1.7MW Solar Plant Overcomes Snow Cover, Frost Heave in Aomori

Loss kept to minimum despite breakdown of PV inverter's cooling system

2019/04/02 23:56
Shinichi Kato, Nikkei BP Intelligence Group, CleanTech Labo

The "Hachinohe Mega Solar Power Plant," a mega- (large-scale) solar power plant with a solar panel capacity of approximately 1.7MW and a PV inverter rated capacity of 1.5MW, is located in the corner of Hachinohe City Kita-Inter Industrial Park in Hachinohe City, Aomori Prefecture, Japan (Fig. 1).

Fig. 1: Located in former Tohoku Plant in Hachinohe City industrial park. Aerial photo shot before expansion. (source: Kyokuto Kaihatsu Kogyo)

This solar plant was developed and is operated by Kyokuto Kaihatsu Kogyo Co Ltd, a manufacturer of custom-designed vehicles such as dump trucks, tanker lorries and garbage trucks, on its former Tohoku Plant. The plant buildings are leased to logistics companies as warehouses. About five and a half years have passed since the mega-solar plant started selling power in September 2013 (See related article).

This is the company's second mega-solar power plant to start operation. Its first plant is in the Fukuoka Plant site in Iizuka City, Fukuoka Prefecture, with a solar panel capacity of 1.5MW and a PV inverter capacity of 1.3MW (Fig. 2). The plant began operation in March 2013.

Fig. 2: Power plant in factory site in Iizuka City, Fukuoka Prefecture (source: Kyokuto Kaihatsu Kogyo)

At both mega-solar plants, Hayamizu Co Ltd (Kobe City) provided design and procurement services while a joint venture (JV) formed by Solar Frontier KK (Minato-ku, Tokyo), Hayamizu and Obayashi Road Corp constructed both plants, adopting solar panels of Solar Frontier and PV inverters of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC).

Aeon Delight Co Ltd, a management company of a leading distributor, the Aeon Group, operates and maintains (O&M) both power plants. Aeon Delight has accumulated experience in rooftop solar systems on Aeon stores, for example. Contracted O&M services include maintenance and management by chief electrical engineers at both sites.

The mega-solar plant in Hachinohe City initially sold power to Tohoku Electric Power Co Inc at 40 yen/kWh (excluding tax) based on the feed-in tariff (FIT) scheme, and has now changed the purchaser to a power producer and supplier (PPS) of Daiwa House Industry Co Ltd.

Favorable power generation even in snow season

The mega-solar plant in Hachinohe City has steadily realized annual power sales of roughly 90 million yen (approx US$808,62) and operating revenue of about 40 million yen over approximately the last five and a half years since it started operation.

In May 2016, the power plant was expanded, with 1,260 solar panels corresponding to about 200kW set up in an unused area to the north of the building which is rented as a warehouse (Fig. 3). The additional solar panels were the same 160W/unit-output products that had initially been set up when the operation started.

Fig. 3: Additional solar panels (source: Nikkei BP)

Following this expansion, the power sales amount has tended to grow more than before.

Compared with other areas in Aomori Prefecture, both the time and the amount of snowfall are relatively less in Hachinohe City. For example, it is said snow will not accumulate much around Hachinohe City even if there is snow cover in Aomori City, which is known for heavy snow.

One of the reasons why the annual power sales are stable is that the decrease in the power generation amount is relatively small when there is snow cover in the city. Even if snow accumulates on the solar panels, it will reportedly melt by around noon in most cases.

That said, snow sometimes falls up to about 50cm around the mega-solar plant in Hachinohe City. To meet the requirements to endure the height and the weight of snow cover, solar panels were tilted by 20° and set up 1m from the ground (Fig. 4).

Fig. 4: Set up 1m from ground, tilted by 20 degrees (source: Nikkei BP)

Foundations free from 'frost heaving' effects

In addition, "frost heave," particular to the north of Japan, occurs around the mega-solar plant in Hachinohe City. Frost heave is a phenomenon where cold air freezes the ground and forms ice layers which become thick and raise the ground level, and it sometimes damages roads and building foundations.

Frost heave could also affect mounting system foundations at this solar plant and might cause mounting systems to distort or become loose after installation. Accordingly, concrete foundations measuring about 150cm underground and 50cm above ground were adopted, applying the same method used for setting up utility poles in this region (Fig. 5).

Fig. 5: Foundations built 150cm underground to counter effects of frost heave (source: Nikkei BP)

When I visited the site for an interview, the ground had been raised up by frost heave in many areas (Fig. 6). However, the construction method appeared to have produced the effect as designed, with the foundations and mounting systems not being affected by the phenomenon.

Fig. 6: Intact foundations despite raised ground in some areas (source: Nikkei BP)

Remote control introduced from beginning

After the plant began operation, one PV inverter was stopped by the safety function as its fan had failed and could not sufficiently cool down the machine. The plant could limit power selling loss, as the PV inverter manufacturer greatly cut the number of days required to replace the fan from the number it had initially told the plant.

In addition, when the outdoor unit of an air conditioner broke down in 2019, the plant could avoid the situation where the PV inverters are stopped by the safety function, as the other air conditioners whose outdoor units were fine could cover for the broken one because the temperature was low at that time of the year.

Regarding PV inverters, Tohoku Electric Power has announced that it is preparing to implement output control. Tohoku Electric Power also sent power producers a request letter for remote control of PV inverters in March 2019.

At the mega-solar plant in Hachinohe City, PV inverters could be remotely controlled from when the plant started operation in September 2013. Kyokuto Kaihatsu Kogyo voluntarily adopted this feature from the beginning in case anything went wrong at its former plant where no resident employees were stationed around the clock.

The company also adopted remote control from the beginning at its mega-solar plant in Iizuka City and used it when Kyushu Electric Power Co Inc implemented output control.

Facility overview