PLC CONTROLLED DUAL-AXIS SOLAR
TRACKING SYSTEM
2021
MASTER THESIS
ELECTRICAL&ELECTRONICS ENGINEERING
FAYSIL ABDULHAMID SULAYMAN ALFIRJANI
Thesis Advisor
PLC CONTROLLED DUAL-AXIS SOLAR TRACKING SYSTEM
Faysil Abdulhamid Sulayman ALFIRJANI
T.C.
Karabuk University Institute of Graduate Programs
Department of Electrical&Electronics Engineering Prepared as
Master Thesis
Thesis Advisor
Assist.Prof.Dr. Hüseyin ALTINKAYA
KARABUK January 2021
ii
I certify that in my opinion the thesis submitted by Faysil Abdulhamid Sulayman ALFIRJANI titled “COMPARISON OF THE EFFICIENCIES OF DUAL-AXIS, SINGLE-AXIS SOLAR TRACKING SYSTEMS AND FIXED PV SYSTEM IN KARABUK” is fully adequate in scope and in quality as a thesis for the degree of Master of Science.
Assist.Prof.Dr. Hüseyin ALTINKAYA ... Thesis Advisor, Department of Electrical&Electronics Engineering
This thesis is accepted by the examining committee with a unanimous vote in the Department of Electrical&Electronics Engineering as a Master of Science thesis. January 27, 2021
Examining Committee Members (Institutions) Signature
Chairman : Assist.Prof.Dr. Mustafa GÖKDAĞ (KBU) ...
Member : Assist.Prof.Dr. Hüseyin ALTINKAYA (KBU) ...
Member : Assist.Prof.Dr. Osman ÇİÇEK (KU) ...
The degree of Master of Science by the thesis submitted is approved by the Administrative Board of the Institute of Graduate Programs, Karabuk University.
Prof. Dr. Hasan SOLMAZ ...
iii
“I declare that all the information within this thesis has been gathered and presented in accordance with academic regulations and ethical principles and I have according to the requirements of these regulations and principles cited all those which do not originate in this work as well.”
iv ABSTRACT
M. Sc. Thesis
COMPARISON OF THE EFFICIENCIES OF DUAL-AXIS, SINGLE-AXIS SOLAR TRACKING SYSTEMS AND FIXED PV SYSTEM IN KARABUK
Faysil Abdulhamid Sulayman ALFIRJANI
Karabük University Institute of Graduate Programs
The Department of Electrical and Electronics Engineering
Thesis Advisor:
Assist. Prof. Dr. Hüseyin ALTINKAYA January 2021, 84 pages
The importance of renewable energy and its share in electricity generation is increasing day by day. And the solar energy has acquired a vital place among different types of renewable energy sources. In this thesis, dual-axis tracking system, single-axis solar tracking system and fixed solar panel system were designed. These three solar panel systems were compared according to their efficiencies and the power they produce. Identical solar panels with a power of 100 Wp were used in all three systems. Solar panels were installed on Engineering Faculty roof of Karabuk University. PLC was used in order to control the biaxial and uniaxial solar panels. The angle of the axes was controlled using astronomical data and a real time clock. The current and voltage values produced by all three panels were measured at 10 minutes intervals and displayed and recorded on the SCADA screen with PLC/SCADA software. The obtained data were analyzed, and the three panels were compared in terms of the power
v
they produced under different weather conditions. Then, the results were evaluated accordingly. According to the data taken from November 10th to November 30th 2020, the dual-axis solar tracker was 5.43% more efficient compared to a single-axis solar tracking system, and it was 24.04% more efficient when compared with a fixed solar panel. With all the evaluations, it was concluded that the efficiency of single-axis solar tracking system was 20.17% more as compared to fixed solar panel.
Key Words : Solar tracking system, PV panel, PLC, SCADA Science Code : 9544
vi ÖZET
Yüksek Lisans Tezi
KARABÜK’TE ÇİFT EKSENLİ, TEK EKSENLİ GÜNEŞ TAKİP SİSTEMLERİ VE SABİT PV SİSTEMİN VERİMLİLİKLERİNİN
KARŞILAŞTIRILMASI
Faysil Abdulhamid Sulayman ALFIRJANI
Karabük Üniversitesi Lisansüstü Eğitim Enstitüsü
Elektrik-Elektronik Mühendisliği Anabilim Dalı
Tez Danışmanı:
Dr. Öğr. Üyesi Hüseyin ALTINKAYA Ocak 2021, 84 sayfa
Yenilenebilir enerjinin önemi ve elektrik üretimindeki payı her geçen gün artmaktadır. Güneş enerjisi, farklı yenilenebilir enerji kaynakları arasında hayati bir yer edinmiştir. Bu tezde çift eksenli ve tek eksenli güneş takip sistemi ile sabit güneş paneli sisteminin tasarımı gerçekleştirilmiştir. Bu üç güneş paneli sistemi verimlilik ve ürettikleri güç bakımından kıyaslamaları yapılmıştır. Her üç sistemde 100 Wp gücünde özdeş güneş paneli kullanılmıştır. Güneş panelleri Karabük Üniversitesi Mühendislik Fakültesi binasının çatısına kurulmuştur. Çift eksenli ve tek eksenli güneş panellerinin kontrolü PLC ile yapılmıştır. Eksenlerin açısı astronomik veriler ve gerçek zaman saati kullanılarak kontrol edilmiştir. Her üç panelin ürettikleri akım ve gerilim değerleri 10 dk aralıklarla ölçülerek PLC/SCADA yazılımı ile SCADA ekranında görüntülenmiş ve kaydedilmiştir. Elde edilen verilerin analizleri yapılarak farklı hava koşullarında ürettikleri güç bakımından üç panelin karşılaştırması yapılmış ve sonuçlar
vii
değerlendirilmiştir. 10-30 Kasım 2020 tarihlerinde yapılan ölçümlere göre çift eksenli güneş takip sisteminin tek eksenli güneş sistemine göre % 5.43, sabit güneş paneline göre ise % 24.04 daha verimli; tek eksenli güneş takip sisteminin de sabit güneş paneline göre % 20.17 daha verimli olduğu sonucuna ulaşılmıştır.
Anahtar Kelimeler : Güneş takip sistemi, PV panel, PLC, SCADA Bilim Kodu : 9544
viii
ACKNOWLEDGMENT
I sincerely thank and acknowledge the support of my supervisor Assist.Prof.Dr. Hüseyin ALTINKAYA. I am deeply indebted to him for his kind guideline during the accomplishment of my thesis. I appreciate his valuable knowledge, his keenness about the research process, and willingness to support.
I acknowledge the efforts of my parents, brothers and sisters offer my sincerest love to my family especially to My Mother and an older brother who has always been with me with their material and moral support throughout my academic studies. They really have endless contributions to my education and career.
