1 Copyright © 2013 by ASME Proceedings of the ASME 2013 Power Conference Power2013 July 29-August 1, 2013, Boston, Massachusetts, USA Power2013-98229 LIFE CYCLE WATER USE FOR ELECTRICITY GENERATION: IMPLICATIONS OF THE DISTRIBUTION OF COLLECTED ESTIMATES James R. Meldrum University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, Colorado 80305, USA Jordan E. Macknick, Garvin A. Heath, and Syndi L. Nettles-Anderson National Renewable Energy Laboratory, Strategic Energy Analysis Center, Golden, Colorado 80401, USA INTRODUCTION Water requirements throughout the electricity generation life cycle have important implications for the electricity sector. Thermoelectric power plant operations are estimated as responsible for around 36% [1] to 41% [2] of total freshwater withdrawals in the United States and 3% of total freshwater consumption [1,3]. However, the life cycle of electricity generation consists of many stages besides power plant operation, including component manufacturing, fuel acquisition, processing, and transport, and power plant decommissioning. The water requirements associated with choices along this life cycle, such as the selection of fuel type or cooling technology, are not well understood. Recent research [4,5] consolidates and harmonizes estimates of water withdrawal and water consumption for the full life cycle of selected electricity generating technologies: coal, natural gas, nuclear, concentrating solar power (CSP), geothermal, photovoltaics (PV), and wind. Harmonization reduces analytical variability by adjusting published estimates to ones based on a more consistent set of methods and assumptions [6]. This study presents the results of this recent analysis and expands upon previous results by investigating the implications that the distributions of collected estimates have upon estimated life cycle water requirements of different electricity generation choices. This study thereby offers additional insight for understanding the water use implications of electricity generation. METHODS As described in more detail elsewhere [4], water use estimates were gathered through a broad search of publicly available sources, including peer-reviewed scientific literature, government reports and statistics, and corporate sustainability reports. Inclusion of gathered estimates in reported results depended on those estimates passing a series of three screens that focused on methods quality, completeness of reporting, and current technological relevance. Only quantified water use, supported by sufficient information and adhering to basic engineering principles, was included. Out of the more than 1,000 references consulted, 138 passed all three screens and contributed unique, usable data. The majority of these references provided primary data on only one or two technologies each. Usable data on water use were classified as referring to either water withdrawals, in the case of water diverted from a water source for use, or water consumption, in the case of the portion of withdrawn water not returned to the immediate water environment after use. Where possible, estimates were harmonized to common boundaries and performance parameters, including thermal efficiency, fuel heat content, and plant lifetime, that match accepted values used elsewhere in the literature and previously reported. Water use factors were developed for each of the three main life cycle stages of seven different electricity generation technologies. As Figure 1 depicts, these three main stages are the fuel cycle, power plant life cycle, and power plant operation; the fuel cycle includes fuel extraction, fuel processing, and fuel transportation, and the power plant life cycle includes component manufacturing, power plant construction, and power plant decommissioning. Where available data substantially differentiate water use among sub- categories of generation technologies, cooling technologies, or fuel cycle characteristics, separate estimates were developed for each sub-category; life cycle water use factors were constructed as weighted sums of the water use factors for each of the three major life cycle stages.