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1,000V System, Asphalt Cut Costs of Solar Plant (page 3)

Hit by flooding from typhoon, unexpected snow cover in 1st year

2014/05/31 19:38
Shinichi Kato, Nikkei BP CleanTech Institute
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Panels feature antidazzle treatment to prevent reflection on JR Kusatsu Line

Ishibe Solar is surrounded by Route 1 to the north, Shoken's asphalt plant to the east, West Japan Railway Co's (JR West) JR Kusatsu Line to the south and the Miyagawa River to the west (Fig. 4). Running across the middle of the site is the Route 1 bypass "Ritto Minakuchi Road", connecting Iwane, Konan City, Shiga Prefecture, and Kamitoyama, Ritto City.

Under these locational circumstances, Shoken was requested by JR West to come up with a measure against solar panel reflection on the JR Kusatsu Line, and adopted an anti-reflection coating for the solar panels (Fig. 5).

Ishibe Solar could be connected with the Kansai Electric Power Co Inc's transmission grid in a neighboring area along Route 1 at a cost of only about ¥600,000. No power ratio restriction was set. Since it started selling power in February 2013, the amount of power generation produced a large upswing from the expected 1,700,000kWh per year to approximately 2,210,000kWh per year.

There were also some problems. Due to rain caused by typhoon No. 18 that landed in September 2013, the level of the Miyagawa River rose and flooded, nearly to the upper part of the concrete foundations. It did not affect the power generation itself. After this flooding, the Ministry of Land, Infrastructure, Transportation and Tourism (MLIT) constructed a pool under the bypass to prevent water from flooding under the bypass, and now water runs into the pool when flooding occurs, as it did in September 2013.

In winter, there was unexpected snow cover. Since this is not a snow zone, no full-scale measure against snow had been taken at Ishibe Solar. Hit twice by snow cover of about 20cm during this winter, the plant did not generate power for one whole day with all the panel surfaces covered with snow.

Additional measures against snow

Kashiwabara Solar, on the other hand, started selling power in April 2014 (Fig. 6). Next to the site to the east is a mountain (Fig. 7). Kinden Corp analyzed in advance the impact of this mountain's shadow using a photovoltaic power generation analysis system dubbed "Solar Navi" and "designed the system so that the impact could be limited to 3% in the morning," Kinden Executive Officer Toshiaki Iwata said. He said Kinden is now verifying the impact on the actual amount of power generation.

Its major difference from Ishibe Solar was the need for measures against snow given its location in a snow zone (Fig. 8). The panels are tilted at 15° at Kashiwabara Solar whereas they are tilted at 10° at Ishibe Solar. The mounting height of the panel's ground side was raised from 60cm to 80cm from the ground. The mounting system was changed from aluminum to iron. The solar panel was also varied from the 322W product to a normal-size 245W product. Shoken explained all these changes were aimed at corresponding to the expected snow cover and vertical loads under snow cover.

As an effort to boost construction efficiency, Shoken also changed the concrete foundation to another type that allows builders to transport two foundations at a time without using any screws and boost the efficiency in transportation and installation accuracy.

As a result, the number of concrete foundations that can be installed in a day soared to a maximum of 300 in Kashiwabara, compared with 60 in Ishibe. The installation of foundations and mounting systems finished in about one and a half months, followed by about two weeks of solar panel installation. It generally takes three months per 1MW, or six months for 2MW, to set up the infrastructure.

In addition, the size of the connection cable was changed from 22 x 22mm to 38 x 38mm. According to Shoken, it chose a thicker cable because the loss in transmitted power was larger than expected due to the large resistance inside the 22 x 22mm cable when transmitting 1,000V power for a maximum distance of 300m at Ishibe Solar.