Hail versus photovoltaics

Will solar modules hold up?

Roman Rubanovich, NENCOM

What will happen to photovoltaic (PV) modules during hail? Is large hail capable of breaking the glass surface of solar panels and damaging the solar cells? Which PV modules are more resistant to hail impacts and harsh climatic conditions? Let’s find out.

Contents

Introduction
PV module structure
Tests and standards
Hail formation
Statistics and trends
Fighting hail
Risk reduction
Additional materials

Introduction

For certified solar modules, hail with a diameter of up to 25 mm poses no danger. During mandatory tests, the modules are shot with ice balls of exactly that size, fired from a special gun at a speed of 23 m/s (82.8 km/h). After the hail impacts, laboratory specialists inspect the modules: they must retain their characteristics and have no visual defects.

Larger hailstones carry more kinetic energy, so they can inflict both obvious damage to the protective glass and hidden damage to the solar cells or conductive busbars.

Due to climate change, we are increasingly encountering extreme weather conditions. At the same time, technology is evolving rapidly: scientists are developing ever more robust and weather-resistant materials. Global experience shows that solar panels damaged by hail typically continue to operate, albeit with a corresponding loss of efficiency. It should be kept in mind that minor damage can worsen over the course of the PV system’s operation.

PV module structure

All modern solar modules in mass production are built almost identically. They are protected on top by tempered glass, which absorbs the main impact during hail. The glass must be not only very strong but also smooth enough to prevent dust accumulation and to self‑clean effectively during rain. At the same time, it must not be too smooth, otherwise sunlight striking the module at a low angle will be almost completely reflected. Specialists in laboratories around the world are constantly experimenting with the microstructure of the glass surface for photovoltaic modules and with special coatings to achieve the optimal combination of conflicting characteristics.

PV module structure © NENCOM

Under the protective glass are the solar cells (typically silicon), connected in series by conductive busbars. Previously, two wide flat busbars per cell were used, which sometimes led to «hot spots», and damage to a single busbar was critical. Later, manufacturers began using 3, 5, and even 10 thinner busbars, thus reducing electrical resistance and distributing current more evenly. MBB (multi-bus bar) technology has proven itself and become the norm. Now, in 2024, some manufacturers use 16 or more ultra-thin round-section conductive busbars on each cell, making solar modules not only more efficient but also more reliable and durable. The quality of the solar cells and conductive busbars affects the hail resistance of PV modules.

PV module LONGi LR7-72HGD 585~620

The solar cells, together with the conductive busbars, are laminated on both sides with a special durable film of ethylene‑vinyl acetate (EVA), resistant to ultraviolet light. This encapsulation protects the cells and busbars from moisture ingress and reduces the likelihood of microcracks forming under extreme loads on the module (wind, snow, hail). The quality of this film cannot be assessed visually when purchasing modules, as it is simply not visible. We can only rely on the manufacturer’s reputation, and the result will become evident after several years — low‑quality laminating films turn cloudy and peel off over time:

Low-quality module after 3 years © NENCOM

The last layer — a polymer or glass substrate — also affects the strength of the solar module. A glass substrate is used in bifacial modules, the rear side of which can generate energy from light reflected off surrounding surfaces.

This entire «sandwich» is typically housed in an aluminum frame, which is also an important protective element for the module under extreme loads.

Glass is the heaviest part of a solar module. One square meter of sheet glass 1 mm thick weighs approximately 2.5 kg. Let’s consider a couple of examples:

1. The single‑sided SHARP NU‑JC440 module for the residential sector has an area of ~1.95 m² and 3.2 mm thick glass. The glass therefore weighs ~15.6 kg, while the entire module weighs 20.7 kg. Thus, over 75% of the module’s weight is glass.

2. The bifacial SHARP NB‑JD585 module for the commercial sector has an area of ~2.58 m² and two glass sheets 2 mm thick on each side. The glass thus weighs ~25.8 kg, while the entire module weighs 32.5 kg. Consequently, almost 80% of the module’s weight is glass.

