Calculating Well-to-Wheel efficiency of electric vehicles

11/4/2016

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.
This article is based is on a writeup by Mr Elon Musk, founder on Tesla Motors (link here). We have presented this with new calculations based on Indian conditions and also have documented multiple use cases.

Use Cases
Here are some use cases, where we calculate the well-to-wheel efficiency and compare the results in terms of efficiency and CO2 emissions.

Small petrol car vs Small electric car
Diesel SUV vs Electric SUV
Petrol scooter vs electric scooter

Small petrol car vs Small electric car

Well-to-Wheel efficiency of a small Indian petrol car
Petrol has a calorific value of 34.3 MJ/liter. (34300000 Joules or 9528 Wh or 9.5 kWh)/liter
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.

Verdict
An small electric car is more than 2.5 times efficient than an equivalent petrol car.

Diesel SUV vs Electric SUV

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.

Verdict
An electric SUV is more than 1.8 times efficient than an equivalent diesel SUV.

Petrol scooter vs Electric scooter

Well-to-Wheel efficiency of a petrol scooter
Petrol has a calorific value of 34.3 MJ/liter. (34300000 Joules or 9528 Wh or 9.5 kWh)/liter
The fully considered well-to-wheel efficiency of a petrol powered scooter 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 scooter giving 50 km/liter has an efficiency of 1/(34.3 divided by (100% minus 33%)) x 50 km/l = 0.97 km/MJ or 0.97 km/277 Wh

In other words, to travel a distance of 1 km, a petrol scooter must expend 1.03 MJ or 286 Wh of energy.

Well-to-Wheel efficiency of an electric scooter
After observing data from users of electric bikes like Hero electric, Morello Yamasaki and also getting test data from upcoming e-bikes like Ather S340, we find that on an average, an electric scooter in Indian road conditions consumes 33 Wh/km
And the power plant efficiency , conversion and transmission losses in electricity in India are 70% or more.
So an Indian electric scooter @ 33 Wh/km has an efficiency of 1/(3600 divided by (100% minus 70%)) x 10^6 x (1/33) km/Wh = 2.52 km/MJ.
We then multiply this by the "The full cycle charge efficiency of the electric bike". Let us take this factor as 90% for ebikes.
Then the final efficiency is 2.52 x 90% = 2.26 km/MJ or 2.26 km/277 Wh

In other words, to travel a distance of 1 km, an electric scooter must expend 0.44 MJ or 122 Wh of energy.

Verdict
An electric scooter is more than 2 times efficient than an equivalent petrol scooter.

Note
Power plant efficiency is bundled with T&D losses. My figure of "70% losses" was a loose surrogate for BOTH generation loss and transmission/distribution loss.
After further research, I discover that:

33% is the efficiency of coal conversion (i.e., power plant efficiency),one of the lowest among major coal -based power producing countries, so I can peg the overall fuel to power generation as 40% because not all fuel is coal.
According to WRI, Indian T&D losses are 27%. The highest in the world.

Therefore the power produced and delivered from 100 units of fuel in India is 40% x (1-27%) = 29.2 units. Therefore the overall losses are 100 - 29.2 = 70.8% just a bit more than my loose estimate.

CO2 Emissions

The CO2 content of any given source fuel is well understood. Coal is 23.8 grams of carbon per mega-joule and Oil is 19.9 grams of carbon per mega-joule.
Applying those carbon content levels to the vehicle efficiencies.

For 1 km of driving,

Carbon footprint of a small petrol car = 3.45 MJ/km x 19.9 g/MJ = 68.66 g/km
Carbon footprint of a small electric car = 1.35 MJ/km x 23.8 g/MJ = 32.13 g/km
Carbon footprint of a diesel SUV = 5.88 MJ/km x 19.9 g/MJ = 117.01 g/km
Carbon footprint of an electric SUV = 3.12 MJ/km x 23.8 g/MJ = 74.25 g/km
Carbon footprint of a petrol scooter = 1.03 MJ/km x 19.9 g/MJ = 20.47 g/km
Carbon footprint of an electric scooter = 0.44 MJ/km x 23.8 g/MJ = 10.47 g/km

This assuming that all the electricity comes from coal. This is not true, quite a bit comes from other sources with a lighter or zero carbon footprint. And even if you take the process of car manufacture but subtract the electricity used in refining oil and making petrol cars, electric vehicles will win out.

The higher CO2 content of coal is offset by the negligible CO2 content of hydro, nuclear, geothermal, wind, solar, etc. The exact power production mixture varies from one part of the country to another and is changing over time. When you consider that, electric vehicles get even greener over time.

