Some of the ways these cities are getting their electricity. Creative commons Despite the gains we've made in renewable energy, Americans' reliance on fossil fuels seems hard to escape. But some cities are leading the way.

The environmental group Sierra Club compiled a list of some of the US cities that are on track to becoming 100% powered by renewable energy in the next 20 years — including some that are already there.

The group defined renewable energy as "carbon- and pollution-free energy collected from renewable, sustainably harvested sources, such as wind, solar, hydro, tidal, and geothermal, as well as energy efficiency.

"Our definition does not include natural gas, nuclear, or any carbon-based energy source."

Here are the 10 cities that are committed to pulling it off: