Originally written to the 2012 National Greenhouse Emissions Factors tables and first printed in edition 120 of ReNew.
Revised, updated and reprinted in ReNew edition 143 to reflect the 2017 National Greenhouse Emissions Factors tables
It is a relatively well known fact that the sticker figures for petrol and diesel vehicle emissions do not reflect their full ‘well to wheel’ emissions, making it hard to do a proper comparison between the emissions from driving an electric vehicle (EV) with an internal combustion engine (ICE) vehicle. In 2012 I worked to address this by doing a full carbon accounting based analysis to make an ‘apples for apples’ comparison between the then only available new EV (the Mitsubishi iMiEV) to a similar use new petrol powered ICE vehicle (a Toyota Corolla).
The conclusions then were – an iMiEV charged exclusively from the state grid emitted moderately to significantly less CO2-e in all states of Australia on city cycle, and only in Victoria was it slightly worse on the combined cycle as compared to the Corolla.
Six years later (and in the light of recent statements from federal Liberal member, Craig Kelly), has the situation changed?
The question that I address in this article is:
Does owning an EV make any difference to your personal transport emissions?
(See note 1 re scope and limitations of this question).
To investigate this, I will look at three scenarios for calculating your personal transport CO2 emissions:
- Buy an EV for city driving, but do no other CO2 reduction measures;
- Combine an EV with a solar array at home;
- Other methods for reduction of CO2 for EV electricity consumption.
Scenario one: Buy an EV for city driving, but do no other CO2 reduction measures
For this scenario, the exact answer will depend on where you live. Burning different fossil fuels such as brown or black coal or natural gas produces different amounts of CO2 and other greenhouse causing pollutants (together referred to as CO2-e. See note 2). NB: From this point I will refer to CO2-e rather than ‘CO2’ or ‘carbon footprint’. On top of this, some states also use hydroelectricity and wind power, which produce significantly less CO2-e.
Therefore, as individual states/territories use different mixes of brown or black coal, natural gas, hydro and wind to produce the energy needed to generate electricity, any analysis of electricity CO2-e will need to take account of where the EV is used.
A second complication is that the figures generally stated for CO2 emissions for new internal combustion engine (ICE) cars are not the full story. As mentioned above, the best figure to use (and what is used in carbon accounting processes) is CO2-e. A comparison of EVs on fossil fuelled electricity and ICE vehicle emissions will need to be made on an ‘apples with apples’ basis.
Calculation 1: Internal combustion engine CO2-e emissions.
Data: green vehicle guide (http://www.greenvehicleguide.gov.au)
Vehicle: Current model Toyota corolla; 1.8L petrol, auto, city cycle, 8.3L/100km
Assumptions:
Vehicle travels: 10,000km per year
City cycle chosen as most comparable to EV use.
Calculations:
Toyota Corolla: At 8.3L/100km, this gives a total of 830L used in a year (= 0.83kL).
Using the national Greenhouse Accounts (NGA) Factors (July 2017), emissions, in CO2-e are:
Direct emissions = burning of the fuel: 1913.2kg of CO2-e (table 4, 2017 NGA factors)
Indirect emissions = extraction, transport etc. of fuel: 102.19kg (table 40, 2017 NGA factors)
Grand total (in tonne CO2-e): 2.0154 tonnes of CO2-e per annum to run your 2017 Corolla.
For completeness, I have included the calculations for 4 vehicles in both the combined and city cycles, as given on the Green Vehicle Guide website. (Note: I have selected the auto option for all 4 cars, as automatics are the most common transmission choice in Australia).
Calculation 2: So what about your EV?
Data:
- Green Vehicle Guide (http://www.greenvehicleguide.gov.au)
- National Greenhouse Accounts Factors, Dept of Climate Change and Energy Efficiency, July 2017
Vehicle:
Current model BMW i3; 129Wh/km (see note 3). Mass market vehicle chosen in order to make ‘like for like’ test cycle comparisons with ICE vehicles. For owners of other EVs or retrofit EVs, try swapping your own figures into the calculations below.
Assumptions:
10,000km per year
EV battery charger efficiency: 93%
Calculations:
{129 x 10,000 x (100/93)}/1000 = 1387kWh per annum
Conclusions from scenario 1: buy an EV and do no other CO2-e reduction measures.
Interestingly, since this analysis was first produced in 2012 (see graph 2) – ICE vehicles have noticeably improved their consumption figures according to the test cycles. However EVs have also improved, as well as the general emissions figures for grid power improving dramatically in some cases. The result again is if you are swapping from ICE to EV for city driving – you have reduced you CO2-e for private travel in all states, and the gap in Victoria is increasing! Again, in Victoria (only) is the Corolla slightly better on the combined cycle – but the gap is also decreasing.
In summary: in 2017, choosing a new BMWi3 over a new Corolla 1.8L auto to use for city driving reduces CO2-e by just over 18% in Victoria, and by 88% in Tasmania. (All other states fall in between). For the combined ICE test cycle, EVs still come out well ahead in all states except Victoria, where it will go up slightly (5.3%). Mind-you this assumes you do no other carbon abatement measures for your electricity use. This option is explored next.
