November 24, 2009
By: Admin
Category: Solar Cells
What Does Solar Cell Mean?
You may have seen a calculator that has a solar cell? calculator that does not need batteries, and in some cases do not even have the off button. As long as you have enough light, so the calculator can be on at any time and forever. You may have seen larger solar panels, such as in housing or traffic lights, haven’t you? In this article I will review how solar cell work so it can deliver the energy and drive an electronic device.
Today the demand for electricity has become a major requirement in all corners. The presence of power plants sometimes do not solve the need for electricity especially in remote areas where the terrain is always an excuse. Here an alternative energy that can be easily found in nature and can be used as an alternative free energy replacing conventional electricity, because it can turn on household electronics such as televisions, radios and lights.
Solar cells made from pieces of a very small silicon coated with special chemicals to form the basis of solar cells. Solar cells generally have a minimum thickness of 0.3 mm is made from semiconductor materials incision with positive and negative poles. Each solar cell produces usually voltage 0.5 volts. Solar cells is an active element (semiconductor) that utilizes photovoltaic effect to transform solar energy into electrical energy.
Solar cells contain a connection (junction) between two thin layers made of semiconductor materials, each of which is known as a semiconductor type “P” (positive) and semiconductor type “N” (negative).
N-type semiconductor made of silicon crystals and there are also some other materials (typically phosphorus) within the limits that these materials can provide an excess of free electrons.
Electrons are sub atomic particles are negatively charged, so that the silicon alloy in this case known as N-type semiconductor (Negative). P-type semiconductor made of silicon crystal in which there is a small amount of other material (typically boron) which caused the shortage of material free electrons. Lack or loss of electrons is called a hole. Because there is no or lack of electrons electrically negative charged then the silicon alloys in this case as a semiconductor type-P (Positive).
Composition of a solar cell, the same as a diode, consisting of two layers, called PN junction. PN junction obtained by staining a pure semiconductor silicon (valence 4) with the impurity valence 3 on the left side, and one on the right impurity stained with valence 5.
The effect of the electric field in a PV cell
Operation of a PV cell
Basic structure of a generic silicon PV cell
Thus formed on the left side that is not pure silicon again and called P type silicon, while the right side is called silicon type N. In the pure silicon there are two kinds of electrical charge carriers are balanced. Positive electric charge carriers called holes, while the negative are called electrons. After a desecration process, in the P type silicon formed holes (positive charge carriers) in a very large number compared with the electron. Therefore, in the P type silicon holes are majority charge carriers, while the electrons are minority carriers. Conversely, in the N type silicon is formed of electrons in a very large number so-called majority carriers, and holes called minority carriers.
In the silicon rod there was interaction between the P and the N. Therefore called the PN junction. When present, the P associated with the positive pole of a battery, while the negative polar associated with the N, then there is a relationship called “forward bias”.
Under forward bias, electrical currents arise in a series due to both types of charge carriers. So the electric current flowing in the PN junction is caused by the movement of electron and the movement of holes. An electric current is flowing in the direction of holes movement, but opposite direction with the movement of electrons. Just to further explain, electrons moving in the conductor material can lead to electrical energy. And electrical energy is called as an electric current that flows in the opposite direction to the movement of electrons.
But, if the P associated with negative pole of batteries and the N associated with positive pole, then now formed a relationship called “reverse bias”. In these circumstances, the hole (positive charge carriers) can be connected directly to the positive pole, while the electrons are also directly to the positive pole. So, clearly in the PN junction there is no movement of majority charge carriers either the holes or electrons. Meanwhile, the minority charge carriers (electrons) in the part P moves trying to reach the positive pole of the batteries. Similarly, the minority charge carriers (holes) in the N also moved to reach the negative pole. Therefore, in a state of reverse bias, in the PN junction there is also output current even in very small amounts (micro amperes). This current is often called the reverse saturation current or leakage current.
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Anything interesting in reverse bias. When the temperature of PN junction raised they will be able to enlarge leakage current. Means that if given the energy (heat), the minority charge carriers in the PN junction grows. Because the light is one form of energy, so if there is light that hit a PN junction may also produce enough energy to generate charge carriers. This symptoms are called photoconductive. Based on the photoconductive symptoms made of photodiode electronic components from PN junction.
In reverse bias, with increasing intensity of light that hit photodiode can increase the level of leakage current. Leakage currents can also be enlarged by increasing the battery voltage (reverse voltage), but the addition of leakage currents were not significant. When the batteries in the reverse bias circuit is removed and replaced with a load of resistance, the provision of light that can cause charge carriers both holes and electrons. If the illumination light is increased, current output was greater. Such symptoms are called photovoltaic. Light can provide enough energy to enlarge the number of holes in the P and the number of electrons on the N. Based on the symptoms of this photovoltaic electronic components can be created photovoltaic cell. Because usually the sun as a source of light, the photovoltaic cell is also called the solar cell (solar cells) or a solar energy converter.
So the solar cell is essentially a large photo diode and designed by referring to the photovoltaic symptoms so that could produce the greatest possible power. P type silicon is the very thin surface layer so that light can penetrate directly reach the junction. Part P is given ring-shaped nickel layer, as a positive output terminal. Under the P is the N type that is coated with nickel as well as the negative output terminal.
To obtain a large enough power required much of solar cells. Usually, solar cells arranged form the shape of the panel, and is called the photovoltaic panels (PV). PV as a source of electric power was first used in satellites. Then PV as an energy source for cars, so there are solar electric car. Now, in foreign countries, PV has started to be used as a roof or wall of the house. Sanyo has made even a semi-transparent PV that can be used as a substitute for glass.
After getting the output of the solar cell is a direct electrical current can be used to load utilized. But also the electric current can be used as a charge stored by the battery to be used when needed, especially at night because there was no sun.
If the solar cell is used for storage into the battery, then the resulting voltage magnitude must be above the battery specification. For example the battery used is 12 volts, the voltage produced by solar cell must be above 12 volts in order to perform charging.
We recommend that before carrying out the charging battery should be empty because the incoming flow will be filled with the maximum. The unit capacity of a battery is the Ampere-hour (Ah) and these characteristics are usually found on the label of a battery. For example a battery with 10 Ah capacity will fill up for 10 hours with the solar cell output currents of 1 Ampere.
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