1 January 2017
By Matthias Holweg
All discussions about transport lead back to the ultimate source of energy – as do most issues facing global society in the 21st century, from what to cook for your evening meal to whether you can justify flying when you go on holiday. As more nations aspire to Western living standards, the energy intensity of our lifestyles is increasingly unsustainable.
In terms of mobility, the petrol-powered internal combustion engine that dominated the 20th century is yielding to a wide variety of alternatives. These include other fossil fuels such as liquefied petroleum gas (LPG) and natural gas; serial- and parallel-hybrid engine technologies (which are part-electrification of the petrol or diesel drivetrain), plug-in hybrids (battery component) and pure electric vehicles (no internal combustion engine).
British sports car maker Morgan, based in Malvern, unveiled this hydrogen fuel cell prototype as the Morgan LIFEcar, with input from Oxford
These are, in my view, interim solutions. The energy-intensive process of digging up lithium in Chile and China and making batteries out of it, plus their considerable weight, means cars that use them are little better than their existing petrol and diesel counterparts. Hybrids and electric vehicles have a decisive advantage in heavy traffic, where their efficiency is optimised – but it’s perverse to admit that a technology is at its best where driving is most inefficient, i.e. in a traffic jam.
While pure electric cars belch no fumes, carbon emissions from generating their electricity can match that of the internal combustion engine. The hydrogen-powered fuel cell is also promising, but there is no guarantee that hydrogen will be ‘green’, as so far most hydrogen is produced by steam reforming fossil carbohydrates.
A key problem for battery and hydrogen vehicles is that the energy density of a tank of gasoline turns out to be pretty good. One litre of petrol has an energy density of 34.2 megajoules (MJ). The comparable figure for electro-chemical energy in a rechargeable lithium-ion battery is 0.9–2.63 MJ/L, depending on the battery quality, while for a litre of gaseous hydrogen, compressed to the current automotive standard of 700 bar pressure inside a special fuel tank, it is 5.6 MJ/L. So the fuel tank in a hydrogen car remains pretty bulky, while compressing the gas robs the process of further energy. There are alternative ways of storing and releasing hydrogen, in substrates or carrier liquids, but so far none makes a convincing case.
We are still waiting for the new ‘dominant design’ to replace the internal combustion engine. Using alternative energy to generate hydrogen could be one way, and emerging metal-air batteries may provide a breakthrough. Yet irrespective of which technology will prevail, someone has to pay for this energy revolution. So for economic reasons alone the internal combustion engine will be with us for several decades to come, and in my view will remain a dominant form of propulsion until mid-century. The internal combustion engine will have to fund the costly development of its successor, or successors.
Matthias Holweg's latest book is Crisis, Resilience and Survival: Lessons from the Global Auto Industry (Cambridge University Press, 2016)
Images © Oxford University Images,