4.2 Energy supply
To move ground vehicles, the basic amount of energy needed at the wheel is deter- mined by the resistance factors stated above. The basic energy consumption is therefore directly affected by a weight reduction of the vehicle. Some energy, however, is lost during the transmission from the engine to the wheel and within the engine itself. The total final energy consumption at the engine of the vehicle is therefore higher than the basic energy consumption at the wheel. Energy is also needed for the energy sup- ply of the vehicle, mainly the exploration, conversion and distribution of a primary energy carrier (e. g. in power plants or refineries) (Fig. 4). The total primary energy consump- tion is therefore higher than the final energy consumption. The difference between the energy input and the energy output of a certain process (power plant, refinery, engine or transmission) is called efficiency and will be stated as energy output in per- cent of the original energy input. While there are no differences between relative final and primary energy savings (in % per 10 % weight reduction), the specific end and pri- mary energy savings (per 100 km and 100 kg weight reduction) are influenced by the ef- ficiencies.
Fig. 4: The energy chain in the transport sector The energy chain in the transport sector
Primary energy use
Energy use by energy supply
Exploration and Conversion
Final energy use at the vehicle
Deposits of primary energy
Refineries/ power plants
Source: [IFEU 2002b]
This study mainly deals with fuels (diesel and gasoline) and electricity as final energy carriers. The efficiency of energy supply is higher for fuels (refineries) and lower for electricity (power plants). The efficiency of electric engines, however, is over 90 % and therefore higher than the efficiency of combustion engines with less than 30 % ([DLR 2001]). While the basic energy consumption at the wheel is independent of the type of engine, the final energy consumption is very different. Differences in energy consump- tion between combustion engines and electric engines mainly show up in the final en- ergy (Fig. 5).