RPCS turns to TerraSmart ground screws on challenging Nebraska solar tracker project

RPCS Array tracker Nebraska

RPCS partnered with GenPro Energy Solutions and the City of Atkinson to build a 209-kW solar array in Nebraska on a particularly challenging site. The city formerly used the Atkinson-owned site for fill, a place where soil, trees, and debris were brought then covered with dirt. This created embedment depths up to 30 feet — three times the norm — which would need longer than normal I-beams that would add significant costs for construction and material. Moreover, loose soil and debris could cause refusal of the post for a regular piledriver.

The City of Atkinson also wanted a tracked system that could provide enough energy to offset the energy consumption of their Water Treatment Plant. Through NPPD’s Buy-Sell Solar Rider, Atkinson can create long-term cash flow for the city through the production of solar energy.

Project developer GenPro Energy Solutions, which specializes in municipal solar development throughout the Midwest, brings design and custom energy solution integration expertise to the project while RPCS helped drive a creative solution to a complex engineering issue.

Don’t miss our EPC Issue in January — subscribe to Solar Builder magazine (print or digital) for FREE today

The solution was to use the DuraTrack HZ v3 single-axis solar tracker by Array Technologies, supplied by RPCS. Array’s mounting technology ensured up to a 20 to 25 percent increase in energy production over fixed-tilt systems. RPCS designs and installs Array tracker systems throughout the country, with hundreds of projects completed to date in the utility and distributed generation markets.

RPCS nebraska solar project

To overcome the embedment issue, the project features TerraSmart‘s ground screw foundation posts, a seamless solution to the challenging nature of the site’s subsurface conditions. TerraSmart and Array solar trackers were integrated for the first time on this project, a partnership forged with the help of RPCS. TerraSmart’s ground screws have a better ability to resist uplift than I-beams in loose soil and can drill into debris, reducing upfront construction costs and eliminating subsurface risks.

“This project is a great example of how teamwork, engineering, and innovative solutions can help overcome site challenges and result in the most efficient design for all parties involved. GenPro’s value engineering, Array’s superior grade tolerance, and TerraSmart’s unique foundation posts all allowed for a system that will maximize power production for the City of Atkinson,” says RPCS Sales Director Dylan Wraga. “There were underground challenges that TerraSmart’s solution was well suited to, and combined with Array’s reliable architecture this system will be producing clean power for many years to come.”

— Solar Builder magazine

Market Driver: When augers, ground screws make economic sense for solar contractors

 

auger-ground-screw

The use of augers and ground screws has been of interest in mounting solar systems for some time, and for the right size job, they offer smaller solar contractors an opportunity to grow their business.

Small site factors

For one, with smaller PV systems, one may not need to spend money on a soil engineering analysis and the cost to permit the design separately. The typical soil type in an area may be known from experience. Perhaps local experience with other construction such as a home foundation or a water line installation can provide clues to the soil type.

A method used by some contractors is to use a hammer drill and ground rod available from an electric supply store and see how easily the rod can be driven into the earth. If the rod hits solid rock 6 inches below the surface, or if the rod is very hard to drive, this could either disqualify the use of ground driven foundations, or in some cases lead to using ground screws rather than augers.

Additionally, many counties and states have published maps showing the soil types for many locations. Other sources of data are well sites where there is often a record by the foot of the surface to depths much greater than one would drive a ground-mount.

Selecting a ground-mount

Once a determination has been made as to the type of soil at a site, the installer should select a ground mount to use at a site. If the soil type is not heavily compacted and not rocky, one can consider the use of augers. Most typically, a ground auger driven 7 to 10 ft. will suffice for most 3- and 4-row landscape arrays.

If the ground is compacted, made up of heavy clay, or has small rocks within the first 10 ft., then a ground screw would probably be a better choice. Ground screws offer lower torque when driving them into the soil and are less likely to break in harder ground. However, in soft, loamy soils a ground screw will not provide big pullout values compared to an auger.

If the ground is too rocky, other options such as post and concrete, ballasted arrays, or rock anchors may be a better alternative. Experience with ground arrays will greatly help in the selection of a ground mounting system.

Driving ground mounts

Some form of tractor or track machine is required to drive ground-driven foundations. These machines are easy to rent and use, and depending on the volume you are doing, worth owning. Small arrays with only 8 or 12 posts are probably not worth the investment, but between that and larger arrays that require a specialized company to drive the mounts, there is a sweet spot that makes financial sense.

