Effect of a limit to the figure-of-merit on thermoelectric generation

Evidence is presented which indicates that the dimensionless figure-of-merit (ZT) of a thermoelectric material has a limit of around 2. In this paper the consequences of the existence of this limit in material performance, on the development of thermoelectric technology is discussed. It is concluded that in specialised applications where efficiency, device compactness and fuel costs are major considerations, the existence of this low material performance limit may well have a capping effect on the planning of future advanced material development programmes. However, in applications where the cost of fuel is low or essentially free, as in waste heat recovery, the economic factor (cost per waft) rather than efficiency, is the overriding consideration. In such applications a limit to ZT will have only a marginal impact on the competitiveness of thermoelectrics as an environmentally friendly source of electrical power. Alternative strategies for effectively increasing the conversion efficiency of thermoelements are discussed.