I love my EV – but is it all what it seems?








A cautious reminder for those thinking of switching to an EV.











Dr Alan Jones, PhD. CEng, FIET.




 Summary

 

Two letters in the July 2023 edition of a scholarly magazine, Engineering & Technology,

describe EV owner experience: a Nissan Leaf driver highlights a range of systemic charging issues while, overall, liking the car.  Meanwhile, a Fiat 500e owner describes similar infrastructure problems, but still feels positive because of cheaper motoring when charging from home.

 

This type of correspondence, while representative of much of what appears in social media about EV experience - relating to range and charging, tends to lack objectivity and calls into question the possibility of owners being influenced by existing beliefs – that EV’s are better for the planet and the pocket than the internal combustion engine (ICE), and therefore, in their mind the downsides of EV ownership needs to be traded against the greater good.

 

This paper attempts to add to the debate on these range and charging issues,  and address two specific questions: will the EV overtake the ICE in terms of range? And, will the charge rate for EV’s increase so as to reduce the charge time to a level equivalent to that of the ICE?

 

The conclusion, on both counts, is that the ICE will continue to outperform the EV.

 

Introduction

 

Filling the tank of an ICE vehicle is simple and quick.  The ubiquitous petrol pump, filling at around 1 litre/second, or transferring approximately 10kWh of energy each second into the petrol tank, is essentially a 36MW power source simply due to the unbeatable high energy density of hydrocarbon fuels.  By comparison, one of the fastest charging EV’s, the Hyundai Ioniq6 Long Range 2WD, charging from an ultra-fast 350kW charger, has an average charge transfer rate (from 20% to 80% charge) of a mere 0.06kWh/second – a limit imposed by the battery, not the charger.  Even Toyota’s recently announced solid-state battery technology, with a range of 700 miles and a charge time of 10 minutes, will only achieve a 5-6 times improvement over the present maximum energy transfer rate (to about 0.33kWh/sec).   

 

Does this matter?  Well, all vehicles need to store energy so that it can be transformed into motive power.  If the petrol pump can dispense energy 30 times faster than an ultra-fast charging station into a yet to be developed solid state battery (10kWh/s against 0.33kWh/s) then that is a distinct advantage in terms of the smaller number of petrol pumps required to fill the present UK fleet of ICE vehicles vs. the much higher number of ultra-fast EV charging stations that will be needed once EV’s become mainstream.

Fortunately, the EV is more efficient at converting stored energy into range (miles)[i] which means the EV only requires about a ¼ of the energy, mile for mile, as the ICE.  

 

This balance between disadvantage vs. advantage of the EV and ICE vehicles

gives some idea of the number of ultra-fast EV charge points needed for hassle free, every day, on-the-go driving to allow the motoring public to transition to an all-electric future. Of course, whether row upon row of ultra-fast chargers in every town is practically realisable, from an electrical distribution and transmission capacity perspective, is another question.[ii]  

 

Rather ironically, it will be the rural areas of Britain, where private transport is a necessity for commuting longer distances for work, shopping and leisure, that the lack of ultra-fast charging stations will be felt most because of the lack of adequate transmission and distribution infrastructure to supply these ultra-fast charging stations with the electrical capacity necessary.  On the other hand this capacity, if available anywhere, will be more forthcoming in urban areas where commuting distances tend to be much lower than in rural areas where the need is greater.   

 

The second letter, mentioned above, also introduces the issue of cheaper EV motoring, especially when charging from home, and a few words are needed here too.  For instance, if everyone transitioned to EV’s overnight the Treasury would be short of around £40bn raised each year from the ICE motoring public.  Surely this deficit will have to hit the EV motorist in some form and at some time with higher electricity prices for charging EV’s.  On top of this, National Grid ESO estimate the cost of connecting an additional 50GW of offshore wind by 2030 at £28bn while the UK government has in mind a figure of £140bn to achieve Net Zero by 2050.   

 

All these factors suggest the price of electricity, and not just for the EV motoring public, will only go one way in future.  With this thought in mind and given the human penchant for inadvertently falling foul of the law of unintended consequences – in this case a cost advantage now does not mean it will remain that way in future, we would do well to bear in mind the caveat emptor principle - let the buyer beware.

 

Let’s now addresses the first of the two questions pertinent to this discussion:-

 

1 Will the EV ever overtake the ICE in terms of range?

 

Several factors influence the answer to this question: the battery, the motor drive train and the combination of the driver and vehicle.

 

1a)   Battery Technology


EV battery technology is presently Li-ion based although there is a lot of research going into alternatives such as lithium salt, solid state batteries, graphene and others.  

 

The research and development is seeking to increase the charge rate, energy storage, temperature operation under charge/discharge conditions and the number of cycles.  Not forgetting to address the loss of capacity with ageing, but most importantly, the cost and sustainability of the materials - and let’s not forget the environmental cost either.  On this latter subject Li-ion has a black mark against it.  Cobalt and lithium, used for the anode and cathode, are both mined.  The former is a huge operation in the Peoples Republic of the Congo where there is clear evidence of the human cost - with children and slave labour, while lithium salt has created environmental concerns in South America.  The EV purchaser as well as EV manufacturers have little to say about this.

 

In simple terms though, the present battery technology operates within temperature limits - usually it has to be water cooled and when charging from rapid chargers is limited to 80% capacity otherwise they can overheat and damage the battery.  

 

The battery capacity can be increased by making the battery larger, say from 70 to around 100kWh, and that will increase range.  However, the battery has a huge mass, typically 350-400kg and a lower energy density on a volumetric basis (kWh/unit volume) than hydrocarbon fuels.  And because of this mass, road friction via the tyres increases leading to increased tyre wear and road damage.  Multi-story car parks may have to restrict the number of EV’s if they are not structurally sound enough to support this increased mass.  

 

With the increased mass comes a physical expression that torque = mass x acceleration.  So as the mass increases  more torque is required.  This leads to more discharge from the battery to produce that torque - hence reduced range is a trade-off as the battery size increases, both from the acceleration component (to change the state of the inertia) and to overcome the higher frictional component.

 

Whether a new type of battery is developed in future depends on many factors.  Cost and availability of materials along with the backlash from the environmental and social cost of Li-ion.  Not forgetting of course that China is the only country that can process lithium so that it is suitable for manufacture into batteries.  Then, don’t forget the other point.  These batteries have a certain life - 10 years (or 100,000 miles) at the most depending on how hard they are worked.  After 5 years or more they lose something like 30% of capacity (a 100kWh battery becomes 70kWh).

 

There were almost 1.5 billion vehicles in the world in 2022.  If these were all Tesla EV’s, each with a battery of typical volume 0.15m3 and say 350kg mass that would represent a total end of life battery volume of around 0.15-0.2 billion m3 together with a total mass of 0.5 billion te.   If they were disposed of and stacked tightly together they would fill 70,000 Olympic-size swimming pools while their combined mass would equate to the water needed to fill 200,000 Olympic-size swimming pools.  


These are big numbers and give some idea of the scale of the problem the world will have to face in a decade or more after switchover to EV’s.  There is a little hope though: in the US they are experimenting with using old, partially degraded EV batteries as energy storage media for solar PV systems that can provide energy back to the grid during evening and night hours when the sun isn’t shining.  The same could apply to wind turbines - charge these aged batteries with excess electricity when the wind blows and then use it to top up the grid network when the wind abates.  Too early to tell yet, but this may extend the useful working life of these batteries by a few years.

 

As for recycling facilities for old EV batteries, there are a small number of facilities in Europe and other parts of the world, but none in the UK.

 

1b) The motor/s in an EV 


EV’s can have either two or four high performance electric motors.  Clearly, four motors are better than two as this gives 4-wheel drive performance.

 

Manufactures of these motors make use of rare earth magnetic materials to increase the flux density (the electromagnetic field strength) of the motor so that the maximum torque (turning moment) per amp of current the motor takes can be achieved.  By reducing the current needed to achieve this torque this minimises the drain on the battery and helps improve the efficiency of the vehicle in terms of miles per kWh of charge.  

