Life-cycle greenhouse-gas emissions of energy sources

Measurement of life-cycle greenhouse gas emissions involves calculating the global-warming potential of electrical energy sources through life-cycle assessment of each energy source. The findings are presented in units of global warming potential per unit of electrical energy generated by that source. The scale uses the global warming potential unit, the carbon dioxide equivalent (CO2e), and the unit of electrical energy, the kilowatt hour (kWh). The goal of such assessments is to cover the full life of the source, from material and fuel mining through construction to operation and waste management.'Most recently, Sovacool (2008) calculated a mean value for the overall emissions by averaging the global results of 19 LCA studies forming a subset of, as stated by the author, 'the most current, original and transparent studies' out of 103 studies. However, a critical assessment reveals that a majority of the studies representing the upper part of the spectrum are studies that can be traced back to the same input data and performed by the same author, namely Storm van Leeuwen. After careful analysis, it must be concluded that the mix of selected LCAs results in a skewed and distorted collection of different results available in the literature. Furthermore, since many studies use different energy mixes and other assumptions, averaging GHG emissions of those studies is no sound method to calculate an overall emission coefficient, as it gives no site specific information needed for policy makers to base their decisions.'The thermal efficiency of fossil-based power plants is reduced when operated at fluctuating and suboptimal loads to supplement wind power, which may degrade, to a certain extent, the GHG benefits resulting from the addition of wind to the grid. A study conducted by Pehnt and colleagues (2008) reports that a moderate level of wind penetration (12%) would result in efficiency penalties of 3% to 8%, depending on the type of conventional power plant considered. Gross and colleagues (2006) report similar results, with efficiency penalties ranging from nearly 0% to 7% for up to 20% wind penetration. Pehnt and colleagues (2008) conclude that the results of adding offshore wind power in Germany on the background power systems maintaining a level supply to the grid and providing enough reserve capacity amount to adding between 20 and 80 g CO2-eq/kWh to the life cycle GHG emissions profile of wind power. Measurement of life-cycle greenhouse gas emissions involves calculating the global-warming potential of electrical energy sources through life-cycle assessment of each energy source. The findings are presented in units of global warming potential per unit of electrical energy generated by that source. The scale uses the global warming potential unit, the carbon dioxide equivalent (CO2e), and the unit of electrical energy, the kilowatt hour (kWh). The goal of such assessments is to cover the full life of the source, from material and fuel mining through construction to operation and waste management. In 2014, the Intergovernmental Panel on Climate Change harmonized the carbon dioxide equivalent (CO2e) findings of the major electricity generating sources in use worldwide. This was done by analyzing the findings of hundreds of individual scientific papers assessing each energy source. For all technologies, advances in efficiency, and therefore reductions in CO2e since the time of publication, have not been included. For example, the total life cycle emissions from wind power may have lessened since publication. Similarly, due to the time frame over which the studies were conducted, nuclear Generation II reactor's CO2e results are presented and not the global warming potential of Generation III reactors, presently under construction in the United States and China. Other limitations of the data include: a) missing life cycle phases, and, b) uncertainty as to where to define the cut-off point in the global warming potential of an energy source. The latter is important in assessing a combined electrical grid in the real world, rather than the established practice of simply assessing the energy source in isolation. 1 see also environmental impact of reservoirs#Greenhouse gases. A Yale University review of hundreds of prior papers, as published in the Journal of Industrial Ecology analyzing CO2 life cycle assessment (LCA) emissions from nuclear power determined: 'The collective LCA literature indicates that life cycle GHG emissions from nuclear power are only a fraction of traditional fossil sources and comparable to renewable technologies.' The study also noted that for the most common category of reactors, the Light water reactor: 'Harmonization decreased the median estimate for all LWR technology categories so that the medians of BWRs, PWRs, and all LWRs are similar, at approximately 12 g CO2-eq/kWh. Speaking of the numerous assumptions and therefore wide results returned by authors of previous individual studies, the Warner and Heath Yale paper states: 'the difference between nuclear power life cycle GHG emissions constructed in an electric system dominated by nuclear (or renewables) and a system dominated by coal can be fairly large (in the range of 4 to 22 g CO2-eq/kWh compared to 30 to 110 g CO2-eq/kWh, respectively)'. The already established electric grid being a necessary input to drive the uranium enrichment systems. With Figure 4 of the paper, expanding on these figures, displaying the median result returned from these other papers as approximately 35 g CO2-eq/kWh when a nation's background electricity 'energy mix' is 'high carbon' that is, primarily coal powered, combined with a slightly lower than typical uranium ore grade input in the range of 0.01% U3O8. To put this number in perspective, average uranium ores are between 0.05% to 0.40% U3O8, with the ore at the most productive uranium mine in the world, McArthur River uranium mine, at approximately 15.76%. The high rate of near 110 grams of GHGs mentioned in this Yale paper, as shown in Figure 4 and discussed in the body of the article, is derived from what the authors consider to be a 'worst-case scenario' that is not 'considered very robust'. As it is inclusive of a combination of unrealistic factors not seen in any country. This is, a high coal usage in the electricity energy-mix combined with the terrestrial mining by conventional methods, of ultra low-grade 'uranium ore' with a '0.0001%' concentration of U3O8. As a way to put this 'ore' concentration into perspective, vast quantities of presently uneconomical uranium in many lignite coal ashes have uranium concentrations five times greater than this. On the other hand, the 4 g CO2-eq/kWh rate mentioned in the body of the paper is, again as Figure 4 shows, a result of an electricity energy-mix that is already low-carbon combined with a more typical, but still low, uranium ore grade of 0.01% U3O8. This combination is considerably different than the hypothetical 'worse-case scenario' of 110 grams, as this latter combination is seen in some select countries. Namely Sweden, Switzerland and the French electricity grid as the most prominent. With this close to 4 gram value, reported by the Swedish Vattenfall study discussed below. In the most common and pertinent case of GHG data from countries with a 'medium carbon' intensity electric grid and input ores of about 0.01%. The median value of GHG emissions was determined to be about 9 grams, as depicted in figure 4 of the Yale paper, when the now world-standard 'centrifuge' enrichment approach alone, is assessed. In 2013 the other less economic approach of 'diffusion' enrichment, that is similarly depicted in figure 4 was retired worldwide. When it operated the median GHG value that the Yale analyst's depict for this old technology was about 15 grams under the same 'medium carbon' grid conditions.