A solar panel also known as a photovoltaic panel or photovoltaic module is an assembly of solar cells that are packaged and interconnected sometimes referred to as photovoltaic cells. The words photo and volt are used to mean light and unit of electrical force in that order. Solar panels are used in big and large photovoltaic systems to generate electricity for residential and commercial applications. For maximum amounts of power, several panels are usually installed forming what is commonly referred to as a photovoltaic array. Solar cells were first made in the 19th
century and since then they have grown to become more powerful and today they can convert more than a quarter of the total sunlight that falls on them into electricity. This research paper will explore how solar panels work and also how they convert sunlight into electricity.The main raw material used in the making of solar cells is silicon, an element that is second in abundance in the world. There are three main types of solar cells; the single crystal cells or monocrystalline cells-these were the first generation of solar cells that had excellent rates of conversion but expensive in their making; polycrystalline cells which were cheap in making with moderate conversion rates; and the amorphous cells that are recent with low costs of production but unfortunately having low efficiency rates. They use very thin layers of silicon as compared to the other two making it suitable for making more portable and affordable consumer goods like watches and calculators. They work better with high temperatures and also react favorably to diffuse and fluorescent light. Most commonly made solar panels are for applications of 12 volts. This needs about 24 cells to produce this voltage, sunshine into electricity (John 1981 p. 76).Solar panels usually consist of several solar cells that are connected either in series or in parallel, this depends on the current and voltage needs of the application. It is the cells that usually absorb sunlight and convert it into electrical energy that is then passed to the control unit for use. Different methods are used in the production of voltaic cells. These include the use of crystalline silicon in ingot form, direct growth of silicon sheets and the thin-film technology. A variety of semiconductor materials can be used in making of solar cells but the most common one is silicon. Small quantities of phosphorus and boron are usually doped with several layers of silicon. The process where by impurities is added to pure semiconductors to come up with what are called intrinsic semiconductors is what is referred to as doping. These impurities are the ones that give the pure material the positive and negative characters necessary for conduction of electric currents (Gunther 1996 p. 77-81).The Mechanism of a Solar Panel
To better understand how this works, we will look at the chemical composition of these impurities and the common semiconductor, silicon. Silicon being a group four element shows that it has room for occupying four more electrons. Two silicon atoms can combine to create stronger bonds by sharing their electrons. The material formed will have no positive or negative bonds, and it is the one that is used to form plates for solar panels. The absence of positive or negative charges renders it impossible for pure silicon plates to generate electricity in solar panels. These panels are therefore created from a combination of silicon and other elements that have positive or negative charges. To get a negatively charged plate, an element like phosphorus that has five extra electrons to offer is used. For a positive plate, boron which has only three electrons to offer can be used. Where these impurities meet with silicon, a junction is formed which becomes a barrier that makes it harder for electrons on the N- side to cross over to the P-side. This creates an equilibrium bringing about an electric field that separates the two sides. The electric field acts like a diode that allows or pushes electrons to flow to the N side from the P side and not vice versa. When photons or light energy hit the solar cell, it breaks the electron hole pairs apart. Each photon usually frees one electron with the same energy causing a free hole to be created. If this occurs close to the electric field or the free electron and the free hole wanders into the range of influence of the electric field, then the electron and the free hole will be send to the N side and P side respectively by the field. This destabilizes the electrical neutrality that existed whereby if an external path of current is provided, then the electrons flow to unite with the holes on the P side sent there by the electric field. The flow of electrons is what produces current and at the same time the cell's electric field causes a voltage. These two brings about power which is the main product from the solar panel (Pollick 2010, p. 7).Whenever photons or energy in terms of light hit the cell, there is a release of electrons that have enough energy that overcomes the electric field, enabling them to move into an external circuit through the silicon. Individual cells in a photovoltaic module act like batteries, when the cell is illuminated; a voltage develops accompanied with a current. A cell can produce a current of up to 0.46V while the current depends on the intensity of illumination. The current output of each cell depends on its size, for instance a 4"x4" cell can give a current output of 3.2A when illuminated with 1000W/m2
. These cells can be combined in parallel or series depending on the needed current values and output voltage. In parallel a required amount of current source capability is provided and in series the desired output voltage is achieved. To avoid overheating of cells especially in cases of partial shading, diodes are included to prevent a reduction in cell operating efficiency (Schiller 2009 p. 142).
Solar Panel Performance
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The performance of any particular cell varies with solar intensity and temperature and it is under these conditions that all the characteristics of performance are measured. For example, the power that the sun can supply per unit area is called the radiation intensity. The distribution of the different colors that make up sunlight is referred to as spectral distribution the amount of solar energy received by a panel and converted into electricity by a panel is referred to as cell efficiency. To fully understand how solar panels work, one has to also look at the factors that affect this performance. These are put into two groups; the internal and the external factors. Effect of the manufacturing process, semiconductor process and the purity of the material constitute the internal factors. These can only be altered by the manufacturers. External factors on the other hand include; the cell temperature and the intensity of the sun. These can be adjusted to optimize cell performance. Amount of current produced by solar cell is directly affected by irradiation although this varies from product to product. Maximum current is reached as irradiation increases. This depends largely on the geographical area in which the application is located and this varies extensively. Another factor that affects the performance of solar cells is temperature; more power is generated as the cell gets cooler. This also varies with products. Cooling the photovoltaic module enhances cell performance. To enhance the performance of photovoltaic cells several modifications can be made to their systems. There are basically two modifications that can be made depending on the external factors that affect their performance. First as it was earlier noted, a reduction in cell temperature enhances its performance. But first one has to understand how the temperatures rose in the first place. Thermal radiation is the main mode of heat transfer in this case. This depends largely on the surface temperatures. Doing this is not easy because any attempt at reducing the effect of heating will reduce irradiation that is needed for the working of the solar cell. Therefore this calls for a carefully chosen cooling system that will address the problem. An increase in irradiation is another measure that can be taken to enhance cell performance. Increase in irradiation is proportional to increase in current ( Edelson 1992, p.95).Solar Panel Output
The power output of a solar panel is the most important variable that should be considered by any one planning to install a photovoltaic cell. This in turn depends on four factors which are; the peak power of the solar panel usually measured in peak-watts-the number of watts a solar panel can produce in optimal conditions; the intensity of light-influenced by the weather conditions, the daylight hours and the distance of the sun from the panel; the number of exposure hours of the solar panel to the sun's light; and the angle at which the panel is exposed to the sun. Because silicon is a shine material, to enhance its efficiency an antireflective should be applied to reduce the loss of photons through reflection. A final measure that is taken before using a solar panel is the installation of a protective gadget around it; this can be a glass plate cover, Solar electricity by Markvart (2000 p. 74)Solar radiations from the sun are collected by solar panels which convert them into electrical energy. These are made up of individual solar cells that function similarly to large semi conductors that make use of a large area p-n junction diode. Exposure of the solar cells to sunlight makes it possible for the p-n junction diodes to convert the sunlight energy into electrical energy that can be used. Photons hitting the surface of the photovoltaic panel generate energy that knocks electrons out of their orbits and therefore are released and pulled by the electric fields in the solar cells in a directional current that allows metal contacts in the cell to generate electricity. More solar panels together with high quality solar cells will bring about more total electrical output produced by a solar panel. This converting of sunlight to the usable electrical energy is known as the photovoltaic effect. There are a number of factors that affect the output of photovoltaic panels among them being weather conditions, shades that are brought about as a result of obstructions of direct sunlight to the panel and the position and angle of installation of the panel. Best results are realized when the solar panels are placed directly to the sun's rays, with no obstructions that cast shades to the panel.