Western dreams: The Alamosa Solar project, the world's largest CPV plant

by Solar Server International Correspondent Christian Roselund

Image by Amonix

Ambition

The Western United States is a big place. The sheer scale of the landscape overwhelms; in many states you can drive hundreds of kilometers in any direction, through prairies, forests, mountains and deserts, without encountering a city.

This land has always attracted ambitious individuals; after the Native Americans came trappers, prospectors for gold and silver, farmers, ranchers, those fleeing religious persecution, and more recently, hippies and entrepreneurs.

In the Western state of Colorado, on the high prairie of the San Luis Valley, facing the wall of the San Juan Mountains, is one of the most ambitious solar projects yet undertaken. Above the rabbitbrush and greasewood are a series of 15 by 21 meter arrays of lenses, rising on hundreds of metal poles like an alien orchard.

This is Cogentrix' Alamosa Solar project, the world's largest concentrating photovoltaic (CPV) project, which we bring you as Solar Server's November 2012 Solar Energy System of the Month.

The San Luis Valley

The location in the San Luis Valley is important for understanding this project. The high, dry climate of the valley has lent itself to limited agriculture, mostly alfalfa, potatoes, lettuce and barley, as well as ranching.

Alfalfa field under cultivation. The valley is seeing limitations on the use of water. Image by Klepastic

However, agriculture in the valley is seeing difficult times. "The San Luis Valley is undergoing a transition away from an agricultural economic base due to increasing restrictions on the use of water," notes Cogentrix Energy Project Developer Jef Freeman. 

With its extremely arid climate and high elevation, the land is ideally suited to another kind of harvest. Freeman notes the "outstanding sunlight characteristics" which make the land ideal for CPV, which requires not only abundant sunlight, but direct, unfiltered sunlight, known as direct normal irradiation (DNI).

Cogentrix is not the first company to notice this. In 2007 SunEdison built an 8.2 MW solar photovoltaic (PV) plant near the town of Mosca, Colorado, which at the time was the largest PV plant in the United States, and the valley boasts some of the highest rates of home PV adoption in the nation.

Capturing the sun

The Alamosa plant is comprised of 3,528 Amonix 7700-60 and 7700-63 CPV "Mega-Modules", mounted on 504 dual-axis tracking units (utilizing hydraulics provided by Hawe), seven to a tracker.

Amonix' CPV technology is based on the use of mulijunction PV cells. Image by Amonix

Each Amonix module uses over 1,000 acrylic Fresnel lenses to concentrate sunlight up to 500 times onto small multi-junction solar photovoltaic (PV) cells. These cells can reach 31% module efficiency, an approximately 10% raw gain in efficiency over the most efficient PV modules without concentration.

CPV manufacturers and developers including Amonix state that this technology can offer a lower levelized cost of electricity than PV technology, however in order to do so CPV, like concentrating solar power (CSP) requires specific light conditions, as well as the use of tracking devices.

The trackers at the Alamosa Solar plant follow the sun's motions throughout the day using a hydraulic system by Hawe, which is driven by a custom-mounted controller. Each of the trackers holds 60 kW of CPV attached to a Solectria inverter, delivering in total 30 MW of capacity.

This makes the Alamosa project almost four times as large as the next-largest CPV plant in the world, the 7.8 MW Navarra Solar Park in Navarra, Spain, and a breakthrough for CPV technology into the big time.

Sealing the deal

The plant is the result of a solicitation process opened in early 2009 by Xcel Energy subsidiary Public Service Company of Colorado. The process, as approved by the Colorado Public Service Commission, helps to meet Colorado's ambitious renewable portfolio standard (RPS) of 30% by 2020 for private utilities.

However, following the sale of electricity to Xcel, several other significant hurdles stood between Cogentrix and its goal of building the plant. CPV technology uses less water than does agriculture, but developers still needed to secure water rights for the project.

