Combatting water scarcity and economic distress along the US-Mexico border using renewable powered desalination
Graphical abstract
Introduction
In 2019, a large consortium of scientists and engineers led by Purdue University laid out a vision for supplying energy and water along the US-Mexico border, endeavoring to develop a future corridor of technological innovation and agriculture [1], [2], [3]. The theory proposed using desalination and renewable energy to create an operational zero-emission source of sustainable water. The novelty of such an approach is in using coastal saltwater desalination to solve a water crisis far from the ocean and fully powering such an infrastructure with renewable energy. To establish a framework for future evolution, a pilot version of the international proposal is presented for the American side of the border. The results presented provide a highly detailed breakdown of the potential infrastructure components needed and their scale and economics for water generation. A pilot level quantity of water to be satisfied is determined, its required energy for production and distribution is modeled and the installed, internal levelized cost of electricity and itemized levelized cost of water are provided. The proceeding paragraphs outline the analysis and introduce the water security issue along the border as well as the methodology used for designing and modeling the RO, pipeline and renewable infrastructure.
Mexico is a top trading partner with the US in terms of goods and services [4], yet the border between these two countries is a contentious region where crime, poverty and resource scarcity are prevalent and agreements between the two countries to share natural resources have been largely unsuccessful [5], [6], [7]. Aquifers and large rivers historically satisfied the agricultural and basic needs of the area; however, the natural replenishment cycle has become increasingly inadequate to sustain the growing regional demands [8], [9], [10], [11]. Sources such as the Rio Grande River basin and Colorado River are already experiencing detrimental shortages [7], [12], hindering groundwater recharge. US counties along the border withdraw approximately 47% [13] of their supply from these now depleting aquifers so local populations must significantly reduce water usage and/or import expensive water from neighboring communities. Otherwise, recharge cycles will cease to operate effectively, making agricultural and societal expansion all but impossible.
With the price of water across the US escalating [14], [15], [16], creating, rather than importing alternative sources of freshwater will likely be necessary. On-site water reuse is limited by both the recovery ratios of the purification process and by what can be returned to local distribution networks. Brackish water desalination is not ideal either as it would draw from the same strained aquifers and rivers. Instead, a more secure and sustainable option is to use abundantly available oceanic saltwater for desalination to provide an auxiliary supply.
The two main saltwater desalination types, thermal and membrane based, were historically competitive at large scale, but membrane based Reverse Osmosis (RO) is often the most energy and cost effective [17], [18], [19], [20], [21], [22], [23], [24]. Many regions around the world, such as the Middle East, India and South Africa, have embraced using saltwater RO for water security [25], [26], [27], [28], [29]. The immediate difficulty with applying saltwater desalination to the US-Mexico border is that it mostly spans landlocked North American territory. This means the only accessible seawater feed sources for this process are at the Pacific and Gulf coasts, necessitating a dedicated infrastructure to deliver the water from these coastal locations.
Fortunately, the renewable offshore wind [30], [31], [32], [33], [34] and solar [34], [35], [36], [37], [38] resources around the border provide satisfactory energy for desalination and distribution respectively. Advancements in these renewable technologies have driven down prices enough to be cost competitive with fossil fuel [39], which ensure healthy economics while maintaining a minimal carbon footprint. Hydraulic drivetrains in wind turbines [40], [41], [42], [43], [44], [45] and tracking systems for solar photovoltaic (PV) panels [46], [47], [48], [49], [50] are a few examples of improvements which can bring down the cost of energy for integrated infrastructure projects such as this one.
The proposed RO plant(s) are the largest ever designed [24], [51] with a capacity of 1000 MGal/day (3.79 Mm3/day), and were simulated using three different process efficiencies [18]. These plants are located where the border meets the Pacific and Gulf coasts. Desalination energy loads were met by offshore wind farms located nearby in areas of high average wind speed and sized using site paraemetrized Weibull distributions to match annual energy production with consumption [52], [53], [54], [55]. A 30 m resolution geospatial terrain and elevation map of the entire border was constructed [56] and used to calculate inland pumping energy intensity. To satisfy the almost 2 GW needed for water distribution, 5 potential solar farms along the pipeline were modeled using optimized tilted and one-axis tracking panels [57], [58]. Solar farms were chosen due to their favorable economics along the full length of the border versus onshore wind which appeared to perform best in Texas exclusively.
One-hundred eight (108) renewable variations, and another 27 using fossil fuel and existing grid energy, were simulated to demonstrate a range of real-world costs and potential configurations. Results showed that renewable-driven variations were cost competitive with “environmentally friendly” fossil fuels. More importantly, renewable variations significantly outperformed fossil fuels in life-time operational water withdrawal, life-time CO2 emissions and systemic job creation [59]. The objective of the project is to design a sustainable clean water infrastructure that is not only beneficial to the population but environmentally responsible. The economic and environmental competitiveness of renewables to power the project allows for the facilitation of both. In doing so, the US-Mexico border can evolve from a resource strained region into one of economic prosperity.
