In this work, a review of the most recent (2015 -2019) published techniques for the control of photovoltaic panels is presented.

1. A PRESENTATION
ON
REVIEW OF TRACKING METHODOLOGIES FOR
PHOTOVOLTAIC (PV) PANELS
BY
K. N. UKOIMA, O. I. OKORO, U. B. AKURU
OCTOBER, 2019

2. ABSTRACT
•In this paper, a review of the most recent (2015 -2019)
published techniques for the control of photovoltaic panels is
presented.
•Published concepts are presented based on functionality and
results.
•The various techniques are considered in terms of complexity,
efficiency and utilization of the PV cell.
•It was observed that even though tracking the sun is not
crucial, the use of either single or dual axis trackers can
maximize the energy harnessed from the sun.

3. INTRODUCTION
•A solar tracker is a purpose specific electromechanical system which
tracks the current direction of the solar rays and constantly aligns the
solar panel module to face the sun directly, thereby ensuring maximum
power density .
•There are two major types of solar trackers - dual axis and single axis
trackers. The single axis trackers have one degree of freedom and track
the sun from east to west. Dual axis trackers have two degrees of
freedom (2 – dof) which provides an additional benefit of following the
elevation of the sun.
• Myriads of research conducted in recent years are concerned with the 2
- dof solar tracking systems.
•Numerous approaches have been widely researched on to attain a higher
accuracy in solar tracking. The various approaches can be broadly
classified as either open-loop tracking types based on solar movement
mathematical models or closed-loop tracking types using sensor-based
feedback controllers

4. Fig. 1: Solar astronomy
SOLAR ASTRONOMY
•Elevation angle: The
elevation angle is the
altitude of the sun.
•Azimuth angle: It is
the angle on a
horizontal plane
between the line due
north and the
projection of the sun’s
rays on the horizontal
plane

5. Solar Irradiance on a Tilted Surface
The solar irradiance on a pv panel has three components. They are: the direct beam IBD,
the diffuse irradiance ID and the reflected irradiance, IR. The equations for the three
components as presented in (Handbook Fundamentals, 2001)
(1)
(2)
(3)
(4)
(5)
(6)

6. Figure 2: Plot of Ibd against solar elevation angle  for different days, d=180, 270,
360
Figure 3: Plot of Id against tilt angle () for days, d = 180, 270, 360

7. METHODS OF SOLAR TRACKING
SINGLE AXIS TRACKERS
In single axis solar tracking, a single pivot is used to track the sun. The major limitation
of these trackers is that tracking is done only on one axis.
1. Kennedy et. al. (2018) presented a low cost implementation of a single axis solar
tracking system that makes use of two light LDR’s and a microcontroller as
principal components. When both LDR’s receive equal light intensity, the panel is
stabilized in a fixed position. An 8.87% increase in output power was recorded
when compared with a fixed solar panel.
Figure 4: Working principle of the two LDRs. Source: (Kennedy et. al., 2018)

8. 2. Wang et al. (2016) designed and implemented a programmable logic controller
(PLC) - based automatic sun tracking system. The design was aimed at systems that
concentrate solar energy on a parabolic trough. The experimental results show that
the error of the system in solar tracking did not exceed 0.6°.
Figure 5: PLC-based automatic sun tracking system. Source: (Wang et al., 2016)

9. 3. Sallaberry et al. (2015) presents a direct tracking error characterization on a single
axis solar tracker. On a parabolic trough that is small in size, the angle position error of
a single axis tracker causes optical losses. Their study focused on estimating, using a
direct procedure, the error of angle position of a parabolic trough collector. For this
tracker, the error in tracking the angle was within ±0.40
Figure 6: Scheme of the rotation angles: tracking angle c, collector inclination c,
collector azimuth c, the longitudinal and transversal angles L and T .
Source: (Sallaberry et al., 2015).

10. 4. Soroush et al. (2019) presented a P&O (perturbation and observation) based
sensorless single-axis tracking method. The angle of incidence is perturbed and the
maximum power point is found in that angle via the inner layer P&O method. The angle
of incidence is corrected via the outer level P&O method. Their proposed method is
not dependent on the azimuth, altitude angle, and geographical equations and it
can be applied in any weather condition.
Figure 7: Schematic diagram of a P O based sensor less method in single axis solar
tracker. Source: (Soroush et al., 2019)

