Correspondence/Rebuttal pubs.acs.org/est
Comments on “Effects of Environmental Temperature Change on the Efficiency of Coal- and Natural Gas-Fired Power Plants”
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regression analyses of plant efficiency on plant operating characteristics, and air and water temperature.1 This approach is entirely different than that of eqs 3a and 3b in van Vliet et al. (Supporting Information), used to estimate the impact of climate change and changing water resources and temperatures on plant useable capacity rather than plant efficiency.2 Based on historical analyses presented in Figure 4 and citing Madden et al., Henry and Pratson conclude that regulation on discharges of thermal effluent as regulated by section 316(a) of the Clean Water are not enforced.1,4 Henry and Pratson, therefore, state that “studies that have assumed open-loop plants reduce output at 27−30 °C will have overestimated the impact of water temperature on efficiency”.1 In their follow up analyses, Henry and Pratson assume that these regulation will also be ignored in the future.1 In addition, in their climate change impacts assessment, described in section 4.3, Henry and Pratson seem to ignore future changes in water availability, more or less assuming that in the future unlimited water or at least the same amount of water is available, although summer water availability is expected to decrease for many river systems in the US.1 Despite their finding on the low impacts of climate change on the electricity production the authors recommend the switch from once-through to closed-loop cooling system because they provide “the added benefit of reducing the temperature impact of climate warming on the efficiency and thus useable generating capacity of existing power plants”.1 In short, the “one order of magnitude” difference between Henry and Pratson and van Vliet et al. appears to be mostly (if not entirely) due to Henry and Pratson’s use of data-based efficiency estimators in combination with the assumption the environmental regulations will not be enforced and ignoring water scarcity. Under these assumptions it is not surprising that the “usable capacity” (efficiencies) they estimate, are not very sensitive to changes in air and water temperature and global warming. The results that Henry and Pratson report are not appropriate for comparing the impacts of climate change on power plant efficiency with the sensitivity of useable power plant capacity to climate change given existing environmental regulations in Europe and the U.S. and potential limits on the availability of cooling water, the primary objective of van Vliet et al. Therefore, we disagree with the conclusion of Henry and Pratson that power plants are (more) resilient to climate change.5
n their August 1, 2016 paper, Henry and Pratson use available historical power plant data and air and water temperatures to argue that the efficiency of power plants in the United States changes little with variations in air and water temperatures.1 Furthermore, they conclude that thermoelectric power plants are more resilient to climate change than previously concluded in Van Vliet et al.1,2 Here, we argue that this conclusion is only valid under the assumption that environmental regulations are ignored and that future cooling water availability will not change. Henry and Pratson estimate useable power plant capacity under conditions of climate change based on estimates of water temperatures for the year 2080 from van Vliet et al, concluding that “the summer average useable capacity of a 40-plant region (similar sample size to that of van Vliet et al. with n = 39 will be reduced by 0.4%”.1,2 They then conflate their work with van Vliet et al. and a similar study by Bartos and Chester and suggest, without further analysis, that the drought component on plant usable capacity is much greater than the temperature component.1−3 van Vliet et al. estimate useable capacity of power plants by simulating streamflows with a large-scale hydrologic model, stream temperatures with a one-dimensional, time-dependent numerical model and thermoelectric power plant characteristics derived from power plant databases.2 Furthermore, van Vliet et al. estimate useable capacity given limitations on available streamflow and assume that environmental jurisdictions in Europe and the United States will enforce environmental regulations for stream temperature.2 van Vliet et al. did not separate the impacts of drought and water temperature impacts, but it seems likely that the latter is at least as important as the impacts of drought. Nevertheless, Henry and Pratson appear to compare the percentage change in plant efficiency as a result of historical air and water temperature variations with the percentage change in useable capacity under climate change due to restrictions on available water supply and violations of state water temperature standards in van Vliet et al.1,2 Specifically, in section 4.3, Henry and Pratson state that their estimate of the impact of climate change on electricity production is significantly lower than those of van Vliet et al. and Bartos and Chester for the open-loop power plants they examined.1−3 Henry and Pratson further found reductions in η with increased Tw (for open-loop plants) up to 1 order of magnitude less than previous estimates.1 Finally they conclude that their results did not “support the conclusions of previous studies that increases in dry-bulb or wet-bulb air temperature will reduce the efficiency of all open- and closed-loop plants”.1 Based on the Henry and Pratson paper Dominic Lenton, states that “A new study based on real-world data casts doubt on predictions from model-based studies that rising global temperatures will significantly reduce output from many power stations.”4 The analysis and conclusions in Henry and Pratson are based on their eq 2, which estimates power plant efficiency by © 2017 American Chemical Society
John R. Yearsley*,† Michelle T. H. van Vliet‡ Dennis P. Lettenmaier§ Fulco Ludwig‡ Stefan Vögele∥ †
UW-Hydro|Computational Hydrology Dept. of Civil and Environmental Engineering University of Washington Seattle, Washington 98195, United States Published: April 11, 2017 5343
DOI: 10.1021/acs.est.7b00561 Environ. Sci. Technol. 2017, 51, 5343−5344
Environmental Science & Technology
Correspondence/Rebuttal
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Water Systems and Global Change group Wageningen University P.O. Box 47, 6700 AA Wageningen, The Netherlands § Department of Geography, University of California, Los Angeles Los Angeles, California 90095, United States ∥ Institute für Energie- und Klimaforschung Systemforschung und Technologische Entwicklung (IEK-STE) Jülich, NRW, Germany
AUTHOR INFORMATION
Corresponding Author
*Phone: (206) 755-2997; e-mail:
[email protected]. ORCID
John R. Yearsley: 0000-0002-2630-9589 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The research reported in van Vliet et al. was financially supported by the European Commission through the FP6 WATCH project and through the FP7 ECLISE project.
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REFERENCES
(1) Henry, C.; Pratson, L. F. Effects of Environmental Temperature Change on the Efficiency of Coal- and Natural Gas-Fired Power Plants. Environ. Sci. Technol. 2016, 50, 9764. (2) Van Vliet, M. T. H.; Yearsley, J. R.; Ludwig, F.; Vögele, S.; Lettenmaier, D.; Kabat, P. Vulnerability of US and European electricity supply to climate change. Nat. Clim. Change 2012, 2, 676−681. (3) Bartos, M. D.; Chester, M. V. Impacts of climate change on electric power supply in the Western United States. Nat. Clim. Change 2015, 5, 748−752. (4) Lenton, D. Impact of climate change on power stations ’not as bad as forecast’, Eng. Technol., August 17, 2016. (5) Madden, N.; Lewis, A.; Davis, M. Thermal effluent from the power sector: an analysis of once-through cooling system impacts on surface water temperature. Environ. Res. Lett. 2013, 8, 035006.
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DOI: 10.1021/acs.est.7b00561 Environ. Sci. Technol. 2017, 51, 5343−5344
