Utah’s electricity customers will be getting a lot less of their power from coal and a lot more from renewable sources over the next several years under a plan PacifiCorp unveiled Thursday.

The owner of Utah’s largest utility plans to retire 16 of its costliest coal-fired power-generation units by 2030, reducing its coal generation by 3,000 megawatts. PacifiCorp still expects to get 20 more years of life from Emery County’s Hunter and Huntington plants.

But two major Wyoming coal plants’ days are numbered under PacifiCorp’s draft Integrated Resource Plan, the utility’s road map for meeting electrical demand in its six-state service area.

Much of that lost power generation will be offset by new solar and wind projects representing 7,000 megawatts, according to Jon Cox, vice president of government affairs for Rocky Mountain Power, a subsidiary of PacifiCorp.

“The numbers we have on carbon emissions with this plan would show us going from a 2005 baseline of 43% reduction in carbon emissions by 2025 and 59% reduction by 2030,” Cox said.

PacifiCorp presented the plan during an all-day meeting Thursday at its Salt Lake City office, 1407 W. North Temple, and plans to field public comment Friday. The utility will file its final plan Oct. 18 with the the six states’ regulatory commissions.

The proposal marks a big pivot toward renewables for PacifiCorp, which has long relied on coal for the bulk of its generation, and represents a step in the right direction toward a more environmentally responsible strategy, according to Sophie Hayes, energy policy expert and attorney with Western Resource Advocates.

“It acknowledges that moving to clean energy benefits ratepayers,” Hayes said. "Also, during this transition from coal to clean energy, it is critical to acknowledge the contribution of coal communities in serving our power needs and to work to provide those communities with new economic opportunities.”

PacifiCorp’s shift away from coal is largely driven by economics and the need to keep electrical rates low.

Under pressure from Oregon regulators, PacifiCorp has been conducting in-depth cost analyses of its coal fleet in recent months. That review, along with others commissioned by the Sierra Club, showed prolonged operation of certain coal-fired units would not be in ratepayers’ best interest. Thanks to falling prices of wind and solar enabled by technological advances and economies of scale as their use spreads, renewables offer cheaper power than aging coal plants.

Various advocacy groups cited those findings in urging PacifiCorp to speed up coal-plant retirements.

The utility’s plan appears to accede to those requests. Two of Wyoming’s Bridger units would close in 2023 and in 2028, way ahead of their planned shutdowns in 2037. Likewise, two Naughton units in Wyoming would close four years early in 2025 and a third would convert to natural gas next year.

“Rocky Mountain Power’s coal fleet is becoming less and less economical as the price of renewable energy continues to fall," said Hunter Holman, staff attorney with Utah Clean Energy. “The energy landscape is changing, and so it is essential that Rocky Mountain Power provide customers with transparency about future energy resource plans and the changing grid.”

Power generation from Utah’s Hunter and Huntington plants has already been reduced due to a glut of solar power generated in California that is available dirt cheap in early afternoon, according to Cox. As Rocky Mountain Power buys this green juice, it can power down the two Emery County power plants, which now burn less coal than they have in the past.

While coal has remained central to Rocky Mountain Power’s generating capacity in recent years, the nation as a whole has been turning away from the black rock in favor of natural gas, which emits much less carbon dioxide per unit of electricity produced, and emission-free renewables.

Natural gas eclipsed coal as the nation’s leading power source a few years ago, with coal now accounting for a quarter of generation and 10% coming from nonhydro renewables, according to the U.S. Energy Information Administration. Moody’s Investors Service predicts coal-fired power could decline to just 11% of U.S. electricity by 2030.

Seen in this context, PacifiCorp’s plan is in line with what has been unfolding across the nation, although a little behind the curve. While natural gas has been touted as “bridge” fuel to a carbon-neutral future, PacifiCorp envisions only limited new generation from natural gas, even though it is abundantly available in Utah, Wyoming and Colorado.

The plan calls for 3,500 megawatts of new wind generation by 2025, mostly developed in Wyoming and some in Idaho, as well as another 3,000 megawatts of solar, with much of that in Utah. Complementing the solar projects will be 600 megawatts of short-term battery storage that will allow power generated in the middle of the day to be used a few hours later as energy demand peaks, Cox explained.

Utah has 1,600 megawatts of solar generation, with nearly 300 of that mounted on the roofs of 36,698 customers’ homes, he said.

Looking to 2038, the plan calls for 4,600 megawatts of new wind, 6,300 megawatts of new solar and 2,800 megawatts of battery storage. PacifiCorp plans to solicit proposals from battery-technology firms to design and build the storage components.

To move wind power out of southeast Wyoming, PacifiCorp will build the 400-mile Gateway South transmission line running into northern Utah. That project has secured necessary federal permits but still needs approval from the Utah Public Service Commission.

“Making the necessary long-term investments to relieve transmission congestion will allow development of additional renewable resources in the near term and facilitate long-term growth of the region,” said Chad Teply, PacifiCorp’s senior vice president for business policy and development.

At a news conference Thursday, Salt Lake City mayoral candidate Erin Mendenhall welcomed the early retirement of PacifiCorp’s four largest coal-powered units.

“It’s great news for the climate and for our next mayor, who will be negotiating with them to get renewable energy into Salt Lake City faster," the city councilwoman said. "This is the kind of significant transformation that power providers all over the country — including and especially Rocky Mountain Power, as they provide power to this serious nonattainment air-quality area — need to be making.”

State lawmakers created a framework earlier this year for local governments to work with the utility toward the goal of powering their communities with net 100% renewable energy by 2030. So far, Salt Lake City, Park City, Moab, Cottonwood Heights and Summit County have voted to opt into the program, with more likely to follow before an end-of-the-year deadline.

Both Mendenhall and her opponent, state Sen. Luz Escamilla, have pledged to try to advance that date to 2023 during contract renegotiations with the power provider next year.

“The faster we can get there," Escamilla said in a recent interview, “the better.”

Tribune reporter Taylor Stevens contributed to this article