The impact of hail damage on U.S. utility-scale solar plants has become a top-of-mind quality, reliability and asset management issue for stakeholders. One of the main reasons for this is the huge uptick in solar projects located in the so-called U.S. “hail belt,” especially Texas, where one solar plant suffered tens of millions of dollars in damage from a hailstorm in 2019 and other sites have incurred losses as well.
Nextracker has acknowledged the key role that smart, reliable solar trackers equipped with monitoring and control software like NX Navigator can play to protect solar modules and mitigate hail and other extreme weather risks. We have been working diligently with developers, plant operators, insurance experts, and testing labs to understand these extreme but recurring events such as hail and improve how the industry deals with them.
The first of our two white papers on mitigating extreme weather risk, published in November 2020, included a significant portion devoted to hail. My colleague Alex Roedel also discussed the topic in his blog post in December. Over the past few months, we have been involved in a flurry of new studies and reporting on the topic, including an in-depth article by PV magazine USA, where I discussed some of the key issues with editor Tim Sylvia.
As I told Tim, “accepting the way that PV modules are tested today for hail might not be the right thing to do going forward. What we as an industry need to consider is some sort of a differentiation. I expect the industry to take an ‘all-in’ approach, in which it takes a collective look at existing testing standards and modifies the severity thresholds in a way that does not penalize all modules.”
I have been working on the reevaluation of hail impact testing and standards as well as investigating risk mitigation approaches with several partners, taking a deep dive into meteorological analyses, lab testing and tracker stow strategies. On the testing and standards front, some of the latest findings and recommendations were presented along with Cherif Kedir of the Renewable Energy Test Center (RETC) at the recent NREL PV Reliability Workshop.
We offered the following conclusions during our presentation:
- Since utility solar projects with favorable economics are being deployed in much of the central and eastern U.S., the data shows that modules in those projects will be exposed to >25 mm hail impact risk within their project lifetimes.
- The industry needs to understand the risk of failure based on current construction materials and methods, especially how susceptible modules are to damage from larger (50-75 mm/2-3-inch-diameter) hailstones.
- In order to reduce risk, active and passive materials and methods need to be explored.
The RETC team has been conducting extensive testing of different PV modules with different bills of materials and front-glass thicknesses with different-sized hailstones and impact energies. The findings strongly suggest that the historically accepted minimum testing practice allowed in the current ASTM E1038 and IEC 61215 PV module hail testing standards may be inadequate to address the highly regional-specific risk posed by hail and should be reevaluated. We recommend that the industry form a task force as soon as possible to examine hail risk, taking into consideration where the modules will be deployed.
One of the takeaways from RETC’s testing is how smart-stowing trackers like our NX Horizon and NX Gemini systems can play an active role in minimizing damage to the modules during a hailstorm. By adjusting the tracker tilt to 15-30 degrees (depending on the module front-glass thickness) when a hailstorm is imminent, test results show that 50-mm-plus hailstones can be safely deflected off the module front glass, greatly reducing any impact harm to the modules.
I have also been working with John Allen of the Allen Weather Risk consultancy on hail analysis and stow strategies to get a deeper understanding of hail-related topics, including:
- A review of the sources of meteorological hail data (and their veracity).
- A gridded estimation of hail-size distribution in the continental U.S., and the probability of hail impact on the various areas mapped in that grid.
- How wind and hail interact and how that affects the hail impact trajectory.
- An assessment of the systems available to anticipate hailstorms for asset owners and operators.
Nextracker will use these findings to not only make our systems more resilient and smarter, but to help our customers—and the industry—evaluate, predict and mitigate the potential risks of hail damage to their power plants.
Download links for Nextracker’s two white papers on mitigating extreme weather risk to utility solar plants can be found here.