Thermoelectric recovery of waste heat-case studies

The use of waste heat as an energy source for thermoelectric generation largely removes the constraint for the wide scale application of this technology imposed by its relatively low conversion efficiency (typically about 5%). Paradoxically, in some parasitic applications, a low conversion efficiency can be viewed as a distinct advantage. However, commercially available thermoelectric modules are designed primarily for refrigerating applications and are less reliable when operated at elevated temperatures. Consequently, a major factor which determines the economic competitiveness of thermoelectric recovery of waste heat is the "cost per watt divided by the mean-time between module failures". In this paper, the authors report the development of a waste, warm water powered thermoelectric generator, one target in a NEDO sponsored project to economically recover waste heat. As an application of this technology case studies are considered in which thermoelectric generators are operated in both "active" and "parasitic" modes to generate electrical power for a central heating system. It is concluded that, in applications when the supply of heat essentially is free as with waste heat, thermoelectrics can compete economically with conventional methods of electrical power generation. Also, in this situation, and when the generating system is operated in a parasitic mode, conversion efficiency is not an important consideration.