Electric Vehicles cut Global warming emissions by 50% - Union of Concerned Scientists

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20 Comments

Raphae Halim

5/5/2016 10:01:26 pm

Very nice article. This calculation gives us the basis to calculate "cost to the planet" of running an electric car. :-)

shalini link

29/6/2016 04:59:58 pm

this idea will help the country from oil crisis and it will help me to get more information from your blog

ulkhem

12/7/2016 12:53:09 am

Even if EVs simply transferred CO2 emissions to a power plant, I would much rather have those emissions in an isolated part of the country than in an already poisonously polluted city.

Kamlesh Mallick

12/7/2016 07:36:45 pm

Well said friend.

7/9/2016 03:18:49 pm

Hi,

Following is my perspective on the data shared above:

1) 15 KMPL for a small gasoline vehicle is too low an assumption for fuel economy. These days small gasoline cars have crossed 25 KMPL barrier. Granted there will be real world variance to the tune of 20% but that would be case with EV too.. as battery performance will vary with Temprature, charging cycle and general usage.

2) Couple of facts here (though author has already highlighted some of them) :
a) 70 % if India's installed capacity is via thermal plants powered by predominately coal.

http://www.cea.nic.in/reports/monthly/installedcapacity/2016/installed_capacity-07.pdf

b) India's transmission and distribution system is ridiculously inefficient. Official figures indicate losses in range of 20% to 30% though 3rd party reports have pegged these above 50%!!.

3) Even CO2 emissions to manufacture an EV are about 1.5 times that of a ICE vehicle.

If you put all of that into perspective an EV in India today would be in effect emitting 80 to 90g /Km as against a typical diesel vehicle with 95 g/km emission and typical gasoline with 100 g/Km.

Today enough low-cost solutions are available to push CO2 emissions of conventional cars down to 80 g/Km without entering PHEV or EV domain.

I don't believe owning a electric car for personal transportation is going reduce CO2 substantially...as yet.

Sateesh Reddy

7/9/2016 04:22:44 pm

Regarding your point on mileage.
Me and my wife drive an i10 Grand and we hardly get 15 kmpl. Many times mileage even dips to single digit.
An electric car in chaotic city conditions win all the time - w.r.t efficiency and thus emissions.

Either-ways, EVs are way better - Atleast once EV's get popular our children wont breathe polluted air that we take in gladly these days.

Amey pednekar

30/9/2016 05:55:44 pm

To start with, no petrol car gives more than 20kmpl mileage. Only diesel cars give close to 20kmpl, but not more than that in real world conditions. Exactly opposite is true for EVs. An EV that claims, say, 200km range on a drive cycle will easily give more than that in city conditions, easily around 300km. As for emissions, even if we consider the worst case scenario that emissions for EVs are equal to those of ICE cars, the difference is that they are centralized in a location. All the emissions are restricted to the power plant, located couple of 100kms away from where you stay as opposed to an ICE car blowing smoke straight at your face. The option of using renewable resources again reduces those emissions. EVs are just a step towards reducing world pollution and not the ultimate solution. Forget everything about emissions, EVs are just better vehicles than the ICE ones. Its only a matter of time before they become popular in India as well

Hemant

13/6/2017 09:58:46 am

90 wh/km translates to 11 km per kWh. I'd love to know which car runs this much on 1 kWh given that generally published figures put it between 7-9 km per kw-h.

PlugInIndia

13/6/2017 11:06:28 am

Hi,

The Mahindra e2o regularly achieves efficiency scores of under 90 Wh/km

During Pune-Mumbai trip - the community gets an astounding
65 Wh/km ratings over a distance of 150 km due to regenerative braking.

Welcome to the magical efficiency of the EV world :)

ezhilarasu link

3/10/2017 06:31:34 pm

Even if EVs simply transferred CO2 emissions to a power plant, I would much rather have those emissions in an isolated part of the country than in an already poisonously polluted city.
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Dileep Kumar

6/10/2018 10:09:57 am

I have a question on WTW analysis done for scooters.
Q: Do you think that cost of 1 Wh for petrol is equal to cost of 1 Wh for coal?
If no, what does the comment "An electric scooter is more than 2 times efficient than an equivalent petrol scooter" matter to a scooter user?
Can we claim, "twice the efficiency of electric scooter equals to half the fuel cost for equal delivery in these two scooters"?
If we cannot claim the above statement, what is significance of showing WTW efficiencies of these scooters?

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4/12/2018 04:17:35 pm

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12/12/2018 04:34:11 pm

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Arvind

27/2/2019 05:35:15 pm

Carbon capture tech is making coal zero emissions - pls highlight this!

https://qz.com/1144298/humanitys-fight-against-climate-change-is-failing-one-technology-can-change-that/

Igor

18/4/2019 08:05:03 pm

A propaganda.
How much efficiency do you get, if you have a coal powering epp, the transmission?
50% is already too much.
A pure propaganda, whatis stated here.

DataCheck

2/11/2019 04:29:11 am

Please provide correct information concerning 70% efficiency of coal plants, generation from best thermoelectric plants are typically around 46%...