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Hi everyone.
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Welcome back to PV solar energy course in the last section.
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We already express the output current of the solar sun as a function of voltage.
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As shown in this equation the output current is equal to for the photo current minus
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I0 times exponential of q times V over Kb times T minus one
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this function can be drawn as shown in the right of
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we can express out the power as 
the output power is equal to the output voltage times the output current
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mean the output power will be V times Iphoto minus.
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I0 times exponential of qV over Kb times T minus one.
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This equation expresses the power as a function of voltage mean we can draw the power as a function of
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voltage. the vertical axis on the right shows this scale of power know that if the power on this scale
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is negative it means that the solar cell is generating power but if the power is positive it means that
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the solar cell is consuming power.
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The Blue curve shows that the power is varying with the voltage and it shows that the power has the maximum
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value
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on 
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the PV curve, the black circle point is called the maximum power point and the power generated at this point
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is power maximum
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this graph.
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demonstrates that
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If the solar cell is in open circuit which means it only produce an open circuit voltage with
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no current.
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This power will equal to zero and when the solar cell is short circuit which you mean it only produce
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a current with no voltage the power.
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Is equal to Zero as well.
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If the voltage is as small as then zero which we call the reverse bias the illuminated solar cell doesn't
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generate power but consume power physically.
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Basically the illuminated solar cell under reverse bias will heat up as the voltage is larger than the
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open circuit voltage.
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The Illuminated solar cell is consuming power as well as a solar cell will heat up as well.
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The voltage at the maximum power point is called the Vmp and the current is the maximum power point is
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called Imp which means the maximum power or Pmax is equal to Vmp times.
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Imp or in other ward, the shaded area under the maximum power point in on the lot represents of our
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generic means the Vmp and Imp are the main parameter of any module and the solar energy sizing depends
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on it.
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One of the most important parameter is the fill factor the fill factor is the ratio between the maximum
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power and the product of the short circuit current and the open circuit voltage or in other ward, the ratio 
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between the product of maximum power point current and the maximum power point voltage to the product
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of short circuit current and the open circuit voltage as shown in this equation.
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The fill factor can be easily visualized in all IV curve.
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Basically the fill factor
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is the ratio between the area shaded in purple and the pink area.
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The pink area including the shaded purple area with other world.
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The fill factor is the ratio between the rectangle with the side of the Vmp and Imp and the area with
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the side of open circuit voltage and short circuit current.
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This means that we can express the maximum power density as a product of fill factor with the open circuit
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voltage and short circuit current.
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It implies that it is impossible for solar cell to have a fill factor equal to one 
means the fill factor
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will always be less than 1 in that case.
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the I V curve should have the shape of rectangle and it's impossible.