California power grid emergencies: What to know about Flex Alerts, other warnings during heat waves

Summer heatwaves can strain California’s electricity supply, prompting energy emergency notifications to appear across highway signs and social media.  

The California Independent System Operator, which operates the majority of the state’s power grid, issues several types of alerts to help prevent uncontrolled blackouts. 

At the highest alert level, Cal ISO orders utilities to begin rotating outages in order to avoid unplanned power failures across the state. But ISO Director of Operational Readiness Tricia Johnstone said only one notification is a direct appeal to consumers: Flex Alerts. 

Other alerts are intended for utilities, neighboring grid operators who may be able to help and market participants, Johnstone said. Market participants include transmission owners and energy generation companies.  

What is a Flex Alert versus an EEA?

When Cal ISO issues a Flex Alert, it asks consumers to voluntarily reduce their electricity use or shift usage to off-peak hours. The ISO sends the alerts when it determines energy supply might not meet demand. They are often called between 4 p.m. and 9 p.m., but can be issued during other times. 

Flex Alerts generally happen when extremely hot summer weather drives up electricity demand in the evening, according to the ISO. Consumers return home from work — or other activities — and turn on air conditioners and appliances, stressing the grid. 

While the ISO could issue Flex Alerts outside of the summer months, Johnstone said they tend to correlate with high heat across multiple days. Conserving during a Flex Alert can help prevent the ISO from needing to order rotating power outages. 

Johnstone said the alert is most effective when the ISO can give the public advance notice. 

“If we put out a Flex Alert in the middle of the day and people have already left their homes for work for the day or for other activities, it'd be hard to expect a response from them in real time,” Johnstone said. 

But the ISO asks utilities to immediately respond to another notification type, an Energy Emergency Alert (EEA), with programs they have in place. There are multiple levels of an EEA. 

• EEA Watch: The ISO issues this if it projects energy deficiencies because available supply is committed or forecasted to be used. It can be issued the day before a projected shortfall or in response to a sudden event. 
• EEA 1: This is issued when real-time or day-of analysis shows all resources are in use or committed for use, and energy deficiencies are expected. 
• EEA 2: At this stage, the ISO is energy deficient and no longer able to provide its expected energy requirements. The ISO may request emergency energy from all resources and has activated emergency programs. 
• EEA 3: Preparing for rotating power outages: In the initial step of EEA 3, the ISO alerts utilities to prepare for rotating outages, but has not ordered them. The grid operator is unable to meet minimum reliability reserve requirements. 
• EEA 3: Ordering rotating power outages: At the final step of EEA 3, the ISO orders utilities to begin rotating power outages. Electricity supply is not sufficient to meet demand and the grid operator can’t maintain required reserve levels. 

If consumers see an EEA issued for a certain time period, Johnstone said they can take steps to conserve energy similar to how they would during a Flex Alert. An EEA and Flex Alert can overlap, too. When the grid operator calls an EEA, a Flex Alert is usually in effect, said ISO Senior Public Information Officer Anne Gonzalez. 

Are there other types of ISO alerts? 

California ISO issues two other types of emergency notifications. Both are geared toward utilities and transmission operators. 

Restricted Maintenance Operations: When the ISO anticipates high demand or stressed grid conditions, it cautions utilities as well as transmission and generation operators to avoid taking equipment offline for routine maintenance. The notification helps ensure all generators and transmission lines are available. 

Transmission Emergency: The ISO issues this when an event — like stormy weather conditions or fires — threatens or limits transmission grid capability. It could involve line or equipment overloads or outages and can be declared system-wide or involve local limitations. In August 2022, a Southern California wildfire tripped transmission lines and knocked out 700 MW of power.

How often have Flex Alerts been issued? 

The state’s grid operator began issuing Flex Alerts in 2000, according to an ISO report. From then until the end of 2022, it has issued an average of about six Flex Alerts a year. But between 2009 and 2019, the ISO issued no more than four of them each year. 

The frequency of Flex Alerts has recently increased. The ISO issued 10 in 2020, eight in 2021 and 11 in 2022. More prolonged, severe and widespread heat waves have contributed to the increase, Johnstone said. Extreme heat events affecting multiple western states stresses the grid more than locally limited hot weather. 

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“We're also managing an increased amount of wildfire activity and things like that, which are impacting major transmission paths and generation,” Johnstone said. “There's been drought in over multiple years, which reduces the hydroelectric supply. So, I think that's really why we've been seeing it more here in the past few years than we had there for a long time.”

Unlike Flex Alerts, the ISO began sending EEA notifications in May 2022. The grid operator used its own emergency designations before then, but switched to the EEA system to improve communications with other grid operators in the West. 

How should I respond to Flex Alerts? 

The morning of a Flex Alert, the ISO recommends consumers take these steps: 

• Pre-cool homes by lowering air conditioning thermostats to 72 degrees 

• Close blinds and drapes to prevent sunlight from heating up rooms

• Turn off unnecessary lights 

• Use dishwashers, washing machines and other major appliances 

• Charge mobile devices and laptops 

• Pre-cook meals 

When a Flex Alert is in effect, usually between 4 p.m. and 9 p.m., the ISO suggests consumers should: 

• Set air conditioner thermostats to 78 degrees or higher, if health permits

• Avoid using dishwashers, washers, dryers and ovens

• Unplug or turn off electrical devices not in use

• Keep blinds and drapes closed and turn off unnecessary lights 

• Use fans when possible

Conserving energy during Flex Alerts can help prevent rotating power outages as well as unplanned blackouts, according to the ISO. 

How do rotating power outages differ from uncontrolled blackouts? 

When the ISO calls on utilities to implement rotating power outage plans, Gonzalez said the grid operator is working to prevent uncontrolled backouts. Rotating outages protect the power grid’s reliability, Gonzalez said, and help avoid unplanned, widespread blackouts. 

“If we didn't use those short rotating controlled outages throughout different neighborhoods, you would risk having a cascading blackout,” Gonzalez said. “That is an unplanned and uncontrolled loss of power that cascades to other grids and it can take many weeks to get [power] back starting again.”

Utilities, not the ISO, directly notify consumers of planned rotating outages, Johnstone said. The ISO looks at the grid’s big picture and coordinates with utilities, which have procedures in place to reduce power consumption in strategic areas. 

The ISO posts the status of the grid, as well as current capacity and forecasted demand, on its website.