The causes of Monday’s massive power outage in Spain and Portugal are still under investigation. But facts on the ground so far point to inconvenient truths as Europe and the United States bring more renewable energy onto their electric grids.
Momentary disruptions are managed all the time in Spain’s heavily wind- and solar-based grid. And while the U.S. system is fundamentally different, grids that serve Texas, California, Florida, Iowa and Great Plains states also manage relatively high levels of renewable penetration. Still, the shift from traditional power generators to solar, wind and batteries has made it harder — but not impossible — for high-voltage grids to absorb sudden disruptions.
The issue involves inertia, the energy stored in the spinning generators used to produce electricity in coal-fired and gas-burning plants, nuclear reactors and hydroelectric dams. Those generators tend to keep spinning when a disruption starts, giving systems the critical seconds they need to respond to a failure.
Solar and wind power and battery storage that lack built-in inertia increase the risk of outages if no other defense is in place, according to a report by the Department of Energy’s National Renewable Energy Laboratory (NREL). Power from traditional generators is synchronized with the rising and falling cycles of alternating currents. Technology known as inverters convert direct current produced by solar and wind farms to the alternating current that delivers electricity to customers.
“The grid is the largest machine on the planet,” said Mario Garcia-Sanz, a program director at DOE’s Advanced Research Projects Agency-Energy (ARPA-E). “As we reduce the number of synchronous generators and the associated inertia,” he said, “the normal grid contingencies can lead to more dramatic swings in frequency, which could result in large blackouts.”
When Monday’s blackout hit, Spain was drawing 59 percent of its electricity from solar panels, nearly 12 percent from wind turbines, 11 percent from nuclear reactors and 11 percent from gas-fired turbines, according to Spanish transmission system operator Red Eléctrica, Reuters reported.
The collapse of the grid covering the Iberian Peninsula happened at 12:38 p.m. local time Monday, according to Eduardo Prieto, head of system operation services of Red Eléctrica. Portugal’s grid operator REN said unexpected fluctuations across high-voltage lines caused parts of the grid to fall out of sync, “leading to successive disturbances across the interconnected European network.”
A U.S. technology company that has monitors installed in the Madrid area recorded unusually sharp swings in voltage levels beginning three hours before the grid collapse “an indication of stress and instability,” said Bob Marshall, chief executive of Maryland-based Whisker Labs. “We saw those oscillations in voltage increase in frequency and amplitude over the next three hours until the grid failure and collapse.”
Once the precisely synchronized currents across Spain’s grid began to gyrate dangerously, it was like a heart arrhythmia: the fluctuations had to flatten out or mechanical systems would cut off power to prevent serious damage to generators.
“The nature and scale of the outage makes it unlikely that the volume of renewables was the cause,” said Daniel Muir, senior European power analyst at S&P Global.
What can be done?
For engineers and grid experts, the first instinct hasn’t been to blame a single power source for an outage across a large network. The triggers for a blackout can be complicated. Imbalances and dangerous electricity fluctuations across a large, integrated, diverse network of energy resources are usually complicated.
To politicians, of course, the answers couldn’t be clearer.
Critics of climate policies aimed at integrating more zero-carbon wind and solar power jumped on the outage as evidence that relying on renewables is too dangerous — “lunacy,” President Donald Trump calls it. Following Trump’s playbook, Energy Secretary Chris Wright pointed a finger at wind and solar power. “It’s very sad to see what’s happened to Portugal and Spain and so many people there,” Wright said. “But you know, when you hitch your wagon to the weather, it’s just a risky endeavor.”
In fact, renewable energy is not intrinsically unreliable, according to NREL’s report, ARPA-E scientists and other experts. Solar, wind and battery systems can be designed and equipped with devices and software that provide the fast response needed for dangerous grid upsets.
The problem is making it happen.
“We have equipment and strategies and plans, but they are not widely deployed or well understood,” said Alison Silverstein, a Texas energy analyst and former top staffer for energy regulators.
But investments in more support for voltage, frequency and reactive power won’t happen without companies and regulators across a decentralized U.S. system getting behind the effort. Inverters are the essential tools.
“The speed of this change continues to challenge grid planners, operators, protection engineers, and many other facets of the electricity sector. Implemented correctly, inverter technology can provide significant benefits,” wrote experts at the North American Electric Reliability Corp., the grid monitor, in a report in 2022. “However, the new technology can introduce significant risks if not integrated properly.”
The grid monitor has issued guidelines on how to address some of these technology issues. But in a 2021 NERC report, it said its advice was too often falling on deaf ears. After an incident in Texas when instability in the surrounding grid caused solar plants with a total capacity of 1,112 megawatts to unexpectedly shut down, NERC said solar operators are not following its guidance. The recommendations “are not being widely and comprehensively adopted” by transmission system operators, either, NERC said.
ARPA-E’s Garcia-Sanz directs a research initiative named Gradients that seeks to develop major new solutions for grid reliability challenges when disruptions start. Advanced inverters coupled with stored energy will deliver the same instantaneous support that coal and gas inertia provide now, he said.
Control rooms equipped to monitor and respond to moment-to-moment grid disturbances must also be part of the solution, he said.
The answer is not to simply return to heavy fossil, nuclear or hydropower generation to supply inertia, he added.
As ever-bigger grid systems evolve with data center expansion and artificial intelligence applications, the risk of bigger disruptions increases. The loss of a very large data center can shock the grid as much as the loss of a big power line or a nuclear reactor that unexpectedly scrams, he said.
“With the inverters we can do things we cannot do with synchronous generators,” Garcia-Sanz said. “Inverters can be more intelligent, able to do things like predictive control,” he said. “We can anticipate things, coordinate things in a different way … because we are applying more intelligence.”
