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Swings in wind and solar power may cause "energy droughts”

Although renewable energy prices have fallen by over 70 percent in the last decade, driving more people to replace fossil fuels with greener, less polluting energy sources, the future probability of large swings in the availability of solar and wind power should be taken into account by grid operators and consumers, according to a new study led by Columbia University.

“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 study senior author Upmanu Lall, a professor of Engineering at Columbia. “You won’t be able to manage variability like this with batteries. You’ll need more capacity.”

Drawing on 70 years of historic wind and solar-power data, Professor Lall and his research team built an Artificial Intelligence model to predict the probabilities of network-scale “energy droughts,” when daily production of renewables fall below a target threshold. Since solar and wind potential, like rainfall, is highly variable – based on the time of the year and the place where solar panels and wind turbines are located – renewable energy droughts will most probably be a recurrent problem in the near future.

By focusing on Texas – the leading state generating electricity from wind power and the fifth-largest solar producer – the scientists estimated that, even if solar and wind generators were spread across the entire state, Texas may soon face persistent energy droughts that could last as long as a year. In the case of other states with less sun and wind available, such shortages will probably be even longer.

“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,” said Professor Lall. “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.”

While in times of low rainfall, water managers use reserves stored in municipal reservoirs or underground aquifers, solar and wind energy systems have no equivalent backup. The batteries used to store excess solar and wind power will only be able to hold the charge for at most a few days, and not even hydropower plants will be fully capable to carry the system through an extended dry spell of intermittent sun and wind.

“We won’t solve the problem by building a larger network. Electric grid operators have a target of 99.99 percent reliability while water managers strive for 90 percent 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,” concluded Professor Lall.

The study is published in the journal Patterns.  

By Andrei Ionescu, Staff Writer

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