Equivalent circuit models define the entire I-V curve of a cell, module, or array as a continuous function for a given set of operating conditions. One basic equivalent circuit model in common use is the single diode model, which is derived from physical principles (e.g., Gray, 2011)
The governing equation for this equivalent circuit is formulated using Kirchoff’s current law for current.
The five parameters in this equation are primary to all single diode equivalent circuit models:
light current (A)
diode reverse saturation current (A)
series resistance
shunt resistance
diode ideality factor (unitless)
For a photovoltaic module or array comprising cells in series, and assuming all cells are identical and under uniform and equal irradiance and temperature (i.e., generate equal current and voltage)