As predicted earlier in the year, the more powerful than usual 2026 El Niño weather pattern in the Pacific has contributed to significant changes in historical solar irradiance patterns on a worldwide basis. This has resulted in major variations in regional performance of photovoltaic power generation projects from baseline projections. Some regions did better than usual, others did worse.
New research from Slovakia-based solar data and software provider Solargis shows that global horizontal irradiance (GHI) levels – the amount of solar radiation reaching a horizontal surface on the ground — departed from long-term seasonal averages, in some places by over 30%. The latest analysis of the June-July-August (Northern Hemisphere summer) season attributes much of this variation to El Niño and widespread areas experiencing higher-than-normal temperatures.
Key findings from the most recent seasonal study include the following:
In North America, the report said, GHI anomalies varied substantially between individual months of the summer season, resulting in a relatively balanced seasonal signal across much of continent overall. The most pronounced anomalies in the continental United States occurred across the central regions, where temperatures exceeded 2.5°C above the long-term average.
Air temperatures across northern Canada were about 4°C above historical averages. The combination of exceptionally warm and dry conditions contributed to widespread wildfire activity across the region, the report said.
“Summer 2026 has demonstrated the extent to which solar resource conditions can diverge from historical averages across major markets,” said Marcel Suri, CEO of Solargis. “For asset owners and investors, understanding the extent to which these variations are weather-driven is essential when assessing performance. Historical data remains fundamental to solar resource assessment, but it needs to be complemented by current, high-resolution resource information to provide an accurate picture of changing conditions.”
Suri points out that variations in the solar resource may be due to a number of complicating factors that are not easily measured or accounted for with historical data and forecasting models. These variations can make it more difficult for solar investors and asset owners to distinguish weather-driven changes in generation from genuine asset underperformance.
Moreover, there is not necessarily a direct correlation between GHI and solar resources. The aforementioned Canadian wildfires, in addition to potentially threatening physical generating and transmission infrastructure, produce smoke that lowers irradiance levels and PV output for projects affected by the resulting smoke and persistent haze.
Lack of rain can also reduce PV output. Recent analysis from Australia-based solar analytics firm Solcast noted that modeled soiling loss near Dallas, Texas, rose towards 2% by the end of August, the highest late-August value in the last 20 years. The increase primarily reflected the absence of rainfall to wash accumulated material from modules, the report said.
Solargis’ Suri says that current resource data is essential for understanding the drivers of measured performance where conditions depart significantly from long-term expectations: “Developers and operators of solar power plants will require ongoing sources of weather information to incorporate extreme conditions in their technical planning and financial models.”
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