21-01-2013, 03:53 PM
SeOLAR ENERGY
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MANUFACTURING OF SOLAR CELL BY CHEMICAL VAPOUR DEPOSITION
Chemical Vapor Deposition is the formation of a
non-volatile solid film on a substrate by the reaction
of vapor phase chemicals (reactants) that contain the
required constituents.
The reactant gases are introduced into a reaction
chamber and are decomposed and reacted at heated surface to form the thin film.
HOT WIRE CHEMICAL VAPOUR DEPOSIION TECHNIQUE
Silicon thin films grown by Hot-Wire CVD were first produced by Wiesmann in 1979.
This technique is improved by Matsumura at the Japan Advance Institute of Science and Technology (JAIST) in 1985.
Later, Mahan in the year 1991 reported that the production of silicon thin films are improved by using hydrogen contents.
Manufacturing process:
Silane (SiH4), or a mixture of silane and hydrogen (SiH4/H2), is introduced into the vacuum chamber, where a filament is resistively heated up to temperatures between 1500-2000ºC.
Molecules impinging on the hot filament are dissociated by means of a catalytic process, after which mainly atomic hydrogen (H) and atomic silicon (Si) are formed.
Chemical reactions occuring on hot filament are SiH4+ hot filament→ -SiH3+H
SiH4+ hot filament→ Si+4H
Solar module designing
The individual cells, each of 10 sq. cm to 100 sq. cm area are inter connected in series and parallel pattern and one module contains about 20 to 40 cells.
Each module may have 3 to 5 columns of cells in series in such a way that one gets desired output.
Since the cells are thin and brittle and electrical connection are soft, they need protection from weather and moisture.
Hence module is encapsulated with a transparent at the top. This encapsulation provides mechanical strength to the cell and also protects the cells from dirt, dust and moisture penetration.
Solar Panel Tilt Angle
The sun moves across the sky from east to west. Solar panels are most effective when they are positioned facing the sun at a perpendicular angle at noon.
Some important angles measured for positioning the solar panel are
1. The declination is the angular position of the sun with respect to the plane of the equator. Its value is given by