Electric Vehicles – thermodynamic efficiency & emissions (5)

Regardless of how fuelled, all road vehicles emit pollution in two main forms: those that cause and health issues. e.g. haze and particulate matter, and ‘greenhouse gasses’ such as carbon dioxide and methane.

Vehicle pollution – 2019. Pic: Original source unknown

Particulate matter from tyres

Particulate matter is constantly shed from tyres -mainly soot and styrene-butadiene. The smaller particulates are airborne and are a minor cancer risk.  https://ncbi.nlm.nih.gov/pmc/articles/PMC1567725/.  The larger particles are washed into lakes streams and rivers etc. Related data is scarce but Sweden calculates particulates from tyres are about 150 tonnes a year. Whilst electric vehicles remain heavier than those fossil fuelled, particulate emissions from tyres may slightly increase. 

Particulate matter from brake linings

Brake linings also cause particulate emissions. These were initially a mix of asbestos cadmium, copper, lead, and zinc and consequently banned in the early 1980s. They are now a mix of fibres of glass, steel, and plastic, plus friction generating antimony compounds; and brass chips and iron filings, plus steel wool to conduct heat. These particulates disperse directly into the air: antimony (Sb) may increase cancer risk.
As electric vehicles primarily reduce speed via regenerative braking, this should substantially reduce brake lining emissions. 

Tailpipe emissions

Electric-only vehicles produce virtually zero direct emissions (excepting via tyre wear). Hybrids produce no tailpipe emissions when they are in all-electric mode, but have evaporative emissions, both directly (and particularly during refueling). Overall, their direct emissions are lower than those of comparable conventional vehicles.

Emissions from energy drawn from fossil-fuel power stations 

An Australian electricity power station. Pic: SMH.com.au.

When comparing the overall emissions of electric versus internal combustion-engine vehicles, if electric vehicles are charged from grid power, emissions from our currently fossil-fuelled power stations must be taken into account. 

Contrary to general belief most of Australia’s electricity power stations are far from efficient. Only four are above typical global efficiency: their averages emissions are 919 kg CO2-per MWh. None are remotely close to the 670 – 800 kg of CO2 per megawatt/hour already achieved by China. India is lagging re efficient fossil fuelled power stations - but now lead the world in large-scale solar power production. Regardless of whether they burn coal, natural gas or oil, all convert less than 40% of the resultant heat into electricity. 

Australia’ power companies are unlikely to build more efficient fossil-fuelled power stations. Even marginally reducing their existing pollution is enormously costly. If done, their output would inevitably be undercut by renewable energy and in ever-increasing amounts. Wind plus solar and (where feasible) hydro, is cheaper, simpler and (apart from manufacturing and erecting costs) virtually pollution free. (Australia’s power station emissions are listed at the end of this article).

Oil-well to vehicle emissions must include extracting, refining and distributing to fuel stations: then burning it vehicles. Such burning only 25% or so of the energy inherent in fuel that has already incurred major losses in its production and distribution.

Quantifying petrol vehicle emissions

Overall, every litre of burned petrol results in 3.15 kg of CO2 emissions: 81% is caused in burning the petrol, 13% by extraction and transportation, and around 6% from refining2. Burning petrol also releases nitrous oxide - that has 300 times the global warming potential of CO2.

The typical Australian passenger car uses about 9.1 km/litre. Driving just one kilometre generates close to 350 grams of CO2 equivalent being emitted into the atmosphere. This is about 4.8 tonnes of CO2 equivalent emissions per car per year.Huge technical efforts (plus outright deception re diesel engines) have been made to limit fossil-fuel powered vehicle emissions. Now, about all than can be done to reduce them further is to vehicle size and performance or to compromise by going hybrid.

Regenerative braking

Regenerative braking (close to impossible in combustion-engine cars) in thermodynamic efficiency is an energetic advantage of all electric vehicles, not just hybrids. It is of particular benefit in stop/start city driving and in very hilly terrain.

Regenerative braking: whilst braking the drive motor acts as a generator – thereby charging the vehicle’s batteries. By doing so the vehicle’s kinetic energy is saved and stored for propulsive use. Pic: Reworked from a concept of the Porter & Chester Institue, Connecticut, USA.

Right now (whilst existing battery technology restricts range between charging), hybrids make sense.  The most efficient model of the Toyota Prius hybrid travels just under 30 km/litre. It emits 31% CO2 as does the average passenger car. Most cars are driven about 14,000 km/year – so its emissions are 1.5 tonnes a year. That is 3.3 tonnes less than a comparable petrol powered car. In the longer term, it is better by far to go all electric - powered 100% by solar.

Toyota Prius Hybrid. Pic: Toyota

Australia’s main power stations - their ages and emissions

Those known (in terms of year built – and kilograms of CO2 per megawatt/hour (MWh) actually produced.

Stanwell (1996): 969 kg per MWh.

Bluewaters (2009): 982 kg per MWh.

Muja CD (1985): 982 kg per MWh.

Mt Piper (1996): 997 kg per MWh.

Collie (1999): 1004 kg per MWh.

Eraring (1982): 1011 kg per MWh.

Vales Point (1979): 1018 kg per MWh.

Callide B (1989): 1019 kg per MWh.

Bayswater (1986): 1031 kg per MWh.

Gladstone (1976): 1052 kg per MWh.

Lidell (1973): 1066 kg per MWh.

Muja AB (1969): 1285 kg per MWh.

Worsley (1982): 1324 kg per MWh.

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