Solar power team

Enel Green Power North America Inc. tackled one of the largest multi-site distributed solar projects in North America-a $290 million, 150-MWdc project in Minnesota-but it came together successfully, thanks to an overall team effort with its contractors.

By Paul MacDonald

Tackling one of the largest multi-site distributed solar projects in North America was by no means straightforward, but it came together successfully for Enel Green Power North America Inc. (EGP-NA), thanks to close coordination with its contractors and suppliers—and an overall team effort.

EGP-NA is well on its way to completing work on all 16 sites of the approximate $290 million, 150-MWdc utility-scale Aurora Solar Project, one of the largest solar projects ever built in Minnesota. It's the largest solar project to date for the company in North America and is expected to be completed by the middle of this year.

The project features a design that consists of multiple small-scale solar sites, ranging in size from 5 MWdc to 15 MWdc. Being a distributed system, it delivers a range of benefits including a reduction in line loss, elimination of transmission costs, and geographical diversification of generation assets. Each of the 16 solar facilities utilizes linear tracking devices to maximize efficiency and production, and they are interconnected to the offtaker's distribution system.

To avoid expensive transmission lines, sites near existing electric substations were selected as much as possible, so power could be sent straight onto the distribution lines of the offtaker, Xcel Energy. The sites are located in mostly rural areas, from north of Minneapolis/St. Paul to southeast Minnesota, covering a total of 920 acres.

With its large number of sites, planning was more critical for Aurora Solar compared to single-site solar power projects, says Jacob Fehlen, supervisor, Solar Electrical Maintenance, and Operations and Maintenance supervisor of the Aurora Project for EGP-NA.

"Having 16 sites was a challenge, to say the least," Fehlen said. "We had upwards of 1,000 people working on the different sites. When you have 16 sites, you essentially have 16 site supervisors on the construction side. If you had one site, you would normally have one site supervisor and a couple of assistant site supervisors."

"It took a lot of effort and a lot of oversight to make sure that we were hitting our numbers and that we were staying on track, construction-wise."

In addition to having an EPC contractor oversee the project, EGP-NA had its own staff working on the project, to make sure it proceeded as smoothly as possible.

"Due to the size of the Aurora project, we brought in Enel staff from other projects, as they were freed up, to help support it, and we had collaborative efforts from our Enel colleagues from Italy as well."

Being an international company, and having built a large number of solar projects in Europe, EGP-NA has extensive internal resources it can call on in other countries.

"We had a lot of help available that way," says Fehlen. "Our vendors were experts in their own fields, but we were able to pull a lot from the company's European experience, to make sure we got the Aurora project right. There have not been a lot of these types of projects built in the U.S. yet."

EGP-NA's site supervisors would visit as many as three sites a day, to check on construction progress and deal with any issues.

"We also had a daily construction progress meeting that everyone participated in," said Fehlen.

Each site supervisor would either attend or phone in to outline the site's plans for the day and the upcoming two to three days. In addition, the company also had bi-weekly and monthly meetings, as required, to review the project and how it was going, big picture.

"Internally, we had our own engineering and design team that were working on project details and getting everything bundled up for the construction people."

Environmental considerations are a high priority for the company, says Fehlen. "It's right in our name: Enel Green Power. We wanted to make sure we got things right. The environmental and land use planning had a front seat in terms of the project—planning and implementing construction activities followed."

Most of the solar sites had been farmland. EGP-NA's concern for the environment extended to making sure that the areas in and around the solar panels were planted with bee-friendly native plants. As part of its application process, the company filed an extensive Agricultural Impact Mitigation and Vegetation Management Plan.

"With a traditional solar plant," explained Fehlen, "you would typically see a gravel base, something with little or no vegetation. We went the other route, with a solon prairie grass mix, that Minnesota used to be covered with years ago. It gives back some of the habitat to the bees and Monarch butterflies and should help to add to their numbers in Minnesota." And the grass mix makes the sites more appealing to the eye.

