Why is energy flow reversible in thermoelectric devices?

The energy flow in thermoelectric devices is reversible because these systems rely on the interaction between heat and electricity through two related, reciprocal mechanisms: the Seebeck effect and the Peltier effect.12

• The Seebeck Effect: When a temperature differential is applied across the junctions of a thermocouple, it generates an electric current, converting thermal energy directly into electricity.12
• The Peltier Effect: Conversely, when an external electric current is applied to the device, it causes heat to be absorbed or released at the junctions. This allows the device to function as a heat pump, effectively using electrical power to provide heating or refrigeration.12

Because any thermoelectric device can operate in either mode, the direction of energy conversion is reversible. While a device may be optimized for a specific purpose—such as power generation or cooling—the underlying physical principles allow for the direct conversion of thermal energy into electrical energy or electrical energy into thermal power.2