Date/Time Operated Two Axis Solar Radiation Tracking System for Baghdad City

The power density received from the sun at sea level is about (1 kW/m2), therefore it is considered an important alternative source of energy. There are many advantageous of getting electrical energy directly from a solar energy directly such as it does not require fuel, operate silently, low cost maintenance, and there is no atmospheric pollution. The disadvantageous of the PV array is high capital cost. However, this kind of alternative source requires further research and development to maximize the conversion efficiency. One of the major problems of the PV system is the variation of the solar power due to the changes in weather conditions such as clouds, fog, dust, rainfall etc. therefore the PV systems requires special design considerations. Some tracking methods use date/time mode where the sun’s position is calculates from formulae or algorithms with the aid of computer. The computer or microcontroller sends signals to the stepper motors to controls the movement of the PV panels according to these formulae. Many methods that uses the calculation of the solar position have been published, the error of these methods have been greater than ± 0.01° in the calculations of the solar zenith and azimuth angle, some of these methods are only valid for a specific number of years [1]. For example, Michalsky’s calculations with uncertainty of greater than ± 0.01° [2]. Blanco-Muriel et al. with uncertainty greater than > ± 0.01° [1]. The best uncertainty achieved for a Solar Position Algorithm (SPA) to calculate the solar zenith and azimuth angle is described by Jean Meeus [3] with uncertainties equal to ± 0.0003°. It was developed by P Bretagnon in 1982 and modified by Bretagnon and Francou in 1987 [3]. A step by step procedure technical report for implementing Jean Meeus algorithm prepared by Ibrahim Reda and Afshin Andreas [4].


Introduction
The power density received from the sun at sea level is about (1 kW/m 2 ), therefore it is considered an important alternative source of energy. There are many advantageous of getting electrical energy directly from a solar energy directly such as it does not require fuel, operate silently, low cost maintenance, and there is no atmospheric pollution. The disadvantageous of the PV array is high capital cost. However, this kind of alternative source requires further research and development to maximize the conversion efficiency. One of the major problems of the PV system is the variation of the solar power due to the changes in weather conditions such as clouds, fog, dust, rainfall etc. therefore the PV systems requires special design considerations. Some tracking methods use date/time mode where the sun's position is calculates from formulae or algorithms with the aid of computer. The computer or microcontroller sends signals to the stepper motors to controls the movement of the PV panels according to these formulae. Many methods that uses the calculation of the solar position have been published, the error of these methods have been greater than ± 0.01° in the calculations of the solar zenith and azimuth angle, some of these methods are only valid for a specific number of years [1]. For example, Michalsky's calculations with uncertainty of greater than ± 0.01° [2]. Blanco-Muriel et al. with uncertainty greater than > ± 0.01° [1]. The best uncertainty achieved for a Solar Position Algorithm (SPA) to calculate the solar zenith and azimuth angle is described by Jean Meeus [3] with uncertainties equal to ± 0.0003°. It was developed by P Bretagnon in 1982 and modified by Bretagnon and Francou in 1987 [3]. A step by step procedure technical report for implementing Jean Meeus algorithm prepared by Ibrahim Reda and Afshin Andreas [4].

Sun-Tracking Methods
Sun-tracking systems are classified into two types: passive and active trackers. Passive solar trackers (mechanical) are based on thermal expansion of a matter, while active trackers (electrical) can be categorized as microcontroller-based electro-optical sensor, PCbased date/time controlled, auxiliary bifacial solar cell based and a combination of these two systems [5].
The date/time tracking method find the solar position by calculates a motion equation of the Earth. The best position for the PV array that

Abstract
Finding energy sources is one of the challenges for the next years. The electricity generated from the solar cells is an important energy source. The sun trackers are used to increase the conversion efficiency of the PV panels. These trackers move the panels to keep the best orientation relative to the sun. In this paper a two axis sun tracker system is proposed to track the sun position for Baghdad city. The tracker system uses a pc or microcontroller to control two stepper motors rotation according to predefined functions in the algorithm. These functions calculates the angle of sunrise each day during the year, sunshine time, and the other functions calculates the azimuth and elevation angles of the sun during the day. These functions control the rotation of the stepper motors during the day and after the sunset it rotates the motors to the initial positions.

Date/Time Operated Two Axis Solar Radiation Tracking System for Baghdad City
Anas Lateef Mahmood* Electronic and Communications Engineering, College of Engineering, Al-Nahrain University, Baghdad, Iraq oriented to the sun is found by a real-time calculation. The position of the PV array can be controlled using devices consist of a microcontroller and motors. The control mechanism of this type of sun tracker is independent from weather parameters change and after the sunset the tracker move the PV panel a desired position. However, this method needs accurate azimuth settings and compensation (Figure 1) [6].
The two-axis tracking system was tilted from the horizontal equal to the latitude angle pointing to south (β=32°) as shown in Figure 2. The sunrise angle in this site is measured in degrees. The sunrise angle is counted in a clockwise direction (CW) with 360° in a full circle. The counting is start from the north direction, where the azimuth value has 0°; east is 90°; for the south it is 180° and for the west it is 270°.

Sun Tracking Equations
The sunrise angle variation during the year can be expressed using Eq. (1) The difference between the sunrise angle calculated from Eq. (1) above and that found in the tables in [7] is <1.3°. This difference can be reduced to <0.7° if the sunrise angle variation expressed using 7th degree polynomial. However, Figure 4 shows the difference between the sunset angle (θ s ) and the sunrise angle (θ r ) (ω = θ s -θ r ) against the day length D L .
Where ω is measured in degree and D L is measured in minutes. It is shown from Figure 4 that there is a linear relationship between ω and D L and can be expressed using the following equation The day length (D L ) variation during the year (2014) is shown The difference between the day length calculated from Eq. (3) above and that found in the tables is <7 minutes and it can be reduced to <2.5 minutes when using 7 th degree polynomial. The variation of the ω/D L in terms of D is found in Eq. (4) below: The sunrise time (T r ) in the year is found in Eq. (5), where (T r ) is measured in minutes.    represent the time to turn ON motor is chosen (e.g. 15 minutes). Starting from 1st January, the program calculates (θ r , D L , and T r ) from Equations (1, 3, and 5) respectively, then it reads the time from a real time clock (RTC). If the time equal T r then it rotate the motor (M1) to an angle θ r . The program start to rotate motors (M1) and (M2) with angles equal to ϕ and θ respectively where,

Conclusion
This paper proposes a two-axis control algorithm for a PV tracking system for Baghdad city. This algorithm uses the date/time mode. In this mode the computer calculates the sun's position from formulae to send signals to the motors. It eliminates the need of any sensor and this can reduce power loss. It also don't affect by changing weather conditions (e.g. clouds, fog, dust, rainfall etc.)

Proposed Tracking Method
Equations (1, 3, and 5) are used to calculate θ r , D L , and T r respectively for the years 2015 and 2016 for Baghdad city. Table 1 shows the values of the relative errors between the values found in 2015 and the values found in 2016 [7].
From the results shown in Table 1 it is shown that the relative errors are small, therefore Equations (1, 3, and 5) can be used to calculate (θ r , D L , and T r ) for any year in Baghdad. In order to obtain a general sun tracking method for Baghdad city the steps explained in the flowchart shown in Figure 6 are followed. First a constant time delay ∆T which