Solar Plant Built Through Japan's 1st 'Recruiting Process'
Frequent lightning interrupts remote monitoring
Showa Village, on a plateau, near the foot of Mt. Akagi, Gunma Prefecture, Japan, is known for its cabbage, konjac and other vegetable cultivation. The "Sun-Farm Sennennomori (Showa Village Solar Power Plant)," a mega- (large-scale) solar power plant with a total solar panel output of about 5.6MW, is situated on this plateau (Fig. 1).
This mega-solar plant is located in "Sennennomori" as its name indicates. It consists of three power plants connected with a high-voltage power grid, utilizing an industrial site in Sennennomori, which has, among other facilities, a golf course and a soccer camp facility.
The Nippon Comsys Corp Group developed, constructed and runs this power plant. The Nippon Comsys Group is well known for constructing many telecom facilities primarily for the NTT Group.
Nippon Comsys provided engineering, procurement and construction (EPC) services and operates and maintains (O&M) the mega-solar plant after completion. The power producer is Comsys Create Corp (Shinagawa-ku, Tokyo), a subsidiary of Nippon Comsys, and is engaged in new business development for the company.
Comsys Create has developed and operates solar power projects with a total output of about 61.2MW at 19 locations. According to Comsys Create, its development projects have stopped at the 19th with no more being planned right now.
Just like the power plant in Showa Village, Nippon Comsys provided EPC and O&M services at these solar plants, whose power producer is Comsys Create. Excluding the CIS chemical compound-type adopted at the 1.8MW-output plant in Azumino City, Nagano Prefecture, crystal silicon-type solar panels of various manufacturers were adopted at all the other solar plants. As for PV inverters, products of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) were adopted at all 17 locations excluding the two with an output of about 12.7MW and 2MW at Rifucho, Miyagi Prefecture, and Ebetsu City, Hokkaido, respectively.
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This mega-solar plant is situated about 660m above sea level. The peaks of Mt. Tanigawa and other mountains in the Joshinetsu region can be seen from around the power plant. With vegetable fields and mountain forests spreading across the surrounding area, it gives the impression as if being in Hokkaido (Fig. 2).
Showa Village boasts farming and abundant sunshine. Given the high altitude, the temperature is relatively low even in mid-summer, and it means the output of crystal silicon-type solar panels, which see power generation efficiency decline during high temperatures, is not likely to decrease even in summer.
Given these circumstances, the area is suitable for solar power generation. Accordingly, many solar panels are arrayed in fields and between the mountain forests in the surrounding area.
The Sun-Farm Sennennomori initially began operation with a solar panel capacity of about 2.419MW and a grid capacity of 1.99MW in November 2013 (Fig. 3). Comsys Create calls this phase 1 project "site A." Generated power is sold at 40 yen/kWh (excluding tax) based on the feed-in tariff (FIT) scheme.
Two phase 2 mega-solar projects began operation in the adjoining site later in October 2017, almost four years after the phase 1 project started selling power. These phase 2 projects are called site B and site C. Generated power is sold at the FIT-based unit price of 36 yen/kWh (excluding tax).
Combining the two phase 2 projects, the solar panel and grid capacities are about 3.920MW and 3.240MW, combining about 2.305MW and 1.99MW at site B and about 1.616MW and 1.25MW at site C, respectively.
TMEIC PV inverters were adopted at all the three sites while solar panels of Sharp are used at site A and those of Kyocera Corp at sites B and C. Steel- and concrete-type foundations and mounting systems were adopted at site A while pile foundations and aluminum mounting systems were adopted at sites B and C. Cost efficiency is higher in the latter (Fig. 4).
Sites B and C obtained the right to grid connection through "Japan's first recruiting process (bids for enhancing the grid capacity)" conducted by Tokyo Electric Power Co Holdings Inc.
Remote monitoring interrupted by lightning
The amount of power generation has trended similarly at site A, where six years have passed since it started selling power in October 2013, and sites B and C, where two years have passed since they started selling power in October 2017.
Despite monthly fluctuations at all these sites, the amount of power generation has continued to outperform the initial estimates at the planning phase by about 10% on a yearly basis.
In the summer of 2019, a failure was found in the telecom capability used for remote monitoring of PV inverters. Of four units set up at site A, one stopped producing power generation data. The power selling meter continued to transmit data, according to which this PV inverter was found to be generating power as usual with no failures in its input/output capability.
Comsys Create believes this telecom capability malfunction was caused by lightning. It is known that the telecom capability might be affected by a surge caused by induced lightning.
To solve this communication disconnection, Comsys Create has requested the manufacturers of the PV inverter and the telecom system to determine the cause and restore communication (Fig. 5).
This process does not seem to be proceeding as swiftly as expected. If the communication system were supplied by the PV inverter manufacturer, the PV inverter manufacturer would take care of the telecom system. In the case of the PV inverter in question, however, the plant individually procured and set up the telecom system independently from the PV inverter manufacturer.
This resulted in a longer time needed for each of the two manufacturers to visit the site and individually examine its product in order to determine whether the PV inverter or the telecom system was causing the problem.