Solar Plants Produced With Progressive Municipality

Technologies to cut construction period, cost

2013/12/16 21:33
Shinichi Kato, Nikkei BP CleanTech Institute

In Takeo City, Saga Prefecture, two large-scale solar power plants have started power generation in the last seven months. They are the 1.5MW "Takeo Hakamano Solar Power Plant" (Fig. 1), which started operation in October 2013 in Higashi-Kawanoboricho, Takeo City, and the 1MW "Takeo Wakaki Solar Power Plant," which started operation in March 2013 in Wakakicho, Takeo City.

Kyudenko Corp constructed both plants, provided EPC (engineering, procurement and construction) services and runs the power generation business. Yasuhiro Yamamoto, senior executive officer and manager of Saga Office, Kyudenko, stressed, "These two power plants in Takeo City are the starting point for Kyudenko's solar power plant operations and will be key footholds when considering the possibility of future solar power generation."

Takeo City in Saga Prefecture is known for its progressive administrative approach, such as outsourcing its library operation to Culture Convenience Club Co Ltd (CCC), thus producing a high profile, vibrant library that has Starbucks Coffee shop and a CCC' "TSUTAYA" book and CD/DVD rental store on the same site. Having approached the introduction of reusable energy with the same attitude, the city requested a design that can easily be used for environmental education, and got involved in finding sites for the construction of these two solar power plants.

Kyudenko is also known as a top-class EPC constructor of domestic large-scale solar power plants, receiving numerous EPC orders, primarily in its local area of Kyushu. Should the landowner of a construction site wish, Kyudenko sometimes even agrees to become not only an EPC constructor but also a power plant operator.

The company, thus far, has put its subsidiary Kyudenko New Energy (Chuo-ku, Fukuoka City, Fukuoka Prefecture), instead of itself, in the position of power plant operator; however, at these two solar power plants, Kyudenko itself serves as the power producer, due to cooperating with Takeo City and strategic factors regarding the Kyudenko Saga Office. Such a flexible attitude is probably one of the reasons why Kyudenko's approach to large-scale solar power plants is greatly appreciated.

Cutting costs for foundations

These two solar power plants in Takeo City were constructed with measures suited for each location, but with basically the same power generation facilities and foundations employed. Takeo Hakamano Solar Power Plant, which started power generation in October 2013, is located on a site adjoining the Nagasaki Expressway whereas Takeo Wakaki Solar Power Plant, which was launched in March 2013, is situated in a village forest.

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Both solar power plants adopted the Korean Hanwha Group's solar panels, Toshiba Mitsubishi-Electric Industrial Systems Corp's (TMEIC's) PV inverters and the mounting system of Hilti from Liechtenstein.

Kyudenko explained it employed the Hanwha Group's solar panels because of their low price as well as performance and warranty that are equivalent to those of Japanese products.

Kyudenko basically chooses TMEIC PV inverters at the mega-class solar power plants to which it provides EPC services.

"TMEIC focuses on the models compatible with power generation as large as 500kW output," said Masatoshi Motomatsu, manager of Renewable Energy Dept, Sales Div, Kyudenko. "We believe TMEIC is the top company in terms of reliability, pricing and procurement of PV inverters."

In particular, he cited the efforts to prevent the PV inverters from automatically stopping through detecting a fault on the power grid side. For example, many PV inverters automatically stop even though there is no malfunction in the plant's power generation facilities, if, for example, only the interconnected power grid momentarily went out due to lightning. In that case, the PV inverters have to be rebooted as soon as possible, or the amount of power sales would be reduced because the PV inverters would not start working.

The control system needed to minimize such a suspension, other than breakdowns, often varies according to the connected electric power company. TMEIC PV inverters can precisely adapt to such a control system by updating software and modifying the configurations and, as a result, minimize the risk of automatic suspension.

Hilti's mounting system is characterized by the small number of components to be assembled because the steel members forming the mounting system are modularized in advance. It features the ease of assembling that cuts the set-up time to about two-thirds compared with the conventional mounting systems manufactured by domestic companies. By cutting the construction time, the mounting system can help to reduce construction cost.

A plastic mesh like those used for selling oranges was arranged at the end of the steel members that support the longer edge of the solar panel arrays on the mounting system (Fig. 2). This is used to prevent birds from nesting.

Efforts to cut the construction period and lower the cost can also be found in the foundations. For example, a method to build the foundations by pouring concrete into a mold without post-processing was employed. This method is suited to cutting the time to build the foundations. The foundations are positioned at about 3.8m from each other so that cement mixer trucks can move along the space between the foundations and directly pour concrete into the molds on site (Fig. 3).

At other large-scale solar power plants, in many cases, cement mixer trucks cannot pass along the space between the foundations. In these cases, the time to build the foundations lengthens and the cost rises because pumper trucks are required to flow cement from the mixer trucks via pipes and hoses.

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Solar panels set up without filling in depression

Some arrangements were also made in accordance with the location at Takeo Hakamano Solar Power Plant. Alongside an expressway, the power plant is situated in a rectangular site facing southeast on the long side, in the central area of which has a deep, rectangular depression extending along the perimeter.

Should solar panels be arrayed and oriented directly to the south in such terrain, it would cause two problems. One is the inability to lay out all the panels for an output of 1.5MW as planned due to the dead spaces created at the site's corners when the panels are not installed squarely in the rectangular space. The other is the need to install panels in the same way even in the depression.

The layout and construction became complicated due to the slopes in the area where the foundations were placed. Furthermore, it was difficult to build the foundations that Kyudenko deployed on slopes. Accordingly, Kyudenko finally decided to lay out the panels facing southwest, which was the option that enabled most panels to be installed.

According to Kyudenko, the construction cost would have been lower if the depression in the central area had been filled in and evened out. However, considering the cost to restore the site to its original state after the termination of the 20-year power generation business, Kyudenko chose to leave the depression as it was and mount the panels at the same height by devising the mounting system (Fig. 4 & 5).

The height of the mounting system was raised only in the depression. The cross-section of the depression looks like a basin with a flat bottom and a steep slope on both ends of the depression. And Kyudenko avoided constructing the mounting systems in the middle of the slope and using a design that would require delicate height arrangement for the mounting systems.

The height of the mounting system was about 25cm, and the solar panels were tilted at 10° on the mounting system.

Kyudenko sets a reference term of power generation facility construction at about one month per 1MW, but announced it took two months to build this facility due to the construction process having taken the depression into consideration. Although the company has not revealed the construction cost, it seems not to have exceeded Kyudenko's reference cost of approximately ¥300 million (approx US$2.9 million) per 1MW.

Meanwhile, Takeo Wakaki Solar Power Plant was constructed on flat land. Partly because of a request by the city, the plant is designed to educate people on solar power generation and the environment. The plant site's peripheral road is accessible to automobiles and pedestrians. And an observation deck was set up at the end of the road so that visitors can enjoy a panoramic view of the related facilities, including the solar panels across the site, PV inverters and the connecting points to the grid of Kyushu Electric Power (Fig. 6).

Boards to explain the mechanism from power generation to transmission and introduce the function of each facility were set up in front of the observation deck and other facilities (Fig. 7).