VDE Americas: Study shows 100% hail stow success despite severe storm exposure
Last year’s hailstorm may have decimated Fighting Jays, but it also provided the opportunity to demonstrate the effectiveness of hail stow to prevent hail damage. In Fort Bend County, TX, within 10 miles of Fighting Jays, three solar projects— Site A, Site B, and Site C, as labeled in Figure 1— successfully weathered the same hailstorm system in March 2024.[1] The first major storm struck on March 15 at about 5:00 p.m. with wind gusts up to 51 mph and hailstones from 30–75 mm as estimated by NOAA’s MESH (Maximum Estimated Size of Hail) radar data. A second, more severe storm hit around 2:30 a.m. March 16 with wind gusts up to 31 mph and hailstones up to 100 mm. While radar does tend to overestimate ground-level hail size, in this case it still indicates the potential for very large and damaging hail.
VDE Americas interviewed project operators to understand the outcomes. Site A stowed to the nearest extreme angle (likely west) and defended against radar-estimated 40–50 mm hailstones without damage. Site B, under construction and already in hail stow (likely east), was hit by radarestimated 50–75 mm hailstones with no damage. Site C went into hail stow and was hit by radar-estimated 75-100 mm hailstones, suffering only minor damage due to flying debris and a known tracker motor issue that prevented one set of rows from stowing properly. The hail damage at Site C helps prove that hail stow worked—unst owed modules sustained hail damage, while stowed modules did not. All hail stow angles were 52° and all projects have 2.0-mm/2.0-mm dual glass panels.
These sites highlight the value of best practices with respect to stow. Namely, hail stow should be used on sites with return intervals ( RI) f or ≥45-mm hail of less than 100 years (this area’s RI was 25–50 years for reference). Operators should use a two-tier hail alert system for hail greater than 25 mm (1 in.) based on regional National Weather Service (NWS) alerts, and project-specific private alerting services. The NWS issued a warning of golf-ball sized hail for this area at 3:30 p.m., about 1.5 hours before the first storms. Other recommendations include stowing early and stowing often, prioritizing hail stow over other stow types, and implementing redundancies to ensure stow works.[2]
Insurance companies are starting to offer premium differentiation to owners who prove the reliability of hail stow systems by documenting stow protocols, events, and tests.[3] For premium differentiation, the industry needs more success stories like Fort Bend County to prove hail stow works. We typically only hear about big losses above deductibles. To this end, we’ve collaborated with NREL, FM, and CAC Specialty to create a crowd-sourced hail data repository, the NREL DuraMAT Hail Forensics Database.
