ST. PAUL — Gov. Tim Walz’s plan for Minnesota to get 100 percent of its electricity from carbon-free sources by 2050 was criticized Tuesday at its first legislative hearing, with representatives from some of the state’s smaller utilities saying they can’t meet that goal.

Commerce Commissioner Steve Kelley told the House climate committee that the Democratic governor’s plan is ambitious. But he said the state’s generating system is “aging and at a critical juncture,” with plants that produce 70 percent of the state’s electricity coming up for potential retirement over the next two decades. He said it will ensure that utilities replace them with wind, solar and other innovative sources, and increased energy efficiency, before turning to fossil fuels.

“Utilities will simply need to demonstrate why clean energy would not work whenever they propose to replace or add new generating capacity,” he said.

Walz’s plan, announced last week, seeks to build on the success of a 2007 law that required Minnesota utilities to get at least 25 percent of their electricity from renewable sources by 2025. The state largely achieved that goal in 2017 thanks to the growth of wind and solar power.