‘Airport Mega-solar’ Constructed on 25-degree Slopes

Color, design arranged in consideration of landscape…

Shirahamacho, in northern Wakayama Prefecture, where forest accounts for about 80% of the entire area, is the transportation and tourist core of the Kii Peninsula, which is blessed with abundant nature and forms part of Yoshino-Kumano National Park and boasts the “Nanki-Shirahama Airport” and “Adventure World,” which is popular because of its pandas.

As you drive south on the Minami Shirahama Road and turn inland from the coast through the forest, orderly arrayed solar panels on a steep slope will come into view just before entering a tunnel. The view of the whole slope covered by black solar panels is nothing but overwhelming.

This solar power plant is the “Nanki-Shirahama Solar Way” run by Kokusai Kogyo Co Ltd (Chiyoda-ku, Tokyo) of the Japan Asia Group. The solar panel and grid capacities are 2.5088MW and 1.995MW, respectively, with an annual power generation expected to amount to about 3,231,429kWh, which is equivalent to the consumption of about 729 general households. Its completion ceremony took place Jan 29, 2019.

Constructed on the site of Nanki-Shirahama Airport owned by Wakayama Prefecture, the tunnel, in fact, runs under the airport, and the solar panels can be viewed from around its mouth. Right above the tunnel is the airport runway. The mega-solar plant was built on the southwest side slopes within the airport site.

Kokusai Kogyo was selected in a public offering for “a solar power generation project using prefectural property (unused areas in Nanki-Shirahama Airport)” placed by Wakayama Prefecture and started constructing the plant in April 2018. Effectively using side slopes of about 34,408m2, the company set up roughly 14,300 solar panels in parallel with the 25-degree slopes.

CIS compound-type solar panels of Solar Frontier KK and two 500kW PV inverters of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) were adopted. JAG Energy Co Ltd provided engineering, procurement and construction (EPC) services and subsequently operates and maintains the plant after the operation began. All generated power is sold to the Kansai Electric Power Co Inc.

Depending on the direction, the Nanki-Shirahama Solar Way can even be viewed from the windows of flights taking off from and landing in Nanki-Shirahama Airport. The solar panels on the upper side slopes can also be viewed slightly further away from the “Airport Park” on the hill adjacent to the airport.

Wakayama Prefecture called for a mega-solar plant project next to the runway of Nanki-Shirahama Airport in fiscal 2015 (February 12 to March 11, 2016). The prefecture announced the rent for the project site and selected a bidder who offered to pay the highest amount.

Some other mega-solar power plants had been constructed before within airport sites using the feed-in tariff (FIT) scheme, such as Kansai International Airport in Osaka Prefecture and Nagasaki Airport in Nagasaki Prefecture. However, both of these solar power plants in the airport sites use unused flat sites in the airports (See related article). It is rare to use side slopes like Nanki-Shirahama Airport.

According to Shingo Shirakawa, a senior staff member of Independent Power Producer & Regional Revitalization Team, Kokusai Kogyo, “The mega-solar project in Nanki-Shirahama Airport was mainly characterized by the attempt to build a large-scale solar power plant on 25-degree slopes, along with the location in an airport.”

Before placing a bid, Kokusai Kogyo reportedly explored a method that enables efficient solar panel construction even on 25-degree slopes. When setting up mounting systems on a slope, pile foundations are usually used instead of stationary foundations. In such case, efficient construction requires consecutive pile driving using multi-purpose heavy machinery or a dedicated pile driver machine. Many of such machines, however, cannot be used on steep slopes.

While searching for a pile driver machine that can be used on steep slopes, Kokusai Kogyo found that Schletter GmbH, a German manufacturer of mounting systems, had a pile driver machine that can be used even on 25-degree slopes.

‘Low reflection panels’ required to participate in bidding for solar project

The company decided to use CIS compound-type thin-film solar panels manufactured by Solar Frontier from the beginning. This was because it was clearly indicated by the prefecture that “given the location within an airport site right above a highway and near residential houses, solar panels need to be low-reflection-type.”

Compared with blue crystal silicon-type panels, CIS compound-type solar panels are characterized by black cells (power generation elements), which reflect direct sunshine less. At both operating solar plants in Kansai International Airport and Nagasaki Airport, Solar Frontier’s CIS compound-type solar panels were adopted and have a positive operation track record.

When constructing panels on the site, the company gave priority to securing safety while working on steep slopes. On 25-degree slopes, the load on workers grows heavier even on sunny days, and if the ground gets wet due to rain, workers could easily slip and fall; the same applied to construction materials and tools. Those who were working on the lower side of the slopes would consequently face the risk of getting injured.

Based on these circumstances, Kokusai Kogyo decided to stop construction when it rained. In fact, the company immediately stopped work owing to sudden rain many times after beginning construction even after the forecast predicted sunny weather.

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