Energy Innovation’s latest study compares the climate impacts associated with electricity generated from natural gas versus coal. The research calculates life-cycle emissions from natural gas and coal, taking into account methane leakage rates, time periods over which the impact is measured, and the quality of gas turbines (and coal plants) being used (and replaced).”
“All three of these variables are required to consider whether gas is a good idea or not. Our study, published in Electricity Journal, concludes that, although natural gas can offer a modest environmental advantage over coal in some circumstances, due to the emission of potent methane gas that is leaked throughout its production, increased investment in expanding natural gas electricity generation capacity is not a sound climate strategy. Our study is available for download on ScienceDirect’s website. For an overview of the study’s findings, methodology, and recommendations, we have written a 2-page issue brief, which can be found here. We hope you find these resources to be timely and of interest.
2 pager: Natural gas: not clean enough Findings. New research from Energy Innovation concludes that under the best of circumstances, natural gas-fired electric power plants can only make a modest dent on abating climate change—and, if developed poorly, with serious methane leaks, or if used to displace energy efficiency or renewable energy, natural gas could instead seriously contribute to the problem. Over a timeframe of 100 years, natural gas with careful leak control offers some reduction in greenhouse gas (GHG) emissions. However, these reductions are not large enough for natural gas to play an expanded role in efforts tomanage GHG emissions.Recommendations. It makes sense to use excess capacity from existing natural gas plants to help shut down the United States’ aging fleet of coal plants. But investment in many more large natural gas power plants would not be sensible. New advanced gas turbines that are flexible – able to ramp up and down quickly while maintaining high efficiency – do have an important role going forward to help integrate variable renewable electricity sources like wind and solar power. But such plants are just one option in a portfolio of strategies available to handle renewables variability. A principal driver of natural gas’s contribution to climate change is leaking methane. It is important, then, that the federal government and the states should put in place stronger regulations to reduce methane leakage to close to zero—and limit other environmental impacts.
Background. Natural gas is made up of mostly methane, which is emitted due to intentional venting as well as accidental leaks at every stage of the natural gas system, from extraction to processing, transmission, distribution, and end-use. Methane is a powerful GHG. It causes 28 times more global warming than carbon dioxide on a mass basis over a 100-year period (34 times more when accounting for climate system feedback loops1). On a 20-year basis, the impact of methane is 84 times larger than carbon dioxide (86 times counting feedbacks). When first released, methane is 120 times more potent than carbon dioxide. These scaling factors (technically called Global Warming Potentials) are used to translate methane into a single composite measure of GHG emissions known as carbon dioxide equivalent measure. The results presented here are based on the figures without feedbacks. Taking into account feedback effects would further weaken the case for natural gas.
Methodology. Energy Innovation’s analytical framework estimates the GHG emissions caused by the generation of one MWh of electricity from both coal and natural gas power plants. The analysis takes into account the three largest sources of emissions. These are: (1) methane – which not only leaks from the gas system but also during coal mining, though at lower levels; (2) smokestack carbon dioxide released due to fuel combustion, and (3) upstream carbon dioxide emission due to combustion in the production and transmission of fuel prior to its reaching the power plant. The efficiency of a power plant significantly drives its GHG intensity, so our methodology tests a range of both gas and coal technology types. “New” represents the type of power plant typically constructed today. “Average” is a composite measure that represents the average plant efficiency taking into account all plants operating in 2012 (weighted according to their production). “Retired coal” uses the average efficiency for coal plants recently shut down. Recent research (Brandt et al. 2014) has increased certainty about the rate of methane emissions from the natural gas system, indicating it is roughly in the range of two to four percent for the United States on average. We analyze two and four percent leakage scenarios to provide likely upper and lower bounds on GHG emissions. On the following graph, the leakage rate is shown in parenthesis for each gas scenario. For example, New Gas (2%) stands for a new natural gas plant with a methane emission rate of two percent. Note as well the three time horizons delineated along the bottom of the graph.
Results. These results illustrate the advantage natural gas has in smokestack emissions, as well as the extent to which methane emissions diminish this advantage. In the first year that GHGs are emitted, if methane emissions are at the high end of the likely range (four percent in our estimation), both new and average gas would be more GHG intensive than new or average coal. Keep in mind new power plants operate for several decades, which means this initial GHG penalty would be incurred, year after year, for many years. These results contribute to the argument that building new baseload gas plants is unadvisable. After 20 years, one MWh from new gas is 16 – 40 percent less GHG intensive than average coal, depending the level of methane emissions. After 100 years, the advantage of natural gas increases. It offers an improvement of 44 – 52 percent above coal. Yet, by this time, emissions reductions must be much more ambitious than this if we are to power civilization in a way that enables a safe and stable climate.”
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