Evaluation of power generation operations in response to changes in surface water reservoir storage

We used a customized, river basin-based model of surface water rights to evaluate the response of power plants to drought via simulated changes in reservoir storage. Our methodology models surface water rights in 11 river basins in Texas using five cases: (1) storage decrease of existing capacity of 10%, (2) storage decrease of 50%, (3) complete elimination of storage, (4) storage increase of 10% (all at existing locations), and (5) construction of new reservoirs (at new locations) with a total increase in baseline reservoir capacity for power plant cooling of 9%. Using the Brazos River basin as a sample, we evaluated power generation operations in terms of reliability, resiliency, and vulnerability. As simulated water storage decreases, reliability generally decreases and resiliency and vulnerability remain relatively constant. All three metrics remain relatively constant with increasing reservoir storage, with the exception of one power plant. As reservoir storage changes at power plants, other water users in the basin are also affected. In general, decreasing water storage is beneficial to other water users in the basin, and increasing storage is detrimental for many other users. Our analysis reveals basin-wide and individual power plant-level impacts of changing reservoir storage, demonstrating a methodology for evaluation of the sustainability and feasibility of constructing new reservoir storage as a water and energy management approach.Mechanical Engineerin

Can switching fuels save water? A life cycle quantification of freshwater consumption for Texas coal-and natural gas-fired electricity

Thermal electricity generation is a major consumer of freshwater for cooling, fuel extraction and air emissions controls, but the life cycle water impacts of different fossil fuel cycles are not well understood. Much of the existing literature relies on decades-old estimates for water intensity, particularly regarding water consumed for fuel extraction. This work uses contemporary data from specific resource basins and power plants in Texas to evaluate water intensity at three major stages of coal and natural gas fuel cycles: fuel extraction, power plant cooling and power plant emissions controls. In particular, the water intensity of fuel extraction is quantified for Texas lignite, conventional natural gas and 11 unconventional natural gas basins in Texas, including major second-order impacts associated with multi-stage hydraulic fracturing. Despite the rise of this water-intensive natural gas extraction method, natural gas extraction appears to consume less freshwater than coal per unit of energy extracted in Texas because of the high water intensity of Texas lignite extraction. This work uses new resource basin and power plant level water intensity data to estimate the potential effects of coal to natural gas fuel switching in Texas’ power sector, a shift under consideration due to potential environmental benefits and very low natural gas prices. Replacing Texas’ coal-fired power plants with natural gas combined cycle plants (NGCCs) would reduce annual freshwater consumption in the state by an estimated 53 billion gallons per year, or 60% of Texas coal power’s water footprint, largely due to the higher efficiency of NGCCs.Mechanical Engineerin

Valuing Distributed Energy Resources for Non-Wires Alternatives

Distributed energy resources (DER) as non-wires alternatives, regardless of owner, have the potential to reduce system operating costs and delay system upgrades. However, it is difficult to determine the appropriate economic signal to incentivize DER investors to install capacity that will benefit both the DER investors and the system operator. In an attempt to determine this co-optimal price signal, we present a bilevel optimization framework for determining the least cost solution to distribution system over-loads. A key output of the framework is a spatiotemporal price signal to DER owners that simultaneously guarantees the DER owners' required rate of return and minimizes the system operation costs. The framework is demonstrated with a case by which the system operator considers utility owned battery energy storage systems, traditional system upgrades, and energy purchase from DER owners. The results show that by valuing DER for non-wires alternatives the utility owned storage system sizes can be reduced, less hardware upgrades are necessary, and upfront capital costs as well as operating costs are reduced.Comment: under revie

Wasted Food, Wasted Energy: The Embedded Energy in Food Waste in the United States

This work estimates the energy embedded in wasted food annually in the United States. We calculated the energy intensity of food production from agriculture, transportation, processing, food sales, storage, and preparation for 2007 as 8080 ± 760 trillion BTU. In 1995 approximately 27% of edible food was wasted. Synthesizing these food loss figures with our estimate of energy consumption for different food categories and food production steps, while normalizing for different production volumes, shows that 2030 ± 160 trillion BTU of energy were embedded in wasted food in 2007. The energy embedded in wasted food represents approximately 2% of annual energy consumption in the United States, which is substantial when compared to other energy conservation and production proposals. To improve this analysis, nationwide estimates of food waste and an updated estimate for the energy required to produce food for U.S. consumption would be valuable

Development of a Rooftop Collaborative Experimental Space through Experiential Learning Projects

The Solar, Water, Energy, and Thermal Laboratory (SWEAT Lab) is a rooftop experimental space at the University of Texas at Austin built by graduate and undergraduate students in the Cockrell School of Engineering. The project was funded by the Texas State Energy Conservation Office and the University’s Green Fee Grant, a competitive grant program funded by UT Austin tuition fees to support sustainability-related projects and initiatives on campus. The SWEAT Lab is an on-going experiential learning facility that enables engineering education by deploying energy and water-related projects. To date, the lab contains a full weather station tracking weather data, a rainwater harvesting system and rooftop garden. This project presented many opportunities for students to learn first hand about unique engineering challenges. The lab is located on the roof of the 10 story Engineering Teaching Center (ETC) building, so students had to design and build systems with constraints such as weight limitations and wind resistance. Students also gained experience working with building facilities and management for structural additions, power, and internet connection for instruments. With the Bird’s eye view of UT Austin campus, this unique laboratory offers a new perspective and dimension to applied student research projects at UT Austin.Cockrell School of Engineerin