Scenario two: Combine an EV with a solar array at home
The next consideration is to ask whether any solar PV system could supply enough electrical energy to meet the annual needs of both a home plus EV charging. A few more calculations are in order:
Assumptions:
- Assuming an energy conscious, energy efficient home to use 5kWh/day (See note 5).
- BMWi3 travelling 10,000 km using 129W/km.
Calculations:
Home usage per annum: 5 x 365 = 1825kWh/yr
Vehicle usage per annum: {129 x 10,000 x (100/93)}/1000 = 1387kWh/yr
Total energy consumption for home and EV/yr = 3212kWh/yr
Ideal energy provision by a 2.5kW PV per annum: 3300kWh/yr
Therefore, as a minimum a 2.5kW system could just provide this a year. Realistically, a 3 to 4 kW system would provide a more balanced energy provision over the summer/winter generation peaks and troughs, depending on individual household usage patterns. (Note: To properly match a PV system size to an individual household is beyond the scope of this article – so I will assume a 4kW system is ample for this example).
Conclusions from scenario 2: buy an EV and install a solar PV system
The simple answer is yes – combining a suitably sized solar PV system, an energy efficient lifestyle and an EV could be argued as together making your home and EV energy consumption ‘carbon free’. BUT: most of your EV charging will be done when at home during the night. So is it really carbon free energy when your PV’s produce no power, and you are potentially charging your EV via coal or gas fired electricity generators? It is certainly far cheaper to charge your EV on off-peak power, (especially if you get a premium feed-in tariff for your PV system during the day), but the sun going down does not magically increase the energy potential (or decrease the CO2-e) of a lump of brown coal!
On the other hand, it certainly can be argued that a grid-connected PV system ‘banks’ excess generation in the day and ‘redraws’ it at night. It follows in this line of thought that by doing so, you have prevented the need for building bigger generators (with bigger base load CO2-e emissions) to provide energy in peak periods. However, it still is a fact that in this scenario, something like 40% of an EV owning household’s electrical energy usage is potentially running off fossil fuelled generation - unless you charge your EV exclusively during the day when the solar system’s output is greater than your total home plus EV power needs.
Therefore, the more nuanced answer to scenario two is you have reduced your CO2-e still further by installing PV panels to go with your EV, but you are not yet ‘carbon neutral’ in your energy usage CO2-e creation.
So how can you make your EV have no nett effect on your overall CO2-e emissions?
One solution to address the CO2-e of your increased overnight usage (or for those unable to access enough sun, wind, micro-hydro or other renewable source of energy), is to subscribe to 100% ‘GreenPower’ or related offerings. These utilise large scale renewable forms of electricity generation, such as wind, solar or hydroelectric generation instead of fossil fuels. (see note 6).
Another solution for those with solar PV systems is to install a rechargeable battery system in combination with your PV system. The batteries are charged by the PV system during the day and you can recharge your EV at any time without resorting to drawing much, if anything, from the grid. However the economics of this scenario are still such that this choice is still significantly more expensive than subscribing to a GreenPower or related option.
In conclusion:
Just as in 2012: in 2018 if you buy an EV over an ICE vehicle and do no other abatement measures, you will significantly reduce your personal transport energy CO2-e emissions. And this is true for all Australian power grids except for one scenario in one state. (Which is in Victoria, where replacing an ICE with an EV for driving that meets the combined ICE test cycle increases CO2-e by 5.3%). Also, given ICE fuel consumption figures have significantly reduced since 2012, it follows that replacing an older ICE vehicle with a new EV will improve this equation further in favour of the EV.
Going forward: as the grid de-carbonises year on year (as it has been doing – see graph 3) EV CO2-e will continue to decrease faster than ICE CO2-e emissions. Plus, with a tailored combination of grid connect solar PV, green power and/or a battery back-up system, these emissions can be reduced significantly further.
Notes:
- This article is limited in scope to the consideration of whether using electricity instead of fossil fuel for your vehicle is capable of making a beneficial change in your ‘carbon footprint’. Lifestyle and policy considerations around and beyond that (including public vs private transport debates, embedded emissions, emissions due to building roads vs public transport infrastructure, etc., etc.) I leave to other forums and articles.
- e.g. The CO2-e for burning transport fuels includes the direct greenhouse potential from NH4 and N2O as well as the CO2 from combustion, as well as the indirect emissions from extraction, refining and transport.
- For comparative purposes – I have stuck to the one, Australian Government, vehicle fuel consumption comparison site to ensure like-for-like test cycle consumption comparisons. Other sites (eg the US http://www.fueleconomy.gov/feg/evsbs.shtml) use different test cycles and give different EV and ICE consumption values – but they are not directly comparable to the Australian test cycles and results, so have not been used.
- Direct and indirect electricity CO2-e emissions per state, per kWh: NGA factors; July 2017, table 41.
- In my work as an energy auditor, I find home energy usage varies incredibly widely. However 5 kW for a well-run, reasonably efficient home of 3 – 4 people is an achievable target, and so have chosen this number based on my experience in the area.
- The economics, politics and credentials of GreenPower and related offerings are beyond the scope of a short paragraph in this article.