The performance of a real thermoelectric power generation (TEPG) device designed to extract waste heat from the exhaust system of vehicles and to directly convert the recovered exhaust energy into. electricity was studied under various driving conditions using a proposed thermoelectric (TE) model in the current work. The proposed model was formulated from the first law of thermodynamics and Ohm's law and from a control volume that represents the TEPG system such that the temperature-dependent material properties of and the spatial-dependent heat flow through the thermoelement can be taken into account in the TEPG performance calculation. The temperature of the fluids, the temperatures at the top and the bottom of the TE modules, and the output power of the device were firstly calculated for the actual TEPG device using the proposed model in combination with the energy conservation equations for the fluids flowing through the heat exchangers. The results agree well with the experimental measurements and other model predictions. The model was then used to probe the effects of a broad design and operating parameters on the TEPG device performance. The results demonstrated strong inter-dependency of the TE module design, the heat exchanger design, the flow arrangement, the flow rates, and the operating conditions, which need to be considered systematically in TEPG device optimization. Finally, an optimal module fill factor of 0.35 was found for the given TEPG and heat exchanger design, which will generate about average 8.1% more output power under a broad vehicle driving conditions with the material usage less than half of that used by the original module design with a fill factor of 0.7704. (C) 2016 Elsevier Ltd. All rights reserved.