Solar Plant Designed With Consideration for Residential Areas

Green solar power plant on former factory site

2014/01/12 15:06
Shinichi Kato, Nikkei BP CleanTech Institute

"Yomeishu" is an alcoholic beverage for medicinal purposes well known by people throughout Japan. "Tsurugashima Solar Power Plant" (Fig. 1) is the mega-solar (large-scale solar) power plant run by Yomeishu Seizo Co Ltd, the manufacturer of this beverage. The output of the mega-solar power plant is approximately 1.9MW.

The mega-solar power plant was constructed where Yomeishu Seizo's former Saitama Factory had been operating from 1961 to 2006. The raw materials of "Yomeishu", including grape sugar, were produced at the factory. Inside the site were the raw material factory, corporate dormitory and a baseball ground. As the production of grape sugar was contracted outside, Yomeishu Seizo closed the factory and cleared the land in 2007, since when it has sought an effective use for the site.

However, the company had a challenge to tackle before starting to effectively utilize the site. The surrounding environment had completely changed compared with the time when the former Saitama Factory had started operation. The surrounding landscape, which was once farmland, had transformed into residential areas.

Accordingly, a plant that would cause smells and noises in the neighboring residential areas could not be constructed. Moreover, the roads around the site were not as wide as they were in the industrial zone. Given these conditions, it was difficult to find any company that would wish to build a new plant there.

Under such circumstances, Yomeishu Seizo accepted a mega-solar power plant construction proposal from Takenaka Corp and started discussing its own entry into the industry as the feed-in-tariff (FIT) scheme for reusable energy was set to begin. A mega-solar power plant would cause few smells and noise in the neighboring residential areas. Excluding the construction period, there would be little traffic involving large trucks, etc.

In addition, the power selling business based on solar power generation, a reusable energy, could complement Yomeishu Seizo's corporate philosophy: "Contribute to enriching healthy lifestyles." The company, as a result, changed its articles of incorporation and decided to enter the power industry.

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To maximize amount of power generation while maintaining vegetation

What characterizes this mega-solar power plant is the request delivered by Tsurugashima City prior to the actual construction. The request was to leave to a certain degree the plants and trees as seen in the former Saitama Factory.

It was not easy to satisfy this request because the amount of power generation would lower should trees be standing around the solar panels and shade the panels depending on the season and time of day. What made it more difficult were weeds on the ground. In general, mega-solar power plants are designed to keep weeds from growing so that the amount of power generation would not decrease due to weeds covering the solar panels.

To prevent the amount of power generation from lowering as much as possible while satisfying the request by Tsurugashima City, Yomeishu Seizo adopted two measures. One was to keep the trees planted along the site's perimeter from shading the solar panels, and the other was to prevent the weeds from growing over the solar panels while still covering the ground.

First, the white oaks planted along the perimeter of the former Saitama Factory were left as they were. The white oaks, which can grow quite tall, had grown higher than 10m. But they were all cut shorter to about 6m. New white oaks were planted in the areas where there was no tree along the perimeter (Fig. 2).

On the other hand, the cherry trees along the perimeter were all cut down. It was because these trees, despite being beautiful when blooming in spring, could cause problems to the neighboring residential areas when their leaves fall in autumn. As white oaks are evergreen, their leaves seldom fall.

Also, the layout of the solar panels was specially arranged. The panels were positioned about 12-20m away from the perimeter so the white oaks would not shade any panels. As a result, as long as the white oaks are 7m or shorter, they do not shade the solar panels even at 15:00 on the winter solstice, the day in the year in which the shadows get the longest (Fig. 3).

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To install the number of solar panels needed to secure the projected amount of power generation despite such a layout, the area of solar panels was expanded from the initial plan of approximately 30,000m2 to 40,000m2.

As groundcover, clover was planted. Given its ability to root well, clover was expected to stop other weeds growing and covering the solar panels. In addition, clover itself does not grow high, and is hence optimal as groundcover that spreads at a low height without covering the solar panels.

