The first thing to look at is how energy comes from the ‘fuel’ such as a wind farm, gas power station or diesel engine. You will appreciate that diesel engines are both hot to touch and noisy. Both the noise and heat are energy that is not being turned into kinetic energy.
A diesel engine will only turn around 30% of the available hydrocarbon energy into kinetic energy. Around 63% is wasted as heat. An EV by comparison will turn around 77% of the energy from the grid into kinetic energy.
Let’s do a hard comparison by comparing efficiency to miles per kilowatt hour: Note miles per kWh are how you compare EV efficiency and range.
• The typical 325kWh per mile EV will do 3.1 miles per kWh
• A diesel car doing 50 miles to gallon (mpg) will get 1.5 miles per kWh
• A diesel car doing 40mpg will get 1.2 miles per kWh
Translating back to mpg that would mean the EV is getting roughly 104mpg which is one hell of an efficiency.
EV efficiency differs between models. The standard Tesla Model 3 with a 57.5kWh battery can do 245Wh/mile that amounts to 137.6mpg. At the other end of the scale the Audi eTron S will manage 444Wh per mile or a thirsty 75.9mpg!
You could even run a petrol generator to power an EV powertrain and still achieve far better mpg than a diesel. This is because it isn’t wasting fuel accelerating and decelerating and generators are designed to turn more energy into kinetic energy and less into heat.
Scale this up to a giant 1MW wind turbine and very little heat comes out for every kWh that would come from a fraction of the turn of the windmill. Energy is lost as heat in the battery and motor but nothing like the rate that the internal combustion engine produces.
How to Drive an EV More Efficiently
Driving an EV is a completely different bag to driving an ICE vehicle. For a start there is a linear relationship between how fast you go and how much ‘fuel’ you consume. There is no multi-speed gearbox on an EV, though in many there are ‘step-down’ gearboxes to put lower revolutions into the wheel from a faster-spinning motor.
With ICE vehicles you can have similar fuel consumption at 70mph to that at 30mph thanks to the multi-speed gearbox.
Unlike most ICE vehicles, EVs use ‘regenerative braking’ where the motor in the wheel slows the car down instead of the brakes, generating electricity for the battery as you go. It is possible to get as much as 15% or more extra battery energy back in a journey from regenerative braking. Many drivers in fact now do ‘one-foot driving’ where they never use the brake pedal at all!
Town and Country Roads – Not Motorways
Thanks to regenerative braking, it can arguably be more efficient to drive on country roads and on city streets than it is on motorways. Motorways were built for ICE cars that get similar efficiency at high speed as lower speeds.
By contrast, an EV spilling kilowatts of energy as you cruise at 70mph isn’t going to do much in the way of regenerative braking. As such if you’re not in a hurry – perhaps driving on holiday where the journey is as much a part of the fun as the destination – then one of those routes with bends, towns and slower stretches could increase your range. EVs can claw back as much as 15% of energy back per full battery discharge using regenerative braking – on a clear motorway run at midnight you’d hardly touch your brakes.
Hills are a Killer!
Sadly the downside to the scenic route above is that smaller roads don’t have cuttings and will crest a lot of hills in Wales, Scotland and the SW of England! EVs don’’t like hills as the increased resistance of the climb, combined with carrying a tonne or so of battery, mean that hilly routes can chew through battery. Using regenerative braking on the way down the hill can recapture much of that excess used but certainly not 100%.
Winter EV driving ranges are as much as 20% lower than summer. This is because cold batteries are less efficient at taking in and releasing energy.
Many cars can be pre-warmed in a garage when plugged into the charger, and programmed to warm the battery using mains electricity before you go out for the day. People with garages that have mains electricity are a minority in the UK so this isn’t for everyone.
As with hills, headwinds can impact EV range, and so can rain. On the surface an EV would want to live on a flat plateau of the Sahara Desert all their lives (perhaps with solar panels on the roof!). However, car manufacturers carefully test their vehicles to withstand arctic cold and all sorts of other weather conditions before release as though these losses are palpable, the majority of EV users don’t live in an EV Utopia!
What does the future hold
Battery efficiency is a key battleground for car manufacturers. With the issues we have described in mind, car and battery companies are looking at all sorts of ways to improve EV efficiency.
Never mind the Tesla Sportster, possibly the sexiest EV ever designed is the Mercedes EQXX concept car. Redolent of the Jaguar E-Type, this car has been built with efficiency in mind from the unctuous shape of the shell right down to the way that the battery is cooled with airflow from the grille.
The ‘average EV’ efficiency is around 3.1 miles per kWh. The EQXX can manage double this at 6.2! This is due to the boffins at Mercedes seeing just how far they could push efficiency without being boring. As you can see here, this Merc is anything but boring!
Without doubt, top end, Tesla Model S Plaid-level EVs will be able to do 620 miles per charge within the next five years without compromising on weight or handling. This is because battery architecture and chemistry is starting to improve at an explosive – or implosive to be more accurate – rate. Energy density is getting ever greater even while safety and efficiency of motors and drive systems are getting better.