Water-Energy Nexus: Moving the People or Resources? Vanderbilt Institute for Energy and A hypothetical consideration of addressing sustainability Environment D. Perrone, J. Murphy & G. Hornberger INTRODUCTION METHODS Table 4: Model Assumptions Energy and water are inexplicably linked, yet rarely do communities collect enough of the Conceptual models were developed (Figures 2 & 3) and quantified according to various Major Model Assumptions Justification Implications appropriate data to understand how the connection may affect their community. The stages of energy and water use. Tables 2 and 3 describe the model by each stage and No significant energy efficiency technological Most detailed and recent data for energy used during If the new technology is more efficient, like it often is, the model interrelated nature of these resources is even more evident when their supplies are scarce. We provide insight to the user input required for the model. Due to data constraints and advances for the fuel cycle & electricity production are from 1994 (Gleick) will over-calculate consumptive water generation since the 1990’s qualitatively describe communities that lack sufficient local water and energy resources for difficulties defining conditions, various assumptions were made for the model (Table 4). National and regional averages approximate Water and energy data is often not reported or collected and Results may be higher or lower than actual their demands as Resource Islands. local scenarios very hard to track down Negligible water is lost through evaporation Evaporative loss is suggested to be 2-3% (CAP) and quality The total amount of water may be high if accounting for ‘lost’ Resource Islands and leaky pipes of local distribution system was not taken into account water during transportation • Resource Islands: Communities located considerable distances from their water and energy Only the community’s reported, direct water This study does not address a life cycle approach so a cradle Water and energy associated with construction and maintenance resources and energy demands were used to grave analysis was not needed of equipment (water & energy) is not accounted for Community is considered an incorporated Boundaries are hard to define due to inconsistency in water Results do not include suburbs or the surrounding metropolitan • Ecological Definition: “Resource islands form when individual plants influence the city and energy boundaries area surrounding soil to alleviate nutrient and temperature stress and foster seedling survival and growth” (Carrillo-Carcia et al 2000). • Definitions are similar in terms of describing a more-livable micro-environment in an RESULTS otherwise inhospitable desert ecosystem. Virtual water and energy resources (the amount of water used in the production of energy and the amount of energy used in the acquisition of water) were analyzed for Tucson, Arizona. Inclusion of virtual water for energy more than doubles the amount of • Example: City of Tucson located in Arizona, United States of America water consumed by the City of Tucson (Figure 3). However, virtual energy used in the acquisition of water is an insignificant portion • Over 335 miles (540 km) from one of its main water sources and 200+ miles (320 km) of the total energy used by the City of Tucson (Figure 4). For the case study, two scenarios were considered to address the from its power supplies (Figure 1). hypothetical question of moving the people to the resources and the resources to the people for Tucson: Scenario 1 Current Conditions (i.e. moving the resources to the people) and Scenario 2 Hypothetical Conditions (i.e. moving the people to the resources) Problem Statement (Figures 5 and 6). Geography (i.e. distance from available water and energy resources) and community size (i.e. demand) directly affect energy and water use. However, quantifying water-energy resource Figure 2: Water for Energy (left) and Energy for Water (right) Water for Energy – Scenario Analysis use is difficult to accomplish, much less comprehend, without a functional conceptual model. Current water-energy nexus models are not useful for city planning or community Conceptual Diagrams development as they call for data that are not typically collected by communities, inevitably using ‘hypothetical’ cities or data. Table 2: Water for Energy Model Description Fuel Cycle Transport Electricity Production Transmission Uses average water • Uses heat content of the • Uses average water • Uses average Project Objectives ion consumption for the transportation fuel, or pipeline consumption data for power transmission line losses processes needed to efficiency, and distance to calculate plants based on their energy and efficiencies to s reg 1.) To develop a model using DESCRIPTION make the energy the total amount of energy source and cooling technology calculate the energy lost in sin Navajo national and regional averages of source consumable by consumed for transport • Calculations are dependent on transmission over distances rner n Ba energy for water and water for users • Calculates the water for the technology • Assumed end user does 4 Co • Exploration energy consumed in transport by • Cooling towers consume not alter energy, so no Figure 3: Tucson water demand Figure 5: Tucson water for energy scenario analysis Jua energy consumption • Extraction & mining using the energy source’s water ~2X the water that once- water is used by the end • Recovery San consumption in its fuel cycle through plants consume user for energy Z ,A 2.) Enable communities to acquire a • Processing • Inherentlydeals with transport • Does not incorporate consumption Energy for Water – Scenario Analysis ille • Refining mode efficiency geographical variations in plant Co cursory understanding of the • Enrichment consumption erv lor ad potential connectedness and impacts • Growing (biomass) g oR rin ive to water and energy use • Energy sources • Location of energy sources, • Energy sources • Transmission line Sp r • Coal, oil, natural electric generating plants, and • Coal, oil, natural gas, distance from generating USER INPUT gas, nuclear, community nuclear, renewables facility to community 3.) Indicate potential directions of renewables • Distance between energy sources • Amountof each source • Transmission line Californ energy for water and water for • Amountof each and electric plants or community • KWh/source/yr efficiency ia Coast , NM source • Transport mode • Type of generating plant al Impo rts Luna energy data collection • KWh/source/yr • Transport mode efficiency • Energy sources used El Paso • Distance/volume fuel • Cooling technology used Pe 4.) Use the City of Tucson, Arizona, • Pipeline efficiency Tucson, AZ Ba rm sin ian USA as a case study to highlight the • (1994). "Water and Davis, S. C., S. W. Diegel, et al. • Gleick, P. H. (1994). "Water Davis, S. C., S. W. Diegel, SOURCES Adapted from asu.edu Virtual Energy impact of geographic location, Energy." Annual (2009). Transportation Energy Data and Energy." Annual Review of et al. (2009). distance from water and energy Review of Energy and Book. Energy and the Environment Transportation Energy Natural gas Electricity source the Environment 19: 19: 267-299. Data Book. resources 267-299. Figure 4: Tucson energy demand Figure 6: Tucson energy for water scenario analysis Transport Fuels Water source Table 3: Energy for Water Model Description DISCUSSION Figure 1: Tucson site map and Resource Local Source Treatment End User The scenario analysis indicates that Tucson is a resource island. For virtual water and energy, transportation and extraction, Island depiction. Distribution respectively, are the most sensitive stages (Figure 5 and 6), confirming the reliance on distant resources to provide a more hospitable Energy used to retrieve water Energy used to treat water to Energy used to distribute Energy expended in the use DESCRIPTION environment in an otherwise arid, resource-deprived desert. If the people were, hypothetically, moved to the resources, less water and from the source area and moveit usable a standards potable and recycled of water by the ‘End Table 1: Characteristics of the City of Tucson, Arizona, USA to treatment facility • Potable water to end users User’ (e.g. heading) energy would be consumed. Although the magnitude difference between scenario one and two is far greater for virtual energy, it only • Surface water (conveyance) • Recycled accounts for 1% of Tucson’s total (virtual and actual) energy (Figure 4 and 6). End use is not important for water for energy o 32°08'N, 110°57'W • Groundwater (pumping) considerations but it plays a significant, if not dominant, role in energy for water. Due to difficulties quantifying the end-use stage Location o Southern portion of Arizona, USA (Figure 1) • Recycled water (collection) • Desalination (movement) (e.g. heating water) of energy for water, this was not included in this case study. Rough estimates, however, approximated end-use o Basin and Range: broad desert valleys and small isolated mountain ranges virtual energy as three orders of magnitude higher than all other stages combined. International imports of energy materials were not o Groundwater aquifers are small and often isolated from adjacent basins • Water sources & volume / year • Source of water • Average electricity • Population of community considered in this study due to difficulty identifying source location. Including international import distances in the scenario analysis INPUT USER o Located in the Tucson basin, a valley composed of alluvial fan sediments • Elevation of source • Size of treatment plant used for distribution of water for energy would greatly increase the magnitude of scenario one through the transportation stage (Figure 5). Economies of Geography • Elevation of treatment facility • Level of treatment pumping o Santa Cruz River is adjacent to the City of Tucson, currently intermittent scale may prove important when considering water and energy use and will be further investigated. • Pump efficiency • Or type of technology • Average electricity rate flow controlled by wastewater discharge • Surface water, groundwater & Energy intensity rates from Conversion of electricity KWh per person o Sun belt: Arid to semi-arid climate CONCLUSION MODEL FRAMEWORK desalination: published literature for water used for local pumping consumption based on o Low annual precipitation (approximately 27cm / year) general horsepower equation treatment depending on source, to KWh/AF: California energy utility Climate hp=(y*Q*H)/ (550*e) technology and quantity treated. Ewp = Xe/Re reporting. Although this model does not use site specific data, it has the potential to expose a community to the data collection needs of water- o Average temperature range from 52° to 85°F (11° to 30°C) Where: Where: energy analysis. The aim is to make communities more aware of the nexus so future planning can account for the intimate o 6.5% increase in population over the past 6 years Y = specific weight of water • Surface water (e.g. SBW Ewp = Energy used for Source data: California Q = flow (cubic feet per second) Consulting, Inc 2006 Municipal pumping (KWh/AF) Energy Commission, 2005 relationship between water and energy resources. Population o 534,685 people, current population as of 2006 H = total head (feet) Water Treatment Plant Energy Xe = Average electricity California's water energy o 96% of people live within metropolitan Tucson E = pump efficiency Baseline Study Prepared for the costs for distribution relationship Final Staff o Approximately 71% of Tucson residents commute to work alone Demographics (compared to 75% U.S. nationally) • Recycled water: Price for Pacific Gas and Electric Company, Bellevue, WA p 55) rate Re = Average electricity Report Prepared in Support of the 2005 IEPR Proc. ACKNOWLDGEMENTS pumping and electricity rate to (Sacramento, CA) This work was supported by the Vanderbilt Institute for Energy and Environment. We also thank the Departments of CEE & EES for & Lifestyle o 3.5% use public transportation. infer average cost of collection CEC-700-2005-011-SF their support.