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Determining the optimum tilt angles for PV modules in a
semi-arid region of South Africa for the summer season
Pierre E Hertzog1 and Arthur J Swart2
1,2Department of Electrical, Electronics and Computer Engineering
Central University of Technology, Private BagX20539, Bloemfontein, 9300
1phertzog@cut.ac.za
2aswart@cut.ac.za
Abstract—Optimizing the output power of any PV array or
module requires a number of factors to be considered,
including the tilt angle, orientation angle and environmental
conditions. Research has shown that PV modules should be
installed at either a tilt angle which equals the Latitude angle
of the installation site or at Latitude plus 10º or at Latitude
minus 10º. These three tilt angle recommendations are based
on the seasonal changes which occur, that affect both the solar
irradiation availability and the inclination of the sun’s rays on
the tilted module’s surface. The purpose of this paper is to
present empirical evidence establishing the optimum tilt angle
for PV modules in a semi-arid region of South Africa during
the summer season. The practical setup is substantiated where
3 identical 10 W polycrystalline modules were used in
conjunction with a fixed load resistor. A LabView software
program was developed to record and display the voltage and
current measurements from the PV modules using a data
logging interface circuit and an Arduino board. Results suggest
that PV modules need to be installed at a tilt angle of Latitude
plus 10º for semi-arid regions during the summer season.
Keywords— Arduino, LabView, Metrology, Direct-beam
I. INTRODUCTION
―Saving our planet, lifting people out of poverty,
advancing economic growth... these are one and the same
fight. We must connect the dots between climate change,
water scarcity, energy shortages, global health, food security
and women's empowerment. Solutions to one problem must
be solutions for all‖. These words, by the current secretary
general of the UN, Ban Ki Moon, highlight the importance
of finding solutions to common global problems, including
that of critical energy shortages.
South Africa is not immune to energy shortages, as the
recent energy crisis lead to the need for load shedding in
South Africa [1]. Load shedding causes huge losses to
commercial, industrial and residential customers, where
even academic, government institutions, health service
providers and non-government organizations suffer [2].
Predictions are that these energy shortages and load
shedding scenarios will increase, thereby necessitating the
implementation of alternative energy sources, such as
photovoltaic (PV) energy systems.
However, one key deficiency of PV modules is their low
efficiencies, where the solar-to-electricity conversion
efficiency can be less than 20% for commercial PV products
[3]. That means that 80% of the absorbed solar energy is
actually dumped by the PV modules as waste heat [4]. These
low efficiencies necessitate the optimum installation of PV
modules according to the relevant environmental conditions
and site coordinates. One of the major factors to consider in
the installation is the tilt angle of the PV modules. Research
by Heywood and Chinnery suggest using tilt angles which
are either equal to the Latitude value of the installation site,
or then Latitude plus 10º or Latitude minus 10º in the
southern hemisphere [5]. The three different tilt angle
recommendations are based on seasonal changes, where a
lower tilt angle is recommended for summer months while
higher tilt angles are recommended for winter months.
However, environmental conditions also influence the
choice of tilt angles. For example, Asowata et al. [6]
recommended, that for a stationary PV panel, a Latitude plus
10º tilt angle should be used for optimum power yield
throughout the year in South Africa. However, their research
was conducted in an area that was declared an ―airshed
priority area‖ due to the concern of elevated pollutant
concentrations within the area, being specifically
particulates [7]. Would the recommendation of Asowata et
al. regarding an optimum tilt angle installation of Latitude
plus 10º hold true for other areas in South Africa, especially
for semi-arid regions where excessive dust and heat are
experienced?
The purpose of this paper is to present empirical evidence
establishing the optimum tilt angle for PV modules in a
semi-arid region of South Africa during the summer season.
Different solar radiation components impacting on the
output power of a PV module is firstly presented. Secondly,
the context of the research site is established followed by the
experimental setup. The research methodology, results and
conclusions complete the paper.
II. SOLAR RADIATION COMPONENTS FOR PV MODULES
PV modules receive direct (beam), diffused and reflected
radiation during varying atmospheric conditions [8]. Direct
radiation is the component which enjoys direct line-of-sight
between the sun and the PV module, with no interruptions
such as cloud movement or tree shading. Diffused radiation
is the component scattered by atmospheric constituents such
as molecules, aerosols and clouds [9]. Reflected radiation
occurs when light energy is reflected off trees or buildings
towards the PV module. Fig. I illustrates direct, diffused and
reflected radiation received by a specific PV module
installed at the Central University of Technology (CUT) in
Bloemfontein, Free State.
