The goal of a solar tracking system is to boost the lifetime energy production of a given site, somewhere between 20 to 30 percent over a 30-year period. But this is not a “set-it-and-forget-it” proposition. Today’s tracker systems are more advanced than ever before, but they require an operations and maintenance (O&M) plan that’s just as sophisticated, if not more.
“The performance analytics of a site will become increasingly defined by O&M activities over a longer time span, as costs associated with system failure and maintenance, labor and transport are compounded,” says Denise Hugo, director of marketing with Array Technologies Inc.
If your O&M planning starts after the project is in the ground, which can happen with today’s time pressures, it is already too late. Reliable PV tracker performance starts with specing and designing the right system to match the project.
A system is only as good as its ability to exist in its environment. Beyond the obvious structural necessities required of any mounting system, tracking functionality can both improve and further complicate the plan for withstanding the elements. Some improvements are simple, like tilting opposite rows toward each other to clean two dusty rows in one pass. Others come from the sophistication of the software.
“We have seen a trend toward greater reliability in the face of the increasing intensity and frequency of weather events,” Hugo says. Array, for example, incorporated a torsion limiter in its centralized DuraTrack HZ v3, which naturally improves the stability of the system during wind events.
“When a heavy wind occurs and wind speeds approach record highs, tracking systems can risk catastrophic failure. The best rule of thumb is to design the tracker system to withstand the full site specified wind speeds at any tilt angle, instead of relying on risky stow strategies.”
Separate UPS [uninterruptible power supply] systems proved to be problematic in early tracking days, which inspired tracker manufacturers to integrate backup power into the trackers themselves or eliminate the need for backup power entirely.
Whether a site’s climate patterns evolve over time, or experience a sudden aberrational event, tracking systems can adjust. SunLink says meteorological stations are integral to intelligent tracking systems.
“The data from these stations can be used to meet ongoing financing and operational requirements,” says Kate Trono, VP of products at SunLink.
More Motors or More Maintenance?
But as my cranky mechanic dad would say when car manufacturers would improve anything (like, going from crank windows to power windows), more sophistication can also mean “more stuff that’s going to break.” Trackers need motors and power sources, which introduce additional points of failure. The answer from tracker manufacturers is to minimize as many of those variables as possible, but which variables specifically depends on the approach of the manufacturer.
Array, a leading supplier of centralized drive tracker systems, believes in minimizing the number of motors and other high-maintenance parts that are needed as well as drawing power from the grid instead of relying on batteries.
“We use the minimum amount of electrical components required for control at each motor,” Hugo says. “Simply put, less moving parts make for fewer problems. By removing the number of smaller, less reliable motorized components and condensing this into a flexibly linked centralized single-axis tracker architecture, we have significantly improved uptime and dramatically lowered O&M costs.”
Movement is also taxing on all of a system’s components, and maintaining hardware is tedious and costly. Some tracker systems may require crews to regularly check the torque on screws or lubricate joints, which can add thousands of hours to an annual O&M budget. NEXTracker, currently the market share leader in global tracker deployments according to GTM Research, says a key in minimizing maintenance needs here is valuing mechanical tension over torqueing.
“Torqueing is by nature inexact because of the many factors that can affect friction — from surface texture to debris, rust and humidity,” says Dan Shugar, CEO of NEXTracker. “By contrast, tension involves the use of hydraulic tools to stretch screws and swage or fasten bolts to a structure. In fact, the swaging of a lockbolt is five times stronger than its nut-and-bolt counterpart fastening system. Regular nuts and bolts have a gap, which can cause loosening by vibration. System hardware that does not require torqueing but instead relies on the tension between components will reduce the need for manual checks.”
Shugar believes the key question to ask when evaluating single-axis trackers is this: Could the failure of any individual hardware component threaten the system’s overall production?
“In the case of a decentralized SAT, for example, each row’s independent motor is powered by its own dedicated solar panel (with integrated battery backup), making external power cables obsolete. This reduces the risk of asset downtime since each row is essentially its own independent system. Having advanced individual, self-powered motors control each row increases the overall resiliency of the solar plant by eliminating the risk of malfunctions that can lead to downtime for a larger portion of the installed capacity.”
Trono says decentralized trackers have gained momentum because they are actually simpler to maintain. Downtime is also minimized by holding spares, which is made possible by highly modular systems.
“No special tools or expertise is required to swap out a motor, for example, and it’s not necessary to take an entire linked-row tracker offline,” she says.
Distributed trackers also streamline engineering between the EPC and the mounting system provider, which can result in meaningful savings in soft costs.
“Consider how self-powered, wireless systems eliminate the back and forth and inevitable drawing revisions concerning connection points, conduit, etc. to each tracker,” Trono says. “Furthermore, since each tracker row is independent, they’re easy to add and remove from a layout. Changes to inverter locations and access roads stay simple rather than cascading through the layout departments of multiple companies.”
