Electrically conductive composites based on insulating polymers and carbon nanotubes (CNTs) have been developed for diverse applications, such as for dissipation of static electricity. Recently, such CPCs are also being studied as potential thermoelectric materials to recover waste heat into electric energy. The thermoelectric effect (also called Seebeck effect) is described as an electrical potential (voltage ∆U) induced by a temperature difference (∆T) between the two sides of a material. The advantages of polymer based thermoelectric materials over traditional materials, like bismuth telluride alloys, are not only their cost efficiency, but also the ease of processing, flexibility, low density, and intrinsic low thermal conductivity. Composites were prepared with polypropylene (PP) as the matrix and singlewalled CNTs (SWCNTs) of the type TUBALL from OCSiAl Ltd. as the conducting component by melt processing in a small-scale twin-screw compounder. For these SWCNTs a very low percolation threshold of ~ 0.1 wt% was found. In addition, the effect of addition of copper oxide (CuO) powder, a nontoxic compound with high Seebeck coefficient, together with CNTs was studied to enhance the Seebeck coefficient (S) of the composites. The effect of SWCNT content on electrical conductivity and S was studied. With the aim to fabricate a simple demonstrator module, an easy and cheap route to switch p-type composites into n-type was developed by adding polyethylene glycol (PEG) during melt mixing. At CNT concentrations of 0.8 wt% and 2 wt% and a fixed CuO content of 5 wt%, the PEG addition converted p-type composites (positive S values) into n-type (negative S). To construct demonstrators, two composites were selected: P-type PP/CNT composite with high S (up to 45 μV/K), and n-type composite (with S up to -56 μV/K) using PEG. The two prototypes with 4 and 49 thermocouples of these p- and n-type composites delivered output voltages of 21 mV and 110 mV, respectively, at ∆T=70 K.