On a clear sunny day, the direct-beam radiation
component contributes about 90% of the total solar energy,
with the diffused and reflected radiation components
supplying the remaining 10% [10]. However, the direct-
beam radiation must be within a -3dB beamwidth of the PV
module as discussed by Asowata et al. [11], which equates
to between 45 and 90º. Considering the Zenith angle at
midday (defined as the angle between the sun and the Zenith
[12]), the direct-beam radiation component may not be more
than 45º lower to either side of this reference.
Figure I: Different radiation beams impacting on a PV module
III. CONTEXT OF THE RESEARCH SITE
South Africa has some of the best solar resources in the
world, where the average daily solar radiation varies
between 4.5 and 7 kWh / m2 [13]. In the heart of South
Africa lies the Free State province with Bloemfontein as the
provincial capital. The main campus of CUT is located in
Bloemfontein where the Faculty of Engineering and
Information Technology resides.
The co-ordinates of CUT’s main campus is 29°07’17.24‖
S (Latitude) and 26°12’56.51‖ E (Longitude) [14], and
serves as the installation site for this research study.
Bloemfontein is a semi-arid region with a daily average
global horizontal radiation of 5.15 kWh / m2 / day [13]. Arid
and semi-arid regions are often characterized by water
scarcity, hot dry weather, large areas of poor soils [15] and
dust storms [16]. Annual rainfall in Bloemfontein is 550 mm
[17] with the majority of rains falling in the summer months.
Annual summer temperatures can exceed 30ºC with severe
dust storms being experiences on occasions [18].
IV. EXPERIMENTAL SETUP
The experimental setup consists of three identical PV
systems comprising 10 W polycrystalline PV modules, a
data logging interface circuit, an Arduino board, LabVIEW
software and a fixed load resistor of 82 Ω (see Fig. II for the
four main block components). The only variable which is
different between the three systems is the tilt angle.
No batteries were included in the experimental setup of
the three PV systems (exact duplicate of each other) due to
uncertain variations which may exist between batteries from
the same manufacturer and with the same model number. In
fact, battery-to-battery variations in e.m.f at a given state of
charge may be in the order of 50 mV due to variations in the
manufacturing process, ageing and charge-discharge cycling
of a single 2.25 V cell [19].
Using a fixed load resistance, instead of a solar charger of
maximum power point tracker with a given load, is an
effective and easy method to start loading PV modules
located outdoors for measurement purposes [20, 21]. The
data logging interface circuit has been reported on by a
number of researchers [22-24] and provides power
conditioning between the PV system and the Arduino board
which is connected to the personal computer and interfaced
with LabVIEW software.
The three PV modules were mounted onto an
aluminum frame and initially set to the same tilt angle equal
to the Latitude of the installation site. The output power of
these modules was then recorded and analyzed using
LabVIEW software in conjunction with an Arduino board.
Results were obtained over a four week period (October
2014) which indicated a coefficient of variation of 1.4%.
This coefficient of variation is calculated using the standard
deviation and mean of the collected data. This ensures the
reliability and validity of subsequent electronic
measurements when the three PV modules are set to the
three different tilt angles (see Table I for the values).
Reasons for using the LabVIEW software in conjunction
with an Arduino board are substantiated in the following
sections.
Table I: Three different tilt angles based on research done
by Heywood [25] and Chinnery [26]
Author
Equations of
latitude
Tilt angle for
Bloemfontein
Time period
used
Heywood
φ − 10°
29º − 10° = 19º
Summer
Heywood
φ
29º
Autumn /
Spring
Chinnery
φ + 10°
29º + 10° = 39º
Winter
Figure II: Experimental setup
Zenith
True North Horizontal Plain
Tilt
A. LabVIEW
National Instruments LabVIEW is a graphical
programming language that has its roots in automation
control and data acquisition. Its graphical representation,
similar to a process flow diagram, was created to provide an
intuitive programming environment for scientists and
engineers. The language has matured over the last 20 years
to become a general purpose programming environment.
LabVIEW has several key features which make it a good
choice in an automation environment. These include simple
network communication, turnkey implementation of
common communication protocols (RS232, GPIB, etc.),
powerful toolsets for process control and data fitting, fast
and easy user interface construction, and an efficient code
execution environment [27].
B. Arduino
The Arduino is an electronic platform designed to
simplify the process of studying digital electronics [28]. The
Arduino system consists of a microcontroller, a
programming language and an Integrated Development
Environment (IDE) [29]. Arduino was born to teach
Interaction Design, a design discipline that puts prototyping
at the centre of its methodology [30]. The designers
attempted to design a user-friendly software and hardware
interface, making freely available the necessary
documentation to support it [31].
