Estimation and Comparison of Thermoelectric and PV Solar Water Usage in the Colorado River Basin States
Creators: name: Feng, Yuzhen 
Publisher: name: University of Nevada, Las Vegas
Year: 2016

description: With the continual expansion of populations in the arid Southwest, energy demands will continue to rise. On the other hand, depleting water levels in reservoirs of the Colorado River Basin is expected to continue as more intense and frequent drought events persist in addition to the rapid development in the region. Currently, the three largest water-use categories in the United States are thermoelectric energy, irrigation, and municipal water, which cumulatively account for 90 percent of the national water use. In the Southwest, most of the total electricity generated is still through thermoelectric means. That is, massive amounts of water are used to boil into steam to move the turbine to generate electricity. With such high dependency on water, higher energy demand in the future will lead to further rise in water demand. Therefore, more energy-specific water usage research is needed to determine the success of water resource management for future sustainability. The objective of this study seeks to estimate and compare the water usage in thermoelectricity generation (i.e. natural gas, coal), and solar energy, in five southwest Colorado River Basin states. The term "water use" includes both water withdrawal and consumption from a water body. While solar energy in general includes both thermal solar (Concentrated Solar Power; CSP) and non-thermal solar (Photovoltaic; PV), CSP is also considered a type of thermoelectricity since it utilizes water intensive steam turbines. Thus CSP was not emphasized as the main focus of this study for the comparison of renewable energy alternative to fossil fuels. Results from the first stage of the study, which was based just on the state of Nevada, showed that with PV solar generating 2.84% electricity of the state total in 2014, Nevada saved approximately 56 million gallons of water. To further investigate other southwest areas and their potentials in solar energy, this study expanded the scope from the first stage study to examine four additional Colorado Basin states that have experienced the most droughts in recent years: Utah, New Mexico, Arizona, and California.
This study was conducted in two main parts: 1) estimation of the amount of water consumption and withdrawal for utility scale thermoelectricity generation and PV Solar energy for the past ten years, and 2) projection and comparison of future water demand in the basin states, based on each state's renewable energy portfolio standards (RPS). To accomplish the research objectives, estimations of operational and pre-operational water usage was determined as a function of the thermal fuel sources, cooling systems, and generator types used by power plants combined with established water coefficients per unit of electricity generated. Operational water use refers to the water withdrawal and consumption throughout the process of generating electricity. Preoperational water use refers to the water used to acquire and prepare the fuel sources. The same calculation was applied to calculate the water use for PV solar electricity generation. 
This study utilizes the system dynamics (SD) model developed from the first stage study to evaluate the interrelationship of thermoelectricity responses from PV Solar energy on water use and their potential for water savings. A model that runs different simulations based on each state's optimal Renewable Portfolio Standards (RPS). Three case scenarios were simulated to examine the projected energy outlooks by 2032. The first scenario examined projections with the present state of conditions on electricity generation by fuel distributions. The second scenario explored the projections based on the optimized expectation of each state's current RPS while the third scenario explored the projections on a modified hypothetical RPS expectation. A sub-scenario was created as a reference case to examine how much water were saved from the current trend of electricity production by renewable sources.
Results from the past water usage estimation show that although electricity demand has been a slow and steady decline for the past decade, energy demand for the future will continue to increase, but at a less intense rate than population growth. Although each state had set RPS goals to advocate for more future electricity production from renewable energy, and corresponding actions have been taken to build more renewable energy based power plants, statistics showed that they are currently still, and will be in the near future, highly dependent on burning fossil fuels. For example, while California holds the lowest percentage of coal-fueled electricity production (0.4%), it shows an increasingly higher dependency on natural gas over the past decade (from 49% in 2005 to 61% in 2014). Results from the model simulation indicate that with each state's current RPS goals, approximately 600 million to 1.3 billion gallons of water can be saved annually. Three out of five study states showed significant water savings with projections on a modified hypothetical RPS that will increase the PV solar energy production amounts while decreasing coal. Improvement on RPS goals would be beneficial for Arizona, Nevada, and Utah, while continual compliance to the current RPS goals would be sufficient for California and New Mexico. This study is reproducible so that it can be replicated using other renewable energy sources to test the potential for water efficient energy fuel replacement. Findings from this study will shed light on water resource management involving the utility scale energy sector. Millions of gallons of water are used every day to produce energy. It is important to better explore energy alternatives in the hope of preventing further water shortage in the Southwest. Policy makers may reconsider whether to develop a more aggressive approach that depends on water conservation from the general public or to redesign current water conservation strategies that target the electric sector.