Texas storms show industry’s solar hail defenses work

Hail risk to solar assets, largely unknown prior to 2018, emerged as projects were deployed in hail-prone regions, such as Texas. This two-part series chronicles a journey in confronting and overcoming a significant oversight in hail protection, ultimately leading to innovative solutions that are reshaping project design and operation.

This first article highlights the benefit of hail monitoring and stow by telling the story of three projects in Texas that were exposed to the same system of hailstorms as Fighting Jays Solar, a large project that suffered major hail damage, but that effectively defended themselves using hail stow. It ends with another analysis suggesting that null events, where severe hail doesn’t damage solar projects, are much more common than we may think. It also offers a way to bring these examples to light.

The solar industry’s blind spot

In fall 2019, while overseeing technical due diligence for tax equity investments of wind and solar projects at a major bank, I faced a startling revelation. Project sponsors were notifying us of the economic nonviability of hail insurance for solar farms and exercising their right to not renew policies. This was the fallout from the Midway solar farm hail loss earlier that year near Midland, Texas, where a catastrophic hailstorm damaged over 400,000 modules, resulting in a reported $70 million insurance claim.

Our industry had made a critical misstep by deploying vast fields of glass in hail-prone regions like Texas without truly understanding the risks or implementing adequate defenses. Our reviews of hail risk had merely confirmed that PV modules met the typical International Electrotechnical Commission (IEC) standard for 25 mm diameter hail resistance—a size that would prove woefully inadequate—and relied on hail insurance to cap the risk.

Our mistaken overreliance on insurance became apparent when we faced the reality of policy nonrenewal. We had examined historical insurance trends, which showed remarkably stable rates and consistent policy renewals, leading us to believe insurance would always be available and affordable. We were lulled into a false sense of security, presuming that insurance underwriters had properly characterized the hail risk. As we would learn, that was far from correct.

In fact, there was no good way of characterizing hail risk for solar projects at the time. Historical hail data, often based on claims, was scarce in remote project locations due to population bias. Moreover, vulnerability curves used for solar in leading catastrophe peril risk models were based on light metal buildings, not acres of glass.

The Midway incident catalyzed the hardening of the hail insurance market, causing premiums to skyrocket, coverage to plummet, and in many cases insurance to become unavailable. This left operating projects at major risk of loss and made many projects yet to be completed unfinanceable without ironclad parent company guarantees to rebuild. That was something only the largest owners could offer that would exist as a liability on their books through at least the end of the financing period.

A quest for understanding and solutions

Driven by this dark realization and a legitimate sense of failure, I dove into researching hail risk and mitigation. I discovered ongoing work by Nextracker and the Renewable Energy Test Center (RETC) demonstrating how tilting modules significantly reduces hail damage—a process we now know as hail stow. For an imminent utility-scale Texas solar project, I included a requirement for hail monitoring and stow, and I added similar language to our group’s term sheet template for new deals.

That was just the beginning. I also needed a targeted and reliable hail risk assessment and mitigation strategy. With that in mind, I reached out to VDE Americas, our engineering consultant for solar technical due diligence. It responded by enlisting VDE’s Dr. Peter Bostock and Central Michigan University’s Professor John Allen, experts in physics and atmospheric sciences, respectively, to develop a new approach to characterizing hail risk using a combination of weather data, hail impact data on solar modules, and lots of math. This effort also led to the formation of a small team at VDE Americas dedicated to hail risk assessment for solar, which I now manage.

The Fort Bend County case study

Nearly five years later, we’re seeing the benefits of hail stow in the public domain. My team recently collaborated with Array Technologies on a study of severe hailstorms in Fort Bend County, Texas, during March 15 to 16, 2024—the same storm system that significantly damaged the Fighting Jays solar project.

Array Technologies trackers are deployed at several utility solar projects in the immediate vicinity to Fighting Jays. Based on initial reports, the company understood that three of these sites—specifically, Cutlass I, Cutlass II, and Old 300—had experienced hail but sustained little to no damage. To better understand event severity and what those sites had done to prevent hail damage, Array Technologies engaged VDE Americas to conduct a forensic analysis.