I recognize the efforts of the university employees, support staff, and my coursemates. I am also thankful to the university administration, the Turkish Government, and the people for their kindness and cooperation.
ix CONTENTS Page APPROVAL ... .ii ABSTRACT ... iv ÖZET... vi ACKNOWLEDGMENT ... viii CONTENTS ... ix
LIST OF FIGURES ... xii
LIST OF TABLES ... xv
SYMBOLS AND ABBREVITIONS INDEX ... xvi
CHAPTER 1 ... 1
INTRODUCTION ... 1
CHAPTER 2 ... 5
LITERATURE REVIEW... 5
CHAPTER 3 ... 14
SOLAR ENERGY AND SOLAR ENERGY POTENTIAL ... 14
3.1. SOLAR ENERGY POTENTIAL OF TURKEY ... 15
3.2. SOLAR ENERGY POTENTIAL OF KARABUK ... 18
3.3. SOLAR CELL ... 20 3.4. SUN ANGLES ... 23 3.4.1. Latitude Angle ... 24 3.4.2. Declination Angle ... 24 3.4.3. Hour Angle ... 24 3.4.4. Inclination Angle ... 25 3.4.5. Zenith Angle ... 26 3.4.6. Elevation Angle ... 26 3.4.7. Azimuth Angle... 27
x
Page
3.4.8. Surface Azimuth Angle ... 27
3.4.9. Incidence Angle ... 28
CHAPTER 4 ... 29
SOLAR TRACKING SYSTEMS ... 29
4.1. ACCORDING TO CONTRL SYSTEM USED ... 29
4.1.1. Closed Loop Tracking System... 29
4.1.2. Open Loop Tracking System ... 30
4.2. ACCORDING TO DRIVING SYSTEM USED ... 30
4.2.1. Passive Solar Tracking ... 30
4.2.2. Active Solar Tracking ... 31
4.3.ACCORDING TO DEGREE OF FREEDOM ... 31
4.3.1. Single Axis Tracking System ... 31
4.3.2. Dual Axis Tracking System ... 32
4.4. ACCORDING TO TRACKING STRATEGIES ... 32
4.4.1. Electro Optical Sensors and Microprocessors ... 32
4.4.2. Time and Date... 32
4.4.3. Time, Date and Sensors ... 33
CHAPTER 5 ... 34
DESIGN OF SOLAR TRACKING SYSTEM ... 34
5.1. DESIGN OF THE MECHANICAL PARTS ... 34
5.2. ELECTRICAL EQUIPMENTS ... 37 5.2.1. PLC ... 37 5.2.2. AI Module ... 38 5.2.3. DO Module ... 38 5.2.4. Poer Supply ... 39 5.2.5. Stepper Motors... 39
5.2.6. Stepper Motor Drivers ... 40
5.2.7. Current Measurement Circuit ... 40
xi
Page
5.2.9. Resistance Printed Circuit ... 43
5.2.10. Relays ... 44
5.2.11. Electrical Panel ... 45
5.3. PLC AND SCADA SOFTWARE ... 46
5.3. MEASUREMENT RESULTS ... 55
CHAPTER 6 ... 64
CONCLUSION AND SUGGESTIONS ... 64
6.1. CONCLUSIONS ... 64
6.2. SUGGESTIONS ... 65
REFERENCES ... 67
APPENDIX A. PARTS OF LADDER DIAGRAM ... 77
xii
LIST OF FIGURES
Page
Figure 1.1. World electricity production by source 2017. ... 1
Figure 1.2. The installed capacity rates in 2019 according to primary sources in Turkey ………..2
Figure 1.3. The electricity production rates in 2019 according to primary sources in Turkey………..2
Figure 1.4. Solar energy installed capacity in Turkey in 2014- July 2020. ... 3
Figure 3.1. Solar energy potential map of Turkey. ... 15
Figure 3.2. Radiation values of Turkey according to months. ... 16
Figure 3.3. Sunshine duration in Turkey. ... 17
Figure 3.4. Solar energy potential map of Karabuk. ... 18
Figure 3.5. Irradiation values in Karabuk. ... 18
Figure 3.6. Sunshine duration of Karabuk . ... 19
Figure 3.7. Poly-Crystalline cell. ... 21
Figure 3.8. Mono-Crystalline cell. ... 21
Figure 3.9. Mono-Crystalline cell and Poly-Crystalline cell. ... 21
Figure 3.10. PV types used in Turkey. ... 22
Figure 3.11. PV types used in Karabuk. ... 22
Figure 3.12. Declination angle. ... 24
Figure 3.13. Inclination angle. ... 25
Figure 3.14. Basic solar angles. ... 27
Figure 5.1. 100Wp polycrystalline solar panel. ... 34
Figure 5.2. Fixed solar panel. ... 35
Figure 5.3. Worm gear reducer. ... 36
Figure 5.4. Single axis solar panel. ... 36
Figure 5.5. Double axis solar panel. ... 37
Figure 5.6. S7-1200 1215C DC/DC/DC PLC. ... 38
Figure 5.7. AI module. ... 38
xiii
Page
Figure 5.9. Power supply. ... 39
Figure 5.10. Nema 24 stepper motor. ... 40
Figure 5.11. Stepper motor driver. ... 40
Figure 5.12. Current measurement circuit... 41
Figure 5.13. Top view of the printed circuit for current measuring. ... 42
Figure 5.14. Bottom view of printed circuit for current measuring. ... 42
Figure 5.15. Voltage measuring circuit. ... 43
Figure 5.16. Top view of the printed circuit for voltage measurement. ... 43
Figure 5.17. Bottom view of printed circuit for voltage measurement. ... 43
Figure 5.18. Resistances printed circuit. ... 44
Figure 5.19. Relays. ... 45
Figure 5.20. Electrical Panel. ... 45
Figure 5.21. Device&Networks view of the project . ... 46
Figure 5.22. Portal View of the project. ... 46
Figure 5.23. Device Configuration view of the project . ... 47
Figure 5.24. SPA calculator interface . ... 48
Figure 5.25. Karabuk University Engineering Faculty coordinates . ... 49
Figure 5.26. PV panels placed on the roof . ... 50
Figure 5.27. Flow chart of the system . ... 51
Figure 5.28. SCADA screen1 ………....52
Figure 5.29. SCADA screen 2………53
Figure 5.30. SCADA screen 3………53
Figure 5.31. Voltage values in November 20, 2020 at 14.20………54
Figure 5.32. Current values in November 20, 2020 at 14.20………..54
Figure 5.33. V-t graph on November 13, 2020………...56
Figure 5.34. I-t graph on November 13, 2020……….57
Figure 5.35. P-t graph on November 13, 2020………57
Figure 5.36. V-t graph on November17, 2020……….58
Figure 5.37. I-t graph on November 17, 2020……….59
Figure 5.38. P-t graph on November 17, 2020………59
xiv
Page Figure Appendix A. Parts of the ladder diagram………78
xv
LIST OF TABLES
Page
Table 3.1. Distribution of the total annual solar energy potential in Turkey. ... 16
Table 3.2. Solar PV capacity by country and territory (MW) and share of total electricity consumption………..……17
Table 5.1. Label values of solar panels. ... 35
Table 5.2. Data obtained for November 20, 2020 between 13.00-15.00 hours. ... 48
xvi
SYMBOLS AND ABBREVITIONS INDEX
SYMBOLS
α : elevation angle β : inclination angle
γs : azimuth angle
γ : surface azimuth angle δ : declination angle θ : incidence angle Ø : latitude angle θz : zenith angle ω : hour angle ABBREVITIONS
DAPV : Dual-Axis PV Panel FF : Fill Factor
FPV : Fixed PV Panel
PLC : Programmable Logic Controller SAPV : Single-Axis PV Panel
SCADA : Supervisory Control and Data Acquisition STS : Solar Tracking System
1 CHAPTER 1
INTRODUCTION
In this developing world, the need for energy and its consumption are increasing day by day. Fossil fuels are still meeting most of the energy needs of the world. However, since the fossil-fueled energy resources are not environmentally friendly and most importantly, they carry the risk of being depleted after a few decades, the trend towards alternative energy sources has increased in recent years. Among these alternative energy sources, renewable energy sources have become inevitable for both our environment and the ecology of the world we live in, since they are clean, environmentally friendly and continuous. Some of the examples of renewable energy resources include hydraulics, solar, wind, geothermal, biomass, wave etc.
