Q. How do battery electric cars work? Return to top

A battery electric vehicle (BEV) utilises an on-board rechargeable battery to store electrical energy. The battery is recharged by connecting it to an electricity supply (usually the 'mains'). When required, energy is drawn from the electric-cells and converted to motive power by the use of an electric motor. Battery storage also enables the use of regenerative braking which tops up the battery when the brakes are applied.

Historically, the lead-acid cell has been the most widely used traction battery - in spite of having a relatively low energy density, it is possible to build cars with a range of up to 60 miles (100 km). Although lead-acid batteries are far from ideal, they have the advantages of proven reliability and an extensive maintenance support network (as they are used by conventional cars). The latest generation of rechargeable traction batteries include nickel metal-hydride (Ni-MH) and lithium-ion (Li-Ion) cells. These provide a significant improvement in performance and range. Despite their relatively high cost, these new battery types have proved to be well suited to automotive applications and are now preferred by most BEV manufacturers.

Most first generation BEVs used direct current (dc) motors that give high torque at low speeds and are easy to control using semi-conductor technology. However, their specific power (kW per kg) does not represent the best possible performance of available motor technology. An alternative is to convert the direct current from the battery to alternating current (ac) using an inverter, which then drives an induction motor. These have increased efficiency, double the specific power and require less maintenance. Alternating current power-trains are also more suited to fast-charging (see below). Disadvantages include higher costs and an increased complexity of the controller, which needs to both act as an inverter and regulate the motor's speed.

Q. What are battery electrics like to drive? Return to top

Driving a battery electric car is a very different experience to using a conventional car. When you turn the 'ignition' key, the first thing you notice is the lack of any engine (or starter-motor) noise. Forward drive is usually selected using either a centrally located or column-mounted 'gear' selector in much the same way as in an automatic - another similarity is that there is no clutch pedal. On depressing the accelerator, a BEV initially moves in almost total silence, which can be a little disconcerting. At low speeds in built-up areas, this can pose a problem as pedestrians are accustomed to listen for approaching cars before stepping into the road. As a result, BEV drivers often make good use of the horn! As the speed picks up, the small amount of 'engine' noise that can be heard is drowned out by wind and tyre noise, which become more noticeable as the speed increases.

Most BEVs have good acceleration (especially at lower speeds) and are more than capable of holding their own in city-driving conditions. Although most commercial models are designed as city cars and will 'top-out' at 40-50 mph, battery electrics can be high performance vehicles – the Tesla roadster is capable of 130 mph and goes from 0 to 60 mph in 4 seconds!

While most battery electric cars do not match the performance of conventional vehicles, current UK models have a range and performance that is adequate for many applications including: city driving, regular drive cycles (such as delivery routes), short range trips (up to 60 miles per day) and where only zero or low emission vehicles are allowed access. As a result, BEVs are most suited for use as 2nd private cars for city use, in commercial fleets (for small loads), and as company 'pool' cars.

Q. How do I refuel a battery electric car? Return to top

BEVs can be slow- or fast-charged. The most common method is overnight charging, which typically takes 6 to 8 hours. A slow-charging unit comprises a transformer to reduce voltage and a rectifier to charge the cells using direct current. Fast charging units usually require the use of alternating current - these can take as little as 10 minutes for a 50% charge.

Given the coverage of the national grid, it is relatively easy to install recharge points as compared with other green fuels. For slow charging, all that is required is access to a standard 13 Amp socket. However, private users without access to a garage or a private road face significant difficulties in getting electricity companies to install roadside recharging points.

Other than connecting up to a mains supply, a national network of fast-charging points has yet to be developed. Only a small number of car parks and parking spaces in the UK currently provide free (or low cost) access to recharging units for daytime 'top-up' refuelling - most of these being located within central London. The level of coverage is to likely to improve in city centres in the next few years, but is unlikely ever to match the number of refuelling stations for some of the other green fuels. For the foreseeable future, unless you drive in central London, BEV users will have to rely on home- or fleet-based charging systems.

See the Energy Saving Trust website for locations of UK recharging points.

