Improving Photovoltaic Panel (PV) Efficiency via Two Axis Sun Tracking System

In this paper two axis sun tracking method is used to absorb maximum power from the sun's rays on the solar panel via calculating the sun’s altitude and azimuth angles, which describe the solar position on the Iraqi capital Baghdad for the hours 6:00, 7:00, 8:00, 9:00, 12:00, 15:00 and 17:00 per day. The angles were calculated in an average approach within one month, so certain values were determined for each month. The daily energy achieved was calculated for the solar tracking method compared with the fixed tracking method. Designed, modeled and simulated a control circuit consisting of reference position truth table, PI Controller and two servomotors that tracked the sun position to adjust the PV panel perpendicular on the rays of the sun. The results obtained by a simulation software MATLAB/Simulink.


INTRODUCTION
Due to the increasing demand for renewable energy resources because it is environmentally friendly as it reduces greenhouse gas emissions and reduces the dependence on fossil fuel energy generation and thus in the future lead to increased reliance on renewable energies at the expense of energies generated by other traditional methods. One of the best sources of renewable energy is solar energy, especially for a country such as Iraq because it is almost continuous throughout the four seasons of the year and it is free and high quality. Also the vast land in this country, which can be grown with huge number of solar panels. The photo voltaic (PV) panels converts solar radiation into DC electrical power and the amount of this real power generated depends on the intensity of the solar radiation falling on the unit area of the PV, which changes with respect to (W.R.T) sun angles from sunrise to sunset. Therefore, the efficiency of fixed PV panels is less than tracking panels because the solar panel produces maximum output energy when the sun is vertical on it (Mishra, et al., 2017).
For this reason, this research is interested in tracking the sun to increase the efficiency of the solar panel.
In (Neville, 1978) a comparative study made between one axis tracking and fixed collectors. That showed there is around 50% declination in the maximum performance of a fixed collector. However, it is 10% for the axis-tracking panel. Although (Hartley, et  showed the comparative study of using tilting tracking and fixed horizontal tracking method for 8 month in Baghdad city. The tilting angle was adjusted every day, but the azimuth angle still constant. It showed that the using of tilting method is more effective at winter with maximum energy gain at winter/February. However, the average insolation was (910) W/m 2 by tilting method and (713) W/m 2 at fixed horizontal method. In (Mishra, et al., 2017) the active tracking was presented, the tracking system was built on Arduino UNO and used of the lightdependent-resistor LDR and a stepper motor which allows accurate tracking of the sun. All This paper depends on the computational method of calculating the altitude and azimuth angle of the sun position during all seasons for Baghdad city. These calculated angles will be database of the sun position that shines on Baghdad to the later researchers and this paper showed comparative results of the sun irradiances between the fixed panel and two axis-tracking panel. The two-axis tracking method is based on two servomotors with efficient and simple control circuit.

PV MODULE
To know the electronic performance of a solar cell it is important to know the PV module equivalent circuit and the output current equation where the equivalent circuit is shown in Fig. 1.
As a result, the characteristics equation is as follows: Eq. (4) produces the voltage current (V-I) curve of the PV as shown in Fig. 2.
It is clear from Eq. (4) that the PV current is mainly depend on photo current which is based on sun irradiance(w/m 2 ) (Jackson, 2008). For this reason, it is important to track the sun to increasing the PV efficiency.

TYPES OF SUN TRACKERS 3.1 Active Trackers
This type of trackers are made by using microcontroller which receives the signal from sensing element that monitors the sun's location during the day like LDR then drive the motor to adjust the PV panel position.

Sun Trackers Based on Solar Geometry
These trackers depend on the fact that the earth rotation about itself and around the sun is constant, hence the sun angles can easy calculated. Therefore, by knowing these angles, the sun can be tracked from specific location regardless the presence of sun rays. Therefore, this type of tracking To get the solar time from the local standard time, the following equations is used.
4.2 Hour Angle (w): it is angle represents a time in terms of degrees instead of minutes where one degree for four minutes. This means fifteen degrees for one hour and it is positive after solar noon and negative before it as shown in Fig. 3. It expresses as follows.

Declination Angle (δ):
is the angular location of the sun south or north of the equatorial plane as shown in Fig. 4 and states as follows. If: Therefore, the sun-tracking can achieved by considering the altitude and azimuth angles as a references position of the two servomotors, which adjust the PV panel position perpendicular to the sun rays at all time as shown in Fig.6.