Several hurdles had to be overcome before construction could begin, including obtaining water rights, a height variance and securing financing. Image by Amonix

"The project required obtaining specific Colorado and Alamosa County variances and permits," recalls Cogentrix VP Freeman. "For instance, to obtain the necessary water rights for potable and lens cleaning water, the project team worked closely with County conservancy officials to develop a program of water augmentation into the San Luis Valley groundwater system."

Also, the height of the project exceeded an existing 15 meter county height limitation. Freeman notes that the project team worked with Alamosa County through the state delegated 1041 permit process to secure permits for construction, including a height variance.

Financing

However, the largest hurdle was likely financing. Here, being the first CPV project of this scale was not an advantage.

"Because the project is the first of its kind, conventional financing was not available," notes Freeman. "Traditional financial institutions required at least two years of operating performance data in order to adequately gauge the risk profile of the project before offering financing terms for review."

The project team was ultimately able to secure a loan from the Federal Finance Bank, backed by a U.S. DOE loan guarantee.

Building the future

In order to meet project deadlines, Cogentrix began work on the project in April 2011 with project partners Stantec and Mortenson, financing the work through its own equity while pursuing the DOE loan guarantee. Cogentrix VP Freeman notes that again, the size of the project and its innovative nature brought challenges.

Cogentrix VP of Development Jef Freeman notes that the greatest challenge was the unprecedented scale of the project. Image by Amonix

"By their very nature, innovative projects such as the Alamosa Solar project often bring equipment supply, construction and operational challenges," observes Freeman. "Each occurred at some point during the construction and start-up of the Alamosa Solar project."

Freeman states that the biggest challenge was the project scale, particularly the 15 meter by 21 meter assemblies. The project also required 45 kilometers of grounding cable throughout the site and 84 km of underground electrical cable for carrying the power produced in the field to the interconnection transmission line at 115 kV.

Hard land: Building for ice, wind and other challenges

Freeman also notes that the physical location, while offering rich solar resources, also presented big challenges.

"The mountainous terrain required the engineering designers to account for extreme temperature variations (-43 degrees up to +35 degrees C), a frost line of 107 cm below site grade, a relatively high water table, and the presence of invasive rodents," notes Freeman. "This required that the selection of materials and equipment met the functional needs of the project while also tolerating extreme conditions."

Finally, the project had to take into account strong winds, which led to equipping each tracker assembly with its own independent anemometer to measure wind speed, so that the assemblies can be moved to the flat, face-up position if winds exceed 45 kilometers per hour (kph). A centralized control system puts the whole field into stow position if wind speeds exceed 48 kph.

Solar harvest

Cogentrix completed the project in only 12 months. Image by Amonix

After roughly 12 months of construction, Cogentrix put the Alamosa Solar project into service in April 2012. Freeman credits the team from three companies with the project's success. "It was imperative to have quality ownership, engineering, construction and operational personnel involved to ensure the project’s ultimate success," states Freeman. 

Freeman notes the combination of engineering talent and Cogentrix and Stantec as well as Mortenson's construction expertise, stating that this combination enabled the project to address the multiple challenges that it faced during the construction process and conclude on time. He describes the plant as a role model for similar plants, noting that the project broke new ground in many ways.

"In order for the conventional commercial lending community to get comfortable with risks associated with innovative projects, an operating track record is needed," explains Freeman. "The Alamosa Solar project is well on its way to establishing such an operating track record."

The facility has an availability of 98%, and is meeting contractual obligations with Xcel Energy. Cogentrix, Amonix, and their project team, working with the federal and local government, have shown that once again, the West can deliver on dreams.

Former Amonix CEO Brian Robertson. Image by Amonix

Footnote: Brian Robertson (1973-2011)

On December 22nd, 2011 former Amonix CEO and Board Director Brian Robertson died in a plane crash in the U.S. state of Pennsylvania, only four months before the Alamosa Solar plant achieved commercial operation. Mr. Robertson was also a co-founder of SunEdison, and a person who left a mark on the solar industry and the world.

We at Solar Server want to take a moment to remember the pioneering spirit of Mr. Robertson, and his contributions to CPV and the solar industry.