The renewable energy sources’ share in electricity production has been increasing day by day. The renewable energy sources such as solar, wind, geothermal and hydro had a share of 22.9% in electricity generation in the world in 2017 as seen in Figure 1.1. Hydraulic energy is known to be the most widely used type of renewable energy in electricity generation in the World and in Turkey, when compared to other renewable energy sources.
2
Especially in the last decade, major investments were made on solar energy in the world and in Turkey. However, the share of solar energy in electricity production is still quite small as compared to other sources. This rate is aimed and as well as predicted to be increased in large numbers in the upcoming decades. As shown in Figures 1.2 and 1.3, the installed solar power capacity in Turkey was found to be 6.57% by the end of 2019. In 2019, solar energy share in electricity production was shown to be 3.19%.
Figure 1.2 The installed capacity rates in 2019 according to primary sources in Turkey [2].
Figure 1.3. The electricity production rates in 2019 according to primary sources in Turkey [2].
As seen in Figure 1.4, Turkey did not have a noteworthy installed capacity of solar power before the year 2014, however, a considerable increase in installed solar power capacity has been observed in the last six years since 2014. The installed power, which
3
was found to be 40.2 MW in 2014, increased to 6232.1 MW in July 2020. In 2019, 9573.8 GWh (3.19%) of electricity out of a total of 300407 GWh, was generated using solar energy [2].
Figure 1.4. Solar energy installed capacity in Turkey in 2014- July 2020 [2].
Solar panels are used in order to generate electrical energy from the sun. PV panels can only convert a small part of the solar radiation coming on them into E.E (electrical energy). In this respect, their efficiency varies from 10 to 25%. Various methods are used to obtain the highest efficiency from solar panels. One of these methods is solar tracking system.
Large scale solar power plants or farms are set up using fixed PV panels. Some medium sized solar power plants, some small powered systems and experimental setups are designed as uniaxial and/or biaxial. Solar energy systems are seen to be overwhelmingly installed using fixed PV panels. The reason for this is that single and biaxial PV panels are currently not feasible and profitable due to initial installation and maintenance costs.
In this thesis, three PV panels of 100Wp power were designed for fixed, uniaxial and biaxial tracking of the sun, and their hardware and software were made accordingly. The powers obtained simultaneously from all three panels were compared.
4
A summary of the literature regarding the thesis has been presented in chapter 2. Theoretical background related to the PV panels has been given in chapter 3. Solar tracking systems have been explained in chapter 4. The design, hardware and software of the prototypes are explained in chapter 5. Finally, results and suggestions are given in chapter 6.
5 CHAPTER 2
LITERATURE REVIEW
In their study conducted in 2020, Jamroen et al. designed, developed and then implemented an automatic dual axis tracking system [3]. The system they designed was aimed at adjusting the PV module accurately through secondary axis and primary axis in order to follow trajectory of sun by logic design by using LDR. In their designed system, they used a pseudo-azimuthal system to get stability during the movement mechanism. LDRs were installed by implementing simple configuration which could mitigate the tracking errors that were caused by complex orientations.
In a study by M. A. Jallal et al., a machine learning algorithm known as DNNRODDPSO was developed using hybridization of a new neural network with an algorithm known as RODDPSO to predict exact amount of energy that was produced using a combination of four double axis solar tracking called as DAST systems [4].
Y. Zhu et al. presented a single-axis tracker for PV system in order to increase the yield of solar radiation [5]. Tracked panel’s normal vector was implemented and characteristics of the structure were analyzed. Their approach was validated numerically based on solar radiation model that was predicted in combination with geometric sun-earth relationships.
In a study conducted by Nadia et al., based on ANFIS, two intelligent and efficient single-axis and dual-axis solar tracking systems were presented [6]. Their paper showed that the ANFIS may be used to implement as well as to design solar trackers. It was implemented successfully in control of solar trackers. They predicted optimum tilt and orientation angles. The results of their simulations showed a higher rate of prediction and a lower rate of mean square error.
6
In a study proposed by Boon-Han et al. in 2020, the industrial design of dual-axis solar tracker on a large scale along with Vertical axis Rotating Platform and Multiple-Row-Elevation were studied [7]. The study comprised a large platform rotating in azimuth direction and some multiple PV module rows that were tracking in direction of elevation. The resolution in azimuth angle and tracking precision were found in their tracking system through body integrated encoder (electromechanical).
In a study by A. Awasthi et al. in 2020, an overview of advances in solar tracking system field was presented. They also emphasized on analysis of the dual-axis solar trackers in terms of performance by using different designs and techniques that were evolved recently [8].
A photovoltaic module converts the energy from sun into thermal or E.E (electrical energy) [9]. A solar tracker may be used for the purpose of extracting max. output power from photovoltaic module. In a study by Hernández-Callejo L. et al., many ways that can be used to produce electricity have been described [10]. Owing to ability of Renewable Energy (RE) to produce electrical energy independent of fossil fuel. Renewable Energy is therefore globally accepted way of electricity production by using utility-scale generation in the form of Distributed Generations (DGs). According to Homadi et al., 2020, solar energy is the source of renewable energy which directly comes from sun in radiation form [11]. Srikumar and Saibabu, in 2018 defined the solar tracking systems as systems that track trajectory of sun along sky and keep them at the optimum angles so that they may produce an optimum power output, thus, increasing the collected energy [12]. According to Kamran et al., in 2018 and Sahu et al., in 2020, there were found to be several researches that had been published for the usage of different Artificial intelligence models for solar tracking system control [13].
According to International energy outlook, the electricity generated globally by the RE sources has the tendency to reach nearly up to 45 trillion kWh by the end of 2050 [14]. In a report by Anton SG and friends, the renewable energy consumption has been set to approximately 20% of its total gross energy consumption until 2020 in Europe [15]. And according to a report by Zafar MW et al., the total installation capacity for the Asian Pacific Economic Cooperation countries (APEC) will touch 6235 GW by the
7
year 2040 and the share of renewable energy share will reach 35% of its capacity [16]. In addition, the South East Asian Nations Association (ASEAN) are expecting to achieve a target of approximately 23% of the primary energy by 2025 [17,18]. Especially, in many parts of the world, Photovoltaic (PV) using RE sources is being used as the top priority alternative in the generation of electrical energy. According to a report of IEA Market report series, the photovoltaic energy will globally reach approximately to a value of 8 trillion kWh by the end of 2050 and will be led by China [18]. Furthermore, the photovoltaic power production initially increased up-to 350 GW in 2017. Now, they expect it to reach to a value of 750 GW in 2023 for the region of Asian-Pacific [18].
