IEEE Power & Energy Magazine - March/April 2021 - 36

4) If CAISO enforced a gas constraint in the day-ahead
market and it subsequently learns from the gas company that the limitation is lifted, the company will no
longer enforce the constraint in the real-time market
but still settle the day-ahead market with the impact
of the constraint.
5) Similarly, CAISO may proactively enforce gas constraints if it anticipates that large imbalances between
gas schedules and the gas consumed could compromise electric or gas system reliability.
6) CAISO has the flexibility to adjust the hourly limitations of the gas constraints to no longer enforce these
limitations as conditions change or if it determines
that the enforcement of the constraint adversely impacts the market.
Figure 6 illustrates the number of days in which the electric market enforced the gas constraint across the different
markets. Overall, the frequency of enforcing gas constraints
has been very low as expected since this only happens when
limited gas supply conditions arise.
The effectiveness of enforcing a gas constraint in the market
to limit gas use in the system greatly depends on how accurate
the limit estimates are and on how timely they are enforced.
As part of the overall electric-gas coordination improvement
with Aliso Canyon, CAISO and the impacted gas company
have close coordination to learn about gas and electric system
conditions. As part of the day-ahead process, CAISO generates and posts the expected gas usages calculated in the twodays-in-advance market solution. This happens two days in
advance of the trading date and provides the first opportunity
to resources and gas companies to learn about the projected
gas usage from the gas-fired generators in the CAISO system.
Based on that projection, gas companies study gas conditions
to assess if such a level of gas usage can pose a challenge, and
they assess mitigating actions that can go back to ISO as maximum gas quotas are enforced in the corresponding markets.
Since the first effort to mitigate risk related to Aliso Canyon restrictions, CAISO has undertaken other initiatives

Number of Days

30
25
20
15
10
5
0

2016

2017

Day Ahead

Year

2018

Predispatch

2019
Dispatch

figure 6. The number of days with gas constraints enforced in the electric market.
36

ieee power & energy magazine

to ensure generators have the market mechanism to reflect
the changing gas conditions in their market bids and costs.
Some of them have been required to redesign entire portions
of market functionality in CAISO's markets. This will also
allow resources to sufficiently recover their costs under gasrestricted conditions.

Final Remarks
The transition toward a decarbonized grid presents unique
challenges in the management and operation of electric systems. The resource mix is quickly evolving with growing
penetrations of variable generation resources, such as the
addition of more renewable resources and the electrification
of transportation. This type of generation introduces large
ramping characteristics that conventional generation, such as
gas-fired resources, will need to help absorb. Gas resources
still represent a significant share of supply in CAISO's system, and efficient dispatch has direct implications on the
overall market performance and pricing. In recent years,
electric-gas coordination has become critical to ensure reliability in both the gas and electric systems when gas supply
may be restricted in specific regions of the system. CAISO's
market includes maximum gas-usage constraints in the market clearing process concurrently with transmission congestion management. This achieves efficient generation dispatch
by sending the right price signals to gas-fired resources. As
the grid continues to evolve with more and different types
of generation resources, other operational challenges may
come into place. The electric system will need to have new
and enhanced market mechanisms to properly manage and
price such conditions.

For Further Reading
" Stakeholder initiative for Aliso Canyon gas-electric
coordination, " Caiso.com. [Online]. Available: https://
stakeholdercenter.caiso.com/StakeholderInitiatives/Aliso
-Canyon-gas-electric-coordination
California Public Utilities Commission. Accessed May
2020. [Online]. Available: www.cpuc.ca.gov
" 2020 summer load and resources assessment, " CAISO,
Folsom, CA, May 15, 2020. [Online]. Available: http://www
.caiso.com/Documents/2020SummerLoadsandResources
Assessment.pdf
" Summer 2020 Southern California Reliability Assessment, " California Public Utilities Commission, San Francisco, Apr. 15, 2020. Available at https://www.cpuc.ca.gov/
uploadedFiles/CPUCWebsite/Content / News_Room /
NewsUpdates/2020/Summer2020-ReliabilityAssessment_
Final.pdf

Biography
Guillermo Bautista Alderete is with the California Independent System Operator, Folsom, California, 95630,
USA.
p&e

march/april 2021

http://stakeholdercenter.caiso.com/StakeholderInitiatives/Aliso-canyon-gas-electric-coordination http://www.Caiso.com http://stakeholdercenter.caiso.com/StakeholderInitiatives/Aliso-canyon-gas-electric-coordination http://stakeholdercenter.caiso.com/StakeholderInitiatives/Aliso-canyon-gas-electric-coordination http://www.cpuc.ca.gov http://www.caiso.com/Documents/2020SummerLoadsandResourcesassessment.pdf http://www.caiso.com/Documents/2020SummerLoadsandResourcesassessment.pdf http://www.caiso.com/Documents/2020SummerLoadsandResourcesassessment.pdf https://www.cpuc.ca.gov/uploadedFiles/CPUCWebsite/Content/News_Room/NewsUpdates/2020/Summer2020-ReliabilityAssessment_ Final.pdf https://www.cpuc.ca.gov/uploadedFiles/CPUCWebsite/Content/News_Room/NewsUpdates/2020/Summer2020-ReliabilityAssessment_ Final.pdf https://www.cpuc.ca.gov/uploadedFiles/CPUCWebsite/Content/News_Room/NewsUpdates/2020/Summer2020-ReliabilityAssessment_ Final.pdf https://www.cpuc.ca.gov/uploadedFiles/CPUCWebsite/Content/News_Room/NewsUpdates/2020/Summer2020-ReliabilityAssessment_ Final.pdf

IEEE Power & Energy Magazine - March/April 2021

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