Heatwaves Slash Solar Output Up to 90% in Iberia

Heatwaves can wipe out up to 90% of hourly solar output in Iberian PV plants

Researchers from the University of Évora in Portugal measured a dramatic, short‑term drop in photovoltaic (PV) performance during extreme heat events on the Iberian Peninsula. In the worst hour recorded – at the Amibil plant in Zaragoza during the 2024 Spanish heatwave – the performance ratio (PR) fell to 90.4 % below normal, meaning the plant produced only about one‑tenth of its expected power for that hour. Similar hourly crashes were seen at the other two sites, with daily losses of up to 17.6 % at the Zebro plant in Portugal during the 2025 heatwave. The study shows that the biggest losses happen during the hottest hours, when module temperatures can exceed 70 °C and inverters thermally derate.

---

Why extreme heat hurts solar panels and inverters

Solar modules lose efficiency as they get hotter: each degree Celsius above the 25 °C reference reduces crystalline‑silicon output by 0.3 %–0.5 %. High ambient temperatures can lead to panel surface temperatures well above 70 °C, triggering the steep efficiency drop recorded in the study. Inverters, which convert DC to AC, also have built‑in thermal protection that reduces their output when internal temperatures rise, a phenomenon known as thermal derating.

The researchers linked the hourly PR collapse to both module heating and inverter derating, rather than the overall length of the heatwave. Short spikes of extreme temperature – even outside the officially defined heatwave periods – produced comparable output cuts, underscoring that it is the peak temperature, not the duration, that matters most.

---

How the study measured the loss

The team examined hourly production data from three small‑scale PV plants – Zebro (37.06 kW, Portugal), Ariza (15 kW, Zaragoza, Spain) and Amibil (64.5 kW, Zaragoza) – across four heatwave events recorded between 2024 and 2025. They paired the production records with meteorological data from the ERA5‑Land reanalysis dataset, which they validated against a weather station installed next to the Amibil plant. Correlation coefficients reached 0.95 for air temperature and 0.98 for global horizontal irradiance (GHI), confirming the reliability of the ERA5‑Land inputs.

To quantify the forecasting error, the researchers compared the actual output with PV‑syst simulations that used the traditional Typical Meteorological Year (TMY) data. The gap – called Energy Not Served (ENS) – was largest during the second Portuguese heatwave at Zebro and peaked relative to TMY predictions at Ariza during the 2025 Spanish event. This demonstrates that TMY‑based models can substantially overestimate generation during extreme heat, because they smooth out the short, intense temperature spikes that cause the biggest losses.

---

What the findings mean for the European solar sector

The authors argue that the industry’s focus must shift from maximizing annual energy yield to building resilience against recurring, hour‑scale losses. As climate change drives more frequent and intense heatwaves across Southern Europe, operators will need to:

1. Select modules with lower temperature coefficients to better tolerate high temperatures.
2. Design inverter cooling and placement to minimise thermal derating – for example, ensuring adequate airflow and shading from direct sun, as discussed in technical guidance on inverter thermal derating.
3. Incorporate high‑resolution weather data (like ERA5‑Land) into performance forecasts and O&M planning, rather than relying solely on TMY datasets.

These steps can reduce the risk of sudden output drops that threaten grid stability, especially during peak‑demand summer afternoons.

---

What it means for Israel

Israel’s solar market faces a similar climate challenge: summer temperatures regularly exceed 35 °C, and rooftop installations can see panel temperatures well above 70 °C on sunny days. Using the typical Israeli residential tariff of ₪0.48/kWh and a typical 10 kWp home system (which yields about 17 000 kWh/year in the central region), a heat‑induced 10 % hourly loss would noticeably reduce revenue for that hour and could extend the simple payback period beyond the usual estimate.

For Israeli installers, the lesson is clear: choosing modules with lower temperature coefficients and ensuring proper inverter ventilation can protect both revenue and system longevity. Homeowners can also mitigate heat effects by adding passive cooling (e.g., reflective back‑sheet, increased spacing) or active cooling (small fans) to keep panel temperatures down.

---

Looking ahead

The Iberian study is a timely reminder that climate‑driven performance volatility is becoming a core design consideration for solar developers worldwide. As heatwaves intensify, the industry will likely see a rise in temperature‑resilient technologies, more sophisticated weather‑aware forecasting tools, and stricter O&M standards. For Israel, adopting these practices now will help keep rooftop solar profitable and reliable, even as summer heat climbs.

---

Sources

• Original study summary from PV‑Magazine
• Detailed journal article in the International Journal of Climate Change Strategies and Management (Emerald)
• Technical background on inverter thermal derating from Aforenergy
• ERA5‑Land validation study (SolarGIS)

Sources & further reading

• Analysis of photovoltaic power plant resilience under Iberian...
• Analysis of photovoltaic power plant resilience under Iberian heatwaves | International Journal of Climate Change Strategies and Management | Emerald Publishing
• S ANNUAL REPORT - IEA-PVPS
• Analysis of photovoltaic power plant resilience under Iberian heatwaves...
• Inverter Thermal Derating: Maximize Solar Efficiency & Output - Aforenergy