11. Dual Axis Trackers
While single axis trackers use a single pivot, dual axis trackers tracks the sun by using
two pivots. Dual axis trackers are mostly applied in the concentrated solar power
applications. Many of the current research on tracking systems have been on dual axis
solar trackers.
1. Ukoima et al. (2019) proposed an approach to the desin of a dual axis controller for
solar panels. Two pairs of Light Dependent Resistors (LDR), an ATMEGA 328P
microcontroller and a servomotor form the principal components of their circuit model.
Their model works by performing averages of the signals generated from four (4)
LDR’s placed at the four corners of a photovoltaic cell. Their result obtained show a
54.71% increase in the generated output power for the tracking system as opposed
to the fixed solar panel. The design was successfully constructed and implemented.
Figure 8: A dual axis controller
for photovoltaic cells. Source:
(Ukoima et al., 2019)

12. 2. A simple electro-mechanical dual axis solar tracking system was developed by
Rashid et al. (2015). The data acquisition (DAQ) card generates pulses which forms the
input for four relays. This is then used to control the two axes of the tracker. Their
results show the efficiency of a tracking system in terms of energy harnesses in
comparison to fixed panels. In the month of March, 20%, additional energy was
produced. In the month of April, 23% additional energy was produced and finally in
the month of May, 21% additional energy was produced. These results confirm the
efficiency of the tracker developed in this study (Rashid et al., 2015).
Figure 9: Solar tracking layout (Rashid et al., 2015)

13. 3. Fathabadi (2016) presents a novel sensorless dual-axis solar tracking system with
high accuracy controlled by the maximum power point tracking unit of photovoltaic
systems. The tracking error of the sun’s direction of their proposed solar system was
0.110. By utilizing their proposed solar tracking system, the efficiency of the energy
harnessed from the sun can be increased by 28.8–43.6%. This however depends on
the season.
Figure 10: Solar tracking system. Source: (Fathabadi, 2016)

14. 4. A preliminary study was conducted by Hong et. al. (2016) on the two axis hybrid
solar tracking method for the smart photovoltaic blind (SPB). Calculations were
performed on the sun’s altitude and azimuth. This was then used to calculate
approximately, the azimuth of panel (AoP) and the hourly slope of panel (SoP) of the
smart photovoltaic blind. The slope of the panel performed tracking of the sun from 0°
to 90°. The azimuth of panel was able to track the sun from -9° to 9°. This limitation is
due to vertical axis rotation.
Figure 11: The proto type model proposed SPB. Source: (Hong et. al., 2016)

15. 5. Towards optimal solar tracking: A dynamic approach was presented in (Panagopoulos
et. al., 2015). Here, calculation for effective and efficient day-ahead solar tracking of
near-optimal trajectories was proposed using policy iteration method. This was based on
the forecasts of the weather from providers that are online. Their result shows that the
output power of a photovoltaic system can be increased significantly, when comparison
is made with that of the conventional methods of solar tracking (Panagopoulos et. al.,
2015).
Figure 12: Abstract azimuth altitude dual axis of the tracker (in vertical single
axistracker). Source: (Panagopoulos et. al., 2015)

16. Figure 13: Angle of incidence of the solar radiation.
•From Fig. 13, it can be seen that as increases, the generated power reduces. L
•et the maximum radiation intensity captured on a solar panel be I = 1000Wm-
2(theoretical assumption), duration of sunshine for a day, t = 12h; 43200s (6am – 6pm)
and the sun collecting area is Sa.
•When the radiation is perpendicular to a stationary fixed panel, the solar collection
area, S = Sacos .
•The sun has an angular velocity of = 7.292x10-5 rad/sec. The total solar energy is
given by: E = ISt. (7)

17. The elemental energy is given by:
dE = ISdt. (8)
The energy for one day is given then by:
For a unit surface area, day.
For a unit surface area,
.his is the ideal energy for a tracking solar panel. It is seen that tracking system (single
or dual axis trackers) produces 57.66% more power than a fixed tracking systems.
This is the ideal energy for a fixed solar panel. In the case of a tracking solar system,
the energy for one day is given by:

18. CONCLUSION
•In conclusion, the principle of ‘heliotropism’ is generally used to track
the suns movement.
•The use of either single or dual axis trackers results in an increase in the
efficiency of the solar energy generated.
•However, it can be inferred from the literatures that trackers do not need
to face the sun directly to be effective.
•When the incident ray is off by 10o, the generated output energy is still
98.5% of the case of complete maximum tracking.
•Even when the location is cloudy and hazy, the annual output gain from
trackers can be in the low 20% range.
•When the location is good, typical gains between 30 and 55% were
recorded annually.

19. THE END
THANKS FOR LISTENING
AND
GOD BLESS