To begin developing a solar inverter system, you first need to understand the different characteristics of solar cells (PV batteries). A PV battery is a semiconductor device whose electrical properties are similar to those of a diode. But a PV battery is a source of electricity that becomes a current source when exposed to light, such as sunlight. The most common technologies at present are monocrystalline silicon modules and polysilicon modules.
RP and Rs are parasitic resistors, which are ideally infinite and zero, respectively. The performance of the PV battery varies depending on its size or the type of load it is connected to, as well as the intensity (illumination) of the sunlight.
The characteristics of the PV battery are described by different operating currents and voltages in different environments. When the battery is exposed to sunlight but is not connected to any load, no current passes through the battery, and the voltage of the PV battery reaches its maximum value. This is called Open circuit voltage (VOC). When the battery has a load, an electric current passes through the circuit, causing the voltage at both ends of the battery to start to drop. When two terminals are directly connected and the voltage is zero, the maximum current flowing through the battery can be determined.
This is called short-circuit current (ISC). Light intensity and temperature can significantly affect the operating characteristics of PV batteries. The current is proportional to the intensity of light, but the change of illumination has little effect on the operating voltage. However, the operating voltage is affected by temperature. An increase in the battery temperature reduces the operating voltage, but has little effect on the generated current.
The following figure illustrates the effect of temperature and illumination on the PV module. The influence of the change of illumination intensity on the output power of the battery is greater than that of the temperature change. This applies to all commonly used PV materials. The important result of the combination of these two effects is that the power of the PV battery decreases with the decrease of illumination intensity and/or the increase of temperature.