Solar electricity potential in Europe © European Communities

Solar panels Photovoltaic Cells Converting Photons to Electrons

The solar cells that you see on calculators and road sings 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), which can then be grouped into larger solar arrays.

Photovoltaic cells are made of semiconductors such as silicon 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.

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. 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.

An atom of silicon has 14 electrons, arranged in three different shells. The first two shells which hold two and eight electrons respectively are completely full. The outer shell, however, is only half full with just four electrons. A silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms.

Pure crystalline silicon is a poor conductor of electricity because none of its electrons are free to move. The silicon in a solar cell usually has phosphorous mixed in with the silicon atoms. Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbor atoms, It doesn’t form part of a bond, but there is a positive proton in the phosphorous nucleus holding it in place.

The process of adding impurities like phosphorous is called doping the resulting silicon is called N-type (“n” for negative) because of the prevalence of free electrons. N-type doped silicon is a much better conductor than pure silicon.

The other part of a typical solar cell is doped with the element boron, which has only three electrons in its outer shell instead of four, to become P-type silicon. Instead of having free electrons, P-type (“p” for positive) has free openings and carries the opposite (positive) charge.

When light, in the form of photons, hits our solar cell, its energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron. The electron flow provides the current, and the cell’s electric field causes a voltage. With both current and voltage, we have power.

This is a PV system we installed in Co Leitrim its 500w and mounted on a tracker.
The Panels are made by Solara and they use our photo on their web site www.solara.de