In the real world, with real-world driving, it seems virtually impossible to get the fuel economy figures that the manufacturers claim for their models. Whether you are talking about combustion engine cars or electric cars, the figures appear to have little relevance in the real world other than to work as a comparison with other makes and models.
In an electric car, however, you can create your own fuel economy measurements extremely easily. Simply record your distance travelled and then measure the amount of electricity used to recharge the car using a plug-in watt-meter.
In order to measure real world economy for electric cars, I carried out a driving test along a fixed route with two different electric cars.
In order to provide a useful comparison, I then tested two combustion engine cars, driving the same route, in order to identify real-world fuel economy and comparative carbon footprint figures for each type of vehicle.
I decided to use my own personal commute to and from work as a test route, travelling in busy traffic. The distance travelled is 7 miles (approximately 11.25 km) each way. The route comprises 2½ miles (4 km) of fast freeways and 4½ miles (7.25 km) of busy inner-city roads.
The tests were carried out in and around Coventry in the United Kingdom in January 2010. Temperatures were around freezing during the whole trial. Cabin heating was used as appropriate.
Noting the temperature is important. Electric cars are less economical in cold conditions than they are in hot conditions. These tests therefore reflect a 'worse case' economy for electric cars. In warmer conditions, it would be fair to expect significantly improved figures on an electric car.
Likewise in cold conditions, combustion engine cars take longer to warm up and are also not at their most economical at the start of their journey.
The full results of these tests are published in The Electric Car Guide - 2015 Edition. The carbon calculations take into account the sourcing of the fuel, and the whole-life carbon cost for building, running and decomissioning the power station providing the energy used by the electric car. It is worth noting that adding these additional carbon figures makes very little difference to the carbon footprint of an electric car.
It is worth stressing that these tests have not been independently verified by any scientific establishment. Consequently, these tests can only ever be used as an indication of relative fuel economy and carbon emissions.
I also feel that it is important that my test could be repeated by anyone else using their own cars and their own routes, and the tests have been simplified in order to achieve this.
All the information and calculations I used in order to carry out my tests are included within this chapter. If a university or a scientific establishment wishes to carry out similar tests in a controlled environment and would like to discuss my test methods, I can be contacted through the Ask Me a Question page of the website www.TheElectricCarGuide.net.
Two electric cars were chosen: a brand new Mitsubishi i-MiEV and a three-year-old REVA G-Wiz dc-drive with old batteries.
The Mitsubishi was chosen as an excellent example of the latest technology electric car. It is a sub-compact car with a roomy interior, providing good performance and range.
The REVA dc-drive was chosen to identify whether an electric vehicle remains environmentally efficient as the batteries degrade and the car gets older. The REVA dc-drive is no longer on sale; it has been replaced by the more efficient REVA i and REVA L-ion. It represents a good test on an older electric car.
At midnight each night, the cars were plugged in until the battery packs were completely charged. The amount of electricity used was monitored using a watt-meter and this was then multiplied by the average carbon footprint for UK electricity during the period the cars were on charge. I was charging the cars overnight, when the power grids are under-used, and the carbon footprint averaged out at 380 g/kWh.
This carbon footprint figure takes into account the carbon impact of sourcing the fuel and transporting it to the power station, the production of the power and the average transmission losses of the power as it is delivered from the power station to the car.
You can view these figures yourself on the How Green Are Electric Cars? web page.
I also recalculated the carbon footprint figures based on the environmental footprint of a coal-fired power station, plus the mining and transportation of the coal. Friends of the Earth estimate that this figure is 1007 g/kWh. I then added 7% to this figure to take into account energy losses between the power station and the home, giving a total of 1077 g/kWh.
Finally, I took into account a carbon footprint for the use of the batteries, using the calculations shown in the book.
The combustion engine cars chosen were a brand new Toyota Aygo 1.0 and a Fiat Panda 1.1.
