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In 2005 I calculated that in Australia, due to our use of coal to generate electricity, electric cars had a higher carbon footprint than conventional cars. 

There's been a lot of water under the bridge since then and now (April 2019) many are promoting electric cars as environmentally friendly, so I thought it was worth a revisit. 

The biggest improvement has been in batteries. These are more efficient, lower cost and safer. And since 2005 we have more renewables, so the carbon footprint of electric cars has shrunk a bit.

Another change is that electricity prices have been driven up, by around 70%, by changes in the energy mix and due to consequent changes to the grid.  Yet this higher price has not been a disincentive to electric cars, as the energy cost is still a lot less than petrol, that attracts a hefty road tax.

My earlier calculations were based on engine and power generation and delivery efficiency.  This time I've taken a simpler path, comparing actual published consumptions, as electric vehicle technology has matured and been tested.  I've chosen three technologies:

  • the new Tesla Series 3 (long range - 523 km), all electric, consumes just 16 kWh/100km
    (claimed - yet the independently measured combined City/highway rate is 29 kWh/100km); 
  • the Toyota Prius, hybrid, that consumes 33 kWh/100km (3.4 litres of petrol/100km*); and
  • the fuel efficient yet conventional Audi A1 that consumes 42.7 kWh/100km (4.4 L/100km*). 

*petrol yields 9.7 kWh/litre.

Conventional petrol driven cars lose a lot of the energy as heat.  While newer cars have more efficient engines, energy is also lost to air resistance, to the tyres and when braking.

Electric vehicles, including hybrids, achieve their low overall energy consumption per kilometre by regenerative braking that recharges the batteries when slowing or stopping: recovering kinetic energy that was invested during acceleration. 

Whereas fully electric cars get their energy entirely from the grid, hybrids use a petrol engine to keep the battery charged and to provide supplemental mechanical power.

But to find out which has the lowest carbon footprint we need to consider where the energy comes from and how it gets to the wheels. Petrol is more energy intensive and produces less carbon dioxide (CO2) per unit of energy (kWh) than coal (2.3 kg of CO2/L petrol). 

Coal produces over a third more more CO2 than petrol for the same quantum of energy. According to the Australian Department of the Environment and Energy (National Greenhouse Accounts) black coal produces 90 kg of CO2 per GJ (0.324 kg/kwh) while petrol produces 67.4 kg of CO2 per GJ (0.242 kg/kWh).

But this assumes the conversion from coal to electricity across the grid to the battery then to actually driving the wheels, is 100% efficient whereas most older coal burning power stations fall well short of total efficiency.  

For example according to the published statistics, Bayswater power station in NSW produces 14,148,670 tonnes CO2-e / 15,944,580 MWh annually (0.89 kg/kWh) or around 38% efficient and this is among the most efficient of the 20th century stock.  Meanwhile, published grid losses have fallen, so maybe some of the recent investment in the grid is paying off.  Back in 2005 7.5% of the electricity generated was lost during transmission. Now just 4.5% is lost.

Batteries too are less than 100% efficient and need to be charged with direct current (DC). This has to be converted from the grid's alternating current (AC) by an 'inverter'.  These too have improved. Newer inverters are said to lose less than 6% and lithium-ion batteries lose between 10% and 20% in the charge discharge cycle (fast charge loses more). In addition they lose about 8% of their charge per month. Cumulatively, we can estimate that in excess of 25% of the electrical energy, generated at the power-station, is lost prior to its consumption in an electric vehicle.

As the following table from the Department's latest report indicates, in Australia most of the energy electric cars consume from the grid comes from CO2 generating sources, predominantly coal.

 

Australian electricity generation by fuel type - 2016-17
(source:  Department of the Environment and Energy website)
     
  GWh Percentage
Non-renewable fuels
  Black coal 118264 45%
  Brown coal 43633.79 17%
  Natural gas 51257.09 20%
  Oil products 6288.439 2%
Total non-renewable 219443.3 84%
     
Renewable fuels  
  Biomass 3625.085 1%
  Wind 12482.78 5%
  Hydro 16531.25 6%
  Large-scale solar PV 672.397 0%
  Small-scale solar PV 7399.259 3%
  Geothermal 0.502 0%
Total renewable 40711.28 16%
     
Total 260154.6 100%

 

Obviously natural gas also produces CO2 but at a lower rate per unit of electrical output than coal: typically around 0.55 kg/kWh (US average). Thus we can estimate that the CO2  released by Australian electricity generators exceeds 0.67 kg/kWh. While this carbon footprint has fallen since 2005 it has not been sufficient to justify the present greenwashing of electric cars.

