Photoelectric Effect

In 1839, a French physicist Edmund Becquerel proposed that few materials have the ability to produce electricity when exposed to sunlight. But Albert Einstein explained the photoelectric effect and the nature of light in 1905 [2]. Photoelectric effect state that when photons or sunlight strikes to a metal surface flow of electrons will take place. Later photoelectric effect became the basic principle for the technology of photovoltaic power generation. The first PV module was manufactured by Bell laboratories in 1954 [3].

3.1.1 PHOTVOLTAIC ARRANGEMENT

A photovoltaic energy system is mainly powered by solar energy. The configuration of PV system is manifested in figure 3.1.

It contains PV modules or arrays, which convert solar energy in the

PV cells are basically made up of a PN junction fabricated in a thin wafer or layer of semiconductor (usually silicon). To understand the electronic behavior of a solar cell, it is useful to create a model which is electrically equivalent, and is based on discrete electrical components whose behavior is well known. An ideal solar cell may be modeled by a current source in parallel with a diode; in practice no solar cell is ideal, so a shunt resistance (RSH) and a series resistance (RS) component are added to the model. The resulting equivalent circuit and the schematic representation of a solar cell are shown in figure 3.1

Photoelectric effect can be defined as a phenomenon in which an electron gets ejected from the conduction band as a consequence of the absorption of sunlight of a certain wavelength by a material either metallic, non-metallic, solids, liquids or gases[4]. The incidence of light on the cell generates charge carriers that originate an electric current if the cell is short circuited. Charges are generated when the energy of the incident photon is sufficient to detach the covalent electrons of the semiconductor—this phenomenon depends on the semiconductor material and on the wavelength of the incident light. Basically, the PV phenomenon may be described as the absorption of solar radiation, the generation and transport of free carriers at the p–n junction, and the collection of these electric charges at the terminals of the PV device