Environmental Engineering Reference
In-Depth Information
The photovoltaic effect is the basic physical process through which a PV
cell converts sunlight into electricity. Sunlight is composed of photons (like
energy accumulations), or particles of solar energy. These photons contain
various amounts of energy corresponding to the different wavelengths of the
solar spectrum. When photons hit a PV electricity. (When this happens del),
the energy of the photon is transferred to an electron in an atom of the cell
(usually silicon atoms). The electron is able to escape from its normal position
associated in the atom to become part of the current in an electrical circuit.[1]
To produce the electric field within a PV cell, the manufacturers create a
junction of two different semiconductors (types P and N). The most common
way of making P or N type silicon material is adding an element that has an
extra electron or has a deficit of an electron. Silicon is the most common
material used in manufacturing process of photovoltaic cells. Silicon atoms
have 14 electrons, where the four electrons in the last layer are called valence
electrons. In a crystal solid, each silicon atom normally shares one of its four
valence electrons in a covalent junction with another silicon atom. The silicon
crystal molecule is formed of 5 silicon atoms in a covalent junction [2].
The process of doping introduces an atom of another element into the
silicon crystal to alter its electrical properties. The element used for doping has
three or five valence electrons. Usually Phosphorus is used to make the N type
(Phosphorus has 5 valence electrons) and Boron the P type (Boron has 3
valence electrons). In a polycrystalline thin-film cell the top layer is made of a
different semiconductor material than the bottom semiconductor layer [3].
3.3.2. Photo-Voltaic Power Plant
The PV industry is rapidly maturing because of worldwide environmental
concerns and its energy production potential due to the widely available free
solar resource. The industry is in a race to achieve grid parity (PV energy costs
equal to conventional utility costs) and increase competitiveness in the energy
markets.
3.3.2.1. Photo-Modules
A number of solar cells electrically connected to each other and mounted
in a support structure are called a photovoltaic module. Modules are designed
to supply electricity at a certain DC voltages such as 12, 24 or 48 volts. The
current produced is directly dependent on how much light hits the module.
Multiple modules can be wired together to form an array. A larger area of a
