Electric Motors Versus Internal Combustion Engines

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Next time you stand for 90 seconds filling your petrol tank, you might think of the enormity of what is happening, in energy terms. Chemical energy is entering your tank at a rate of typically 17 million Joules/second, or 17 megawatts—equivalent to the energy given off by 17,000 one-bar electric heaters! This large number is the basis of many difficulties, much glossed over in the rush to all-electric cars. 

In making personal mobility all-electric, two important considerations must be weighed. The first is that electric motors convert electricity to motion three times more efficiently, in energy terms, than the internal-combustion engine does with gasoline. The second is that we do not recharge an electric battery in 90 seconds. Neither of these avoid the difficulties I now describe.

When electronics first became portable in the early 1970s, the battery was a carbon-zinc type. All the global research in the fifty years since then has produced a lithium-ion battery, which has six times the density of energy storage; this, in turn, is still more than forty times less dense than the energy stored in petrol. For direct comparability in performance, the car battery has to be forty times bigger in volume than the gasoline tank!

Consider Dinorwig Power Station, the biggest hydropower energy-storage plant in the UK—capable of generating 1,700 megawatts for a period of 5.3 hours and devote it solely to recharging batteries; after that, the dam is empty, and we must wait for it to be refilled. If we could charge the battery as fast as a petrol tank is charged, we could charge 1,000 cars simultaneously (at 90 seconds each) for 16 hours – a total of 240,000 cars, already including the factor of 3 in efficiency mentioned above. This number of cars is less than 1% of the current British fleet, and we have to add on all the trucks and vans used in all the logistics that keeps our supermarkets, high-streets, and industrial sites stocked. Where will all this new electricity come from?

In practice, something of the order of 70% of Britain’s entire existing electricity-supply capacity would be needed to keep our personal mobility by motor vehicles. When we get coded messages that we will have to rethink the purposes for our travelling at all, it is this gulf in energy sources that lies at the heart of the conundrum, not personal lifestyles.

Several other problems beset electric cars. A typical house in the UK draws 2-3kW of electrical power, averaged over the year, with peaks of order 5kW in winter. A single slow charger for a car draws 7kW, with a fast-charger drawing 15kW. The substations in most suburbs were installed before the need for recharging car batteries, and most will need to be upgraded to handle the extra demand. 

Given also that 40% of UK cars do not have a garage and are parked on the street, there is also the problem of how they will be charged. Cars used by commuters will need charging points, either at home or place of work, or both. As many local authorities have bylaws preventing electric cables from crossing pathways, how will suburban commuters be assured that they can charge their cars? In the last major winter storm in 2012, when the M25 London orbital road was gridlocked, it was electric cars with flat batteries that delayed the clear-up.

At the same time, Britain’s adoption of net zero means that it has to decarbonize home heating. At present, this is mostly done cheaply and efficiently with natural gas. The average energy used per day in our personal mobility and logistics is relatively constant through the year, with small excursions downward on weekends and variations over seasons. This is in contrast to the future demand for electric heat to replace gas heating: here, there exists a factor of between 8 and 10 between the use of gas in winter and summer. The current gas grid copes with that by a faster flow of gas. This feature would also be required for a future grid capable of handling all our heat demands. 

Where will all this extra electricity – averaging more than the grid of today – come from? Will the current transmission system be able to cope? If both heating and mobility are to be provided without fossil fuels, the UK will need to more than treble the energy in the current electricity grid. Renewable energy cannot make up the difference. We simply do not have the area, onshore and offshore, for sufficient wind and solar farms. One current problem of nuclear energy—the cost of decommissioning power plants at the end of their operational life—will visit solar and wind farms with a vengeance. Renewable power yields more kilograms of hazardous waste per kW power generation than does nuclear power.

An Extinction Rebellion protestor recently promised me that the back-up electricity for major hospitals would be provided by batteries in 2025. The $58m Elon Musk battery installed outside Adelaide, South Australia to power that city for 30 minutes would cover the emergency wards of Addenbrookes Hospital in Cambridge for 24 hours on a single 80% to 20% discharge. After that, it would need to be replaced by another battery on a dozen container lorries. The current back-up is provided by two 1500kVA diesel generators, which run for as long as fuel is available and cost $320,000. The idea of a 180-fold reduction in cost and a simultaneous extension of battery life to cover a week while power pylons are repaired after a major storm—all to be achieved in 5 years—is ludicrous.

These interlocking problems demand a full and rigorous systems-engineering analysis, now totally absent in the public debate. The 2008 Climate Change Act created the Committee on Climate Change and gave it enormous power to oversee the decarbonization of the UK economy. As an unelected body, the committee displays many of the worst features of the administrative state. I believe that it has been in grossly negligent in dodging the complexity of electric vehicles, and the related issue of the enforced switch to electricity for domestic heating. Committee members don’t have to face the consequences of their policies from voters; politicians, who do have to face the voters, hide behind the committee as an alibi to duck their accountability. 

Put simply: infrastructural engineering capability to provide for electric cars and electric heating by 2050 is a massive and probably unachievable ambition. To attempt to accelerate it, to 2030, is madness. The rest of the world can look at Britain and choose whether to laugh or weep. One thing it shouldn’t do is emulate us.

Michael Kelly is Professor Emeritus of Technology at the University of Cambridge in England. 

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