Most of the electricity produced in Colorado still comes from burning coal, but even the state’s two largest coal burners are adding more renewable energy.

The Tri-State Generation and Transmission Association and Platte River Power Authority each recently announced plans for new renewable energy sources.

“We’ve seen the prices dropping, and we’ve been able to add these renewable energy projects,” said Lee Boughey, a spokesman for Westminster-based Tri-State.

Tri-State announced this month that it would add a 150-megawatt wind farm in Kit Carson County.

Platte River Power, based in Fort Collins, is set to add a 22-megawatt solar installation near Wellington.

“Their recent investments in wind and solar represent real progress and are important steps toward diversifying their power supplies,” said John Nielsen, energy program director at the environmental group Western Resource Advocates.

Colorado has a Renewable Energy Standard that requires investor-owned utilities to get 30 percent of their electricity from renewable sources by 2020.

Municipal utilities have a 10 percent target, and rural electric cooperatives, under a bill in the legislature, would have a 15 percent target.

Platte River Power and Tri-State are wholesale electricity generators and do not fall directly under the standards for renewable energy. Tri-State provides electricity to 44 rural electric cooperatives in four states, including 18 in Colorado.

Platte River Power serves municipal systems in Estes Park, Fort Collins, Longmont and Loveland.

About three-quarters of the electricity the two companies generated in 2014 came from coal, according to company figures.

And so, while there have been advances in adding natural gas and renewable energy generation, coal remains king in Colorado.

In December 2014, 58 percent of Colorado’s electricity generation came from coal-fired plants, and renewable sources made up 15 percent.

By comparison, Minneapolis-based Xcel Energy, Colorado’s largest electricity supplier, cut its coal-fired generation to 53 percent in 2014 from 65 percent in 2005.

Xcel, an investor-owned utility, projects coal will be 46 percent of generation in 2020 and renewable sources 28 percent. About 26 percent will be natural gas.

Still, Tri-State and Platte River Power slowly are adding renewable sources.

Tri-State has added 800 megawatts of renewable resources since 2008, Boughey said, and 24 percent of its electricity came from wind and hydropower in 2014.

In 2013, for example, Tri-State contracted with the city of Boulder to buy electricity from the Boulder Canyon Hydroelectric facility.

The new Kit Carson wind farm is being built by Juno Beach, Fla.-based NextEra Energy at a cost of $240 million and will sell power to Tri-State on a 25-year contract.

While the prices for renewable energy are coming down, Tri-State’s Boughey said the challenge is adding transmission to tie in those resources.

Tri-State is building a 72-mile line between Burlington and Wray at a projected cost of $40 million.

“Building transmission lines is time-consuming and costly,” Boughey said.

Tri-State’s member cooperatives also added 54 megawatts of distributed renewable-energy resources, and an additional 15 megawatts are under development. Distributed resources are smaller generation projects that include wind, solar, hydropower and recycled-heat projects, Boughey said.

In October, Tri-State put out a call for proposals for additional renewable-energy projects and those are now under review, Boughey said.

Platte River Power generates less than 5 percent of its power from wind and, at the moment, none from solar. About 20 percent of the authority’s power comes from hydroelectric plants.

The authority board, however, has set a goal for reducing carbon emissions from power generation by 20 percent by 2020 and 80 percent by 2050.

Coal-fired power plants are the largest single source of carbon dioxide emissions — about 30 percent of the nation’s 2014 total, according to the federal Energy Information Administration.

Carbon dioxide is the main greenhouse gas linked to climate change in numerous scientific studies.

And so, the Platte River Power Authority board’s request is aimed directly at the company’s three large coal-fired plants.

The federal Environmental Protection Agency has drafted rules that would require Colorado to cut back power plant carbon emissions by 35 percent by 2030.

Platte River Power is well on the way to raising its renewable energy to 32 percent by 2016, said John Bleem, the authority’s planning and customer service director.

That figure includes hydropower and renewable energy credits purchased from renewable-energy installations in other states, Bleem said.

As for trying to get to the goal of an 80 percent cut in carbon by 2050, Bleem said “we’ve been crunching the numbers.”

That goal has to be met in the context of maintaining reliability of the system and keeping rates among the lowest of wholesale suppliers, Bleem said.

Platte River Power sells kilowatt-hours to its municipal systems for about 5.5 cents a kilowatt-hour, Bleem said. That is about half the rate Xcel charges residential customers.

The steps taken by Platte River Power and Tri-State allow them to better integrate renewable energy on their systems, said Western Resource Advocates’ Nielsen.

“With this experience in hand, resistance to these technologies decreases and utilities become much more open to acquiring additional renewable energy,” Nielsen said. “Our hope is that this will be the case with both Platte River and Tri-State.”