Vehicle efficiency as low as 1.3% for even small cars
AskPablo has a wonderful post on Triple Pundit about calculating the "well to wheel" efficiency of automobiles:
With gasoline prices as high as they are many people are concerned about vehicle efficiency. Other people who are concerned about their impact on the future of our climate care about vehicle efficiency as well. Where does the energy that we put into our cars actually go? And what is the overall efficiency of a car?
I believe that Pablo's post does much to illustrate the various impacts on fuel consumption, and I highly recommend it.
However, I think Pablo does miss out on one key calculation of efficiency. The point of driving anywhere is generally to get you from Point A to Point B. But note carefully that the purpose is to get YOU the driver (or the driver and passengers) from Point A to Point B, and not the vehicle. We rarely drive just to move our car from one place to another.
So to get a true efficiency calculation, we need to add in the amount of work done to move the car separately from the work to move the person. A simple way to do this is to use the percentage of the mass of the payload compared to the mass of the car. I couldn't find gross vehicle weight for Pablo's car, a Toyota Matrix XR, online, but let's assume that it is 2500 pounds. Then let's assume that the average driver is 175 pounds and that, for the sake of this calculation the overwhelming majority of trips are single occupancy trips. With those three assumptions, we see that the driver makes up only 7% of the total mass being moved from one place to another. Therefore 93% of the work being done is to move the car from place to place, while only 7% is to move the person from place to place. (To be totally accurate, we should probably separate out the impact of mass from the impact of drag coefficient, but I'll leave that to Pablo since he is more skilled than I.)
So while Pablo calculates a well-to-wheel efficiency of his car at 19.9%, I think the true efficiency is closer to 1.3%: 19.9% vehicle efficiency * 7% payload-vehicle efficiency.
That's really astounding: 98.7% of the energy input is really a form of waste. No wonder bicycles are one of the seven wonders of a sustainable world.