Record high temperatures throughout Southern California triggered the state's first major power blackout since the energy crisis, leaving 70,000 customers in the dark for 21 minutes.
The problems weren't the result of power plant meltdowns or market manipulation but something more mundane: Too many people used their air conditioners at the same time.
The state's grid operator declared an emergency at 6:21 p.m. Monday when hotter-than-expected weather pushed electricity demand above anticipated levels and threatened to overload a key transmission line.
To prevent widespread power problems, the California Independent System Operator said Tuesday, it ordered Southern California Edison Co. to immediately cut electricity usage by 300 megawatts, triggering a rolling blackout that hit pockets of homes and businesses throughout the utility's 11-county territory. The utility said 300 megawatts was enough electricity to power about 300,000 homes.
Power was restored to the affected customers at 6:42 p.m., and there were no further reductions, according to Southern California Edison, a unit of Edison International of Rosemead.
Officials at Cal-ISO, which runs the electricity transmission grid for about 75% of California, said that the state did not run short of power but that there was not enough in the south.
In essence, heavy air conditioner use pushed up demand faster than Cal-ISO could increase supply by turning on power plants. The problem was compounded by a key transmission line that was too jammed to deliver backup supplies from the north.
The incident shows that California's fragile transmission system is still prone to overloading and is not flexible enough to shift power around the state in a pinch, market watchers said.
Even so, Cal-ISO and others contend that the outage was merely a heat-wave-triggered anomaly and not a sign of systemic troubles that could recur during the summer.
Temperatures throughout Southern California hit unexpected highs Monday, soaring to the upper 80s and low 90s, with readings of 93 in Los Angeles and 94 in Yorba Linda.
"In Los Angeles, it was 8 degrees hotter than forecast; San Diego was 7 degrees hotter -- that's a significant difference" for the utilities that plan their power needs based on weather forecasts, said Gregg Fishman, a Cal-ISO spokesman. He said some electricity plants were offline for maintenance and could not be restarted in time to satisfy the energy shortfall.
"Those are the sorts of temperatures you get in the summer, but we're not ready for it in March," said Severin Borenstein, director of the UC Energy Institute in Berkeley. "This really is not an indication of problems for the summer. It does not mean that California has a shortage of generating capacity."
Said Ron Nunnally, director of federal regulation and contracts at Southern California Edison: "In reality we have a much better resource picture today than we had several years ago. I don't think it's a precursor to what will happen in the summer or a return to curtailments."
Nunnally said the company first turned to customers included in the utility's interruptible power program, a set of primarily business users that agree to curtail their energy consumption in return for lower rates.
Southern California Edison also cut power to customers that volunteered for programs that turn off air conditioners and agricultural pumping when necessary, he said.
Although the company got a "significant response" from its voluntary curtailment programs, demand wasn't reduced fast enough to prevent a blackout, Nunnally said.
Limited capacity on a key north-south transmission line prevented the grid operator from importing enough power to fill the void in Southern California. The line at issue, called Path 26, has three 500-volt cables stretching from the Bakersfield area to Palmdale. Cal-ISO has begun an investigation to find out "the nitty-gritty details" of Monday's failure, Fishman said.
The last time Southern California Edison customers experienced a blackout came May 8, 2001, while the state was still struggling to extricate itself from an energy crisis that yielded power emergencies and soaring electricity bills -- and, later, charges that certain energy companies had manipulated the market to boost their profits.