The industry’s discussion on the impact of different wind conditions on solar tracker design and performance and the importance of comprehensive wind engineering research, testing and analysis has gone from a quiet breeze to gale-force intensity over the past year.
However, the absence of well-defined structural codes for PV installations has led to conflicting wind testing methodologies, mitigation features and strategies. Different methods can lead to different results, leaving owners, IEs and module manufacturers struggling to interpret and evaluate types of testing and results. The industry may have taken a strong first step, but it has yet to take the giant leap into enforcing standardized values presented to owners, independent engineers (IE) and module manufacturers.
NEXTracker pioneered the first scaled dynamic models and tests that replicated aeroelastic instability with partner CPP Wind Engineering, leading to our ground-breaking blog, white paper and webinar trifecta about designing for the wind. Since then, a plethora of webinars and papers from other tracker companies and trade publications have addressed this crucial reliability topic. Terms like “aeroelastic stability” and “torsional galloping” have risen from geeky obscurity and entered the lexicon of construction professionals, independent engineers and solar power plant owners.
While this upleveling of the conversation and greater awareness of—and attention to—the issue of potential wind-caused tracker damage has no doubt been beneficial for the industry as a whole, it has also raised serious questions about which methodology or approach is correct. As renowned wind testing expert David Banks of CPP has noted, “There may be several ways to approach this, but they should all give the same answer.”
In this difficult environment, finding ground truth as an IE among conflicting reports from well-reputed wind engineering companies is an epic struggle. At NEXTracker, we believe that third-party peer review provides the best opportunity to provide the clear signal amongst the noise.
We have completed a peer review of our entire aeroelastic testing regimen as well as CPP’s original approach with Dr. Girma Bitsuamlak of the University of Western Ontario for NX Horizon, with the review underway for NX Gemini.
This process has proven why such comprehensive reviews should be required for all solar tracker structures. It forced us to reevaluate the theory to offer consistent sets of explanations in line with the observations and data patterns, strengthen our argument as to the type of instability that is witnessed at low and high tilts, and help re-shape and consolidate the state of the art. There were four rounds of review where we sent in our tested data for Dr. Bitsuamlak to do his own independent analysis for validation, establishing further confidence in the test procedures and data.
For example, while the industry has become more educated on the need for testing and analysis on the dynamic effects of wind on trackers, the full range of possible aeroelastic instability concerns has not been fully appreciated. The one effect that has received the most attention, torsional galloping is but one of several dynamic effects that must be assessed.
This means that while some manufacturers may be working on this one dynamic effect, they may have overlooked and continue to be vulnerable to the others. Not all structures are solving the same problems.
One major effect not commonly discussed is torsional divergence —which occurs when wind vortices shed off both edges of a tracker row, making the tracker rotate wildly through its entire tracking range and triggering large torsional loads and potential catastrophic failure. This type of dynamic stress mode is critical, since it can result in failures to trackers even at very low wind speeds, often before a stow speed has been triggered.
Further the wind engineering community cannot seem to agree on whether to call this phenomenon torsional galloping or torsional divergence – and this baseline assumption can have large down stream effects on the overall reliability of a structure, leaving IEs poorly positioned to determine which problems are the correct ones to solve.
Regardless of what term is used, we are looking for resiliency of the system and long term performance in the field.
Module pressures, static and dynamic loads, and tracker stability now can and should be verified through the peer review process. Owners and IEs must continue to push for suppliers to abide by these standards to get high-quality systems. Otherwise, wind-caused failures in the field will continue to be a black eye for the industry.
The discussion continues on December 10 with the NEXTracker-sponsored GTM webinar, “Driving the Standard: Wind Testing, Solar Trackers, and Peer Review.” Please join our subject matter expert panel of Dr. David Banks of CPP Wind Engineering Consultants, Dr. Girma Bitsuamlak of the University of Western Ontario, and moderator Molly Cox of Wood Mackenzie Power & Renewables and me as we take a deeper dive into this important topic. To register for the webinar, click here.