What Sunday’s Outage Revealed About Transmission, Load Shedding, and Grid Coordination
On Sunday, May 25, more than 125,000 Louisiana households experienced brief but widespread power outages. It wasn’t a hurricane or a lightning strike. In fact, the weather was relatively calm. The culprit? A regional reliability directive known as a load shed order, triggered by the Midcontinent Independent System Operator (MISO) to protect the stability of the grid.
What followed was a sudden drop in power supply for Entergy and Cleco customers, some with just minutes of warning.
Here, I’m unpacking the different technical bits of this equation to get deeper into how this system works.
MISO: The Grid’s Regional Dispatcher
MISO, Not Like the Soup
MISO (pronounced MY-so) is the Midcontinent Independent System Operator, one of several Regional Transmission Organizations (RTOs) that oversee the electric grid across large regions of the U.S. MISO spans 15 states and manages electricity flow, pricing, and reliability over a vast area.
Louisiana utilities like Entergy and Cleco joined MISO in 2013, giving our region access to a larger and more competitive electricity market. This move has paid off:
Being part of MISO has generally meant lower wholesale energy costs and enhanced reliability for Louisiana ratepayers. It’s like getting to split a pot of gumbo with 14 neighbors instead of cooking your own every night.
MISO South vs. MISO North: One Grid, Uneven Connections
One Team, Two Stadiums
While MISO is a unified grid operator, it has two distinct regions: MISO North (which includes states like Illinois, Indiana, and Minnesota) and MISO South (including Louisiana, Mississippi, and Arkansas).
Here’s the catch: these regions are connected by a very limited set of transmission lines. That means MISO South can’t easily import large amounts of power from the North when demand spikes or local generation is down.
Think of it like a single football team with players split between two stadiums. Same playbook, same coach, same goal.
But here’s the twist: there’s only one narrow tunnel connecting the two stadiums. If the South runs low on players or equipment, the North can send help, but not fast, and not many at a time.
So when the Southern stadium gets hit with a tough opponent (like a heatwave), and half their starters cramp up, they look to the North for backup. Problem is, that cramped tunnel slows the reinforcements. Even though the North has a full bench, they can’t get players to the South in time. The crowd starts booing, the lights flicker, and the Southern team has to sit out a few plays.
On May 25, MISO South experienced a critical increase in demand and directed a 600 megawatt load shed – meaning the grid had to cut the amount of electricity that would power a small city in a matter of minutes.
What Is a Load Shed?
When grid operators like MISO issue a load shed, it’s a last-resort tool to prevent a cascading failure, a chain reaction where one outage triggers another across the high-voltage system. These events can lead to widespread, uncontrolled blackouts lasting hours or even days.
Here’s what’s at stake:
In short, load shedding sacrifices a small slice of the grid temporarily to save the entire system from collapse.
Transmission End Zones
Gridlock in the Backfield
Transmission end zones occur when a region is at the far edge of the network and has limited connection points. That makes it harder to get help during emergencies and creates price disparities when congestion occurs. If Louisiana wants the full benefits of MISO membership, we need more robust connections to the rest of the field.
A Question of Timing
Not Quite a Two-Minute Warning
One of the most curious aspects of May 25th is how quickly things unfolded. Entergy has stated it received only three minutes of warning from MISO before being ordered to shed load.
This raises questions worth exploring: What did MISO know, and when did they know it? If power plants like River Bend had been offline for days, and temperatures were trending upward, was the supply shortage truly a surprise? Or was there a gap in modeling or communication?
These aren’t questions of blame, they’re questions of system coordination. And understanding that timing is critical to improving future resilience. The more we understand these coordination mechanisms, the better prepared we’ll be for future grid events.
Resilience Isn’t Just About Storms
Hard Hats and Back-up Plans
Entergy’s Resilience Implementation Plan, filed in 2023, focuses on hardening infrastructure against hurricanes, flooding, and other climate-related risks. That work is essential and deserves recognition.
The load shed wasn’t the result of one bad decision or a single point of failure. It was the outcome of a tightly constrained system operating close to the edge, with limited slack and little room for error.
Last Sunday’s event suggests the need to evolve our definition of resilience to include non-weather risks, like tight supply margins, transmission congestion, and rapid demand shifts. Louisiana doesn’t just need to weather the storm; we need to navigate the calm with just as much precision.