Power Plant Engineering

NON-CONVENTIONAL ENERGY RESOURCES AND UTILISATION 77

Polarization is internal chemical, electrical, thermal effect within the fuel cell resulting in inef-

ficiencies. Polarization the cause of internal energy loss and is measured by in terms of polarization

voltage Vp.

Vp = vo – vc

VP = Polarization voltage of the cell = Voltage Drop

= No load voltage Vo – On load voltage V.

0

0.1

0

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.2

A B C

∆Vp

Vc

Vo

Cell Voltage V

c

Current Density Id
Fig. 2.22. Polarisation curve.
As the load on the cell (Is × A = I) increases, the internal electro-chemical reactions trying to
oppose the cause also increase. The internal losses increase and the terminal voltage Vc drops. These
internal losses and inefficiencies increasing with current are called Polarization. The drop in voltage Vp
is called Polarization Voltage VP.
Power per Cell Pc,
Power = Voltage × Current
Pc = Vc × 4
The power of a cell increase with the increase in current density, and reaches a saturation point
at due to polarization effects.

(^) 0.20.4
0.6
0.8
1.0
1.2
1.4
(^01000) 2000 3000 4000 5000 6000 7000
Power Density (kW/m )
2
Current Density (A/m )^2 Id
Power
Voltage
0
1
2
3
Cell Voltage (Volts) V
c
Fig. 2.23. Power-Current Density Curve.