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Over a decade ago 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. 

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. On the other hand, in this new mix we have more renewables, so the carbon footprint of electric cars has shrunk a bit.

Grid losses have also 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.

As I pointed out a decade ago batteries 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. Back them I calculated that about 25% of the electricity was lost as heat.  Newer inverters are said to lose less than 6%.

Back then the calculations were based on engine 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 16 kWh/100km; 
  • The Mitsubishi Outlander, hybrid, consumes 18.4 kWh/100km; and
  • The fuel efficient yet conventional Audi A1 that consumes 42.7 kWh/100km (= 4.4 litres of petrol/100km). 

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. 

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. 

Petrol yields 9.7 kWh/litre - and produces 2.31 kg of CO2.  

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, to actually driving the wheels, is 100% efficient whereas most older coal burning power stations fall well short of total efficiency.  The same applies to petrol driven cars with newer cars being much more efficient. 

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 there are several even less efficient. 

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%

 

 

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

  • the hybrid and plug-in Mitsubishi Outlander produces around 5 kg of CO(after adding a little for grid and conversion losses);
  • the conventional petrol driven Audi A1 produces about 10 kg of CO2; while
  • the fully rechargeable electric Tesla series 3 produces around 13 kg of of CO2 (after adding a modest 10% for grid and conversion losses).

In the past decade the environmental impact has changed significantly in favour of rechargeable electric vehicles in Australia. Yet due to our highly carbon intensive and aging electricity generation it is still more environmentally friendly to drive a small petrol driven car than to drive an all electric car - particularly in NSW or Queensland.

As it was a decade ago a low carbon footprint continues to favour by hybrid technology: where a petrol engine keeps the battery charged and/or provides supplemental mechanical power.

Hybrids also have the advantage 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.

In Australia, if we want to match European performance and make fully electric cars really worthwhile, we need to find a new base-load electricity technology to replace carbon. 

We have have a highly centralised urban society with 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 is now effectively saturated generating much more electricity than they need at times while falling short at others.  The cost of wind-power is entirely due to the capital and maintenance cost of the equipment and associated grid. So in practical terms any more investment to make up for times of shortfall significantly adds to electricity costs.  As a result South Australia, that is too remote to share with NSW or Queensland, has close to the highest electricity prices in the world. 

Fortunately, in the Australian electricity market overall South Australia is a very small component.

While subsidised PV Solar is an option for domestic electricity it to is too variable for base load applications, at least the wind blows at night. 

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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