Under orders from state regulators, the company that supplies electricity to most of southern California said it will expand a key conservation program, meaning more $200 checks for residents who agree to shut off air conditioners -- and probably larger electricity bills for those who don't.

Southern California Edison and most other electricity providers already offer discounts to families who volunteer ahead of time to let the company shut off their air conditioners during power emergencies. The company said 5 percent of its 3.8 million customers already take advantage of its discounts, which range from about $50 to $200, depending on how long customers allow their systems to be shut off.

Shutoffs generally occur during "Stage 2" emergencies, when electricity use in the state surges past 95 percent of generating capacity, as it did July 25. The president of the California Independent System Operator said Californians' failure to conserve energy could lead to rolling blackouts -- short, involuntary interruptions across the state.

The Public Utilities Commission on Tuesday ordered Edison to expand the program of voluntary interruptions and build several small power plants by next summer

"Last month's heat storm, and the evident and surprising growth in demand that had occurred even before the heat storm, gave rise to the need for further action," Commissioner Michael Peevey wrote in the order.

Peevey also directed San Diego Gas & Electric and Pacific Gas & Electric, which supplies power to most of northern California, to assess the need for such steps in their territories.

Edison is already able to reduce electricity use by 390 megawatts by turning off the air conditioners in the 184,200 households that participate. The company installs radio-activated device in the air conditioner when the customer signs up.

Peevey's order calls for 300 additional megawatts of capacity.

The program is voluntary and participation does not appear to be limited. A spokesman wasn't immediately able to say how Edison would rope in more volunteers, but possibilities might include increasing the discounts or advertising the program more heavily.

But what's good for thrifty and ascetic might not be so good for people who keep the pool filter running and the thermostat at 75 degrees through the night. Peevey indicated in the order that Edison could recoup the higher costs through higher rates, a move that the commission would have to approve. That could happen before next summer, according to Susan Carothers, a spokeswoman for the commission.

Murrieta resident Eliza Johnston hinted at one possible reason why only 4.8 percent of Edison's customers take advantage of the discounts. Johnston said she and her husband kept their electricity bill to $213 last month by relying mainly on fans and breeze, but she said she felt safer always having the air conditioner available. The heat can be hard on her 6-year-old and 7-year-old, she said.

For that reason, she said they probably wouldn't participate in an expanded program of discounts.

"I would recommend it for my in-laws," she added.

Peevey ordered Edison to build several plants that would enable it to generate another 250 megawatts of electricity on notice as short as 10 minutes. Known as "peakers," such plants are smaller and less efficient than the generators that remain on throughout the day.

Gil Alexander, an Edison spokesman, said five or six peakers could meet the commission's requirement. The plants generally cost about $40 million each to build, Carothers said.

- Contact staff writer Chris Bagley at (951) 676-4315, Ext. 2615, or cbagley@californian.com.