Carbon-neutral cars running on thin air

10th October 2016
Alice Matthews

The search for environmentally-friendly means of transport becomes ever more urgent when we look at climate change statistics. A study from the US National Oceanic and Atmospheric Administration found that the concentration of CO2 in the air reached 400ppm in 2012/2013, the highest since scientific measurements began, and with the year 2014/2015 being the warmest on record it doesn’t show signs of stopping. 

One way to combat CO2 pollution is to harness it to make fuel itself, something that Audi has been doing in two of its plants in Germany. E-gas is a fuel produced through a process of electrolysis and methanation: renewably-generated electricity is first used to break water into hydrogen and oxygen. Then the hydrogen is reacted with CO2 to yield synthetic methane. This technology has existed for many years, however it has only recently become financially viable.

The advantage of e-gas is that it is virtually carbon-neutral. As a result of its method of production, cars fuelled with e-gas only release as much CO2 during combustion as was chemically bound during production. In contrast, cars powered by traditional fossil fuels add to the amount of CO2 in the atmosphere when they are used.

The chemical composition of e-gas is nearly identical to fossil-based natural gas, so technically it could be distributed to all Compressed Natural Gas (CNG) filling stations to replace its non-renewable counterpart.  Audi estimates that the gas from one of its plants in Werlte could power 1,500 Audi A3 Sportback g-tron vehicles 15,000km every year.

On paper, therefore, Audi’s offering appears strong. However Dr Paul Fennell, reader in clean energy at Imperial College London, raises the question of efficiency. He said: “You can take electricity and convert it to fuel for your vehicle with about 13% efficiency. If you compare that to taking electricity and charging up an electric vehicle, then that can be done with about 80% efficiency.” Therefore it may not yet be cost-effective enough to implement e-gas technology, but any attempt to solve our soon-to-be crippling power crisis should be welcomed with open arms.

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