Understanding EV emissions: Are electric vehicles really so great?
Does it really make a difference to your emissions if you buy an EV but run it on fossil fuel generated electricity, compared to sticking with the petrol guzzler? Bryce Gaton re-examines this issue.
This article was first published in Issue 143 (Apr-Jun 2018) of Renew magazine.
Does owning an EV make any difference to your personal transport emissions? In the light of recent statements about EV emissions from Liberal MP Craig Kelly, it seemed a good time to revisit my 2012 analysis of carbon emissions from electric vehicles (EVs) compared to petrol vehicles.
In 2012, the result was positive for the only new EV available in Australia at that time—the Mitsubishi iMiEV—when stacked up against a comparable small car, the Toyota Corolla. The iMiEV had lower emissions when driven in all states in Australia on the ‘city cycle’ (modelling typical car use around the city). Only in Victoria on the ‘combined’ city/country cycle did the EV have slightly higher emissions—and that situation could be avoided if it was charged using solar and/or GreenPower.
Six years later, the grid has changed, and the EV and petrol car offerings have changed. So has the result changed too?
To investigate this, I will look at three scenarios for calculating your personal transport CO2 emissions:
- Buy an EV for city driving, but take 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 1: Buy an EV for city driving, but take no other CO2 reduction measures
For this scenario, the answer will depend on where you live. Individual states and territories continue to use different mixes of brown or black coal, natural gas, hydro, wind and solar to generate electricity used in EV charging. These different generation methods produce different amounts of CO2 and other greenhouse pollutants (together referred to as CO2-e).
For petrol- or diesel-powered internal combustion engine (ICE) vehicles, the figures generally stated for CO2 emissions are not the full story. For ICE vehicles, CO2-e includes the CO2 from combustion, plus the direct greenhouse potential from CH4 (methane) and N2O (nitrous oxide) and the indirect emissions from extraction, refining and transport. Adding in these factors enables an ‘apples-for-apples’ comparison.
These factors for both electricity and petrol emissions are sourced from the National Greenhouse Accounts (NGA) Factors report published by the Department of the Environment and Energy and last updated in July 2017. The data on energy/fuel use is sourced from the Green Vehicle Guide (www.greenvehicleguide.gov.au, see note 2).
Calculation 1: Internal combustion engine CO2-e emissions
Vehicle: Current model Toyota Corolla; 1.8 L petrol, auto, city cycle, 8.3 L/100 km
- Vehicle travels 10,000 km per year
- City cycle chosen as most comparable to EV use.
- 10,000 km per year at 8.3 L/100 km gives a total of 830 L used in a year
- Direct emissions = burning of the fuel: 1913.2 kg of CO2-e (see table 4 in NGA Factors)
- Indirect emissions = extraction, transport etc of fuel: 102.19 kg of CO2-e (see table 40 in NGA Factors)
- Grand total: 2015.4 kg (2.0154 tonnes) of CO2 -e per year to run your Corolla.
- For completeness, Table 1 shows the calculations for four vehicles in both the city and combined test cycles, using data from the Green Vehicle Guide website. I have selected the automatic option for all four cars as automatics are the most common transmission choice in Australia.
Calculation 2: So what about your EV?
Vehicle: Current model BMW i3; 129 Wh/km. A mass-market vehicle was 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.
- Vehicle travels 10,000 km per year
- EV battery charger efficiency of 93%
- 10,000 km per year at 129 Wh/km and charger efficiency of 93% gives a total of 1,387,096 Wh = 1387 kWh
- Table 2 shows the CO2-e emissions calculations for the BMW i3 in each state and territory in Australia.
Conclusions from scenario 1
Interestingly, since I first undertook this analysis in 2012, ICE vehicles have noticeably reduced their fuel consumption on the city and combined test cycles; e.g. the Corolla has reduced from 9.9 to 8.3 L/100 km on the city cycle. This is reflected in the reduction in emissions shown for the Corolla between Figure 2 (2012) and Figure 1 (2017).
However, EVs have also reduced their energy consumption over this time (the BMW i3 uses 129 Wh/km compared to 135 Wh/km for the iMiEV modelled in 2012). A more dramatic change, at least in some states, has been the reduction in grid emissions intensity, particularly in SA and Tasmania—in Tasmania, this has almost halved.
The headline result again is that if you swap from ICE to EV for city driving, you have reduced your CO2 -e for private travel in all states—and the gap in Victoria is increasing!
