Solar Tracking

DOI: 10.4018/978-1-5225-2950-7.ch006

Abstract

Basing on the provided information in the first to four chapters where it was clearly demonstrated that, the maximum utilization of solar energy depends upon determining the exact location of the sun position. By proper calculation and computer programs, the solar path for any geographical location can be tracked. Thus, a clear idea about the prospects of solar energy for any location can be obtained and accordingly decisions and, measures can be adopted for harnessing solar energy in that area. Basing on this information a general formula for on-axis sun-tracking system has been derived using coordinate transformation method. The derived sun-tracking formula is the most general form of mathematical solution for various kinds of arbitrarily oriented on-axis sun tracker, where azimuth-elevation and tilt-roll tracking formulas are specific cases. The application of the general formula is to improve the sun tracking accuracy because the misalignment of solar collector from an ideal azimuth-elevation or tilt-roll tracking during the installation can be corrected by a straightforward application of the general formula. Moreover, the rotation angle in a single axis tracker is calculated. The calculated rotation angle can be used to determine the number of motor revolutions to move the tracker to its optimum position.
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Introduction

Photovoltaic energy involves the conversion of Sunlight into electricity. The efficiency of converting radiant solar energy into electrical energy is the critical point that influences the choice of solar energy as a form of alternative energy. The energy generated from PV panels is related with temperature, irradiance and incident angle of the solar radiation and so on. There are two ways to improve the PV technology performance. One is to use different materials or add other dopants to manufacture the PV modules. The other one is to use a tracker as the device for orienting a solar PV module toward the Sun. In order to achieve the highest conversion efficiency, the Sun light has to impinge the module surface perpendicularly. The earth not only has one year rotational motion around the Sun, but also a daily motion around its own axes. Therefore, different kinds of solar tracking could be used. Here, one can mention two types of tracking:

• Long term tracking, where the most common ones are those related to daily, fortnightly, seasonally, half-yearly and yearly tracking by determining the optimum solar collector orientation according to these periods. This kind of tracking is treated in details in Chapter 5 and this kind of tracking is widely in use all over the world. Moreover, it is common practice for traditional photovoltaic (PV) modules to be installed at a fixed angle in a wide and flat area so as to generate the maximum amount of power. In this case the optimum tilt angle and azimuth angle should be determined. There are many techniques developed to determine the optimum tilt angles for different latitudes and surface azimuth angles. Soulayman and Hammoud (2016) presented a modified general algorithm to optimize the tilt angle for mid-latitude zone. Stanci and Stanci (2014) proposed an equation to optimize the tilt angle at latitudes from 0o to 80o. Benghanem (2011) proposed a method to calculate the optimum tilt angle in Madinah, Saudi Arabia. Yan, Saha, Meredith and Goodwin (2013) determined the optimum tilt angle and orientation in Brisbane, Australia. Furthermore, Optimum tilt angles for other areas such as Carbondale, Illinois, USA (Gong and Kulkarni, 2005), Sanliurfa, Turkey (Kacira, Simsek, Babur and Demirkol, 2004), Taipei, Taiwan (Chang, 2009a), Burgos, Spain (De Miguel, Bilbao and Diez, 1995), etc. have been reported. However, the fixed tilt PV system using yearly optimum tilt angle has relatively lower efficiency, but daily, weekly, fortnightly, monthly and even seasonally adjustment of the tilt angle can increase the efficiency of a solar system remarkably.

• Short term tracking, where a device for orienting a solar PV module toward the Sun during the day is used. The efficiency of a PV panel can easily be increased by sun tracking systems which are investigated by many researches. The generated power is directly proportional with the collected solar radiation in a solar system. Maximum sun power collection is possible by adjusting solar system position with respect to the Sun’s location. This adjustment can be realized more easily with two axes Sun tracking systems than single ones which is cheaper and simpler to design. The tracking systems include closed and open loop control mechanisms. The PV panels are positioned by the help of photo sensors and feedback controllers. The disadvantage of the closed loop system is that the system spends more energy than the generated one in the case of quick weather changes. The open loop one is based on calculations of the seasonal weather and the sun position. The hybrid control is made up of both closed and open loop tracking systems (Seme and Stumberger, 2011).

The different aspects of short term tracking will be treated in this chapter.

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