What is Photovoltaic Effect
The photovoltaic effect is the basic physical process through which a PV cell converts sunlight into electricity Sunlight is composed of photons--packets of solar energy. These photons contain different amounts of energy that correspond to the different wavelengths of the solar spectrum.
In a photovoltaic cell, the photons of the incidental solar radiation break the ties of the semiconductor's electrons, thus allowing the electrons to move freely in the semiconductor. The positions left free by the electrons act as positive charges and take the name of "holes". The photovoltaic cells generally consist of two thin regions, one above the other, each with specially added impurities called dopants. The result is that one region is of "type n", with an excess of electrons (negative), while the other is of "type p", with an excess of positive holes. This 2-region structure, called a p-n junction, produces an internal electric field. When the photons create free electrons and holes in proximity to the p-n junction, the internal electric field makes them move in opposite directions: the electrons move towards the side n and the holes move towards the side p.
So a tension (electromotive force, e.m.f.) is generated between the p and n regions, with p positive and n negative. Using wires, the side p and n are connected to a "load", e.g. a light bulb, and an electric current runs through the load.
Crystalline form of is the material most commonly used to make photovoltaic cells, which typically measure 12cm x 12cm. The cells are assembled together to obtain photovoltaic modules with a surface of approximately half a metre squared (Fig. 2).
Other types of cells are those in polycrystalline and amorphous silicon, which are not as efficient, and those with more than two junctions, which are more efficient but also more expensive. At the moment considerable efforts are being made to develop plastic cells with polymers, which should
have lower costs but also reduced efficiency.
Photovoltaic systems are made up of many panels connected in series and in parallel; this modularity permits the systems to be highly flexible. A photovoltaic system can be a stand alone
system or a grid connected) system. In both cases it is necessary to convert the continuous electric
current supplied by the cells into alternate current through the use of an inverter .
Figure 0-1.2: Photovoltaic Effect
The energy of a photon is transferred to an
electron in an atom of the semiconductor device. With
its newfound energy, the electron is able to escape from its normal position associated with a single atom in the semiconductor to become part of the current in an electrical circuit. Special electrical properties of the PV cell a built-in electric field provide the voltage needed to drive the current
through an external load.
Solar Cell is capable of directly powering any device, but since Solar Cell is only capable of providing
Energy during Day, at night a form of battery backup is required. For this purpose we use a battery.