Free Markets, Free People

thermodynamics

Coal powered, er electric cars, not as efficient as EPA claims?

Why I’d be shocked, shocked I tell you if that was the case.

The tease:

The Green Machine is now exposing how the US Government can choose to create data that disobey the laws of thermodynamics so that the worthless government policy of favoring plug in vehicles over gas or diesel powered vehicles can be supported by the public. Yes the US EPA chooses to make 34.4% equal to 100%.

Hmmm … I’m hooked, let’s see why:

The EPA allows plug in vehicle makers to claim an equivalent miles per gallon (MPG) based on the electricity powering the cars motors being 100% efficient. This implies the electric power is generated at the power station with 100% efficiency, is transmitted and distributed through thousands of miles of lines without any loss, is converted from AC to DC without any loss, and the charge discharge efficiency of the batteries on the vehicle is also 100%. Of course the second law of thermodynamics tells us all of these claims are poppycock and that losses of real energy will occur in each step of the supply chain of getting power to the wheels of a vehicle powered with an electric motor.

So the 118 mpg equivalent that the EPA allows the Honda Fit is nonsense?  Tell me it ain’t so!

Well it is simple the US EPA uses a conversion factor of 33.7 kilowatt hours per gallon of gasoline to calculate the equivalent MPG of an electric vehicle.

Dr. Chu Chu of the Department of Entropy is instructing the EPA on thermodynamics in coming up with the 33.7 kwh per gallon. On a heating value of the fuel 33.7 kwh equals 114,984 BTUS which is indeed the lower heating value of gasoline. The fit needs 286 watt hours to travel a mile and the Green Machine agrees with this for the 2 cycle US EPA test with no heating, cooling or fast acceleration. Using this amount of energy per mile and the 33.7 kwh “contained” in a gallon of gas, the EPA calculates the Fit gets 118 MPG equivalent.

All of these calculations are in fact flawed as the generation of electricity, the transmission and distribution of electricity, the conversion of the AC electricity into DC electricity, and the charging and discharging of the vehicle batteries all have energy losses associated with these activities. The average efficiency of power generation is perhaps 42.5%, the transmission and distribution efficiency is perhaps 90%, the AC to DC conversion and the battery charge discharge efficiency is about 90%. Multiplying all these efficiencies one can calculate that the overall efficiency is 34.4% to get electric power from fuels at the power station into stored electrons within the plug in vehicle’s batteries.

On this basis the 118 MPG equivalent is 40.6 MPG actual for the Honda Fit which is not much of an improvement to the gasoline version of this vehicle that has an EPA rating of 35 MPG combined for city and highway driving.

Uh, that’s quite a little downgrade in performance, isn’t it?  Nothing like being 190% off, EPA.

However, I am glad to see the administration has finally taken the politics out of science and has “real” science again serving the public’s best interest.

~McQ

Twitter: @McQandO