 

These motors, depending on the operating speed, are usually highly efficient - 85-95% compared with the ICE where 25% is to be expected.  Limiting the speed with which one drives as well as not accelerating harshly can also minimise the drain on the battery and thus extend the range available from the battery.  Beyond this the motor can act as a brake, so instead of turning the kinetic energy of the vehicle into heat (via the braking system) when the driver wants to slow down the motor can act as a generator and use the excess kinetic energy that needs to be dissipated by helping charge the battery.

 

Beyond this and beyond installing controls around the motor to electronically limit speed and acceleration there is little more that can be done to extend the battery range.  

 

1c) The vehicle and driver behaviour


In terms of the vehicle and driver behaviour there is a balance to be struck here, as is discussed below.  

 

The less the mass of the vehicle the more miles/kWh of battery.  On the other hand, the larger the battery capacity the more range.  So, as the mass goes down the miles/kWh goes up, although as the battery size increases and the range increase the inverse is true for the miles/kWh performance simply because of the additional frictional load between the tyres and the road, and the energy needed for acceleration.  

 

As the aerodynamic shape of the vehicle will have already been optimised the friction component that increases with speed will already be at a minimum.  Of course, driving conditions matter a lot in terms of range.  Wet conditions increases drag - hence friction forces go up.  Tyres running partly deflated increase friction too - so drivers beware.  Having a roof rack is bad news, as it towing.  And if it’s cold or hot outside, or you are driving in the dark watch out for the battery capacity falling at an unexpectedly rapid rate.

 

You may have heard of an expression used to describe driving style - light on the pedal, or light on the gas.  This is a driver who accelerated slowly while increasing speed. The torque needed to accelerate from 0-60mph in say 4 seconds is a huge lot more than if it took 12 seconds, as is the drain on the battery.  Beyond this, getting to some desired speed and then trying to maintain this speed as constant as possible is beneficial to battery capacity, as is driving at a slower speed to minimise the frictional (windage) forces.

 

After this discourse let’s return now to the question - will the EV ever overtake the ICE in terms of range?  Let’s first eliminate driver behaviour and the vehicle characteristics, because these are mostly common to both.  But if a creative person wanted to get inventive they would do something about the tyres - maximum pressure to minimise the surface contact and minimise the rolling friction.  Getting rid of them altogether would be fantastic and these advantages would benefit both the ICE and EV, but could you envisage a car without tyres - a hovercar or a flying car - a drone car perhaps!

 

The motor performance is mostly optimised so there is little new technology emerging here to further extend the range of EV’s.  This leaves the battery.  Ideally we want to maximise the energy density (kWh per unit of mass).  Maximising the volumetric density (kWh per unit of volume) may help better/smaller vehicle designs to emerge that would have a smaller footprint and better aerodynamics leading to lower frictional forces.  Will this happen - the answer has to be yes, but when and how long it will take is unknown.  We know that technology and the understanding of how to exploit technology is increasing rapidly.  The question always comes down to: will it be a breakthrough technology, ie. a game changer or simply a set of incremental, small steps.  The latter is more likely.

 

Conclusion to Question 1

 

So, to answer the first question, yes, it is likely there will be improvements in EV battery range, in time.  Will it, for the average motorist who cannot afford a high end EV that costs more than say £25,000, mean they can get more range out of their EV than they could from filling up a 40 litre tank in an ICE they owned previously then the answer is, most probably, no.  And certainly not by 2030 and 2035 when it will become illegal to sell a new ICE in Scotland and England respectively.  

 

Although some EV makers claim a 400 mile range that is the theoretical range from a 100% charged, new 100kWh capacity battery. In practice, and under real-world conditions the range is likely to be much less than this.  That then leaves the typical ICE motorists free to fill up, travel around 400 miles or more and then choose one of the 8365 petrol forecourts in the UK (with approximately 80,000 petrol pumps between them) from which to replemish their tank.  

 

Over this period it is probable that the typical EV motorist driving a modestly priced vehicle will still aim to achieve a maximum 200 mile range - and many will fall short of this.  And by the time they are down to 20% charge they will begin to experience range anxiety and be looking for one of the present 44,000 UK public charge points in the hope they will be both vacant and work - and reports suggest that many don’t work.  The Society of Motor Manufacturers and Traders, out of interest, has advised the government that 2.3 million charging points will be needed by 2030 to keep up with demand.  It is unlikely  this target will be met.

