Simulative designing of Thermal High Performance Storages for electric bus heating

Abstract

Introduction: Battery electric buses are facing huge challenges when interior heating is required on winter term conditions, since the heating demand can exceed the power that is required for traction. As state-of-the-art solutions for providing interior heating, diesel fueled heaters, electric resistance heaters or electric heat pumps are used. However, when using diesel fueled heaters, local emissions are emitted. When using electric resistance heaters, electric energy from the battery is consumed cutting the range of the vehicle up to more than 50 %. When using heat pumps, overall energy consumption for interior heating is reduced as well as range reduction. However, it is still very significant on cold ambient conditions. Additionally, a second heater as to be used, since the thermal output of available heat pumps is not sufficient on temperatures below -10 °C. To overcome this challenge, the use of a Thermal High Performance Storage (THS) as stand-alone heating solution or additional heater can be used, as already proposed in past publications. The THS can be electrically charged simultaneously to the traction battery. The stored energy afterwards is used for heating the interior. The benefit of using a THS for interior heating is that no local emissions occur and no energy from the battery has to be used for heating. Compared to currently used batteries, a THS can be up to 90 % cheaper, 50 % lighter and 40 % smaller. To exactly identify these potentials, a simulative designing method is required for designing the optimal THS for the specific use case. The presentation of this designing method and the tools used for this will be shown by the proposed poster. Materials and Methods: To define the goals of how a THS should be optimized, a wide literature review was investigating the topic of electric buses in general. Target of this was the conclude all vehicle related aspects, the use of a THS as heating solution has impact on. To implement simulation models, the environment of Dymola / Modelica is used. Results: The resulting designing method is of a holistic approach. It considers aspects like the reference scenario, the vehicle type, energy consumptions (heating, traction, production), ecological aspects, economical aspects or charging / discharging rates of the used energy storage systems (battery and THS). By this, the optimization of a THS is done in a way to be optimized for the overall vehicle, not just for the aspect of heating. The implementation of the designing method within the simulation environment of Dymola / Modelica is done in a way, that every partial model can be replaced in future. This allows to use less or more detailed models for any part of the overall simulation model. Conclusion: With the presented designing method of a THS, a step towards maximizing the potential of a THS as heating system in electric buses is done. The holistic approach is highly innovative. By using Dymola / Modelica as simulative environment, linkage with other tools is possible which rises the flexibility simulation tool.