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.
Credit: Sathaye, J., O. Lucon, A. Rahman, J. Christensen, F. Denton, J. Fujino, G. Heath, S. Kadner, M. Mirza, H. Rudnick, A. Schlaepfer, A. Shmakin, 2011: Renewable Energy in the Context of Sustainable Energy. In IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation [O. Edenhofer, R. Pichs-Madruga, Y. Sokona, K. Seyboth, P. Matschoss, S. Kadner, T. Zwickel, P. Eickemeier, G. Hansen, S. Schlömer, C. von Stechow (eds)], Cambridge University Press.
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.
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, and coal and adjusted these estimates to a consistent set of methods and assumptions specific to each technology. NREL also researched the life cycle greenhouse gas emissions for natural gas, although these results are still in the process of being published.
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.
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.