 

2 Will the charge rate for EV’s increase so as to reduce the charge time to a level equivalent to that of the ICE?  


Addressing this question requires an evaluation of two elements, the battery and the charging infrastructure.

 

2a) The battery


Transferring charge into a battery is a complex electrochemical process and one limited by the internal impedance, or resistance of the battery - which varies throughout the charging cycle, and also by temperature constraints to prevent the battery overheating and damaging the cells.  

 

Even the most modern solid state battery being developed by Toyota will only achieve an average energy transfer rate of around 0.3kWh per second, or about 30 times less that that from filling an ICE’s tank with petrol.  Of course, filling a petrol tank is relatively easy.  The tank is vented to allow gas to escape while the liquid hydrocarbon fuel is pumped under relatively low pressure, but sufficient to achieve around 1 litre/second flow rate.  Charging an EV battery requires pressure too, this time the pressure is represented by voltage.  Most EV’s on the market are rated at 400V or below, but there are now several manufacturers who have adopted an 800V battery, simply by adding more cells in series.  One manufacturer, Lucid, has even moved to 900V. 

 

This higher voltage is said to reduce the charge time as well as have beneficial heat implications from the smaller current flow (both into and out of the battery). To give some relative performance figures here, Tesla - which operates at a maximum of 400V, is said to add up to 170 miles of range or 42kWh in 15 minutes charging from a super charger (250kW) station.  Not everyone, indeed very few average motorists, can afford a Tesla, but for comparison a Lucid Air EV at 900V is said to charge at the equivalent of 20 miles per minute (that’s roughly 5kWh per minute based on 4 miles/kWh)  compared with the Tesla at some 3kWh per minute.  So, this increase in battery voltage, from 400 to 900V certainly increases the charge rate - from 3 to 5kWh per minute, bearing in mind these figures are approximate and dependent on information available from manufacturers.  Real life experience may differ.  

 

To emphasise this comparison - the charge rate from hydrocarbon fuels is anywhere up to 10kWh/second, so even this elevated voltage is far from the charge rate achieved by ICE vehicles.  And it is rather ironic that to an extent the average ICE motorist spends longer paying for their fuel compared to filling their tank while for the EV motorist the reverse is true.  This observation is bound to have severe and negative implications for the motoring public once the switchover to EV’s is complete ( long, long queue’s at public charging stations) and this point leads us on the second part the answer to this question - the charging infrastructure.

 

2b) The charging infrastructure


The charging infrastructure comprises of the individual charging points as well as the electrical distribution network required to provide power to the charging points.  Rural vs. urban areas deserve a mention too.

 

Firstly, let’s talk about the charging points.  For rapid charging you can forget charging from a 240V ac mains outlet socket, or even the more typical fast charger, rated at 7kW ac and found on the walls of private houses that have been installed for the sole purpose of charging EV’s.  Chargers rated at 50kW represent what is termed, rapid, but even here an EV with a decent size battery, say 50-70kWh, will take over an hour to charge - hardly comparable to filling a tank with petrol.  Charging stations at this rating might typically be found in public or private car parks, typically supermarket car parks where vehicle owners can spend time shopping while charging.  


This brings us to ultra-rapid chargers rated at 100kW or even as high as 350kW - called super chargers.  These, more powerful chargers operate at a dc level rather than alternating current, ac, in order to transfer charge as rapidly as possible into the dc battery.  These sorts of charging stations can usually be found at motorway service stations rather than in towns while rural areas may find that 7kW chargers are the best that are available in both public or private spaces, although some garages may in future invest in 50kW chargers if distribution capacity exists and a financial case can be made to cover the investment.

 

In urban areas, however, even the powerfully rated charging stations that can potentially reduce charge times to less than an hour, and typically 15-30 minutes, are not suitable for all vehicles.  For instance, most modestly priced EV’s have batteries that are capped at 50kW while some of the higher performance makes/models at 125kW charging rate, and even the 900V Porsche Taycan’s battery is limited to 270kW.  Furthermore, these rates do not extend throughout the charge cycle due to the risk of overheating and in order to protect the battery the charge rate is reduced, and even capped at 80% of battery capacity.  