CALCULATING CLEAR SKY INSOLATION
The direct insolation (H) applied on a two axis tracking PV panel with known latitude, altitude over the sea level and the time can be calculated by the following the equation ( While the insolation with respect to horizontal plate )Mohamed, et al., 2017) is given by:

POSITION CONTROL CIRCUIT
The general block diagram of the position control circuit is shown in Fig. 7 which compares the α, γ reference position with the current position then the error signal enters PI controller to adjust the location of the PV panel via DC servomotors.
The proposed system tracks the sun position at 6, 7, 8, 9, 12, 15 and 17 time o'clock. This means long period of time between the previous and the next position, where one hour is the minimum period. Therefore, the PI controller is more suitable choice than PID controller when the speed of the system isn't an issue (Rao, 2013).
The speed of the motors are proportional to error signal. Consequently, when the motor is near enough the wanted position, it move slowly. Else, it turns fast where this is a proportional control.
The advantages of using servomotors among others type of motors are its holding torque, has 90% of the rated torque at high speeds, quiet, no vibrations, their high efficiencies and it supplies about double their rated torque for short time (

SIMULATION AND RESULTS
The location of Baghdad capital of Iraq was studied, where the altitude over the sea level is (34) meters, latitude is (33.312805) and longitude is (44.361488) for 6:00, 7:00, 8:00, 9:00, 12:00, 15:00, 17:00 time o'clock in all the four seasons. So as to find the insolation on two axis tracking PV panel and fixed PV panel in addition to the angles α, γ, ϴz. A program is written using MATLAB/Simulink software (appendix A&B). Fig. 8 and Fig.9 show the variation of the altitude angles along the year for example at 12:00 o'clock in winter/December it reaches its minimum value 33  then increases slightly until arrives to spring/March 53  next continues directly increasing to reaches its maximum rate at summer/June 80  lastly decreasing to 37  at autumn/November. These measurements explained intensively in Table 1 Table 2. show the range of variation of azimuth angle at deferent seasons from the east to the west and its draw w.r.t. month and hour is shown in Fig. 10 and Fig. 11. The smallest range in winter about 133  whereas increases at spring to 181  then becomes maximum at summer 213  and again decreases to 177  at autumn.  Fig.'s 12, 13, 14 and 15 show the sun irradiances (w.r.t.) time during the day uses a fixed tracking at winter, spring, summer and autumn seasons respectively. These calculations was done w.r.t. horizontal plane according to Eq. (18). Where it shows that, the sun irradiances increases at the beginning of sun rise even arrives its maximum point at 12:00pm o'clock for each season. Then reduced to zero at sunset because the altitude angle increases during the beginning of the period of sunrise even 12:00pm o'clock, but decreases during the 12:00pm o'clock to the sunset. However, it has the best value at summer/June 12:00pm o'clock, which is the value equal to 950 w/m 2 because the altitude angle is high and the worst value at 12:00pm o'clock in winter, which is equal to 420 w/m 2 , because the altitude angle is low. Fig.'s 16, 17, 18 and 19 show the improvement of sun irradiance at PV panel uses two-axis tracking. Which ensure that the position of the PV is perpendicular to the sunrays during the day and the altitude angle is 90  for most of the day. Consequently, the energy gain at different season via two axes tracking system can be calculated according to Eq. (19). It expresses as below:

Season
Saving daily energy = (the daily energy of the two axes tracking system) -(the daily energy of a fixed tracking system w.r.t. horizontal plane) In general, the daily energy was found in a linear approximation method as expression below: Finally, Fig. 20 shows the simulation module of the vertical position control using DC servo motor1, which tracks the altitude angle of the sun while the Fig. 21 shows the reference position and the actual position of the PV panel that tracks the sun's altitude angle in summer/June. However, the Fig. 22 shows the simulation module of the horizontal position control using DC servo motor 2 which tracks the azimuth angle of the sun in in summer/June too, while their results shown in Fig. 23. The proportional-integral (PI) controller was tuned by trial and error, where the proportional constant (kp) was equal to 45, while the integration constant (ki) equal to 200. The specifications of servomotors is shown in appendix (C).

CONCLUSION
The sun angles of the sun were calculated at Baghdad was varied in wide range through the year. Therefore, at fixed panel position more losses will be in active power. These positions tracked by two servomotors of the PV panel, which improved the efficiency of the PV and energy is saved during all the season, but it was bigger at winter because the altitude angle at winter had much enhancement. Where it was before tracking low around 33  at 12:00 o'clock of December, but after tracking became 90  . Therefore, it is improved than the summer. Finally, it can be concluded that large energy losses will be at the fixed PV panel position, which saved via PV panel tracking system. The position control was simple and efficient using servomotor that offers high torque at low speed controlled by PI controller that is simple and easy implemented. In addition, the sun angles that calculated in this paper could be database for other researches about sun tracker in location of Baghdad.