DEVELOPMENT OF SUN TRACKING STRUCTURAL CONCEPTS BASED ON THE POSITION OF THE SUN FOR THE TERRITORY OF THE CITY OF KRAGUJEVAC

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1 DEVELOPMENT OF SUN TRACKING STRUCTURAL CONCEPTS BASED ON THE POSITION OF THE SUN FOR THE TERRITORY OF THE CITY OF KRAGUJEVAC N. Kostić, M. Bojić, M. Blagojević, V. Marjanović, M. Miletić, Faculty of Engineering, University of Kragujevac, Serbia Utilization of solar energy is very important for a sustainable supply of buildings with electricity and heat. This paper gives analyses of necessary values for development of sun-tracking systems for more efficient generation of electricity from solar energy. Typical angles were analyzed for positioning the mechanism on the territory of the city of Kragujevac. Requirements for the development of a suntracking system are defined for Kragujevac along two axis of rotation. It is suggested that tracking by rotating around the east-west axis would be done on a daily, and along the north-south axis on an hourly basis. The use of sun tracking systems largely influences energy efficiency in exploitation of solar energy. At the end of the paper, based on the results of the suggested conception which enable exquisite development of the design, a solution of the sun tracking system is given. Key words: sun tracking, solar angle, energy efficiency, design concept INTRODUCTION Research related to the production and exploitation of energy today is oriented towards renewable resources. The main reasons for this is the benefits which are based on the inexhaustible resources, energy efficiency, reduction of CO2 emissions and the conservation of the environment. An energy source which is increasingly being exploited through technical development is solar energy. Modern research is oriented towards increasing the efficiency of systems which use solar power. The direction, in which a substantial increase in efficiency of solar systems can be made, is by systems tracking the sun. Numerous authors indicate the fact that efficiency is increased by using systems for solar tracking [1, 3, 4, 6, 7]. Aside from that, research is directed towards finding a favorable andle for a stationary solar system [2, 5, 6, 9]. Authors which are developing systems for solar tracking have defined two basic types of systems. There are single-axis [1], and dual-axis systems [2, 3, 4, 5] depending on the rotational axis along which tracking is performed. Certain authors are oriented towards practical use [3]. 1

2 The motivation behind this paper is achieving a greater efficiency of solar systems. The research its self is oriented on the territory of the city of Kragujevac in Serbia, so that in time it would be possible to practically utilize the suggested solutions in Serbia. These solutions will lead in efficiency since they are specifically tailored to this location. IDENTIFYING THE PROBLEM Exploitation of solar energy represents an important step in the conservation of the environment. In order for solar energy to be harnessed, it is necessary to create systems which are economically justified and have sufficient efficiency. Solar systems achieve greatest efficiency when the incoming sun rays fall at a 90 angle on the solar collector surface or PV panel. The problem with developing a system for tracking the sun is in calculating the range of angles for positioning the system and defining clear structural development goals, which is the orientation of this research. This paper is modeled from the research of author Jasmina S. [9], which is based on defining optimal values of angles for solar panel placement for the city of Belgrade. Mathematical description Figure 1 shows values needed for calculations Figure 1. Incoming angle of sun s rays [8] The incoming angle and its range are defined by equation (1), [8]. cos(θ) = sin(l) sin(δ) cos(β) cos(l) sin(δ) sin(β) cos(z S ) + cos(l) cos(δ) cos(h) cos(β) + sin(l) cos(δ) cos(h) sin(β) cos(z S ) + cos(δ) sin(h) sin(β) sin(z S ) The used variables are: L longitude of desired location, 2