C. LabVIEW user interface
Voltage readings are obtained from the Arduino board by
using the analog read function in LabVIEW. The obtained
values are then multiplied by a predetermined factor for
calibration and to compensate for any interface losses. The
immediate value is displayed on the front panel of the
LabVIEW software that is visible on the screen of the PC.
This value is then filtered by a Butterworth Filter before it is
written into a matrix. The filter is used to filter out high
frequency components that come from the Arduino’s analog
read circuit and any other high frequency noise present in
the data logging system.
Voltage readings from the Arduino board represent PV
module output voltages, currents and surface temperatures.
Current readings are obtained by measuring the voltage
across a low value high power precision resistor (10 Ω 10 W
1%). Voltage readings are obtained by using a standard
voltage divider circuit (147 kΩ resistor in series with a 100
kΩ resistor). Temperature readings are obtained by using a
thermistor which is connected to the back of the PV module.
One way of comparing the performance of the three PV
systems was to record the amount of samples where the
output power of each module exceeded a set limit (3.5 W in
this research). In order to have a record of the percentage of
time that each PV module produced more than 3.5 W of
power, a shift register was used in which the value was
incremented each time a sample’s value were above the set
limit. The accumulation of these values was automatically
written into a singular file at the end of each day.
Another way to evaluate the performance of each of the
three PV systems was to record the Watt hours (Wh)
generated by each module. This was done by calculating the
mean power for a specific number of samples and then
multiplying that mean power with the time in hours
represented by those samples. This results in an
instantaneous Wh value for a specific number of samples
taken within a 24 hour period. The LabVIEW user interface
is shown in Fig. III where the following is discernable [28]:
the total amount of samples that are to be recorded and
written to a single file (see A);
the Arduino board that is used for the sampling (see B);
the set limit for the power sample count (see C);
the calibration factor for the current (see D) and voltage
of each module (see E);
the instantaneous power for each module (see F);
the accumulated Wh for each module (see G),
a limited logged history as well as the instantaneous
values of the current (see H), voltage (see I) and power
(see J); and
the total sample count which has been completed (see
K).
Figure III: LabVIEW user interface
V. RESEARCH METHODOLOGY
The purpose of this research is to present empirical
evidence establishing the optimum tilt angle for PV modules
in a semi-arid region of South Africa during the summer
season. The area is located in the heart of South Africa
(Bloemfontein, Free State) that enjoys 55% of its annual
rainfall between January and April [32].
An experimental research design is used where all three
PV modules were initially set to the same tilt angle of 29º
(Latitude value of the installation site). Four weeks of data
(October 2014) were then recorded to observe any
significant differences between the three systems (see Fig.
IV). A coefficient of variation of 1.4% was calculated
indicating that all three systems were performing equally
well.
The three PV modules were then set to three different tilt
angles (see Fig. IV), resulting in only one different variable.
All other variables (environmental conditions, orientation
angles, load resistances, etc.) were standard for the three
systems. Data was recorded from mid November 2014
through the end of January 2015 which corresponds to the
summer months for the installation site. The tilt angles of
PV 1 and PV 3 were then swapped around for the month of
February, in order to ensure the validity and reliability of the
collected data. This ensures that the variable under scrutiny
is the tilt angle, and not the PV system itself. Power sample
counts above 3.5 W and Wh results were used to determine
which tilt angles produced the highest output power for this
period. PV surface temperatures were also recorded where
the data is depicted in figures and tables in the next section.
PV 3 19 Deg
PV 2 29 Deg
PV 1 39 Deg
PV 3 39 Deg
PV 2 29 Deg
PV 1 19 Deg
October 2014
PV 1 = 29 Deg PV 2 = 29 Deg PV 3 = 29 Deg
November 2014 February 2015
to January 2015
Figure IV: Experimental setup of the PV modules
VI. RESULTS AND DISCUSSION
Two measurements, namely the amount of power samples
above 3.5 W and Wh per day were used to determine the
optimum tilt angle of the PV modules. Fig. V depicts the
number of power samples above 3.5 W for two weeks
during November 2015. It can be seen that PV 1 (tilt angle
of Latitude minus 10º) had the highest sample count of more
than 3500, with PV 3 (tilt angle of Latitude plus 10º) having
the lowest power sample count of 3000. These results are
further verified by the Wh measurements displayed in Fig.
