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Major Solar Megawatts for Missouri

Major utility Ameren Missouri recently completed the company's first solar center-the largest investor-owned utility scale solar facility in Missouri-a 5.7-MW project covering more than 19 acres northwest of St. Louis.

By Vicky Boyd

Like many trends that hit the East or West Coast first and then make their way to America's heartland, utility-scale solar farms have followed suit. Spurred partly by state mandates and attractive incentive programs, several large projects in North Carolina, Nevada, Arizona, and California have come online. Those four states account for 34,208 of the 43,686 megawatts of solar projects nationwide that are operating, under construction, or under development as of August 2015, according to the Solar Energy Industry Association (SEIA).

The benefits of solar power generation are not lost on Midwestern utilities and developers as they continue to build and bring projects online.

When Ameren Missouri commissioned the 5.7-MW O'Fallon Renewable Energy Center near O'Fallon, Missouri, it was the largest investor-owned utility-scale solar project in Missouri. The title won't last for long as the utility already has plans for a 15-MW project on 70 acres about 80 miles northwest of St. Louis, which is slated to come online in 2016.

The two solar projects are part of the overall Integrated Resource Plan that Ameren filed with the Missouri Public Utilities Commission. In it, the utility outlined its plans to phase out 1,800 MW of coal-fired power by 2033 and replace it with 400 MW of wind, 600 MW of clean natural gas, and the remainder from other clean or renewable sources—including solar.

At the same time, a Missouri initiative passed in 2008 is driving renewable energy projects. The ballot measure requires that investor-owned utilities obtain 15 percent of their annual retail sales from low-carbon sources by 2021. Of that, two percent must come from solar.

If utilities generate energy within Missouri, they receive a 1.25 multiplier compared to out-of-state generation or purchases. In other words, in-state generation is worth 25 percent more for compliance purposes.

"We are working to diversify our mix of generation sources and transition to cleaner and renewable energy sources," said Ameren Missouri president and CEO Michael Moehn, when he kicked off the O'Fallon project. "Building this solar facility is a critical part of this goal."

St. Louis, Missouri-based MC Industrial Inc. became involved in September 2013 when it submitted a bid in response to a request for proposals issued by Ameren Missouri, said MCI project engineer Patrick Maloney.

During the proposal phase, Ameren selected an existing piece of land about 35 miles northwest of St. Louis and asked the contractors to find the most efficient way to design and construct a five-MW (DC) solar project.

"The non-uniform site layout made it a challenge to find the most cost-effective solution for the owner," said Maloney. "Using a collaborative and creative approach, the design team was able to maximize the energy production, given the size of the property, and offered a 5.7-MW (DC) option."

Ameren awarded MCI the engineering, procurement, and construction (EPC) contract in November 2013, prompting several months of further engineering and design, Maloney said.

 
  

A division of McCarthy Building Companies, MCI already had a strong relationship with Ameren Missouri, having built other projects for the utility.

"There's a long-term relationship between MCI and Ameren, and we have a good working relationship and a lot of trust there," Maloney said.

As this would be MCI's first solar project, it tapped expertise within McCarthy's Southwest Division and formed a joint-venture partnership for the O'Fallon project.

"McCarthy is a nationwide company that does work across pretty much the whole spectrum of construction," Maloney said. "The Southwest Division specifically does a lot of work in California, Arizona, New Mexico, Nevada, and Colorado and has extensive experience building solar projects. They've done several solar projects, and we were really happy to go within the company and use their knowledge and expertise to figure out what it would take to build a solar project of this scale. With the Southwest Division, we were able to leverage the strengths of the entire company."

Kansas City-based Burns & McDonnell was MCI's design partner and the lead on the electrical, civil, and structural engineering.

Extensive soil and pile load testing was conducted before construction began to make sure the project team understood the site-specific conditions. Those results influenced the racking system choice-the Powers Steel Ground-Mounted Solar Structure supported by 10-foot-long C channel piles, which were driven 6.5 feet into the ground using pile-driving machines.

"The loads that the racking system would be put under weren't excessively high, so the engineer was able to determine that going with a concrete foundation system wouldn't be necessary," Maloney said. "Given the loads, we could go with a driven-pile approach."

Using driven piles also simplified construction and was less labor intensive.

Based on the site's latitude and longitude and local weather patterns, a fixed-axis system was selected because of its cost-effectiveness. The additional cost associated with a single-axis tracking system would not have yielded a proportional increase in energy generation, he said.

The O'Fallon site is off Missouri Highway 79, and an existing gravel service road offered access to the existing Belleau Substation. But additional road grading and widening were done to ensure delivery trucks could turn around and offload materials and equipment before leaving.

Although the nearby highway proved convenient for transport, Maloney said they also had to carefully schedule deliveries to ensure trucks weren't backed up on the roadway waiting to drop materials or equipment.

 
When Ameren Missouri commissioned the 5.7-MW O'Fallon Renewable Energy Center near O'Fallon, Missouri, it was the largest investor-owned utility-scale solar project in Missouri. The title won't last for long as the utility already has plans for a 15-MW project on 70 acres about 80 miles northwest of St. Louis, which is slated to come online in 2016. 
  

"We had to bring trucks in one at a time to make sure we didn't have too many of them on site, or more than we could unload at one time," he said. "The modules and all of the racking systems were the two biggest things we had to coordinate delivery on. There was a lot of work planning how this was going to happen."

The 19,000 Trina solar panels were manufactured in China and had the farthest to travel to reach the site.

The suppliers were chosen based on how their equipment and products fit with the project location, site orientation, local weather conditions, solar facility design, and MCI/McCarthy Southwest Division team's experience with them.

The L-shaped site was divided into three sections, with work starting in one and moving sequentially to another. "We started with the grading and the earth work, and when we'd get it done in one area, we'd move to the next area," Maloney said. "A crew would be right behind with the next step. It ended up working pretty well after everybody figured out the best methods with the fewest interruptions."

After grading, for example, geotextile fabric was put down and the entire site was covered with six inches of Missouri Department of Transportation Type 5 rock to prevent weeds from growing and to create a firm surface.

Next the piles were driven, the rafters bolted to the piles, and the purlins set perpendicularly on the rafters and secured with Tek screws. The solar panels were set in the purlins, arranged two high in portrait view, and secured using clips and Tek screws. The modules were plugged together into strings, and the strings ran along the purlins to a combiner box hung off the racking system at the end of the row.

The string wiring was secured and organized using a wire management system. From the combiner box, underground DC cabling was installed to one of three 1,500 kW inverters from Eaton of Moon Township, Pennsylvania.

The inverters convert DC power to AC power, which a medium-voltage transformer stepped up to 34.5 kV. Both pieces of equipment were set on a concrete pad by a crane. AC cabling was run from the transformer to the point of interconnection, where the power was fed into the utility grid.

Based on the size and the newness of utility-scale solar in Missouri, much of the available workforce was not familiar with this type of work, Maloney said. So MCI again drew from its internal resources.

"We utilized the knowledge and experience of our superintendents who had built solar projects in Arizona and California to help train the local workers," Maloney said. "The superintendents spent several days working with the general foreman and foreman-level workers to share their experiences and best practices. The major subcontractors also had experience on other solar projects at the general foreman and foreman levels."

Construction started in May 2014, but much of the summer proved to be unseasonably rainy.

Only by working on several fronts and re-sequencing certain portions of the work were the weather impacts minimized, and the project was able to stay on schedule, Maloney said.

 


March/April 2016