This project highlights the first nation level approach to using saltwater desalination to solve inland water sustainability and presents results that are both thorough in their calculation and detailed in their breakdown. A flowchart is presented in Fig. 1 to help readers follow the methodology used in the analysis. Additionally, the manuscript has been divided in meaningful sections which the reader can refer to. Section 2 consists of a background on water accessibility in the US-Mexico border region. Section 3 describes the water usage profile of the region, details the reasoning behind the water load met by the project and introduces reservoir water storage. Section 4 describes the methodology used for calculating the power production from renewables and their respective results. Section 5 covers the costs associated with each component and metrics behind the socio-economic and environmental impacts of the project. Section 6 discuss the economic results of the analysis, considerations for future optimization and design changes and Section 7 concludes with a note of the project’s feasibility and importance.
Section snippets
Background: The Socio-Politics around water accessibility along the US-Mexico border
While the purpose of this project is to design a sustainable clean water infrastructure for the American side of the US-Mexico border, also of great interest are the underlying socio-political issues that plague the area. As previously stated, the US and Mexican government have attempted to share the natural water resources along the border. Sources such as the Rio Grande river basin and San Pedro aquifer straddle the border and thus both parties are entitled to their benefits. To handle these
Water requirements
As with most large-scale resource infrastructure projects, determining the quantity of the target resource to offset or supplement can be a difficult and subjective task. The water requirements along the US-Mexico border include cities and towns on or near the border that contribute to the total water withdrawal in the region. To characterize this, United States Geological Survey (USGS) water data was compiled for the entire set of US counties which border with Mexico [13]. The total water
Renewable power production infrastructure methodology
Wind and solar energy can provide a recurrent source of clean and sustainable electricity, with the added benefit of highly reduced operational water withdrawal over fossil fuel technology. Detailed in this section is the integration of offshore wind turbines and solar panels into the project’s energy infrastructure. Studies show that US coastal waters near the border experience high average wind speeds and harbor the opportunity to further expand the US offshore wind industry [30], [31], [32],
Project versions
To cover the wide range of designs that this project may take to achieve optimal economics, 3 major configurations of the piping and desalination structure were considered. The first two being if the desalination plant was sized to meet the total water requirement along the border and placed solely on the west or east coast. Pumping was scaled by adding extra pipes so that physical fluid properties did not change. The third configuration was if the water production was split between the east
Results and discussion
Without obtaining water security, the US-Mexico border region will only become more impacted by shortages and economic tension. This analysis presented a concept for achieving this security in a sustainable fashion using renewables and saltwater desalination. By constructing this concept, a tangible value can be placed on the cost of producing this water and providing it to the region. Proposals such as this are very scarce in academic literature and even fewer report outcomes at such a
Conclusion
Water usage along the US-Mexico border has been shown to exceed what the local resources can supply. This causes socio-political and economic stress across the US and Mexican regions along the border through dry riverbeds and wells. Without adequate planning, the natural water in the area will continue to unsustainably deplete. The above analysis presents a range of potential configurations for water security infrastructure along the US-Mexico border. One-hundred eight (108) renewable and 27
CRediT authorship contribution statement
Michael Roggenburg: Methodology, Formal analysis, Visualization, Validation, Writing - original draft. David M. Warsinger: Project administration, Supervision, Visualization, Writing - review & editing. Humberto Bocanegra: Methodology, Writing - review & editing. Luciano Castillo: Conceptualization, Funding acquisition, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References (143)
- et al.
Overview of systems engineering approaches for a large-scale seawater desalination plant with a reverse osmosis network
Desalination
(2009) - et al.
Hydraulic-electric hybrid wind turbines: Tower mass saving and energy storage capacity
Renew Energy
(2016) - et al.
Techno-economic analysis of a hydraulic transmission for floating offshore wind turbines
Renew Energy
(2020) - et al.
Review on sun tracking technology in solar PV system
Energy Rep
(2020) - et al.
Global Techno-Economic Performance of Bifacial and Tracking Photovoltaic Systems
Joule
(2020) - et al.
The Wind Integration National Dataset (WIND) Toolkit
Appl Energy
(2015) - et al.
The National Solar Radiation Data Base (NSRDB)
Renew Sustain Energy Rev
(2018) - et al.
Identifying and characterizing transboundary aquifers along the Mexico-US border: An initial assessment
J Hydrol
(2016) - et al.
Energy efficiency of batch and semi-batch (CCRO) reverse osmosis desalination
Water Res
(2016) - et al.
Batch counterflow reverse osmosis
Desalination
(2021)