Wednesday, February 20, 2008

Water for Transportation - publication on "electric miles"

A paper of mine has been published online today in the journal Environmental Science and Technology. The paper describes how much water is used, that means consumed and withdrawn (which are two different concepts) for driving a vehicle on electricity as "fuel". This pertains to electric vehicles (EV) or plug-in hybrid electric vehicles (PHEV) while they travel on battery power alone.

First, two basic definitions:

water withdrawal is that water which is taken from a source, run through a process, and returned to the source or some other source.

water consumption is water that is withdrawn but not returned to the source due to evaporation (for example - in cooling processes for steam power plants) or evapotranspiration (evaporation from through plants).

Due to water consumed and withdrawn for cooling steam electric power plants (coal, nuclear, geothermal, solar concentrated power, and most natural gas), we can associate that water usage with the electricity generated from the plant. Assuming that an EV or PHEV is charged with electricity from the generic U.S. grid, each mile driven by a average light duty vehicle (a car, pickup truck, or SUV) will consume 0.2-0.3 gallons of water and withdraw 8 gallons of water. This is approximately 2-3X more water consumption and 12X more water withdrawal than when driving a light duty vehicle on petroleum gasoline.

Does this mean we should not pursue EV and PHEV technology? ABSOLUTELY NOT.

There are many benefits to the integration of EV/PHEV vehicles which include the ability to use a diversity of fuels sources - anything that can end up generating electricity (burning stuff to produce steam, nuclear power, wind power, photovoltaic solar, etc.). The ability to use a variety of transportation fuels by way of the electric grid is very powerful and important.

While the water consumption and withdrawal is higher than using petroleum gasoline, we can easily plan and accommodate for the increase in water usage per mile. The use of EV/PHEVs will occur gradually, and water resources will not be the limiting factor for their adoption. Full speed ahead for electric cars.

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