1,000V System, Asphalt Cut Costs of Solar Plant (page 2)
Hit by flooding from typhoon, unexpected snow cover in 1st year
Fig. 2: Components can be installed efficiently by indicating their positions with chalk, a similar method to road construction, thanks to the asphalted surface. Above is Kashiwabara Solar. (source: Nikkei BP)
Fig. 4: Shoken Ishibe Solar. Located in Shoken's asphalt plant and surrounded by Route 1, JR West's Kusatsu Line and the Miyagawa River. Ritto Minakuchi Road runs across the middle of the site. (source: upper by Shoken, lower by Nikkei BP)
Thanks to the drainage ditch set up when asphalting the ground, the plant site is well drained even on rainy days. And this brings about a noticeable effect where construction efficiency can be kept almost equivalent to that on sunny days. At mega-solar power plants where mounting systems are set up directly on the ground, construction would generally stop for one to three days after rain.
Recycled asphalt lowers cost for paving
Shoken used its own material for asphalting, and Omi Doro Doboku (Koga City, Shiga Prefecture) surfaced the ground. A large portion of the material was "recycled asphalt" that Shoken collected when re-surfacing old roads. Recycled asphalt sufficiently meets the objectives of surfacing the ground for mega-solar power plants, where asphalt does not need to endure the friction caused by automobile tires like normal roads.
Recycled asphalt needs to be laid while it is heated after being collected and finely crushed. Accordingly, Ishibe Solar (Fig. 3) in the "Ishibe Ascon Plant," which has a recycled asphalt material plant, only used recycled asphalt because it could be immediately laid after being heated. Meanwhile, Kashiwabara Solar mixed the recycled material with new asphalt in a proportion of 1:1 because the heated material would cool down while being conveyed.
Panel temperature kept from rising even above asphalt
However, it was a concern that the surface temperature of the paved ground may rise more due to strong sunshine compared with ground such as soil and lower the amount of power generated by the crystal silicon solar panels. In light of this, Shoken minimized the asphalt area that was exposed to the sun by arranging the solar panel's installation angle and the space between the panels in rows next to each other, in an effort to limit the rise in the surface temperature of the solar panels. At Ishibe Solar, the solar panels are tilted at 10° while the rows of panels are spaced 60cm from each other.
1,000V-compatible system enables 3 PV inverters to form 2MW plant
Meanwhile, the adoption of a 1,000V-compatible solar power generation system also has the effect of lowering both initial investment and maintenance costs.
Compared with more widely used 600V systems, the number of panels in a string that connects solar panels in series can be increased, and, as a result, the number of strings in an overall power generation system, cables and connecting boxes would decrease.
Kyocera Corp's 1,000V-compatible solar panel was deployed.
"Ishibe Solar and Kashiwabara Solar were one of the mega-solar power plants that introduced the panel ahead of others in Japan," Senior Managing Director Iwao Fuchigami of Kyocera Solar said.
In particular, as the panel that Ishibe Solar adopted was a 322W model that increased the number of solar cells connected in series from the usual 60 to 80, the number of foundations, mounting systems and cables in the overall power plant could be cut further.
The two plants also use fewer PV inverters compared with other plants. Many 2MW mega-solar power plants using 600V equipment have introduced four 500kW-class PV inverters. On the other hand, Ishibe Solar and Kashiwabara Solar reduced the number and installed three units of 1,000V-compatible 630kW and 665kW PV inverters, respectively. Both were products of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC).
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