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New research shows that compound energy droughts – when the grid loses both wind and solar energy inputs – can last nearly a week in some parts of the United States.
In a paper published in the journal Renewable Energy, a team at the Pacific Northwest National Laboratory (PNNL) explains that grid operators need to know where and when energy droughts will occur and how long they will last so that they can prepare to pull energy from different sources and manage grid-level battery systems that can store enough electricity to deploy during times when energy is needed most.
“When we have a completely decarbonized grid and depend heavily on solar and wind, energy droughts could have huge amounts of impact on the grid,” Cameron Bracken, lead author of the article, said in a media statement.
Bracken noted that in the past, researchers studied compound energy droughts on a state or regional scale. However, not much has been studied on a nationwide scale.
To find out more about the risk of energy droughts over the entire continental US, Bracken and his colleagues dug into weather data and then used historical energy demand data to understand how often an energy drought occurs when that energy is needed the most.
The team examined four decades of hourly weather data for the continental US and homed in on geographical areas where actual solar and wind energy plants operate today. Weather data included wind speeds at the height of wind turbines as well as the intensity of solar energy falling on solar panels. Times when the weather data showed stagnant air and cloudy skies translated into lower energy generation from the wind and solar plants—a compound energy drought.
“We essentially took a snapshot of the infrastructure as of 2020 and ran it through the 40 years of weather data, starting in 1980,” Bracken said. “We are basically saying ‘Here is how the current infrastructure would have performed under historical weather conditions’.”
The researchers found that energy droughts can occur in any season across the continental US, though they vary widely in frequency and duration. In California, for instance, cloudy and windless conditions might last several days, whereas the same conditions might last for only a few hours in Texas.
Utah, Colorado, and Kansas experience frequent energy droughts both over several-hour timescales as well as several-day timescales. The Pacific Northwest and Northeast, meanwhile, seem to experience energy droughts that last several hours more frequently than several days. The different timescales (hourly versus daily) will help inform the energy drought’s impact on the grid.
Overall, researchers found that the longest potential compound energy drought on an hourly timescale was 37 hours (in Texas), while the longest energy drought on a daily timescale was six days (in California).
Simply knowing the where and how of energy droughts is just one piece of the puzzle. Bracken stressed that a drought of solar and wind power won’t necessarily cause an energy shortage. Grid operators can turn to other sources of energy like hydropower, fossil fuels, or energy transmitted from other regions in the US.
But as the nation aims to move away from fossil fuels and rely more on solar and wind power, grid operators must understand whether energy droughts will occur during times when the electricity demand might exceed supply. Climate change brings hotter summers and more intense winter storms, and these are times when people use more energy.
To understand the possible connection between energy droughts and energy demand, the team mapped their historical, hypothetical generation data onto 40 years of historical energy demand data that also covered real power plants across the continent.
The data showed that “wind and solar droughts happen during peak demand events more than you would expect due to chance,” Bracken said, meaning that more often than not, windless and cloudy periods occurred during times when power demand was high. For now, Bracken isn’t certain that the correlation means causation.
“This could be due to well-understood meteorological phenomenon such as inversions suppressing wind and increasing temperatures, but further study is needed,” Bracken said.
