Final Blackout Study Calls for More Reserves, Warns of Diablo & Pacific Line Risk

Details on the key causes of the mid-August blackouts are out, and consistent with an earlier analysis. They highlight market and planning flaws and a system thin on the cushion of extra power, or resource adequacy, the grid requires. The final analysis also points to an acute concern over two scenarios: a sudden loss of power from the 2,300 MW Diablo Canyon Nuclear Plant, and the loss of the Pacific DC intertie. The transmission line moves significant hydropower resources from the Pacific Northwest as far as Los Angeles in the summer.

The report, released Jan. 13, delves into inaccurate supply and demand scheduling that resulted from defects in a part of the California Independent System Operator’s day-ahead market, known as the residual unit commitment market process. It calls for the California Public Utilities Commission to push the private utilities to give community energy complete data on customer use to avoid inaccurate load scheduling. The errors and data shortcomings resulted in needed power being exported from California. It also finds the CPUC overestimated the amount of solar and wind resources that would be available, particularly during net peak times, as the sun sets.

“Although this combination of factors led to an extraordinary situation, our responsibility and commitment going forward is to be better prepared for extreme climate change-induced weather events and other operational challenges facing our evolving power system,” the chiefs of the grid operator, CPUC and California Energy Commission state. Their jointly developed report stresses that “no single generator or resource type led to the rotating outages.” The report also looks at near misses during heat waves on Aug. 17-19 and over the Labor Day weekend.  

The report’s recommendations include strategies for bolstering summer supplies. In a related proceeding to increase power reliability this summer, known as Emergency Reliability, the grid operator is calling for the CPUC to increase the planning reserve margin during peak and net peak hours from 15% to 17.5%. Gary Ackerman, the Western Power Trading Forum executive director, called CAISO’s proposal “the most important part of the future recommendations embedded in the Root Cause Analysis.”

Operating reserve concerns

CAISO is required to have sufficient operating reserves to keep the grid flowing in the event a major power plant or transmission line crashing. The grid operator states in the new report that the most “severe single contingency” it may face would be the loss of Diablo or the Pacific Intertie.

In fact, one of Diablo’s two units has been offline for weeks, and it is the third time in six months. It’s not expected to come back into service before early June. The first issue arose in mid-October, and it was at a moment when the grid operator was calling for conservation. The 1,150 MW Unit 2 was forced offline because of a leak in cooling fluids in the electrical housing. To compound matters, the 1,150 MW Unit 1 at that time was already offline undergoing planned maintenance.  Unlike the previous two times, the latest forced outage of Unit 2 is because of vibration issues.

On the issue of the Operator’s other worst-case scenario, in mid-August the Pacific transmission lines was threatened by two fires. High mid-August heat caused it to lose 330 MW of carrying capacity.

Repairing resource adequacy

The report revealed that one category of Resource Adequacy—system RA—fell short. Supply cushions that had been lined up to meet local or flexible capacity were not found to be deficient. But system resource adequacy suffered from unexpected outages in the natural gas fleet—up to 2,000 MW, including a loss of 246 MW from a Pacific Gas & Electric power plant because of a dispatch error. In addition, a thunderstorm in PG&E territory caused a loss of wind and solar power that had been counted as available capacity.

The report calls for the CPUC to modify its resource adequacy program to reflect severe weather conditions and the availability of resources as the sun begins to set. It must count available capacity of solar and wind resources to better reflect their “time-dependent” nature, it states. 

It recommends immediate and long-term market improvements “to ensure that California’s transition to a reliable, clean, and affordable energy system is sustained and accelerated.”

That includes CAISO’s work with stakeholders on market rule and practice improvements so that they are in place by June 2021 to ensure the market mechanisms “accurately reflect the actual balance of supply and demand during stressed operating conditions.” Power suppliers underscheduled needed load by a combined 1,274 MW and 1,546 MW during net peak load, on Aug.14 and 15, respectively. In addition, flaws in the residual unit commitment process, which provides additional reliability checks based on CAISO forecasts of load after it’s cleared the integrated forward market, caused the grid operator to export needed power during the western-wide heat wave.

On Aug. 14, nearly 500,000 customers—300,000 in Pacific Gas & Electric territory and 234,00 in SCE—had their power cut for up to two and half hours. The next day, 321,000 customers—234,000 in PG&E territory—had their power turned off for up to one and a half hours.

The CPUC noted that demand response programs under performed, providing about 1,000 negawatts. However, its load drop analysis is inexact, the agency admits. In addition, the grid operator notes it could not determine all available demand response produced by the CPUC programs due to a lack of transparency.

CAISO will hold a call to discuss what it’s doing to prepare to ensure reliability this summer on Jan. 19 at 2 PM.

—Elizabeth McCarthy