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Scenes as California Power Use Hits New Peaks
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Some days are easier than others. This past week -- when California ISO's system sequentially set two new peak demand records on Tuesday, September 7 (45,165 MW), and again on Wednesday, September 8 (45,597 MW) -- illustrates what a difference a day can make in the lives of grid operators and utility dispatchers.
This had already been a record setting summer for California's grid. Five times in the previous seven weeks, moderate heat waves over Southern California pushed peak-hour demand to levels well above the July 1999 record figure of 43,609 MW 1. New peak demand figures were established three days in a row July 19-21, then twice again August 10-11. Even utility Southern California Edison announced a new all-time delivery record of 20,518 MW on August 10.
And there was certainly enough warning that system demand on September 7 could well top the 44,872 MW number set on August 11. Coming off a Labor Day holiday weekend marked by a lingering high-pressure system and some record temperatures over Northern California cities, there was sure to be a pent-up demand for residential and commercial air conditioning later in the day. Despite a heavy schedule of "Flex Your Power" ads being run on radio and TV stations to encourage conservation and peak-load shifting, operators knew that the third day of a heat wave brings a significant boost to energy use -- people can go only so long before resorting to the a/c.
As a precaution, California ISO issued a "restricted maintenance order" that morning and let power plant operators know they should be ready for a dispatch call.
Still, there was plenty of confidence in being able to meet the expected load without difficulties. There seemed to be sufficient in-state generation on-line or on standby, and imports from the Pacific Northwest and Desert Southwest were strong -- as much as 9,800 MW in some hours was scheduled and available.
The statewide picture looked good, with over 7,000 MW of surplus power on the books at noon -- over and above the 7 percent required reserve margin for each hour. One local trouble spot was in the Santa Rosa/Petaluma area, about 70 miles north of San Francisco. An extensive wildfire had been spreading throughout the weekend, threatening The Geysers, where Calpine Corporation and some munis own and operate geothermal power plants. Pacific Gas & Electric had been forced to take four transmission lines out of service in the area for several days, and that meant that about 400 MW of Calpine’s geothermal energy was shut in.
Aside from the lost generation, the situation merited careful watch from reliability coordinators. While PG&E rerouted power over other lines to ensure constant distribution to Santa Rosa and environs, transmission voltage frequencies fluctuated. As always, the dynamic equilibrium of demand and supply required careful balancing and close coordination among grid operator, distribution utility and power generators.
By 1 pm, however, the trend of energy consumption began diverging upward from ISO projections at just about the same time that the reserves chart plummeted by 1,000 MW. California ISO managers never confirm specific power plant outages, but it appears from the daily listings of non-operational units that sometime between 11 am and 3 pm two fairly significant generators fell off line: the 775 MW Ormand Beach No. 2 and the 227 MW Huntington Beach No. 4.
What had been a comfortable cushion of reserves thinned precariously as the supply and demand curves rapidly approached convergence. That 7,000 MW reserve slimmed to about 1,150 MW, according to ISO figures. Over the next three hours, the charts wobbled and dynamic equilibrium shifted. Several small hydroelectric units in Northern California were pressed into service, as were generators previously on maintenance waivers.
All the while, PG&E crews were cleaning the North Bay transmission lines of soot, ash and fire retardant. Shortly after 1 pm, the lines were re-energized and within the hour, power flows were restored from The Geysers units.
Just in time, too. By 4 pm, California ISO had established another record peak of 45,165 MW, almost 600 MW above the morning’s projections. Though it may have appeared touch-and-go for a little while, the new load was matched without any need for declaring a Stage One alert or requesting specific power curtailments from utility customers beyond the voluntary “Flex Your Power” efforts.
That’s not the end of the story. The next day, despite moderating temperatures, Californians used even more electricity and California ISO scheduled 45,597 MW over its lines at 4 pm—the seventh day this year that a new peak level was achieved.
There was little drama this time, as operators had the luxury of healthy reserve margins and no direct threats from wildfires, transmission outages or wobbly voltage frequencies. The supply curve remained steady and well above the lines of demand throughout the day.
The Bottom Line: California power officials had been projecting since early April that Summer 2004 would likely be a record peak year, due to a resurgent economy and the effects of a housing development boom in some of the state’s hottest, driest areas. Overall energy consumption this summer is not that much greater than expected, thanks to relatively mild temperatures. But the peaks are getting “peakier,” ISO officials noted, even without extreme temperatures. That makes it all the more imperative that new utility demand-response programs be employed and that voluntary conservation efforts, including the “Flex Your Power” continue.
Note: “Flex Your Power” and the California ISO’s latest transmission plans are just two of the many featured topics that will be covered as part of Law Seminars International’s “New Directions for California Energy Markets” conference, September 16-17, in San Francisco. I will serve as co-chair of the meeting, along with Dan Fessler, the former president of the California Public Utilities Commission. Our keynote speaker is Joe Desmond, California’s Deputy Secretary of Energy and Governor Arnold Schwarzenegger’s point person for energy policies. For agenda and registration information, please call LSI at (800) 854-8009.
Arthur O'Donnell is Energy Central's Editorial Director, Newsletters.
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