AN3432 datasheet(6/24 Pages) STMICROELECTRONICS

6 / 24 page

Photocurrent production basics of silicon solar cells

AN3432

6/24

Doc ID 019041 Rev 1

Considering the example of a 190 W solar panel. In standard test conditions (STC)

@Tamb = 25 °C, Voc = 33 V, Isc = 7.89 A:

αIsc = 0.05%/°C; αVoc = -0.4%/°C at an operating temperature range of -40 °C, 85 °C.

That is, the Voc deviation is 26% versus Voc (STC)

Then, Isc max is 3% higher than Isc (STC)

1.4

Hot spot phenomenon

The hot spot phenomenon happens when one cell of the panel is shaded while the others

are illuminated, and when this shaded cell is not able to exhaust its generated power

dissipation.

The shaded cell behaves as a diode polarized in reverse and generates reverse power Ps.

The other cells generate a current that flows through the shaded cell and the load Rload.

Any solar cell has its own critical power dissipation Pc that must not be exceeded and

depends on its cooling and material structures, its area, its maximum operating temperature

and ambient temperature. A shaded cell may be destroyed when its reverse dissipation

exceeds Pc. This is the hot spot.

The manufacturers usually define a breakdown voltage Vc. Its value depends on the solar

cell technology (poly-silicon or mono-silicon) and the manufacturing process.

Voc(-40 °C) = 33 +

Voc(-40 °C) = Vocmax = 41.6 V

33 · -0.4

100

· (-40 -25)

Isc(85 °C) = 7.89 +

Isc(85 °C) = Iscmax = 8.13 A

7.89 · 0.05

100

·(85 - 25)

AN3432 Datasheet(PDF) 6 Page - STMicroelectronics