How NREL is improving GHG calculations for power plants

With clean energy and energy security important in the national dialogue, the financial, power generation, power purchase, and policy making communities are seeking more precise information on greenhouse gas (GHG) emissions from various sources of energy. These stakeholders need credible estimates of GHG emissions from power plants (both existing and planned) to develop and comply with environmental and energy requirements, and to help quantify the financial implications of a potential future carbon cost for specific electricity generation technologies.

The National Renewable Energy Laboratory’s (NREL) life-cycle assessment (LCA) harmonization project gives these stakeholders more precise estimates of GHG emissions for renewable and conventional electricity generation technologies. The research also clarifies inconsistent and conflicting estimates in the published literature, reducing uncertainty. Results can inform analysis and decision-making by policymakers, project developers, investors, manufacturers, and utilities or can be used to develop estimates for specific projects.

The results of NREL’s study are detailed in a special supplemental issue, Meta-analysis of Life Cycle Assessment, of the Journal of Industrial Ecology, a peer-reviewed international journal owned by the Yale University School of Forestry and Environmental Studies. Overall, the harmonization process increased the precision of life cycle GHG emission estimates in the literature while having little impact on the median--or central tendency--of these estimates. Results of this research reveal, for instance, that from cradle to grave; solar, wind, and nuclear energy emit similar levels of GHGs per unit of generated electricity, whereas life cycle GHG emissions from coal-fired electricity are about 20 times higher than for those technologies.

LCA Literature Review

NREL considered more than 2,100 published life cycle assessments of electricity generation technologies—renewable, fossil, and nuclear. Systematic review, comprising three rounds of screening by multiple independent experts, narrowed the field to select references that met strict criteria for quality, relevance, and transparency. Only 14% of the original pool of references passed this review process. Figure 1 compares the screened life cycle GHG estimates for hydropower, ocean, geothermal, biopower, solar (photovoltaic [PV] and concentrating solar power [CSP]), wind, nuclear, coal, and natural gas technologies.

Figure 1. Comparison of as-published lifecycle greenhouse gas emission estimates for electricity generation technologies. The impacts of the land use change are excluded from this analysis. Source: Figure 9.8 of Sathaye et al. (2011)

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