Power Plant Engineering

NON-CONVENTIONAL ENERGY RESOURCES AND UTILISATION 83

For a loop made of copper and constant wires, the value of Seebeck coefficient a is 0.04 mV/K.

For a temperature difference of 600 K between the junctions, a voltage of 24 mV will be developed. In

order to achieve higher potential difference many generators have to be connected in parallel.

For increasing the useful power output, parallel and series connections are used.

Parallel connection Series connection

Fig. 2.28. Cascading of Thermoelectric Generators.

2.19.2 Performance

The thermo-elements of a thermoelectric generator are made up of semiconduc-tors p and n

type. Heat is supplied to the hot junction and from the cold junction heat is removed. Both the junctions

are made of copper, see Fig. 2.29.

Let T 1 = source temperature [K]

To = sink temperature [K]

Lp, Ln = length of semiconductor elements [m]

Ap, An = cross-sectional area of thermoelectric elements [m^2 ]

kp, kn = thermal conductivity of elements [W/mK]

ρp, ρn = electric resistivity of elements [Ω-m]

kp, kn = thermal conductivity of elements [W/K] =

kA

L

Rp, Rn = electrical resistance of elements [Ω] =

L

A

ρ

αp, αn = Seebeck coefficient [V/K]

πp, πn = Peltier coefficient [V]

Seebeck coefficient, αp, n =

0

Lt

T

V

∆→ T

∆
∆
Peltier heat,αp, n = πp, n I
When a current (I) flows through the junction of two elements, Peltier heat is produced. This is
called Peltier effect. The Peltier coefficient.

πp, n = ap, n. I

From Ist law of thermodynamics as applied to upper plate (as control volume), the temperature

difference (T 1 – To) will generate a Seebeck voltage, apn (Tl – To). There will be an electrical current I

which will flow through the external load RL.

Fig 2.29. Circuit Diagram of Thermo-

electric Power Generator.

I

Ap

p

I

An

n

T 1 Q 1

RL

VL

I

Qo Qo

Lp Ln