Europe's July heatwave brought unusually high solar irradiance across much of western Europe, according to analysis using the Solcast API. Persistent high-pressure systems limited cloud formation across the west and north of the continent, lifting irradiance well above typical July levels. At the same time, however, wildfires in France and Spain, together with Saharan dust outbreaks across the Mediterranean, added aerosols to the atmosphere and increased the risk of panel soiling.
Strong Positive Anomalies Across Western and Northern Europe
The strongest positive irradiance anomalies were recorded across western and northern Europe, where cloud cover was suppressed for much of the month. Southern England, Wales and Ireland saw irradiance up to 35% above usual July levels, while northern France, the Low Countries and western Germany were up by around 25%. Southern Norway and Sweden recorded irradiance around 15% above usual.
These conditions were linked to the same slow-moving high-pressure systems that drove the month's extreme heat. High pressure tends to stabilise the lower atmosphere and reduce cloud development. However, the continued high temperatures from June into July will have reduced PV module efficiency, partly offsetting the benefit of higher irradiance.
Southern Europe: Wildfire Smoke and Saharan Dust Take a Toll
Across southern Europe, wildfire smoke and Saharan dust reduced the benefit of otherwise clear, high-irradiance summer conditions. Smoke from these fires reduced clear-sky irradiance across parts of southern France and Spain, with some smoke also spreading into neighbouring areas. Saharan dust outbreaks also crossed the Mediterranean at times, adding haze across parts of Spain, Italy and Greece.
In southern Spain, where July irradiance is normally high at around 8.1 kWh/m² per day, monthly irradiance fell by as much as 4% to around 7.7 kWh/m², with larger reductions during individual smoke or dust events.
Soiling Risk: A Growing Concern for PV Operators
Aerosols not only reduced irradiance but also created a soiling risk where particles settled on PV modules and were not removed by rain or cleaning. Using PM2.5 and PM10 concentrations in the HSU soiling loss model, Solcast estimated significant end-of-month soiling impacts for uncleaned panels across several locations.
In Valencia, the estimated soiling impact reached 5.6%. This reflected both smoke from the nearby Vall d'Uixo wildfire and repeated Saharan dust episodes, with no appreciable rainfall events to clean panels during the month.
Madrid saw a lower estimated impact of 2.2%, where nearby fire impacts were less prolonged and Saharan dust was less significant. In Bordeaux, nearby wildfires brought intense smoke pollution late in July, but rainfall events limited the estimated soiling impact to a peak of 0.6%.
Local Conditions Drive Different Operational Risks
The site-level soiling estimates show how similar regional aerosol conditions translated into different operational risks depending on local particulate exposure and whether enough rainfall occurred to clean module surfaces.
Valencia represented the high-accumulation case. PM10 exposure persisted through several parts of the month, while limited rainfall meant the modelled soiling loss continued to rise. Madrid provided a more moderate example. PM10 levels were lower than Valencia, and the modelled soiling loss increased more slowly, limiting the end-of-month impact. Bordeaux offered a contrasting case. Particulate levels increased late in the month, but rainfall limited accumulation on uncleaned panels and kept the modelled soiling impact low.
Broader Context: A Year of Extreme Solar Resource
The July heatwave and irradiance anomalies continue a trend of extreme solar resource variability across Europe in 2026. Most of Europe saw significantly more solar than normal across the first half of 2026. Analysis using the Solcast API shows that much of Europe recorded irradiance between 5% and 10% above the long-term average during the first six months of the year.
The pattern began in winter, when cold, dry air reduced cloud cover across parts of eastern and northern Europe, boosting irradiance even as storm systems reduced solar resources in the west. Spring further reinforced this surplus trend. With El Niño conditions developing from April onwards, the positive anomaly is forecast to persist into year end, particularly across central and western areas, with some regions finishing around 5% above normal.
Implications for PV Operators
For solar asset owners and operators across Europe, the July weather patterns present a mixed picture. While northern and western Europe benefited from exceptional irradiance gains, the efficiency losses from elevated temperatures and the soiling risks in the south require careful management.
Solcast's analysis underscores the importance of dynamic soiling modelling for PV operations. By explicitly modelling soiling rates for specific project locations, operators can move beyond static derate factors and simulate dynamic dust accumulation and rainfall cleaning events, supporting data-based cleaning planning and more accurate loss factor modelling.
As climate variability intensifies and extreme weather events become more frequent, the ability to anticipate and respond to regional irradiance anomalies and soiling risks will be essential for optimising PV performance across the continent.