3 δ declination, β tilt of the surface relative to the horizon, Z S azimuth angle of the surface, h - hourly angle. When the tilt of the surface relative to the horizon is β=0, the incoming angle is determined by a much simpler equation [6, 7, 8]: sin(θ) = sin(l) sin(δ) + cos(l) cos(δ) cos(h) Declination can be defined as [8]: δ = 23,45 sin 360 (284 + N) 365 Where, N (0-364 days) is the ordinal day of the year. The rotation axis of the Earth is always at an angle of from the real normal of the revolution plane, and which passes through a common point of the rotation axis and revolution axis. The hourly angle used in equation (2) is calculated as [7, 8]: h = ±0,25 (Number of minutes from local solar noon) Here the sign determines the time to and from noon. The previous equation can be used to calculate the incoming angle for rotation around the east-west axis. Based on incoming angle values it is easy to define the angle at which the sun tracking mechanism should be positioned relative to the horizon: α = 90 θ Solar azimuth angle represents the value which should be followed along the north-south axis. Azimuth angles can be calculated using the following equation [8]: sin(z) = cos(δ) sin(h) cos(θ) If the sun projects rays on the horizontal plane behind the east-west azimuth angle line for morning hours the value is π + Z, and for afternoon hours, when the azimuth angle passes the east-west line the value is π Z. This research is oriented towards the area of Kragujevac which is located at L = latitude. Calculating the azimuth angle for the needs of this research is done for the period from 8AM to 4PM. Interesting days for observation are: 21 December (solstice) day 344, 21 Jun (solstice) day 172, 22 March (equinox) day 81, 22 September (equinox) day

4 RESULTS Calculation results For rotation around the east-west axis the in incoming angle is applicable. The range of this angle for the entire year is between 22,3 and 69,23 for 12 hour periods, and the calculated values are presented in figure 2. The average daily change in angle per day is 0,26. This value is very important for continuing angle change throughout the day when creating a system for solar tracking. The angle which defines the position of the solar tracking systems in relation to the horizon on a daily level have a range of 20,8 to 67,7, which is also presented in figure 2. Angle degree, [ ] Altitude angle Inclination Day number of the year Figure 2. Incoming angle and tilt angle around the east-west axis over the course of a year Figure 3 presents azimuth angle values. The observed interval is from 8AM to 4 PM. Values for March 22 nd and September 22 nd are very similar. This angle is defined for following the north-south axis movement, keeping in mind that the solar tracking system is oriented south. At noon the value of this angle for all days of the year is 0. 4

5 Solar azimuth angle in degree, [ ] December Jun September March 0-208:00 9:00 10:00 11:00 12:00 1:00 2:00 3:00 4: Time interval, hours Figure 3. Azimuth angle values for characteristic days For AM hours angle values are negative, and for the PM hours they are positive. For an 8 hour interval the angle range is in an interval of to for various days, while for 4PM this range is from 75.2 to The maximal range of the angle for the period from 8AM to 4PM is 150,4. This value is important for designing and creating a system structure for solar tracking. For linear tracking it is possible to adopt values for March 22 nd and September 22 nd. Creating a system concept for solar tracking Basic requirements which are imposed when designing the system are given in table 1: Table 1. Requirement list for designing the system for solar tracking Subsystem Requirement Subsystem Function Request Dificulty Anchoring to the roof Element bracket. Maintains compactness of the system and maintains connection to the roof. Strong demand Enables change of system angle on a daily level. For continual tracking this angle changes by 0,26 daily. This Rotation around east-west axis angle has a minimal value of 20,8 to a maximal value of Strong demand 67,7 relative to the horizon. An angle range of 46,9 should be ensured Rotation around North-west axis Enables system angle change on an hourly basis. For continual tracking this angle changes by 15,03 every hour. Continual tracking of 135,27 Strong demand 5

6 should be ensured from to Propelling subsystem Subsystems which enable propulsion and achieving desired positions of the system. This can be achieved through the use of various motors or manual adjustment depending Strong demand on availability and economical restrictions. It is possible to achieve this using one or more propulsion subsystems. Reducing subsystem The subsystems which enables the defined change of angle as a function of time. Reducing should be used only in combination with certain propulsion subsystems. Demand A subsystem which is used Subsystem for defining and for adjusting shortcomings in following current position of the system functionality and Desirable the sun possible automation of the control process. In case of stopping the system due to undesirable weather conditions or other reasons for the system s inability to Subsystem for retracting to a function, this subsystem fixates the system in a safe posi- safe position Desirable tion so that any damage can be prevented. This position should be achievable at any given time. This subsystem can ensure desirable positions in a longer System for fixating on an optimal angle value time interval, if a change in the system s operational regime Desirable is necessary. Based on a detailed analysis a list of requirements has been created which enables the execution of system production. Depending on specific use and economical aspects based on suggested concepts it is possible to develop systems which propelled manually or by various motors. Designing the system is based on finding mean values, resulting in continual tracking continual change of angle values over time. Based on the presented requirements it is possible to easily create a system, which is the theme for further research. It is necessary to previously achieve a level of efficiency for various versions of this conception. 6

