What are battery-electric and hybrid vehicles?
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Battery-electric and hybrid vehicles

What are battery-electric vehicles?

Battery-electric vehicles are powered by motors that draw electricity from on-board storage batteries, which act as an "engine" to propel it. Electric vehicles don't produce pollution from the tailpipe or through fuel evaporation, which means they have great potential to reduce greenhouse gas (GHG) emissions and smog-forming pollutants. Depending on the source of electricity used to recharge the batteries, the vehicles can also have low overall (life-cycle) GHG emissions.

Despite these environmental benefits, the use of purely battery-electric vehicles hasn't reached significant levels in Canada for three reasons: the cost; the size and weight of the battery; and the lack of an adequate refuelling infrastructure. Automakers have been developing electric vehicles for several decades, with limited commercial success. However, users in California, where clean air mandates are being put into action, have adopted some purely electric vehicles.

The batteries now used in electric vehicles limit the average vehicle's driving range to between 100 and 200 kilometres, depending on the battery type. The batteries must be recharged often, which takes up to eight hours each time, compared with the few minutes needed to fill up with gasoline. They are also heavy and bulky, which limits acceleration and top speed. Most batteries must be replaced after 400 to 500 charges – an expensive proposition that offsets the advantages of using low-cost electricity as an energy source.

Automakers and governments in Canada and the United States are developing batteries that are smaller and lighter, can be recharged more quickly and will store more power. Researchers are also developing aerodynamic designs and experimenting with lightweight materials (such as carbon fibre and plastic body parts) to reduce vehicle weight and energy demand.

The final goal is to build light-duty battery-electric vehicles that offer acceleration and speeds that are similar to conventional vehicles. To achieve broad consumer acceptance, battery-electric vehicles will also need to have a driving range of close to 300 kilometres between rechargings and a battery life of 5 to 10 years.

A number of batteries under development might enable electric vehicles to meet these performance requirements. Some of these batteries are already being used in the few electric vehicles commercially available on the market, while others are being tested in prototype electric vehicles.

What are hybrid electric vehicles?

Hybrid electric vehicles (HEVs), on the other hand, combine a battery with a conventional internal combustion engine. Thus they offer the extended driving range and rapid refuelling of conventional vehicles, together with many of the energy and environmental benefits of electric vehicles. A few hybrid vehicles are widely available on the market today, with many manufacturers planning on introducing hybrid electric/gasoline vehicles in the next few years.

HEVs can use either a series or a parallel system. These systems differ in how they integrate the workings of the two power-generating units. Most popular today is the parallel hybrid system, which Toyota and Honda use.

Parallel configurations tend to be more flexible and powerful than series hybrids. But they are also more complex and can be more costly. Three types of parallel designs have emerged:

• 300-volt systems that have an internal combustion engine that can supply continuous power, with a 300-volt electrical motor supplying the difference between engine power and peak power demand. Although this is usually the most fuel-efficient parallel configuration, relatively large batteries are needed, which increases the cost of vehicles.
• 150-volt systems also use an electric motor to make up the difference between engine power and peak power demand. However, because the electrical motor produces less power than a 300-volt system, the internal combustion engine needs to be larger, which reduces fuel economy. Batteries are smaller than those for 300-volt systems.
• 42-volt systems, also known as "mild hybrids," trade efficiency (less electric power is produced) for cost reductions. They feature an integrated "starter-alternator" located between the engine and transmission. This helps save energy with automatic idle shut-off, launch assistance to the engine, elimination of the torque converter for automatic transmissions (or at least a reduction in size), electric brakes and regenerative braking. These systems can't operate as zero-emissions vehicles or even offer a significant power assist to the engine.

Two examples of vehicles that have adopted the parallel hybrid design are the electric Toyota Prius and the Honda Insight.