Monday, June 13, 2011

Water Use in Electricity Generating Technologies - A Review of Operational Water Consumption and Withdrawal Factors for Electricity Generating Technologies
Executive Summary:This report provides estimates of operational water withdrawal and water consumption factors for electricity generating technologies in the United States. Estimates of water factors were collected from published primary literature and were not modified except for unit conversions. The presented water factors may be useful in modeling and policy analyses where reliable power plant level data are not available. Major findings of the report include:
• The power sector withdraws more water than any other sector in the United States and is heavily dependent on available water resources. Changes in water resources may impact the reliability of power generation.
• Water withdrawal and consumption factors vary greatly across and within fuel technologies. Water factors show greater agreement when organized according to cooling technologies as opposed to fuel technologies. Once-through cooling technologies withdraw 10 to 100 times more water per unit of electric generation than recirculating cooling technologies; recirculating cooling technologies consume at least twice as much water as once-through cooling technologies.
• A transition to a less carbon-intensive electricity sector could result in either an increase or decrease in water use, depending on the choice of technologies and cooling systems employed. Concentrating solar power (CSP) technologies and coal facilities with carbon capture and sequestration (CCS) capabilities have the highest water consumption values when using a recirculating cooling system. Non-thermal renewables, such as photovoltaics (PV) and wind, have the lowest water consumption factors.
• Federal datasets on water use in power plants have numerous gaps and methodological inconsistencies. Federal agencies are currently coordinating to improve these data. Water use factors discussed here are good proxies for use in modeling and policy analyses, at least until power plant level data improve.
• Impacts of the power sector on freshwater availability can be reduced by utilizing dry cooling or by using non-freshwater sources for cooling. However, these alternatives are limited by locally available resources and may have cost and performance penalties.
Improved power plant data and further studies into the water requirements of energy technologies in different climatic regions would facilitate greater resolution in analyses of water impacts of future energy and economic scenarios. This report provides the foundation for conducting water use impact assessments of the power sector while also identifying gaps in data that could guide future research.
Freshwater use impacts can be reduced by utilizing dry cooling or by using non-freshwater sources as a cooling medium. Initial work suggests that the performance penalty for CSP facilities switching from wet cooling to dry cooling results in an annual reduction in output of 2%–5% and an increase in the levelized cost of producing energy of 3%–8%, depending on local climatic conditions. Using national averages, the annual performance penalty for switching from wet cooling to dry cooling for nuclear plants is 6.8%, combined cycle plants 1.7%, and other fossil plants (including coal and natural gas steam plants) 6.9% . Further efforts are needed to evaluate performance and cost penalties associated with utilizing dry or hybrid cooling systems for fossil fuel facilities using carbon capture technologies. Utilizing reclaimed water, such as municipal wastewater, is another approach that could lessen the impact of the power sector on freshwater resources and wastewater treatment facilities. The legal and physical availability of municipal wastewater, especially in rural areas, may be a limiting factor to its widespread usage, and the cost and performance penalties of utilizing such sources must be investigated further

by Jordan Macknick, Robin Newmark, Garvin Heath, and KC Hallett
National Renewable Energy Laboratory NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
March 2011; April 6, 2011

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