Researcher(s)
- Lucy Zimolka, Meteorology and Climatology, University of Delaware
Faculty Mentor(s)
- Kelsey Malloy, Geography and Spatial Sciences, University of Delaware
Abstract
As solar energy has become an increasingly important part of our electric grid, it is important to understand the weather conditions that reduce solar power production. Prolonged periods of unusually low surface solar radiation, known as solar suppression events, can decrease the amount of energy produced by solar panels and reduce solar energy generation. This study investigates meteorological conditions associated with these events to help maintain a reliable electrical grid and improve solar energy forecasting
Summer (June-August) ERA5 reanalysis data from 2000-2025 were analyzed for the southeast and southwest regions of the United States. Datasets including cloud cover, geopotential height, mean sea level pressure, relative humidity, temperature, vertical velocity, and surface solar radiation downward were tested. Solar suppression events were defined as periods when surface solar radiation fell below the 10th percentile threshold, and conditions meeting this criteria were analyzed for the Southeast, Southwest, and a combined dataset. Weather conditions during solar suppression events were compared to average summer conditions using anomaly maps, composite maps, and time series analyses in Python.
The Southeast experienced 466 solar suppression days, while the Southwest experienced only 13. During these events, the Southeast had a greater cloud cover (52%) than the Southwest (32%), indicating that increased cloudiness is a major contributor to reduced solar radiation. In addition, the southeast showed stronger upward vertical motion, which helps support cloud formation and prolonged cloudy conditions. Mean sea level pressure is the strongest signal, with the southwest showing a negative anomaly and the southeast showing a positive anomaly. The opposite signs could indicate different large-scale weather patterns affecting each region.
These findings improve our understanding of the weather patterns responsible for prolonged periods of low solar radiation and can help improve solar energy forecasting as renewable energy becomes a larger part of the electrical grid.