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Solar Panels

The devices used in photovoltaic conversion are called solar panels. When solar radiation falls on solar panels, it is converted directly into dc current. Main advantages associated with solar panels are that they have no moving parts, require little maintenance, and work quite good with beam or diffuse solar radiation. Also they are readily adapted for varying power requirements because a cell is like a ‘building block’. The main factors limiting their use in the past was that they ware still rather costly and that there is was very little economy associated with the magnitude of power generated in an installation. However, significant developments have been made in the last few years. New types of solar panels have been developed, innovative manufacturing processes introduced, conversion efficiencies of existing types of solar panels increased, manufacturing and installation costs reduced and the volume of production steadily increased. The present annual world production of solar panels or photovoltaic panels is already around 60 MWp, while production in India is around 1.5 MWp. As a result of these developments, solar panels are now being used extensively in many consumer products and appliances, and it is possible that in the future they may become one of the most important sources of free renewable solar energy.

The first solar panels were made in the 1950’s from silicon crystal. And even today silicon is the material mostly used for making solar panels. Single crystal silicon cells are thin wafers about 300 um thick, sliced from a single crystal of p-type doped silicon. Metal electrodes made from a Ti-Ag solder are attached to the front and back side of the each solar cell. On the front side of solar panel, the metal electrode is in the grid with formation which permits the sunlight to go through, while on the bottom side, the metal electrode covers the surface completely. An antireflection coating is added on the top of solar panels, with thickness of just 0.1 um, and a thin transparent sheet is also put on the top surface to complete the assembly. In order to obtain high currents and voltages in solar panels, solar cells are fixed side by on a back-up board and connected all together to form a solar module. Apart from single crystal silicon, solar cells are now also made from polycrystalline silicon and amorphous silicon.

Two important steps are involved in an inner working of a solar panel.
1.) Creation of positive and negative charge (called electron-hole pairs) in the solar panel by absorbed solar energy.
2.) Separation of the two charges by a potential gradient within the solar cell. For the first step to occur, the solar panel must be made of an energy absorbent material to absorb solar energy associated with the photons of sunlight.
Materials suitable for absorbing the solar energy of the photons are semiconductors like silicon, cadmium sulphide, gallium arsenide,..

In conclusion in spite of the past high initial cost, photovoltaic solar panel systems are now being used increasingly to supply electricity in remote villages for electrification and to pump water and irrigation as well in big city centers and households for consumer products and appliances.