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Nevada solar project faced rocky conditions

McCarthy Building Companies faced a number of challenges on the Turquoise Solar project, including rocky conditions, but TerraSmart, known for its ability to forge into arduous soils with its proprietary ground screw foundation, ably installed the solar r

By Tony Kryzanowski

The 61-megawatt (MW) Turquoise Solar project in Nevada began producing power in November—and that in itself is significant, because many in the industry wondered if it could even be built given the list of challenges presented by the site.

The solar array is located on undulating terrain near the base of a mountain composed of igneous rock on and below the surface. The amount of workable space available on the site to install the total array for optimum performance was definitely at a premium.

It took the combined efforts of engineering, procurement, and construction (EPC) contractor McCarthy Building Companies, which prepared and implemented their design concept, and foundation and racking supplier/installer TerraSmart, using every tool in their toolboxes to deliver the required power production performance from this challenging project—on budget and on time.

The $60 million Turquoise Solar project, purchased from Sumitomo Corp. in 2019, is now owned by Greenbacker Renewable Energy Company. The array is a single-axis fixed-tilt system with 156,000 bifacial solar modules supplied by ET Solar, connected to TMEIC Ninja inverters specifically chosen to maximize production from this spatially unconventional and expansive array.

This is Greenbacker Renewable Energy's largest solar installation in Nevada. The power generated is wheeled through the NV Energy transmission system to provide a portion of the 300 MW required by an Apple data center campus located near the solar array. Apple is purchasing the power under a Green Energy Rider Agreement with NV Energy.

The project, located in the Reno Technology Park 15 miles northeast of Reno and 25 miles from the California border, was well known within the industry. Several developers were involved with it before Greenbacker Renewable Energy acquired the project and engaged McCarthy Building Companies as the EPC on the project. Over the years, many industry suppliers reviewed the project and declined to participate, deeming the construction of a stable and durable foundation for the array on this undulating, mountainous terrain as not feasible or economical using their systems. Knowledgeable of TerraSmart's ground screw foundation, Greenbacker suggested to McCarthy that it would likely be the solution for Turquoise Solar. The suggestion proved providential. It was the breakthrough that the project needed and since its completion, industry developers have taken notice.

 
The Turquoise Solar project in Nevada is located on undulating terrain near the base of a mountain composed of igneous rock on and below the surface. The amount of workable space available on the site to install the total array for optimum performance was definitely at a premium. 
  

Rob Turner, TerraSmart's director of Civil and EPC Operations, says that his phone has been ringing off the hook since the successful completion of the project, including from EPCs who passed on Turquoise Solar. One developer has even presented them with four potential projects that the developer's own engineering department had deemed uneconomical before the completion of this project.

"Talking to multiple developers and EPCs that I know in the industry, they were really shocked when they found out that we had completed this project," says Turner. "We looked at it and knew that it was going to be challenging with the slopes and with the entire site layered with rock, but this is the type of project that TerraSmart does—and has been doing for the past 10 years."

Mark Skidmore, director of Design and Engineering for the Renewable Energy & Storage Group at McCarthy Building Companies, says that the project likely would not have been built without the TerraSmart ground screw foundation and racking system. Not only did it make the project technically feasible, it was also a cost-effective solution.

 
 TerraSmart owns a fleet of rock drilling and ground screw installation equipment to manage all aspects of site preparation and installation themselves. TerraSmart's construction team of over 75 was able to successfully complete the Turquoise Solar project, adhering to extended safety protocols, all the while overcoming the site's igneous rock and ledge.
  

"The site is picturesque but very steep, with some locations at 15 degrees or more elevation in the array fields. Outside the array fields, it gets even steeper as it heads toward the peak," Skidmore says. "It was a very challenging site from the grade and topography perspective. And because it is very hilly, there are hydrology implications where the water collects on these slopes and gets naturally channelled. That type of water flow is the enemy of any construction site."

The terrain was particularly daunting for hardware delivery and for workers, many of whom benefited from enrolling in McCarthy Building Companies' Training within Industry (TWI) program as part of this project. It is a workforce development and training/retraining program based on the concept of Learn, Perform, Repeat that was originally developed by the U.S. War Department in the 1940s to help workers acquire new skills while on the job.

