**3. Partial shading Effect**

PV systems are extremely susceptible to partial shading. On account of various environmental conditions such as rain, clouds, and storms, it is not possible to obtain uniform irradiance at all times. In addition, PV array also suffers shading from nearby buildings and trees. This shading effect leads the PV module to yield less output power [22]. PSCs can lead to the following:


Shading one cell results in a drop of current flowing through it when compared to the unshaded cells of its string. As a result, unshaded cells are forced to carry high current, and shaded cells will be restricted to the string current. This leads to a drop in the output power of the PV string. A bypass diode is connected across the shaded cell string to moderate the effect of shading. Through this, unidirectional flow of current is achieved. Figure 6a,b shows the effect of partial shading on (I–V) and (P–V) characteristics of PV system.

**Figure 6.** Characteristics of (**a**) I–V and (**b**) P–V under PSCs.

## **4. MPPT Algorithms**

Each PV module has a different MPP in different atmospheric conditions. Thus, to extract maximum power from it, MPPT algorithms are used. These algorithms are imposed through electronic converters. Though these techniques enhance the performance of PV system, designers are generally concerned about tracking GMPP under PSCs. These algorithms are implemented through microcontrollers. The duty ratio of the DC converter employed is adjusted by these algorithms after frequent sampling of some PV module parameters. This changes the impedance seen by the PV module, resulting in achieving

maximum power. These MPPT techniques are classified as shown in Figure 7. The following sections explain the basics of these techniques comprehensively, while recent advancements in each are listed in the tables at the end of each classification separately.

**Figure 7.** MPPT Techniques Classifications.