Workshop Report: Developing a Research Agenda for the Energy Water Nexus

The energy water nexus has attracted public scrutiny because of the concerns about their interdependence and the possibility for cascading vulnerabilities from one system to the other. There are trends toward more water-­‐intensive energy (such as biofuels , unconventional oil and gas production, and regulations driving more water consumption for thermoelectric power production ) and more energy-­‐intensive water (such as desalination, or deeper ground water pumping and production). In addition demographic trends of population and economic growth will likely drive up total and per capita water and energy demand, and due to climate change related distortions of the hydrologic cycle, it is expected that the existing interdependencies will be come even more of a concern. Therefore, developing a research agenda and strategy to mitigate potential vulnerabilities and to meet economic and environmental targets for efficiently using energy and water would be very worthwhile. To address these concerns, the National Science Foundation (NSF) sponsored a workshop on June 10-­‐11, 2013 in Arlington, VA (at NSF headquarters) to bring together technical, academic, and industry experts from across the country to help develop such a research agenda. The workshop was sponsored by NSF Grant Number CBET 1341032 from the Division of Chemical, Bioengineering, Environmental and Transport Systems. Supporting programs were: Thermal Transport Processes, Environmental Sustainability, and Environmental Engineering.Center for Research in Water Resource

Implementation of Brackish Groundwater Desalination Using Wind-Generated Electricity: A Case Study of the Energy-Water Nexus in Texas

Growing populations and periodic drought conditions have exacerbated water stress in many areas worldwide. In response, some municipalities have considered desalination of saline water as a freshwater supply. Unfortunately, desalination requires a sizeable energy investment. However, renewable energy technologies can be paired with desalination to mitigate concern over the environmental impacts of increased energy use. At the same time, desalination can be operated in an intermittent way to match the variable availability of renewable resources. Integrating wind power and brackish groundwater desalination generates a high-value product (drinking water) from low-value resources (saline water and wind power without storage). This paper presents a geographically-resolved performance and economic method that estimates the energy requirements and profitability of an integrated wind-powered reverse osmosis facility treating brackish groundwater. It is based on a model that incorporates prevailing natural and market conditions such as average wind speeds, total dissolved solids content, brackish well depth, desalination treatment capacity, capital and operation costs of wind and desalination facilities, brine disposal costs, and electricity and water prices into its calculation. The model is illustrated using conditions in Texas (where there are counties with significant co-location of wind and brackish water resources). Results from this case study indicate that integrating wind turbines and brackish water reverse osmosis (BWRO) systems is economically favorable in a few municipal locations in West TexasMechanical Engineerin

Air quality impacts of using overnight electricity generation to cahrge plug-in hybrid electric vehicles for daytime use

The air quality impacts of replacing 20% of the gasoline powered light duty vehicle miles traveled with plug-in hybrid electric vehicles (PHEVs) in the region served by the Pennsylvania, New Jersey, Maryland classic grid are examined. Unutilized, base-load nighttime electricity generating capacity is assumed to charge PHEVs that would subsequently be used during urban commutes. The net impact of this scenario on the emissions of precursors to the formation of ozone is an increase in nitrogen oxide (NOx), volatile organic compound (VOC) and CO emissions from electricity generating units during nighttime hours, and a greater decrease in NOx, VOC and CO from mobile emissions in urban areas during daytime hours. The changes in maximum daily 8 h ozone concentrations, predicted using a regional photochemical model (CAMx), are decreases in ozone concentrations between 2 and 6 ppb that are widespread across the urban areas, and increases in ozone concentrations of up to 8 ppb in highly localized areas. Air quality indicators beyond maximum daily ozone concentration are also evaluated, and in general indicate air quality improvements associated with the use of PHEVs. However, a limited number of air quality indicators worsened with the use of PHEVs, suggesting that overall impacts of the use of PHEVs will be complex.Mechanical Engineerin

Where does solar-aided seawater desalination make sense? A method for identifying sustainable sites

AbstractGlobal water planners are increasingly considering seawater desalination as an alternative to traditional freshwater supplies. Since desalination is both expensive and energy intensive, taking advantage of favorable natural and societal conditions while siting desalination facilities can provide significant financial and environmental returns. Currently, policy makers do not use a location-specific integrated analytical framework to determine where natural and societal conditions are conducive to desalination. This analysis seeks to fill that gap by demonstrating a multi-criteria, geographically-resolved methodology for identifying suitable regions for desalination infrastructure where 1) available renewable resources can offset part of the fossil energy load; 2) feedwater characteristics reduce the total energy needed for desalination; and 3) human populations have capacity and willingness to pay for desalinated water. This work demonstrates the method with a quantitative global analysis that identifies favorable sites for solar-aided seawater reverse osmosis desalination (SWRO) based on specific target criteria. Location-based data about natural conditions (solar insolation, ocean salinity, and ocean temperature) are integrated and mapped with social indicators (water stress, prevailing water prices, and population) to identify regions where solar-aided SWRO has the highest potential. This work concludes that water-stressed tropical and subtropical cities show the highest potential for economically sustainable solar-aided SWRO