Assessment of the energy efficiency of the propulsion system in an electric vehicle. Methodology and results

Electric vehicles are claimed to be superior in terms of energy efficiency when compared to vehicles propelled by an IC-engine. This is particularly true, if we weigh the gross energy content of the fuel used against the uptake of electricity to charge the batteries. However, a passenger vehicle needs energy also to keep the cabin temperature warm or cold, depending on the season. Especially in winter conditions the cabin heating is a challenge, as an abundance of excess energy as in an ICE car is not available in an EV. Furthermore, considering the amount of energy needed to operate the vehicle is not sufficient, as this vehicle stage is only a part of the complete energy chain that includes also preparation and distribution of the fuel vs. electric power generation and distribution. All these stages need to be assessed to find out the true efficiency, and to be able to estimate potentials for reduction of GHG gases, CO2 in particular. This paper describes assessment of the energy efficiency of two EVs, converted from normal ICE-driven cars using mostly commercially available components. Test programme consisted of various driving cycles, as well as low ambient temperatures. Furthermore, efforts were made to separate the contribution of every sub-system to the overall efficiency. The results indicate that total energy efficiency is heavily dependent on type of driving - urban or highway. In addition, it was noted that low ambient temperature also deteriorates performance and efficiency quite considerably