The electric car and the CO2 emission

The electric car and the CO2 emission

My electric Car! by tonyhall

More and more the “world wide” politics promotes the development and production of electric cars, shown as a possibility, at least for the mobility, to reduce the pollution.

Consequently, car manufacturers are working hard to offer electric vehicles, but I wonder:
What certainties have we that electric cars really affect the overall CO2 reduction and what doubts have we still to solve?
It is true that electric vehicles don’t emit CO2, but the electricity they use is generated by an industrial process with CO2 emission.

To answer to the question I sought the help of two engineers, specialists in vehicles and electricity, who, on previous occasions, have helped me to take me technically to this world: Eng. Roberto Barbiero and Ivan Maio.
I would like to elaborate with them some topics about electric vehicle and I would like to start from the well-known CO2.

To do this, we’ll try to compare the emissions of electric cars to the conventional ones.
These data are available on line, with some research work, of which we show the sources for those who want to deepen the theme.

Let’s start with a chart showing the global carbon cycle.

Mixing the use of fossil fuels with changes in land use, man is responsible for the emission of about 29 GT/per year of CO2, which alters increasingly the normal flow of emission and the natural absorption of CO2, spoiling, so, their balance.


The Global Carbon Cycle. (Source: figura 7.3 dell’IPCC AR4).

The second chart explains the portioning of this “pie” about the CO2 emitted in the world by man and the percentage allocation.



The world of the traction, vehicle, ship etc. is worth in total 25.7% (5.8 + 15.9 + 4) of the CO2 emitted, while the portion concerning to the electricity and heating is worth 43.9% and so on.

The following example estimates the emissions of a vehicle of A-segment with three different engines: electric, petrol and diesel.

The estimated parameter is one of the most known: the average amount of CO2 produced, directly or indirectly, riding 1 km through these three types of engines.

With the electric engine, a reasonable estimation (based on NEUC cycle) of average electric energy required for an electric vehicle of segment A is equal to 0.17 kWh/Km (1).

If we use traditional fossil fuels, coal and oil, to produce electricity, the CO2 emitted (2) ranges from 0.74 to 0.89 kg/kWh, neglecting the loss for the same energy transport, which can be significant, the electric vehicle in 1 km will produce:

0.17 kWh × [0.74, 0.98] kg/kWh = between 130 and 170 gr di CO2 x km.


Photo by PeteLinforth (Pixabay)

Only nuclear and hydropower plants can do much better, indeed the emissions are reduced to one-tenth or one thirtieth.

Concerning the nuclear generation, the average emissions is 0.1 kg/kWh and the hydroelectric 0.03 kg/kWh.
We have excluded the photovoltaic sources, because the estimation of their equivalent emission is less reliable due to very strong greenhouse gas involved in manufacturing.

Let’s see now the internal combustion propellers: average plausible values of fuel required for our vehicle are 0.067l/km for a gasoline engine (15 km/l) and 0.05 l/km for a diesel one (20 km/l).

The resulting CO2 emission for 1 km, according to the emission data (2), are:

gasoline: 0.067 l/km × 2.36 kg/l = 158 gr of CO2 x km;

diesel: 0.05 l/km × 2.7 kg/l = 130 gr of CO2 x km.

As shown, if the electric energy is produced by fossil fuels, there is not an appreciable reduction in CO2 emission.

Part of the current 25% of CO2 emissions related to transports, would simply move to electric generation without changing the total amount.

To have important benefits on emissions, there should be an electric power generation using low emission sources as solar, wind power etc.

But which of these sources are available in Italy/ Europe?


Photo by MB-Fotografie

Or, simply, it should reduce the energy demand of vehicles, so to consume less, the vehicle must weigh less.

A further consideration: reducing the vehicle weight, the electric traction allows to reduce consequently the electric motor; contrary to the internal combustion engines in which, out of certain limits and in particular for diesel one, this is not possible because of the problems related to the excess of limits emission.

So, if we really want to drastically reduce the CO2, we have only one solution: everyone get on the electric bike, neither the diesel one because impossible do realize, goodbye SUV&Co.

Seriously, it is certain that electric or hybrid vehicles can improve the environmental protection, but our certainties tell us: only if they are small cars and with at least 60% a city use.

Here is the doubt: but, according to the current offer, if, at the end, the CO2 pie chart doesn’t decrease, then why many car companies are developing, with significant investments, electric or hybrid cars of medium/large size, and why customers, like us, should pay more to have the same CO2 emission?

(1) Hawkins et Al., Comparative Enviromental life Cycle Assessment of Conventional and Electric Vehicles, Journal of Industry Ecology, V.17, n.1, on page 53-64, 2012
(2) The following data about the CO2 emitted from different type of power plants can be found on the website of U.S. Energy Information Administration, Another interesting site to explore the theme CO2 .

Translated by Federica Izzo

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