In addition to simply navigating the rocky, hilly site, Turquoise Solar also challenged workers with high heat and severe cold due to its location in the desert. Most of the work was done during the winter months. The project was also impacted with extra safety precautions required because of the COVID-19 pandemic. McCarthy took extra care to address all these safety issues with workers.

 
In addition to navigating the rocky, hilly site, Turquoise Solar also challenged workers with high heat and severe cold due to its location in the desert. Most of the work was done during the winter months. 
  

On a scale of one to ten in terms of challenging projects, Skidmore says he would rate Turquoise Solar as an eight.

What made the project even more challenging is that local authorities issued a conditional use permit for the site. So the EPC could not level the site and design and build the array as a typical rectangle or polygon. It required more of a mosaic design spread out over a larger area. McCarthy invested in planning and design during the early stages of the project, which definitely paid dividends by keeping the project on schedule. Helping out with the design were McCalmont Engineering and Baker Electric from an electrical perspective, and Aztec Engineering from a civil design perspective.

"We really had to treat this site as-is and preserve the natural attributes of the land," says Skidmore. "That meant dealing with steep slopes, minimal grading, and not disturbing drainage features so that large volumes of water could funnel through the site."

Despite the site generally receiving low precipitation annually, McCarthy still had to plan for the worst-case scenario by identifying natural water flow and collection areas. This information in hand helped the EPC plan the location of array components, and it ultimately required a water crossing beneath a road.

Skidmore says that the actual array design went through a number of iterations based on what they encountered on the site and in consultation with TerraSmart as they prepared the site and began their foundation and racking installation work. Project construction began in October 2019 and was completed about a year later, in November 2020.

 
 The Turquoise Solar array is a single-axis fixed-tilt system with 156,000 bifacial solar modules supplied by ET Solar, connected to TMEIC Ninja inverters specifically chosen to maximize production from this spatially unconventional and expansive array.
  

James Kelton, TerraSmart project manager for the Turquoise Solar array project, says that while he has been involved in deploying the company's proprietary ground screw foundation and racking solution in mountainous conditions before, this project was definitely the most daunting construction and installation challenge he had ever faced. It was also a baptism by fire for the company's newly-launched TerraCivil division, which was responsible for creating access and levelling locations for various segments of the overall array.

With the launch of its TerraCivil division, TerraSmart has added to its turnkey services, resulting in even more seamless project installation. On the Turquoise Solar project, the company provided much of the on-site civil engineering and construction, surveying to designate foundation locations in coordination and consultation with the EPC design team, rock drilling and ground screw installation, and racking system supply and installation. It features the company's GLIDE racking system specifically designed to work with its ground screw foundations, which can be installed on slopes up to 30 percent. There were array locations on Turquoise Solar with as much as 25 percent slope, so having this capability with the GLIDE racking system helped McCarthy build within its permit parameters with less ground disturbance.

From a civil perspective, Terra-Smart helped to redirect and repurpose a significant amount of surface rock for construction of drainage channels.

TerraSmart owns a fleet of rock drilling and ground screw installation equipment to manage all aspects of site preparation and installation themselves, which when considering the economics of projects like the Turquoise Solar site, speaks for itself.

"TerraSmart had a solution that was very flexible for this kind of situation, and it really helped them stand out as an option for this site," says Skidmore. "I'm really not aware of another racking system that can handle the variety of slopes, pitches, and soil conditions that we had on this site."

Because the project site was so undulating, the ability to adjust the height on TerraSmart's telescoping legs that fit into the ground screw mechanisms helped to minimize shading issues and also helped to ensure that modules were placed at the optimal design angle. TerraSmart also deployed three different racking table sizes to work within the available space.

"Everything from our ground screws, to the legs, to the racking system has variable degrees of adjustability, and it all starts with drilling the ground screw in the rock," says Turner, adding that the ground screw system was developed over a decade ago responding to developers wanting to build solar sites in places like the American northeast where there are significant amounts of granite below ground. The system also works well in areas prone to frost heave conditions.

"I think where we are unique is that not only do we offer the product, we also offer the installation, and now we also offer the civil work required ahead of that installation," says Kelton.

He says it's one thing to build on a site with 20 to 25 percent slope while continuously encountering rocky soil and extreme weather conditions—but then to wrap up a project on time and cost-effectively is where TerraSmart truly shines.

 


Fall 2020