Specification SHARP

Sometimes in bifacial modules, a transparent polymer is used instead of the rear glass, which allows cost and weight to be reduced. In theory, double‑glass modules (also known as «glass/glass» or «dual‑glass») are more durable than modules with a polymer backsheet («glass/backsheet» or «single‑glass») thanks to glass’s exceptional resistance to atmospheric exposure. In practice, however, the reliability of a solar module depends on the quality of its components and the manufacturing process.

Tests and standards

We have examined how most modern PV modules are constructed and determined that the strength of materials and manufacturing technology directly influence hail resistance. But how can this resistance be measured and modules compared? Testing laboratories and standards come to the rescue. During mandatory certification, solar modules undergo numerous tests developed by the International Electrotechnical Commission (IEC), including salt fog resistance (IEC 61701), ammonia atmosphere resistance (IEC 62716), dust and sand resistance (IEC 60068), and hail impact resistance (IEC 61215).

In fact, the international standard IEC 61215 provides not only for evaluation of solar modules’ hail resistance (hail test), but also for numerous trials, such as «thermal cycling test», «humidity‑freeze test», «damp‑heat test», «static mechanical load test», «bypass diode thermal test» and many more.

Hail impact resistance trials of PV modules under IEC 61215 are conducted as follows. A pneumatic setup fires ice balls of specified size and mass at a given velocity at 11 points on the photovoltaic module:

Hail Test 35 mm © Kiwa PVEL, animation by NENCOM

In the IEC 61215 standard, a schematic illustration of a suitable setup is provided as an example, featuring a horizontal pneumatic launch system, a vertically mounted PV module, and a speed sensor that measures the time it takes for an ice ball to travel the distance between two light beams. The speed sensor must have an accuracy of ±2% and be positioned no more than 1 meter from the surface of the module under test:

© International Electrotechnical Commission

In practice, other types of horizontal and vertical launch systems may be used, including slingshots and spring testers. The launch velocity must be maintained within ±5%, with an allowable deviation from the target of ±10 mm. The impact points specified in the standard cover the corners and edges of the modules, the conductive busbars between cells, the edges of individual cells, the mounting points of the module to the supporting structure, and the area above the junction box:

Impact points on PV module © NENCOM

The solar module must be securely fixed in accordance with the manufacturer’s instructions, and its surface must be positioned perpendicular to the trajectory of the ice balls’ flight.

The test ice balls are formed in a freezing chamber at a temperature of −10±5 °C. To verify their mass, a scale with an accuracy of ±2% is used, while the mass and diameter deviations must be within ±5% of the specified value. Each ice ball is carefully inspected for cracks, then placed in a special storage container at −4±2 °C. The artificial hail must remain in the container for at least one hour before use. The time between removing an ice ball from the container and its impact on the module must not exceed 60 seconds.

We will discuss later how real hailstones are formed and grow in a thundercloud. Now we need to understand the speed at which they fall to the surface and the kinetic energy they carry before impact.

The formula for the maximum (terminal) falling velocity of ice fragments is determined by the balance between gravitational force and air resistance. For a spherical hailstone, the terminal velocity $v_t$ can be expressed as follows:

$$v_t = \sqrt{\frac{2mg}{\rho C_d A}}$$

In this formula, $m$ is the mass of the hailstone (kg), $g$ is the acceleration due to gravity (~9.81 m/s²), $\rho$ is the air density (~1.225 kg/m³ at sea level), $C_d$ is the drag coefficient (~0.47 for a sphere), and $A$ is the cross‑sectional area of the hailstone (m²).

The table presented in the IEC 61215 standard shows that larger ice balls can attain higher velocities. Our calculations confirm this, and for clarity we decided to add the kinetic energy of hail (as the primary destructive factor) to the table, calculating it by the formula $E_k = \frac{1}{2} mv^2$

For comparison: raindrops fall to the ground at approximately 10 m/s

The table shows that when the hailstone diameter increases threefold (25 → 75 mm), its mass increases 27 times, its velocity by 1.7 times, and its kinetic energy by 80 times.

In real-world conditions, wind as well as upward or downward air currents can affect the falling speed of hail. Furthermore, natural hailstones, especially large ones, often have irregular shapes and therefore — as opposed to spheres — a different drag coefficient.

