24/03/2014 10:58 GMT | Updated 23/05/2014 06:59 BST

Replacing the Internal Combustion Engine: Why the Future Is Electric

By Professor Paul Ekins

The internal combustion engine (ICE) was one of the iconic inventions and mass technologies of the 20th century. It made fortunes for successful entrepreneurs and companies, and resulted in some of the largest corporations of the present day.

But its sun is setting, weighed down by an accumulation of challenges from high CO2 emissions at the global level, to city pollution at the local level. So the search is on for the iconic vehicle engine technology which is sustainable, but will also satisfy humans' desire for mobility, speed, comfort and status.

The energy system models that are part of my academic stock in trade suggest that the drive train of the Ultra-Low Emission Vehicles (ULEVs) of the future will be electric.

One class of promising electric vehicles is those driven exclusively by batteries. Of course, these have been around a long time. At one point in the late-19th and early-20th centuries it looked as if they would be dominant engine technology, but ICEs won out in the end. However, battery electric vehicles (BEVs) never went away, and I clearly remember the research conducted on one specimen in the basement of Imperial College London when I was an electrical engineering student there in the late '60s and early '70s. This specimen bore no resemblance at all to the much more mainstream-looking vehicles that are being rolled out now by the likes of Nissan, Renault and BMW.

Another of the front-runners coming up fast is fuel-cell electric vehicles (FCEVs). Vehicle FCs have mainly been deployed in buses so far, but several of the big car makers have plans to launch commercial FCEV cars in the next few years. Meanwhile governments are taking these plans seriously, facilitating the deployment of the infrastructure that will allow motorists to recharge and refuel of these vehicles with the speed and convenience they're used to.

But infrastructure is not the only challenge that these new engines will need to overcome if they are to substitute for ICEs. For BEVs to provide serious competition to liquid fuels, batteries need to become lighter, need to use less scarce materials, and need to store more power. BEVs are also only low-carbon if the electricity source that charges them is also low-carbon. This dimension of their performance, therefore, depends on the decarbonisation of the whole power system, or on the BEV having solar cells to keep the batteries topped up - both massive technical challenges.

The carbon footprint of the fuel source is just as challenging for FCEVs, the dominant fuel for which is likely to be hydrogen. The major source of hydrogen is currently through the re-forming of natural gas, but that results in as much carbon dioxide as burning natural gas. One possible remedy is to generate hydrogen through the electrolysis of water, but again, that only leads to hydrogen with a low carbon footprint if the electricity is decarbonised, and at present the efficiency of such electrolysis leaves much to be desired.

Finally there is the issue of cost. Both BEVs and FCEVs are significantly more expensive than comparably performing ICE vehicles, and these costs need to come down by 50% or more, while performance is improved, for ICEs really to begin to feel the heat.

To the ambitious engineer these challenges present almost unlimited opportunity, the chance to be the Benz, Daimler, Diesel, Peugeot or Ford-equivalent who designs and produces the iconic engine of this century. We may expect that society will thank such designers and producers by making them very rich indeed.

Paul Ekins is Professor of Resources and Environmental Policy at University College London and Co-Director or the UK Energy Research Centre.

This evening Professor Ekins will be speaking at "Eco Machines: Designing the Cars of the Future" hosted by Intelligence Squared and Shell at Imperial College London.