Week 2 Challenge
A common criticism of electric vehicles regarding emissions is that they simply transfer the CO2 emissions to the power plant. The obvious argument is that the grid power is produced from a variety of means - like hydro, wind, geothermal, nuclear, solar, etc. that involve no CO2 emissions. PluginIndia wrote a blog few years back trying to dispel many myths associated with electric vehicles. But this time, how about getting our hands dirty. We work out some calculations to show that electric vehicles, even if powered by electricity generated by coal powered plants (majority of electricity generated in many Indian states still comes from Coal), are much more efficient than oil based vehicles and as a result release less CO2 emissions.
The fully considered well-to-wheel efficiency of a petrol powered car is equal to
The energy content of petrol (34.3 MJ/liter) minus the refinement & transportation losses (about 33% in India), multiplied by the km per liter.
So a regular petrol car giving 15 km/liter has an efficiency of 1/(34.3 divided by (100% minus 33%)) x 15 km/l = 0.29 km/MJ or 0.29 km/277 Wh
In other words, to travel a distance of 1 km, a small petrol car must expend 3.45 MJ or 955 Wh of energy.
Well-to-Wheel efficiency of a small Indian electric car
After observing data from users of the Mahindra e2o electric car, we find that on an average, an electric car in Indian road conditions consumes 90 Wh/km
We know that 1 Wh = 3600 J, so 90 Wh = 324,000 J. And the power plant efficiency, conversion and transmission losses in electricity in India are 70% or more.
So an Indian electric car @ 90 Wh/km has an efficiency of 1/(3600 divided by (100% minus 70%)) x 10^6 x (1/90) km/Wh = 0.93 km/MJ.
We then multiply this by the "The full cycle charge and discharge efficiency of the electric car". Let us take this factor as 80% for the e2o.
Then the final efficiency is 0.93 x 80% = 0.74 km/MJ or 0.74 km/277 Wh
In other words, to travel a distance of 1 km, a small electric car must expend 1.35 MJ or 375 Wh of energy.
Well-to-Wheel efficiency of a diesel SUV
Diesel has a calorific value of 38.4 MJ/liter. (38400000 Joules or 10666 Wh or 10.6 kWh)/liter
The fully considered well-to-wheel efficiency of a diesel powered SUV is equal to
The energy content of diesel (38.4 MJ/liter) minus the refinement & transportation losses (about 33% in India), multiplied by the km per liter.
So a regular diesel SUV giving 10 km/liter has an efficiency of 1/(38.4 divided by (100% minus 33%)) x 10 km/l = 0.17 km/MJ or 0.17 km/277 Wh
In other words, to travel a distance of 1 km, a diesel SUV must expend 5.88 MJ or 1633 Wh of energy.
Well-to-Wheel efficiency of an electric SUV
After from the official EPA data of the Tesla Model X electric SUV, we know that that it has an efficiency of 237.5 Wh/km
We know that 1 Wh = 3600 J, so 237.5 Wh = 855,000 J. And the power plant efficiency, conversion and transmission losses in electricity in India are 70% or more.
So a Tesla Model X electric SUV @ 237.5 Wh/km has an efficiency of 1/(3600 divided by (100% minus 70%)) x 10^6 x (1/237.5) km/Wh = 0.35 km/MJ.
We then multiply this by the "The full cycle charge and discharge efficiency of the electric car". Let us take this factor as 90% for the Tesla.
Then the final efficiency is 0.35 x 90% = 0.32 km/MJ or 0.32 km/277 Wh
In other words, to travel a distance of 1 km, an electric SUV must expend 3.12 MJ or 867 Wh of energy