California officials responsible for the state's electric grid are scrambling to avoid blackouts in southern California this summer following news that a major nuclear power plant will be offline indefinitely.

The effort to avoid a repeat of the costly power outages that plagued the state in 2000 and 2001 includes bringing old plants back online, commissioning new transmission lines and activating a multipronged emergency response system to cut power demand at peak times.

"We're not forecasting blackouts, but during very hot periods, either a very hot day or an extended heat wave, there are going to be challenges in southern California," said Steven Greenlee, a spokesman for the California Independent System Operator (CAISO), which manages the power grid that serves 30 million people.

The problem stems from breakdowns at the San Onofre nuclear power plant, located between Los Angeles and San Diego, which normally produces about 8 percent of the state's electricity. The plant's owner, Southern California Edison, announced earlier this month that both reactors at San Onofre would remain offline all summer as investigators determine what caused steam tubes in the plant to show premature wear.

To help fill the gap, California grid operators have called back into service two gas-fired units at an aging power plant in Huntington Beach that had been retired in January.

The state also accelerated the completion of two major transmission lines - Barre-Ellis and Sunrise Powerlink. Barre-Ellis connects two key southern California substations, while the 117-mile (188-km) Sunrise Powerlink electric "superhighway" connects Imperial County to San Diego.

The two measures together will almost make up for the loss of San Onofre's output, grid operators say.

AIR CONDITIONING RUSH HOUR

In case the summer brings especially hot weather, the state has also reactivated two different emergency alert systems for the public and for businesses.

The Flex Alert program, which has been on the shelf for years, will inform the public via television, radio, email and even text message to limit their consumption by turning off lights, air conditioners and other household appliances during peak hours.

That's especially important during what CAISO's Greenlee refers to as the "air conditioning rush hour" between 4 p.m. and 6 p.m.

"People come home and the first thing they want to do is crank up the air. That sucks a lot of juice," he said.

CAISO has also activated an emergency program for businesses that use a lot of power, such as manufacturers and refineries. On days of extreme demand, the state can trigger the system, which will notify utilities to tell their large industrial users to limit or shut down their operations.

This summer may also test some power market reforms implemented in the wake of the California electricity crisis of 2000 and 2001, when millions of Californians experienced large-scale blackouts.

The blackouts, eventually found to have resulted from manipulation of the electricity market by now-defunct Enron Corp, were estimated to have cost the residents and businesses between $40 billion and $45 billion.

Following the crisis, CAISO sped up implementation of its "day-ahead" electricity market. Under that system, generators and purchasers agree on their needs ahead of time, giving the grid operator an early indication if demand is going to outstrip supply.

WEATHER KEY

Officials say that weather is now the key factor determining whether blackouts will occur.

A hot summer with prolonged heat waves or the unexpected failure of another power plant or transmission line could trigger rolling blackouts, warned a report in May by the North American Electric Reliability Corporation (NERC), a quasi-governmental agency that monitors bulk power systems.

The dry California winter has also increased the risk of wildfires this summer, which could force major power lines out of service.

"We have confidence in our mitigation plan," said Greenlee. "We may have to scramble, but we believe that we're going to be covered," he said.