California power outages suspended--for now

But experts warned that outages could resume Thursday evening or Friday if Californians slack off in recent conservation measures. The threat of blackouts looms for roughly the next week, warned the California Independent System Operator (ISO), which manages the power grid that transmits 75 percent of the state's power.

"The conservation is good news," said Kellan Fluckiger, chief operating officer of the ISO. "But in my mind it's clearly a crisis in terms of the number of actual or threatened shortages we've had."

The lights will likely stay on during the weekend, when schools and many corporations shut down. But Fluckiger warned that offices could go dark again on Monday, when usage resumes to peak weekday levels.

In a midday news conference, Fluckiger urged California's residents and businesses to limit their usage of electricity, especially Thursday from 5 p.m. to 10 p.m. PST--peak demand time, as countless street lights flicker on and residents come home from work, turn on lights, turn up the heat, and cook dinner.

"Consider the millions and millions of customers and let's do quick math," Fluckiger said. "I've got one 100-watt bulb, and 1 million customers turn off one extra bulb. That's 100 megawatts. We've got 10 million customers, so if they all turn off one bulb that could be 1,000 megawatts. You get the picture: Conservation can really make a huge difference."

The current reprieve in the state's controversial energy crisis is likely to be little comfort to the 1 million commercial and residential power users who were in the dark Thursday. The blackouts began at 9:45 a.m. and affected 1,000 megawatts of power. On Wednesday, blackouts snuffed out lights for as many as 500,000 users.

The blackouts struck with little or no warning to customers throughout Northern California, from roughly Bakersfield to the Oregon border. The blackouts, which lasted until about 1 p.m., persisted for about one hour, then rotated into another randomly selected block of customers on the power grid.

Numerous businesses in the Silicon Valley--ground zero for the nation's technology industry--have suffered outages in the past two days. On Thursday, office workers at companies ranging from San Francisco-based career portal GeekGirl.com to the South San Francisco campus of biotechnology giant Genentech headed outside as their cubicles went dark.

Corporations that have voluntarily agreed to interruptible service may be particularly at risk, the ISO said. So-called interruptible customers agree to cut off huge loads of power supply to receive monthly discounts on their energy bills. Typically, the customers get the discounts and must enforce conservation rules but rarely have to deal with blackouts.

Fluckiger would not say how many interruptible customers were without power Thursday but noted that "significant" numbers of them have been completely without power since shortly after 5 a.m. Thursday morning. On Wednesday, many were out for nearly 18 hours.

"They will be off for the bulk of the day, absent some significant change," Fluckiger said Thursday. "I understand this places an enormous burden on the businesses that sign up for this...They never intended that power would be out for this long."

Sunnyvale, Calif.-based Loudcloud, which provides Internet infrastructure operations for corporate clients, was in the dark Wednesday for at least 2 hours and faces more blackouts Thursday.

Loudcloud's Network Operations Center monitored the Web sites of the company's customers, which include Nike.com and Britannica.com. When it detected power interruptions around 12:15 p.m., the center's backup battery kicked in. A diesel generator, which has the ability to run constantly for up to 36 hours, then took over to power the clients' sites.

"We are one of those companies that customers rely on to keep their Internet operations up and running, so we've been getting lots of calls," said Loudcloud spokeswoman Charlotte Harrington. "One of the primary reasons customers go with a Loudcloud solution is to put the whole process in someone else's hands, no worries. When the power went out, my computer went dark, but our customers stayed up."

The energy crisis is likely to sting other Silicon Valley technology companies. The energy supply to utility companies other than Pacific Gas and Electric in the tech-heavy San Francisco Bay Area has also been curtailed. Tech companies that rely on the popular Sacramento Municipal Utility District and Silicon Valley Power will experience the same magnitude of blackouts as PG&E customers.

E-commerce companies that rely on smoothly functioning Web sites, often powered by servers in the Silicon Valley, lose anywhere from $1 million per hour to $1 million per minute when the power goes off. That's because customers can't place orders online, and the region's highly paid work force can't be productive.

Although it was not caused by a blackout, a November blowout at Seattle-based e-tailer Amazon.com showed how costly even a brief outage is. During the Thanksgiving holiday weekend, Amazon suffered a series of outages. Investment firm Thomas Weisel Partners estimated that one 20-minute outage deleted roughly 20,000 product orders and $500,000 in revenue.

Although the state's two largest utility companies, PG&E and Southern California Edison, are teetering on the brink of bankruptcy and cannot pay their energy suppliers, the ISO insisted that finances are not the main cause of the blackouts.

California imports at least 20 percent of the energy it requires, typically from Arizona and the Pacific Northwest. An unusually cold and dry winter has inflated demand for energy to heat homes, while dozens of hydroelectric facilities and reservoirs in the West are nearly empty of water.

For example, Fluckiger said, the $1.14 billion Helms Pumped Storage Plant near the Courtright Dam near the Oregon border has almost no water in its upper reservoir and an extreme shortage in the lower reservoir. As of 11 a.m. Thursday, it had enough water to provide electricity only for about an hour.