7 CONCLUSION This research influences the improvement of solar tracking system implementation for the territory of Kragujevac, Serbia. The calculated angles enable the production of a reasonably economically justified efficient solution for solar tracking. The incoming angle ranges from a minimal value of around 22,3 to a maximal value of 69,23. The range which should be provided for angle change when creating a sun tracking system is around 46,9. The total azimuth angle range is For 12PM this angle has a value of 0. A system for solar tracking should ensure a connection to the roof structure. Aside from this, it is necessary to ensure a rotation around two axes. The system is placed facing south. For continual tracking of the rotation around the east-west axis the daily angle change is 0,26, while the rotation around the north-west axis is an hourly angle change is 15,03. The specific example of the system purposely is not presented; this analysis allows a range of possible solutions. Every solution should be adapted to the specific problem so it can function at an efficient and satisfactory level. Systems for solar tracking can be developed for tracking in steps, where the angle change would be done in specific time intervals according to the optimal position independent of each axis. Also it is possible to develop systems for linear tracking the sun which presents requiring solutions. These methods represent approximate solutions of sufficient efficiency. Aside from that there is a possibility of creating a system which tracks the sun according to its exact position, however the profitability of this systems with currently available technology would not be justifiable. A complete development of these solutions presents the direction of further research where it will be possible to experimentally confirm calculated values. After this it is necessary to examine the exact benefits of the increase in efficiency with the use of these systems. REFERENCES: [1] B.J. Huang, F.S. Sun, Feasibility study of one axis three positions tracking solar PV with low concentration ratio reflector, Energy Conversion and Management, Volume 48, Issue 4, April 2007, Pages [2] Ahmet Şenpinar, Mehmet Cebeci, Evaluation of power output for fixed and two-axis tracking PVarrays, Applied Energy, Volume 92, April 2012, Pages [3] George C. Bakos, Design and construction of a two-axis Sun tracking system for parabolic trough collector (PTC) efficiency improvement, Renewable Energy, Volume 31, Issue 15, December 2006, Pages [4] Giuseppe Marco Tina, Salvina Gagliano, Giorgio Graditi, Angelo Merola, Experimental validation of a probabilistic model for estimating the double axis PV tracking energy production, Applied Energy, Volume 97, September 2012, Pages [5] Minghuan Guo, Zhifeng Wang, Wenfeng Liang, Xiliang Zhang, Chuncheng Zang, Zhenwu Lu, Xiudong Wei, Tracking formulas and strategies for a receiver oriented dual-axis tracking toroidal heliostat, Solar Energy, Volume 84, Issue 6, June 2010, Pages

8 [6] K.K. Chong, C.W. Wong, General formula for on-axis sun-tracking system and its application in improving tracking accuracy of solar collector, Solar Energy, Volume 83, Issue 3, March 2009, Pages [7] Sebastijan Seme, Gorazd Štumberger, A novel prediction algorithm for solar angles using solar radiation and Differential Evolution for dual-axis sun tracking purposes, Solar Energy, Volume 85, Issue 11, November 2011, Pages [8] Kalogirou S., Solar energu engineering, Elsevir, San Diego, California, [9] J. Skerlić, M. Bojić, D. Nikolić, D. Cvetković, J. Radulović, Optimal slope of a solar collector using particle swarm optimization algorithm, 43rd International Congress & Exhibition on Heating, Refrigeration and Air Conditioning, SMEITS-KGH 2012, Pages , Belgrade, Serbia. ACKNOWLEDGMENT This paper is a result of two investigations: (1) project TR33015 of Technological Development of Republic of Serbia, and (2) project III of Integral and Interdisciplinary investigations of Republic of Serbia. The first project is titled Investigation and development of Serbian zero-net energy house, and the second project is titled Investigation and development of energy and ecological highly effective systems of poly-generation based on renewable energy sources. We would like to thank to the Ministry of Education, Science and Technological Development of Republic of Serbia for their financial support during these investigations. 8