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Concerns over aging solar power plants in Japan, but management business booming

This photo shows a mega-solar power plant installed on a mountain slope in Yokoze, Saitama Prefecture, on July 5, 2021. Weeds peek out from between the panels. (Mainichi/Ei Okada)

TOKYO -- The Japanese government is rushing to expand solar power generation to drastically cut the country's greenhouse gas emissions, but the plants already in operation are aging. As there is limited room to build new large-scale solar plants, businesses keeping generating efficiency high and existing facilities online long term are booming.

    About 18,000 solar panels blanket a vast field in the town of Shibayama, Chiba Prefecture, about 5 kilometers southeast of Narita Airport. If you look closely, you can see white dots here and there on the panels.

    "They're bird droppings. If not cleaned up, the stuff will accumulate and cause hot spots," said Masafumi Oshiro, general manager of the investment management department of SBS Asset Management Co., a logistics facility development company based in Tokyo's Sumida Ward that operates this mega-solar plant.

    "Hot spots" here refers to when bird droppings, fallen leaves and other factors cause increased electrical resistance in solar panels, resulting in heat. Not only does this reduce power generation efficiency, but it can also lead to panel failure and fires.

    Bird droppings dot some of the solar panels in Shibayama, Chiba Prefecture, on July 15, 2021. If not cleaned off, the droppings can lead to decreased power generation efficiency and panel failure. (Mainichi/Ei Okada)

    This power plant went online in 2013, and according to Oshiro, hot spots, rust and dirt became noticeable from around the fifth year of operation. An examination of the plant's output found that its power generation efficiency -- the amount of electricity generated per quantity of solar radiation -- had dropped about 10% by 2019, the plant's seventh year. That amounted to more than 10 million yen (about $89,920) in lost electricity sales revenue per year.

    The company operates 14 solar power plants across Japan, and power generation efficiency had been declining at an average rate of 1.6% per year as of the end of 2018. Washing the panels with water at nine locations, including a facility in Shibayama, improved the power generation efficiency at eight of them.

    The government's goal is to reduce greenhouse gas emissions by 46% by fiscal 2030 compared to fiscal 2013 levels. The Ministry of the Environment has announced a proposal to add 20 million kilowatts to the current target of 64 million kilowatts of solar generating capacity in fiscal 2030.

    With the introduction of the feed-in tariff (FIT) system in 2012, the construction of mega-solar power plants took off in many areas, but the pace has stalled since. The number of suitable sites for these plants, which require large open areas, is decreasing, and the importance of continuing to use existing facilities efficiently is increasing.

    But recent studies have shown that equipment deteriorates more quickly than previously thought. In business plans for solar power plants, it is common to assume that generating capacity will decline by 0.5% per year as panels deteriorate. However, when the Central Research Institute of Electric Power Industry tested four types of solar panels from 2016 to 2021, the generating capacity declined by up to 1.6% per year on average.

    In response, several maintenance and management businesses have emerged to help reduce the "aging" of existing facilities.

    In May, Tokyo's Koto Ward-based ORIX Renewable Energy Management Corp., a subsidiary of ORIX Corp., launched a maintenance and management service. Drones equipped with thermographic cameras take aerial photos of solar panels to check for hot spots. And the firm uses artificial intelligence to analyze shifts in the amount of electricity generated and detect abnormalities early.

    This photo shows the entrance to a solar power plant buried under weeds in Shimotsuke, Tochigi Prefecture, on Aug. 6, 2021. Many small power plants are said to be inadequately maintained and managed. (Mainichi/Ei Okada)

    West Holdings Corp. based in Hiroshima, which develops and operates mega-solar power plants, began a "revitalization business" in 2020, buying used power plants and reselling them after renovations, as it did not expect a large increase in new construction. They mainly buy mega-solar power plants that sprang up in the early days of the FIT.

    The company purchases used power plants including those with panels shaded by trees or fences, panels packed so tightly that it is impossible to inspect them, and panels facing north. And they improve the power generation efficiency by adjusting the angle of the panels, relocating them, cleaning them, and weeding around them. Then, they sell those plants packaged with management services such as automatic output monitoring.

    As existing power plants are aging, the need for maintenance and management is increasing, but competition is also intensifying. One contractor in Chiba Prefecture who cleans panels sighed, saying, "The number of other companies entering the market has increased rapidly, and we're now in a price war." While they now clean 1.6 times more solar panels than they did three years ago, the unit price has fallen. "We can't make a profit unless we handle large volumes," the contractor said.

    On the other hand, there are many small-scale power plants without adequate maintenance and management. In early August, a Mainichi Shimbun reporter visited a solar power plant in a residential area in the city of Shimotsuke, Tochigi Prefecture, and found the entrance gate overgrown with waist-high weeds.

    The solar panels were also partially covered with the weeds, and although the plant was FIT-certified, there were no signs indicating the name of the company or the person in charge of maintenance and inspection, which are required to be posted visible from the outside.

    Solar power plants with an output of less than 50 kilowatts are not required to have a person in charge of electrical safety. Sloppy management has also emerged, so the Ministry of Economy, Trade and Industry, which has jurisdiction over solar plants, has started a questionnaire on the status of inspections.

    The smaller the power plant, the greater the proportion of maintenance and management costs. Power plants certified immediately after the introduction of FIT in 2012 with an output of 10 kilowatts or more are guaranteed a high price for their electricity for 20 years, making them profitable even if their generation efficiency is low.

    However, these preferential terms will gradually expire starting in 2032. The management cost burden will become even greater, and there are concerns that there will be a rapid rise in the number of closed and abandoned solar power plants.

    Mitsuhiro Yamazaki, a chief researcher at the New Energy and Industrial Technology Development Organization, pointed out, "To make solar power a foundational power source, it's important not only to increase the number of plants but also to ensure good maintenance at many existing plants."


    A feed-in tariff is a system under which electric power companies purchase electricity generated from renewable energy sources for a certain period at a fixed price. In Japan, the system was launched in 2012 to promote the spread of renewable energy. The program covers solar, wind, hydro, geothermal, and biomass power, and the government certifies facilities that meet the requirements. The purchase cost for power companies is added to the electricity bills of households and businesses as allotted funds for renewable energy power generation promotion.

    (Japanese original by Ei Okada and Mayumi Nobuta, Science & Environment News Department)

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