Scientists from the University of Évora in Portugal have analyzed the performance of three photovoltaic plants in Spain and Portugal during four extreme heat events recorded between 2024 and 2025. They found that heatwaves can cause significant yield losses concentrated during the hottest hours of the day, while also exposing limitations in conventional methods used to forecast PV energy production.
High temperatures reduce the efficiency of crystalline silicon modules by around 0.3% to 0.5% for each degree Celsius above 25 C. During heatwaves, module temperatures can exceed 70 C, accelerating the degradation of encapsulants, cables, and other components, while also triggering thermal derating in inverters.
In the study “Analysis of photovoltaic power plant resilience under Iberian heatwaves,” published in the International Journal of Climate Change Strategies and Management., the researchers explained they analyzed hourly production data from three PV plants: Zebro in Portugal (37.06 kW), Ariza in Zaragoza, Spain (15 kW), and Amibil, also in Zaragoza (64.5 kW).
The researchers compared production data with meteorological information from the ERA5-Land reanalysis dataset, which was validated using a weather station installed alongside the Amibil plant. The comparison showed strong agreement, with correlation coefficients of up to 0.95 for air temperature and 0.98 for global horizontal irradiance (GHI), confirming the suitability of ERA5-Land for the analysis.
The team examined four heatwaves officially identified by Spain’s AEMET and Portugal’s IPMA weather agencies: two in Spain (July–August 2024 and June 2025) and two in Portugal (August 2024 and May–June 2025). In addition to maximum temperatures, the researchers assessed heatwave intensity using cumulative hours above 35 C (DH35).
The 2024 events were found to be the most severe, with maximum temperatures reaching 39.4 C in Portugal and 38.9 C in Spain.
The results showed that yield losses were concentrated over a limited number of hours, coinciding with the highest module and inverter temperatures. The largest hourly decline in performance ratio (PR) reached 90.4% at the Amibil plant during the 2024 Spanish heatwave, while the largest daily loss was recorded at the Zebro plant, where output fell by 17.6% during the 2025 Portuguese heatwave.
However, the researchers noted that PV performance generally recovered on the same day or the following day once thermal stress decreased.
The study attributes the losses mainly to higher operating temperatures and inverter thermal derating rather than to the overall duration of heatwaves. Short periods of extreme temperatures outside officially classified heatwave periods were also found to cause comparable reductions in output.
A key part of the research involved comparing PVsyst simulations based on Typical Meteorological Year (TMY) data with simulations using actual ERA5-Land weather inputs. The authors found that relying exclusively on TMY datasets can systematically overestimate PV generation during extreme heat events.
To measure the difference, the researchers calculated Energy Not Served (ENS), defined as the gap between energy predicted using TMY data and the electricity actually produced. The largest discrepancies were observed at the Zebro plant during the second Portuguese heatwave, while the highest relative deviation occurred at Ariza during the 2025 Spanish heatwave.
According to the researchers, these findings show that typical meteorological years do not sufficiently capture the growing impact of extreme weather events on PV performance.
The authors conclude that the challenge for the European solar sector is increasingly shifting from maximizing annual generation to improving the resilience of PV installations against recurring production losses during periods of extreme heat.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: [email protected].
Comments
Please login to comment
Thursday, July 16, 2026
4:00 pm – 5:00 pm CEST, Berlin, Paris, Madrid
Tuesday, July 14, 2026
6:00 am – 7:00 am CEST, Berlin, Paris, Madrid
The June issue of pv magazine Global is out now!
Available in print and digital – get your copy today!
Thursday, September 9, 2026
11:00 am – 12:30 pm CEST, Berlin, Paris, Madrid
pv magazine USA hosts its third multi-day virtual event on advancing U.S. solar and energy storage markets, covering financing, supply chains, and distributed energy’s role in grid resilience.
Entries open in seven categories: Modules, Inverters, BoS, BESS, Manufacturing, Sustainability, Projects.
April 01 – August 31, 2026
A two-day conference in Austin, Texas, bringing together leaders in US solar manufacturing, equipment specification, and factory execution.
Saudi Arabia is accelerating its clean energy transition—join the SunRise Arabia Clean Energy Conference 2026 in Riyadh to explore how solar PV and energy storage are powering its digital economy.
Showcase your brand across all our platforms: from 13 websites in 7 languages to our magazines, daily newsletters, industry events and more. Reach your audience the right way!
You have no items in your basket.
