The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) has developed a new approach to assessing greenhouse-gas emissions from energy sources such as coal, wind and solar that should help stakeholders decide which energy projects to build.

NREL analysts looked at more than 2,000 studies across several energy technologies, applied quality controls and greatly narrowed the range of estimates for greenhouse-gas emissions.

The study found that greenhouse-gas emissions from wind power and solar photovoltaics are about 5% of those from coal and that nuclear energy emissions are on par with those from renewable energy.

Renewables such as solar and wind produce far fewer greenhouse-gas emissions than coal, oil or natural gas while in operation. But the meta-analysis looked even deeper, at emissions estimates starting with the manufacture of solar panels, wind turbines, coal plants or natural-gas lines, all the way to the emissions estimates for decommissioning the sites.

Increasingly, lenders, utility executives and lawmakers are scrambling to get the most precise information on greenhouse-gas emissions from various sources of energy, and they are frequently frustrated by the huge range of those estimates.

State and local lawmakers, weighing the merits of a new coal-fired plant versus a wind farm, for example, are eager to know not just the relative financial costs, but also the impacts on the environment.

Project developers, investors, manufacturers and utilities all can use NREL's estimates as building blocks to making their own estimates of specific projects or to guide policy, NREL explains.