Effect of methane leakage on the greenhouse gas footprint of electricity generation
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For the purpose of generating electricity, what leakage rate renders the greenhouse gas (GHG) footprint of natural gas equivalent to that of coal? This paper answers this question using a simple model, which assumes that the comprehensive GHG footprint is the sum of the carbon dioxide-equivalent emissions resulting from (1) electricity generation and (2) natural gas leakage. The emissions resulting from electricity generation are taken from published life-cycle assessments (LCAs), whereas the emissions from natural gas leakage are estimated assuming that natural gas is 80 % methane, whose global warming potential (GWP) is calculated using equations provided by the Intergovernmental Panel on Climate Change (IPCC). Results, presented on a straightforward plot of GHG footprint versus time horizon, show that natural gas leakage of 2.0 % or 4.8 % eliminates half of natural gas’s GHG footprint advantage over coal at 20- or 100-year time horizons, respectively. Leakage of 3.9 % or 9.1 % completely eliminates the GHG footprint advantage at 20- and 100-year time horizons, respectively. A two-parameter power law approximation of the IPCC’s equation for GWP is utilized and gives equivalent results. Results indicate that leakage control is essential for natural gas to deliver a smaller GHG footprint than coal.
KeywordsTime Horizon Methane Emission Global Warming Potential Methane Leakage Leakage Estimate
The authors thank Indrani Pal for reviewing a preliminary draft of this paper, and three anonymous referees whose feedback helped to improve the clarity and rigor of the presentation.
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