7 Electricity for Transport
The use of electricity from renewable sources as the energy source for vehicles is another option to decarbonise the fuels used in the transport sector. In addition to decarbonising transport fuel use, electrification of the vehicle fleet has significant local environmental and health benefits, as electrification will also reduce local pollutant emissions.
There is a continuum of options for the electrification of vehicles (Figure 7.1). A vehicle that relies 100% on electricity (from either the grid or an off-grid source) for motive power is referred to as an electric vehicle (EV) or sometimes a battery electric vehicle (BEV).38 An EV dispenses entirely with the internal combustion engine, and a battery pack supplies electricity to an electric motor, or motors, to convert the electricity into mechanical power. The battery also provides all the auxiliary power required (e.g. lights, air conditioning).
In the middle of the spectrum of electrification options for a vehicle (Figure 7.1) lie PHEVs. These have a smaller battery than EVs and are plugged into the grid to charge the battery. They combine an often downsized ICE with the capability for all-electric driving in charge depleting mode. PHEVs can be charged from the grid and have sufficient battery storage and powertrain designs to allow pure electric operation over a certain distance depending on driving patterns and battery size. The ICE provides power when the battery has reached its minimum discharge level or under certain driving conditions. With significant deep discharging and charging, the batteries need to be more robust than light hybrid configurations and even EVs. As a result, R&D into extending the battery life of PHEVs is a very important cost reduction strategy.
PHEVs can be set up with "series" or "parallel" configu-rations. In the parallel configuration either the electric motor or the ICE can drive the vehicle, or both where extra power is needed. In the series configuration, the drive system becomes pure electric and the ICE is used only to charge the battery.
The distance that a PHEV can travel on the battery alone is usually used to categorise the degree of electrifica-tion. Thus a PHEV40 is a PHEV with a range of 40 km on the battery only. This type of vehicle configuration will often allow the majority of driving to be done on electricity from the battery alone. Meanwhile, the retention of an ICE means that the total range of the vehicle on electricity and liquid fuels is comparable to today's ICE vehicles. The size of the battery required to achieve a given electric driving range will depend on the size and weight of the vehicle.
Figure 7.1: The range of electrification options for vehicles