It is important to note that a chunk of ice is not an entirely rigid body, so upon impact it cannot transfer all of its kinetic energy to the PV module. The actual impact energy will be the portion of the kinetic energy absorbed by the module, resulting in its elastic deformation or damage. The remaining energy will be lost to deformation of the ice body itself, converted into heat and sound, and carried away by fragments upon its breakup.

Artificial hail production © Kiwa PVEL

Laboratory hail under IEC 61215 is extremely dense (~0.92 g/cm³), so its impact energy usually greatly exceeds that of natural hail. The density of natural hail averages around 0.64 g/cm³ and can range from ~0.32 g/cm³ in slushy conditions to ~0.99 g/cm³ (very rarely).

The lower density of natural hail leads to a reduction in terminal falling velocity, thereby decreasing kinetic energy. Moreover, the impact of a «softer» chunk of ice will exert less localized stress on the module due to the longer interaction time and larger contact area.

Despite the fact that the IEC 61215 standard provides for six sizes of hailstones, only the first — 25 mm — is mandatory for certification. For this reason, the vast majority of solar modules available on the market today have exactly this level of confirmed hail protection. The hail impact resistance class is always indicated in the test report, and some manufacturers, such as LONGi, also include it in their specifications:

PV module LONGi LR5-54HTH 420~440M

Currently, all LONGi modules intended for the European market have been tested for hail resistance at a diameter of 25 mm in accordance with the IEC 61215 standard. In May 2024, the company announced the start of production of bifacial «Ice-Shield» series modules, resistant to hail impacts up to 45 mm in diameter, but only for the US market. The increased strength is achieved by using a thicker front glass (3.2 instead of 2 mm) with a special coating, which raised the module’s weight by 7.7 kg.

Specification LONGi

LONGi opposes the production of PV modules of excessively large size. This is partly due to logistical issues and the safety of on‑site operations, but there is also another reason. Research by LONGi in 2021 showed that the larger the area of tempered glass, the lower its strength. Below is the correlation between surface stress and glass width:

LONGi specialists approached the TÜV SÜD laboratory to compare the hail resistance of modules measuring 2256×1133 mm (2.56 m²) and 2384×1303 mm (3.11 m²), providing three samples of each. Firing was conducted with ice balls 35 mm in diameter at a velocity of 27.2 m/s. All three larger-area modules were shattered, while the 2.56 m² module withstood the impacts.

In December 2023, SHARP Solar successfully passed tests of its NU‑JC series modules for resistance to hail with a diameter of 40 mm. Such a size is not included in the IEC 61215 standard table, but it is present in the Swiss VKF standard, which is more demanding due to the specific environmental conditions of the Alpine region.

PV module SHARP NU‑JC series © NENCOM

SHARP solar modules of the NU‑JC series have long been available on the European market. Our company is an official partner of SHARP Solar: we sell PV modules from this manufacturer wholesale and retail, and we also use them to build photovoltaic systems in Bulgaria.

In Switzerland and Austria, a so‑called «hail register» is maintained, in which various construction products, including photovoltaic modules, are classified into five levels of hail impact resistance: from HW1 (10 mm) to HW5 (50 mm). For PV modules, the minimum required resistance level is HW3 (30 mm). This classification not only allows the correct selection of solar modules for a specific region, but can also affect insurance coverage for hail damage. The testing regulations were developed under the guidance of the Cantonal Fire Insurance Association (VKF).

Documentation VKF

At first glance, the VKF testing methodology resembles that of IEC 61215, even using the same impact points, but the ice balls have different density, dimensions, velocity and temperature. Under the VKF regulation, ice density is 0.87 g/cm³, slightly lower than the 0.92 g/cm³ specified in IEC 61215, yet still significantly higher than the average for natural hail, which is 0.64 g/cm³. This slight reduction in ice density leads to a lower terminal velocity of hailstones and, consequently, reduced kinetic energy.

We have added the three hail sizes for testing PV modules under the VKF regulation (red font) to the table of sizes according to IEC 61215 (blue font):

From the table, it can be seen that the minimum protection level under the Swiss VKF regulation must provide resistance to hail impacts with a kinetic energy of 3.51 joules, which is 1.76 times higher than required by the IEC 61215 standard.

