n our last post on Blowback
, we observed and opined that any movement forward exerts a force in the opposite direction, and that it is natural. However, this story
on water consumption seems to be more than just natural clever shaping, it seems seriously wrong.
Plug-in Cars Could Drain U.S. Water Supply,
By Jennifer Bogo
March 7, 2008
"A 30-mile commute in a gasoline-powered car would require the withdrawal of 18.9 gallons
of water, according to a study he co-authored this week
in the journal Environmental Science & Technology. The same commute in a plug-in hybrid electric vehicle (PHEV), meanwhile, would take a whopping 318 gallons
All told, electric miles necessitate threefold the water consumption and 17 times the water withdrawal of gasoline miles. But wait, aren’t PHEVs the environmentally friendly choice
? “If you are a plug-in hybrid owner and you have wind or solar power at your house
, then you can feel really good about your plug-in hybrid using very little water, if any,” Webber told PM. “If you’re a hybrid owner and are plugging your car into the standard U.S. grid, then your car is not very clean, nor is it water-free
With the grid’s current composition, electricity production requires about 136,000 million
gallons of freshwater per day, accounting for over 40 percent of all daily freshwater withdrawals in the nation. That’s because coal-fired
and nuclear power plants
that use steam to drive a turbine typically use water—vast amounts of water—to cool and condense the steam at the exhaust."
And here's the disclaimer, followed by the restatement.
"Though most of this water is returned to the source
(albeit at a higher temperature), a 17-fold increase in demand
would pose a real problem for water-stressed regions
, making power plants more vulnerable to shut down during times of drought."
n truth, to make a meaningful statement about water consumption, one needs to quote, well, the consumption
, not the amount of water that is used to cool the plant.
Otherwise, it's the rough equivalent of saying that hydropower plants withdraw all of the water that goes through the dam's turbines.
According to this EPRI document
most conventional power plants use from 200 gallons up to 900 gallons per MWH, depending on whether the plant uses natural gas, coal, or nuclear fuel, and depending on the cooling technology employed. (in that order)
The misrepresentation in this story thus seems staggering.
If you take 500 Gallons per MWH
as a blend between all of your plants, and each KWH of electricity gives you four miles, then actual water consumption to go the 30 miles
in the story is much closer to four gallons
not 318 gallons. Water consumption per MWH for a new natural gas plant is around 250 gallons per MWH
. At that rate of consumption and at an average of 20 MPG, the amount of water per electric gallon of gas is about 1.25 gallons
. Most thermal plants will use around 3 gallons
. Of course, there is no water consumed at all with wind power or solid state solar plants.
And what about the water used to refine gasoline?
The number varies greatly, but the ConocoPhillips refinery in Billings, Montana processes 62,000 bbls of crude oil
, or 2.6 million gallons per day. That is 879 million gallons of crude oil per year. The water usage for the plant is 456 million gallons. That works out to be 0.52 gallons of water per gallon of crude oil
processed. The study
uses a range of 1.4 to 2.9 gallons of water per gallon of gasoline.
And what about the water consumed in the Tar Sands
? Or in Saudi Arabia
where they use massive water flooding?
ow, if you read the abstract of the original report
, you will see that it says that electrics require 3 times the water consumption
and 17 times the water withdrawal
. The story above
even says that. But with a headline that says "Plug in Cars could drain the US water supply,"
and the lead paragraph saying "a whopping 318 gallons
", it's hard to see.
But it's even harder to see how the authors' work
could have generated such a headline, given their own conclusion.
"Overall, we conclude that the impact on water resources from a widespread shift to grid-based transportation would be substantial enough to warrant consideration for relevant public policy decision-making."
At Plug In Partners
, we conclude that plug-ins powered by combined cycle natural gas plants
use slightly less water than gasoline vehicles, and that plug-ins powered solely by coal and nuclear facilities will consume significantly less than the study's 3 times rate
. We further conclude that the larger 17 fold increase
number is mostly useful as a highly misleading headline.
Another writer from another publication could have just as easily written this headline:
Plug in Cars powered by Renewables will save US Water Supply.