Tesla motors has been a shining beacon for electric vehicles, rising to prominence whilst most of their brethren buckle under financial, technical and market problems. Tesla has been able to produce an extremely high quality product as evidenced by its receipt of the highest possible grade by Consumer Reports. The savvy and patient management by Elon Musk has allowed the company to make it through many inevitable challenges without running out of cash to make the big commercial push. Most people assume that not only is the Tesla a sexy high performance sports sedan, but also that it is extremely efficient and great for the environment because it is electric. But is it?
How does one measure efficiency? Simply put, how much of the energy available in the fuel is turned in to kinetic energy to move the car? In a conventional car, this is how much of the chemical energy contained in gasoline is turned into rotational energy by the internal combustion engine. In modern cars, this turns out to be about 30%. But this is the best efficiency point of the engine. A more realistic point to choose is 25%. To figure it out for the Tesla (or any grid-charged electric vehicle) is a little more complicated. First you must find out the efficiency of the power plant generating the electricity, whether it is coal, natural gas, nuclear, solar or wind. From 2000 to 2009 the overall efficiency of US power generation increased from 35.5% to 40% thanks in large part to a 50% increase in the use of natural gas at the expense of coal, and to a lesser extent, the increase in renewable sources of energy which still account for only a minor fraction of the energy mix. Next, there are losses involved in the transmission of the electricity from the plant to the charging station for the electric car. The DOE estimates these losses to be 9.5%. Next, there is the charging and discharging cycle for the batteries, estimated by the DOE at 85% and 95% respectively.
Efficiency of the Tesla: 29.2%
Efficiency of a gasoline car: 25%
And for self promotional purposes, the efficiency of a vehicle powered by one of our CCI engines: 52% (or with waste heat recovery, significantly higher still)
What does this mean? Well, the cost of fuel to the end user of a Tesla is a lot less than that of a gasoline car, but that is at a huge up-front expense that you are unlikely to recover over the life of the vehicle. Is there a marked difference to the environment? That takes another analysis regarding the emissions of different kinds of power plants vs. gasoline engines (and then merits looking at natural gas powered vehicles!). But the takeaway should be that while the Tesla Model S is a great car, if your motivation for purchasing it is to save the planet, you’ve got to think a little deeper before writing the check.
Note* this article was modified from it’s original by using an efficiency less than the best point for a gasoline engine as a more realistic scenario. Thanks to SuperDuper from MotorTrend forum.