Story highlights

Coal will remain the largest U.S. power source, an Energy Department report finds

Greater production and conservation efforts will reduce oil imports, the study projects

Renewable energy will provide 16% of American electricity by 2035, it concludes

CNN  — 

U.S. carbon emissions plunged during the 2007-2009 recession, and conservation efforts, a weak recovery and more use of natural gas will help keep those levels down for another 15 years, the Energy Department reported Monday.

Coal-fired power plants will remain the largest source of U.S. electricity throughout that period at nearly 40% of total output, the department projects in its annual report on the future of energy. But the Energy Information Administration’s 2012 report finds that emissions of the greenhouse gases blamed for a warming climate are likely to remain below their 2005 levels until 2027.

“These projections reflect increased energy efficiency throughout the economy, updated assessments of energy technologies and domestic energy resources, the influence of evolving consumer preferences and projected slow economic growth,” the agency’s acting administrator, Howard Gruenspecht, said in a statement accompanying the report.

Overall, the share of fossil fuels as an energy source is expected to drop from 83% to 77% in 2035, the report states.

Carbon-dioxide emissions fell by 3% in 2008 and nearly 7% in 2009 as the U.S. economy hit the skids, the report found. Those emissions are expected to resume their growth at a rate of about 3%, keeping them below 2005 levels for another 15 years, the EIA projects.

Meanwhile, increased domestic production, improvements in automotive mileage standards and higher international crude prices are expected to reduce the demand for imported oil between now and 2035, the report states.

Improvements in efficiency are projected to cut into the growth of electrical demand, and increased natural gas production will make natural gas more competitive with coal as a source of power-plant fuel, the study concluded.

The United States is likely to be a gas exporter by 2021, the report states. Natural gas will grow from about 24% of U.S. electrical generation to 27% in 2035, while renewable energy – solar, wind, biofuels and hydroelectricity – are expected to grow from 10% of American consumption in 2010 to 27% in 2035.

The use of nuclear power, meanwhile, is expected to dip slightly, from about 20% of 2010 production to 18% in 2035.