IEEE Power & Energy Magazine - March/April 2021 - 31

balancing areas, natural gas providers, and the California
Department of Forestry and Fire Protection.

Gas System in California

facility is a key part of the gas system in the Los Angeles
Basin. The leak impacted the overall gas market, including
gas-fired generating plants in that area. Following the leak,
the withdrawal and injection of gas in this storage facility
were largely restricted. Aliso Canyon supplies gas to 17
natural gas-fired power plants, accounting for more than
9,000 MW of generation capacity, while also indirectly
impacting more than 40 plants, totaling 20,000 MW in the
southern part of the system.
The California Energy Commission, CPUC, Los Angeles Department of Water and Power, and CAISO formed
an interagency task force in consultation with SoCalGas to
assess the risks of the limited supply availability that Aliso
Canyon introduced to the gas and electric markets. Among
the various risks, this assessed the reliability risks of load
interruption in the electric market.

10:00 p.m.

8:00 p.m.

6:00 p.m.

4:00 p.m.

2:00 p.m.

12:00 p.m.

8:00 a.m.

10:00 a.m.

6:00 a.m.

4:00 a.m.

2:00 a.m.

Net Load (MW)

12:00 a.m.

Supply (MW)

The gas system in California is defined in two major areas:
one in Northern California, covered by Pacific Gas and Electric (PG&E), and one in Southern California with Southern
California Gas Company (SoCalGas). These companies supply gas not only to gas-fired generators but also to residential and industrial customers. Electric generators are deemed
noncore customers, and, when the gas supply is limited, curtailments apply to noncore customers first.
The majority of the natural gas in California is supplied
from locations outside of the state, including Canada, the
U.S. Rocky Mountains, and the U.S. Southwest. California
has its gas supplied through the interstate gas pipeline system, composed mainly of Kern River, El Paso, Gas Transmission Northwest, Transwestern, Ruby, and Mojave Pipelines. PG&E and SoCalGas deliver gas through the intrastate
40,000
pipeline system known as the backbone gas system, which is
35,000
further distributed through local pipelines. Large customers,
30,000
such as some electric generators, may be connected directly
25,000
to the backbone system.
20,000
15,000
In addition to some independently owned storage facili10,000
ties, both PG&E and SoCalGas own and manage gas storage
5,000
facilities within their service territory. Such facilities expand
0
the gas capacity to meet the demand that otherwise would
require additional pipeline infrastructure. The SoCalGas
system has four storage facilities interconnected through the
transmission pipeline system, namely Aliso Canyon, Honor
Time
Ranch, La Goleta, and Playa del Rey. PG&E owns three
Nuclear Natural Gas Large Hydro
main gas storage facilities: McDonald Island being the largImports Renewables Batteries Coal
est storage, followed by Pleasant Creek and Los Medanos.
Unlike electricity, natural gas moves slowly in the pipelines at rates of no more than 30 mi/h. This requires the use of figure 2. A daily supply profile on a summer day of 2019.
gas from storage facilities to complement the supply from the pipelines to meet expected demand.
28,000
Both PG&E and SoCalGas are
operators for their gas systems.
26,000
Analogous to an electric system,
24,000
there is a need to balance the gas
supply from the pipeline system
22,000
2012
and storage with the demand of
20,000
customers. When supply is lim2013
ited to meet all of the expected gas
18,000
2014
demand, gas system operators can
2015
16,000
issue curtailments for gas deliv2016
3-h Ramp
eries, typically starting from the
2017
14,000
of 15,639 MW on
2018
Net Load of
large noncore customers, such as
1 January 2019
5,439 MW on
12,000
electric generators.
2019
5 May 2019
In October 2015, Aliso Can10,000
yon natural gas storage located in
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Southern California experienced a
significant gas leak. This storage figure 3. The progression of net load curves for CAISO's system.
march/april 2021

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IEEE Power & Energy Magazine - March/April 2021

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