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Japan's Northernmost Mega Solar Plant Fighting Against Snow (page 2)

5-year struggle over tilt angle, height of mounting system

2013/12/22 19:34
Kenji Kaneko, Nikkei BP CleanTech Institute
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Measures to make snow slip off even at 30 degrees

When it comes to measures against snow cover, the "tilt angle" of the panels on the mounting system and the "height" between the back of the panels and the ground are significant factors. The tilt angle needed to be acute enough for the snow on the panels to slip off while the panels have to be set at a height so they would not be buried in snow even after heavy snow.

Snow on the panels would slip off more easily as the tilt angle sharpens. But the amount of power generation would be lower as the sun would shine over the panels at a slant. The higher the panels are mounted, the less they are likely to be buried under snow. But the installation cost would rise.

In addition, the panels' shadows grow longer and shade other panels more in the morning and afternoon as much as the tilt angle is sharpened and the mounting height is raised. If spaced far apart enough not to shade other panels, however, the number of panels that can be installed on the site would decrease.

In the verification test, NEDO explored the optimum balance in the paradoxical relation between the amount of power generation and measures against snow cover by changing the tilt angle and the height from the ground depending when the panels were installed.

In phase 1, the tilt angle was 33°, and the mounting height was 2m. The panels were tilted at 33° because they can generate the most amount of power at that angle in light of the sun's culmination altitude. And it was estimated that snow would not accumulate to 2m given past records. However, the snow on the panels did not slip off at an angle of 33°.

Consequently, in phase 2, the tilt angle was sharpened to 45°, and the height was lowered to 1m. Then, the snow on the panels slipped off, but the fallen snow accumulated to over 1m under the panel and covered the lower area of the panels.

In phase 3, the tilt angle was unchanged (45°), but the height was raised back to 2m (Fig. 3). As a result, the snow slipped off the panels and once fallen did not cover the panels.

In phase 4, the panels were tilted at 30° with an "arrangement to make snow slide off more easily" added to the panel surface to verify its effect (Fig. 4). The arrangement included, for example, a measure to fill in the slit between the panel frame and the glass surface by injecting silicon caulking (Fig. 5). This was because it had turned out that snow tended to stay on the panels because of the gaps and slits on the solar panel's surface. The arrangement had a significant effect with snow slipping off most panels even at an angle of 30°.

On the other hand, the raising of the solar panels, a measure taken in parallel with the caulking, did not work efficiently. The measure was meant to space the lowest row of panels from the upper panels by raising the lowest row when mounting them. Snow accumulating on the upper panels would slip beneath the mounting system from the space with the lowest row, instead of accumulating only under the lowest row.

Exactly as expected, the snow on the upper panels slid down from the space to the inner side of the mounting system. But the accumulated snow beneath the mounting system caused pressure on and distorted the panels on the lowest row from the ground. Hence, NEDO gave up applying this measure.

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