SHARP solar modules of the NU‑JC series with an HW4 rating withstand hail with kinetic energy of up to 11.1 J, which is 5.58 times higher than the requirement for mandatory certification.

The VKF regulation provides for the use of ice balls cooled to −20 °C, whereas under the IEC 61215 standard their temperature must be −4 °C.

Specialists from the Swiss SUPSI PVLab laboratory conducted a study by firing artificial hail with diameters of 25, 40 and 70 mm at a Hopkinson bar. They aimed to analyze the pulse shapes generated by impacts of ice balls at −20 °C and −5 °C.

Hail impact −5 °C and −20 °C © SUPSI PVLab

It was found that ice at −20 °C produces a shorter impulse and a higher peak load, significantly increasing the likelihood of local damage to solar modules.

Now, engineers at SUPSI PVLab are developing a new test stand that will allow firing hailstones up to 100 mm in diameter at a velocity of 46 m/s (166 km/h).

As of 25 June 2024, the hail register lists 94 VKF certificates for photovoltaic modules, including brands such as Trina Solar, JA Solar, JinkoSolar and LONGi, which we have previously used in our projects. Of these, 52 certificates confirm hail protection at level HW3, 31 confirm level HW4, and 11 certificates — HW5 (from six manufacturers).

HW5 products are not mass-market. They are primarily building-integrated photovoltaics (BIPV) and so‑called «solar tiles» with thick glass. Among the holders of the fifth protection level, we found only one product that visually resembles mass‑produced modules — the e.Prime M HC from Austrian manufacturer Energetica Industries (unfortunately, now bankrupt). The glass thickness, frame and overall weight of this PV module significantly exceed standard figures. Interestingly, many «solar tile» models, despite an impressive glass thickness of 7 mm (4+3), did not reach the fifth protection class and received only HW4 certification.

HW5 Examples

The PVEL (PV Evolution Labs) laboratory, part of the Kiwa group, conducts its own tests in the United States using ice balls up to 55 mm in diameter. According to data from SPC (Storm Prediction Center) for the period 1995-2019 in the US, in 68% of cases hailstones did not exceed 25 mm in diameter. Thus, the remaining 32% of cases carry a potential risk of damage to solar modules:

© Kiwa PVEL

PVEL offers all interested parties independent testing of solar modules for resistance to hail impacts of various sizes, taking into account the region of use and its associated risk level. Interestingly, PVEL’s tests show that modules with identical structural parameters (size, weight, glass thickness) often yield completely different results. This underscores the critical importance of material quality and manufacturing processes.

Kiwa PVEL Laboratory

The RETC (Renewable Energy Test Center) laboratory, part of the VDE group, also conducts independent tests of photovoltaic modules in the United States. Both laboratories go well beyond the mandatory requirements for hail resistance. In particular, after firing ice balls at the modules, they carry out endurance tests simulating temperature fluctuations and wind loading, which helps uncover hidden damage.

Endurance tests © RETC

Microcracks in the cells, as well as some other types of internal defects, cannot be seen with the naked eye. For this purpose, electroluminescence (EL) imaging is used:

EL test © Clean Energy Associates (CEA)

When a reverse current is applied to the solar module, the cells begin to emit luminescent (non‑thermal) radiation in the near‑infrared range, which is captured by a special camera in the dark. The software analyzes the captured image and automatically classifies the damage by type.

In 2023, RETC specialists conducted a statistical analysis of all their hail tests over more than three years, covering photovoltaic modules from various manufacturers, power ratings, and sizes, and divided them into two groups:

1. Bifacial modules with 2 mm glass on each side;

2. Monofacial modules with 3.2 mm glass and a polymer backsheet.

It turned out that the second group is approximately twice as durable:

PV hail resistance © RETC

This is due both to glass thickness and to glass characteristics. In monofacial modules, tempered glass is generally used, while in bifacial modules thermally strengthened (semi‑tempered) glass is typically employed.

The manufacturing technology for both types is identical: the glass is heated to ~650 °C, then uniformly cooled by air flows on both sides. As a result, the outer layers contract more quickly than the inner ones, generating stress and increasing the glass’s strength. The only difference is that when producing tempered glass, the cooling occurs faster, creating even higher surface stress:

Tempered glass © RETC

Fully tempered glass is not only stronger but also safer, because when shattered it forms numerous small fragments with blunt edges. The problem is that cooling glass less than 3 mm thick makes it very difficult to create the required temperature gradient between the inner and outer layers. Glass with a thickness of 2 mm is simply too thin for full tempering on most production lines, which is why it ends up being semi‑tempered.