“The appropriate tracker choice, one with robust components and minimized failure points, will guarantee the best performance over time,” Hugo says. “With the increased efficiency of other BOS components, such as the inverters, highly reliable tracked projects can actually incur less total O&M costs compared to fixed-tilt.”
Data is the future
While my dad had a point — that new advances in technology create new issues — what he didn’t see was the extended benefits of improved performance. This is where data changes the game in O&M and the lifetime value of a tracking system. Smart devices and the Internet of Things means even the largest solar plants can be monitored down to the component level.
“Data is essential to deploying O&M resources efficiently,” Trono says. “Row-level tracker intelligence complements other data systems to give a complete picture of system performance.”
There are always outlier incidents that require immediate analysis to determine if action is required. Having access to minute-by-minute tracker performance data helps system owners and their O&M partners understand when and where to place maintenance resources to manage assets effectively while keeping down LCOE. The correct course of action, though, can only come from setting up a software and O&M strategy that interprets the data correctly.
“The data that this constant monitoring produces can become overwhelming for system owners,” Shugar says. “To understand the true implications of system issues, an intelligent cloud-based O&M strategy must be developed that weighs the cost of truck rolls against possible impacts to system performance and the value of the energy produced. Just collecting data doesn’t reduce O&M costs. It’s how intelligent tracking systems and asset managers use that data that reduces truck rolls and increases long-term ROI.”
And this is the note to end on because the biggest strides to be made in solar tracker O&M going forward will be made in data and control.
“As an industry, we’ve only scratched the surface when it comes to harnessing the power of integrated data and control systems,” Trono says. “Unfortunately, many data systems are siloed because of security concerns or integration challenges. In the future, we will see advanced control systems that can be used to improve the performance and future product design of both tracking and fixed-tilt systems.”
Chris Crowell is managing editor of Solar Builder.
Tracker System Profiles
DuraTrack HZ v3
Array Technologies’ tracker architecture is designed to withstand the elements, not to stow. Unlike trackers that rely on active stow to attempt to survive inclement weather, the DuraTrack HZ v3 is designed to reliably handle the full site loads at any tracker angle. Array’s tracker incorporates a mechanical load mitigation system based on a unique torsion limiter gear and redundant mechanical stops. The system is automatic and doesn’t require power backup, wiring, anemometers, controllers or regularly scheduled maintenance to function, which eliminates backup systems, potential failure points and a ton of maintenance.
How does it save time and cost?
Array Technologies’ trackers are designed to deliver the lowest cost of ownership and the highest value, forged from decades of experience. DuraTrack HZ v3’s streamlined design lowers installation and O&M costs. It is built with minimal failure points and zero scheduled maintenance over a 30-year lifespan.
Powered by NEXTracker’s self-powered motor drive, each row of the NX Horizon system can now be built with significantly less steel and can be optimized for wider rotation angles. As a result, customers will maximize yield, pay less for O&M and reduce the impact on the environment significantly. NEXTracker designed a mechanically balanced system that has no overturning moment at the core of the NX Horizon tracker. This allows NEXTracker to bring down the number of piers needed for one row of solar panels by up to one third.
How does it save time and cost?
NEXTracker’s NX Horizon tracker needs less steel than conventional trackers, allowing for quicker installation. Customers won’t need drive shafts or extra cabling to power the trackers, speeding the process up even further. NX Horizon is self-grounded, so customers won’t have to pay costs and labor for installing grounding washers, braided straps, bare copper wire and grounding rods. Zero welding is required. NEXTracker’s patented fasteners make mounting the panels quick and easy.
One of the most popular features of SunLink’s TechTrack Distributed is the balanced row bearing design or “virtual pivot.” The bearings arrive at the jobsite preassembled, and the installation team can quickly and easily bolt the assemblies to the top of the posts. The bearings then form a cradle in which to rest the torque tubes — the heaviest component in the system — during their installation. Plus, at every stage of racking assembly and module installation, the system remains balanced, eliminating the need to take precautions to restrain it from swinging. The most innovative feature of the TechTrack is Dynamic Stabilization. The design utilizes an active, sensor-enabled component to change the damping and stiffness of the structure in response to real-time environmental conditions. This dynamic design dramatically enhances load management and reduces required steel.
How does it save time and cost?
TechTrack Distributed has no gaps at the bearings or splices, which can add up to several feet on each tracker. Instead it enables clean, continuous tables of 90 modules with one small gap at each slew drive. TechTrack Distributed packs more power into a given area, maximizing the potential of the site. In addition to generous installation tolerances and the flexibility of unlinked rows, TechTrack Distributed is designed to contour with North-South changes in grade of up to 2 percent post-to-post. For example, on a site that would have required extensive grading or very long and heavy posts to keep the array flat, TechTrack has enough flexibility built in to eliminate those costs.
— Solar Builder magazine