Akshay_Mahajan B.E Project
- 1. BE Project Final Review “Design & Development of Solar Tracking Mechanism for Ganged Heliostats” Presented by Akshat Mehta B120020804 Nilesh Baraskar B120020813 Vineet Bhoyar B120020818 Akshay Mahajan B120020863 Guided by Prof. Prakash M. Gadhe Department of Mechanical Engineering Maharashtra Institute of Technology, Pune-411 038 2016 - 2017
- 2. AIM The aim of the project is to design and develop a solar tracking mechanism for an array of ganged heliostats that is easy to operate and can be applicable for a profitable solar central receiver system unit. Objectives The objectives of this project were: Design development of the mechanism for solar tracking for a system of ganged heliostats. Fabrication of the specific parts for optimization. To optimize the existing model for cost reduction. To carry out weight reduction for an optimized system. Software analysis of the model.
- 3. INTRODUCTION What is Solar Power? The sun is the most plentiful energy source for the earth. All form of energy like wind, fossil fuel, hydro and biomass energy have their origins in sunlight. Solar energy falls on the surface of the earth at a rate of 120 peta-watts, this means all the solar energy received from the sun in one days can satisfied the whole world’s demand for more than 20 years. The worldwide demand for energy is expected to keep increasing at 5 percent each year. Solar energy is the only choice that can satisfy such a huge and steadily increasing demand. PV Power System
- 4. Concentrated solar power uses mirrors and tracking systems to focus a large area of sunlight into a small beam. Contrary to photovoltaic, CSP uses heat of the sun's radiation to generate electricity. A wide range of concentrating technologies exists; among the best known are the parabolic trough, the compact linear Fresnel reflector and the solar power tower. Various techniques are used to track the sun and focus light. CONCENTRATED SOLAR POWER Central Receiver System
- 5. WAYS TO HARNESS SOLAR POWER
- 6. • Multiple receivers and arrays of ganged heliostats relates to a system of concentrating and harvesting solar energy. It utilizes arrays solar energy harvesting units. • Each said solar energy harvesting unit comprises array of ganged heliostats and a central receiver. • Each array of ganged heliostats has a common positioning mechanism for azimuthal as well as altitudinal solar tracking. • In each altitudinal orientation, a minuscule predefined push is given by an actuator, wherein the magnitude of time between two said pushes linearly varies as per the angle formed by previous location and consecutive location of any oscillating member. • Arm affixed with each rotatable shaft and coupled with a linear actuator provides the ability to rotate the rotatable shaft in clockwise or anticlockwise direction. GANGED HELIOSTATS
- 7. • According to the given prototype, a plant was setup at Bhor, Pune . We visited the plant where this system has been manufactured. • At this plant, 12 ganged heliostats have been kept in array. There are 2 shafts used in this mechanism. One is the actuating shaft which is connected to the stepper motor. • At the stepper motor, a lead screw is connected which rotates due to torque received by motor. A ball nut is attached on the lead screw which actuates according to the shaft. • And other is the rotating shaft. It is connected to another motor. The heliostats are actually mounted on this shaft. This shaft shows the azimuthal movement of the sun. DESCRIPTION OF PROTOTYPE
- 10. Testing & Problems Encountered • After the assembly of the system was completed on the MIT Campus Terrace, we took trials for the next one month for tracking the movement of sun at different times of the day, for different pin positions of the heliostats, at different locations of sun in the sky. During the course of time, following problems were encountered by us. Problems Encountered • Complete weight reduction of the system: No FEA analysis was done while designing of the system resulting in bulky and costly system. • Torsional deflection of the rotating shaft due to load of heliostat on the shaft: It was found that the rotating shaft had torsional deflection resulting in improper tracking of the heliostat • Insufficient contact between roller and shaft: As the setup was manufactured at Bhor where the resources monetary resources and parts available at bhor plant location the actuating shaft used had inherent deformation hence the. These led to insufficient contact between shaft and roller. • Vibration on the system: The vibration of the mirrors due to wind and some manufacturing errors. • Deflection of heliostat stand: The load of the shaft taken by the heliostat stands resulting in deflection of the heliostat stand. • Pin location: Pin locations were to be decided for accurate tracking. • Overloading of motor: Overloading of the motor due to bulky and heavy structure of the system • Disengagement of jaw coupling: The jaw coupling used to transmit the power in one direction only as while returning the jaw coupling use to disengaged.
