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Photovoltaic Panels

The photovoltaic panel or solar panel is what most people think of when they use the term solar energy. These panels are generally comprised of several layers. On the top is a protective glass panel and on the bottom is a backing layer of tough metal or ceramic. On the top side, just under the glass panel, is a non-reflective coating that ensures sunlight is not lost to reflection. Just under this are the electrical connections and then finally two layers of a semiconductor. The diagram below is an example of a classic solar panel design. There are variations on the way the layers are constructed, but the general architecture always follows this same pattern.

When solar panels were first invented, they generally harvested less than 6% of the energy they received from the sun. Modern advances, however, have pushed the energy capturing abilities of some solar panels to as high as 29%. Laboratory testing has even produced panels that are 40% efficient, with application to the consumer market only a few years away. There is also ongoing investigation into lens technology that may increase efficiency to 50%. Most solar panels, once installed, harvest around 11 to 15% of the energy available to them due to many factors that affect the efficiency including temperature, angle to the sun, how clean the panel is, and so on.

The Photovoltaic Effect

The semiconductor layers are the active components of a solar panel and they rely on the principle of the photovoltaic effect, which was discovered by Alexandre-Edmond Becquerel in 1839. Becquerel was a French physicist who did a great deal of research in light, electricity, and optics.

In the photovoltaic effect, electrons within a semiconductor can be “detached” from the orbits of their atoms and allowed to flow freely within the material. If there was only one layer of semiconductor, nothing much would happen with the electrons and they would simply resume their positions within the atoms. However, when two dissimilar materials are brought into close contact, one positively charged and one negatively, the negative material will tend to lose electrons and the other will want to gain electrons. However, because they are not in direct contact, the electrons will not be allowed to flow. This will create a voltage difference.

The voltage difference is what drives the electrons. By attaching the two layers together through an external circuit, the electrons can be allowed to move from the negative to the positive. In so doing, they can also be harnessed to do external work in the form of electricity.

The Photoelectric Effect

The photoelectric effect is the underlying physical cause of the photovoltaic effect. When electrons are excited by light, they break free of their orbits and become independent of the atom. This phenomenon was first observed in 1887 by Heinrich Hertz, but it took Albert Einstein in 1905 to completely explain why the photoelectric effect occurs.

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