Those of you who like back-of-envelope maths can quickly use the above numbers to calculate that to travel 100 km:

  • the hybrid Toyota Prius produces around 8 kg of CO2;
  • the conventional petrol driven Audi A1 produces about 10 kg of CO2; while
  • the fully rechargeable electric Tesla series 3 produces between 13 kg and 24 kg of CO2  (after allowing an additional 25% for transmission, inverter and battery losses).

Obviously the Audi A1 is a smaller car than the Tesla or the Prius and the Tesla is a sports-car, with performance that might be more fairly compared to a Mercedes-Benz E-Class or perhaps the hybrid Lexus RX450h.  The petrol driven E Class produces about 17 kg of CO2 per 100km (7.4L/100km) while the comparable Lexus hybrid produces about 13 kg of CO2 per 100km.

So if you are concerned about your carbon footprint there is presently little advantage in buying an all-electric car in most of Australia. Your best option remains a hybrid.  Alternatively a small advanced conventional petrol driven car like the Audi remains an environmentally friendly solution.

Hybrids presently have the additional advantage over all electric cars in that they are not as distance or location constrained (you can get petrol almost anywhere); do not require any charging time; and replacement batteries (when the time comes) are smaller and thus considerably cheaper.

So if someone gave me a Tesla series 3 or the new plug-in Jaguar I-Pace I would probably keep it for showing off around town, with a relatively clear environmental, if not egalitarian, conscience. Both have brilliant performance statistics and are very cool. Unfortunately this performance is difficult to realise when our maximum speed limit is 110 km/hr, and given present charging restrictions, I'd prefer a more conventional car for trips into the country or to drive to Melbourne or Brisbane.

The main incentive, should the purchase price fall to match that of a typical family car, is the relatively low cost of electricity compared to fuels purchased at a petrol station that attract a road tax. Thus, at present, plug-in vehicles travel on roads that the owners are not paying for while the average family currently pays just over a thousand dollars a year in fuel excise. While this can be tolerated for a short time, while numbers are small, it will need to be corrected as numbers grow. Perhaps all-electric vehicles will need to be levied a thousand dollar registration premium to compensate? Might this cause those who make such a purchase without being informed of this likelihood to get upset?

At the moment the main beneficiaries of this tax avoidance are cruising around in up-market luxury sports-sedans. Do they really need government subsidised charging stations as well, when hybrids do it better?  It seems to me that the Sir Humphreys, advising their politicians, might have suggested that such a policy was: 'courageous'.

In Australia, if we want to match European attainment and make fully electric cars environmentally worthwhile, we need to find a new low-carbon base-load electricity technology to replace coal. Yet there remain some significant constraints to achieving this.

We have have a highly centralised urban society with very long loss-making grid lines between centres. Unlike Europe it's a dry continent with insufficient hydro resources to make a big difference and while there is ample wind and solar in remote areas there are few well-placed wind prospects within a practical distance of Sydney or Brisbane.

South Australia and Tasmania have many excellent wind prospects but South Australia, like Denmark, is now effectively saturated with wind, generating much more electricity than the State can consume at times while falling short at others. 

As I have explained elsewhere, the cost of wind-power is entirely due to the capital and maintenance cost of the equipment and associated grid. So in practical terms adding more wind turbines, or batteries, to make up for times of shortfall, adds significantly to electricity costs.  As a result South Australia, that has prematurely retired its thermal base-load generation, and is too remote to share excess generation with NSW or Queensland, has close to the highest electricity prices in the world. 

Fortunately, compared to the Australian electricity market overall, South Australia, like Tasmania, is a small component.

While subsidised PV Solar is an option for domestic electricity, it's even more variable than wind and requires a large battery if the household is to be removed, even partially, from dependence on the grid.  At least the wind still blows just as much in winter; at night; or when it's cloudy. 

The present solar subsidy is funded by a small increase in electricity price, levied on everyone else.  As the table above shows domestic PV solar is presently a small contributor.  But if it were to become more significant the present subsidies would become increasingly unsustainable, perhaps limiting it's potential.  The subsidies are already criticised for discriminating against those who rent; or don't own a suitable dwelling; or who lack the capital to invest.

So - it's back on my hobbyhorse - we need to replace those filthy and unhealthy coal burning behemoths and their increasingly catastrophic ash-dams with nice clean nuclear stations. If we do it in-situ, the existing grid and cooling infrastructure could be upgraded and the workforce and local residents would enjoy the improved environment.   

Just ask the French who get 72.3% of their electricity from nuclear reactors and export inexpensive electricity to most of their neighbours.  

 

 

 

 

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