IMPROVING THE EFFICIENCY OF A PHOTOVOLTAIC SYSTEM BY INCORPORATING TRACKING SYSTEM AND MPPT: A REVIEW <s> Dual-axis tracking <s> The performance of a photovoltaic (PV) panel is affected by its orientation and its tilt angle with the horizontal plane. This is because both of these parameters change the amount of solar energy received by the surface of the PV panel. A mathematical model was used to estimate the total solar radiation on the tilted PV surface, and to determine optimum tilt angles for a PV panel installed in Sanliurfa, Turkey. The optimum tilt angles were determined by searching for the values of angles for which the total radiation on the PV surface was maximum for the period studied. The study also investigated the effect of two-axis solar tracking on energy gain compared to a fixed PV panel. This study determined that the monthly optimum tilt angle for a PV panel changes throughout the year with its minimum value as 13° in June and maximum value as 61° in December. The results showed that the gains in the amount of solar radiation throughout the year received by the PV panel mounted at monthly optimum tilt angles with respect to seasonal optimum angles and tilt angel equal to latitude were 1.1% and 3.9%, respectively. Furthermore, daily average of 29.3% gain in total solar radiation results in an daily average of 34.6% gain in generated power with two-axis solar tracking compared to a south facing PV panel fixed at 14° tilt angle on a particular day in July in Sanliurfa, Turkey. <s> BIB001 </s> IMPROVING THE EFFICIENCY OF A PHOTOVOLTAIC SYSTEM BY INCORPORATING TRACKING SYSTEM AND MPPT: A REVIEW <s> Dual-axis tracking <s> In this paper, a new micro-controller based solar-tracking system is proposed, implemented and tested. Thescheme presented here can be operated as independent of the geographical location of the site of setting up. Thesystem checks the position of the sun and controls the movement of a solar panel so that radiation of the suncomes normally to the surface of the solar panel. The developed-tracking system tracks the sun both in theazimuth as well as in the elevation plane. PC based system monitoring facility is also included in the design. <s> BIB002 </s> IMPROVING THE EFFICIENCY OF A PHOTOVOLTAIC SYSTEM BY INCORPORATING TRACKING SYSTEM AND MPPT: A REVIEW <s> Dual-axis tracking <s> This paper deals with a multipurpose dual-axis solar tracker that can be applied to solar power systems. This tracker employs a declination-clock mounting system that locates the primary axis in east-west direction. Based on this mounting system, normal tracking strategy and daily adjustment strategy are developed for flat Photovoltaic (PV) systems and Concentrating Solar Power (CSP) systems respectively. While the former strategy keeps the tracking errors smaller than the pre-specified values, the latter one simplifies the tracking process by adjusting the primary axis once a day and driving the secondary axis to rotate at a constant speed of 15°/h. Results of the accuracy test indicate that the tracking error of the normal tracking strategy is within 0.15°. The other strategy may have greater tracking errors, but its annual average cosine loss for flat PV systems is estimated to be below 1.3%. Furthermore, in the test on the output of the PV modules, it is found that the average energy efficiency of the normal tracking PV, compared with the fixed PV, is more than 23.6%. And the average energy efficiency of the daily adjusted PV is more than 31.8%. Results of the experiment show that the two tracking strategies are both feasible for the developed tracker. <s> BIB003 </s> IMPROVING THE EFFICIENCY OF A PHOTOVOLTAIC SYSTEM BY INCORPORATING TRACKING SYSTEM AND MPPT: A REVIEW <s> Dual-axis tracking <s> Abstract High concentrating photovoltaic is one of the most promising photovoltaic techniques that possesses up to now the highest photo to electric conversion efficiency. However, due to the small tolerance in the misfit angle between the incoming solar light and the normal of the solar cell panel, an accurate solar tracking is necessary in order to maintain the high performance. Although increasing the tracking frequency in conventional solar tracking strategy enhances the tracking accuracy, it also increases the moving frequency of the tracking system and the mechanical wear. In order to overcome this limitation, a more efficient solar tracking strategy has been provided by utilizing an open-loop mode to actively control and alter the tracking frequency instead of using constant tracking frequency. The code for controlling of tracking frequency is pre-programmed according to the theoretical solar velocity in different time and date. By correlating the movement from the azimuth and the altitude freedom, the total moving frequency of the solar tracking system has been reduced. As a result, it effectively decreases the moving frequency of the tracking system, which saves the required external energy to drive the tracking system and improves its reliability. <s> BIB004
Dual-axis tracking involves the rotation of the solar panel about two perpendicular axes. Thus, the system has two degrees of freedom, namely rotation about the azimuth axis and rotation about the elevation axis. The dual-axis tracker is more accurate than a single-axis tracker as the variations along the elevation angle is taken care of. Since the dual-axis tracking system involves sensing along two axes, a complex control system is used. Fig. 6 shows the two axis position control of the solar panel. Bingol, Altintas and Oner BIB002 designed a dual-axis tracker with the sensors placed inside four hollow cylindrical tubes. The assembly was mounted on the solar panel making 45° with the panel plane. The difference in the observed light intensity was taken as the criterion for operating the stepper motor to move the panel towards the direction of the sun. Kacira et al BIB001 studied the effects of two-axis solar tracker on photovoltaic panels with respect to fixed panels in Turkey. A gain of 34.6% in the generated power was attained with the use of two-axis solar tracking solar panel when compared to a south facing panel at 14° tilt angle. Patil et al designed, fabricated and tested a two-axis equator based solar tracking mechanism controlled using computer. The design of the system was such that the operation of the tracker consumed a very small fraction of the generated power. The structural components were designed taking into consideration the self-weight, wind forces and the imposed load due to tracking motion. The equator based tracking algorithm was fed to the system and it was installed and tested for tracking errors. The correction factors were added and the system was found to have a maximum deviation of 3° over a day. The observed increase in the output of the photovoltaic module was about 30%. Wu, Zhang and Wang  proposed a two-axis sun-tracking mechanism. The U-3PSS (Universal -3 Prismatic Spherical Spherical joint) solar tracker was a redundant design while U-2PSS was its nonredundant counterpart. The trackers were tested for workspace and energy consumption to determine the optimum design. The study found that the U-3PSS tracker had a bigger workspace and smaller energy consumption than the U-2PSS tracker. A dual-axis tracking system was developed for photovoltaic conversion panels in Ourgla city by Khadidja et al  . Tracking PV modules result in an increase in yield of 15% to over 35% when compared to fixed mounted PV installations. A two-axis tracking system has been developed and mounted on the PV panels and the solar insolation, power generated and the panel efficiency were calculated for the entire day and conclusion were drawn from the results. Though generating the tracking trajectories for a system is complex, the tracking system reduces the losses incurred due to shading. Yao et al BIB003 developed dual-axis tracking system with two strategies. The normal tracking mode ensured low tracking errors while the daily adjustment mode altered the primary axis once a day. The former strategy yielded an increase of 23.6% and the latter strategy showed an increase of 31.8% in the efficiency of the panel. Mi et al BIB004 proposed a solar tracking strategy that utilizes an open-loop mode to control and alter the tracking frequency of the system. This proved to be more efficient than the conventional tracking system using constant tracking frequency. High concentrating photovoltaics require accurate tracking system for high performance. Increasing tracking frequency increased efficiency as well as moving frequency of the system and mechanical wear. Thus varying tracking frequency strategy was introduced. The program for controlling the tracking frequency was written based on the theoretical solar velocity in different time and date. The use of the proposed system reduced the moving frequency of the tracking system which saved the energy required to drive the system and reduced mechanical wear.