Melt-mixed polypropylene (PP) composites with singlewalled carbon nanotubes (SWCNTs) were used as thermoelectric materials which can convert a temperature difference between the two sides of the material into a thermovoltage. The effect of SWCNT content on Seebeck coefficient (S), electrical conductivity, and power factor was studied. In order to enhance these values for p-type composites, several strategies were applied. These involve (a) variation of the SWCNT modification, (b) incorporation of a high S copper oxide, (c) variation of melt-mixing conditions, and (d) addition of an ionic liquid. To generate n-type composites, additives like polyethylene glycol (PEG) and a non-ionic surfactant polyoxyethylene 20 cetyl ether were simply added during the melt-mixing procedure, inducing a switching from positive to negative S value in the pressed films. Finally, two prototype thermoelectric generators using both p- and n-type PP based materials could be manufactured.