Q14Wind and Solar Energy Systems

V-I Characteristics of PV Cell, Module, and Array

A photovoltaic cell's I-V (current-voltage) characteristic under illumination shows a nearly constant current region at low voltage (limited by the photo-generated current, roughly proportional to incident irradiance), transitioning near the 'knee' of the curve into a nearly constant voltage region at higher voltage (limited by the cell's open-circuit voltage), with the Maximum Power Point (MPP), the operating point maximizing the product of voltage and current, located at this knee. Short-circuit current (Isc) is measured at V=0, and open-circuit voltage (Voc) is measured at I=0, both key cell parameters.

A PV module is formed by connecting multiple cells in series (voltages add while current remains that of a single cell) to reach a practical output voltage (commonly 12V, 24V, or higher nominal ratings), extending the I-V curve's voltage axis proportionally to the number of series cells while keeping the current axis unchanged. A PV array is formed by further combining multiple modules in series (extending voltage further) and parallel (extending current, since parallel branches' currents add at a given voltage), allowing the same fundamental I-V curve shape to be scaled to whatever total voltage and current rating a specific installation requires, from a small residential rooftop system to a utility-scale solar farm.

This modular series-parallel combination capability is precisely why photovoltaic systems can be economically deployed across such a wide range of scales, from a single small panel powering a remote sensor to vast utility-scale solar farms comprising hundreds of thousands of individual cells, all built from the same fundamental cell-level I-V characteristic scaled appropriately through series and parallel interconnection.