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Coal-Fired Electricity Generation Results – Life Cycle Assessment Harmonization

Over the last 30 years, researchers have conducted hundreds of life cycle assessments of environmental impacts associated with coal-fired electricity generation technologies. These life cycle assessments have shown wide-ranging results.

To better understand the greenhouse gas (GHG) emissions from utility-scale, coal-fired electricity generation systems (based on subcritical pulverized, integrated gasification combine cycle (IGCC), fluidized bed (FB), and supercritical pulverized coal-combustion technologies), NREL developed and applied a systematic approach to review life cycle assessment literature, identify primary sources of variability, and, where possible, reduce variability in GHG emissions estimates through a "harmonization" process.

Harmonization for coal-fired power technologies was performed by adjusting published GHG estimates to achieve:

  1. Consistent values of two coal power performance parameters: thermal efficiency and combustion CO2 emission factor (CEF);
  2. A consistent system boundary, by addition of coalbed methane emissions from mining in the upstream stage and subtraction of the emissions from transmission and distribution in the downstream stage; and
  3. Consistent global warming potentials (GWP) (based on IPCC 2007).

The as-published and harmonized life cycle greenhouse gas emissions for coal technologies are summarized in the figure below.

Chart that shows a side-by-side comparison of coal-powered technologies. For help reading this chart, please contact the webmaster.

As-published and technology-specific harmonized estimates of life cycle GHG emissions for coal-fired electricity generation considering all four evaluated technologies as a group and each evaluated technology independently.

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Overall, this analysis shows that life cycle GHG emissions from coal-fired electricity generation are much greater than those from renewable and nuclear energy systems. In addition, the harmonization process increased the precision of life cycle GHG estimates for all coal technologies, with relatively little impact on overall central tendency.

Harmonization Impact on Variability and Central Tendency

Overall, harmonizing for all parameters (thermal efficiency and combustion, CO2 emission factor (CEF), a consistent system boundary, and global warming potentials (GWPs)) reduced the variability of published GHG emission estimates for all coal technologies by 40%–60% (based on interquartile rankings). Harmonization reduced the interquartile range (IQR) of the published estimates across all technologies from 265 g CO2e/kWh to 114 g CO2e/kWh, a decrease of 57%.

Of the parameters harmonized, adjusting reported data to a consistent carbon dioxide emission factor had the greatest impact on reducing variability in estimated life cycle GHG emissions estimates from coal-fired systems.

Harmonization reduced the median of the published estimates across all technologies from 1,001 g CO2e/kWh to 979 g CO2e/kWh, a reduction of approximately 2%.

Comparison of Harmonization Impacts on Specific Coal Technologies

For subcritical, IGCC, and supercritical coal combustion technologies, harmonization reduced the variability (based on IQR magnitudes) of the published life cycle GHG emission estimates by approximately 40% to 60%, without changing the central tendency by more than approximately 10% for any technology.

For FB combustion, harmonization resulted in a 15% increase in the median, but a 32% decrease in the overall range of estimates despite an increase in the IQR. The relatively large shift in median and the opposing shifts in IQR and range for FB is attributed to the small pool of estimates for FB technology.

Given the tightness of the distribution of the harmonized estimates across several key coal combustion technologies, the harmonized data can be used as starting points for comparing coal-fired electricity generation projects with other electricity generation options without requiring a full life cycle assessment be conducted with each new project.