As a result, bifacial modules with thin semi‑tempered glass (which describes almost all bifacial modules on the market at present) are extremely sensitive to process errors at every stage: manufacturing, loading, transport, unloading, installation, and operation. The glass in such modules breaks more frequently, sometimes «spontaneously» and for no obvious reason, especially when dealing with excessively large modules.

Alternatively, manufacturers may use thicker glass, establish dedicated tempering lines for thin glass, or employ chemical strengthening, as Corning does in the production of its proprietary Gorilla Glass. All of this will undoubtedly increase manufacturing costs, but will make solar modules more durable.

Hail formation

Hail grains form in powerful updrafts of thunderclouds. Even in summer, the temperature in the upper part of a thundercloud is significantly below zero, which creates conditions for the formation of ice crystals. Hail begins to form when an ice crystal merges with supercooled water droplets that have remained liquid at temperatures down to −40 °C due to the absence of nucleation centres such as aerosol particles or other impurities.

© Min Hee Kim, Jaeyong Lee & Seung-Jae Lee

Updrafts can keep hailstones from falling as they grow. If a thundercloud is large and contains plenty of moisture but only moderately strong updrafts, the result can be a large amount of small hailstones. A more powerful updraft can hold large hailstones aloft, allowing them to become even larger. In some cases, a supercooled droplet can turn into a hailstone the size of a baseball (over 70 mm in diameter) in just 20-30 minutes.

Supercells, which are powerful thunderstorm clouds with a rotating updraft (mesocyclone), amplify this process. Conditions inside supercells promote the intensive growth of ice crystals, leading to the formation of large hailstones.

Supercell structure © Kelvinsong

Statistics and trends

In May 2019, hail damaged about 400 thousand PV modules at the Midway Solar power plant in West Texas, resulting in previously unimaginable insurance losses of 80 million dollars. The danger of hailfall is greatest in regions where cold, dry air masses meet warm, moist air, as well as in mountainous areas where the terrain enhances convection.

In the USA, a region known as «Hail Alley» is particularly famous for its exceptionally large hailstones. This area covers much of the Central High Plains, including Denver. Its high elevation leads to the formation of deeper cold layers within thunderclouds. Large hail is also common in India and Bangladesh, Central Europe, eastern Australia, the prairies of central Argentina, and parts of the Sahel in central Africa.

In most parts of the world, large hail is a rare phenomenon. The map below shows the global average annual probability of large hail, normalized per 100×100 km area, for the period from 1979 to 2015 according to the US National Center for Atmospheric Research (NCAR):

© National Center for Atmospheric Research, USA

In Europe, large hail is quite often recorded in the Alps (Slovenia, Austria, Switzerland, northern Italy) and the Pyrenees (border between Spain and France, Andorra). The map below shows the annual number of hail events in Europe for the period from 2004 to 2014 according to the European Environment Agency (EEA):

© European Environment Agency (EEA)

Climate change is making large hail increasingly frequent both worldwide and on the European continent. In 2023, the ESWD (European Severe Weather Database) received 9 627 reports of large hail (diameter over 20 mm). Out of these, 1 931 reports concerned very large hail (>50 mm), and 92 reports concerned giant hail (>100 mm). All three figures were the highest ever recorded in the database, making 2023 the third consecutive record hail season:

© European Severe Weather Database (ESWD)

Italy was hit hard on 19 June 2023, when three supercells produced hailstones up to 10, 14 and 16 cm in diameter. A hailstone about 16 cm in size fell in Carmignano di Brenta, setting a new record for European hailstone size. In dozens of villages and towns, cars, roofs and windows were damaged, and at least 111 people were injured.

