Regulators want to hear what ­citizens think about Xcel Energy's giant coal-fired power plant in Becker, Minn.

As long as they keep it to three minutes.

As a courtesy to prominent climate activists, the state Public Utilities Commission has set aside time at its Dec. 5 meeting to hear their views on a procedural matter with implications for the future of coal-based electricity in Minnesota.

Polar explorer Will ­Steger and St. Paul attorney Barbara Freese, author of "Coal: A Human History," are among the activists who want ­regulators to consider shutting down the two oldest coal units at Xcel's Sherco power plant by the end of the decade.

"The issue is not to slate these huge units for closure right now," Freese said in an interview. "The question is whether we can do it in 2020. Closing units this big really takes years of planning."

Sherco units 1 and 2 supply about 20 percent of the electricity used by Xcel's 1.2 million Minnesota customers. The plant 45 miles northwest of the Twin Cities also has a third, newer unit. Altogether, the plant burns three trainloads of coal daily and is the state's largest greenhouse gas emitter.

Xcel is spending $33 million on mercury and other emission controls to keep Units 1-2 running for now. But the ultimate fate of those units will be examined in the utility's next long-range plan, which is to be presented to the PUC in 2014.

The key decision facing state regulators is what questions Xcel should study in its long-range plan. The five-member commission usually doesn't hear public testimony on such ­procedural matters.

But some climate activists believe the only question is how soon the two oldest units can be retired. When Steger, Freese and Rose Thelen, founder of Beyond Coal Central Minnesota, asked to speak to that point last month, the commission decided to delay the Xcel vote until next week so anyone else could offer comments.

Freese, a former assistant state attorney general who helped establish the state's first carbon pricing in the 1990s, said state law sets a goal of reducing greenhouse gases by 30 percent by 2025. She said utility commissioners are required by law to ­consider that goal as they regulate power companies.

Anyone who has something to say can sign up by next Monday by phone or e-mail, but the registration is first come, first served. The commission said it will allow 30 minutes for all speakers, with no more than three minutes per speaker.

Steger, whose Minneapolis-based foundation is dedicated to addressing climate change, said he's been traveling around the state talking and listening to people about climate change.

"I think in three minutes I can make my point pretty clear," he said.

David Shaffer • 612-673-7090 Twitter: @ShafferStrib