Last year, the Minnesota Legislature passed a law requiring the state’s electrical utilities to transition to 100 percent carbon-free energy sources by 2040. That means replacing power sources that produce carbon dioxide such as coal and natural gas with renewable sources such as solar, wind, hydropower and biomass.But how do you define “carbon-free” and what guidelines will be used to make sure utilities are meeting that standard? “We’re really hoping that carbon-free actually means carbon-free,” said B. Rosas, a policy manager with the advocacy group Climate Generation. Rosas talked to Paul Huttner about the organization’s efforts. To hear the full conversation, click play on the audio player above or subscribe to the Climate Cast podcast.