Energy use in Mendocino County has risen 27 percent — more than three times the state's average — since medical marijuana was legalized in 1996. Humboldt County's usage has risen 51 percent, more than six times the state's average, according to PG&E.

Growers and law enforcement officials attribute the spike to indoor pot growing, which requires energy-sucking fans, air filters and high-intensity lights.

Indoor pot gardens can use as much as 20 times the electricity as the average household, said Peter Lehman, director of Schatz Energy Research Center at Humboldt State University.

Statewide, energy consumption per household has increased 8 percent since 1996. Sonoma County's energy use rose by 9 percent, while Lake County's rose by 14 percent.

Indoor marijuana gardens have come under fire as wasteful, hypocritical and unnecessary, since marijuana already grows like a weed in the North Coast's Emerald Triangle.

"Plants are the original solar collectors," Lehman said. "They're very good at it."

Lehman said the problem is "particularly egregious here. It's expensive, it's bad for the environment, and it's wasteful. It's a misuse of a precious energy resource."

"It's amazing," said Matthew Cohen, executive director of Northstone Organics Cooperative Inc. in Mendocino County, a medical marijuana collective. "You have these progressive liberal folks who eat organic and maybe even drive a Prius but continuously burn 8,000 watts."

Northstone grows its plants outdoors and in greenhouses.

The average California household used 561 kilowatt hours in 2009, according to PG&E. In Humboldt County, the average was 673 kilowatt hours, and among PG&E's Mendocino County customers, it averaged 768 kilowatt hours.

Mendocino County's figures could be even higher because they don't include the city of Ukiah. It prohibits outdoor marijuana growing, forcing pot cultivators to move indoors.

Ukiah has its own electric utility, and usage figures were not available.

Law enforcement officials see unusually high energy consumption as a way to demonstrate probable cause when it comes time to obtain search warrants, said Bob Nishiyama, head of the Mendocino Major Crimes Task Force.

Indoor growers can spend as much as $4,000 a month on electricity, he said.

Cohen is part of a growing movement that promotes sustainable pot production, which means outdoor cultivation. He said there's no difference between indoor and outdoor pot if both are tended in the same, careful manner.

But Mendocino growers say pot dispensaries overwhelmingly want marijuana grown indoors, claiming it's of higher quality. They complain that Bay Area dispensaries won't even consider buying marijuana grown outdoors.

The National Organization for the Reform of Marijuana Laws has not taken a position on the issue, said state coordinator Dale Gieringer.

The energy use debate may be heating up. Oakland officials are already thinking about it as they make plans to permit large, industrial marijuana growing operations.

"They're talking about doing carbon offsets," Cohen said. "Is it OK to drive your Hummer around if you're donating to carbon offsets?"

Mendocino County grower Jim Hill believes the problem will sort itself out over time, sooner rather than later if voters legalize marijuana for all personal uses in November. If that happens, the supply of marijuana is expected to rise, causing prices to fall.

North Coast growers are already reporting a glut that has lowered the amount they receive for their product to about $2,000 a pound, down from about $4,000 several years ago.

"Eventually, there won't be any indoor" growing, Hill said.

PG&E officials declined to discuss the impact of indoor marijuana cultivation on energy use.

"What our customers do in their own homes is none of our business," said PG&E spokeswoman Brandi Ehlers.