The first major storm struck on March 15, 2024, between 5:00 p.m. and 6:30 p.m. CDT, bringing powerful wind gusts up to 51 mph and hail sizes ranging from 30 mm to 75 mm across the project areas. The second, even more severe storm hit in the early hours of March 16 (2:30 a.m. to 3:30 a.m. CDT), with wind gusts up to 31 mph and massive hailstones exceeding 100 mm in some areas.

The exposure varied by project. Old 300 and Fighting Jays experienced 75 to 100 mm hail on March 16, Cutlass I and Cutlass II encountered 40 to 50 mm and 50 to 75 mm hail, respectively, on March 15, and Cutlass I saw a small amount of 50 to 75 mm hail on March 16. The timing of the overnight storm was particularly unusual, as hailstorms rarely occur in the early morning hours. They usually occur in late afternoon or early evening.

Despite experiencing two >500-year hailstorms within hours, characterized by high winds and hail sizes up to 100 mm recorded by radar, we found that these projects implemented hail stow and reported minimal to no damage. All three projects integrate 2-mm glass-on-2-mm glass modules and use Array Technologies trackers, and thus were in 52° hail stow. We were not able to learn in which direction the trackers were stowed relative to wind at the time of hail. Cutlass I and II reported no damage, while Old 300 suffered minor damage due to wind-blown objects and a tracker motor issue that left about 40 modules unstowed, a proof point for hail stow.

These results provide compelling evidence of hail stow’s effectiveness and the importance of overnight hail stow. However, it’s important to note that while hail stow can dramatically reduce risk, it’s not a guarantee against all damage.

Stowing away from the wind is best, but we haven’t figured out how to predict wind direction when hail falls. It often changes from the prevailing direction of the storm. We weren’t able to discern in which direction Old 300, Cutlass I or II were stowed relative to wind direction, but we can confidently say, based on modeling and other hail loss events we’ve done forensics on, that implementing hail stow in either direction significantly reduces the risk of loss, typically far below the $15 million to $20 million insurance sublimits now available for large solar projects.

Industry chatter had suggested the Fighting Jays location was classified with low to moderate hail risk. This was likely based on a FEMA hail risk map that appears to be based mostly on loss claims and thus can be misleading due to population bias.

Radar data solves this problem. VDE Americas has developed more accurate hail risk maps using data from the National Weather Service’s NEXRAD radar system, which we then calibrate using spotter data, records of hail size observed by trained hail spotters. By comparison, our ArcGIS-based hail return interval maps, which account for both spotter and Doppler radar data, clearly show the Fort Bend County area as a high risk for hail.

Validating hail stow effectiveness with more data

While the Fort Bend County study demonstrates the effectiveness of hail stow protocols on three projects, the solar industry needs many more examples for underwriters to consider hail stow a reliable solution. Owners only make insurance claims for losses above deductibles, meaning we have a long list of loss events, but virtually no null events.

To create a more balanced data set, we’ve initiated a Null Hail Event Study in collaboration with the Solar Energy Industries Association (SEIA) and the insurance providers CAC Specialty and FM Global. Our goal is to find at least 25 projects that experienced severe hail (>45 mm) but were in hail stow—either by design or by chance because hail fell when tracker rows were at high tilt angles. We plan to anonymize the data and make it publicly available through the National Renewable Energy Laboratory (NREL) DuraMAT DataHub.

In support of this effort, we’ve used our database to identify nearly 200 severe hailstorms within 5 km of 165 solar projects >50 MW. These projects use various technologies: 73% use crystalline PV modules, 27% are thin film, and 80% have single-axis trackers. While some projects reported hail damage, many have not, suggesting hail losses were mitigated. Please contact me (jon.previtali@vde.com) if you’d like to contribute to the study.

As our industry continues to grow and face new challenges, the lessons we’ve learned about protecting against hail loss are proving invaluable.

In Part 2 of this series, I’ll explore the best practices that have emerged from these experiences, offering specific, actionable insights for safeguarding solar projects against hail damage.

Jon Previtali is a 20-plus-year veteran of the solar power industry who has worked in project development, operations, asset management, finance, and engineering. He is currently the vice president or digital services and product manager for hail risk assessment and mitigation services at VDE Americas.

The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.

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