VII, where PV 1 produced 50 Wh on the 15 of November
2014, as compared to the 46 Wh produced by PV 3. The
monthly averages for power samples above 3.5 W are
displayed in Fig. VI while the monthly averages of the Wh
measurements are shown in Fig. VIII. These results suggest
that a PV module, installed at a tilt angle of Latitude minus
10º, produces more output power than those installed at
different tilt angles in this semi-arid region. The highest
power sample counts (2793, 2491 and 2708) and Wh
readings (43.2, 42.4 and 47.6) occur for a tilt angle set to
Latitude minus 10º for the months of November through
January.
Figure V: Power samples above 3.5 W for November 2015
However, in February 2015 the trend reversed! This is
due to the fact that the researchers swapped the tilt angles of
PV 1 and PV 3 at the end of January 2015. This was to
verify that the tilt angle, and not the PV system, was
responsible for the higher output power. This is confirmed
by the results shown in Fig. VI and Fig. VIII, where PV 3
(now set to Latitude minus 10º) now has the highest output
power for the month of February 2015 (2800 power sample
count above 3.5 W and an average Wh reading of 49.7 W).
Figure VI: Average power samples above 3.5 W for the three PV modules
Figure VII: Wh measurements for November 2015
Figure VIII: Average Wh measurements for the three PV modules
The path of the sun is longer and the elevation angle
higher during the summer months in the southern
hemisphere, thereby suggesting high PV module surface
temperatures. Fig. IX displays the results of the PV
module’s surface temperature, where PV 1 (tilt angle equal
to Latitude minus 10º) had the highest recorded value of
56ºC on the 28 November 2015. This is due to the fact that
0
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Power samples above 3.5 W
PV 1 = Lat - 10 PV 2 = Lat PV 3 = Lat + 10
November December January February
PV 1 2793 2491 2708 2707
PV 2 2674 2356 2649 2749
PV 3 2428 2069 2471 2800
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Monthly averages for power samples
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Watt hours
PV 1 = Lat - 10 PV 2 = Lat PV 3 = Lat + 10
November December January February
PV 1 43.2 4 2.4 47.6 48.3
PV 2 42.0 4 1.3 46.7 49.0
PV 3 39.7 3 8.9 45.7 49.7
38.0
40.0
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46.0
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Watt hours
Monthly averages for power in Wh
more direct-beam radiation is received by the PV module
giving rise to its higher output power as shown in the
preceding figures. The maximum surface temperature for
PV 1 was higher than that for PV 3 during November,
December and January (see Fig. X). However, this trend
reversed in February 2015 due to the fact that these two
module’s tilt angles were swapped around. The fact that the
lower tilt angle (Latitude minus 10º) produces a higher
surface temperature correlates to research done by Ozemoya
et al. [33].
Figure IX: Surface temperatures for the three PV modules in November
2015
Figure X: Average surface temperatures for the three PV modules
VII. CONCLUSIONS
The purpose of this paper was to present empirical
evidence establishing the optimum tilt angle for PV modules
in a semi-arid region of South Africa during the summer
season. Three identical PV systems were installed at CUT in
Bloemfontein were specific data was collected over a four
month period. PV system reliability and validity was firstly
established by having all three systems set to the same tilt
angle with all experiencing the same external variables (e.g.
environmental conditions and load resistances). A
coefficient of variation of 1.4% was established indicating a
higher level of similarity between the three systems. Three
different tilt angles were then used, with PV module 1 being
set to Latitude minus 10º, PV module 2 to Latitude and PV
module 3 to Latitude plus 10º. Results from the power
sample count above 3.5 W and from the Wh calculations
indicate that PV module 1 produced the highest output
power for the months of November 2014 through January
2015. However, PV module 3 claimed this right in Febuary
2015, as its tilt angle was changed from Latitude plus 10º to
Latitude minus 10º.
Based on these results, it is recommended that PV
modules be placed at a tilt angle of Latitude minus 10º for
semi-arid regions in South Africa during the summer season.
Possible limitations of this study include the fact that only
one research installation site was used and that data has not
yet been collected for the winter periods. Recall that
research by Asowata et al. [6] suggested an annual optimum
tilt angle of Latitude plus 10º for higher yields of output
power. Obtaining results for the winter months and adding
them to these results may verify if pollution intensive areas
differ significantly from semi-arid areas in terms of what the
recommended annual tilt angle for PV modules should be to
produce optimum output power.
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PV 2 45.4 4 7.4 50.2 49.0
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44.0
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Pierre Hertzog received his DTech: Electrical: Engineering degree
in 2004 from the Central University of Technology. His research
interests include alternative energy and automation &
manufacturing systems.
James Swart received his DTech: Electrical: Engineering degree
in 2011 from the Vaal University of Technology. His research
interests include engineering education and alternative energy. He
is currently an Associate Professor at the Central University of
Technology.