	Installing racking on the Aurora Solar Project brought its own challenges-the 16 different sites had different topographies and soil types. On some sites, there were three or four different soil types.

Reclamation plans for the sites call for the land to be turned back into farmland after the 25-to-30-year life of the solar project.

They worked carefully with the existing trees on each of the sites. "There was a little bit of trimming, typically done on the perimeter of the sites," said Fehlen. "Most times, we were able to move or shift the panels so that we were able to get away from the permanent vegetation that was already established. In some situations, there was re-planting of trees and shrubs on the perimeter."

Doing renewable energy in Minnesota is not new to EGP-NA; the company owns and operates two wind farms in the state, Prairie Rose and Minnesota Wind, which have a combined installed capacity of 230 MW.

"That helped because we had people that have worked with local government and the state government in Minnesota who were able to help us with aspects of the Aurora project."

Since there were 16 sites involved, the required civil work varied.

"With a conventional single-site build-out, you level an area, making it as flat as possible, and build your drainage so that water gets off the site. But we had some sites where the topography needed to be adjusted further, which would typically involve a small Bobcat and a dozer."

The region, however, was hit with heavy rainfall during construction and this resulted in some water pooling. EGP-NA's contractor dealt with this through the use of pumps and associated equipment.

"We had continual rain pouring, day after day, and no soil is going to be able be take up all that water," says Fehlen.

Installing the racking brought its own challenges—the 16 different sites had different topographies and soil types. On some sites, there were three or four different soil types.

"We did not use any concrete to support the racking, as part of our reclamation plan, and we wanted to limit the impact the piles would have on the soil.

Our civil engineers were able to determine what depth the piles needed to be, depending on the soil samples." The piles were 10 to 16 feet deep. They sometimes ran into granite and other hard rock in the drilling.

With 16 sites, the question arises as to where you would start.

"We've got a range of sizes from 5 MWdc to 15 MWdc, and the larger sites were the top priority-we wanted to start them first simply because of the amount of time it was going to take to complete them."

All 16 sites had staging or laydown areas, but component storage was centralized in the Twin Cities area. Sometimes there was limited space for laydown, meaning that component deliveries were very tightly managed. "Components were distributed to the sites as needed," says Fehlen. "We had trucks running between the Twin Cities and the remote sites on a regular basis." Typically, any components delivered to the sites were used within two to three weeks—and sometimes sooner, depending on the site's progress.

Delays due to the wet weather, and the sometimes extended pile driving that was required because of rocky conditions, reinforced the soundness of the decision to proceed with all 16 sites at the same time.

Getting all those materials to the sites involved using everything from interstate highways to state highways and county roads. "In some cases," explained Fehlen, "we invested in upgrading the roads leading to the sites. There may have been a main road within a quarter of a mile of a site, and then there would be a dirt road to the site that might not have been built up well enough to take the loads. We worked with the county governments, and those roads were beefed up."

EGP-NA was able to achieve some economies of scale with such a large project, both in terms of construction and negotiating power with suppliers. "There is an advantage to using and installing the same solar panel thousands of times and advantages to using the same tracking equipment," says Fehlen. "Also, if you run into shipping damages or manufacturing defects, you can just pull components from another site that is not as far along in construction."

The flip side is that due to the large size of the project, they needed to order components far in advance of construction starts. Solar panel companies do not exactly have 477,000 solar panels sitting around on a shelf.

In the end, all 16 sites of the project are on their way to successful completion, with the extreme weather conditions proving to be the biggest challenge, says Fehlen. "As the projects progressed, we went from very wet weather to cold weather, and you have to multiply the varying weather by 16 times."

Fehlen credits a large part of their success to the team approach EGP-NA took with the project. "We looked at it as having the synergy between EGP-NA, the EPC, and the subcontractors." It was a huge project, and it took everyone's best efforts, he says.