Dioxide-contaminated Land Revived as Solar Power Plant

2014/06/30 10:53
Kiyotaka Nakanishi, Nikkei BP CleanTech Institute

Hashimoto City is situated in the northernmost part of Wakayama Prefecture and adjoins Osaka Prefecture to the north and Nara Prefecture to the east. "Wakayama Hashimoto Solar Way," a solar power plant that construction consulting company Kokusai Kogyo Co Ltd (Chiyoda-ku, Tokyo) has developed in Hashimoto City, was completed in April this year (Fig. 1).

The plant, where 2,832 solar panels are arrayed across the 12,500m2 area of land, has an output of 708kW. The solar panels are the product of Toshiba Corp (SunPower Corp of the US), and the PV inverters are the product of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC).

Wakayama Prefecture enjoys so much sunshine that it can be counted within the top ten prefectures that boast the highest annual amount of sunshine across Japan. It is, however, largely mountain forests with a small amount of large flatland.

The site of "Wakayama Hashimoto Solar Way" is also not completely large flatland. Elongated north-south, approximately one-third of the land on the south side slopes. The central area of the power plant site is strangely left vacant (Fig. 2). There is a reason for this. Buried under the area where no solar panels are set up is a gigantic concrete container that seals soil contaminated by dioxide.

The site was polluted by dioxide, which was once a major social issue. The site had originally been owned by an industrial waste disposer, but the prefecture took over the land from the disposer for ¥100 million (approx US$985,707) in 2003 to accelerate its pollution control measures. The land was left idle for ten years even after being decontaminated. In July 2013, Wakayama Prefecture made a public offering of the land's rental use as a solar power generation project site. Kokusai Kogyo was chosen as the power producer.

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Wakayama Prefecture gained agreement with a community group, which had led the local movement against the dioxide pollution, before attracting a solar power plant to the site.

"The group welcomed the plan with no particular objections," a prefectural government officer said.

The group, however, made one condition: that the area where the concrete container is buried be excluded from the construction area, citing concern that the polluted soil sealed underground might leak. The amount of power generation would be decreased accordingly.

Power supply that local people can use during major blackouts

This power plant also plays the role of a power supply that local residents can use at times of major blackouts. By switching to the PV inverters featuring stand-alone operation capabilities during a blackout, power can be supplied to electric devices from the emergency power outlets attached to the mounting systems (Fig. 3). Simple emergency sheds to store portable batteries that can be used as night-time shelters, etc., and reserve stocks for disasters were also set up (Fig. 4 & 5). The proposal for these contributions to the local community was one of the reasons why Kokusai Kogyo was selected from the candidates.

The land where "the determination for realizing a recycling-oriented society" was pledged is now covered with solar panels.