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Seafront Solar Plant Withstands Wind, Wave, Ground Subsidence (page 3)

'Overload' helps PV inverters work at maximum efficiency around noon

2014/04/28 13:40
Shinichi Kato, Nikkei BP CleanTech Institute
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However, the panels already generated more power than the rated output of PV inverters and PV inverters limited their output between 11:00 and 14:00 most days around March. As April approached, the time when the amount of power generation reached the PV inverters' rated output gradually became earlier.

In light of the amount of power generated in spring, the amount of output control by PV inverters seems to further increase in summer, when the sunshine gets stronger. However, it does not have to be that way, according to Mitsui.

Solar panel power generation is related to factors including the kind of solar panels, temperature, the amount of sunshine and the amount of moisture in the air. In summer, the temperature rises as the amount of sunshine increases. With crystalline silicon solar panels, the decline in power generation efficiency caused by the cell temperature rise could be more significant than the increased amount of sunshine.

MES is also focusing on what impact the rise in the amount of moisture in the air could bring. The amount of moisture increases as summer approaches. Then, the increased amount of sunshine sometimes does not contribute so much to the rise in the amount of power generation due to the diffusion of near-infrared wavelength light that facilitates solar cells to generate more power. In addition, the amount of power generation could rise more in spring because the temperature is lower and the amount of moisture in the air is less.

Measures against wind, wave overtopping

The solar panels were tilted at 10°. This was a measure against strong winds from the north, along with the aim of setting up as many panels as possible. Facing the sea, the north side of the site is exposed to strong winds. The higher the angle at which the panels are tilted, the stronger the mounting systems for them have to be, and that could cause the construction cost to rise.

As the plant faces the sea, Mitsui also considered measures against wind and wave overtopping over the seawall. By enhancing the approximately 2m-high enclosing embankment built about 60m from the seafront, the plant prevented strong north winds from directly hitting the underside of the panels (Fig. 5). However, since the plant is located in an area where the reference wind speed is set at 32m, the plant was designed with a larger-than-necessary margin of safety excluding the effect of the enclosing embankment.

As for the foundation, Toko Electrical Construction's concrete molding, "PC (precast) Pile," was assembled like a curb (Fig. 6). Given the location in a landfill site, the mounting system could twist and be damaged if it were unable to adapt to tremors caused by earthquakes or irregular subsidence if long concrete foundations or pickets were used. As PC Pile features sufficient rigidity when built like a curb, it is said to be easier to prevent the mounting systems from being damaged even if the panel angle varies.

In the outer rows where the wind is stronger, the number of piles to be built like a curb was increased from 2 to 3, and transverse piles were added in an effort to boost toughness (Fig. 7).

On the south side where the PV inverters and transformers were installed, a large amount of sand and equipment are prepared as measures to stop oil from spreading if it leaks. Oita Works acquired ISO14001 authentication for environmental management systems. The facility management of the mega-solar power plant also complies with the same criteria, and management aimed at lowering environmental load is being sought at the plant.