Q. Are battery electric cars better for the environment? Return to top

The principle advantage of battery electric cars is that they are the only commercially available zero-emission vehicles (ZEVs). However, emissions are produced during the generation of electricity, the amount depending on the method of generation. Therefore, the emissions need to be considered on a life cycle basis - so as to include power station emissions.

Taking carbon dioxide and methane emissions into account, all BEVs charged from the mains (using an average UK fuel mix) show a significant reduction in greenhouse gas emissions (per mile). Using a petrol baseline, the figures suggest a reduction of around 40%. The benefits are mainly due to the fact that BEVs are significantly more energy efficient than conventional vehicles; electric power-trains are particularly well suited to stop-start, low-speed operation and use almost no energy when stationary. Also regenerative braking improves fuel efficiency by up to 20%. These emission reductions are predicted to further improve with the introduction of cleaner generating plant. However, if renewable electricity is used, then life cycle greenhouse gas emissions are virtually zero - this is a true zero-emission car.

For regulated emissions (per mile), assuming the average UK generating mix, carbon monoxide and hydrocarbons are significantly reduced for BEVs. However, life cycle emissions of particulates, nitrogen oxides and sulphur oxides are significantly increased. Having said that, these are emitted from power-stations which are well away from urban areas. As is the case with greenhouse gas emissions, if renewable electricity is used, then life cycle regulated emissions are also reduced by almost 100%.

Q. How much do battery electric cars cost to own? Return to top

Ownership costs for battery electric cars are higher than for their petrol or diesel equivalents. This is principally due to their higher purchase price. Typically for new car (or small van) the price is increased by up to 80%. Due to the high cost of the batteries, these are often not included within the purchase price. Instead they are often leased for £60-£70 a month. If the battery is purchased outright, further capital is required every 3 to 5 years for battery replacement (depending on battery type).

Other changes in ownership costs include vehicle excise duty ('road tax') - as electric vehicles are exempt, BEV owners will save around £100 per year compared to an average conventional car. There remains some uncertainty about annual depreciation rates and resale values for BEVs due to the unknown length of battery-life and the low demand for battery electrics as compared to other green car types. If anything, rates are likely to be higher than for a conventional car (ie BEVs lose their value faster than conventional cars).

Additional capital costs are also incurred by BEV users who install additional recharging equipment. Costs per standard charge point are of the order of £500-£2000, depending on the difficulty of installation. Fully installed fast-chargers cost between £10,000-£30,000 per point (depending on whether an on-board or off-board fast-charging system is used).

Q. How much do battery electric cars cost to run? Return to top

Some running costs are significantly less for BEVs than for conventional cars. In particular, fuel costs are very low due to the competitive price of electricity (fuel duty is zero-rated) and to the high efficiency of the vehicles themselves. Taking into account the high fuel economy of battery electric cars, the fuel costs can be as low as 1.0-2.5p per mile (dependng on tariff). For a typical annual mileage of around 10,000 miles per year, switching from a conventional car to a battery electric could save you around £800 in fuel costs. But, and it is a big BUT, if the battery lease is considered as a running cost, then the saving on fuel is cancelled out by the monthly battery leasing cost.

For drivers in and around London, the other major running cost to consider is the congestion charge. All battery electric cars currently receive a 100% discount on the London Congestion Charge (although BEVs need to be registered and pay an annual £10 fee). With a £8 payable daily charge, this could provide a potential annual saving of up to £2000 - and is the reason that most UK BEVs are currently sold in London.

Q. Where can I buy a battery electric car? Return to top

Back in 2002, several major motor manufacturers were selling a range of battery electric cars in the UK. These included the Peugeot 106E, the Toyota RAV4 Electric and the Ford 'Think!’. However, these did not sell well are no longer available as new cars. However, a number of new style specialist 'EV' companies have recently launched a range of small electric vehicles designed for city use. These include the Reva G-WIZ micro-car (imported from Bangalore), The NICE (No Internal Combustion Engine) MEGA City Car and the Bradshaw 600 mini-van. The more established Citroen Berlingo is also still available in van or car form.