Solar Tracking

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 0^o to 80^o. 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.