Ohm's Law is a fundamental principle in electrical engineering that relates the voltage, current, and resistance in an electrical circuit. It states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points, with the constant of proportionality being the resistance (R) of the conductor. Mathematically, Ohm's Law is expressed as:
V = I * R
When it comes to photovoltaic (PV) cells and solar panels, Ohm's Law is essential in understanding their behavior and characteristics, particularly in a specific operating condition called the "I-V curve" (current-voltage curve). The I-V curve of a photovoltaic device describes how its current output varies with different voltage levels.
Voltage (V): In the context of PV cells and solar panels, voltage refers to the electric potential generated by the cells when exposed to light. When photons from sunlight strike the semiconductor material of a PV cell, they create an electric field that causes electrons to move, generating a voltage across the cell.
Current (I): The current represents the flow of electrons in the circuit, and in the case of PV cells, it is the electrical current produced when electrons are set in motion due to the absorbed photons. This current can be used to power electrical loads or charge batteries.
Resistance (R): The resistance in the PV cell and solar panel system primarily comes from the internal resistance of the cell and the external load connected to the cell. The internal resistance is due to the properties of the semiconductor material used in the cell, and the external resistance is determined by the connected electrical load.
So, how does Ohm's Law apply to the behavior of photovoltaic cells and solar panels?
In the dark: When a photovoltaic cell is not exposed to sunlight (in the dark), it behaves like a simple resistor. In this case, Ohm's Law is applied to calculate the voltage across the cell for a given current or vice versa, based on the cell's resistance.
Under illumination: When the photovoltaic cell is exposed to light and generating power, its behavior becomes more complex. The current output depends on the voltage applied across the cell and the light intensity (irradiance) it receives. As the load resistance changes, the voltage and current will vary according to the I-V curve of the cell. Ohm's Law still applies locally to small segments of the curve, but the relationship between voltage and current becomes nonlinear due to the nature of the semiconductor material and the physical processes involved.
Overall, Ohm's Law provides a useful starting point to understand the behavior of photovoltaic cells and solar panels, but for a comprehensive understanding, more complex electrical models and equations are used to describe their behavior under different operating conditions and loads. These models often include parameters like the diode equation and various loss mechanisms to accurately predict the performance of PV systems.