- 11. DC STEPPER MOTOR • A stepper motor is a brushless DC electric motor that divides a full rotation into a number of equal steps. • A DC stepper motor is used in the heliostat system to provide the necessary push for actuating shaft during tracking of sun in altitudinal direction i.e. east-west movement. • It allows the system to track out the daily movement of the sun and thus due to forward push, the heliostats gets focused on the receiver plate. • The motor used in the system is a standard DC stepper motor manufactured by Srijan Control Drives, Pune. It is symbolized as STM – 1101(S) having a torque of 28 kg-cm. • While testing of the system, after a few trials; motor used to get stopped and was unable to give the push. The strokes were unable to revolve and carry out the further operation. Thus, its speed gets decreased to zero. • The main reason for stalling for motor was, it was unable to handle the system load and thus to provide enough torque for providing push.
- 12. • Thus, after calculating torque required for motor to efficiently handle system load is 34 kg-cm. • Therefore from manufacturer’s catalogue motor with higher toque was selected so that it gives minimum torque of 34 kg-cm. • Thus motor symbolized as STM 1102 with a standard torque of 40 kg-cm was selected and proposed for modification.
- 13. CHANGE IN COUPLING • A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation. • The coupling used in the system is a universal jaw coupling. It is flexible type of coupling. • A jaw coupling is a type of flexible coupling used for general power transmission and in motion control applications. It is designed to transmit torque by connecting two shafts while damping system vibrations and accommodating misalignment, which protects other components from damage. • Jaw couplings are composed of three parts: two metallic hubs and an elastomer insert called as spider. The three parts press fit together with a jaw from each hub fitted alternately with the lobes of the spider. Jaw coupling torque is transmitted through the elastomer lobes in compression. • But during various trials of system, due to axial tension of the shaft, the coupling used to get detached. Due to this, shaft was unable to receive complete torque transmitted by the motor. Thus, system’s efficiency also got affected due to this condition.
- 14. • In our system, the major problem occurred due to axial motion and not because of shaft misalignment. Thus it was necessary to have a coupling which will handle axial tension. • Therefore rigid flange coupling was chosen as an alternative. • A Rigid flange coupling is a driving coupling between rotating shafts that consists of flanges one of which is fixed at the end of each shaft, the two flanges being bolted together with a ring of bolts to complete the drive. • As the flange coupling has rigid construction and higher strength, it was able to handle axial tensions of the shaft. The two flanges attached with bolts didn’t get detached due to the load. Thus it was beneficial to use this type of coupling. • Another advantage of this coupling is that, it is simple in construction. Thus it is easy to manufacture when compared with jaw coupling. • According to the shaft dimensions, the coupling was designed and manufactured and thus assembled in the system. • One of the aim of our project is also Weight Reduction of System • Thus we further tried to design the coupling in order to reduce the weight too. • For this, finite element analysis of coupling was done so as to check the stress and deformation. The result of analysis are :
- 15. As seen in the stress analysis in figure 43, majority of the outer part of the flange is blue that is it is not at all stressed. It can be eliminated thus optimizing weight and thereby reducing the load on the motor. Further, maximum deformation is 0.01mm. • Stress Analysis : • Deformation Analysis :
- 16. The optimized flange is :
- 17. HELIOSTAT MOUNT HINGE Self weight of the heliostat assembly obtained from the CAD model is 6kg and wind load is 163N. For this load case static structural analysis was performed on both existing and proposed models in ANSYS 16 to get the following results. Proposed model Old model Results: Old Model Deformation 11.3mm Old Model Max Stress: 472MPa Proposed Model Deformation: 3mm Proposed Model Max Stress: 35MPa
- 18. CONNECTING FLANGE The heliostats are mounted on rotatable shaft. The rotatable shaft is discontinuous so as to provide sufficient support. There are three shafts and are connected to one another via a solid shaft and flange system. The flanges are welded at the two ends of the solid shaft. The heliostat weight and wind load will give rise to a torsional moment on the flange system. In the current model we have a solid shaft of 25mm diameter. Structural analysis was performed on the shaft and the flange. A twist with a deformation of 1.23 mm at the end of the flange was observed. Old Model Deformation 1.23mm Old Model Max Stress : 260MPa