The new record stood for just five days, and on 24 June Europe was struck by the true «hail of the year», when 855 reports were submitted to ESWD in a single day. Heavy hail was observed in France, Switzerland, Italy, Slovenia, Croatia, Austria, the Czech Republic and Slovakia. 119 people were injured, all in Italy. The hail caused significant damage, including damage to solar panels and complete shattering of the windshields of many cars. The largest hail fell in the Italian town of Azzano Decimo, where a chunk of ice measuring 19 centimetres was discovered:

Largest hailstone in Europe © Marilena Tonin

This find is very close to the world record set on 23 July 2010 in Vivian, South Dakota, when an 8‑inch hailstone (20.3 cm) was recorded. It should be noted that Azzano Decimo was struck by giant hail twice in two years. Professional photographer and «storm chaser» Marko Korošec photographed the damage to photovoltaic modules following the record hail in Azzano Decimo on 24 June 2023:

PV modules shattered by record hail © Marko Korošec

For Bulgaria, 2023 also proved to be very rich in large hail. A record report was received on 6 August 2023 from the town of Dulovo in Silistra Province. Fortunately, there were no casualties, but crops were damaged, and houses and cars were affected. Hailstones reached 13 centimetres in diameter (orange triangle on the map):

© European Severe Weather Database (ESWD)

Fighting hail

Hail causes significant damage to crops, fruit, vehicles, buildings, domestic animals and people, prompting farmers and property owners to seek protective measures. Combating this phenomenon is a pressing challenge; however, assessing the effectiveness of different methods remains difficult due to natural conditions that prevent precise and controlled experimentation.

Cloud seeding with ice‑forming agents is one of the best‑known methods for fighting hail. This method involves introducing particles of silver iodide (AgI) or «dry ice» (solid carbon dioxide) into thunderclouds. Microscopic particles are captured by supercooled droplets, transforming into crystals that become hail embryos. These artificial crystals compete with natural ones for the available moisture in the cloud, which leads to the formation of numerous small hailstones instead of a smaller number of larger ones.

© North Dakota Cloud Modification Project

Despite decades of research and application, the effectiveness of cloud seeding remains a matter of debate among scientists, and reports of its efficacy are highly contradictory. Data show that sometimes cloud seeding can have the opposite effect. Moreover, questions remain regarding the environmental safety of this method, as the long‑term effects of silver iodide on the environment are not yet fully understood.

Silver iodide © Ice Crystal Engineering (ICE)

Another well‑known method of fighting hail is firing acoustic cannons — a practice in use for over 100 years. These devices generate sound shock waves directed vertically upward, which theoretically should prevent hail formation in clouds. However, the effectiveness of acoustic hail cannons has not been confirmed by scientific studies.

Exhibition of hail cannons in Padua, Italy

Hail cannons were a fashionable farmers’ pastime in Europe between 1896 and 1905, after which their widespread use was abandoned due to extreme ineffectiveness. Some farmers still purchase and use hail cannons today:

Hail cannon © Stephen Kloosterman

Assessing the effectiveness of hail mitigation methods is extremely challenging due to the uniqueness of each thunderstorm cloud and the impossibility of creating identical conditions for comparison. Unlike laboratory studies with controlled variables, weather conditions vary, making it difficult to draw conclusions about the real‑world efficacy of the technologies used. At the same time, continuing scientific research and refining statistical evaluation methods are crucial for finding reliable and safe solutions.

On the other hand, even successful weather modification in one region can lead to unpredictable consequences in others. From this perspective, passive protection of property using modern ultra‑durable materials seems more sensible than actively altering the weather. For example, a reliable way to protect crops from hail may be the use of strong, elastic knitted anti‑hail nets:

Anti‑hail nets © Agroflor

Slight shading provided by such nets often benefits many agricultural crops, but for a solar power plant this would mean a loss of power. To enhance the level of passive protection of PV modules against hail, more durable and resilient glass with a sufficiently high light transmittance coefficient is required.

Risk reduction

Although it is impossible to completely eliminate the risk of solar panels being damaged by hail, we can reduce the likelihood of such damage or mitigate its consequences. Here are seven tips from NENCOM for protecting your investment in a photovoltaic system:

1. Purchase PV modules only from reputable manufacturers and through official distributors. Price should not be the determining factor when selecting components for a solar power plant. The market contains a large number of low‑quality products and counterfeits of well‑known brands. Key selection criteria include a long track record, an impeccable reputation and the financial stability of the manufacturers. Almost all manufacturers offer multi‑year warranties on solar modules, but most will cease to exist long before the warranty period expires.

2. Do not buy PV modules of large size without a clear necessity, especially for residential systems. The larger the glass area, the less resistant it is to hail impacts under equal conditions. The optimal size of a solar module for a residential photovoltaic system — no more than 2 m². In recent years, we have observed a trend toward using large PV modules intended for commercial systems in residential installations, due to their lower cost per 1 Wp (watt‑peak). Such modules are optimal for constructing large ground‑mounted power plants, but not for mounting on the roof of a private house.

3. Trust the installation of photovoltaic modules to experienced professionals who strictly follow the manufacturer’s instructions. Do not forget that violating the rules for transporting, unloading, storing, and installing solar modules leads to the annulment of the warranty.

Installation of PV modules © NENCOM

Improper installation also increases the likelihood of damage in strong wind or hail. Keep in mind that any damage to solar panels caused during force majeure events or natural disasters, including lightning and hail, is not covered by the warranty.

4. It is advisable to install PV modules at an angle of at least 15° to the horizontal surface, where possible. The greater the tilt angle, the fewer hailstones will strike the module (due to the smaller projected area), and the lower the energy of their impacts.

PV modules tilted at 60° © NENCOM

Of course, strong wind during hail can introduce unpredictable variations. In any case, a tilt of 15° or more ensures effective self‑cleaning of solar modules during rain. When choosing the optimal tilt angle in each specific case, you need to take into account many factors, including the installation site, wind load, cost of the mounting structure, azimuth, energy consumption schedule, and much more. Consult a professional for advice.

5. Make sure to insure your photovoltaic system. Carefully review the insurance contract: it may contain numerous exclusions and stipulations, especially in regions with complex climatic conditions. Some insurance companies may refuse to insure photovoltaic modules. A reputable manufacturer and the presence of a certificate confirming enhanced hail resistance will increase your chances of securing a policy or reduce the insurance cost.

6. If you own a small photovoltaic system consisting of several modules with easy access to them (boat, camper, flat roof of a house or ground-mounted installation) — keep suitable protective materials on hand and monitor the weather forecast. One possible solution — a sturdy three-layer air-bubble film:

Purchase a roll 150 cm wide and cut the film into individual sheets with some allowance. For example, if the module size is 113×172 cm, prepare sheets of film sized 150×200 cm. As a practice, try securing the protective film on one module using reinforced adhesive tape. Wrap the edges of the film around the aluminum frame and make several turns of tape around the module. Try not to stick the tape directly to the solar module — only to the film, so that you can easily remove the protection later. Make sure that the film is secured firmly and will not be blown away by the wind.

When expecting large hail, use several layers of bubble-wrap film. In case of giant hail, you can place a sheet of plywood slightly larger than the module between the layers of film to distribute the impact energy across the entire surface, including the frame. Improvise based on your experience and the specific situation.

Do not take risks! If hail has already started and you have not managed to install protection on the solar modules — keep yourself and your loved ones safe by staying in shelter.

7. Keep in mind that PV modules broken by hail can, in some cases, cause a fire due to the formation of an electric arc on damaged busbars. For example, on December 20, 2018, severe hail struck Sydney (Australia), damaging many cars and house roofs. A 200 kW solar power plant installed on the roof of Tacca Industries five years earlier was also affected. Although the PV modules were disconnected from the load after the storm, three days later they caught fire:

The PV modules burned after hail © Tacca

Ignition of damaged panels can occur in sunny weather, especially under load when they produce a lot of energy. The «old‑type» modules — with square cells and a small number of busbars — are more susceptible to this risk. Modules with «Half-cut cell» and «Multi-bus bar» technologies are less exposed to this risk due to a more even distribution of current within the module.

Therefore, after the panels have been damaged it is very important to take prompt measures by consulting specialists. Photovoltaic modules produce direct current (DC), the arc of which is much more stable and dangerous than the arc of alternating current (AC):

DC electrical arc ~600W © NENCOM

Additional materials

In this section, we have compiled several scientific studies related to hail formation, its forecasting methods, and damage reduction:

Hail Hazard Research