Thursday, September 17, 2009

Do You Really Save Energy When You Buy a New Car?

There has been much discussion about trading in older cars for new under the "Cash for Clunkers" plan.

There is one thing that rarely gets mentioned in energy savings from car replacement. That is, when you manufacture an automobile, it takes all kinds of energy to do it. It takes a lot of heat to melt down those ores into metal, minerals into glass, and fossil fuels into plastic. It takes a lot of energy to transport those materials around in their various forms from mining to installation on a car platform. It takes lots of energy to run an assembly plant what with moving production lines, lights, heat in the paint booth, water for various processes, etc. So, compare the btu's it takes to make a new replacement car every, say, ten years, to the extra fuel per gallon my old 1966 Ford Fairlane uses. I wonder about the net savings in energy from purchasing a new car. After all, it takes more energy to build 4.3 new cars in the time I've kept my Fairlane.

Okay, I'm just curious enough to see if this is true. Let's use the new Toyota Prius, admittedly a mileage king, for comparison. I looked up energy values in btu's online. Here is some math:

1. It takes roughly 113,000,000 btu's to manufacture a new Toyota Prius which gets 45 miles per gallon.

2. There are approx. (coincidentally) 113,000 btu's in a gallon of gasoline.

3. It takes approx. 31,362 btu's of energy per pound to build 90% of automobiles; the Prius takes more due to the battery component, at 38,650 btu's per pound. So, it took approx. 103,440,000 btu's to build the 1966 Fairlane and 113,000,000 to built the Prius.

4. Let's assume a 10 year replacement cycle. If you buy a new Prius every ten years in the time you own the 1966 Fairlane, that means you will buy 4.3 Priuses. 4.3 times 113,000,000 btu's equals 485,900,000 btu's.

5. Drive 150,000 miles in the Fairlane at 18 mpg and at 113,000 btu's per gallon, you've used 941,629,000 btu's of energy. Drive the same 150 miles in a Pruis and you've used 376,629,000 btu's.

6. 941,629,000 minus 376,629,000 equals 565,000,000 which is the amount of btu's that the Fairlane used in fuel over 150K miles than the Prius.

7. 485,900,000 minus 103,440,000 equals 382,460,000 which is the amount greater of energy used to build 4.3 Priuses as opposed to the one Ford Fairlane.

8. 565,000,000 minus 382,460,000 equals 182,540,000 btu's, which is the amount of energy saved by buying 4.3 Priuses instead of keeping the Fairlane for 43 years.

So about the net savings/loss of energy, if the sources of data I used were correct, it appears that fewer but's are used via the 4.3 newly-made cars. BUT: What about money? What's that extra 182,460,000 btu's worth in money in relation to the cost of 3.3 extra cars purchased over the course of 43 years? More calculations needed.

9. The Fairlane cost about $3,000 in 1966, but there's the time value of money, and since 1966, the inflation factor has been approximately six, so 6x$3,000 equals an $18,000 cost of the Fairlane for our purposes of comparison.

10. The new Prius costs approx. $25,000 (not fully equipped), so using our 4.3 factor of Priuses bought every ten years, thats $107,500.

11. The extra btu's of energy that the 66 Fairlane cost over 43 years compared to buying 4.3 new Priuses is mostly in extra gasoline used. So, the extra 182,540,000 btu's divided by 113,000 btu's per gallon, gives us a quantity of approximately 1616 gallons of gasoline. Now gasoline didn't always cost as much over the past 43 years, but let's be on the generous side and allow $3.00 per gallon for it. Multiply 1616 times $3.00 you get $4,848.

12. The cost of 4.3 new Prius cars comes to $107,500, minus the adjusted cost of the 1966 Ford Fairlane, which we figure is around $18,000, equals $89,500.

13. So, if you kept the Fairlane since '66, you would have been out $4,848 in extra fuel costs, but you spent an additional $89,500 on new Priuses (or their equivalent) every ten years, for a net difference of $84,652. The question is, would you rather spend an extra $84,652 to save 182.54 million btu's? This works out in large measure because the btu's to build a car are less expensive than the fuel to power it.

Of course, this is simplified math and to some extent flawed logic. We have to take this a step further. If you are driving the 43 year old car constantly over that period of time, you are going to rack up more mileage, probably 4.3 times, which will drive up the cost of fuel enormously. If you multiply 4.3 times 3,333 gallons for the Prius it equals 14,332 gallons vs. 4.3 times 8333 equals 35,832, a difference of 21,500 gallons, which at $3.00 per gallon amounts to $64,500 which number is probably skewed against the 43 year old car by using an arbitrary, contemporary price for a gallon of fuel. To attempt greater accuracy, we'd have to pro-rate the value of the fuel over time adjusted for inflation and for these purposes that's too complex.

So, $84,652 minus the extra fuel cost of the Fairlane of $64,500 is still a savings of $20,152.

Of course, there are other things to consider, such as when you upgrade and buy a new car, you get the latest technical upgrades which include safety features that the 43 year old car doesn't have. The added maintenance cost of a car with 645,000 miles on it would be considerably more than 4.3 cars with 150,000 miles each on them. In the case of the Prius, however, the estimated battery life of the car is approx. seven years and replacement of these vital parts will be thousands of dollars which you'd never see on a Fairlane.

Driving a newer car costs the motorist more money in insurance and licensing costs than an older one, which are not related strictly to energy consumption or technical considerations. This does adds more expense to the operation of the 4.3 Prius cars.

One thing that you can't quite measure in numbers is this. When you get in that '66 Fairlane, it's still a noisy, smelly, damp, drafty, rattley, loose, old heap. That's why they call 'em clunkers. The newer ride, be it a Prius or something else, is much more comfortable and pleasant to drive.

Just something to think about.

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