Publication DetailsTitle : Water Consumption Factors for Electricity Generation in the United States
Publication Date : October 07, 2016
Authors : U. Lee, J. Han, A. Elgowainy
Abstract : In many regions of the United States, water availability is of concern due to growing demand and limited supply. In these regions, water is also an essential resource for most power generation technologies. Thermal power plants, which generate 87% of the total electricity in the United States, typically require a large amount of water for cooling purposes. Depending on types of cooling technology and prime movers, water loss or “consumption” through evaporation vary significantly. Hydropower plants with reservoirs “consume” large amount of water through evaporation due to the typically large surface area of the reservoir. Because water consumption rates vary by region due to different climate conditions, regional variation of water consumption due to hydropower generation should be considered. The objective of this study is to estimate the water consumption factor (WCF) for electricity generation, which is defined as the water consumed per unit of power generation (e.g., gallons of water per kWh of generated electricity). In particular, this study evaluates the variation in WCF by region. For hydropower, water consumption from hydropower reservoirs is calculated using reservoir’s surface area, state-level water evaporation data, and background evapotranspiration. Note that water consumption in multipurpose reservoirs is allocated to hydropower generation based on the share of the economic benefit of power generation among benefits from all other purposes (e.g., irrigation, flood control, navigation, etc.) Thus, the balance of water consumption is allocated among all other purposes based on their estimated economic benefits. For thermal power plants, the WCFs by types of cooling technology and prime mover are estimated. Because cooling technologies and prime mover types vary by region, the WCF for thermal power generation also exhibits regional differences. The WCFs from hydropower and thermal power generation are aggregated to the national-level and also to each North American Electric Reliability Council (NERC) utility region. The national average WCF for electricity is estimated at 0.58 gal/kWh considering the average U.S. electricity generation mix in 2015. At a facility-level, the WCFs of thermoelectricity and hydropower are 0.33 and 4.4 gal/kWh, respectively, while the shares of thermo- and hydro-power generation are 87% and 6.3%, respectively. The WCFs have been implemented in the Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET®) model developed by Argonne National Laboratory. GREET is a life cycle analysis tool that evaluates energy use and emissions, as well as water consumption on a life cycle basis. This study allows researchers to analyze lifecycle water consumption for various energy production and conversion pathways. While the economic benefits approach was employed to allocate WCF to hydropower generation in multipurpose reservoirs, other approaches for estimating the hydropower WCFs are subjects for future analysis and updates to the GREET model.