The machine used will need some form of rotary head such as the small Bobcats used to dig holes for pole buildings and fence posts. Alternately, some farm tractors have a rear-mounted rotary

driver used for fence posts that may be used.
Most equipment rental yards can supply a small track machine normally used with a hole-digging auger. With the hole-digging auger removed, an adaptor can be used to mate the drive head to fit augers and ground screws. A 2 in. hex adaptor that fits the machine can be purchased by the installer if not available from the equipment rental yard with the machine.

The amount of torque required to drive a ground mount should not be more than a nominal 3,000 lbs. If more torque is required, or if the mounts are breaking, than the wrong mount was selected. If augers break, a ground screw should have been used. If ground screws break, then a non-driven mount should be used.

If occasionally a mount breaks due to an undetected boulder or other issue, a traditional post and concrete mounting should be used. In the case of Groundwater, a 50-kW project in Portland, Ore., where over 400 augers were used, eight anchors broke due to large sporadic rocks and were replaced with eight concrete-mounted posts.

Calculations and measurements

There are many resources available covering the use and calculations for commercial construction using augers and ground screws. These include Chance Hubble manuals, and other commercial suppliers of augers. However, there are some general guidelines one can follow summarized below.

Augers have a pitch determined by the blade angle. Our auger is a 10-to-1 auger. Using a 10-to-1 auger, each ft lb of torque driving the auger provides approximately 10 times the uplift capability when driven to 10 ft of depth. For example, if an auger is driven with 500 lbs of torque to 10 ft. the pullout will be approximately 5,000 pounds. Typically, augers are driven much harder, resulting in tested pullup values of 20,000 to 30,000 lbs. Most often, augers driven in reasonable soil values will dramatically exceed the pullout values actually required to resist pullout or overturn of the array.

In the case of ground screws, they are typically applied to more dense soils and solids with rock intermixed. A ground screw should not be used in solid rock.
Ground screws in hard soils have pullout values of 1,500 to 5,000 lbs at a depth of 5 ft., however this estimate is entirely based upon the soil density. The use of ground screws in soft soils will not provide a satisfactory base for a solar array.

The use of a torque measurement gauge is recommended as an additional check on the drive torque and resulting pullout capability. Some modern machines one can rent or buy have a built-in torque gauge. Additionally, there are devices that can mount between the hydraulic head and the ground mount to measure the torque. However, a careful operator will have some sense of the amount of effort required to drive the ground mounts, and in most cases can successfully install and drive ground arrays without a torque head.

Cliff Schrock is an engineering consultant with SunModo.

 


On the Scene

Ready to rack

AP Alternatives’ Ready Rack mounting hardware is designed for both large utility-scale projects and small commercial projects. The small helical anchors and quick-install cross bracing make the simple system robust even for high wind zones. The mini-tilt brackets are adjustable and allow for quick field alignment of the post height. This allows the anchor posts to be installed rapidly and any terrain variation can be accounted for by simply adjusting the tilt bracket up or down to achieve the best aesthetics on an ungraded site. This system is nimbly installed with an attachment that fits on a skid steer.

— Solar Builder magazine

TerraSmart’s new TF3L ground-mount is lighter, adds more panels per foundation

TerraSmart ground mount TF3L

TerraSmart introduced the latest edition to its racking portfolio, the TF3L. Similar to TerraSmart’s TF2P, the TF3 Landscape Racking System is designed to maximize construction efficiency on large-scale utility-solar sites thus saving the client from unnecessary civil work. In addition, the TF3L accommodates more panels per foundation, reducing overall site cost and optimizes panel capacity.

“TerraSmart’s latest TF3 Landscape system is designed to be much lighter than any of the other parts in our current racking portfolio resulting in longer peak performances of our field employees,” says TerraSmart CEO Ryan Reid. “We are able to install within longer hours and complete projects in much shorter time periods. The new system allows us to maximize efficiency on solar construction sites and continue to stay ahead of the curve with future solar projects benefitting the client, developer and end user.”

RELATED: Pre-assembled mounting structures speed site installation by 35 percent

The TF3 Landscape racking system is configured with 6 high rows by 8 long columns and has a tilt angle of 35 degrees. Yielding to a max table size of 6 x 8, the rack accommodates more panels per foundation and optimizes panel capacity. The system is also paired with TerraSmart’s versatile ground screw foundation that can work in any soil condition, saving time and budget on every site.

