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2021 Summer readiness

Following the extreme heat wave of August 2020 and subsequent rotating power outages, the California ISO is proactively working with its partners and stakeholders to identify challenges and solutions for reliably decarbonizing the grid, and to raise public awareness about the electricity system needs.


A historic heat storm impacted the western US for several consecutive days in mid-August 2020, causing energy supply shortages that led to two rotating power outages in the ISO footprint on August 14 and 15. Since then, the California ISO — in coordination with state agencies and stakeholders throughout the state and the West — has embarked on a deep dive into the causes of the outages and the joint development of actions to be taken to prevent supply gaps in advance of summer 2021. This page is dedicated to providing easy access to data and reports related to the causes and the lessons learned from the August outages and provides a ‘one stop shop’ for all the activities, updates and identified improvements for ensuring grid reliability for summer 2021 and beyond.

Analysis of August 2020 outages

Detailed reports outline multiple causes of supply shortages and market impacts:

Planning for future heat waves

The California ISO has pledged to collaborate with the Governor’s Office, the state Legislature, state agencies, and stakeholders throughout the state and the West to deliver action items from the joint Preliminary Root Cause Analysis to mitigate impacts of a power grid under high stress conditions.

CEO’s Report to Board of Governors - Sep 22-23, 2021

CEO’s Report to Board of Governors - Jul 7, 2021

CEO’s Report to Board of Governors - May 19-20, 2021

CEO’s Report to Board of Governors - Mar 24-25, 2021

CEO’s Report to Board of Governors - Feb 3-4, 2021

CEO’s Report to Board of Governors - Dec 16-17, 2020

CEO’s Report to Board of Governors - Nov 18-19, 2020


Summer loads and resources assessment

The Summer Assessment uses historical and current data, statistical modeling, and simulations to give the expected energy supply conditions for the upcoming summer for the California ISO balancing authority.

2021 Summer Loads and Resources Assessment

Initiatives supporting 2021 summer readiness activities

Market enhancements for summer 2021 readiness – The purpose of this initiative is to focus on near-term efforts necessary to enhance market rules and procedures to help ensure grid reliability in summer 2021.


Below are training sessions to help ISO stakeholders prepare for the 2021 summer release initiatives.

Apr 21, 2021  Resource Adequacy Enhancements Presentation | Video | Initiative
Apr 27, 2021  Summer 2021 Readiness Part 1 Presentation | Video
Apr 28, 2021  FERC 831 Presentation | Video | Initiative
Apr 29, 2021  Summer 2021 Readiness Part 2 Presentation | Video
Jun 24, 2021 Summer 2021 Readiness Part 3 Presentation | Video

2021 policy initiative roadmap process – Annual roadmap process is a comprehensive planning process for evolving the ISO markets. Policy development focused on addressing issues identified in the preliminary Root Cause Analysis such as resource adequacy reforms, scheduling priorities and improved market incentives during tight supply conditions.

Engagement opportunities

Public meetings provide stakeholders with an update on activities and an opportunity to engage in the summer readiness planning process.

  • 2021 Summer readiness update - Sep 24, 2021
  • 2021 Summer readiness update - Aug 31, 2021
  • 2021 Summer readiness update - Jul 29, 2021
  • 2021 Summer readiness update - Jun 23, 2021
  • 2021 Summer readiness update - May 26, 2021
  • 2021 Summer readiness update - Apr 14, 2021
  • 2021 Summer readiness update - Feb 25, 2021
  • 2021 Summer readiness update - Jan 19, 2021
  • DMM report on system and market conditions, issues and performance for Aug/Sep 2020 - Dec 18, 2020
  • 2021 Summer readiness update - Dec 8, 2020

Flex Alerts

A Flex Alert is a call for consumers to voluntarily conserve electricity when there is a predicted shortage of energy supply, especially if the grid operator needs to dip into reserves to cover demand. When consumers reduce electricity use at critical times, it can prevent more dire emergency measures, including possible power outages.

To prepare for summer 2021, and to better align Flex Alerts with current conditions, we will be developing several changes to the program, in coordination with the CPUC, utilities and others.

Visit for conservation tips, to subscribe for Flex Alerts and more.

Read about Flex Alerts


Background, fact sheets, and news releases related to 2020 heat waves

CPUC’s Summer 2021 Reliability webpage