**2. Basic operational principles**

Direct use of solar energy can be performed in essentially two different ways: (1) the transformation of sunlight directly into electricity in semiconducting devices that are more popularly known as solar cells; and (2) the collection of heat in solar collectors. The transformation of solar radiation into electrical current is referred to as "photovoltaic energy conversion" (PV), and this is the meaning of the word "photovoltaic energy conversion."

The photovoltaic effect is responsible for this phenomenon. The phenomena that can cause a potential difference to occur at the interface of two materials that are not identical is referred to as the "photovoltaic effect," and it is described using the word "photovoltaic effect." As a result, the entire field that studies the conversion of solar energy into electricity is referred to as "photovoltaics," and its acronym stands for "photovoltaic electrics." The term "photovoltaics" comes from the combination of the Greek word for light ("photo") with the Italian name of an early electrical researcher, Alessandro Volta (1745–1827), which is shortened to "Volt." Since most people do not know what the word "photovoltaics" means, the term "solar electricity" has become the most frequent way of referring to PV solar energy.

Three primary processes are necessary for the photovoltaic effect to take place: (1) the generation of charge carriers as a result of photon absorption by the materials comprising a junction; (2) the subsequent separation of the photo-generated charge

carriers within the junction; and (3) the collection of the photo-generated charge carriers at the terminals of the junction.

#### **2.1 History of photovoltaic effect**

The discovery of the photovoltaic phenomenon is attributed to a French physicist named Alexandre Edmond Becquerel in the year 1839. During the course of his experiments using metal electrodes and electrolyte, he noticed that the conductivity increased as the amount of light increased. Willoughby Smith made the discovery that selenium possesses photovoltaic properties in the year 1873. Actually, when a material absorbs light at a frequency over a threshold frequency that varies with the substance, electrons are released. This phenomenon is called the photoelectric effect, and it is closely related to the photovoltaic effect. Taking into account the fact that light is presumed to be made up of individual energy quanta (photons), Albert Einstein was able to explain this phenomenon in 1905. This type of photon's energy can be calculated as *E h* = ν, where h is Planck's constant and ν is the frequency of the light.

In 1921, Albert Einstein published the paper on the photoelectric effect for which he received his sole Nobel Prize. After another decade, the first pure semiconductor was developed in 1931. Solar cells were first used for space applications in the 1950s. In a short amount of time, Hoffman Electronics was able to surpass the previous record for solar cell efficiency, achieving highs of 10 and 14% in the years 1959 and 1960, respectively. The earliest solar cells, which had an efficiency of roughly 8%, were invented in 1957. A short time after that, the first PV cell made of amorphous silicon was developed, and the capacity of PV systems reached 500 kW. This amount continued to rise, reaching its highest point of 21.3 MW in the year 1983. A highconcentrating photovoltaic (PV) facility with a capacity of 175 kilowatts (kW) was finally constructed in the state of Arizona in the United States in the year 2002. A new PV technology efficiency record of 40% was set 4 years later. In 2012, when the global PV capacity hit 100 GW, production prices dropped drastically to \$1.25 per watt. The first solar-powered aircraft completed a global flight in 2016 [3]. The global PV power potential is shown in **Figure 1**. Solar photovoltaic generation will increase by 23 percent, from 156 GWh in 2015 to 821 GWh in 2020, making it the fastest-growing renewable energy source after wind and ahead of hydropower. PV capacity additions experienced an exceptional rise (a record of 134 GW) in China, the US, and Vietnam. Unquestionably, solar PV is moving toward becoming the most affordable choice for producing power globally, and in the years to come, it is anticipated to draw significant investment [4].

### *2.1.1 Construction and working of photovoltaic cell*

Photovoltaic cells are a type of electrical device that are capable of transforming the energy from light into electric current. The solar cell is an example of a photovoltaic cell. This type of cell is often referred to as a PV cell, which is an abbreviation for "photovoltaic cell." A solar cell is composed of its most fundamental component, a diode with a p-n junction. Photoelectric cells, of which solar cells are a type, are devices in which the presence of light causes a change in the electrical properties of the device (such as the current, the voltage, or the resistance). One sort of cell that fits within this category is the solar cell.

In the process of fabricating solar panels, modules that have been constructed from solar cells and then joined together are utilised. These modules are then

**Figure 1.** *Monocrystalline structure.*

incorporated into panels. When producing at their best levels of efficiency, the vast majority of single-junction silicon solar cells have an open-circuit voltage that falls somewhere in the range of 0.5 to 0.6 volts on average. This occurs when the cells are functioning at their optimal levels. This by itself is not a particularly large quantity, but you need to keep in mind that these solar cells are on the diminutive side. An enormous solar panel has the potential to provide a considerable amount of energy that is kind to the environment.
