The overarching narrative about the emergence of solar energy as a mainstream generation source has long been focused on the rapidly declining price of panels. It is a simple story to understand: as panels plummeted in price, solar energy became affordable enough to compete with conventional generation. In a similar way, price declines in inverters and other balance of system costs have helped hasten solar energy’s emergence as a go-to fuel source for utilities and other customers.
The more recent spike in the adoption of trackers in utility-scale solar projects is yet another sign of the solar industry’s maturity. Thanks to improved reliability and a huge reduction in the cost of trackers over the past two years, about 80 percent of new utility-scale plants built in the U.S. now utilize trackers. “It’s about the economics. You get 18 to 25 percent more plant output and you pay far less than that in added costs for the tracker,” said Dr. Mark Preston, Vice President of Engineering for tracker manufacturer Array Technologies. “The lower the tracker costs go, the better that return looks.”
Not All Trackers Are The Same
As trackers have quickly become an indispensable component of successful utility-scale solar projects, developers have started to become increasingly choosy about which trackers to select. What developers have discovered is simple: not all trackers are the same. Indeed, any notion that trackers are interchangeable commodities was erased by the recent release of the report, Risk and Economic Analysis on Two Tracker Architectures, which was conducted by the independent research laboratory TÜV Rheinland PTL (TÜV).
TÜV’s researchers closely examined the two most common types of tracker architectures: one that is driven by a single motor linked to multiple tracker rows by a rotating driveline (referred to as Architecture 1) and another where each row operates as a self-contained unit with a dedicated PV panel, battery, motor and other tracker system components (referred to as Architecture 2). TÜV found that the difference between these two different architectures is vast, with a major advantage going to utility-scale plants employing Architecture 1 – the type of system Array Technologies manufactures.
Operations and Maintenance Costs
Among the most notable findings in the report was about the amount of maintenance required to keep each type of tracker architecture up and running. “With a system like Array’s, what the report says is that you have to visit a 100 megawatt site once a year to make a repair,” said Preston. “In a multi-row, electronic stow tracker system, repairs average two a day.” The implications of this finding are significant. For example, not having to devote the same amount of time and resources to maintaining a tracker means that those employing architecture 1 have nearly 16 percent lower fixed O&M costs. That equals $6.4 million over 30 years at a 100 megawatt facility.
Other findings by TÜV’s researchers help explain this huge disparity. Among them are that Architecture 1 has 733 times fewer lifetime part failures; requires 433 times less labor hours for servicing the tracker; and loses 39 times less energy due to component failures. All of this helps explain why the report came to the conclusion that Architecture 1 has a nearly 7 percent lower levelized cost of energy (LCOE) and a 4.6 percent higher net present value (NPV) compared to Architecture 2.
The Impact of Torsional Harmonics
Another key focus of the TÜV researchers delved into the issue of how torsional harmonics, also known as galloping, contributes both to tracker failures and damage to solar panels. In a nutshell, galloping takes place when horizontal winds pass over a row of panels and creates vortices that push the panels up slightly; at the end of the row, the vortices disappear and the wind reverses and causes additional panel movement. “That phenomenon will keep pushing on the row and that oscillation grows to the point where there’s some kind of damage to the panels,” said Preston. “That can happen as low as 10 miles per hour in certain circumstances, so even on a normal day you are vulnerable to this.”
But vulnerability to panel damage due to galloping is largely dependent on the architecture of the trackers. TÜV’s report found that Architecture 1 actually reduced the likelihood of galloping by preventing torsion buildup and distributing maximum loads while Architecture 2’s reliance on a safety algorithm that stows panels at a 30 degree angle increases the likelihood of galloping.
The fact that the choice of tracking systems can meaningfully impact the performance of solar panels is something that is likely to get the attention of developers. “That is a very expensive issue to deal with,” said Preston. “In the end, trackers have become more significant and impactful to a plant’s operations and performance over its lifetime. If you assume trackers are a commodity and all of them are the same, that is a huge risk.”