Describe and draw the current-voltage (V-I) characteristics of a PV cell.
A photovoltaic (PV) cell is a device that converts sunlight directly into electricity through the photovoltaic effect. The current-voltage (V-I) characteristics of a PV cell describes the relationship between the current flowing through the cell and the voltage applied across it.
The V-I characteristics of a typical PV cell can be represented by the following graph:
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Current (I) ----| \ ___
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|____________/
Voltage (V)
In this graph, the x-axis represents the voltage (V), and the y-axis represents the current (I).
Initially, with zero or low external voltage applied, the current is low, and the voltage is close to zero. As the voltage across the cell increases, the current also increases, following an exponential curve. Once a certain voltage threshold called the open-circuit voltage (Voc) is reached, the current begins to increase more linearly.
The point where the current reaches its maximum value is called the short-circuit current (Isc). At this point, the voltage across the cell is almost zero, as the current flows easily through the circuit without any resistance from an external load.
As the voltage increases beyond the short-circuit point, the current starts decreasing gradually due to the internal resistance of the PV cell. At a certain voltage called the maximum power point (Vmp), the product of current and voltage (power) is maximized, representing the maximum output power that can be obtained from the PV cell.
Beyond the maximum power point, the current decreases more rapidly, and the curve gradually flattens as the cell approaches its saturation point, where the current tends to stabilize at a minimum value and the voltage reaches its peak value called the saturation voltage (Vsat).
It is important to note that the slope of the V-I curve may vary depending on factors such as temperature, sunlight intensity, and the characteristic properties of the PV cell itself.