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Post-nuclear grid withstands heat wave

By: Morgan Lee |

The San Onofre nuclear power plant
The San Onofre nuclear power plant , now idle, once produced 20 percent of San Diego’s electricity, — K.C. Alfred

San Diego’s power grid withstood its biggest challenge to date, smoothly handling record electricity consumption during an intense heat wave that scorched the county — and without the aid of the San Onofre nuclear plant.

Electricity supplies held up without nuclear power thanks to the region’s workhorse natural gas power plants and a new transmission lifeline linking San Diego to out-of-town power plants including wind and solar farms in the Imperial Valley, according to a preliminary assessment by San Diego Gas & Electric.

Demands on the electric grid for San Diego and southern Orange county broke all previous records on Monday afternoon, and then again on Tuesday, as millions of people retreated to air-conditioned spaces to escape hot, muggy weather. Temperatures rose above 90 on the San Diego coast and 107 farther inland during the four-day heat wave that started a week ago.

On Tuesday, the thirst for power climbed to 4,890 megawatts in areas served by San Diego Gas & Electric. The previous all-time peak load of 4,687 megawatts occurred on Sept. 27, 2010.

Twin reactors at San Onofre used to fulfill 20 percent of San Diego’s year-round power needs, up until the plant’s breakdown in January 2012. Without the plant, some state and federal energy officials questioned if San Diego would be able to maintain reliable electrical service during an energy crisis.

Jim Avery, senior vice president for power supply at San Diego Gas & Electric, described this heat wave and power crunch as a scenario that appears less than once in a decade.

September heat waves are typically blown in from the inland desert on dry Santa Ana winds. This time, heat was propelled by offshore forces linked to Hurricane Odile as it reached Southern Baja California.

To keep up, grid managers dispatched the entire local fleet of major natural gas power plants, from modern state-of-the-art generators in Escondido and Otay Mesa, to aging facilities like the Encina Power Station in Carlsbad and small plants sprinkled across San Diego County.

Electricity came in small doses from other local sources: the Kumeyaay Wind farm on the Campo Indian Reservation, utility-scale solar arrays at Borrego Springs and hydroelectric turbines above Lake Hodges.

Imports from beyond SDG&E territory, meanwhile, accounted for about 45 percent of supplies at the time of Tuesday’s power peak.

Avery of SDG&E credited a major new set of transmission lines, the Sunrise Power link, with expanding the ability to import electricity from east of San Diego, where 450 new megawatts of renewable power capacity has come online at new solar and wind plants.

The 500,000-volt link was completed within months of the shutdown of San Onofre. It stretches 117-miles from San Diego east into the Imperial Valley, roughly doubling import capabilities of the parallel Southwest Powerlink, built 25 years earlier.

Power reserves never fell below a 7 percent margin in excess of needs, the first threshold for emergency procedures.

Avery downplayed the supportive role of rooftop solar. By 4 p.m. on Tuesday, at the top of the electrical crescendo, local solar output had fallen with the angle of the sun and incoming cloud cover, he reasoned.

“Rooftop solar did absolutely nothing to mitigate the problems we have on our systems right now,” Avery said.

San Diego’s rising peak power demands stand in sharp contrast to statewide trends.

Peak power use across most of California has been on the decline since hitting an all-time high of 50,270 megawatts in July 2006. The high point of this year was 45,090 megawatts at 5 p.m. on Monday, according to the state’s main grid manager, the California Independent System Operator.

San Diego-based energy expert Bill Powers said air conditioning was the main perpetrator of San Diego’s new power-use record. To reverse current trends, he said SDG&E needs to vastly expand its efforts at improving the efficiency of air conditioning systems and staggering their use when power supplies are tight.

During this week’s heat wave, SDG&E activated programs providing incentives for conservation, reducing peak demands on Tuesday afternoon by 66 megawatts, or 1.3 percent of peak demand.

Of those power reductions, about 25 megawatts came from financial incentives to more than 28,000 customers who have agreed to have their air conditioning turned off partially or completely when supplies are tight. A newer program that provides rewards for turning up automated thermostats produced 1 megawatt of savings.

Despite the grid’s command performance under pressure, SDG&E asserts that plans for new gas-burning power plants at Otay Mesa and Carlsbad are warranted in order to retire an even greater share of older, inefficient natural gas generators at scattered locations.

The 60-year-old Encina facility, San Diego County’s largest power source, is among a series of coastal plants being phased out by California regulators in an effort to protect marine life from ocean-water cooling systems.

Conservation groups are lobbying for more time to flesh out clean-energy alternatives. SDG&E calls that approach irresponsible.

“Nobody has put a solution on the table to displace the need for those generators,” Avery said. “You do have people who raise the issues of, ‘Well the lights are on, we didn’t have a problem.’ They are completely forgetting about the fact that we have some old machines that fortunately held together through this heat storm.”

To reduce peak power demands in the future, SDG&E is pushing a proposal to overhaul residential utility bills and gradually introduce time-based pricing. That would eventually allow the utility to more effectively reward conservation and punish consumption when power supplies are tight.