What is the consequence of having less temperature difference between the hot and cold junction?

When there is less temperature difference between the hot and cold junctions, the output of the thermoelectric device, such as a thermocouple or a thermoelectric generator, will indeed be lower. This is due to the fundamental principle that the efficiency and output of these devices are largely driven by the temperature difference between the two junctions.

In thermoelectric systems, a greater temperature gradient allows for more substantial energy conversion from heat to electrical energy. When the difference in temperature decreases, the generated voltage and, consequently, the power output also decline. This is consistent with thermoelectric characteristics, where the Seebeck effect governs the output voltage generated by the temperature differential. Thus, a smaller temperature difference yields a reduced output.

A better understanding of this concept highlights why achieving a substantial temperature difference is critical for maximizing the efficiency of systems that rely on thermoelectric principles.