Additional benefits of the TF3 landscape module orientation rack include:

• With an integrated wire management, the rack has no extra parts or pieces. This allows workers to simply tuck and go, resulting with a forty-percent reduction in man-hour installation time.
• The ultra-lightweight design allows for easier handling aiding in a longer peak performance of field workers.
• The two-piece simplified hardware stacks increase connection velocity.
• The featured Smart Bracket adapts to steep slopes, minimizing civil work and expediting project schedules.

Designed to meet the most rigorous international standards, the TF3 Landscape Racking System complies with the NEC, is UL 2703 Edition 1 certified and is CPP wind tunnel tested. The system can withstand winds up to 150 miles-per-hour and snow weight up to 60 pounds per square-foot. It is protected under a 20-year limited warranty, ensuring the system’s bankability and reliability over the life of the project.

— Solar Builder magazine

TerraSmart completes New York’s second largest solar project

Terrasmart 3

The second largest solar project in the state of New York, Shoreham Solar Commons, was completed last month by TerraSmart. Situated on a former golf course, Shoreham will produce 24.9 MW AC of photovoltaic energy for the town of Brookhaven assisting the local utility, Long Island Power Authority, in reaching New York’s 2030 fifty-percent clean energy goal.

TerraSmart was chosen by Shoreham’s general contractor, Eldor Electric, because of the velocity of its installation methods and the ability to save time and money on civil and site work. Unique in that Shoreham was built on a former golf course, the land had an intense irrigation system. TerraSmart’s unique steel forged tip on its ground screws penetrated through the irrigation lines thus saving time, money and eliminating the need for site grading. For Shoreham Solar Commons, TerraSmart combined its turnkey services of site surveying, foundation installation, ground screw installation and the Terrafarm racking system.

Terrasmart

“There were many underground challenges for this project and TerraSmart’s dexterity to handle any unforeseen circumstances positioned us as the right choice when it came to mitigating any and all potential site uncertainties,” says TerraSmart CEO Ryan Reid. “With our ability to install faster and exceed the construction timeline, TerraSmart was pleased to have placed Shoreham Solar Commons ahead of schedule.”

Shoreham Solar Commons is situated on 150 acres of land that is now repurposed to produce clean energy for up to 3,500 homes in the town of Brookhaven while eliminating 29,000 tons of harmful greenhouse gas emissions per year.
For eight years, TerraSmart has been a leader in solar racking, engineering, design and manufacturing of turnkey, ground-mount racking solutions for commercial-to utility-scale solar projects. Bringing more than thirty years’ experience in structural engineering and steel fabrication, TerraSmart has built over 1.8 GW’s of ground mount projects across the United States.

TerraSmart’s innovative ground screw foundation and racking systems have transformed the solar industry by minimizing project risks, ensuring successful installation in all soil types and offering the most cost-effective solutions. For more information, visit www.TerraSmart.com.

— Solar Builder magazine

TerraSmart to open N.Y. office to support growing Northeast solar business

TerraSmart logo

In January 2018, TerraSmart, an innovator in ground mount racking solutions for utility-scale solar projects, will open an operational hub in Selkirk, New York. The 10,000 square-foot facility was strategically chosen to support its growing construction operations in the Northeast and will serve as a blueprint to set up future construction hubs across the country in locations where solar is expanding.

Situated on thirty acres of land, the multipurpose yet cutting-edge facility will provide efficient support to field operations nearby. The hub will house TerraSmart’s custom installation machines and be a service center for all of its machines and trucks, therefore aiding in quicker response time. The building will also serve as a training facility for all East Coast construction staff enabling them proper certification of TerraSmart’s proprietary install techniques. Additionally, the hub will act as a product showroom for clients to come view, learn and be trained on the vast products and machines TerraSmart utilizes to install a solar farm.

“It’s very satisfying to call Selkirk TerraSmart’s construction home. New York has been a great state for solar and we are looking forward to creating more solar jobs to support our expanding construction activities across the Northeast,” says TerraSmart CEO Ryan Reid. “The facilities’ design and purpose will serve as the blueprint of which TerraSmart will use to set up future construction hubs, thus supporting our continuous pursuit of enhancing the solar construction experience for our clients.”

Q&A: We get the inside scoop on Terrasmart’s new Robo-Surveyor

— Solar Builder magazine