Optimisation of thermoelectric module geometry for ‘waste heat’ electric power generation

Abstract

In this paper the ‘performance’ of a commercially available thermoelectric module (Peltier cooler) is investigated when operated in the Seebeck mode as a generator, to convert low temperature ‘waste heat’ into electrical power. Calculations based upon a realistic theoretical model of a single couple ‘generator’, which takes into account contact effects, indicate that a significant increase in the electrical power output from a module can be achieved by modifying the geometry of the thermoelements. The increase in power output is not accompanied by a significant reduction in conversion efficiency. Measurements on three commercial modules with the same number of thermocouples and with the same thermoelement cross-sectional area but different thermoelement length confirmed the predicted improvement in output power when the hot side of the module was attached to a simulated heat source at 120 °C with the cold side maintained at ambient. A decrease in the length of the thermoelements by 55% was accompanied by an increase of 48% in the electrical power output while the conversion efficiency was reduced by less than 10%. This improvement in ‘performance’ will be less in an actual generating system where the heat is derived from a flow of water. Nevertheless, it is concluded that in principle thermoelectric generators, when used over a long period of time (20–25 years), can provide on-site electrical power from low temperature waste heat at cost which is competitive to that generated by conventional utilities.