Fact: EVs are far more efficient in fuel use than petrol powered cars. This blog will show you why. One argument against EVs is that you are simply moving pollution from the internal combustion engine (ICE) exhaust pipe to a power station’s chimney and that there is no difference in energy efficiency. Rubbish.
Based on the 2009 EV efficiency figures, they are 200% more efficient than ICE cars when efficiency is calculated from the moment fossil fuels are extracted from the well to the point it is turned into forward motion by the vehicle. We will now go through a three-step calculation to show you how ICE cars and EV cars compare. First, tank to wheel and then power station to wheel and finally, well to wheel.
Tank to wheel
ICE cars run while sitting in traffic and then at optimum efficiency turn around 30% of the fuel into forward motion. The widely accepted wheel to tank efficiency is around 16% in all driving conditions.
EVs are much better, though there are a few losses.
There is a loss of power when the battery turns the motor, even without a gearbox, of around 10%. Some of this comes out as heat, while there is friction in the drive train. We will work on an efficiency between motor and wheel of 90%.
In order to convert the electricity from the grid to the wheel there are three stages: It goes into the battery as Alternating Current (AC) power, sits in the battery as Direct Current (DC) power and then must be converted via inverter to AC again to power the motor. This causes a loss of 10%.
There is a loss of power when charging the battery. Let’s forget Tesla’s and Nissan’s claims, as frankly, all motor industry claims are a little fantasy-land. Based on Tesla and Nissan users claims there is a loss of 20% between plug and battery.
The calculation is:
Drivetrain and motor efficiency 0.9 x AC inverter 0.9 x charging 0.8 = 68% efficiency.
Therefore efficiency from the battery to the wheels is 400% more efficient than from an ICE tank to the wheel.
Don’t celebrate just yet – the efficiency halves in the next calculations.
Power station to wheel
The figures we are using are based on the 2009 grid electricity energy mix in the US that is very comparable with the UK’s energy mix. We are running on the assumption that we only use natural gas, based on renewables balancing out coal at the other end of the spectrum.
When a gas turbine burns natural gas it has a similar efficiency to that of an ICE engine at maximum efficiency – it blasts a jet of gas against a turbine. However some of the unused heat is used to superheat steam that is blasted against another turbine, and this recaptures a further 30% of the energy from the fossil fuel. A high estimate of the energy produced from a natural gas turbine is 60% but we will use 50% as there are losses between the turbine and the transmission wire.
There are a series of losses between the gas turbine and the plug socket that your EV will be plugged into. This is around 7%, though this figure is falling as technology makes gains.
Between the natural gas tank and the power going into the wheels, the calculation is thus:
0.5 power station x 0.93 transmission loss x 0.68 car efficiency = 31% efficiency.
Well to wheel
We then need to measure the cost of power extraction from the ground and pumping it into the grid:
9% is lost when the fossil fuel is extracted.
1.5% is lost in the pipeline between the well and the power station.
0.91 extraction x 0.985 pipeline x 0.31 power station to wheel = 0.277 or roughly 28% efficiency from well to wheel.
The calculations we are using for ICE engines are 14% from well to wheel. That means for every kilo of fossil fuel you use, you get 200% more power from an EV than you do from an ICE engine.
When you write a blog like this it is inevitable that people are going to pick holes in your calculations. Let’s be honest: the data we are using is based on 2009 calculations for both ICE and EV vehicles.
A more recent calculation based on changing fossil fuel use put a Tesla Model S at 32% in 2012 based on US emissions. That increases it to 228%.
Argument 1: ICE engines were far less efficient than they are today. Yes, but how much? Since 2009 we have had a number of car companies admit to cheating their emissions data. If you have six hours to spare, please do calculate the real world tank to wheel efficiency of a VW Blue Motion Polo and comment below. We’d love to hear from you, particularly if you can find the real world data!
Please also calculate the real world data for an average EV built in 2016. We’re willing to bet that efficiency is actually higher today than it was in 2009. Go for it – sit to the maths!
Argument 2: the oil companies are running the US and UK governments and oil and coal use are likely to increase.
Power station efficiency has significantly increased since 2009. The change hasn’t begun fully to kick in – Trump needs to build more coal powered stations and dig more coal pits. That will take at least four years. May? It will take years to reverse the good work of the UK government that has been going on since 1990. Ultimately those selling power to the grid want efficiency as inefficiency costs them money.
The more likely scenario is that green energy will eclipse fossil fuel power in terms of price per kilowatt hour in the next few years. Why then use dirty fuel?
While EVs are not zero emission, EVs are far better for the environment than ICE cars. You can’t argue with that one. If you wanted ultimate efficiency in transportation, go on a vegan diet (meat production is extremely carbon intensive) and only walk to your destination!
Written By Richard Shrubb