Here is an essay on the working of thermoelectric power generator, explained with the help of a suitable diagram.
Thermoelectric power generator converts heat directly into electricity or transform electrical energy into thermal power for heating or cooling. Such devices are based on thermoelectric effects involving interactions between the flow of heat and of electricity through solid bodies.
All thermoelectric power generators have the same basic configuration, as shown in the figure.
A heat source provides the high temperature, and the heat flows through a thermoelectric converter to a heat sink, which is maintained at a temperature below that of the source. The temperature differential across the converter produces direct current.
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The vast majority of research in the field of thermoelectric over the past 10-15 years has been in the area of thermoelectric power generation. The driving force behind most of this research seeks ways to improve our utilization of energy. Consider that less than a fourth of the energy content in the gasoline in your car actually goes into useful work to move the vehicle.
The majority of the energy escapes as heat loss to the ambient primarily through the vehicle exhaust and radiator. Likewise, the U.S. manufacturing industry discharges roughly one-third of the energy consumed as thermal losses to the atmosphere or to cooling systems. This heat loss is measured in Quads (1015 Btu!!) and represents a huge opportunity for thermoelectric to someday impact energy consumption.
Thermoelectric waste heat recovery is the process of recapturing this lost heat and converting it to electrical power.
For any thermoelectric power generator (TEG), the voltage (V) generated by a TEG is directly proportional to the number of couples (N) and the temperature difference (ΔT) between the top and bottom sides of the TEG and the Seebeck coefficients of the n- and p-type materials (αn and αp).
Power output from a TEG is a function of the temperatures, the materials (and device effective) figure of merit (Z) and also a function of how well the generator resistance (R) matches the resistance of the attached electrical load (R Load).
To convert waste heat at reasonable efficiencies, one needs:
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(a) Large temperature differences (hundreds of degrees C),
(b) High figure of merit (Z) materials (Z=1 or higher), and
(c) The ability to match the electrical loads with the thermoelectric resistance.
In addition, any high Z material must be capable of being incorporated into a device without significant losses that would degrade the device effective Z in order to achieve the efficiencies described in the equations above.
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As depicted in Figure, heat flow from the exhaust stream must be extracted and conducted through the TEG in order to be converted. This heat must then be exhausted at a lower temperature to maintain the desired temperature difference across the TEG.
While waste heat recovery is the driving force for much of the TE power generation research, other application areas could utilize many of the same material and device advancements, namely direct generation, co-generation and energy harvesting.
Uses of Thermoelectric Power Generator:
A thermoelectric generator is a unique heat engine in which charge carriers serve as the working fluid. It has no moving parts, is silent in operation and very reliable. However, its relatively low efficiency (typically around 5%) has restricted its use to specialized medical, military and space applications where cost is not a main consideration.
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During the past 10 years thermoelectric has attracted increasing attention as a ‘green’ and flexible source of electricity able to meet a wide range of power requirements. Relatively recently it has been realized that in situations where the supply of heat is cheap or free, as in the case of waste heat, efficiency of the conversion system is not an overriding consideration.
The use of waste heat as an energy source particularly at temperatures below 140°C substantially increase the commercial competitiveness of this method of generating electrical power.