Seasonal forecasts suggest the upcoming Australian summer is likely to see cloudier than usual conditions, potentially reducing solar generation across key regions, especially along the East Coast. The El Niño-Southern Oscillation (ENSO) is forecast to remain neutral or briefly shift into a weak La Niña phase, slightly increasing the likelihood of wetter, cloudier conditions in the region. Analysis of historical Neutral and La Nina years shows irradiance is typically down up to 10% though fortunately impacts are lower in some solar-rich regions.
Forecast models from major agencies, including ECMWF, DWD, and UKMO, indicate a consensus for likely above-average cloud cover across much of Australia during the summer months. The East Coast, which has a high concentration of rooftop solar, is expected to experience increased cloud anomalies, likely due to moisture from the Pacific.
However, areas just inland of the Great Dividing Range, where many large utility-scale solar farms are located, are less likely to see significant cloud anomalies, as the range acts as a natural barrier to Pacific moisture. Notably, Melbourne, a key population centre and source of distributed generation, stands apart from the broader forecast showing no clear indication of increased cloud cover in the seasonal outlook.
Historical analysis using data from the Solcast API aligns with these seasonal forecast predictions. By examining the historical irradiance patterns during non-El Niño summers, similar trends emerge, with cloudier-than-average conditions concentrated along the East and West Coasts.
Inland areas west of the Great Dividing Range have historically experienced smaller reductions in irradiance, supporting solar performance in regions critical to Australia's utility-scale solar sector. The southeastern state of Victoria, including Melbourne, has shown near-typical irradiance levels under similar climatic conditions, reinforcing the seasonal model's projections for the region.
The ENSO phase plays a pivotal role in shaping Australia's weather patterns. La Niña events typically lead to wetter, cloudier summers in eastern Australia, in stark contrast to the drier, sunnier conditions seen during El Niño phases. While neutral ENSO conditions are the most likely outcome this summer, there is a slight chance of a weak La Niña forming. Current forecasts suggest that if La Niña does develop, it will likely be short-lived, minimising its potential impact.
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