Minnesota has a new law that will require utilities to use wind, sun and cleaner-burning fuels to produce a quarter of the state's electricity by 2025, a standard that advocates called among the most aggressive in the country.

Gov. Tim Pawlenty was to sign the bill Thursday at University of Minnesota's Initiative for Renewable Energy and the Environment.

"It's easy to talk about and pass a 25 by 25 requirement," Pawlenty told business leaders on Wednesday. "Now we have to talk about how we get there."

The Minnesota law, which sailed through the Legislature, replaces an objective that encouraged power producers to draw 10 percent of retail electricity from renewable sources by 2015.

"It will be the strongest, most aggressive renewable energy standard in the country," said Rep. Aaron Peterson, a rural Democrat who sponsored the bill.

Under the law, all utilities except Xcel Energy Inc. would be bound by the 25-by-2025 standard. Xcel, which delivers half of Minnesota's electricity, would have to meet a 30 percent by 2020 benchmark.

There are escape valves, including an energy credit trading system to help producers struggling to meet the standard. Utility regulators could also delay or modify the timeline if they determine that the cost of meeting it would significantly increase customer bills.

The law comes as states around the country stake out far-off goals for renewable energy. More than 20 states have some type of renewable requirement or good-faith objective. Colorado is moving toward a standard of 20 percent by 2020, while New Hampshire Gov. John Lynch challenged lawmakers last week to adopt a 25 percent by 2025 requirement.

Minnesota's numerical goal trails targets already in place for Maine and New York. But those states had been getting a significant amount of electricity from large-scale hydropower facilities before their standards were adopted, according to a November report from Minnesota legislative researchers based on data from the Interstate Renewable Energy Council and the Union of Concerned Scientists.

By a 2004 federal government estimate, Minnesota depended on coal for almost half of the power produced within its borders and used hydroelectric, wind and other renewables for about 8 percent.

"As of a percentage of where all their electricity will come from, Minnesota is now in the lead with this policy in terms of supporting new renewable energy development," said Jeff Deyette, energy analyst at the Union of Concerned Scientists.

Clean-energy advocates are pressuring Congress to adopt a goal of getting 25 percent of the nation's energy — electricity, motor fuel and other power — from renewable sources by 2025. They are promoting wind farms, solar power, ethanol and biodiesel as ways to reduce reliance on foreign imports.