The effect of the clover had two contrasting outcomes depending on where in the site it was planted. There were places where the groundcover effect was achieved, but there were places where it was not fully achieved. Yomeishu Seizo analyzed this problem and concluded it could be attributed to location. The land slopes slightly from the southwest corner to the southeast corner. Clover is thick and dense in the moist southeast side, to which rainwater runs, while many other kinds of weeds have grown in the southwest side, where the clover did not root well (Fig. 4).

Based on these circumstances, weeding is likely to be needed more frequently in the areas where clover did not grow well, compared with other mega-solar power plants. Yomeishu Seizo already weeded the plant twice in the summer. The weeding cost about ¥2 million (approx US$19,214) each time.

There were other considerations that needed to be paid to the residential areas. For example, in the southeast side at the lowest point of the mega-solar plant, an embankment was built by piling up soil to prevent a large amount of water from running from the plant into the residential areas after heavy rain (Fig. 5). Some concrete garbage collection sites were also set up for the local residents in such a form that they cut into the mega solar power plant's site.

In addition, sand in the site was sometimes stirred up and blown by the wind into the surrounding residential areas while the plant was under construction. As a measure to prevent this, sprinklers and stopcocks have also been installed (Fig. 6). Water is drawn from a well.

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Panels' output set about 1.3 times more than PV inverters'

As for power generation facilities, Takenaka's approximately 30cm-high concrete foundations were installed after evening the slope on the ground where the solar panels would be set up. Mounting systems were assembled with the concrete foundations, and the solar panels were tilted at 10° and mounted on the foundations at a height of about 64cm from the ground.

The solar panels' total output is approximately 2.576MW, roughly 1.3 times the PV inverters' output of 1.9MW. Yomeishu Seizo took into consideration the transmission loss between the solar panels and PV inverters as well as the site's location, where the hours with adequate solar irradiation can be limited and the solar panels can scarcely generate power at their maximum capacity.

A total of 10,304 single crystal silicon solar panels with 250W output produced by Mitsubishi Electric Corp were installed. As for the PV inverters, three 500kW models and one 490kW model with a conversion ratio of 97% or more manufactured by Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) were introduced.

A system to monitor the status of power generation was also adopted. It shows various items such as the intensity of solar radiation, ambient temperature, the temperature of the solar panels, DC power input from the collecting boxes to each PV inverter and AC power output from each PV inverter, so they can be understood at a glance.

As of October, the total amount of power generation was about 25% more than the estimate since the plant started selling electricity in July. As for the factors behind this, Yomeishu Seizo cited the solar panel's output, which was larger than the manufacturer's description, and the larger-than-expected effect of installing the solar panels whose total output is higher than the PV inverters' output.

Learning facility jointly constructed with city

An environmental learning facility is being constructed next to the mega-solar power plant under an agreement with Tsurugashima City. This environmental learning facility, slated to open in March 2014, is the city's first case of adopting the public meeting method to explore the future of new public projects. Yomeishu Seizo has planned and designed the facility needed by the local community by collecting opinions from local residents through an open process.

The company gathered opinions from the local residents while holding discussions with Toyo University, which is located in the neighborhood. As a result, it was determined to establish the facility as a place to experience solar power generation, which contributes to environmental education, and as a base to reduce damage should the local community be hit by a disaster.

Yomeishu Seizo is providing the land for the environmental learning facility while Tsurugashima City is constructing the building for environmental education. To be set up in front of the building are 42 units of Mitsubishi Electric's solar panels, the same ones as those used in the solar power plant, and a 10kW secondary battery.

Moreover, one of the "Leaf" electric vehicles (EVs) being leased to Tsurugashima City will always be kept at the facility. For the EV, the facility will be provided with an EV charger. Nissan Motor Co Ltd is a local company that has an alliance with Tsurugashima City, just like Yomeishu Seizo. The charger and the 10kW secondary battery for emergency use will be powered by the 42 solar panels.