In a study performed by Hafez A. et al. and Nsengiyumva W. et al., solar tracking system was shown to be divided theoretically into 2 rotation types as single and dual axis type [19,20]. The above-mentioned systems can easily operate various input measurement devices which may be divided as passive tracking and active tracking systems [19,21]. In another research by Hafez A. et al., closed and open loop based controls systems were shown to control the axes of rotation of the tracking system. In a study conducted by Batayneh W. et al., and Chin C. et al., single-axis rotation was integrated to the tracking systems in order to follow the trajectory of sun in E-W direction [22,23]. In recent studies, focus has been made on dual-axis tracking system modeling through implementation of a low-cost hardware. In a study conducted by Motahhir S. et al. on low-cost tracker, it was found to have increasingly developed to reduce the possible investments on the installations in practice [24]. In another study by Cruz-Peragón F., dual axes solar tracking system was investigated in order to ensure the economic efficiency as well as potential of the flat-plate systems [25]. In addition, according to Yılmaz S. et al. and Seme S. et al., the solar tracking systems that employ light dependent resistors have received a tremendous interest for a potential low-cost tracker [26,27]. Solar tracking systems have played an essential role in applications of different PV systems for the past few decades, for instance PV greenhouses [28], Photovoltaic storage systems [29], large-scale PV plants [30] and rooftop PV systems [31]. Several studies have provided different tracking systems as well as their limit up to which the incident of radiation exceeds over the tracked panels in a fixed-panel system, for example, V-axis tracker proposed by Li [32], NS axis and IEW trackers
8
proposed by Chang [33, 34], and double-axis tracker proposed by Senpinar [35]. Many studies have presented the determination and evaluation techniques of the best solar tracking type that is based on energy gain and the tracking accuracy. Okoye [36] has analyzed solar resources on all tracking types, especially double axis tracking and found it to be 1.86% to 31.52% high as compared to the yields achieved through single-axis tracking systems. Therefore, as expected, the dual-single-axis tracking ought to be recommended. Jacobson [37] has considered only the single axis tracking system and he provided comparison between NS axis tracking and V axis tracking. He suggested using V axis tracking but not at high latitudes. In another study performed by Bahrami et al., [38] the annual performance versus the latitude was analyzed in all single axis tracker types, and IEW axis tracking was proved to be the best for the latitudes that were below 26 degrees. And the V axis tracking was found to be the best for other latitudes. In a study on PV plants, Martin [39] worked on six PV plants installed in Spain and he pointed out the complexity found in dual-axis trackers during operation and when the maintenance is underestimated. Furthermore, Bahrami and his friends [40,41] combined some technical feasibility of the systems with the economic feasibility through the use of an indicator which was called the electricity at levelized cost. Results in the studies have shown that single-axis tracking is advantageous as compared to dual-axis tracking if total PV system cost for installation is relatively low. Authors have designed the energy-efficient solar tracking systems which at certain times are actuated during the day from the sunrise to the sunset [42,43].
In a study by Batayneh et al.,[42] a discrete V axis tracking system actuated thrice a day in azimuthal plane was proposed. According to their experimental results, it was shown that the energy yield was about 91 to 94 percent as compared to continuous tracking system. In a similar study by Zhong et al., [43] IEW axis tracking system with the PV tilt angle that is adjusted four times annually was proposed which would absorb a 96 percent of the annual radiation as in dual-axis tracking system. Another study performed by Mirzaei et al. [44] demonstrated experimentally that while considering energy consumption in the tracking mechanism, tri-axis tracking performs far better than both continuous and dual-axis tracking in the regions having long sunshine hours. Antonanzas [45] made a real-time tracking algorithm which can maximize the energy production under different changing weather conditions and in his results, there was a
9
3.01% increase in radiation. Furthermore, Fernandez et al. [46] presented a series of new mathematical expressions for different single-axis tracking systems. Their models focused on the traditional approach which considers solar position by maximizing the global solar radiation. Apart from these single-axis optimization approaches, there are several studies that focus on less common optimizations, like the shading analysis [47,48] and also the usage of bifacial photovoltaic panels [49,50]. In a study conducted by Eldin et al., 2015 and Nenciu and Vaireanu, 2014, [51,52] it was reported that the tracking system tracks the sun direction and when the sunbeam gets perpendicular to the surface of the solar concentrator or the photovoltaic module, maximum value of the solar energy is thus captured. The previous researches conducted on PV systems determined that approximately 20 to 50 percent more solar energy may be captured through solar trackers in the PV systems depending on geographical locations [53].
In a study performed by Barker et al., it was reported that the dual-axis solar tracker can move in two freedom degrees, therefore it can easily track the sun in two different directions that are daily motions and seasonal motions [54]. In a study conducted by Eke and Senturk in 2012, [55] it was clearly stated that the dual-axis solar tracker is far more accurate when tracking the sun path as compared to the single-axis tracker. In another study by Roth et al. in 2005, [56] it was found that the output power of photovoltaic module can be increased up-to nearly thirty three percent (33%) when compared to the fixed PV type using a dual-axis solar tracking system. Both single-axis and dual-single-axis tracking systems are have two types which can be classified as the sensor based and the sensorless solar trackers [57]. In a study, Syafii et al. [58] reported the utilization of sensorless small-sized dual-axis solar tracking system which uses altitude and azimuth angles that are provided using a database in 2015.
Due to the pollution and shortage of fossil fuels, being a kind of renewable and clean energy source, solar energy has drawn more attention, especially when it comes to electricity generation. The process of solar energy conversion to electrical energy is conducted through CSP systems or flat PV systems. The output power that the above-mentioned systems can produce depends on some factors including amount of energy that they receive from the solar radiation. The researchers have conducted studies on optimal angle of the solar collector in order to increase the power output [59-60]. As
10
the position of the sun changes throughout the day, solar tracker is considered to be a more efficient way of contributing to the energy production. Therefore, more and more researchers are conducting studies on solar trackers.
A review of different types of the solar trackers was carried out by Nsengiyumva et al., (2018) and AL-Rousan et al., (2018) [61,62]. But, many of the solar tracking designs were the small-scale prototypes that were used for research purposes, especially the ones emphasizing on an electronic control system. In another study by Nsengiyumva et al., in 2018, the large-scaled solar trackers were foreseen as a vital criterion to mitigate the overall cost of the solar tracking system. Nowadays, two types of solar trackers are being used mainly based on the movement capability; single-axis tracker [63-64] and dual-axis tracker [65-68]. In a study conducted by Clifford and Eastwood [69,70], a passive solar tracker was activated by the aluminium/steel bi-metallic strips and was controlled using a viscous damper. In their study, Poulek and Libra [71] designed a simple single-axis solar tracker which was based on a completely new arrangement of the bifacial solar cell that was directly connected to a DC motor.
In a study conducted by Roth et al., [72] an azimuth-altitude dual-axis solar tracker was proposed which was guided through a closed loop serve system, and was able to be operated automatically. In another study by Batayneh et al., [73] a dual-axis solar tracking system was proposed with an altitude-azimuth mounting that was controlled using a designed fuzzy controller. Previous studies have confirmed the use of solar trackers in various solar collector systems. In a study conducted by Kim et al., [74] the single polar axis tracker was applied to a CPC solar collector. In a study conducted by Kacira et al. in July in Sanliurfa, [75,] an average gain of 34.6% was shown in generated power daily with dual-axis solar tracking system as compared to a fixed Photovoltaic panel. In another study by Abdallah and Nijmeh, [76] a dual-axis sun tracking system was designed for a PV system. The system surface was observed to show an increase of up to 41.34% in collected energy as compared to the fixed surface. In a study by Batayneh et al. (2019), it was proposed that a discrete single axis solar tracker gets activated only thrice a day based on the optimal angle calculations. The results achieved after experimentation demonstrated that this tracking system yields about 90% to 94% of the solar energy which is produced by a similar system of
11
continuous solar tracking system [77]. Abdollahpour et al. (2018) built a somehow unique system of the solar tracking through using an image processing system [78]. The working principle was based on the opaque object and its shadow’s relationship i.e., if the angle between object and surface is larger, the shadow will be longer when the surface will be perpendicular to sun rays. For instance, if the sunshine has an angle of 90◦ then there will be no shadow casted on the surface.
In CSP systems, single-axis solar trackers which are designed for the flat PV systems cannot be implemented due to their low accuracy. Their low accuracy may lead to a greater loss of the solar energy that is intercepted by the receiver. Using a tracker that is designed for the high-accuracy tracking purposes in a flat PV system will lead to extra operational costs in control process. Such a mounting system was used by Bakos et al. in their study [79] for improving the efficiency of the parabolic trough collector (PTC) practically.
