UNDERSTANDING LOAD SHED
The Balancing of Electric Supply and Demand
When the demand for electricity exceeds supply, sometimes people lose electricity to prevent extended outages for customers or damage to the entire system managed by our reliability coordinator Midcontinent Independent System Operator. This is called load shedding.
Load shed may occur if there is a shortage of electricity supply, or to help prevent power lines from becoming overloaded. Several factors can lead to load shedding, including extreme weather, unplanned plant outages, transmission constraints, unavailability of purchased power or a combination of these situations.
How does load shed work?
MISO decides when load shed is needed in any part of Entergy’s four-state service area, which is part of their south region. Load shedding is always a last resort to prevent more extensive and prolonged power outages that could severely affect the reliability of the power grid.
Before it turns to load shedding, MISO has other measures it may take to try and overcome a power shortfall, such as importing more power from other resources or tapping into emergency reserves. It can also order its members, like Entergy, to make a public appeal to customers to voluntarily reduce their energy consumption to prevent forced outages.
Why are some customers more affected than others?
Outages during a load shed event limit the power to various customers who are grouped together by turning on and off the conductors that feed electricity to their homes or businesses.
- The groups are determined by the amount of power that must be saved at the time the outages occur and can vary greatly depending on the current conditions. We do our best to avoid critical customers, which include essential services and facilities critical to public health and safety, such as hospitals, fire and police departments, and water systems.
- As one group of customers completes its outage cycle, the next group is removed from service and the first is returned to service. Isolated cases may occur where a circuit breaker operation to restore service at the end of an outage cycle would require manual rather than automatic operation, which takes longer.
What can I do to help prevent a load shed event?
When MISO orders a public appeal, we will ask customers to minimize energy usage as much as possible until the system strain has passed. You can help:
- Lower or increase your thermostat, running your heater or air conditioner less, depending on the time of year.
- Unplug electronic devices and turn off lights that are not in use.
- If you can, take advantage of mother nature. If it’s cold, open blinds, drapes and curtains when the sun is shining to let in warmth.
- Hold off on doing chores. Delay laundry, washing dishes and other non-essential uses of electricity.
- Wash clothes with cold water, shower quickly instead of taking a bath, cook foods at the lowest possible setting and refrain from opening the oven door while baking.
Who is MISO?
Entergy has been a member of the Midcontinent Independent System Operator, one of the nation's largest regional transmission organizations, since December 2013. MISO is a not-for-profit member-based organization that ensures reliable, cost-effective delivery of electricity across all or parts of 15 U.S. states and one Canadian province. In cooperation with stakeholders, MISO manages approximately 65,000 miles of high-voltage transmission and 200,000 megawatts of power-generating resources across its footprint.
Being a part of MISO allows Entergy to better coordinate and optimize generation, transmission, gas across MISO’s entire region and the U.S.
Learn more about the U.S. electricity grid and markets here from the U.S. Environmental Protection Agency.
Why can’t you provide more notice before shedding load?
While we try to provide as much notice as possible to customers regarding outages as a result of load shed, unfortunately we can’t always do that.
As we’ve shared, load shedding is implemented as a last resort and requires immediate action. When the order to execute by MISO is received our customer service teams begin the process of alerting customers, but the outages follow quickly and often before notifications can be made. This could happen at any time, day or night, and we are provided little notice and we must comply with the order from MISO to prevent longer, widespread uncontrolled outages.
How does a cold weather event differ from a hot weather event?
Simply put, it requires more energy to warm your home than it does to cool it. During unprecedented weather events, like extreme cold temperatures in the South, your home’s heating unit must work very hard to keep you at your desired temperature.
The greater the difference between the outdoor temperature and the desired indoor temperature, the more electricity your heating or air conditioning unit will use. Thus, extreme winter temperatures in the South result in more electricity demand than extreme summer temperatures do.
Why don’t you turn off street lights to conserve electricity?
Street lights are a very small percent of our electric demand and we do not have the ability to remotely turn them off.
Why is load shed necessary?
Load shedding occurs when the demand for electricity approaches supply and we are forced to reduce power demand by removing some customers to prevent longer, larger outages. The reduction of power ensures adequate reserve margin and helps prevent a failure of the larger electrical grid.
Because electricity in power lines cannot be stored, generation and load must always match up or the grid enters blackout territory. Load shedding is always a last resort to prevent more extensive and prolonged power outages that could severely affect the reliability of the power grid, like the biggest blackout in North American history in 2003 that affected eight northeastern states and plunged 50 million people into darkness for 31 hours.
On Aug. 14, 2003, a high-voltage power line in northern Ohio brushed against some overgrown trees and shut down. Over the next hour and a half, three other lines sagged into trees and switched off, forcing other power lines to shoulder an extra burden. Overtaxed, they cut out tripping a cascade of failures throughout southeastern Canada and eight northeastern states.