Visit to Plant

Okinawa's 1st Battery-equipped Mega Solar Plant Realized Without Subsidy

Integrated control of PV inverters limits drastic changes in output

2018/12/04 18:23
Shinichi Kato, Nikkei BP Intelligence Group, CleanTech Labo
Print Page

The completion ceremony for a mega- (large-scale) solar power plant built with a storage battery system took place in Nakijinson, Kunigami-gun, Okinawa Prefecture, Japan, Nov 9, 2018 (Fig. 1). This is said to be the first solar power plant built with a storage battery system in Okinawa's main island. It started selling power in September 2018.

Fig. 1: Completion ceremony (source: Nikkei BP)

The plant was developed and is run by Marutoyo Shouji LLC (Urasoe City, Okinawa Prefecture), which is engaged in real estate business.

Its solar panel and PV inverter capacities are about 3.3MW and 1.99MW, respectively, and the plant is also provided with a storage battery system of about 1.714MWh. The storage battery system's inverter has a capacity of 2MW.

The storage battery system is used to limit the power plant's "output fluctuation within 2% per minute." This means a synthetic output calculated by coordinating the fluctuation range of the mega-solar plant's grid capacity and the storage battery system's charge/discharge control is kept within 2% per minute of the rated capacity of PV inverters, as is required by The Okinawa Electric Power Co Inc.

Given the small grid scale in Okinawa's main island, it became difficult from an early stage to connect large-scale solar power generation facilities with the grid in a bid to keep the frequency from fluctuating after the feed-in tariff (FIT) scheme was implemented. Since the applications for grid connection surpassed 57MW, it has been subject to achieving the "fluctuation in power generation within 2% per minute" by building storage battery systems on-site for solar power plants with an output of 300kW or more that acquired facility approval.

Local company Top One KK (Kohagura, Naha City) provided engineering, procurement and construction (EPC) services. In search of a partner that could realize a control system while keeping "fluctuation in power generation within 2% per minute" using a storage battery system, Top One entrusted electrical engineering to DURI Co Ltd (Kobe City), which had been introduced by UCL Corp (Shibuya-ku, Tokyo), a company it dealt with when purchasing solar panels.

DURI realized this system by combining a control system of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) to introduce the technology of solar and wind power plants built with storage battery systems, in which South Korea has moved ahead of Japan, and to positively run it at solar power plants in Japan.

TMEIC supplied the storage battery system in addition to PV inverters for solar power generation. The adopted storage batteries are products of LG Chem Ltd of South Korea.

The plant adopted solar panels of Jinneng Clean Energy Technology Ltd of China. This company markets its panels under the brand name of Jinergy, and UCL serves as its general agent in Japan. A total of 9,216 single crystal silicon panels (360W/unit) were supplied.

UCL delivered Jinergy solar panels and TMEIC PV inverters and storage battery system to the plant.