'World's Largest' Floating Solar Plant Operates on Reservoir (page 2)
Flood-prevention reservoir to supply income, emergency power at times of disaster
Method used to float solar panels on reservoir
How did they manage to float approximately 4,500 solar panels on the reservoir? Instead of metal mounting systems used with the on-land systems, plastic members similar to rafts attached to the solar panels are floated on the reservoir (Fig. 3). Even though the plastic mounting systems are floating on the water, they still have to prevent the solar panels from moving excessively and the solar panels from tilting due to changes in the water level.
Construction is carried out by connecting the raft-like plastic members, carrying them to the designated position by ship and mounting 20 solar panels on each row. This process is repeated, and the solar panels are stabilized (Fig. 4). Those floats are subsequently anchored on four corners so that the overall system cannot be taken away by the wind or water movement. On windy days, the devise applied to the member connection area can absorb the welter generated by waves on the reservoir surface.
According to West Holdings, in a cross-sectional view, the reservoir is shaped like a basin with an almost flat bottom and a wall climbing up on a slant toward the shore. What matters to this reservoir is the descent of the water level, rather than the ascent, the company said. Should the solar panels be floated in a widespread pattern that they almost reach the shore, the panels close to the shore could affect the overall power generation performance by moving on to the ground when they touch the bottom of the reservoir due to the low water level.
Based on this situation, the solar panels are designed to float away from the shore where they can adapt to a 9m gap in the water level. The 9m gap was set up as an index considering that the water level is not likely to lower more than a certain level as there are springs at the bottom of the reservoir, the company said (Fig. 5).
The member to attach solar panels is hollow and is called a "float." This member is a product of Ciel et Terre International of France. It was employed because solar power plants floating on reservoirs, etc, are more advanced in Europe and the US than in Japan. Even so, it was unusual to apply this method to large-scale plants like the one in Okegawa, West Holdings' Executive Director Nagashima said. Therefore, another member jointly developed with the West Holdings Group was introduced.
West Holdings deployed solar panels manufactured by JA Solar Co Ltd of China, which Ciel et Terrre recommended as the optimum product for its float. The solar panels are tilted at 15°, which was determined to minimize the impact of wind pressure and ensure the amount of power generation at the same time. Given the little amount of dust on the reservoir, the setup at this almost flat degree is not likely to lower the amount of power generation that much due to dirt, compared with the models set up on land.
To generate power with solar panels floating on water, other technologies are also important: technology to block the moisture that would penetrate from the backside and side surfaces of a solar panel, technology to prevent short circuits caused by moisture penetrating the electric joints, and technology to prevent electricity loss due to lower insulation resistance in the humid environment.
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