single-stage one- or multiple-element thermoelectric generators (TEG) and thermoelectric coolers (TEC)
are used. Due to the performance limits of thermoelectric material, TEG [1,2] and TEC [39] of two stages or more should
be applied to improve the level of thermodynamic performance. In some special fields, the heat rejected from a thermal
machine may drive a TEC through the use of a TEG,