project under development in Chiba prefecture in Japan.

Power Max sells electricity generated by the floating system to Kyushu Electric Power Company, a local Investor-owned utility, under the nation’s feed-in tariff program and the company will pay leasing fees to the city for the next 20 years. The city uses the revenues to pay the maintenance cost of farming properties in the city.

“We will see how (well) this system performs for the next few years and we will decide whether we will expand (floating solar systems to other reservoirs),” the city official said.

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