Okinawa Yanbaru Seawater Pumped Storage Power Station

The Okinawa Yanbaru Seawater Pumped Storage Power Station (沖縄やんばる海水揚水発電所) was an experimental hydroelectric power station located in Kunigami, Okinawa, Japan and operated by the Electric Power Development Company. It was the world’s first pumped-storage facility to use seawater for storing energy. Its maximum output was 30 MW. Construction of the plant started in 1987 and was completed in 1999 at a cost of ¥3.2 billion. It was dismantled in 2016.

Facility
The power station was a pure pumped-storage facility, using the Pacific Ocean as its lower reservoir, with an effective drop of 136 m and maximum flow of 26 m3/s. Its pipelines and pump turbine were installed underground. Its maximum output was approximately 2.1% of the maximum power demand in the Okinawa Island recorded on August 3, 2009.

The upper reservoir, artificially excavated, was approximately 600 m away from the shoreline and approximately 150 m above sea level. It had an octagonal planar shape with a maximum width of 252 m. Its maximum depth was 25 m and its effective storage capacity was 564000 m3. The entire inner surface of the reservoir was covered with an impermeable liner to prevent seawater from leaking and damaging the surrounding vegetation.

Fiber-reinforced plastic tubes were adopted for the penstock and the tailrace instead of steel tubes in order to avoid seawater corrosion and adhesion of barnacles. The pump turbine was partially made of stainless steel resistant to seawater.

A 66 kV line connected the power station with the power grid of The Okinawa Electric Power Company.

History
The power station was a pilot plant funded by the Agency for Natural Resources and Energy and constructed by the Electric Power Development Company. A five-year verification operation was conducted beginning on May 16, 1999. The Japan Society of Civil Engineers presented the company an Outstanding Civil Engineering Achievement Award on May 26, 2000 for its construction of the plant.

The operator could not put the power station into practical use because the demand for electric power in Okinawa had not grown as predicted, and the plant was not profitable as a business. The power plant was dismantled in July 2016.