Hail Risk for Utility-Scale Solar PV
Hail, especially in the US and increasingly abroad, is one of the most consequential weather risks for utility-scale photovoltaic (PV) assets, even though hail large enough to damage solar modules is rare in any given location. Thus, hail is not necessarily the most frequent cause of loss, but a single large hail event can damage a large fraction of a project simultaneously and produce substantial insured losses. Day-to-day risk is the probability that a particular storm will produce hail of sufficient size, velocity and trajectory to damage solar modules, coupled with the ability of the plant to detect the storm and move trackers into a protective position. Long-term risk is the changing climatology of severe hail over a 25–35-year asset life, combined with increasing PV deployment, evolving module construction and uncertainty in climate projections. Financial institutions evaluating hail-risk should be aware of the nuances of hail risk when evaluating solar projects in locations where hail may occur that is large enough to damage the plant, as detailed below.
1. Hail and solar plant risk
Hail risk for solar plants is a major bankability and insurance issue, not only an O&M issue. The December 2025 IEA-PVPS Task 13 assessment explicitly identifies hail and convective storms as important extreme-weather risks and emphasizes that damage can be both catastrophic and sub-catastrophic, with apparently minor damage producing accelerated degradation over time. [1]
Three points organize the discussion, 1) there is a nonlinear relationship between hailstone size and solar module damage potential, 2) the IEC qualification test does not require testing with larger hailstones, and 3) damage is varied and can be nuanced or delayed.
Hail impact energy, or damage potential, scales approximately with hailstone mass and impact velocity squared. Hailstone mass increases roughly with the cube of diameter, so modest increases in diameter produce very large increases in impact energy. A 50-mm (2 inch) hailstone is therefore not merely twice as hazardous as a 25-mm (1 inch) hailstone; its mass is about eight times greater before differences in terminal velocity are considered. Hailstones also have irregular, generally sphere-like, shape, with different densities associated with their formation process in a given severe thunderstorm.
Qualification results should therefore be compared using the specified test conditions.
This matters because the standard PV qualification test is considerably less demanding than the hail environment encountered at many utility-scale sites, e.g., in the southern Midwest United States. The basic IEC 61215 hail test uses 25-mm ice balls at approximately 23 m/s. Optional higher-severity tests extend to 35, 45, 55, 65 and 76 mm, with increasing impact velocities. [2] Most commercial modules pass the basic IEC test, even though hail larger than the test specification occurs regularly in higher-hail-risk regions. If the glass survives the strike, there may still be ancillary damage that affects solar plant performance.
Damage is often obvious, but sometimes less so. Hail can fracture the front glass, damage cells and interconnects, create microcracks, or initiate defects that subsequently propagate through thermal cycling and mechanical loading. The result may be an immediate power loss, an increase in degradation rate, hot spots or, in severe cases, electrical and fire hazards.
For a utility plant, the consequences are amplified by DC-string architecture. Damage to individual modules can reduce string current, while widespread module damage can turn a short-duration weather event into months of replacement, inspection and lost generation.
2. Hail risk climatology and prediction
Hail risk assessment for solar plants increasingly combines a hail-return-period assessment for a specified hailstone diameter or larger with a dynamic probability-of-damage assessment. Traditional hail-risk studies, which have been in use for many years for damage assessments for other industries, estimate hail frequency from historical observations, radar-derived climatologies and severe-weather databases, often producing metrics such as the annual probability of hail exceeding 25 mm, 40 mm, or 50 mm. These studies remain essential and at the core, but they do not capture the impacts of stow or other solar plant protection strategies.
Modern hail-risk systems combine numerical weather prediction, weather radar, satellite observations, lightning, and site-specific hail algorithms to initiate pre-emptive protective measures. The objective is to determine not simply whether severe convection is approaching or occurring but whether a particular solar plant is likely to experience damaging hail, and to provide enough lead time for tracker protection.
Available warning time must exceed the detection-to-stow response time, including consideration of data latency, alert transmission, any operator validation, command issuance, movement of the slowest tracker row and final-position confirmation, with a safety margin. Alert radius and hail-size thresholds should reflect site-specific storm approach speeds and uncertainty; a radius alone does not guarantee lead time because storm systems and their severe thunderstorm outflows may develop quickly and move at surprisingly high speeds across the ground surface . Settings should also account for unnecessary stows, lost generation and tracker cycling.
Thus, hail stow algorithms are among the most important new physical mitigation measures for single-axis-tracking plants. Instead of leaving modules at their normal tracking angle, the tracker rotates toward a steep or near-vertical orientation so that hail strikes the module at a smaller angle, reducing the normal component of impact velocity. The reduction in damage depends on hail trajectory relative to the module surface. [2] Reported or manufacturer stated reductions in damage depend on the tested module construction, tracker configuration, stow angle and impact conditions; they should not be generalized but rather assessed for a given project design.
A complicating factor is that severe thunderstorms also contain strong wind gusts and a steep hail-stow position can increase structural wind loads or expose backside equipment, even if module hail damage risk is reduced. The rack control system therefore must integrate hail and wind hazards, tracker response time, mechanical limits and communications reliability relative to the degree of hail-hardening of the solar modules.
