Dealing with difficult, uneven terrain is now the norm for solar project developers pursuing jobs in the Northeast, Midwest and Southeast. These sites with dramatic slopes and undulations are doable with most modern solar racking and tracker foundations, but they just involve more risk and higher costs due to the significant earthwork and longer foundation pile lengths.
We’ve covered some ways various tracker manufacturers have been overcoming these challenges and avoid site grading costs. This week, the global leader in solar tracker market share (at 29 percent) officially launched its answer.
Nextracker’s NX Horizon-XTR is a terrain-following, single-axis tracker that addresses the sloped, uneven, and challenging terrain problem by foregoing the “straight-line row” design constraint. Instead, it conforms to the existing ups and downs of north-south ground slope undulations and follow natural site contours.
The XTR concept started over 3 years ago, when SOLV (formerly Swinerton Renewable Energy), pushed Nextracker to develop a terrain-following solution. The result is the XTR product line, which was exclusive to SOLV for a few years before officially being rolled out globally. Early returns on utility-scale sites showed savings in the millions attributable to reduced grading and shorter piles (yes, steel piers can be shortened both above and below grade while following the terrain).
“NX Horizon-XTR’s ability to follow terrain can significantly reduce earthwork, allowing these otherwise-infeasible sites to become economically and environmentally viable solar projects,” said VP of engineering, Donny Gallagher of SOLV Energy. “Less earthwork means lower upfront costs and improved scheduling. XTR has allowed us to win more projects by making us more competitive in our project bids, while also lowering our impact on the environment.”
These first projects have shown CAPEX and operating expense savings in the range of 30 to 90 percent less “cut and fill” earthmoving work and piers up to 36 inches shorter. For Silicon Ranch, being good stewards of the land goes along with every solar project too, so conforming to the native ground contours with Horizon-XTR and avoiding extensive earthwork is a big plus.
“There are some things you cannot out-engineer, and in my experience well-established topsoil is one of them,” said Nick de Vries, SVP Technology & Asset Management at Silicon Ranch. “Earthwork is especially painful as it affects a solar project three times: first performing grading, next reseeding the exposed dirt, and later fixing the inevitable erosion and hydrology issues that come from the lack of well-vegetated topsoil.”
So, what changes were made to the Horizon design to make the -XTR version happen? Not many, according to Alex Roedel, Senior Director, Design & Engineering at Nextracker.
The mechanical parts are all the same. The slew gear and motor needed an upgrade to take into account the additional load needed to turn the tracker. And then of course the torque tube incorporates bends that follow the terrain.
Roedel reminds that Nextracker doesn’t rotate around the torque tube, which makes this possible.
“We have a pin with this swinging motion. Because of that, and we’re a balance tracker. Meaning, the weight of the tracker is at the modules. Because of that, the center of gravity is also the center of rotation where most other folks have the rotation around the torque tube. So we have a lot more play in our trackers. And with True Capture, we can move nimbly and quickly.”
Most of the dramatic change with Horizon-XTR is in the up-front analysis because instead of worrying about one plane, you have “10 to 13 planes,” Roedel notes. “So, we built in-house automation for how to analyze the civil surface without losing a huge amount of time.”
Over 50 gigawatts of NX Horizon trackers are deployed in the field. Today over 15 NX Horizon-XTR sites are operational and dozens of additional projects are under design and construction in the U.S. and abroad (over 3 GW of cumulative projects).
“We worked closely with them and project owners to integrate their requirements and complete lab and field-tests of a terrain-following tracker,” said Nextracker CEO and founder Dan Shugar. “As the world races to meet clean energy goals, NX Horizon-XTR opens a new frontier for solar developers to affordably build on sites that were previously cost prohibitive, while treading lighter on the environment.”
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