TOP PLANT: Alamosa Solar Project, San Luis Valley, Colorado

Courtesy: Daniel O’Connor Photography

Owner/operator: Cogentrix of Alamosa LLC
As the largest solar plant of its type in the world, the 30-MW Alamosa Solar Project is currently enjoying its place in the sun. The innovative project consists of 504 concentrating photovoltaic (CPV) solar trackers, each featuring a CPV solar cell panel assembly mounted on a support column. The modular design of the assembly allows the project to easily accommodate future improvements in cell technology.

The Alamosa Solar Project’s site on 225 acres in southern Colorado’s San Luis Valley was chosen specifically for its outstanding sunlight characteristics, which are necessary for concentrating photovoltaic (CPV) technologies. Among the positive attributes of the location are its high elevation (7,800 feet above sea level)—which means there is less atmosphere for the rays to pass through and, hence, greater insolation—and the presence of an existing 115-kV transmission line for interconnection.

The Alamosa Solar Project consists of 504 dual-axis, pedestal-mounted trackers supporting modules that produce approximately 60 kW each, providing enough power for about 6,500 Colorado homes. The facility, commissioned in May, provides electricity to customers of Xcel Energy’s subsidiary, Public Service Company of Colorado.

The project is projected to generate approximately 76,000 MWh per year, which displaces approximately 249 million cubic feet of natural gas that would have been used by a comparable conventional natural gas–fired power plant. This eliminates the generation of approximately 43,250 tons per year of carbon dioxide (CO2) emissions, based on the U.S. Environmental Protection Agency’s estimate of 1,135 pounds of CO2 generated per MWh. In addition, the CPV facility has very minimal water needs.

Facility Overview

J.E. (Jef) Freeman, Jr., vice president of development at Cogentrix Energy Power Management, the project’s developer, told POWER in September that a hydraulic system rotates and tilts the assemblies throughout the day so the surface of each panel maintains an optimal angle with the sun.

“Another functional benefit of this design is that the CPV system makes efficient use of the available land,” Freeman said. “One MW of rated capacity is installed on 7 acres, compared to the approximately 8 to 10 acres typically needed for other solar technologies. The CPV technology is also easier to permit and install, with no special grading, water use, or other site treatment, minimizing the impact on the local natural environment.”

The CPV solar trackers are Amonix 7700 models, each featuring the company’s proprietary module assembly mounted on a support column, Each tracker assembly is 70 feet wide by 50 feet high and contains 7,560 Fresnel lenses that concentrate sunlight approximately 500 times onto multi-junction solar cells manufactured by Boeing-Spectrolab. A hydraulic system supplied by Hawe Hydraulics North America rotates and tilts the assembly throughout the day so the surface of each panel maintains an optimal angle with the sun. Each tracker has its own inverter (manufactured by Solectria Renewables) that converts DC power output from the solar cells to AC power. As an added bonus, the assembly’s modular design will easily accommodate future cell technology updates.

Major contractors for the project were Mortenson Construction (general contractor/construction manager), Stantec (lead design firm), and Ampirical Solutions (electrical switchyard engineering, procurement, and construction contractor).

The Alamosa Solar Project has a number of interesting design features, according to Freeman:

  • Each 70-foot by 50-foot tracker assembly moves around a pivot point that is approximately 20 feet above site grade (Figure 1).
  • Approximately 16,000 cubic feet of concrete, requiring more than 1,800 batch trucks, was used for site construction.
  • The facility has more than 28 miles of grounding cable throughout the site and more than 52 miles of underground electric cable for transferring power from the field to the transmission grid.
  • The advanced Ethernet network on site connects more than 2,500 unique devices, utilizing over 20 miles of fiber optic cable and 548 network switches.

Currently, the Alamosa Solar Project has a site staff of five; an additional lens-cleaning staff of typically four workers is under contract and employed when needed.

1. Preparing for sunny days. The Alamosa Solar Project consists of 504 concentrating photovoltaic solar trackers. A solar panel support column is shown with the drive assembly being positioned at the top. Each tracker has its own inverter that converts DC power output from the solar cells into AC power. Courtesy: Daniel O’Connor Photography

Dealing with Project Obstacles

“The biggest challenge was the project scale itself,” Freeman said. “Each tracker assembly contains 7,560 Fresnel lenses and multi-junction solar cells. For the total project, this equates to approximately 3.8 million of each of these components.”

An additional hurdle for the project was the physical location. The high desert plateau required the engineering designers to account for extreme temperature variations (from –45F to over 95F), a frost line of 42 inches below the site grade, a relatively high water table, and the presence of invasive rodents. Freeman said that “overcoming these challenges required that the selection of materials and equipment met the functional needs of the project while also tolerating extreme conditions.”

The project also had to take into account strong seasonal winds that scour the San Luis Valley floor, Freeman said. Winds have historically blown from the San Juan Mountains to the west, across the valley floor, and up against the Sangre de Cristo Mountains to the east. The Great Sand Dunes National Park and Reserve is along the eastern range and largely results from the valley sediment being deposited there.

To protect the equipment from wind damage, each tracker assembly has its own anemometer to measure wind speed to enable the assemblies to be moved into a flat, face-up, stowed position when winds are over 28 mph, Freeman explained. Additionally, a centralized control system provides backup wind speed measurements from three meteorological stations on site and will put the entire field into stow position when wind speeds exceed 30 mph.

The project encountered some challenges related to obtaining state and Alamosa County variances and permits. For example, to obtain the necessary water rights for potable and lens-cleaning water, the project team had to work closely with county conservancy officials to develop a program of water augmentation for the San Luis Valley groundwater system.

“Another challenge was due to the fact that the project’s solar tracker assemblies have a maximum height of over 50 feet, which exceeds county height limitations,” Freeman said. “Once again the project team worked with the county, through the state-delegated 1041 Permit process, to successfully secure all needed permits for construction, inclusive of a height variance to enable the project to move forward.”

Securing Financial Backing

“The Alamosa project will be vital to the eventual commercialization of CPV technology by representing the first utility-scale implementation,” Freeman said. The first hurdle for the project team was to find financing. Because the project is the first of its kind, conventional financing was not available. Traditional financial institutions required at least two years of operating performance data in order to adequately gauge the risk profile of the project before they would offer financing terms for review.

The project team ultimately secured a low-interest loan from the Federal Finance Bank under the U.S. Department of Energy’s Loan Guarantee Program. In order to meet commercial operation deadlines, the project went into construction well in advance of securing the loan, which required significant upfront equity from the project developer until it was refunded from loan proceeds once financing finally closed. Construction was completed in approximately 12 months, and the facility successfully achieved commercial operation in April.

A Model for Future Solar Energy Projects

The ultimate success of the Alamosa Solar Project may have a significant impact on the financing of similar projects in the future. In order for the conventional commercial lending community to get comfortable with risks associated with innovative projects, an operating track record is needed. Freeman added that “the Alamosa Solar project is well on its way to establishing such an operating track record.”

By their very nature, pioneering projects such as the Alamosa Solar Project often encounter equipment supply, construction, and operational obstacles. Each occurred at some point during construction and startup of the Alamosa project. It was imperative to have “quality ownership, engineering, construction, and operational personnel involved to ensure the project’s ultimate success,” Freeman explained.

“The combination of engineering talent at Cogentrix with the complementary talent at Stantec and Mortenson enabled the Alamosa Solar Project to address all challenges and become what is now the largest facility of its type in the world, “ Freeman said. “As a result, it is the ideal role model for similar projects going forward.”

Angela Neville, JD is POWER’s senior editor.

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