Integrated Monitoring System Employed for 10MW Solar Plant
High-speed, large-volume data processing at a low cost using building management system
Fig. 1: Approx 10MW-output mega-solar "Ako Solar Power Plant" built in an industrial park on the former salt farm. The beautiful sight of neatly arrayed solar panels. (source: upper by Shimizu, lower by Nikkei BP)
Fig. 2: The state of power generation by each string being displayed in different colors that grow redder as it approaches full output so anybody can immediately recognize the situation. Display examples on April 8, 2014. The upper left is around 7:45, the upper right is around 10:50 when the output was full, the lower left is around 14:20 when the output started to fall and the lower right is around 17:30 when power generation is almost over. (source: Shimizu)
Ako City, Hyogo Prefecture, is known as the land of Chushingura (otherwise known as the Forty-seven Ronin) as well as the town of "Ako salt," for which salt farms once spread across the Seto Inland Sea. Nishihama Industrial Park was also developed on a former salt farm, which is a 10-minute drive from Banshu-Ako Station on JR West's Ako Line.
Leading general constructor Shimizu Corp built "Ako Solar Power Plant," a mega (large-scale) solar power plant with an output of approximately 10MW, at the site and started selling power in April 2014 (Fig. 1).
The construction site extends to 160,314m2, which corresponds to about four times the size of Koshien Stadium, home to a professional Japanese baseball team. Shimizu had acquired the site with a plan to build a subsidiary's plant, but gave up on the plan and eventually left it idle.
Locations with abundant sunshine are suitable for salt farms where salt is made by evaporating seawater. Needless to say, Nishihama Industrial Park enjoys abundant sunshine throughout the year, and a stable amount of power generation could be expected if a mega-solar power plant were to be constructed there.
3.5 billion yen construction cost financed by Dai-ichi Life Insurance through subsidiary
This was the first solar power generation project for the Shimizu Group; however, it had already been engaged in engineering, procurement and construction (EPC) services for mega-solar power plants for some time. The Shimizu Group is slated to provide EPC services for Japan's largest class mega-solar projects such as the 116MW-output plant being constructed in Rokkasho Village, Aomori Prefecture, and the 250MW-output plant on the former Kinkai Salt Farm in Setouchi City, Okayama Prefecture.
Ako Taiyoko Hatsuden (Chuo-ku, Tokyo), a special purpose company (SPC) financed by Shimizu, is the power producer of Ako Solar Power Plant. The project cost of roughly ¥3.5 billion (approx US$34 million) was procured from Shimizu Group financial subsidiary Shimizu Finance.
For the Shimizu Group, Shimizu Finance provides financing needed for the group's projects including construction. Shimizu Finance raised the funds needed for the construction of this solar power plant from Dai-ichi Life Insurance Co Ltd. Shimizu expects to recover the initial investment in about seven years.
System integration to be 'essential for 10MW or larger power plants'
Ako Solar Power Plant integrated various systems required for estimating the power generation situation and the amount of power generation. As long as the systems are integrated, all data are transmitted through one optical fiber cable with data transmission technologies integrated as well. Such a system is unusual.
At many mega-solar power plants, the power generation situation is monitored and confirmed with respect to each PV inverter or "string" that connects between 11 and 19 solar panels in series.
Some cutting-edge mega-solar power plants, on the other hand, have introduced a system to monitor the connected power grid or predict the amount of power generation, a video-based ITV (industrial television) monitoring system and a security monitoring system.
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When introducing several monitoring systems like this, data was previously transmitted by each system's transmission technology. The cost for introducing different systems and transmission cables as well as for their maintenance has been a challenge for the plants that use several different monitoring systems.
Ako Solar Power Plant enabled the entire data transmission via one cable, integrating those systems into one. A building energy management system (BEMS) was utilized. This move was aimed at accelerating data transmission and lowering cost by integrating multiple monitoring/analyzing systems and large-volume data into one management system.
Cost benefits from the integrated system can be expected at 10MW or larger mega-solar power plants. Its introduction is likely to become a requirement at mega-solar power plants of this size.
For example, the plant currently displays the measured situation of power generation per string in real time (every minute) on the overall plant map in different colors using this system so the situation can be immediately recognized (Fig. 2).
Should a problem cause some strings to show a sharp drop in the amount of power generated, it can be easily recognized by a different color tone. Featuring the capabilities to compare such information as weather changes, temperature and the amount of sunshine with the expected amount of power generation, the system will further improve its prediction accuracy.
6 months to set up from foundations to panels
Approximately 12MW-equivalent 48,342 single-crystal silicon solar panels manufactured by Sharp Corp and 20 PV inverters by Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC) have been installed at Ako Solar Power Plant.
Sharp's solar panel was selected because its performance and warranty, compared with others, were superior among the single-crystal silicon panels that boast relatively high power generation efficiency. As for the reasons why it adopted TMEIC's PV inverter, the plant cited its reliability backed by overwhelming achievement and performance it has shown at other mega-solar power plants in Japan and high compatibility with Sharp's solar panels.
The mounting height was set at 50cm from the ground. This is because the builders could set up panels by standing without ladders or other tools. According to the plant, this will make it easier to maintain the installation accuracy and stability, shorten the installation time and eventually lower construction cost.
The foundations were made by placing molds and pouring concrete into them on site (Fig. 3). Compared with the method that uses wooden frames, the cost would rise, but it can boost accuracy and cut the time to make the foundations.
Given the 9,208 foundations required for the roughly 10MW-class plant, the cost increase could be absorbed. Seventy molds had initially been used, but the number was increased to 150 to raise the pace of making the foundations.
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By forming each array with 84 solar panels and keeping the number of foundations small at 16 per array, the plant boosted efficiency during the installation process, from foundations to panels, and shortened the real construction period to six months.
Other schemes were as follows. Considering the efficiency in construction and operation, a maintenance road was set up (Fig. 4). In anticipation of shade from a building that might be constructed in the adjoining idle land to the west, which is owned by another company, space with no solar panels was secured (Fig. 5). Other schemes include the installation of solar panels that take advantage of the slopes in the site (Fig. 6) and the laying of wire racks at a certain height in view of flooding by typhoons, etc. (Fig. 7).
The Shimizu Group is planning to expand both EPC services and power generation business from now on.
"We came to understand the solar power generation business as a power producer by launching our own power plant," said Tsuneo Kobayashi, deputy general manager of Engineering Headquarters at Shimizu and president of Ako Taiyoko Hatsuden. "We will reflect this experience on our future EPC services."
With such an aim in mind, Ako Solar Power Plant proactively introduced new technologies and proprietary schemes while adopting different mounting systems and solar panels and verifying their strength, salt resistance and power generation situation in addition to the mega-solar power plant (Fig. 8).