When we are discussing the

thermoelectric generator, we need to take into account the application of the Seebeck

effect to the electrical generation. As has previously been shown in fig. 1,

the carriers in both p-type and n-type material are moving from the hot side to

the cooler side. In the determination of the thermoelectric performance, we

assume that the heat transfer occurs only between the two branches, excluding

the heat transfer by radiation. The efficiency of the thermoelectric generator

is given by the ratio between electrical energy provided to the load and the

total heat flow from the hot junction 16. The equation can be written as:

(6)

The

performance of the thermoelectric material, the p-type and n-type

semiconductor, can be expressed by a dimensionless figure of merit or ZT, with

the equation:

(10)

Where

? is the Seebeck coefficient of the material, ? is the electrical resistivity

of the material, ? is the thermal conductivity of the material, and T is the

working temperature. We call the value of ?2/? as the power factor.

The relation between efficiency and the figure of merit can be written by the

following equation:

(11)

When we are discussing

about power generation that has thermal process in the system, the maximum

efficiency will have the value of Carnot cycle, which is equal to the first

part of the equation. The second part of the equation shows the relation

between efficiency and ZT, where the higher ZT leads the efficiency closer

towards the efficiency of the Carnot cycle 3. In the determination of the

total efficiency, it is also important to include geometric parameters such as

length and area which is excluded from the equation 3,16-19.

From

the equation of the ZT above, we can see that it is related to several

parameters. It is important in the research of thermoelectric to find the

suitable material because some of the parameters mentioned before has an inverse

relationship with the other, when one parameter goes up, the other goes down.

In the figure below we can see the relation of those parameters with the carrier

concentration of the materials: