Solar cells today are mostly made of silicon, one of the most common elements on
Earth.
The crystalline silicon solar cell was one of the first types to be developed and it is still the
most
common type in use today. They do not pollute the atmosphere and they leave behind no
harmful
waste products. Photovoltaic cells work effectively even in cloudy weather and unlike
solar
heaters, are more efficient at low temperatures. They do their job silently and there are no
moving parts to wear out. It is no wonder that one marvels on how such a device would
function.
To understand how a solar cell works, it is necessary to go back to some basic atomic
concepts. In the simplest model of the atom, electrons orbit a central nucleus, composed
of
protons and neutrons. each electron carries one negative charge and each proton one
positive
charge. Neutrons carry no charge.
Photovoltaic cells produce electricity directly fr...
Electric Vehicle Charging Station
Smart Car: White and green electric car charging -...Every atom has the same number of electrons as there
are
protons, so, on the whole, it is electrically neutral. The electrons have discrete kinetic
energy
levels, which increase with the orbital radius. When atoms bond together to form a solid,
the
electron energy levels merge into bands. In electrical conductors, these bands are
continuous but
in insulators and semiconductors there is an 'energy gap', in which no electron orbits can
exist,
between the inner valence band and outer conduction band [Book 1]. Valence electrons
help to
bind together the atoms in a solid by orbiting 2 adjacent nucleii, while conduction
electrons,
being less closely bound to the nucleii, are free to move in response to an applied voltage
or
electric field. The fewer conduction electrons there are, the higher the electrical resistivity
of
the material.
In semiconductors, the materials from which solar sells are made, the energy...