4 Scientific and technical background
In this section, the basic scientific and technical background of the results will be pre- sented briefly. First, the physical resistance factors will be explained to have a better understanding of the basic energy consumption and weight induced energy savings. Af- terwards the efficiency of engines and energy supply will be discussed for the dif- ferent energy sources to have a better understanding of the differences between basic, final and primary energy. Finally, the potential of secondary effects by weight reduction will be considered.
4.1 Resistance factors Energy consumption can be distinguished at three different levels. These levels are
the basic energy consumption ‘at the wheel’ (determined by the resistance factors),
the total final energy consumption at the engine of the vehicle (also influenced by the efficiency of the transmission and the engine) and
the primary energy consumption (also influenced by the efficiency of energy supply).
The basic energy consumption of ground vehicles is due to several resistance factors that a vehicle has to overcome during its operation. The main resistance factors are: