2.2 The principle of thermoelectric power generation for a single thermoelectric couple

If a temperature difference is maintained between two sides of a thermoelectric couple, thermal energy will move through the p-type and n-type pellets. As these pellets are electrically conductive, charge carries are transported by this heat. This movement of heat and charge carriers creates an electrical voltage called the Seebeck voltage. If a resistive load is connected across the thermoelectric couple's output terminals, current will flow in the load and an electrical voltage will be generated at the load [6]. A schematic diagram of a single thermoelectric couple, configured for thermoelectric power generation, with the output terminals of the couple connected to a volt meter in order to measure the open-circuit voltage Voc is shown in Figure 3(a), and connected to a resistive load RL in Figure 3(b).

Figure 2. A three couple thermoelectric module.

Figure 1.

A single thermoelectric couple.

where ρ<sup>p</sup> is the electrical resistivity of the pellet in Ohms-cm, Lp is the length of the pellet in cm, and Ap is the cross-sectional area of the pellet in cm2 found by:

The thermoelectric couple resistance Rc, ignoring the resistance of the copper interconnects, is the addition of the resistance of the two thermoelectric pellets:

The resistance of the copper interconnects is typically in the micro ohm region, and compared with the resistance of the Bi2Te3 thermoelectric pellets, which tends to be in the milliohm region, is significantly smaller in value and hence can be

The thermal conductivity λ of each pellet can be found and/or measured, with a

1.2 � <sup>10</sup>�<sup>3</sup> W/cm K, and for an n-type Bi2Te3 pellet of 1.4 � <sup>10</sup>�<sup>3</sup> W/cm K [10]. The

where λ<sup>p</sup> is the thermal conductivity of the pellet in watts/cm kelvin, Lp is the length of the pellet in cm, and Ap is the cross-sectional area of the pellet in cm<sup>2</sup>

It should be noted that the electrical resistivity ρ is the reciprocal of the electrical

where I is the current through a constant cross-sectional area A and length L

If a load resistance RL is now connected across the output terminals of the thermoelectric couple, as shown in Figure 3(b), the current I can be expressed as:

2.2.5 Calculating the current I when a load resistor RL is connected across the

Similarly, the thermal conductivity of the n-type pellet Kn can be found by:

2.2.4 Calculating the thermal conductivity Kp and Kn of the thermoelectric couple

typical conductivity for a p-type Bi2Te3 thermoelectric pellet of around

thermal conductivity Kp of the p-type thermoelement can be found by:

Kp <sup>¼</sup> <sup>λ</sup>pAp Lp

Kn <sup>¼</sup> <sup>λ</sup>nAn Ln

<sup>σ</sup> <sup>¼</sup> <sup>I</sup> � <sup>L</sup>

conductivity σ and can also be found using:

thermoelectric couple output terminals

when a voltage V is applied [8].

17

Similarly, the resistance of the n-type pellet Rn can be found by:

Rn <sup>¼</sup> Lnρ<sup>n</sup> An

2.2.3 The thermoelectric couple resistance Rc

Thermoelectric Energy Harvesting

DOI: http://dx.doi.org/10.5772/intechopen.85670

considered as negligible.

thermoelements (legs)

Ap <sup>¼</sup> width � depth measured in cm<sup>2</sup> (3)

Rc ¼ Rp þ Rn measured in Ohms (5)

measured in watts cm kelvin (6)

measured in watts cm kelvin (7)

<sup>V</sup> � <sup>A</sup> measured in siemens (8)

.

measured in Ohms (4)

Figure 3.

A single thermoelectric couple configured as a thermoelectric generator with a volt meter measuring the opencircuit voltage Voc (a) and in (b) with a load resistor RL connected across the couple's output terminals [7].