In a study conducted by Mavromatakis and Franghiadakis, a novel single-axis solar tracker was presented that had the ability to move collector's plane through a special support structure in two directions [80]. Previous studies show that the solar trackers have been widely used in various solar collector systems. In a study conducted by Chin et al., an active single-axis solar tracking system was presented that was used in the flat PV systems [81]. The experimentally performed test results showed around 20% efficiency when compared to the fixed solar panel. In a study, Chang performed tests on the flat PV system that was mounted on the single-axis tracker and he found a gain of 17.5% when the single-axis solar tracking panel was installed with the yearly optimal angle [82]. According to the studies conducted by Duffie and Beckman [83] and Mousazadeh et al. [84], it was found that on cloudy days, when the solar disk is not visible and direct radiation does not reach the collectors, collectors located on a fixed horizontal position would collect more energy than those with astronomical tracking.
In a study by Diaz-Dorado et al., [85,86] a model was devised that would consider the specific arrangement of cells in the PV modules, and also the position of every module on the tracking surface, in order to optimize and characterize the design of the tracking
12
plants. In another study conducted by Martinez-Moreno et al., [87] a predictive model was proposed to estimate the power losses that were caused through shading, and the model did not require any information related to the cells and modules connections. In a similar study, for the purpose of optimizing energy costs considering the design parameters, Perpi-nan [80] found a method called as the Ground Cover Ratio (a ratio of the area of the PV module and the area occupied by Photovoltaic plant). In a study of the productivity of the PV system, Navarte and Lorenzo [88] worked on different solar tracking types and presented three hypotheses regarding the estimation of losses due to shading.
In a study conducted by M.J. Clifford et al., [90] a mechanical solar tracker was designed which was activated through the bi-metallic strips and was controlled using a viscous damper. In another study by E. Lorenzo et al., [91] the theoretical aspects of the single axis vertical tracking system were introduced which were specifically associated with design of the tracking system and the shadowing of different trackers and their features were taken into consideration. B.J. Huang and F.S. Sun [92] presented a PV module of a three position single axis solar tracking system that can easily adjust the position in three fixed angles (during morning, noon and afternoon). If a continuous or non-stop tracking is performed throughout the daylight, the efficiency of the system can be increased.
In a study conducted by A. Yazidi et al., [93] a dual-axis solar tracking system was presented that was controlled by both fuzzy controller and PID. The dual-axis tracker consists of two DC motors which are used to rotate the PV cell in 2 axes. In a study, T.A. Ocran et al. [94] devised a fuzzy logic controller that operates for the maximum power tracking of the standalone photovoltaic system. The fuzzy logic controllers were also compared with conventional PI controllers in terms of performance. They demonstrated that the fuzzy logic controllers developed faster and better tracking capabilities at the different optimal operating points. In a study by H.-C. Lu and T.-L. Shih, [95] a design was presented for the active solar panel of a dual-axis tracking system including a fuzzy controller with maximum power point tracking. Their system tracks the sun in order to improve the efficiency of photovoltaic cells. This mechanism
13
mainly consists of two motors which allow the shafts to rotate in order to keep the PV panel in an optimum position.
14 CHAPTER 3
SOLAR ENERGY AND SOLAR ENERGY POTENTIAL
The mass of the Sun, which is known to be one of the 200 billion stars known in the Milky Way Galaxy, consists of hot gases and emits radiation in the form of heat and light. Sun is a medium-sized star that is located closest to the Earth at an average distance of 150 million km from it, and the Sun is known to be at the center of the Solar System. Its diameter is 1392x105 km and its mass is approximately 1.989x1030 kg, that is 332950 times the mass of the Earth. The mass of the sun consists of hot gases and emits heat and light. The Sun is known as a photo sphere with a surface temperature of approximately 5900K (Kelvin). After the fusion reaction of ~ 8.9x1056 protons, that is, the hydrogen nucleus in the sun, 3.4x1038 of the protons turn into helium nuclei per second. With a matter-energy conversion rate of 4.26x106 tons per second, 3.83x1026W, or in other words, petroleum energy equivalent to 9.15x 1010 mega tons is emerged. Photons that are emerged and have high energy (cosmic, gamma and X-rays) ensure life continuity on Earth with photosynthesis and undertake an important role in determining the climate and weather of the Earth.
Solar energy can be defined as a radiant energy that is released during the fusion process (transformation process of hydrogen into helium gas) in the core. According to the researches, solar energy intensity outside Earth's atmosphere is known to be approximately 1370 W/m2; however, the energy reaching the earth surface changes between 0-1100 W/m2 because of the atmosphere. A small part of this received energy that reaches the world is many times higher than the current energy use of the humanity. Studies on solar energy utilization showed especially an immense increase after the 1970s. Since then, the solar energy systems showed a decrease in cost and the technological progress, and currently, it is accepted as an environmentally clean energy source.
15
Not all the solar radiation reaches the surface of earth because atmosphere reflects back up to 30% of it. Only 50% of the solar radiation passes through atmosphere and reaches to the surface. Owing to this energy that reaches the Earth, the Earth’s temperature rises, thus, the survival of living entities becomes possible. Solar radiation also causes ocean ripples and wind movements. Almost up to 20% of the sun's radiation gets trapped in the clouds and atmosphere. Only Less than 1% of the solar radiation coming to the earth is consumed by plants during photosynthesis. The plants produce sugar and oxygen by utilizing water, sunlight and carbon dioxide during the process of photosynthesis, which is the vegetation source on earth. Sun is the direct or indirect source of all energies on the Earth other than nuclear energy [96].
3.1. SOLAR ENERGY POTENTIAL OF TURKEY
Turkey's solar energy potential has been shown in the Figure 3.1 below. The Western Black Sea region, including the province of Karabuk, is one of the regions with the least sunlight exposure as compared to other regions. The Mediterranean region and southeast Anatolia region are the regions that receive the most sunlight.
Figure 3.1. Solar energy potential map of Turkey [97].
16
Table 3.1. Distribution of the total annual solar energy potential in Turkey [98]. District Total Solar Energy
(KWh/m2 – year) Insolation time (hour/year) Southeastern Anatolia 1460 2993 Mediterranean 1390 2956 Eastern Anatolia 1365 2664 Central Anatolia 1314 2628 Aegean 1304 2738 Marmara 1168 2409 Black Sea 1120 1971
Figures 3.2 and 3.3 shows the average value of radiation and sunshine duration in Turkey according to months, respectively.
Figure 3.2. Radiation values of Turkey according to months [97]. 0 1 2 3 4 5 6 7
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1.79 2.5 3.87 4.93 6.14 6.57 6.5 5.81 4.81 3.46 2.14 1.59 Ir radi at ion (kWh /m 2-day) Months
17
Figure 3.3. Sunshine duration in Turkey [97].
In Table 3.2, the solar energy potential of some countries and its share in total electricity consumption in 2015-2019 are given.
Table 3.2. Solar PV capacity by some country and territory (MW) and share of total electricity consumption [99].
