Study Suggests Planning for Grid-Based Light-Duty Vehicles (PHEVs or EVs) Should Factor in Impacts on Regional Water Resources
A study by researchers at the University of Texas at Austin has concluded that converting light-duty transportation from full gasoline power to electric power by using either plug-in hybrid electric vehicles (PHEVs) or battery electric vehicles (EVs) is likely to increase demand for water resources—primarily due to increased water cooling of thermoelectric power plants to accommodate increased electricity generation. The study assumes continuation of the current electricity generation mix, for methodological ease, even while recognizing that “changes will happen.”
The potential increase in usage, assuming wide-spread adoption of PHEVs and EVs, represents a significant potential impact on regional water resources and should be considered when planning for a plugged-in automotive economy, according to the study by Carey King and Michael Webber, published online in the journal Environmental Science and Technology.
The authors of the study, which has already been sensationalized with headlines such as “Plug-in Cars Could Drain US Water Supply”, are careful to point out that they are not saying that the negative impacts on water resources make the shift to grid-based transportation undesirable, but rather that such impacts should be quantified ahead of time to avoid unnecessary conflicts. The study concludes with the suggestion of several steps and policies that can be promoted to enable sufficient water access for enhancing PHEV market success.
King and Webber calculated that in displacing gasoline miles with electric miles, approximately 3 times more water is consumed (0.32 versus 0.07–0.14 gallons/mile) and more than 17 times more water is withdrawn (10.6 versus 0.6 gallons/mile) primarily due to the increased cooling needs.
Water consumption describes water that is taken from a concentrated source and not directly returned—e.g., a closed-loop cooling system for thermoelectric steam power generation where the withdrawn water is run through a cooling tower and evaporated instead of being returned to the source. Water withdrawal describes water that is taken from a concentrated source, used in a process, given back from whence it came, and available again for the same or other purposes—e.g., an open-loop cooling system for thermoelectric steam power generation that withdraws cool water from a reservoir into its condensing unit and discharges that heated water back into the reservoir.
The typical US driver would drive 4,500, 7,100, and 8,600 electric miles per year in a PHEV20, PHEV40, and PHEV60, respectively. For example, it takes 114, 72, and 59 million PHEV20, PHEV40, and PHEV60, respectively, to drive 500 billion electric miles annually. [Total miles driven in 2003=2.66 trillion] Since there are 234 million gasoline LDVs on the road today, displacing one-sixth to one-fifth of gasoline miles with 114 million PHEV20s, or 49% of the vehicle fleet, sounds feasible, but with annual sales rates of cars and light trucks/SUVs amounting to 17 million vehicles per year, it would take 7 years if every vehicle sold were a PHEV20. Comparing the displacing of the same 500 billion gasoline miles with electric miles of PHEV60s requires replacement of 25% of cars, light trucks, and SUVs, for which the tradeoff would be annual water consumption of 160 Bgal/yr compared to 35–70 Bgal/yr using gasoline. Also, 5,300 Bgal/yr would be withdrawn instead of 300 Bgal/yr. These increases in water usage represent approximately 0.2–0.3% and 3%, respectively, of overall US water consumption (100,000 Mgal/d freshwater in 1995) and withdrawal (408,000 Mgal/d in 2000).
...Water rights and access are also largely a regional issue due to varying laws, rain patterns, river paths, and groundwater supply. Thus, in order to implement the electron automotive economy where a substantial number of miles are driven electrically, the water demands need to be assessed on a regional basis. This means that some relatively wet regions of the United States may be able to support more PHEVs at lower cost than other relatively dry regions. Also, dry regions can focus on cooling techniques that require little water or electricity generation technologies, such as wind and photovoltaic solar that do not consume and withdraw water. Most importantly, public policy decisions that promote PHEVs or electric vehicles need to consider the impact on water resources beforehand because the increased demand for water withdrawals is potentially quite substantial and could impact water availability or rights for irrigation, municipal, and other competing purposes.
The authors suggest four initial steps and policies:
Promote research and development of distributed generation and renewable energy sources that use little to no water and can possibly be located onsite where PHEVs are charged.
Develop regional water plans that consider increased demands for electricity for PHEVs in order to ensure adequate water access in light of competing water demands for municipal and irrigation uses.
Move to generate more electricity by methods that do not withdraw such large amounts of water.
Use reclaimed, saline, or other water sources that are suitable for thermoelectric cooling, but unsuitable or unable to be treated economically for drinking.
Carey W. King and Michael E. Webber. The Water Intensity of the Plugged-In Automotive Economy. Environ. Sci. Technol., ASAP Article, 10.1021/es0716195