First domestic mega solar power plant that sells power at nighttime. (Source: Hayashi Kensetsu)

A 6.5MWh Li-ion storage battery installed in the plant

Li-ion storage battery manufactured by LG Chem Ltd

"DC link" system incorporated (PV inverter monitor)

On February 1, 2017, Hayashi Kensetsu, a construction company based in Isa City, Kagoshima Prefecture, started operation of a mega (large-scale) solar power plant with a large storage battery installed for selling power during nighttime hours. The plant was constructed on land owned by the city in Okuchi-Ota of Isa City.

The solar panels have a capacity of approximately 1.2MW, and the PV inverter features a rated output of 1MW, while the Li-ion storage battery has a capacity of 6.5MWh.

The solar power plant is named the "Hayashi Solar System Takayanagi Power Plant." All the power generated by the solar panels is stored in the storage battery from daybreak to 6:00pm, and all the stored power is discharged from the storage battery for six hours from 6:00pm to midnight for transmission to the grid of Kyushu Electric Power Co Inc (Kyuden). The feed-in tariff (FIT) scheme is applied to the transmission, and the power is sold at a tariff of ¥36/kWh.

For this project, Isa City invited public participation in the solar power generation project utilizing the idle city land in September 2013, and Hayashi Kensetsu was selected as the developer.

Limited margins of Kyuden's local grids and the higher contribution to construction cost to improve upper stream grids (¥4.3 to 6.3 billion or approx US$37-55 million) are behind the power plant deploying this power sale pattern.

The high construction contribution cost was quoted by Kyuden when Hayashi Kensetsu, which was selected as the developer, completed the site preparation work and started the foundation work for the solar power facility.

Responding to the quote, Hayashi Kensetsu negotiated with Kyuden, asking the company to examine the possibility of changing the time of power transmission by installing storage battery equipment to realize grid connection without construction work for the grid; the company also asked Kyuden for selective negotiations on grid connection.