Low-Energy Fridays: If Our Grid Goes Down, How Do We Get Our Lights Back On?
Two weeks ago, tens of millions on the Iberian Peninsula lost electricity. While the reason for the disturbance could take years to discern, it’s likely that no single cause led to the blackout. Previous issues of this type and magnitude resulted from a confluence of mishaps and misfortune. If the American experience is any gauge, a final assessment of the event won’t be available for a while.
The Iberian event is a reminder of how fast things happen in the world of electricity. Unlike other utilities, such as gas or water, electricity is consumed immediately. In order to protect equipment from voltage or frequency variations that could harm mechanics or electronics, power plant operators, utilities, and large customers install technology that disconnects facilities from the grid when things go awry. Advancements in these technologies mean that disconnections can occur nearly instantaneously. This is what happened in Spain and Portugal, where power plants—some large enough to serve more than a million homes—disconnected from the grid when they sensed it was out of sync, ironically making the system even more unstable. A cascading process of generation and load rapidly disconnecting from the grid exacerbated its imbalance, resulting in a complete blackout.
The lights are back on in Spain and Portugal, but the event raises at least two questions: Has the United States experienced similar blackouts? When blackouts occur, how is the electric system restarted and service restored?
As for the first question, yes—the United States has experienced blackouts. It’s important to note the distinction between a “blackout” and “rotating outages,” sometimes referred to as “rolling blackouts.” Rolling outages are not blackouts, but rather are targeted and intentional interruptions of electricity conducted to balance demand and supply while maintaining some extra power to make up for sudden disruptions. Blackouts are uncontrolled and result in the mass disconnection of generation from the grid, bringing everything to a halt.
The most recent major blackout event in the United States happened in 2021 during Winter Storm Uri. While limited to the intra-Texas grid, the event was significant and lasted a number of days. However, the Texas experience was more an example of a multi-day lack of available supply due to frigid temperatures, frozen power plants, and undeliverable gas supply than the result of an unstable grid. The closest U.S. parallel to the Iberian event was the Northeast Blackout of 2003, which affected 50 million Americans and Canadians.
In the 2003 blackout, North America experienced its largest disruption in electricity supply, resulting in billions of dollars in economic damage and leaving some customers in the Northeast United States and Canada without power for days. The event started in Ohio due to several factors including insufficient and unclear transmission planning obligations, utilities’ and grid operators’ lack of situational awareness of the grid, and the failure of a utility to adequately manage trees in its transmission rights of way.
These issues were exacerbated by a lack of grid services that could have been called upon to alleviate the impact of multiple transmission outages. The 2003 blackout didn’t affect further geographic areas because the affected area was essentially disconnected from the broader grid after the problems arose; however, the damage had been done. After only a few hours (culminating in a rapid few minutes of cascading outages), the Northeast was completely without power.
Spain re-energized its entire system within 24 hours, and Portugal needed only half that time to reach 100 percent restoration. As for the Northeast Blackout, the system mostly came back online within 30 hours. The process of restarting a system from a blackout is methodical and completed in a stepwise manner rather than all at once, as disorderly restoration runs the risk of another blackout. The restoration process starts with blackstart units, which are capable of starting up from a shutdown without assistance from the grid or other power plants. In lieu of blackstart units, direct transmission ties can be used to bring power from other areas to start up non-blackstart generating units. Imports or power from blackstart units are then directed toward other generating stations that require outside power to restart and coordinate with the grid. The power from newly connected generators is used to bring on others, and so on, while load is reconnected to slowly balance the grid.
As we wait for the Iberian blackout’s causes to be determined, we hope Europeans use it as a learning opportunity the way the United States did following the 2003 event. Congress passed sweeping energy policy legislation with more robust electricity reliability expectations, which the Federal Energy Regulatory Commission (FERC) and the North Electric Reliability Corporation (NERC) have implemented over the past two decades. Lessons learned from reliability events routinely inform the standards set and enforced by FERC and NERC, and we can learn from the Iberian blackout as well—even if it takes years to determine the root causes.