Wednesday, April 02, 2008

PHEV's and Water Consumption


In 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.

Here is the story and the claims.

Plug-in Cars Could Drain U.S. Water Supply,
Researcher Says
By Jennifer Bogo
Popular Mechanics
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."

In 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?

Now, 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.






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3 Comments:

Blogger fkramer said...

At CalCars.org we investigated this when the story came out, and on March 10 we posted an analysis which includes a criticism by the original report's author, calling the news headline "unnecessarily alarmist."

http://www.calcars.org/calcars-news/927.html

-- Felix Kramer, Founder, The California Cars Initiative

1:50 PM  
Anonymous Anonymous said...

So if we get all the people who use toasters and hair dryers and made them stop plugging in we could save more water. Then we get all the giant TV sets and home theaters to unplug and we are really cooking, Oh stop cooking with electric and no more clothes dryers. There we saved the world !

What a poor study they did to determine the water use. Did they counts all the megawatts of power that goes to waste each night. We can plug in at night and save all the waste. Now that's a fact.

9:11 PM  
Anonymous John Spradley said...

The solar panels that charge my 100% pure electric car are the first to collect frost and dew here in Southern California. Our vegetable garden benefits from the runoff. Our air conditioner in the summer drips about 8 gallons of water per day, which waters our car's batteries and garden. Our electric car and its charging system actually reduce our water needs.

6:21 AM  

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