- EVs have a purely electric drivetrain
- No local emissions
- Range can be restricting
Electric cars are powered entirely by electricity with no need for petrol or diesel propulsion. Production models rely on batteries to store charge, hence are known as battery electric vehicles or BEVs.
More manufacturers are offering electric cars and vans, but how do they differ from hybrid or normal models?
Despite powering a quarter of the cars first produced at the dawn of motoring, for years electric propulsion was only deployed in experimental and specialist vehicles.
British drivers may remember milk floats – small open-sided vans near-silently driving around streets, making deliveries while powered by easily recognised banks of lead-acid batteries not that different to a conventional car’s starter battery.
Since the 1990s, environmental concerns and a desire to move away from fossil fuels reinvigorated research into electric cars, with the most notable experiment being the General Motors EV1.
How does an electric car work?
Now alternative fuels have become a mainstream research area for all manufacturers, a number of electrically assisted cars have joined the market. Hybrid and plug-in hybrid technology is now mainstream, but many manufacturers now offer fully electric models without any form of combustion engine to increase range.
In a battery electric vehicle, the simplest conversion of stored energy to movement takes place. Charge from the battery pack is fed to the motor in a controlled way, causing the motor to rotate and thus, turn the wheels.
Unlike a conventional car, an electric motor produces maximum torque from very low rotations per minute, and can operate at very high speeds; this can remove the need for a gearbox other than a simple reduction gear.
In fact, most electric vehicles on the market avoid gearboxes entirely as building something strong enough to withstand electric torque is expensive and heavy.
Reverse is implemented by simply reversing the direction the motor turns. For obvious reasons, the speed is usually limited.
Cars fitted with all-wheel drive will often feature a motor for each driven axle, or a motor per wheel in high performance models.
Improvements in technology have coincided with a new focus on environmental marketing, and allowed the creation of infrastructure to support driving electric vehicles further.
Higher-density, and thus lighter, battery packs have been developed, better understanding of charge/discharge cycles and temperature control, and lower-drain accessories such as headlights, heaters and radios have also contributed to a greater range, though it’s worth noting that the laws of energy and physics still apply; most technology around electric cars is focused on improving driver habits and behaviour.
How do the batteries in an EV compare to petrol?
- Battery packs are rated in kilowatt hours, or kWh
- 1 litre of petrol is equivalent to 9.7kWh
- Diesel contains 10.7 kWh of energy per litre
Battery packs are rated in kWh or Kilowatts per hour. A watt is in essence a unit of energy; it denotes the rate of energy transfer. What you can do with that energy depends on the kind of car you are driving and the motors it is using, how fast you want to go, and how arduous the conditions are.
A small car like the Smart Forfour Electric Drive has a 17.6kWh battery pack, meaning that a drain of 17.6kW will deplete the pack in an hour.
Fully draining a battery is bad, however, and in all cases a reserve of capacity will be maintained to protect the cells. At the other end of the scale, Tesla’s Model S has a minimum of 75kWh, with an option for 100kWh.
On the subject of scales, the 2017 Smart Forfour tips them at 1,200Kg, in Electric Drive form. That’s an increase of 225Kg over the petrol model. The Tesla Model S battery pack weighs 540Kg.
For comparison filling up the 975Kg Smart Forfour petrol’s 35-litre petrol tank adds just 26Kg to the dry weight, and it gets lighter as range is used up. Yet it provides almost 350kWh of potential energy.
Charging your electric car
- Charging rate relies on being able to get energy into the car
- Home supplies limited to 10 Amps – or 2.3 kW
- Dedicated wallbox home chargers can provide 3.6kW or 7kW
- Superchargers can provide 120kW
- Tesla designed for fast battery pack swaps
It is possible to charge your electric car via a normal 13A three-pin socket. There are some limitations however; these sockets are designed for energy consumption far lower than that needed by a car, and can provide 10 amps, or 2.3kWh, at most. To refill a battery storing the equivalent of 17.6kWh takes as long as that implies – 7 to 10 hours depending on temperature.
