Solar photo voltaic power generation system

Photovoltaic (PV) technology converts one form of energy (sunlight) into another form of energy (electricity) using no moving parts, consuming no conventional fossil fuels, creating no pollution, and lasting for decades with very little maintenance. The use of a widely available and reasonably reliable fuel source the sun with no associated storage or transportation difficulties and no emissions makes this technology eminently practicable for powering remote scientific research platforms [2]. Indeed, numerous examples of successfully deployed systems are already available around the globe [7, 8]. The completely scalable nature of the technology also lends itself well to varying power requirements i.e. from the smallest autonomous research platforms to infrastructure-based systems. This technology can be limited, however, by annual fluctuations in solar insolation, especially at extreme latitudes. Based on semiconductor technology, solar cells operate on the principle that electricity will flow between two semiconductors when they are put into contact with each other and exposed to light (photons). This phenomenon, known as the Photovoltaic effect was first discovered by

Fig. 2.1 Solar cell Edmund Becquerel in 1839. Actual development of PV technology began in the 1950s and gained greater impetus through the NASA space program during the 1960s. Research continues today at national laboratories and within private industry, focusing on increasing conversion efficiencies and mass production strategies to further lower the cost of producing PV modules. Solar photovoltaic systems convert solar energy directly into electrical energy. Basic conversion device used is known as a solar photovoltaic cell or a solar cell as shown in fig. 2.1. Although other light sources may also produce photovoltaic electricity, only sunlight based PV cells are considered in this chapter. A solar cell is basically an electrical current source, driven by flux of radiation. Solar cells were first produced in 1954 and were rapidly developed to provide power for space satellites based on semiconductor electronics technology. Its terrestrial applications were considered seriously only after the oil crisis of 1973, when a real need of alternative energy source was felt globally. Efficient power utilization depends not only on efficient generation in the cell but also on the dynamic load matching in the in the external circuit. Major advantages of solar PV systems over conventional power systems are as under: 1. It converts solar energy directly into electrical energy without going through thermal mechanical link. 2. Solar PV system is reliable, modular, and durable and generally maintenance free. 3. These systems are quiet, compatible with almost all environmental, respond instantaneously to solar radiation and have an expected life span of 20 years or more. 4. It can located at the place of use i.e. onsite and hence no distribution network is required. It also suffers from some drawbacks which can be overcome by the technology in future, such as: 1. At present the cost of solar cells are high, making them economically uncompetitive with other conventional power sources. 2. The efficiency of solar cell is low. 3. As solar energy is intermittent, some kind of electrical energy storage e.g. battery is required which makes the whole system more expensive. 2.2 Components of Photovoltaic system 2.2.1 PV Panels PV panels tend to work much better in cold weather than in hot climates (except for amorphous silicon panels). Add a reflective snow surface and the output can sometimes exceed the rating for the panel. Array currents up to 20% greater than the specified output have been reported. In general, PV materials are categorized as either crystalline or thin film as shown in fig. 2.2 and they are judged on two basic factors: efficiency and economics. For remote installations where the actual space available for PV panels is often quite limited, the greater conversion efficiency of crystalline technology seems to have the advantage. It is also worth noting that the conversion efficiency of thin-film panels tends to drop off rather rapidly in the first few years of operation. Decreases of more than 25% have been reported. This performance deterioration must be taken into account when sizing the array for a multi-year project. However, there are still applications where the lighter weight and greater flexibility of the thin-film panels may be more suitable. Which PV technology is more appropriate for a given application will need to be determined on a case-by-case basis [14].

Fig. 2.2 Types of solar cells

Fig. 2.3 OFF grid Residential Solar PV system Mono-crystalline silicon panels should be utilized when a higher voltage is desirable. This would be in an instance where the DC power has to travel some distance before being utilized or stored in a battery bank as shown in fig. 2.3. These panels are also the most efficient PV technology, averaging 14% to 17%. New technology charge controllers, which allow for a higher array voltage than the battery bank voltage, somewhat obviate the advantages of the mono-crystalline panels. Polycrystalline silicon panels have efficiencies of 12% to 14% and can often be purchased at a lower cost per watt than mono-crystalline silicon panels. This type of panel sees the widest use in polar applications. Thin-film technologies include amorphous silicon, cadmium telluride, copper-indium dieseline, and others (refer fig. 2.2). Although the cost of these panels appears attractive at first, it is important to note that the efficiencies are comparatively low. The 8% to 10% efficiencies seen in new panels quickly degrade to about 3% to 6% after several months of exposure to sunlight. Furthermore, amorphous silicon and cadmium telluride modules are sensitive to a much narrower band of colors, and the winter shift to redder sunlight results in slightly poorer performance. Newer, triple-junction thin film technologies appear to have higher efficiencies and less degradation over time, but they are still subject to the same problems mentioned above, if to a lesser degree. The somewhat flexible nature of thin-film technology may make it appropriate for some applications, but in general, the higher efficiencies and more robust nature of the crystalline silicon modules make them a better choice for polar applications. Regardless of the technology employed, the researcher would be well advised to look for modules with heavy-duty aluminum frames, UL ratings, easy-to-use junction boxes, and a long warranty (20+ years). All of these are indicative of a quality unit that will withstand the rigors of the polar environment.