The control decision hierarchy should define priority when wind and hail triggers coincide, permitted rotation direction, any restriction on crossing zero tilt during gusts, and the final orientation relative to wind direction. The tracker manufacturer and structural engineer of record should confirm that the movement path and final position are within the project design limits. Procedures should also define behavior after loss of power or communications, after-hours responsibility, escalation for unacknowledged alerts and manual override. The supervisory control and data acquisition (SCADA) system should record achieved row positions and generate alarms for incomplete stow; command issuance alone is not evidence of protection.
3. The solar module in a hail environment
The industry uses a hail-resiliency curve: probability of module failure as a function of hail diameter, mass, velocity, angle and impact location. Recent testing programs are attempting to reproduce realistic hail because natural hailstones are irregular, can tumble, and can have substantially different aerodynamic and mechanical characteristics from laboratory projectiles.
Module construction matters substantially. Glass thickness, glass type and tempering, cell architecture, frame stiffness, rear support and the mechanical coupling between the glass and frame all influence failure probability. Thicker tempered front glass can improve resistance, but glass thickness alone does not establish survival under large-hail impacts. Selection should be supported by enhanced hail testing of the proposed module bill of materials and mounting configuration. [2] The additional cost of these modules, and impacts on insurance and other factors affect whether such a decision is warranted.
Financial institutions should request to review the hail climatology for the project location, module specifications, and high-energy hail test results rather than simply accepting IEC hail certification. The relevant question is not only whether a module passes a 25-mm certification test in a relatively hail-prone project location, but also how well the modules survive hail of 50 mm or larger where relevant to site exposure, and the hail damage probabilities given the hail stow algorithm, if applicable. Test reports should identify projectile mass, velocity, impact locations and angles, mounting details, and post-test electrical and cell-crack assessments.
4. Climate variations may shift hail frequency
A 2026 Nature Geoscience study (Battaglioli et al.) [3] reconstructed global occurrence of 50-mm+ hail (2 inches or greater) from 1950–2023 using atmospheric reanalysis and statistical modelling. It found that the trend is strongly regional rather than globally uniform. Europe showed the clearest widespread increase in very large hail, associated with increasing low-level moisture and atmospheric instability. Northern Italy was among the strongest areas of increase. Parts of the Southern Hemisphere, including South Africa and northern Argentina, showed declining trends in large hail.
Based on this study, it would be incorrect to assume hail-risk is increasing everywhere as the global atmosphere warms. This is because the atmospheric physics and thermodynamics of severe thunderstorm development are highly non-linear and sensitive to the vertical structure of the atmosphere and moisture distribution, not just temperature. Warming increases the ability of the atmosphere to hold moisture in vapor form and can increase convective instability, the strength of the vertical wind speed within a given storm and potentially accommodate larger hail aloft. But warming also raises the melting level, which can reduce the size and number of hailstones reaching the ground. Changes in wind shear, humidity and storm organization or storm paths associated with a changing climate can increase or decrease the hail risk in a given location.
The same study found that hail-related economic losses increased in Europe, the United States and Australia, but for different reasons. In Europe, increased very-large-hail occurrence contributed materially to the loss trend. In the United States and Australia, increasing exposure and vulnerability were more important than changes in the underlying hail climatology. This distinction is highly relevant to solar because PV deployment itself is rapidly increasing the value exposed to hail.
A separate 2026 Nature study (Zhang et al.) projects a shift toward larger near-surface hail and greater overall global hail damage potential by late century, with substantial regional variation. [4] Its kinetic-energy-based damage potential is not a prediction of PV losses, and by late-century actual trends in hail size and damage can be assessed directly and quantitatively. Together, these findings support regional climate scenarios and uncertainty analysis rather than extrapolating a historical trend or applying a uniform global uplift to project risk.
5. Implications for financial institutions assessing solar projects
A project-specific solar plant hail risk assessment should incorporate at least five components:
- High-resolution historical hail climatology
- Extreme value analysis
- Climate-conditioned uncertainty and sensitivity analysis, with explicit treatment of uncertainty
- Module-specific vulnerability analysis based on specifications and enhanced hail-test evidence
- Tracker-stow performance and strategy, including delayed, incomplete or unavailable stow
These analytical inputs should be supported by end-to-end commissioning evidence. The operating plan should define periodic testing, maintenance, training and auditable changes to alert thresholds, firmware and control logic. The approved stow strategy should be consistent with equipment warranties and insurance requirements. Loss estimates should reflect verified stow availability and recovery assumptions, supported by critical spares and a replacement plan.
The economics should consider both expected annual loss and low probability, and high-severity losses. A 1-in-50-year event denotes an estimated 2% annual exceedance probability from the hazard model, not a predictable time interval between storms. The loss distribution should also capture repair costs and business interruption, including replacement lead times.
If an event occurs, post-storm diagnostics are important. Aerial infrared imaging can identify abnormal cells and strings; electroluminescence provides much more sensitive detection of cell cracking; and comparison with pre-event baseline imagery helps owners distinguish storm-induced damage from pre-existing defects. Baseline imaging and post-event IR/EL assessment support, but do not by themselves establish attribution. [1] Weather observations, time-stamped stow and operating records, and pre-event condition evidence should also be retained.
For financiers, solar plant hail risk should be addressed comprehensively, and hail resilience should be designed into the project rather than relying on insurance as the primary mitigation. The combination of higher-resilience modules, module-specific hail testing, a verified automated stow strategy and site-specific probabilistic forecasting can materially reduce tail risk from solar plant hail loss.
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