For a relatively low fee, a dedicated home charger or wallbox can be installed. These use wiring standards similar to an electric stove, and can either provide 16A for around 3.4kW, or 32A for 7kW, bringing the charge time for a smaller electric car down to 2-3 hours.
Charging at a commercial point typically costs between 9p to 12p per kWh; a flat connection fee or membership fee will apply. Home charging will carry similar rates, but take longer.
Commercial charging stations for locations with three-phase electricity can charge at 22kW, and are available at fairly moderate cost for private installation.
The rate of charge above 80% capacity slows considerably, so it’s typically assumed you'll keep a car between 25% and 80% charge with fairly short charging periods.
AC – alternating current - charging cables adhere to two types. In Europe including the UK, the Type 2 plug is standard, and most charging stations will include a Type 2 socket so owners of Japanese or American cars with Type 1 connections can use an adaptor cable.
Direct current charging bypasses the on-board conversion in the car, but requires a charger compatible with the vehicle’s specific setup.
Tesla Supercharger stations provide 120kW via DC, but are dedicated to Tesla cars only. Other cars feature additional connections for DC charging – such as the BMW i3’s Type 2 plus CCS rapid charging socket.
Tesla has designed its cars to have the battery packs swapped in 90 seconds, making a network of battery exchange stations possible.
However, demand for the service has been low, and it’s unlikely that any manufacturer will pursue this route; the future may involve standardisation of batteries so one service centre could cater for many cars.
Are electric cars reliable?
For the most part, yes, electric cars are incredibly reliable. Since the earliest battery-assisted models have been around for over two decades, the batteries themselves have proven remarkably robust. Early Nissan Leafs are driving around with 500,000 miles on in some parts of the world, still on their original batteries.
There are side effects to the electric drivetrain, too. Capable of 20,000 to 40,000 hours of operation before failure, the motors themselves should outlast the bodies and there’s no clutch or gearbox to wear out.
Using the motor as a generator to brake and recharge the batteries also ensures wear on the brake pads is minimal, and a set of brakes can last considerably longer than regular hydraulic systems. Without oil and fumes contaminating hoses and connectors, the wiring and plumbing should also last much longer.
Do I need an electric car?
If you make short journeys, or live in a city with punitive taxation based on vehicle emissions or strict ULEZ areas, there are good reasons to drive an electric car. Reduced noise pollution, minimal wear and of course, the reduced reliance on fossil fuels and creation of smog and greenhouse gases are all worthy considerations.
In fact, outside of the limited range of many models, there are few disadvantages; the question should really be 'can I use an electric car yet?'. If you drive more than 30-40 miles in a day, or make long journeys frequently, the answer is no; only the most expensive examples can compete with petrol cars.
Although the technology and refinement are well suited to motorway and performance use, increased speed comes with increased power consumption so only the highest-capacity cars are really suited to faster journeys. At present, battery electric cars are less versatile and adaptable than their conventional counterparts.
Smaller cars like the Smart Forfour benefit from optional heated seats and steering wheel, which have a lower consumption than using the in car heater. On the Forfour, demisting or air conditioning can take 1kWh and cut your range by around 10%; programmed pre-heating using power when plugged in is a vital feature.
Environmentally, local emissions are reduced, even eliminated, but there is still an impact generating the electricity to charge the car and in manufacturing.
Which electric cars can I buy now?
There's an ever increasing range and variety of electric cars on the British market, and that's sure to expand in the future.
- BMW i3 (also available as a range-extender hybrid)
- Citroen C-Zero
- Hyundai Ioniq
- Kia Soul EV
- Nissan Leaf and e-NV200 Combi
- Peugeot iOn
- Renault Zoe, Kangoo ZE
- Tesla Model S, 3, X
- Smart Fortwo and Forfour Electric Drive
- VW e-Up and e-Golf