Literature Review: 1. The Solar Tracker, a device that keeps photovoltaic or photo-thermal panels in an optimum position perpendicularly to the solar radiation during daylight hours, can increase the collected energy up to 50% commercially. Theoretical calculation of the energy surplus in the case of tracking collectors is as follows: Assume, the maximum radiation intensity is 1= 11oo W-m 2 falling on the area (perpendicular), the day length is t=12h=43000 s, the projection of the sun beam on PV cell, which is oriented perpendicularly to the radiation direction, is equal S=S0cosø and the angle ø is changing in the interval (π/2-, - π/2) during the day where S0 is the collector area. The angular velocity of the Sun moving across the sky energy is equal dw= I Sdt. Which is fallen on the collector area S 0 =1 m 2 during one day. - C. Praveen(2012) 2. Solar energy is the rapidly gaining importance as an energy resource. To make solar energy more variable, efficiency of solar panel system must be maximized. A feasible approach to maximize the efficiency of solar panel systems is sun tracking. Moving a solar panel, along with the direction of sunlight; it uses a geared motor to change the position of the solar panel; the motor is controlled by the PIC16F84A microcontroller, which detect the sunlight using photocells. - By Kais I. Abdul-lateef (2012)
3. The proper model of the dual axis solar tracker is capable of tracking the sun throughout the year. The dual axis tracker provides higher output power when compared to the single axis tracker and fixed panel. According to the measured reading the efficiency of the Dual axis tracker is found 81.68%higher that than of fixed panel where as the efficiency of the single axis tracker is only32.17% higher than that of fixed panel. - Dhanbal.R (2013) 4. The formula for diffraction efficiency (η) of thick Phase transmission holograms, which is illuminated (Reconstructed) at Bragg s angle is given by Coupled wave theory, assuming refractive index variation to be sinusoidal as: η=sin ν Where n1 is the depth of refractive index modulation is the film thickness, λ is the free space wavelength of the reconstruction light beam and θ is Bragg s angle. - R.Ranjan (ISBN: 978-1-61804-175-3) 5. The sensor-based feedback controller consists of the LDR sensor, differential amplifier, and comparator. In the tracking operation, the LDR sensor measures the sunlight intensity as a reference input signal. The unbalance in voltages generated by the LDR sensor is amplified and then generates a feedback error voltage. The error voltage is proportional to the difference between the sunlight location and the PV panel location. At this time the comparator compares the error voltage with a specified threshold (tolerance). If the comparator output goes high state, the motor driver and a relay are activated so as to rotate the dual-axis (azimuth and elevation) tracking motor and bring the PV panel to face the Sun. -
6. According to Sanzidur Rahaman a dual axis sun tracking system has been successfully designed, built and tested. It follows the sun s path from morning to evening and then gets back to the initial position facing towards east side. So the system saves lot of energy by keeping the motors off during night period. This tracking technology is very simple in design, low in cost and accurate in tracking. - By Sanzidur Rahaman (2013) 7. The invention of Mata Dionisio is to characterized by the arrangement of the centre of gravity of the main structure of the secondary substructures and the solar panels or modules, very close to and beneath the main line of rotation such that the forces to be applied in order to achieve rotation are very small. - Mata Dionisio Silvestre (2007) 8. The Patent of Jawed Qador state that the Conventional tracking systems typically use cadmium-sulfide (CdS) photo sensors. However, these sensors have a non-linear luminosity-to-resistance curve and the characteristics may vary widely from one sensor to another, which is detrimental to the accuracy of the tracking system. - Jawed Qador (2011) 9. Mark Scanlon designed high efficiency, environmentally friendly frame system that supports a plurality of photovoltaic solar collecting panels (PV panels). The system comprises an array frame to which the plurality of PV panels
is mounted, actuators or other locomotion devices to rotate the frame and panels, and a control mechanism. The array frame system derives its high efficiency from its balanced nature. Since the inner and outer frames are always in balance, a minimal amount of force is required to rotate the system to track the sun. This small amount of force requires very little power and hence is highly efficient. - Mark Scanlon (2010) 10. According to the Scanlon, each PV panel in the plurality of PV panels may be separated by a distance from neighboring PV panels sufficient to minimize shadowing by each PV panel by and upon the neighboring PV panels. Any remaining potential inter-panel shading is eliminated through the control mechanism by rotating the panels in the opposite direction the sun is moving in the morning after sunrise and in the evening before sunset ("backtracking"). - Scanlon- Mark (2010) 11. According to the Lee, Embodiments of the solar concentrator system can be combined with trackers, such as the embodiments of single or dual-axis solar trackers disclosed herein. In such combinations, the reflective surface may be pointed toward the sun through the course of each day, such that the sunlight is incident to the reflective surface at a roughly constant angle throughout the day. Alternatively, the reflective surface could be fixedly positioned in alignment with the path of the sun as it moves across the sky. Due to the nature of the curved reflective surface, incident light may converge on the absorber even as the sun moves relative to the solar concentrator system during the course of a day. - Lee (2007)
12. The sun trackers are used for efficiency improvement. The diurnal and seasonal movement of earth affects the radiation intensity on the solar systems. Sun-trackers move the solar systems to compensate for these motions, keeping the best orientation relative to the sun. The most efficient and popular suntracking device was found to be in the form of polar-axis and azimuth/elevation types. - Mousazadeh (2009) 13. Solar thermoelectric generators (STEGs) are solid state heat engines that generate electricity from compatibility theory to provide analytic solutions to concentrated sunlight. This model of Lauryn uses thermoelectric device efficiency in idealized materials with temperature-dependent properties. With today's materials, a STEG with an incident flux of 100 kw m 2 and a hot side temperature of 1000 C could achieve 15.9% generator efficiency, making STEGs competitive with concentrated solar power plants. -Lauryn.L (2012) 14. Sun tracker that employed a single dual-axis AC motor to follow the Sun and used a stand-alone PV inverter to power the entire system. The proposed onemotor design was simple and self-contained, and did not require programming and a computer interface. The developed system increased the energy gain up to 28.31% for a partly cloudy day. -Jing-Min Wang (2013)
15. The system designed by Vandana is successfully tracks the Sun on dual axis. It follows Sun from East to West and back to East in a cyclic manner (Horizontal Motor Module) and also tracks the Angular Movement of the Sun, i.e., Seasonal Movement (Vertical Motor Module).The system also tackles the problem of cloudy weather. In cloudy weather, it remains still and catches the Sun again as it slips out of clouds. The system saves a lot of energy. The system will be in sleep mode when the night falls. In the day time, motors are also in Sleep Mode when light falls on the LDRs of equal intensity. Vandana V. Thakare