Electric grids powered by renewables like wind and solar energy are less vulnerable to blackouts, according to a new study. The findings answer a major worry about so-called weather-dependent sources of renewable energy that has driven backlash to these technologies in some areas.

“The impacts of fluctuating renewable energy sources (RESs) have been widely debated throughout the global energy transition,” says study team member Fangxing Li, who studies the design and operation of electric power systems at the University of Tennessee in Knoxville.

Solar and wind power can’t simply be fired up whenever they are needed, and some people have suggested that weather-dependent renewables make grids more unstable during extreme weather conditions. High-profile power failures during extreme weather events have sometimes been blamed on renewables, leading to a backlash to wind and solar power in some places.

But other researchers have argued that wind and solar power tend to be available even during wild weather, and there has been little hard data to sort out the real story. “Given the ambitious goals for high penetration of RESs and carbon emissions reduction in future power systems, a comprehensive understanding of RES roles in blackouts is urgently needed,” says Li.

Li and his collaborators analyzed data on 2,156 blackouts that affected 378 cities across the 48 continental U.S. states between 2001 and 2020. They combined this with data on weather conditions and the proportion of wind and solar integrated into regional grids to determine the effect of both weather conditions and renewables on blackouts.

Power systems with a higher proportion of weather-dependent renewables are not more vulnerable to blackouts, the researchers report in Nature Energy. In fact, the blackouts that do occur in these heavily renewable grids are likely to be less intense, with fewer affected customers, shorter duration, and/or a less pronounced mismatch between electricity demand and supply.

What’s more, blackout frequency decreases as renewables penetration increases. And the greater the proportion of renewables in the grid, the less renewables actually contribute to blackouts. This greater resiliency of high-renewable grids is likely due to the fact that renewables tend to be part of modernized power systems with up-to-date planning and operation. However, the researchers intend to conduct further investigations to determine the reasons behind their observations, Li reports.

The team also used a deep learning computer model to understand the typical climate conditions when blackouts happen, zeroing in on hot, dry, windy days in summer and spring and autumn storms. Power system operators need to plan ahead to ensure stability of the electricity supply when such conditions are forecast, the researchers say.

Not surprisingly, grids are more vulnerable to blackouts during extreme weather. But high-renewable grids are not more so. Renewables are not responsible for blackouts in bad weather conditions, the analysis indicates.

Instead, blackouts happen because of bad weather and bad luck: “it is likely because extremely high or low temperatures burden the power system with a considerable demand increase; then, other non-natural disturbances (for example, vandalism, equipment failure and so on) become ‘the final straw’ leading to blackouts,” the researchers write.

The findings suggest electrical grids that are heavily reliant on solar and wind power are not fragile or unreliable as is sometimes assumed. However, more analyses of other power systems with different scales and different degrees of interconnection will be needed to understand how general this pattern is, the researchers say.

Source: Zhao J. et al. “Impacts of renewable energy resources on the weather vulnerability of power systems.” Nature Energy 2024.

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