Promising that a solar project will operate without interruption for more than 20 years is a selling point for the technology, but it isn’t entirely truthful. Certain components, including solar panels, are often warrantied for 20 to 25 years and can feasibly continue generating energy at incrementally lower efficiencies as they age. However, PV inverters have the demanding task of converting the sun’s rays into useable electricity and only come with five-, 10- and, on rare occasions, 15-year warranties.
A solar technician inspects wiring on a single-axis solar tracker project. Burns & McDonnell
Inverters are often the components on an array that need fixing, but they aren’t the sole culprit in system underperformance. Solar panels can degrade when damaged by microcracks or hail impact. At higher megawatt ranges, some older tracker projects experience actuator faults, halting the sun-following movement that grants them additional generation.
Many projects are reaching their middle-age of operation, and legacy components aren’t the easiest to source if they malfunction. So solar manufacturers are building product lines specifically for repowering older projects and imploring installers to learn the skillset of reviving downed arrays with newer hardware.
Downtime on a solar project means someone’s losing money, but repowering efforts can lead to renewed levels of efficiency and many more years of high performance.
“There’s no one magic bullet solution that really fits everything,” said Kyle Burns, electrical engineer at large-scale solar EPC Burns & McDonnell. “It’s really on a case-by-case basis. There are a bunch of tracker manufacturers and a bunch of module manufacturers and a bunch of inverter manufacturers. There’s so many permutations in between there, between different equipment vendors, that there is a lot of specialization on each individual project that makes each one so different.”
A sea of string inverters
Brandon Davis, sales director of distribution at SMA America, said residential solar projects installed 10 to 15 years ago primarily used string inverters. Their popularity fell when rapid shutdown requirements were adopted and the market shifted to using microinverters and optimizers. Now, those warranties on older string inverters are either sunsetting or inactive.
“I’ve seen various testaments that 400,000 inverters need to be replaced in the next five years,” Davis said.
String inverters of that era were heavier, likely didn’t have system monitoring and lacked modern safety features, like arc fault and ground fault circuit interrupters. They also had lower power classes than the string inverters of today.
They’re not easily replaced nowadays, Davis said, because many residential installers have worked mostly with microinverters and don’t have the string inverter skillset.
The difficulty of replacing components on an existing rooftop solar array depends heavily on what project records have been kept. If there are project records, then a technician will have a better idea of how everything is laid out. If not, then there’s a lot of troubleshooting ahead.
Technicians can work with manufacturers’ applications engineers by sending existing plan sets to determine which inverter product is the right fit for replacement and what else might need modified. It can save someone from tearing up a whole array, instead of just fixing what needs replaced.
SMA’s solution for replacing older string inverters on residential arrays is the Sunny Boy Smart Energy, a hybrid inverter capable of working at the lower power classes of legacy string inverters. The Sunny Boy has monitoring and backup capabilities that weren’t available with previous inverter models.
“Yes, it takes time, and yes, you’ve got to learn, and there’s iteration in doing it,” Davis said. “But once you get through three to five projects, you can start to take some of the stuff that we have as a product and actually upsell. Give customers more features, more value, more benefit and make a little more money on something. Make something that feels like a headache and turn it into an opportunity.”
Remedying past faults
tenKsolar famously ceased production of its hardy all-in-one solar module and racking product in 2017 after the kitted technology experienced widespread microinverter failures. Five years later, tenKsolar returned to market under new ownership and a new name: Global RAIS.
Technicians replace faulty microinverters on a tenKsolar project. Global RAIS has partnered with NEP to address widespread microinverter failures on the legacy PV technology. Global RAIS
Global RAIS is reintroducing tenKsolar’s interconnected-cell solar module and racking product in phases, and one of its early goals is repowering those faulty microinverters. The company partnered with inverter manufacturer NEP to modify its 800-W microinverters for repowering purposes.
Greg Cox, co-founder and president of Global RAIS, estimates that about 20% of microinverters on tenK projects have failed, representing about 90,000 microinverters that need replacing.
Many tenK projects have a microinverter architecture different from other flat rooftop projects, because they were grouped together in what is called a redundant inverter bus (RIB). That orientation makes them operate as a single unit. In the initial repowering projects, old failing RIBs were removed and replaced with NEP microinverters. Those legacy solar projects now have the bonus of microinverter-level monitoring showing real-time production.
“We’ve seen systems that were heretofore producing 30%, 40% of their capability, back up to 100%,” Cox said.
Some of these arrays being repowered date back to 2011.
“If you’re an owner of an array, you’ve got two options. You can either try to repower it, or you can scrap it and put something else there, which is expensive and, honestly, it doesn’t make sense because the modules are still producing power,” Cox said.
Trackers out of rotation
The economies of scale are much heavier in the utility solar market. As with every solar project, malfunctioning components are a cause for downtime, but solar trackers introduce new wrinkles in array upkeep.
Over time, slew drives, the mechanical component that rotates single-axis solar trackers, can experience slowdown or fail entirely. Some legacy manufacturers have folded, so their drives are no longer available for replacement.
The United States alone is home to millions of rows of solar tracker projects. Matt Schneider, a utility solar consultant and founder and principal of Solar Perspectives, estimates that 1 MW of a downed solar project is worth $35,000 in annual losses. At a larger scale, independent power producers are beholden to the utilities their projects are interconnected to, and if they don’t meet the generation in a power purchase agreement, they can face penalties and even pay for replacement power to make up for the loss.
Kinematics is repowering older solar tracker projects with updated controls and actuators. Kinematics
“Over 10 years, a repower will pay for itself 10-times over,” Schneider said. “It’s all economics.”
Kinematics, a longtime motion control manufacturer, has geared some of its product line to repowering underperforming solar tracker projects. Kinematics has offered both slew drive and tracker control replacements on existing projects, an effort that was bolstered by acquiring tracker control company P4Q earlier this year.
“In the last two or three years, we have doubtless been part of this market passively, inasmuch as: If there’s a part that fails, somebody’s going to get a spare to do the replacement,” said Magnus Asbo, chief product and strategy officer at Kinematics. “What is changing is that the volume is enough that we want to participate more directly and bring some expertise to it.”
Kinematics developed actuator and tracker control systems capable of replacing third-party components. For repowering controls, each tracker has a control unit that connects to a larger network control unit. All of those will be replaced, but by introducing newer controls, legacy tracker projects can be updated with features like hail stow angles, backtracking and overcast light optimization.
Asbo said there is more than 1 GW of U.S. solar tracker projects needing some degree of repowering — a number expected to grow annually.
Repowering ahead
Replacing components on a solar array won’t always be the solution for system owners. In some cases, repowering one component can cascade into replacing others, like inverters incompatible with certain modules. Modern hardware, like large-format solar panels, can affect the civil aspects of existing arrays. Sometimes a project’s return on investment makes more economic sense without repowering.
Credit: Burns & McDonnell
While the demand for repowering projects is increasing, the practice of building solar has also become more standardized as utility-scale arrays grow exponentially. Those early arrays look more like boutique endeavors compared to where the market is now.
Future O&M and repowering needs for the projects going in the ground today may be more one-size-fits-all.
“People are getting much more experience with designing solar. It’s becoming a much more mature industry,” said Adam Doiron, engineering and project leader at Burns & McDonnell. “I think the challenges are going to decrease from a scale perspective.
“If you told somebody that you were in solar for utility-scale 10 years ago, you were talking about 10-MW systems, and now 10 MW is just a small commercial site,” he continued. “It really changes things based on just the volume that exists now vs. a while back. And, usually, the repowering efforts are for older systems that were just a little more technically unique at the time.”