 

Needless to say, while the 7kW charger is relatively common - maybe found in groups of 10-12, in some public spaces, higher capacity chargers are more rare.  The EV motorist should not forget either, to carry a full selection of charging cables in their boot because these charging stations are not necessarily compatible - just like the different EV vehicle charging sockets.

 

So why don’t we find myriads of high performance charging stations adorning public space?  The answer is simple, and leaving the high cost to one side for a moment, the reason is down to limitations on the electrical distribution network.  If these ultra-rapid charging stations were to appear in considerable numbers there would  not, at present at least, be sufficient spare capacity, or the renewable generation to back up this capacity, on the existing high voltage network.  It would be overloaded.  It will take many years to expand the electrical transmission and distribution networks along with huge sums of money to provide the capacity required.

 

Conclusion to Question 2

 

While in time further improvement will be made with increased battery voltage and battery technology the charge rate of EV’s is unlikely to achieve that of the humble petrol pump, at something like 10kWh/second.  Having sufficient transmission and distribution network capacity, and sufficient renewable energy to power it, will take years and have significant cost implication for the EV motoring public.  The implication is clear, huge queues for charging stations - one’s that work that is.  The alternative is to charge from home and don’t drive too far.

 

Summary


The ubiquitous petrol pump that dispenses hydrocarbon-based fuels at a rate around 10kWh per second into ICE fuel tanks day in and day out is safe, readily available and provides the average motorist with the ability to achieve something in the order of 1 mile per kWh and a range of 400 miles or more.  The average EV by comparison, while approximately four times more efficient at converting stored energy into range, certainly at present and likely for the foreseeable future, is unable to achieve the same practical range on a single charge or achieve the charge rate and hence charge time comparable to that of an ICE vehicle

 

Unless political will along with significant capital investment is forthcoming in the near future to add large additional quantities of renewable energy onto to the transmission network and to reinforce local high voltage distribution networks to enable many times the number of high power EV charging stations to be installed to keep pace with the expansion in EV ownership then the future of EV transport appears to be confined to one of range anxiety.  And even then the average EV driver will be left asking themselves questions, such as: where is the next charging station? do I have enough charge to get there? how long will the queue be? how long will I have to wait, etc?  The consolation being that if I can get home I can charge my vehicle using my 7kW charger – providing there has not been a power cut!

 

If any or all of this hypothetical scenario comes to pass in future years then this massive socio-technological experiment in phasing out the use of hydrocarbon based fuels for transport will have failed.  If this were to happen then we might see yet another documentary, this time called - "Who Killed the Electric Car[iii] – Once Again.”

 



[i] Typically, an ICE vehicle achieving an average of 40mpg approximates to 0.9miles/kWh of energy consumed.  By contrast, and EV might be expected to cover 3.5-4.0miles/kWh simply because the efficiency of the EV drive train – the battery and motors, is so much higher than the ICE, where so much of the energy is lost as heat.

 

[ii] Given that renewable electricity only accounts for something like 40% of the annual electricity generated and available for consumption at present and as times goes by there will be further additional demand and even if renewables can keep pace the transmission and distribution infrastructure will need to undergo massive changes and uprating to get the renewable sources of generation, often in remote locations, to where the demand exists.

 

[iii] Documentary film director, Chris Paine, produced two excellent films, Who Killed the Electric Car and a sequel, Revenge of the Electric Car.  The former explores the history, creation, limited commercialisation and subsequent destruction of the battery electric vehicle in the USA, specifically the GM EV1 in the mid-1990’s. The latter goes behind the closed doors of Nissan, GM and Tesla to examine the story of the global resurgence of electric cars. Both are worth watching.

Comments

Popular posts from this blog

Constraint Payments for Wind Farms: an example of market failure!

Cost of Net Zero and who pays? HM Treasury Review - a possible market failure for some!

An investigation into the potential impact of a high-voltage electricity transmission infrastructure project on Dumfries & Galloway