A cap can extend to refineries or concrete plants whose emissions can't be supplanted by using renewable fuel sources. (sciencemag.org)
Democrats are still drafting the energy package, which also will include a boost in automobile fuel efficiency standards and requirements to use more renewable fuel sources like ethanol. (reuters.com)
However, the promise of fusion - based energy defies the common sense belief that an array of renewable fuel sources is needed to shift away from dirty carbon - based fuels. (treehugger.com)