From hail in the Midwest to hurricanes in the Southeast, wildfires in the West and dust storms in the Southwest, US solar projects face location-specific threats potentially causing billions of dollars in annual losses. Modules and inverters get the most focus in protection efforts, while measurement technology, especially pyranometers and reference devices, is often overlooked. Yet accurate irradiance data is essential for performance monitoring, warranty claims, and sound operational decisions, whatever the weather.
Irradiance data is vital for distinguishing weather-related underperformance from equipment failure. Advanced sensors offer precise, temperature-compensated measurements, but data can be misleading if it is compromised by extreme weather, causing further problems for a project. To ensure reliability in less than ideal conditions, sensors need to be chosen, installed and operated with local risks taken into consideration.
Hail hazards
Hail has been the most damaging type of extreme weather to PV sites in recent years. Pyranometers, often mounted on tracker arms or high points, are directly exposed. While domed glass, the de facto standard shape, helps deflect impacts, it’s critical to have a pyranometer with sufficiently strong dome material, such as borosilicate glass, which features strong resistance to cracking and shattering.
Sites in Europe and the US Midwest, where hail is becoming increasingly frequent, have shown that material resilience is more important than added shielding. Mechanical protection adds cost and complexity, while choosing a pyranometer with more robust dome materials offers reliable, low-maintenance defense.
Beyond equipment spec, post-event inspections are essential. Even if domes appear intact, microcracks or internal misalignment can affect accuracy. Quick checks after a hailstorm help maintain data reliability.
Lightning and surges
Lightning-induced surges are a serious threat to pyranometers, especially at sites with long cable runs and elevated mounting points. Even with surge protection devices (SPDs) in place, improper grounding or other design flaws often lead to sensor failure. Effective protection against lightning for sensors and a whole system requires a comprehensive strategy that goes well beyond just installing SPDs.
Tracker booms or pyranometers mounted high on masts are also more exposed to lightning. Mechanical protection like nearby rods may help but cannot replace electrical safeguards. Ultimately, a layered defense including SPDs, grounding, clean cable layout, and routine checks is the best way to protect data integrity. These practices are critical for developers to maintain reliable irradiance data and avoid costly sensor replacement or downtime.
Rain and flooding
Even if mounted above flood levels, sensors can suffer from long-term moisture damage from being close to water. Enclosures rated at least IP66, quality seals, and corrosion-resistant connectors are essential. In flood-prone zones, elevated wiring and raised conduits can add further protection. Post-storm inspections can spot early issues like moisture ingress or signal loss, preventing long-term degradation.
Heavy snow
In snowy climates, heated pyranometers and ventilators help manage frost and light snow, but are less effective in extreme cold or during “snow bridging” – when snow arches over the dome without actually touching it. This insulates the snow from any heat, rendering internal heaters inside the sensor ineffective. In these cases, manual clearing or additional snow management measures are often necessary to maintain continuous irradiance data.
Extreme heat
Sustained high temperatures can cause sensor drift, degrade materials, and shorten cable life. This can be combated with temperature-compensated sensors and UV-resistant high-temp cabling.
Heat-absorbing surfaces should also be avoided. Materials within the sensor, such as adhesives, seals, and electronic circuits may degrade more rapidly when regularly exposed to temperatures over 50 C to 60 C.
Selecting temperature-compensated sensors with robust thermal design and validating their performance with field data is essential. Sites in extreme heat zones may also require more frequent calibration intervals to ensure long-term data accuracy. Likewise, securing and routing cables thoughtfully can reduce strain and extend operational life under extreme heat conditions.
Dust and sand
In arid regions like the US Southwest, dust storms and persistent airborne particles can significantly increase soiling on sensors, leading to skewed irradiance data and a mismatch with actual plant performance. Lessons from long-term operations in the Middle East and North Africa have shown that consistent cleaning protocols are effective in maintaining data accuracy. Sensor ventilators have shown mixed results in these environments, as they tend to clog or fail under prolonged exposure to dust and sand. Some operators also deploy dual sensors: one cleaned regularly and one left soiled, to model soiling loss over time.
Beyond soiling, sand-laden winds can cause long-term abrasion and pitting on pyranometer domes. This wear reduces optical clarity and impairs measurement precision. Using non-abrasive cloths and deionized water, and avoiding dry wiping, is essential to protect the optical surface during maintenance.
Data resilience
As extreme weather becomes a permanent fixture of the US solar landscape, developers must rethink how they design and maintain performance monitoring systems. Especially in light of new financial pressures on US developers and asset owners, investing in high-quality monitoring equipment and knowing how to maintain their accuracy has never been more critical.
Sensors that are engineered for longevity and environmental resilience help minimize O&M costs over the system’s life. Reliable irradiance measurements depend on durable hardware and a well-considered system strategy, both of which also ensure that sensors perform consistently across a wide range of conditions, offering the most accurate performance data possible throughout their service life and your site’s lifespan.
About the author
With over two decades of experience in meteorological and irradiance instrumentation, Wayne Burnett serves as the CTO of EKO Instruments USA, where he supports advanced measurement solutions for the renewable energy sector.
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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