Researchers model seasonal solar and wind energy output to predict backup power needs. (Image: Christoffer Riemer/Wikimedia)

Researchers at Columbia University, supported in part by a grant from the U.S. National Science Foundation, conducted a study that modeled the seasonal variability of solar and wind power. The team examined decades of data to measure variability trends over time and the impact on power grids. As the shift to renewable energy gains momentum, variable supply is an important consideration.

"Designers of renewable energy systems will need to pay attention to changing wind and solar patterns over weeks, months, and years, the way water managers do," said Upmanu Lall, a co-author of the study. "You won't be able to manage variability like this with batteries. You'll need more capacity."

Batteries would fall short as backup power sources for extended droughts. The batteries used to store surplus solar and wind power only hold a charge for a short period of time, and solar and wind power have no other renewable alternatives.

"These findings suggest that energy planners will have to consider alternate ways of storing or generating electricity, or dramatically increasing the capacity of their renewable systems," Lall said.

The team studied solar and wind availability at airports to assess how much variation could occur with a completely renewable energy grid. The findings show that the seasonal potential of solar and wind power can vary by almost a third.

"In a fully renewable world, we would need to develop nuclear fuel or hydrogen fuel, or carbon recycling, or add much more capacity for generating renewables, if we want to avoid burning fossil fuels," Lall continued.

"We won't solve the problem by building a larger network. Electric grid operators have a target of 99.99% reliability, while water managers strive for 90% reliability. You can see what a challenging game this will be for the energy industry, and just how valuable seasonal and longer forecasts could be.”

Next the team plans to predict energy floods — when excess energy is produced — and droughts. Understanding how to forecast and manage the inevitable surplus and deficit of solar and wind power output will result in more reliable and sustainable power grids.