Visit to Plant

4 Types of Foundations Adopted for 15MW Solar Plant (page 3)

All possible measures taken for water discharge using permeable anti-weed sheets

2016/02/11 17:51
Shinichi Kato, Nikkei BP CleanTech Institute
Print Page

Water discharge capacity maintained using anti-weed sheets as permeable as the ground

All areas where the solar panels would be set up were covered by anti-weed sheets (Fig. 3). Daiwa House has basically, thus far, covered all the areas upon which to set up solar panels with anti-weed sheets at the mega-solar power plants to which it has provided EPC services. The same method was also adopted at this plant.

Fig. 3: Every area to set up solar panels was covered by anti-weed sheets. The water retaining capacity was maintained by adopting a product as permeable as the original ground. (source: Nikkei BP)

The Daiwa House Group did not implement full-fledged land reclamation in the former golf course because of the need to limit its development within the "development activities" permitted when building the golf course. This also benefited the group by alleviating the development cost and in terms of water discharge measures.

At golf courses, water discharge systems are optimally structured in accordance with the undulations and other conditions of the terrain. Drainage ditches, for example, are provided in areas where the natural water discharge function is insufficient. Without full-fledged land reclamation, additional water discharge facilities can be kept to a minimum.

The water discharge function includes the land's water retaining capabilities. In the case of this mega-solar power plant, the ground surface was to be changed from the grass of the golf course to anti-weed sheets. Accordingly, the company adopted Unitika Ltd's "AG200" as an anti-weed sheet, which can realize almost equivalent permeability to that of the previous grass on the ground surface.

At the explanatory meeting for local residents, interest was particularly high in the water discharge measures because the meeting was held immediately after the landslide disaster in Hiroshima Prefecture that followed a severe rainstorm in August 2014.

The Daiwa House Group said it had gained an understanding at the meeting after explaining that the plant would maintain the same water discharge environment as that during the time of the golf course through the existing water discharge facilities and the adoption of highly permeable anti-weed sheets, and so forth.

The plant varied the way of using the anti-weed sheets in accordance with the geographic circumstances.

In flat areas, crushed stones were laid over the anti-weed sheets (Fig. 4). The crushed stones, along with the anti-weed sheets, prevent weed growth. The stones also prevent the anti-weed sheets from deteriorating and being blown away. So as to prevent the stones from rolling out of the areas, the plant built embankments on the perimeter of each area.

Fig. 4: Crushed stones were spread over the anti-weed sheets in flat areas. Measures were also taken to prevent the stones from rolling away. (source: Nikkei BP)

The areas with crushed stones accounted for less than 10% of the entire site. The plant selected fine particle-sized stones that looked good and would not easily roll away.

In the sharply sloping areas where no crushed stones could be spread, the ground surface was covered by nothing but the anti-weed sheets. Piles were driven in the ground from the upper side of the anti-weed sheets, preventing the sheets from being blown away.