Hi everyone. 1
Welcome back to PV solar energy course in the last section. 2
We already express the output current of the solar sun as a function of voltage. 3
As shown in this equation the output current is equal to for the photo current minus 4
I0 times exponential of q times V over Kb times T minus one 5
this function can be drawn as shown in the right of 6
we can express out the power as the output power is equal to the output voltage times the output current 7
mean the output power will be V times Iphoto minus. 8
I0 times exponential of qV over Kb times T minus one. 9
This equation expresses the power as a function of voltage mean we can draw the power as a function of 10
voltage. the vertical axis on the right shows this scale of power know that if the power on this scale 11
is negative it means that the solar cell is generating power but if the power is positive it means that 12
the solar cell is consuming power. 13
The Blue curve shows that the power is varying with the voltage and it shows that the power has the maximum 14
value 15
on 16
the PV curve, the black circle point is called the maximum power point and the power generated at this point 17
is power maximum 18
this graph. 19
demonstrates that 20
If the solar cell is in open circuit which means it only produce an open circuit voltage with 21
no current. 22
This power will equal to zero and when the solar cell is short circuit which you mean it only produce 23
a current with no voltage the power. 24
Is equal to Zero as well. 25
If the voltage is as small as then zero which we call the reverse bias the illuminated solar cell doesn't 26
generate power but consume power physically. 27
Basically the illuminated solar cell under reverse bias will heat up as the voltage is larger than the 28
open circuit voltage. 29
The Illuminated solar cell is consuming power as well as a solar cell will heat up as well. 30
The voltage at the maximum power point is called the Vmp and the current is the maximum power point is 31
called Imp which means the maximum power or Pmax is equal to Vmp times. 32
Imp or in other ward, the shaded area under the maximum power point in on the lot represents of our 33
generic means the Vmp and Imp are the main parameter of any module and the solar energy sizing depends 34
on it. 35
One of the most important parameter is the fill factor the fill factor is the ratio between the maximum 36
power and the product of the short circuit current and the open circuit voltage or in other ward, the ratio 37
between the product of maximum power point current and the maximum power point voltage to the product 38
of short circuit current and the open circuit voltage as shown in this equation. 39
The fill factor can be easily visualized in all IV curve. 40
Basically the fill factor 41
is the ratio between the area shaded in purple and the pink area. 42
The pink area including the shaded purple area with other world. 43
The fill factor is the ratio between the rectangle with the side of the Vmp and Imp and the area with 44
the side of open circuit voltage and short circuit current. 45
This means that we can express the maximum power density as a product of fill factor with the open circuit 46
voltage and short circuit current. 47
It implies that it is impossible for solar cell to have a fill factor equal to one means the fill factor 48
will always be less than 1 in that case. 49
the I V curve should have the shape of rectangle and it's impossible.