Friday, June 29, 2012

Hummer Versus Prius




There was a rumor that was circulating a few years ago. I recall it being on the internet, but not in the mainstream media.

It went, that because a Toyota Prius used lithium batteries, and that mining lithium caused so much environmental damage, the Hummer was actually better for the environment over the long term. Really?

A number of writers have since clearly disproved this. See their valid analysis here:


http://www.pacinst.org/topics/integrity_of_science/case_studies/hummer_versus_prius.html

http://www.pacinst.org/topics/integrity_of_science/case_studies/hummer_vs_prius.pdf


However, I did my own simple analysis. It was not difficult at all. The hardest part is finding the correct numbers.

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Prius - Weight Of The Battery:


The weight of the Prius battery varies according to the source. 

176-lb. Li-ion battery pack  (80 kg)

53.3 kg, or, 117.5 lb

68 kg, or 149.6 pounds

2001-2003 Prius' battery pack: 110 Pounds total weight, (50 kg) 

Assume the heaviest weight, of 176 pounds, or 88 kilograms. 


And, according to: http://toyotapriusbattery.com/repair.html, the replacement cost for the Prius battery is about $4000.  

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Curb Weight Of The Vehicles:

Hummer:   6400 to 6614 pounds, assume 6500 pounds
Prius: 2932 pounds
Prius excluding battery pack: 2756 pounds

Difference: 3744 pounds (1.872 tons)

Including the battery, the Hummer is 2.2 times as heavy. 
The Hummer is 2.3 times as heavy, excluding the battery. 

I will assume that the steel, plastic, rubber and other materials for both the Hummer and Prius come from the same or similar sources. And so no major difference in the environmental impact of these materials. 

3744 extra pounds of materials is 21 times the weight of a 176 pound battery pack. And the battery pack actually includes a lot of non lithium parts such as a frame, plastic holders, etc. So, the weight of the lithium itself is actually lower. 


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Gasoline, and CO2 Impact:

Assume 200K miles over the lifetime of both vehicles.

Hummer:   9 to 10 MPG 
Prius:   48 to 51 MPG

The Hummer gets about 5 times worse mileage than the Prius!  But I guess everyone knew that.  


Gasoline required for 200K miles:

Hummer:   200K/10 mpg = 20,000 gallons
Prius: 200K/50 mpg = 4,000 gallons

Difference: The Hummer will consume 16,000 more gallons of gas over 200K miles. At $4 per gallon, that will cost an additional $64,000 over the life of the vehicle.  


CO2 Over 200K Miles:

Assuming 19 pounds of CO2 per gallon

Hummer:  20,000 gallons * 19 pounds 
= 380,000 pounds
= 190 tons of CO2

Prius: 4,000 * 19 pounds
= 76,000 pounds
= 38 tons of CO2 


Difference:
The Hummer will create 152 more tons of CO2 over the life of the vehicle! 


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So, the criticizers say that because of some pollution created by the lithium ion battery, the Hummer is better for the environment than a Prius, over the life of the vehicle.  

If that is the case, the mining and production of the 176 pound battery pack (0.088 ton) lithium ion battery that costs $4000 would require the equivalent of the additional resources of at least:

3744 more pounds (1.872 tons) of steel, plastic, rubber, and other materials used in the production of the vehicles. 

Plus, 16,000 gallons of gas (96,000 pounds, 48 tons, that would cost $64,000 at $4 per gallon) 

Which would be burned up and produce 152 tons of CO2.

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So, does the $4000 Prius battery require that many resources to produce? Or, in its manufacture, and lifetime of use, does it create the equivalent environmental damage of 48 tons of C02?

Does that make sense? 

I think not. 

It is not believable at all! 



3 comments:

  1. Excellent material Roger. I have a 2004 and love it. My previous vehicle got 24mpg and I now get 48mpg. It's saved me $4,000 in fuel in less than four years and is on track to be a free car in less than six years (bought it used for $10k).

    Mileage stats here: http://fayfreethinkers.com/forums/viewtopic.php?p=22606#p22606

    They are planning to use lithium in future models of the Prius but haven't last I checked. All Nimh so far.
    Also, regarding the replacement cost of the NiMH batteries, there is a $1,500 or so core trade in value, so replacement should be more like $2,500 or even less. See:
    http://www.greencarreports.com/news/1078138_toyota-hybrid-battery-replacement-cost-guide

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