Cows graze in the shadow of the coal fired Chalk Point Generating Station, on May 29, 2014 in Benedict, Maryland.   - 

The EPA’s plan to curb carbon-dioxide emissions lets each state figure out how its going to reach its goal. 

There are already big differences among states in one area: the cost of electricity for their residents.

In March, folks in Wyoming were paying ten cents per kilowatt hour, but people in Massachusetts paid nearly double.

“The biggest factor here is that there’s just a lot of different generation mixes across the states," said Harrison Fell, a professor with the Colorado School of Mines.

Wyoming gets almost all of its energy from coal, while in Massachusetts it’s mostly natural gas, according to the Georgetown Climate Center.

 “The more coal intensive you are, the bigger impact the rules will be,” said Andrew Kleit is a professor of energy and environmental economics at Penn State.