DESIGN OF SOLAR TRACKING SYSTEM

There have been a lot of research on how to improve the performance of parabolic trough collectors for the past few decades. One way of doing so is the incorporation of solar tracking system to the design of parabolic trough collector. Even though various approach have been established on how to improve its design and better way of incorporating it with parabolic trough collector but there are still a lot to be done in the aspect of the design of highly efficient algorithm, ease of control, size of equipment and use of readily available material which will eventually have an impact on the overall design cost. Therefore, this paper worked on the design of a horizontal single axis NorthSouth solar tracking algorithm. The algorithm was implemented with the use of national instrument LabView® 14 software programme linked with Galil DMC-3x01x single axis motion controller. The Galil DMC-3x01x motion controller in collaboration with DC motor, encoder, etc. was used to drive the parabolic trough collector in order to follow the sun from sunrise to sunset. Error estimation was carried out in order to ascertain the performance of the solar tracker. The designed algorithm was able to track the sun effectively from sunrise to sunset with minimal error obtained.

There had been a lot of work carried out on tracking system but starting from the recent studies, in 1997, Stone and Sutherland [7] presented a multiple tracking measurement system which consist of more than 100 heliostats for tracking the sun's location at an interval of 1 hour from early part of the morning to later in the evening.  in 1998 designed a two-axis sun tracking system to boost the thermal operation of a compound parabolic concentrator. Development of a sun tracking system was carried out by Yousef [9] in which the nonlinear dynamics of the tracking device were controlled with the use of a fuzzy logic control procedure applied on a PC and maintained by an interfacing card comprising of a sensor data acquisition function, motor driving circuits, signal conditioning circuits and serial communications. In 2004, Roth et al. [10] designed and constructed a sun tracking system with the use of pyrheliometer to evaluate the direct solar radiation. It was controlled by a closed loop servo system comprising of a four-quadrant photo-detector to determine the sun's location and two little DC motors to control the instrument platform so that the sun's image stayed at the centre of the four-quadrant detector always. Moving down to the most recent studies, Bin-Juine et al. [13] developed and tested a single-axis 3 positions sun tracking PV in Taipei (Taiwan) and they came up with increase in energy generation of 39% for a particular day. Yingxue at al. [14] worked on a dual-axis multipurpose solar tracker. The tracker uses declination mounting-system on both flat photovoltaic and concentrating solar power system with its axis positioned in an east-west direction. They compared the average energy efficiency of the system with the one that has a fixed PV and concluded that the one with the tracking system is 23.6% more efficient than that of fixed PV. Similar to the work of [14], Laughlin et al. [15] designed a low profile two-axis solar tracker which was tested on a concave mirror by measuring its receiver temperature. The tracker concept is based on translational motion which is composed of two coplanar and perpendicular linear actuator attached to a single linkage arm and pivots. Fabienne et al. [16] worked on error characterization on a single axis solar tracker by adapting to the International standard IEC 62817 testing procedure for photovoltaic tracker. The optical losses due to tracking error (which was obtained to be 0.4°) was calculated by using incidence angle modifier obtained with ray-tracing simulation. Even though there has been various work done on solar trackers there are limitations of solar trackers for parabolic trough collectors especially in the aspect of algorithm generation and design for the single axis tracking.
In order to improve on the efficiency and performance of the parabolic trough, it is essential to harness maximally the amount of irradiation coming from the sun. Therefore, presented in this study is the Algorithm, design and experimentation of a single axis solar tracker on parabolic trough collector. Horizontal tracking axis positioned in the North-south direction was adopted. The implementation of the design was assembled from components that are readily available in order to encourage a low cost solution and less specialized parts.

II. DESIGN
In order to be able to collect energy from the sun, it is required to calculate the position of the sun relative to the collection device which in our case is a six series connected PTC. The arrangement and installation of the PTC's are as shown in Fig 1. The development of the necessary equations using a unique vector method and the solar tracking elements/component that makes up the whole system configuration are summarized below.

A. Geographical location
The research was carried out in Jeddah, Makkah province Saudi Arabia. The geographical coordinate of the location is 21°32'36'' north latitude and 39°10'22'' East Longitude. Jeddah features a humid desert/arid weather which retains its hot temperature in winter at a range of 15°C at dawn to 28°C at noon. While its summer temperature is around 43°C at noon to 30°C in the evening [16].

B. Sun Tracking Algorithm
The six series connected PTC's axis of rotation is positioned or oriented in the horizontal north-south direction while tracking the sun from east to west during the day and returns back to east (home position) at sunset. Even though the collectors can be oriented in the horizontal east-west direction, it has the disadvantage of lower performance during the early (morning) and late (evening) hours of the day due to cosine loss [18] which makes the north-south positioning more desirable in this design. Moreover, more energy can be harvested by the horizontal north-south tracking during the summer than that of the horizontal east-west orientation which complements our geographical location and the essence of the whole system design.
The algorithm is designed based on a closed loop system. The mathematical formulae used in the design of the algorithm are summarised below.
1) Hour angle The movement of the earth about its axis can be described with Hour angle. As it can be seen in the Fig 2 below, Hour angle is regarded as the angle between the meridian parallel to sun rays and the meridian containing the observer. The hour angle may be measured in degrees or time with 24-hour clock equal to 360° and it increases by 15° in every 1-hour. By using the concept of solar time due to the consideration of 24hr clock and to completely predict the sunrays direction relative to a point on the earth surface. An expression of the hour angle from solar time can be given as: For the design of tracking algorithm it is imperative to be able to predict the time and location of sunrise and sunset and the length of the day.
In order to estimate the SST and SSR which will enable us also to determine the length of the day, it is required to determine the hour angle for both SST and SRT. Therefore, for a flat local horizon the altitude angle is zero at sunset (assuming that the solar altitude at sunset is equal to horizon angle) and the hour angle at sunset (ω ) can be given as Where N is the number of days, A and B are coefficients of the equation.  In as much that the local clock time is of little concern in the design of solar tracking system it is very important in time conversion analysis. The knowledge of local standards, the day of the year and location is a requirement for conversion between solar time and clock time. The relationship between LC, EOT and LCT can be given as

