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Pueblo solar power

Renewable Energy Systems (RES) has wrapped up con-struction of the largest solar facility in Colorado, which is also the biggest solar project east of the Rockies: the156-MW Comanche Solar Project, near Pueblo.

By Vicky Boyd

Much like the months of practice that go into a carefully choreographed ballet, countless hours were spent planning the 156-megawatt Comanche Solar project near Pueblo, Colorado, even before the first shovelful of dirt was moved.

The pre-project homework, along with weekly and daily meetings with managers of their respective trades during construction, helped ensure Renewable Energy Systems Americas Inc. (RES) completed the solar project on schedule.

"Pre-planning for a large-scale project of this size is really critical," said Sean Rooney, vice president of construction for Broomfield, Colorado-based RES. "We planned everything, from 'are we going to start in the northwest corner or are we going to attack it from two directions?' to 'how do we choreograph the trades to get the site work progressed just ahead of the pile-driving crews?'

"It really is a critical part because you have to manage all this activity that has to be well coordinated. You have a lot of workers that you need to keep efficient and keep safe."

At 156 MW, Comanche Solar was the largest photovoltaic project in Colorado as well as the largest PV project east of the Rocky Mountains when construction was completed earlier this year.

It was also the largest solar project that RES had built.

But the energy developer, builder, and operator already had experience building 10-MW to 40-MW solar projects in the U.S., Canada, and France. In the U.S., RES had also constructed several 100-MW to 400-MW wind farms. Project planners were able to leverage that expertise when they began tackling the Comanche Solar project, which sits on 900 acres of former pastureland southeast of Pueblo.

"We had a lot of corporate know-how on how to plan and execute large-scale projects," Rooney said.

In a complex series of financial transactions, Sun-Edisonacquired the project from Community Energy Inc. of Radnor, Pennsylvania, in June 2014. At the same time, SunEdison had set up TerraForm Power Inc. as a Yieldco and issued an initial public offering of $533 million.

The Comanche Solar project was to be one of the TerraForm Power call right projects, where TerraForm would have right of first refusal to purchase the project from SunEdison once it went online.

 
  

How SunEdison's current Chapter 11 bankruptcy will affect this arrangement is unknown.

Comanche Solar was developed by Community Energy, which did most of the initial legwork, such as securing land leases and obtaining permits.

According to a news release, the $253 million project was financed through SunEdison's non-recourse First Reserve Warehouse. This funding mechanism was designed to expand as projects moved into construction without incremental equity contributions by SunEdison.

The project will generate more than 300 gigawatt hours of energy annually that will be sold to Public Service Company of Colorado (a subsidiary of Xcel Energy) under a 25-year power purchase agreement.

Xcel Energy, which serves about 1.4 million customers, awarded the PPA through an open solicitation. Comanche Solar was selected over other energy sources, including natural gas.

RES became involved after it answered a request for proposals from SunEdison in early 2015. Even before submitting a bid, the Colorado company did "quite a bit of pre-planning to make sure we understood what we were getting into," Rooney said.

RES had worked with SunEdison on other projects, which had created a level of familiarity.

"When it came time to negotiate our contract and work through all of those business deals, it always helps to know who you're dealing with," he said.

Once RES was awarded the contract, work shifted into full-scale preplanning and coordination during the second and third quarters of 2015.

Even details such as dust mitigation and recycling the tremendous amount of packing materials from the 500,000-plus PV panels had to be factored in.

RES subcontracted out the mechanical work to Arraycon of Sacramento, California, and electrical work to Northern Energy and Power (NEP) of Thornton, Colorado.

Although Comanche Solar was permitted as a single project with only one interconnection, it sits on two separate parcels of land about a mile apart. The western parcel is about 500 acres, with the one to the east being about 400 acres. As a result, RES decided to split the work so each operation, such as pile driving, would be conducted simultaneously on both sites.

 
 Once RES was awarded the contract, work shifted into full-scale preplanning and coordination for the Comanche Solar project during the second and third quarters of 2015. Even details such as dust mitigation and recycling the tremendous amount of packing materials from the 500,000-plus PV panels were factored in.
  

"When you look at how we executed it, we executed it almost as two different projects," Rooney said. "We attacked the west side and the east side really simultaneously. After we planned it, it really was the most efficient way to do it. But definitely when you split it into two different sites, you need two sets of crews."

The parcels were located about 10 minutes southeast of downtown Pueblo just off of Interstate 25, making material deliveries simple. Each site also had its own 10-acre laydown space.

In addition, the project was about two hours and 20 minutes from RES' Broomfield office, enhancing overall project communication.

"It really allowed us to have very timely face-to-face meetings with our contractors and with our internal teams," Rooney said. "It wasn't a plane trip—it was a 2 1/2-hour ride down to the site. The communication was really one of the nice advantages of being so close, and we took full advantage of this."

Construction began in August 2015, with RES crews self-performing the site work and building access roads.

The sites, which were previously dryland pasture, were fairly flat and required only a minimal amount of work that included smoothing out a few terraces.

"If you looked at just the sheer size of the project, we tried to keep the land as undisturbed as possible," Rooney said. "It helps for two reasons. It reduces the cost and it really helps with the dust control."

 
Although Comanche Solar was permitted as a single project with only one interconnection, it sits on two separate parcels of land about a mile apart. The western parcel is about 500 acres, with the one to the east being about 400 acres. 
  

Geologic surveys indicated what Rooney described as really nice conditions of sand with a little bit of clay that aided pile driving.

Much of the work was scheduled through the winter. In Colorado, weather can change quickly, going from sunny and 50-plus degrees Fahrenheit to freezing temperatures and snow in just a few hours.

"You never know what type of weather you're going to get," Rooney said. "During most of it, we had very, very reasonable weather, but we had our share of snow events that we dealt with."

High winds, frequently reaching 60 mph, created challenges, especially when workers were trying to install panels.

"Wind events come up very quickly, and they're a bit harder to predict than precipitation," he said. "They became even more acute with our module phase. At some point, you have to shut down the module installation."

That's because the modules can act as sails, creating unsafe working conditions even when winds are as low as 20 mph. A few times, prolonged winds kept workers away for a couple days in a row.

Site work was completed in about three weeks, and then multiple pile-driving machines were brought onto each site and started in the northwest corner of the two sites in parallel.

If there was an issue with one of the piles, the rigs kept going and a different machine came in to work on the troublesome pile. Between each step, quality control was performed.

After a measured amount of time, straight trenchers and electricians came in to lay wiring.

The project involved 502,056 polycrystalline Trina panels and NEXTracker single-axis tracking systems. The decision to go with a single-axis tracking system rather than a fixed mount was made prior to RES' involvement. But Rooney said it likely was more cost-effective.

"The farther south you go, single-axis trackers make more sense," he said. "Most of the value out West is from single-axis trackers."

Installation of the single-axis tracking systems and panels was completed in rows, with the rows then wired into combining boxes.

Those, in turn, were tied into blocks based on circuitry and fed through one of 75 TMEIC inverters.

Like many large-scale PV projects, Comanche Solar involved numerous repetitive steps. But Rooney again pointed to their work up front for the project's relative smoothness.

"The key to our success was pre-planning, and there were weekly planning sessions where we coordinated and integrated multiple contractors and trade workers in the same general area. We had to coordinate between the mechanical and electrical to keep them both efficient and productive, to get finished and not get in each other's way."

The weekly sessions weren't written in stone, which allowed for flexibility on a daily basis.

RES completed the mechanical and electrical work on the balance of system side of the project in April.

 


September/October 2016