Vehicle accessories such as lighting, air-conditioning and power steering have a mechanical power requirement representing around 2% of the overall energy content of fuel used in light vehicles (and considerably less in heavy vehicles) (IEA 2007, DOE 2008). Implementing more efficient ancillary systems means less fuel is consumed in powering them.

Application relevance

All vehicles are equipped with accessories or equipment that can be optimised for efficiency, or alternatively powered. Some modifications, such as LED bulb installation, can be applied to both truck and trailer.

Air conditioning represents the largest usage of energy for vehicle accessories, and this area has received most attention in research and development.

Potential benefits

High intensity discharge lamps (HIDs) and light-emitting diodes (LEDs) can improve lighting efficiency by two to ten times over conventional incandescent and halogen lamps, thus reducing fuel consumption. Better designed vehicle air conditioners can also reduce fuel consumption significantly while providing the same or equivalent cooling.

More efficient alternators and power steering pumps could also improve fuel economy by a further 1%; however, fuel savings are not assured and may be difficult to quantify without before-and-after comparison.

Key implementation considerations

Lighting represents a small proportion of overall costs, and substituting LEDs or HIDs can increase the lighting cost up to ten-fold. With this in mind, it is important to estimate the existing fuel usage associated with the accessories, and to quantify the costs for upgrading these systems to determine the investment case.

While fuel savings are demonstrable in passenger vehicles due to a reduced load on the alternator, the relative benefits within a heavy vehicle application will be proportionally lower. Although there is no reason to suggest that this benefit is not transferable to heavy vehicles, the fuel efficiency benefit is more difficult to quantify due to distinctly different duty cycles and the much higher proportion of fuel used for moving the load.

For the full report, see Fuel for Thought – Identifying potential energy efficiency opportunities in the Australian road and rail sectors (opens in a new window) PDF 1.5 MB.