2015 2016 2017 2018 2019 Share
of total Country or
territory Added Total Added Total Added Total Added Total Added Total consumption China 15,150 43,530 34,540 78,070 53,000 131,000 45,000 175,018 30,100 204,700 3.9% (2019) European Union 7,230 94,570 101,433 107,150 8,300 115,234 16,000 131,700 4.9% (2019) United States 7,300 25,620 14,730 40,300 10,600 51,000 10,600 62,200 13,300 75,900 2.8% (2019) Japan 11,000 34,410 8,600 42,750 7,000 49,000 6,500 55,500 7,000 63,000 7.6% (2019) Germany 1,450 39,700 1,520 41,220 1,800 42,000 3,000 45,930 3,900 49,200 8.6% (2019) India 2,000 5,050 3,970 9,010 9,100 18,300 10,800 26,869 9,900 42,800 7.5% (2019) Italy 300,000 18,920 373,000 19,279 409,000 19,700 20,120 600,000 20,800 7.5% (2019) Australia 935,000 5,070 839,000 5,900 1,250 7,200 3,800 11,300 3,700 15,928 8.1% (2019) United Kingdom 3,510 8,780 1,970 11,630 900,000 12,700 13,108 233,000 13,300 4.0% (2019) South Korea 1,010 3,430 850,000 4,350 1,200 5,600 2,000 7,862 3,100 11,200 3.1% (2019) France 879,000 6,580 559,000 7,130 875,000 8,000 9,483 900,000 9,900 2.4% (2019) Spain 56,000 5,400 55,000 5,490 147,000 5,600 4,744 8,761 4.8% (2019) Netherlands 450,000 1,570 525,000 2,100 853,000 2,900 1,300 4,150 6,725 3.6% (2018) TURKEY 584,000 832,000 2,600 3,400 1,600 5,063 5,995 5.1% (2019) Vietnam 6,000 6,000 9,000 106,000 4,800 5,695 Ukraine 21, 432 99 531 211 742 1,200 2,003 3,500 4,800 1.3% (2019) WORLD TOTAL 59,000 256,000 76,800 306,500 95,000 401,500 510,000 627,000 83,000 3.0% (2019) 0 2 4 6 8 10 12
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 4.11 5.22 6.27 7.45 9.1 10.8111.3110.7 9.23 6.87 5.15 3.75 D urat ion (hou rs ) Months
18
3.2. SOLAR ENERGY POTENTIAL OF KARABUK
The solar energy installed power in Karabük is 0.67 MW. A private company in Karabuk has a PV plant consisting of 2804 units in an area of 12000m2 on the roof of a shopping mall. With this, 150 thousand kWh of electricity is produced and 50 thousand kWh is used for domestic consumption. The solar energy potential map of Karabuk province, its irradiation values and sunshine duration have been given in Figures 3.4, 3.5 and 3.6 respectively.
Figure 3.4. Solar energy potential map of Karabük [100].
Figure 3.5. Irradiation values in Karabük [100]. 0 1 2 3 4 5 6 7
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1.49 2.36 3.39 4.4 5.79 6.08 6.07 5.36 4.29 2.83 1.72 1.24 Ir radi at ion (kWh /m 2-day) Months
19
Figure 3.6. Sunshine duration of Karabük [100].
3.3. SOLAR CELL
Solar cells also called as photovoltaic cells are the semi-conductor substances which carry out the conversion of sunlight reaching their surfaces into E.E (electrical energy) directly. Generally, the solar cells with square, rectangle or circle shaped surfaces are around 100 cm², and they have a thickness between 0.1 to 0.4 mm. These cells work on the photovoltaics principle which is; when light is incident on them, the electrical voltage is produced at their ends. The electrical energy source delivered by the cells is actually the solar energy reaching the surface of the cells. The conversion efficiency is around 5% to 30% depending on solar cell structure. Many solar cells are connected either in parallel or series and are fixed on a surface; the structure is known as a photovoltaic module or solar cell module in order to increase power output. The modules are connected in such a way, depending on the power demand, to create a system ranging from a few Watts to a few MEGA Watts.
Photovoltaic cells can be produced using many different substances. Today, the most used materials are as follows: Crystal Silicon (c-Si, p-Si), Gallium Arsenide (GaAs), Amorphous Silicon (a-Si), Cadmium Telluride (CdTe), Copper Indium Diselenide
0 1 2 3 4 5 6 7
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1.49 2.36 3.39 4.4 5.79 6.08 6.07 5.36 4.29 2.83 1.72 1.24 D urat ion (hou rs ) Months
20
(CuInSe2) and Optical Concentrator Cells. Since the most widely used solar cells among them are c-Si and p-Si types, some comparative information will be given only about these two types of solar cells. Generally, the monocrystalline solar panels are thought of as premium solar products. Main advantages of the monocrystalline panels are sleeker aesthetics and higher efficiencies.
In order to make solar cells for the monocrystalline solar panels, the silicon is first formed into bars and then cut into wafers. Such types of panels are known as “monocrystalline” to specify the silicon used is the single-crystal silicon. As the cell is composed of single crystal, electrons which generate the electricity flow have more space to move. Therefore, monocrystalline panels are efficient as compared to their respective polycrystalline counterparts.
Generally, the polycrystalline solar panels are known to have low efficiencies as compared to monocrystalline panels; however the advantage that they have is the lower price. Furthermore, polycrystalline solar panels have a blue hue which is black in monocrystalline panels.
The polycrystalline solar panels are made up of silicon as well. However, manufacturers melt several small fragments of silicon in order to form wafers for panels instead of using the single silicon crystal. Also, polycrystalline solar panels are called as “multi-crystalline” or “many-crystal silicon”. As there are various crystals found in each cell of polycrystalline panels, there is comparatively less freedom for electron motility. As a result, the polycrystalline solar panels are known to have low efficiency ratings as compared to monocrystalline panels.
While the efficiency of monocrystalline cells is between 15 to 24%, the efficiency of polycrystalline cells varies between 14 to 19%. Figure 3.7 below shows a poly-crystalline cell and the Figure 3.8 shows a mono-poly-crystalline cell.
21
Figure 3.7. Poly-Crystalline cell.
Figure 3.8. Mono-Crystalline cell.
Figure 3.9. Mono-Crystalline cell and Poly-Crystalline cell.
Figure 3.10 shows the PV types used in Turkey, whereas, Figure 3.11 shows the PV types used in Karabuk.
22
Figure 3.10. PV types used in Turkey [97].
Figure 3.11. PV types used in Karabuk [100].
3.4. SUN ANGLES
There are certain angles between the rays of sun and the surfaces on the earth. By obtaining information regarding these angles, solar energy can be used in the most efficient way. The solar radiation incident on the surface of fixed or mobile solar
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000 26000 28000 0 10 20 30 40 50 60 70 80 90 100 monocrystalline silicon policrystalline silicon thin copper film tape cadmium tellurium amorphous silicon Turkey PV type area energy that can be produced (KWh
-K Wh /ye a m2 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000 0 10 20 30 40 50 60 70 80 90 100 monocrystalline silicon policrystalline silicon thin copper film tape cadmium tellurium amorphous silicon
Karabuk PV type - area - energy that can be produced (KWh - year)
K Wh /ye a r m2
23
panels varies with the latitude and the longitude of the location of the plane, and the date and the time period of that particular day. The position of the plane where the system is installed as well as the angle of inclination play an important role in the value of the radiation falling on the solar panel. Therefore, these angles that determine the position of the sun must be known. Especially in solar energy systems, these concepts are very important in calculating the radiation falling on the surface and also in determining the position and angle of the panels. The sun rays falling on the panel surface at any position vary with the time period of that particular day. Therefore, there are certain angles that need to be known. In order to benefit from solar energy efficiently, panels should follow the solar position according to these angles. The definitions and commonly used formulas for some terminologies related to solar angles used for fixed and mobile solar PV systems are as follows.
3.4.1. Latitude Angle
The angle formed according to the center of equator is called as the latitude angle (Ø). The north and the south of the equator are positive and negative, respectively and they vary between -90º ≤ Ø ≤ 90º. In order to define any location on Earth’s surface, latitude and longitude are used. According to the location, Turkey is at 26º-45º East longitude and 36º-42º North latitude [101-103].
