What happens when the sun doesn’t shine?

From pv magazine USA

The phenomenon that occurs when the sun doesn’t shine and the wind doesn’t blow is known as a “compound energy drought,” and researchers at PNNL studied these droughts and found that in some parts of the country, they can last nearly a week.

“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,” said Cameron Bracken, a scientist at PNNL.

It’s important for grid operators to know where, when and for how long energy droughts occur so that they can call on other energy sources as well as manage grid-level battery systems to store enough electricity needed during times when energy is needed most.

The team recently published the findings in Renewable Energy and will present them at this week’s annual meeting of the American Geophysical Union. The researchers report that the paper is the first to provide a uniform standard of what a compound energy drought is and how long it can last in different parts of the country.

The researchers researched 40 years of weather data and then used historical energy demand data for the entire country in order to understand how often an energy drought occurs when that energy is needed the most. The weather data included wind speeds at the height of wind turbines as well as the intensity of solar energy on solar panels. The team focused on areas where there’s currently a lot of solar and wind generation and looked at the times when the weather data showed stagnant air and cloudy skies that resulted in lower energy generation.

“We essentially took a snapshot of the infrastructure as of 2020 and ran it through the 40 years of weather data, starting in 1980,” said Bracken. “We are basically saying ‘here is how the current infrastructure would have performed under historical weather conditions.’”

The researchers found that energy droughts happen at any time of year in various regions, and for varying frequency and duration. In some areas, Texas, for example, energy droughts are frequent but last only hours. While in other areas, such as in California, they may be of a longer duration but are less frequent. Researchers noted that the longest energy drought happened in California and lasted for six days. Understanding the duration and frequency will help predict the drought’s impact on the grid.

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