On Thursday, Washington state's House of Representatives passed a bill that will require 100 percent of the state's electricity generation to be carbon emissions-free by 2045.

A previous bill was passed in the state's Senate in early March, though the House amended its version, so the Senate will have to vote again on the bill's updated language, according to the Associated Press. However, the bill previously passed the Senate on a 28-19 vote, and it is expected to pass again. The legislation was part of a key campaign promise made by Governor Jay Inslee, who is expected to sign the resulting bill.

Washington has massive hydroelectric resources as well as a 1.1 gigawatt (GW) nuclear power facility in Richland, Washington. Seventy-five percent of the electricity it produces is already free of carbon emissions.

Still, Washington does rely on some coal-fired power to this day, which will have to be phased out to comply with the new rule. The House measure that passed on Thursday "would require utilities to eliminate coal as an energy source by the end of 2025 as the first step toward a goal to provide carbon-free electricity by 2045," according to the Associated Press.

Last year, the state's last remaining coal plant in Centralia, Washington, scheduled the retirement of its two coal-fired turbines: the first by 2020 and the second by 2025. Washington utilities also receive coal-fired electricity from the Colstrip plant in Montana, but they are scheduled to stop paying for Colstrip electricity by 2022.

Washington follows Hawaii, California, and New Mexico in supporting rules that eliminate carbon emissions from the energy sector by 2045. Hawaii has historically had some of the highest electricity costs in the nation, because so much of its electricity was powered by imported petroleum. While California had long-since phased out coal when it passed its 100-percent carbon-free bill, its dependence on natural gas will be hard for the massive state to break.