Solar Power Plant Designed for Coastal Industrial Zone
Waste treatment site being cleaned-up turns into educational base for reusable energy
Ukishima, Kawasaki City, is an area of reclaimed coastal land in a corner of the Keihin Industrial Zone. It is an industrial complex that has long supported Japan’s economic growth, where numerous mainstay plants of many industries are still operating. With typical industrial plant views such as masses of iron and crowded pipes and chimneys seen everywhere, it has recently become well known as a photogenic spot for so-called “plant nerds” who love the views of industrial plants. Ukishima is also said to be an essential spot for night-view industrial plant cruises on houseboats.
Ukishima Solar Power Plant is located in the heavy chemical industry complex, a district where a substantial plot of land needed for large-scale solar power plant construction is not usually likely to exist (Fig. 1). It was constructed with the aim of effectively using an area of land that underwent a 20-year cleanup period after being used as a general waste treatment site. It started operation in August 2011 and can be referred to as Japan’s first plant that is in the 7MW class (maximum output).
Joint project by Kawasaki City and TEPCO
Ukishima Solar Power Plant was constructed as a joint project by Kawasaki City Government and Tokyo Electric Power Company (TEPCO), along with the Kawasaki City’s PR/educational facility “Kawasaki Eco Kurashi-mirai-kan Museum.” Kawasaki Eco Kurashi-mirai-kan Museum features exhibits to study solar power generation and an observatory that provides a panoramic view of the adjoining solar power plant.
Why did the joint project incorporate such a PR facility? According to Kawasaki City, it is because the project also put weight on the execution, penetration, promotion and education of global environmentally conscious measures such as the introduction of renewable energies including solar power plants. This could be described as a typical approach by industrial cities where the amount of power consumption and carbon dioxide (CO2) emissions tend to be high. As well as Ukishima Solar Power Plant and the PR/educational facility, the joint project includes Ohgishima Solar Power Plant, which is also built on reclaimed land.
Based on the above factors, the location of Ukishima is considered favorable. It is highly accessible via public transport from metropolitan areas, which makes it easy for a lot of visitors to come. Its position facing Haneda Airport across a stretch of water is also convenient because the solar power plant can be viewed from the airport and the planes about to land there.
At Ukishima Solar Power Plant, Kawasaki City leases the land and TEPCO owns the power generation facilities. TEPCO is responsible for the EPC business, which provides all engineering, procurement and construction needed, as well as its operation and maintenance. Operations started in August 2011, with all the generated electricity systematically interconnected to TEPCO’s power grid and used for its power services.
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Efficient power generation without interfering with the saste treatment site’s cleanup process
Other Ukishima Solar Power Plant features are it not interfering with the cleanup of the general waste treatment site and the measures taken against strong winds and salt damage caused by the seaside location.
Toshiba built the plant while Sharp and Toshiba Mitsubishi-Electric Industrial Systems (TMEIC) manufactured the solar panels and PV inverters, respectively. There are 37,926 single crystal silicon solar panels installed with 198W maximum output and 28 PV inverters with 250kW rated output.
The land cleanup will be completed by continuing a 20-year cycle of putting filling on the waste, letting rain penetrate the filling, sucking up the penetrated water with pumps and discharging it into Tokyo Bay after purifying the water. Therefore, measures against land subsidence are important when setting up the solar panels.
As a measure against land subsidence, the number of panels set on the mounting system was reduced to six per unit so that if subsidence occurs the number of solar panels to be affected can be limited.
To accelerate land purification, efforts were made to enable rain to penetrate more when setting up the foundation and solar panels. The foundation on which the mounting system is set up has a hollow in the center of the flat concrete mass (Fig. 2). Such a style was adopted with the aim of making rain falling on the solar panels penetrate into the ground as much as possible. The solar panels were also set up after securing a horizontal space so rain can reach the ground easily.
With a space secured for maintenance vehicles needed for purification work, it looks like an airport runway extending into the mass of solar panels.
The measures against strong wind and salt damage and other efforts typical for coastal areas can be found in the foundation and mounting system design, the solar panel angles and the PV inverter installation. For example, the thickness of the concrete foundation is designed to be about 45cm thick by the coast where the foundation supports facilities on the windy side while the thickness is about half that on the inner side in consideration of impacts from strong wind.
Given the resistance against pressure from strong winds that could not be achieved sufficiently at 30°, which is said to be optimum for power generation, the tilt angle of the solar panels is set at 10°.
As for salt damage, the PV inverter housing is shifted to a tougher container type (Fig. 3). One container houses four PV inverters, and a total of seven containers are set up across the site.
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Total power generation 1.3 times more than estimated by 2nd year
Because Ukishima Solar Power Plant has been constructed this way, the amount of power generation has greatly outperformed the initial estimates since its operation started in August 2011. Annual power generation was estimated to be approximately 7.4 million kWh based on its 7MW maximum output performance. But it greatly outperformed these estimates and reached about 9.45 million and 9.74 million kWh in the first and second years, respectively. The total output for the first two years reached 19.2 million kWh, roughly 1.3 times the estimate.
Ohgishima Solar Power Plant, which was constructed as a joint project by Kawasaki City and TEPCO, just like Ukishima Solar Power Plant, started operation four months after Ukishima in December 2011. The plant employed Kyocera’s polycrystalline silicon solar panels and Hitachi’s PV inverter and generated about 15.1 million kWh in the first year, 1.1 times the annual output estimate of 13.7 million kWh based on its 13,000kW maximum output.
As factors behind this upswing in power generation, Kawasaki City cited the more-than-expected amount of solar irradiation, the small error and high uniformity of the deployed solar panels’ output performance and the optimal construction that enabled the installed components to demonstrate their specified performance. Although Kawasaki City has not revealed details yet, it seems that the higher-than-expected efficiency of the overall system including the PV inverter also made a contribution, considering the power generation amount outperformed the estimate even more at Ukishima Solar Power Plant.