Saturday, August 04, 2012

SOLAR CELL

solar cell is also called as photovoltaic cell is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric cell when exposed to light, can generate and support an electric current without being attached to any external voltage source.



Basic structure of silicon based solar cell




Photovoltaics
 is the field of technology and research related to the practical application of photovoltaic cells in producing electricity from light, it is often used specifically to the generation of electricity from sunlight.

The operation of a photovoltaic(PV) cell requires 3 basic attributes:
(1) The absorption of light, generating either electron-hole pairs or excitons
(2) The separation of various types of charge carriers
(3) The separate extraction of those carriers to an external circuit.


The solar cell works in three steps:

  1. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon.
  2. Electrons (negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel the potential and this electricity is captured.
  3.  Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.
An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.


The efficiency of a solar cell may be broken down into reflectance efficiency, thermodynamic efficiency, charge carrier separation efficiency and conductive efficiency. The overall efficiency is the product of each of these individual efficiencies.



Silicon based solar cell


The silicon solar cell


This diagram shows a typical crystalline silicon solar cell. The electrical current generated in the semiconductor is extracted by contacts to the front and rear of the cell.

The top contact structure which must allow light to pass through is made in the form of widely-spaced thin metal strips it is also called as fingers that supply current to a larger bus bar.

The cell is covered with a thin layer of dielectric material - the anti-reflection coating, ARC - to minimise light reflection from the top surface.

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