The conversion of thermal energy into electrical energy is based on the Seebeck effect, which states that an electric voltage will arise in a conductor if it is subjected to a temperature difference. This effect is technically implemented in flat thermoelectric modules (TEM) also called Peltier elements. The current will flow if these modules are positioned between a heat source and a heat sink and an electric device is connected. The modules' efficiency not only depends on the material quality, but also increases as the temperature difference grows.
Development of thermoelectric generators for vehicles at the DLR
In order to improve the vehicles energy efficiency the DLR Institute of Vehicle Concepts in Stuttgart is carrying out the development and system integration of thermoelectric generators (TEG). The waste heat from the exhaust gas, which represents 1/3 of the fuel energy, is used as heat source. The coolant can be used as heat sink.
The system development of the TEG technology for vehicle application is done under consideration of all positive and negative overall system interactions. Intelligent solutions thus need to be found, for example, to minimise the load on the motor cooling system due to additional heat input or rather to control it in a beneficial way, or to limit the back pressure produced with the heat transmission as effective as possible. Considering driving cycles as WLTC or NEDC, the weight is the biggest negative influence on the overall system. Therefore the work at the DLR Institute of Vehicle Concepts concentrates among others on maximising the power density.
At the start of each development stage, stationary thermal simulations are carried out to evaluate different TEG designs regarding their performance. By means of a dynamic TEG model the TEG can be evaluated in the overall vehicle model.
The development of the TEG components for vehicle application is done using CAD and CFD programs. This design engineering and thermo mechanical analysis led the DLR Institute of Vehicle Concepts to develop a highly integrated TEG design. In addition, with a new holistic design method the design and optimisation of the technology is done under consideration of the positive and negative influences on the overall vehicle system. The aim is to maximise the efficiency enhancement at minimum cost.
Current work achieved an outstanding increase of the power density which led to an important advance for an even greater efficiency in the overall vehicle system. The reached power density is currently by far the highest one in the world for vehicle application.
The manufacture of the TEG components is carried out as well. After producing the individual components the prototypes can be assembled and analysed experimentally at the Institute’s hot gas test bench.
Furthermore, several hardware integrations of TEG in passenger cars were performed and measured successfully at the Institute’s dynamometer.
The Institute‘s hot gas test bench