Both of these cars are economical sub-compact city cars that produce low levels of carbon emissions. The manufacturers' own CO2 footprint figures show that, in official tests, the Toyota Aygo produces a tank-to-wheel footprint of 106 g CO2/km, while the Fiat Panda produces a tank-to-wheel footprint of 119 g CO2/km.
These figures only reflect the tank-to-wheel emissions, not the well-to-wheel emissions. For our tests to be comparative to the electric car tests, well-to-wheel calculations have to be used.
In order to calculate the carbon footprint in real conditions, I filled the fuel tank at the start of the test. I then measured the fuel economy in litres at the end of each test by refilling the fuel tank. I calculated the CO2 footprint based on the amount of fuel used, using the 'well-to-wheel' CO2 figures published in The Electric Car Guide - 2015 Edition.
|Distance Travelled||14.1 miles||14.1 miles|
|Total Electricity Cost||26p||24p|
|Average CO2 per kWh||380g/kWh||380g/kWh|
|CO2/km electricity usage||46.66g/km||43.73g/km|
|CO2 battery usage||3g/km||6g/km|
|Total CO2 per km||53.73g/km||50.36g/km|
These figures show remarkable fuel economies and a low recharge cost for the electric cars. The carbon footprint is also low, which is helped by using off-peak electricity. Off-peak electricity is much more carbon friendly than using electricity during peak times.
When electric cars are powered by coal-fired power stations, the carbon footprint is significantly higher than when they are powered by most other sources.
Using the figures of 1077g/kWh for coal-fired power, including the mining and transportation of the coal and the energy losses between the power station and the home; this is what the CO2/km would look like if I charged up using coal power:
|Mitsubishi i-MiEV||REVA G-Wiz|
|CO2/km electricity usage based on coal power||152.28g/km||142.74g/km|
These figures are substantially higher than the published figures for small combustion engine cars. However, when tested on a like-by-like basis, the figures for combustion engine cars are also significantly different to the official figures.
Official CO2/km emissions tests that are used as part of the official European economy tests are carried out in a laboratory. They take into account the carbon footprint of the fuel burnt in the engine and not the entire carbon footprint, taking into account the extraction and refinement of the crude oil and the transportation of the refined oil to the fuel station.
As the CO2 figures for the electric cars includes these costs, they have to be applied to the combustion engine cars in order to provide a like-for-like comparison. The research that explains how these figures are calculated are published in The Electric Car Guide - 2015 Edition.
|Toyota Aygo||FIAT Panda|
|Distance Travelled||14.1 miles||14.1 miles|
|Fuel Used||1.33 litres||1.51 litres|
|Total fuel cost||£1.71||£1.94|
|Official CO2 per km (tank to wheel)||106g/km||119g/km|
|Actual CO2 per km (tank to wheel)||136.48g/km||154.94g/km|
|Actual CO2 per km - well to wheel||164.46g/km||186.70g/km|
As you can see, the carbon footprint figures that I achieved in my test are significantly higher than the official CO2 figures.
|Mitsubishi i-MiEV||REVA G-Wiz||Toyota Aygo||FIAT Panda|
To put these figures into context, I recently measured the amount of energy used by a Bosch tumble dryer. To dry a single load of clothing used 2.97 kWh of electricity - almost exactly the same amount of energy used by the REVA G-Wiz in these tests, and only marginally less than the Mitsubishi i-MiEV.
A family of four can quite easily wash and dry four loads of clothes per week. That is the equivalent of around 56 miles (90 km) of driving every single week, or a total of almost 3,000 miles - 4,800 km - of driving each year.
If clothes could be dried outside on a washing line or a clothes airer for even six months every year, the energy saving would be enough to drive a considerable distance using the electricity saved.
The Electric Car Guides are the definitive series on electric car ownership and use. They are available from Amazon and all good book retailers.
Click on the button below for information on which guide is the right one for you, pricing and availablity.Get a guide now!