Life Cycle Assessment Harmonization Results and Findings
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The data from the Life Cycle Harmonization Project show that life cycle greenhouse gas (GHG) emissions from technologies powered by renewable resources are generally less than from those powered by fossil fuel-based resources.
Only the very highest estimates for biopower overlap with the range of a fossil-fueled technology, and the central tendencies of all renewable technologies are between 400 and 1,000 g CO2eq/kWh lower than their fossil-fueled counterparts without carbon capture and sequestration (CCS). For fossil-fuelled technologies, post-combustion CCS can bring total life cycle GHG emissions within the upper 25th percent of the range of several renewable technologies. Biopower with CCS can display significantly negative GHG emissions (without considering the impacts of land use change). Nuclear power exhibits a similar interquartile range and median as do technologies powered by renewable resources.
The results of the systematic review portion of the project were published in the Special Report on Renewable Energy Sources and Climate Change Mitigation of the Intergovernmental Panel on Climate Change.
The key drivers of variability include system boundary assumptions, assumed lifetime of the technology, impact assessment method (e.g., global warming potentials [GWPs] of assessed GHG emissions), technological performance factors such as thermal efficiency and capacity factor, and primary energy resource characteristics such as solar resource and fuel heating value.
The published life cycle greenhouse gas (GHG) estimates for hydropower, ocean, geothermal, biopower, solar (crystalline silicon photovoltaic, thin film photovoltaic, and concentrating solar power), wind, nuclear, coal, and natural gas technologies are compared in Figure 1.
With the exception of putting the estimates on a common functional basis (g CO2e/kWh), no harmonization was performed at this stage. Distributional information was calculated based on the as-published data: minimum, 25th percentile value, 50th percentile value, 75th percentile value and maximum. The interquartile range (between the 25th and 75th percentile) is highlighted in the figure.
In subsequent project phases, NREL reviewed as-published life cycle greenhouse gas emissions estimated for solar (crystalline silicon and thin film photovoltaics and concentrating solar power), wind, nuclear, coal, and natural gas, and adjusted these estimates to a consistent set of methods and assumptions specific to each technology.
Figure 2 compares as-published results to harmonized life cycle greenhouse gas emissions for solar (photovoltaics and concentrating solar power), wind, nuclear, coal and natural gas technologies. The distributional information was calculated based on the harmonized data and compared with the as-published data: minimum, 25th percentile value, 50th percentile value, 75th percentile value, and maximum. The interquartile range (between 25th and 75th percentile) is highlighted in the figure.
Findings from the Harmonized Data
Like the published data, the harmonized data shows that life cycle greenhouse gas emissions from solar (both photovoltaic and concentrating solar power), wind, and nuclear technologies are considerably lower and less variable than emissions from technologies powered by combustion-based natural gas and coal technologies.
Harmonization doesn't significantly change the central tendency (as indicated by the median value) of any of the technologies evaluated. Harmonization does, however, reduce the variability of GHG emissions estimates to varying degrees (as indicated by changes to the interquartile range and the overall range).
The detailed results from the harmonization research are published in a special supplemental issue of the Journal of Industrial Ecology on Meta-Analysis of LCA, as well as, the harmonization of unconventional gas published in the Proceedings of the National Academy of Sciences.
For summaries of the life cycle analysis review, analysis, and harmonization results, see the IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation: Renewable Energy in the Context of Sustainable Development.
For technology-specific results of review, analysis and harmonization of published LCA estimates, visit:
For technology-specific results of review and analysis of published LCA estimates, visit:
See Methodology to learn how the project was conducted.
For questions about this project, contact Garvin Heath via our Webmaster page.