Dwight D. Eisenhower once said that it is not only necessary to do the right thing, but to do it in the right way also. Sustainability is all too often just a fluffy word that implies doing the right thing, it is important to make sure we are doing it the right way.
When it comes to renewable energy, reports generally promote the greenness of these technologies compared with fossil fuels. Most of the time, electricity generated from renewable technologies is considered carbon dioxide free. However, if examined beyond direct emissions and from a life cycle perspective, renewable technologies do have an environmental impact during, for example, the manufacturing or building phase of the system. It is therefore necessary to consider impacts over the full life cycle of a technology, especially when aiming to compare different energy pathways. As clean energy increasingly becomes part of the energy mix, lenders, utilities, and policy makers need the most comprehensive and accurate information on GHG emissions from the various available technologies to inform investments, strategic planning and policy.
This information comes from a time, energy, and data-intensive process requiring sophisticated methodology called a Life Cycle Assessment (LCA). LCAs have been used since the 1970’s; however, despite the ever-growing body of life cycle assessments on electricity generation technologies, inconsistent methods and assumptions have lead to a wide range of outcomes, which impede comparison across studies and the aggregation of results.
Many reasons explain such variability, such as the dynamic development of this industry, the lack of transparency in modeling assumptions, and the broad array of technologies it represents. Renewable energy systems’ environmental performance is also highly geo-dependent and driven by external factors that influence electricity production. This wide variability in environmental performance can lead policy makers to consider LCA as an inconclusive method.
Equalizing the body of previous research around a narrow set of methods and assumptions is necessary to generate robust results to assess and compare environmental performance of different energy technologies. Towards this end, the National Renewable Energy Laboratory (NREL) led the Life Cycle Assessment Harmonization Project.
The project highlighted several key, sensitive parameters to provide a better understanding of the variability in LCA results, and proposed a methodology to establish a simplified, streamlined approach based on regressions built on these key parameters. In order to further expand the use of LCA in industry, the project also provided a simpler, more efficient approach to assessing environmental impacts. Simple and easy access to robust environmental assessments is crucial for projections on energy generation, greenhouse gas emissions, and the development of regulatory policies.
NREL conducted the project in two phases. First, analysts evaluated more than 2,100 published LCAs for electricity-generation technologies. Then, NREL developed a meta-analytical procedure called “harmonization” that applied common metrics to 25 percent of published references and succeeded in narrowing the huge range of estimates – in some cases by 80 to 90 percent – to a robust median, improving precision, and giving stakeholders a much clearer look at the likely environmental impacts of various projects.
Like the published data, the harmonized data shows that life cycle greenhouse gas emissions from solar, wind, and nuclear technologies are considerably lower and less variable than emissions from technologies powered by combustion-based natural gas and coal technologies. While the process didn’t significantly change the central tendency of any of the technologies evaluated, it did reduce the variability of GHG emissions estimates to varying degrees.
There are some interesting conclusions from the results. First, as expected, fossil fuels have the highest greenhouse gas emissions per kwh of electricity generation, as well as an enormous variation in estimates, even after harmonization. NREL also researched the life cycle greenhouse gas emissions for natural gas, but these results are still in the process of being published. Secondly, the harmonization of the various renewable energy technologies affected the variability of results very differently. After harmonization, the relatively high potential for biobased materials remained that way; on the other hand, the harmonization of Concentrated Solar Power drastically reduced the variability of the LCA estimates.
Finally, the analysis sheds light on the reality behind some controversial technologies. Some have stated that the life cycle emissions of nuclear energy are deceivingly high due to the amount of concrete needed to build a power plant, but the studies show this to not be true on a per kwh basis, in fact the results showed that it was lower than solar energy. Also, while the median for natural gas is significantly below coal, the high end estimates (although not yet harmonized) is still at the median for coal. With reports suggesting that the methane leaks involved in natural gas transportation are higher than previously estimated, this result is very significant.
In any case, because the effects of climate change will be measured in degrees, not the black or white picture that is too often painted, this effort and a continued refinement of the life cycle effects of electricity generation are invaluable.
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