3.4.2. Declination Angle
The angle between the equator plane and the sun lights is called Declination angle (δ). This angle occurs due to an angle of 23.45 degrees between rotational angle of Earth and the orbital plane. Declination angle tends to be positive on the north and it varies between the angles -23.45º ≤ δ ≤ 23.45º. It is at the highest point (23.45º) on June 21st, whereas, it is at the lowest point found to be -23.45º on December 22nd in winter. The declination angle has been shown in Figure 3.12 below.
24
Figure 3.12. Declination angle.
3.4.3. Hour Angle
The angle between longitude of the specified location and longitude of the sun lights is called the Hour angle (ω). Angle before noon time is taken as (-) and after noon time is taken as (+), respectively. The hour angle is found to be 0 at noon. It is defined as difference taken between the noon time and the desired time on a particular day and is calculated by the multiplication of the difference found by 15 which is a fixed number. The number is the angle calculated at 1 hour rotation of earth around Sun. The expression used in order to calculate the hour angle from the solar time is given in equation 3.1 as;
ω = 15 (𝑡𝑠−12) (3.1) where ts is solar time given in hours [102-104].
3.4.4. Inclination Angle
Tilt angle, denoted as (β), is defined as the angle taken from the inclined panels and horizontal plane. Tilt angle is found to be north oriented in Southern Hemisphere and south oriented in Northern Hemisphere. This angle may vary between the angle 0º ≤ β ≤ 180º. When the plane of the panel is rotated in the east-west horizontal axis with just a single adjustment daily, tilt angle of that particular surface is found to be fixed for
25
that day. The afore-mentioned angle can be calculated by equation 3.2 given as follows;
β = | Ф – δ | (3.2) Whereas, when that plane tends to be rotated on the east-west horizontal axis with some continuous adjustments, tilt angle of that particular surface can be calculated by equation 3.3 given as;
tan β = tanθ𝑧. | cos γ𝑠 | (3.3) In case of a plane rotation about the north-south horizontal axis with some continuous adjustments, tilt angle of that surface can be calculated through the following equation given as;
[tan β = tan θ𝑧 . | cos (γ - γ𝑠) | (3.4) Figure 3.13 below shows the inclination (tilt) angle.
26 3.4.5. Zenith Angle
Zenith angle (θ𝑧) can be defined as the angle between the vertical axis and the line to the sun. There are some basic solar angles that exist on the surface of the earth and are shown in the Figure below. The angle is found to be 90 degrees during the sunrise and the sunset, whereas it is found to be 0 degree at noon time. This angle can be calculated depending on some other angles [26,82,105].
cos θ𝑧 = cosδ . cosθ . cosω + sinδ . sinθ (3.5) 3.4.6. Elevation Angle
The angle between the horizontal plane and the line to the sun is called the solar elevation angle (α). Solar elevation angle is complement of zenith angle which is known to be 9 degrees. This angle is calculated by equation given as;
α = 90 -θ𝑧 (3.6) 3.4.7. Azimuth angle
Solar azimuth angle (γs) can be defined as the angle between south or north position of sun and direct solar radiation. Solar azimuth angle is found to be (+) when taken from south to west and (-) when taken from south to east. This angle is 180 degrees at noon time. The azimuth angle can be calculated by the equation given below.
γs = cos-1 [(sin(α) . sin(Ф) - sin(δ) / cos(α).cos(Ф)] (3.7)
27
Figure 3.14. Basic solar angles.
3.4.8. Surface Azimuth Angle
Surface azimuth angle, denoted as (γ), can be defined as the angle between projection of normal to surface which is on a horizontal plane and the line that is due south. Surface azimuth angle is found to be 0 in south, positive (+) towards west and negative in east (-). This angle varies between negative 180 degrees and positive 180 degrees [103, 104].
3.4.9. Incidence Angle
The angle found between radiation incident on surface directly and normal of that particular surface is called the Incidence angle and is denoted by (θ). The angle is (θ=0º) when the incidence angle is found to be steeper to the sun rays. Furthermore, if the angle is determined to be parallel to sun rays, it is found to be (θ=90º). The tilt and the incidence angles are depicted in Figure 4 below.
The incidence angle that has been defined is used in design of the solar energy systems. It is calculated by equation (8) given below; [103-105]
28
29 CHAPTER 4
SOLAR TRACKING SYSTEMS
Solar tracking systems are the systems designed to follow the sunlight throughout the day in order to get energy from PV panels in the most efficient way. In this part of the thesis, solar tracking systems (STS) will be classified according to the control systems used, drive systems, number of axis (degree of freedom) and tracking strategies, and information regarding these systems will be given accordingly.
Solar tracking systems can be classified according to the drivers used, control system used, tracking strategy used and last but not the least according to degree of freedom in the movement that is exhibited by system.
4.1. ACCORDING TO CONTROL SYSTEM USED
The single-axis tracking systems are almost the best solution for the small photovoltaic modules. Such systems generally involve axis tilt adjustment or manual elevation on second axis that is adjusted at some regular intervals whole year. This system is cheaper than the other systems. This system can be moved vertically or horizontally depending on location of the sun as well as the weather.
4.1.1. Closed LoopTracking System
When the sensors are used in order to detect the timely position of sun and the obtained information is returned to the system as a feedback, the microprocessor or the comparator used in system easily detect the error and send the required signal to motors in order to correct the error. Such a system is considered to be running on the feedback control system principle. The driving system that is used for movement of such a
30
tracker is not important in this case as it may be a passive system or a pre-defined algorithm based on mathematical calculations for the trajectory of the sun.
4.1.2. Open Loop Tracking System
This is a type of system which uses a controller to give the driving signal to motors mainly on basis of input data and the operating algorithm of system alone. This system has no characteristics of evaluating or observing the output data in terms of the desired output. Therefore, it is simpler and cheaper to implement this system when compared with closed loop tracking system. However, this system does not involve any rectification process, thus the algorithm alone needs to achieve the desired goal.
4.2. ACCORDING TO DRIVING SYSTEM USED
4.2.1. Passive Solar Tracking
Passive solar tracking system does not involve any mechanical drives in order to rotate the panels towards sun’s radiations. But, this system uses compressed gas fluid that has a low boiling point or some shape memory alloys used as actuators which force the panels to show angular movement to re-establish the equilibrium on receiving some unbalanced illumination. When one side of system comprising liquid gas receives greater amount of the heat energy compared to other side, the gas starts expanding and moves towards other side of tracker. This causes unbalanced gravitational pull and thus forces panels to tilt. The panels keep tilting until a point is reached where there is an equal illumination [106]. Although this system is known to be less complex and effective, it fails to provide higher efficiencies at lower temperatures.
4.2.2. Active Solar Tracking
This system uses some mechanical gear trains and electrical drives in order to orient the panels at a point normal to sun’s radiations. The system uses motors, sensors and microprocessors for solar tracking and are found to be more efficient and accurate than passive solar trackers. However, such systems consume energy because they need to
31
be powered. The sensors tend to receive illumination at different points and create differential signal. This signal is then used by the microprocessor or the comparator to determine the movement in appropriate direction when trackers are not properly aligned with the sun. Accordingly, the required signal is given to motors. The whole process stops at the point where sensors receive an equal illumination and PV module is properly aligned with sun’s radiations.
4.3. ACCORDING TO DEGREE OF FREEDOM
The degree of freedom specifies number of directions towards which an independent movement may occur. The solar tracking systems are classified into single and double axis tracking systems based on this. In order to determine the appropriate directions and locations, some parameters such as latitude, longitude, angle of incident, declination angle, elevation angle, zenith angle, solar azimuth angle play an essential role.
