SALEM — As Oregon prepares for legal marijuana July 1, the state’s energy agency is looking for ways to curb electricity use by indoor pot growers.

Indoor marijuana gardens are well-known power hogs, but Oregon faces a dilemma as it researches how to extend its energy efficiency programs to the cannabis industry: federal money that typically helps pay for efficiency projects cannot be used for any activities that involve pot.

“We don’t have answers to that yet, which is why we’re looking at it so carefully,” said Rachel Wray, a spokeswoman for the Oregon Department of Energy. “It is an emerging energy issue and we pay attention to those.”

Power-hungry grow lights and ventilation systems are not just an environmental issue.

Small, consumer-owned utilities across Oregon purchase electricity from the Bonneville Power Administration on a tiered system, which allows smaller utilities to purchase power at lower rates. Those rates could attract indoor growers, but the increased demand for electricity might drive up rates for all utility customers.

That prompted Ashland City Manger Dave Kanner to call for the state to adopt energy efficiency standards for indoor agriculture.

The Oregon Department of Energy tasked Diana Enright, program and policy adviser to agency director Michael Kaplan, with working on the intersection of pot and power.

Wray said cannabis remains “a small part of (Enright’s) policy portfolio,” but Enright attended a conference in December on energy demand from the marijuana industry. She is also following efforts to address the issue in two other states with legal recreational pot, Colorado and Washington.

In Colorado, Boulder County enacted a cannabis carbon tax, Enright said. Oregon state government is not currently considering anything similar.

On July 1, adults aged 21 and older can posses up to four marijuana plants. Growing those four plants indoors with lighting, climate control, ventilation and equipment to boost carbon dioxide to improve plant growth typically uses as much electricity as running 29 new refrigerators, according to one report by a California scientist. It is also equivalent to the total energy used by an average U.S. home.

“So you can start to see where the energy consumption is huge,” Enright said.

The Northwest Power and Conservation Council estimated in September that energy demand from pot growers in Washington, Oregon, Idaho and Montana will nearly double over the next 20 years.

The anticipated increase in energy demand from legal recreational marijuana also caught the attention of investor and consumer-owned utilities. At a hearing in February, Portland General Electric government affairs analyst Brendan McCarthy told lawmakers on the committee working to implement legal pot that 85 percent of residential transformer problems it handles are caused by indoor marijuana grows.

McCarthy said there is currently a shortage of information about energy demand from pot grows. Utilities want the information so they can deliver the power cannabis growers need and plan for energy efficiency measures. McCarthy said utilities also need that information so they can keep employees and customers safe.

“It doesn’t help us for someone to say, ‘We’re gonna start a pottery business and we’re gonna have a lot of kilns running,’” McCarthy said. “We’ve heard that.”

Power-hungry pot gardens can rival the energy intensity of data centers, with lights as intense as in operating rooms and air circulating at 60-times the rate of ventilation in a modern home.

The increase in energy usage that accompanies growth of the marijuana industry has been documented when states legalized medical pot.

After California legalized medical marijuana in 1996, per capita residential electricity usage increased by 50 percent in Humboldt County, according to research by Evan Mills, a senior scientist at the Lawrence Berkeley National Laboratory in California, published in the journal Energy Policy in 2012.

Enright said Mills’ research is still the “most definitive work” on energy consumption by pot growers.

Mills estimated at the time that indoor cannabis cultivation and transport of the product was responsible for 1 percent of national energy consumption or $6 billion each year. The study also looked into the amount of greenhouse gas emissions from pot gardens.

“One average kilogram of final product is associated with 4,600 kg of carbon dioxide emissions to the atmosphere, or that of 3 million average U.S. cars when aggregated across all national production,” Mills wrote.

Criminalization of marijuana was only part of the reason growers favored indoor gardens; the environmental control has also allowed them to increase yields and control pests and other issues. Mills wrote that indoor marijuana growers could reduce the energy intensity of their operations by as much as 75 percent, if they adopt commercially available technologies such as those used by indoor agricultural greenhouse operators.

This story first appeared in the Oregon Capital Insider newsletter. To subscribe, go to oregoncapitalinsider.com