Kyokuto Kaihatsu Kogyo Co Ltd, a manufacturer of special purpose vehicles such as dumpers, tankers and garbage trucks, started operating a 1.5MW-output mega- (large-scale) solar power plant on the site of its former Tohoku Plant in Hachinohe City, Aomori Prefecture, in September 2013 (Fig. 1).
This is Kyokuto Kaihatsu Kogyo's second mega-solar power plant; the first, launched in March 2013, has an output of 1.5MW and is in its Fukuoka Plant in Iizuka City, Fukuoka Prefecture. Adjoining an expressway, the former Tohoku Plant is located in Hachinohe City Kita-Inter Industrial Park.
Foundations not affected by 'frost-heaving phenomenon'
Leveraging the experience gained at the mega-solar power plant in its Fukuoka Plant, Kyokuto Kaihatsu Kogyo designed the power plant in Hachinohe City in light of climate conditions that are unique to Hachinohe City.
In the northern regions of Japan, the "frost-heaving phenomenon" occurs where the soil heaves due to thickening ice layers generated by frost in the soil. Power generation facilities cannot be installed as designed when the land is heaving.
The foundation has to be one that does not transmit impacts from this frost-heaving phenomenon to either the mounting systems or the solar panels. Accordingly, the company created a concrete foundation measuring roughly 150cm underground and 50cm above ground (Fig. 2) by applying the method used for setting up utility poles.
Snow cover sometimes reaches around 50cm in the surrounding area of the construction site. To meet the load bearing values calculated from the height and weight of such snow cover, the solar panels were set up 1m above the ground and tilted at 20° (Fig. 3). In Fukuoka, on the other hand, they were set up about 60cm from the ground and tilted at 10°.
In the winter of 2013-14, the snow cover grew higher than usual to about 60cm on some days, but it never affected the panels that were installed 1m above the ground.
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