A greater zT indicates a greater thermodynamic efficiency, therefore, zTis a method for comparing the potential efficiency of different materials. Values of 1 are considered good; values of ~3 are essential for thermoelectrics to compete with mechanical devices in efficiency. To date, the best reported peak zT values in bulk materials are in the 1.5-2 range.
The Seebeck effect is used in the thermoelectric generator, which functions like a heat engine, but is less bulky, has no moving parts or emissions, needs no maintenance, and is typically less efficient. It has a wide use in power plants for converting waste heat into additional power (a form of energy recycling), and in automobiles as automotive thermoelectric generators (ATGs) for increasing fuel efficiency. Space probes often use radioisotope thermoelectric generators with the same mechanism but using radioisotopes to create the required heat difference.
The Peltier effect can be used to create a refrigerator which is compact and has no circulating fluid or moving parts; such refrigerators are useful in applications where their advantages outweigh the disadvantage of their very low efficiency.Thermocouples and thermopiles are devices that use the Seebeck effect to measure the temperature difference between two objects, one connected to a voltmeter and the other to the probe. The temperature of the voltmeter, and hence that of the material being measured by the probe, can be measured separately using cold junction compensation techniques.