14. How efficient is a thermoelectric cooler?
Efficiency relates to the amount of energy produced from a machine versus how much energy one puts into it. In heat pumping applications, this term is rarely used because the energy-in is very different from the service provided. We supply electrical energy to a TEC, but the result is heat pumping.
For thermoelectric modules, it is standard to use "coefficient of performance", not efficiency. The coefficient of performance (COP) is the amount of heat pumping divided by the amount of supplied electrical power. In other words, COP tells you how many units of heat pumping you will get for each unit of electrical power you supply.
It is possible, in certain situations, to pump more watts of heat than the watts of electrical power input. COP depends on the application, heat pumped, and temperature differential required. Typically, the coefficient of performance, heat pumped then divided by input power, is between 0.4 and 0.7 for single stage applications. However, higher COPs can be achieved with optimized, custom thermoelectric modules.