Specifically, in 2017, choosing a new BMW i3 over a new Corolla 1.8 L auto to use for city driving reduces CO2 -e by just over 18% in Victoria and by 88% in Tasmania, with all other states falling somewhere in between.
For the combined ICE test cycle, the EV still comes out well ahead in all states except Victoria, where emissions are slightly higher (5.3%). Mind you this assumes you take no other carbon abatement measures for your electricity use. This option is explored next.
Scenario 2: Combine an EV with a solar PV system at home
If you combine an EV with a solar PV system, you can reduce your transport-related emissions even further.
But how big a PV system will you need to meet the annual needs of both a home and EV charging? This will of course depend on your home usage and transport miles. Assuming you travel 10,000 km/year in your BMW i3, a quick calculation can estimate how much extra PV generation you will need to cover that travel:
BMW i3 travelling 10,000 km/year and using 129 Wh/km = 1387 kWh/year (at 93% charger efficiency).
Ideal energy provision by a 1 kW PV system in Melbourne = 3.8 kWh/day (average) or 1387 kWh/year (coincidentally the same as the BMW i3 usage figure!). This will vary based on location, but Melbourne is at the lower end of generation in Australia.
Thus, an additional 1 kW of PV would in many cases cover the EV’s charging needs over a year. Realistically, a larger system will be needed to provide more balanced energy provision over the summer/winter generation peaks and troughs and to cater for less than ideal installations. And if you want the system to cover the EV charging load directly (rather than just over the whole year), at least some of the time, you’ll need a system sized at least to the maximum draw of the charger (for most currently available chargers, that’s between 2.4 kW and 7.2 kW); alternatively, you can use a smart charger like the Zappi EV Charger which can scale back the charger draw to just use excess PV: a PV diverter for EV charging. We will look more closely at matching your PV system to your EV requirements in a later issue of ReNew.
Conclusions from scenario 2
While adding sufficient PV to cover your EV usage will reduce your emissions, are you then carbon-free? The extent to which you are carbon-free will depend on when you charge your EV.
Many people will choose to charge during the day from PV power if their car is at home, maximising the extent to which they are carbon-free. This can also be a cost-effective strategy: for those on lower feed-in tariffs and higher grid tariffs, using as much of your solar energy as possible on-site will likely maximise your return from your solar system.
There will be situations when it isn’t possible to charge from your PV system (e.g. for those using the car away from home during the day). In addition, even if you are charging during the day, there will be times when the PV generation doesn’t cover the charging requirements, depending on the weather, your PV system’s size and the charger’s power draw. You are then potentially still charging your EV via coal- or gas-fired electricity generators (depending on your state’s electricity generation).
In these scenarios, even though your PV system generates more than you use, you won’t be completely carbon-free. But it can be argued that a grid-connected PV system ‘banks’ excess generation in the day and ‘redraws’ it at night. By generating at peak periods, it can also be argued you have prevented the need to build bigger generators (with bigger baseload CO2 -e emissions) to provide energy in peak periods.
In summary, for most people, this scenario will reduce your CO2 -e still further, but you are unlikely to be completely carbon-free.
Scenario 3: GreenPower or battery
So how can you make your EV have no net effect on your CO2-e emissions? One solution is to subscribe to 100% ‘GreenPower’ or related offerings. These use large-scale renewable forms of electricity generation, such as wind, solar or hydroelectric generation instead of fossil fuels (see note 4).
Another solution for those with solar PV systems is to install a battery system. The batteries are charged by the PV system during the day and you can then recharge your EV at any time without resorting to drawing much, if anything, from the grid. However, the economics of this scenario are such that this choice is still significantly more expensive than subscribing to GreenPower or a related option. You’ll also need to ensure that the battery and its inverter can cope with your charging requirements.
Just as in 2012, in 2018 if you buy a new EV compared to an equivalent new ICE vehicle and take no other abatement measures, you will significantly reduce your personal transport energy CO2 -e emissions. This is true for all Australian state power grids except for one scenario in one state. 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 continues to decarbonise, EV CO2 -e will continue to decrease faster than ICE CO2 -e emissions. Plus, with a tailored combination of grid-connected solar PV, GreenPower and/or a battery backup system, these emissions can be reduced significantly further.
So all we now need in Australia are some affordable EV options to buy! Things are looking up; fingers crossed, by late 2018, we should finally have three or four new EVs to choose from: the Renault Zoe, the Renault Kangoo ZE van (both available in limited numbers now), the Hyundai Ioniq and the Nissan Leaf.