hours 7
And longitude correction can be given as local longitude longitude of standard time zone meridian 15 hours D is equal to 1 (hour) if the location is in a region where daylight savings time is currently in effect, or zero otherwise. 7) Zenith angle ( and Altitude angle ( ) The angle formed between the central ray of the sun and the vertical plane can be regarded as solar zenith angle while the altitude angle is the complement of the solar Zenith angle. Fig. 3 shows the relationship between zenith angle, altitude angle and azimuth angle for better understanding. The equation of zenith and altitude angle can be given as: sin sin sin ∅ cos cos cos ∅ degrees 8 90 9 Where ∅ is the latitude angle and it is the angle formed when a line is drawn from a point on the earth surface to the centre of the earth and its equatorial plane. It is of optimum importance to be able to calculate the zenith angle and altitude angle at any location at any given time for solar tracking design. 8) Solar Azimuth angle (A) From Fig. 3, solar azimuth angle (A) can be measured from due North in a clockwise direction. It should be noted that there are other ways of measuring the Azimuth angle rather than from the north-pointing coordinate and in a clockwise direction. The solar azimuth angle can be calculated in two ways and the equations are given as: sin 0 then A 360° A′′ Otherwise sin 0 and A A′′ The sun's position in the sky can easily be determined in terms of date, time and location since azimuth angle and altitude angle equations are gotten in terms of latitude, declination and hour angle. Figure 3 The Altitude angle (), Zenith angle (θ _z ) and Azimuth angle (A) of an Earth surface coordinate system. 9) Incidence angle ( ) and tracking angle ( Angle of incidence and tracking angle are essential in the design of solar energy system. Since the radiation of the sun that could reach a collector aperture is reduced by the cosine effect of incidence angle, therefore the determination of the angle between the vector perpendicular to the aperture of the collector and the rays of the sun is regarded as incidence angle. The incidence angle for horizontal single axis north-south tracking can be given as The tracking angle at the other hand is the amount of rotation required to align the axis of the collector aperture normal to the central ray of the sun. At least one axis of the collector aperture is required to be aligned to the sun's central ray. With this in mind, horizontal single axis north-south tracking is being adopted in this paper. The tracking angle for north-south horizontal tracking can be given as tan (13) B. Sun tracking system Solar tracking system plays an important role in the process of following the sun's trajectory (i.e. the normal beam of the sun) throughout the course of the day which results in the increase in performance of the collector. Therefore it is highly imperative to provide a high accuracy system of tracking. The elements/ components that makes up the sun tracking system are summarized below 1) Drive mechanism/transmission Since the sun's position have been ascertained through the development of algorithm it is necessary to ensure that the solar collector system utilizes this algorithm to follow the sun so as to produce solar energy during the day. Therefore, the drive mechanism employed for the design is a chain drive mechanism. The PTC's are connected in such a way that three PTC are arranged as one unit while the remaining three are arranged as another unit and then the two units are connected together by chain drive to a dual shaft geared DC motor as shown in Fig. 5 bellow. The DC motor rotates the collectors using a speed reduction transmission system (worm speed reducer) with a gear ratio of 1:100 while the rotational speed of the DC motor used was 1800rpm. The diagram of the drive mechanism/ transmission system can be seen in Fig. 5.  The gear reduction according to the number of driven and driving teeth of the chain drive mechanism can be given as

Gear reduction
driven gear teeth driving gear teeth 60 9 6.667 14 So, the total speed reduction from the motor to the collectors is 666.7 which gives enough torque to drive the 6 collectors with a DC motor of 1KW power.
2) Control system, PV and Battery storage unit The control system is made up of four units as shown by Fig.6. The computer unit utilizes the designed algorithm to calculate the position of the DC motor at certain time and sends a command to the motion control card (Galil DMC-3x01x single axis motion controller).
The motion control card is used to control the position of the motor by driving the DC motor. This is done by counting the steps of the motor until it gets to a specified position before it stops. It then sends a feedback to the computer unit to wait for further command.
The motion control parameters (i.e. the normal PID parameters) for the system are selected to avoid any overshoot or oscillation of the PTC during tracking. Once the normal PID parameters have been stored by the motion control card and the position of the DC motor have been obtained by the motion control unit, it calculates the speed profile including the acceleration, constant, and deceleration (starting and constant speed) and deceleration of the obtained position and send it as an analog command to the power amplifier. The power amplifier receives the analog signal from the motion control card and converts it to pulse width modulated signal and send it to the encoder of the DC motor. The encoder sends back its position to the motion control card as a feedback signal for motion command termination. collector. er. Fig. 10 vement of .667 from Therefore, making 1° hat for the Nation accordan The LabV (VI) as it nal Instrumen nce to Fig. 12 View® progra t was describe nt LabView® and the front am main cont ed by the sun t  Fig. 13. ubroutines

D) Perfo
The