LifeCycle Energy Analysis for YOUR car

Time to step away from the "vanilla" car and estimate the total energy used to manufacture and drive a particular car over its lifetime.

The GREET model developed at Argonne National Lab considers how much energy it takes to manufacture the "average" car. We take a bold step and make the assumption that the manufacturing energy increases linearly with the weight of the car, so if my car weighs 30% more than your car, it took 30% more energy to manufacture my car than yours.

This is not an exact calculation, but will serve for a rough estimate. From the GREET model results, the energy to build a car (the "vehicle cycle") is about 30MJ per pound for a conventional car with an internal combustion engine, and about 39MJ per pound for a hybrid vehicle.

The other numbers we need to keep in mind is that there is 121MJ in a gallon of gasoline, and 138MJ in a gallon of diesel.

We're ready to do a rough comparison. The table below shows a few cars with their kerb weight, the energy to manufacture them, the real-life fuel economy, the total fuel energy for 150,000 miles, including the well-to-pump energy ("fuel cycle"), and finally, in the right-most column, the total energy consumed in making the car and driving it for all those 150,000 miles (but excluding any repairs).

 

Lifecycle Energy Analysis
(assuming total 150,000 miles)

Car	Vehicle Weight (lbs)	Mfg. Energy (GJ)	Real Fuel Efficiency (MPG)	Fuel Energy (GJ)	LifeCycle Energy (GJ)
Toyota Prius	3042	119	50	436	545
Toyota iQ	1808	60	43	506	566
VW Golf TDI 1.6L	2998	99	50	497	596
VW Golf TDI 2.0L	2994	99	40	621	720
Honda Fit	2489	82	35	622	704
Honda Odyssey	4337	143	20	1089	1232
Audi A4 Avant 2.0 TFSI	3461	114	24	908	1022
Audi A4 Avant 2.0 TDI	3527	116	39	637	753

For total lifecycle energy, Toyota Prius, the only hybrid model in the table, does exceedingly well, better even than tiny Toyota iQ which in Japan falls in the "2Box" category, that is, a box on wheels that fits two people. Two very good friends.

The VW Golf with the 1.6L diesel engine does only a little worse than the Prius, the one with the 2.0L engine quite a bit worse. Here is a clear example of CelloMom's idea that, carbon and dollar wise, you can have your cake and eat it too: the 1.6L Golf will be cheaper to buy, cheaper to drive, and give you the feelgood factor of significantly lower carbon emissions.

The smaller Honda Fit has nearly the same total lifecycle energy as the Golf with the larger engine; but it is significantly cheaper to buy, as well.

At 1232GJ total lifecycle energy, the Odyssey minivan consumes 2.5 times more energy than the Prius, which is not so great considering you can transport only 1.4 times as many people in the minivan. Energetically speaking the minivan is more attractive only if you have five or more passengers to move every day, e.g. if you share the school commute with friends.

The Audi A4 station wagon makes sense only for the most frugal engine: for the less frugal ones you might as well buy a minivan and get more cargo space and passenger flexiblity, foregoing the carbon feelgood factor. Here the cost equation is less clear, since the diesel version has a higher purchase price. But at a fuel economy of 39mpg for the diesel, as compared to 24mpg for the gasoline version, the frugal diesel is still cheaper overall.