Photovoltaic Cells

Photovoltaic Cells (Converting Photons to Electrons)

The solar cells that you see on calculators and satellites are also called photovoltaic
(PV) cells, which as the name implies (photo meaning "light" and voltaic meaning
"electricity"), convert sunlight directly into electricity. A module is a group of cells connected
electrically and packaged into a frame (more commonly known as a solar panel).
Photovoltaic cells are made of special materials called semiconductors such as
silicon, which is currently used most commonly. Basically, when light strikes the cell, a
certain portion of it is absorbed within the semiconductor material. This means that the
energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons
loose, allowing them to flow freely.
The solar cell works in three steps:
- Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such
as silicon.
- Electrons (negatively charged) are knocked loose from their atoms, causing an electricpotential
difference. Current starts flowing through the material to cancel the potential and
this electricity is captured. 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.
PV cells also all have one or more electric field that acts to force electrons freed by
light absorption to flow in a certain direction. This flow of electrons is a current, and by
placing metal contacts on the top and bottom of the PV cell, we can draw that current off for
external use, say, to power a calculator. This current, together with the cell's voltage (which is
a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell
can produce.

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