4.3.1. Single Axis Tracking System
Single axis system involves movement in one axis where rotation is conducted to align the panel in a way that is perpendicular to sun’s radiations. It has been shown that the most preferred orientation is alongside north meridian axis [84]. The discrete single axis tracker has been proposed which actuates only three times a day and is based on optimal angle calculations [73]. The results obtained from experiments have shown a yield of about 90% to 94% of solar energy in such systems.
Several configurations of such single axis systems that include vertical alignment module (VSAT), horizontal alignment module (HSAT), tilted module (TSAT), horizontal with tilted modules (HTSAT) and polar aligned module (PSAT) have been investigated so far. SATs are found to be less complex and cheaper. However, they are less efficient as compared to DATs.
32 4.3.2. Dual Axis Tracking System
This system involves two axes rotation that are generally perpendicular to each other. Dual axis tracking system requires control system that is more complex and is found to be efficient as compared to single axis trackers (SATs). The experiments conducted on 300 kW dual axis parabolic collector have shown that the system has the ability to boost the efficiency by 15% to 17% when compared to the single axis tracking system [107].
4.4. ACCORDING TO TRACKING STRATEGIES
4.4.1. Electro optical sensors and Microprocessors
This system makes use of sensors to detect the sun’s position. The signal is first fed to microprocessor. The microprocessor, then, instructs the motors through a signal. There have been such designs for solar tracking system that have used sensors such as 3 light dependent resistors, dc motor with reduction gears and electronic circuit [108]. In those proposed systems, the sensors were used to give inputs to electronic circuits which in turn actuated the motors.
4.4.2. Time and Date
This tracking system only uses the pre-defined algorithms that are based on some mathematical calculations regarding the trajectory of sun in order to determine sun’s position at some particular time to orient the photovoltaic panels accordingly. In this system, there is no sensor or feedback loop involved. Therefore, only algorithm is responsible for efficient working of system.
4.4.3. Time, Date and Sensors
This system works on some predefined algorithm. However, it is used to have a check on overall operation of sensors that are involved. These verify the exact position of sun and accordingly, drive and orient the panels. Dual-axis hybrid tracking system was proposed for mixed tracking strategy that was used, the open loop tracking that was
33
based on the solar movement model and the closed loop tracking system that fed back the signal which was found to be proportional to the generated output power [109].
34 CHAPTER 5
DESIGN OF SOLAR TRACKING SYSTEM
Three PV panels with a power of 100W were placed in three separate mechanical setups, and the movement of single-axis and dual-axis solar tracking systems were controlled. The open circuit voltage and short circuit current of all three systems were measured and recorded at 10 min intervals. Load resistors, inverters and charging units were not used in the systems. Maximum power point tracking (MPPT) was not performed. In this part of the thesis, design and production stages, hardware and software of the three systems (fixed PV panels, single axis and dual axis solar tracking PV panels) whose prototypes were made are explained.
5.1. DESIGN OF THE MECHANICAL PARTS
The mechanical setups that were used to carry and move the 670x970x25 mm polycrystalline solar panels, whose figure and default data are given in Figure 5.1 and Table 5.1 respectively, were designed as follows:
35
Table 5.1. Label values of solar panels.
Model Type
LXRN100P
Brand Name Lexron
Electrical Characteristics
Rated Maximum Power (Pmax) 100Wp Power Tolerance Range 5% Open Circuit Voltage (Voc)
(Typical value) 22.10 V
Maximum Power Voltage (Vmp)
(Typical value 18.00 V
Short Circuit Current (Isc)
(Typical value) 6.45 A
Maximum Power Current (Imp)
(Typical value) 6.11 A
Max System Voltage 1000 V Max Series Fuse Rating 10.0A Weight (Typical Value) 8.5 Kg Module Application Class A
All technical data at standart test condition: E=1000W/m2 𝑇𝑐=25ºC
PV panels are placed on mechanical supports made up of profiles. The inclination angle of the fixed panel can be adjusted between 30 to 60 degrees with a mechanical system. Since the inclination angle for Karabük is 39 degrees, the panel is fixed at this angle. Figure 5.2 shows the fixed panel.
36
Single axis solar panel moves in east-west (right-left) direction. Worm gear reducer has been used to provide this movement. Reducer type is S30 and gear ratio is 1/50. With the reducer, the torque of the step motor is increased by decreasing the rpm. With this mechanical system, 360 degree movement capability is provided to the PV panel. It is seen that the reducer mechanical system is a bit more expensive compared to the mechanical systems where other equipment such as linear actuators are used, but it provides much wider and more precise movement. Figure 5.3 shows worm gear reducer and Figure 5.4 shows single axis solar panel.
Figure 5.3. Worm gear reducer.
37
Double axis solar panel moves in east-west (right-left) and north-south (up-down) direction. Two worm gear reducers have been used to provide these movements. This system has capability to move 360 degrees in the east-west direction and 180 degrees in the north-south direction. Both axes can move simultaneously at the same time. Figure 5.5 shows a double axis solar panel.
.
Figure 5.5. Double axis solar panel.
5.2. ELECTRICAL EQUIPMENTS
5.2.1. PLC
S7-1200 1215C DC/DC/DC type PLC was used in order to control and remotely monitor the fixed, single-axis and dual-axis solar tracking systems (STS). The PLC that has been shown in Figure 5.6, has 14 digital inputs (DI), 10 digital outputs (DO), 2 analog inputs (AI), 2 analog outputs (AO), 2 PROFINET ports and 125 KB memory.
38
Figure 5.6. S7-1200 1215C DC/DC/DC PLC.
5.2.2. AI Module
6 AIs are needed for measuring the current and voltage values of the PV panels but there are 2 AIs on the PLC. For this reason, SM 1231 module with 8 AIs shown in Figure 5.7 has been added to the PLC.
Figure 5.7. AI module.
5.2.3. DO Module
A total of 15 DOs are needed for driving the step motors and controlling the relays. There are 10 DOs on the PLC. Therefore, SM 1222 module with 8 DO shown in Figure 5.8 has been added to the PLC.
39
Figure 5.8. DO module.
5.2.4. Power Supply
Power supply in Figure 5.9 has been used to feed the AI module and DO module of PLC and step motor drivers. The power supply has 240W, 220V AC/24V DC ratings.
Figure 5.9. Power supply.
5.2.5. Stepper Motors
A total of three Nema 24 type stepper motors were used in this experimental setup. Of three, two were used in the dual-axis solar tracking system, and one was used in the single-axis solar tracking system. Step motors enable the axis movements of PV panels. The shaft of step motors was connected to worm gear reducers. The purpose behind this was to reduce the mechanical load on the stepper motors and to obtain high torque at lower revolutions. The step angle of the stepper motor shown in Figure 5.10 is 1.8º.
40
Figure 5.10. Nema 24 Stepper Motor.
5.2.6. Stepper Motor Drivers
Three CWD556 type drivers were used to drive stepper motors. Detailed information The driver seen in Figure 5.11.
Figure 5.11. Step motor driver.
5.2.7. Current Measurement Circuit
Since the measurement of the currents of PV panels is conducted using the analog inputs (AI) of the PLC and as AIs of PLC function between 0-20 mA or 0-10 V, a current measurement circuit was needed. The 𝐼𝑠𝑐 currents of PV panels were found to be 6.45A. In order to measure the current of the PV panels by the PLC, the printed circuits of Proteus/ISIS circuit as shown in Figure 5.12 were made.