- 19. CONNECTING FLANGE With a deformation of 1.23mm at the end of the flange the deformation at the end of the heliostat is found out by basic proportionality. Thus at the height of the heliostat it would result in a total deformation of 7mm which is very high to maintain good focus of sun rays. In order to limit the deformation under 3mm the diameter of the shaft is increased from 25 mm to 30mm increasing the weld length by 31mm on each side. With this change we will get a deformation of 0.62mm at the end of the flange and 3mm at the heliostat end. Proposed Model Deformation: 0.62 mm Proposed Model Max Stress: 135MPa
- 20. ROTATABLE SHAFT • Three piece rotatable shaft are mounted on two rollers on each. Each piece supports three heliostats. The self weight of the rotatable shaft as well as of the heliostat assembly was considered for the structural analysis of the rotatable shaft. Exaggerated view of deformation and stress was shown to give an idea to the viewer. • Max Stress obtained was 26 MPa and deformation was 1.21mm. Deformation : 1.21mm Max. Stress: 26MPa
- 21. ACTUATING SHAFT The actuating shaft gives push to the heliostat assembly via a pin connected to the heliostat arm. The thrust given by the motor gives reaction on the pins. Structural analysis was performed in order to ensure the safety of the pins and heliostats. Deformation : 0.28mm
- 22. Plate Thickness: 3mm Max Stress: 97 MPa DAILY MOVEMENT TUNING PLATE This plate is used for daily minor adjustments done at the beginning of the day for the complete focusing of the sun rays. Plate Thickness: 3mm Max Stress: 95 MPa
- 23. RATCHET AND PAWL MECHANISM Problem Identified • The rotatable shaft support the entire weight of the all the 9 heliostats and stretches for 9 meters. As the commercially available shaft material is only 3.25 meters in length. • Due to this the rotatable shaft is made from multiple pieces and joined together by flange type couplings. However, due to more number of parts the deformation in the individual shafts ads up and the end opposite to that of the liner actuator experiences maximum deflection under loading. • As the flange couplings are connected by bolts there is inherent compliance between the shaft parts. It is of the utmost importance to reduce the deflection under loading in order to maintain the focus of the heliostats. Solution • In order to eliminate the deflection of shaft across the shaft support needs to be provided at the opposite end of the linear actuator. • This support must be such that it moves along with the actuator in discrete steps at the same time it locks on to the step firmly on which the actuator is. • Ratchet and pawl mechanism was chosen as it is self sufficient and the need for human intervention is minimized.
- 25. FEA OF COMPONENTS RATCHET: • It is a square shaped shaft having unidirectional teeth. The teeth are spaced according the pushes that the linear actuator is giving the mechanism. The load acting on the teeth is half the weight of the heliostats. The results of the analysis are show below in figure 25. Max Stress: 43.141 MPa Max Deformation: 0.1 mm • The material selected for the ratchet is Mild Steel for which the FOS is 5.8. The dimensions of the ratchet are shown below in figure. (All dimensions are in mm)
- 26. PAWL • It is a stepped shaft with its one end shaped such that it locks the ratchet in one particular position in which it is. It also allows the movement of the ratchet in the opposite direction. Other end of the pawl is shaped like a handle which allows the disengagement of the pawl in order to allow the movement in that direction conditionally. The step on the pawl is used as a seat for the compression spring. Similar loads as of the ratchet act on the pawl. The results for the stress and deformation analysis are shown below in figure. Max Stress: 74.38 MPa Max Deformation: 0.002 mm • The material selected for the Pawl is Mild steel for an FOS of 3.36. The dimensions of the pawl are as above in figure
- 27. CASING & SPRING • The casing has the function to hold all the components together in a sound manner and provide housing for the ratchet. In the casing the ratchet passes through a square shaped hole. Perpendicular to it the pawl enters the casing. The casing also provides a cover against which the spring exerts a force. The cover is bolted to the casing using two bolts. Two plates extend from the casing up to the rotatable shaft arm. A casing of ratchet and pawl is represented in figure . • A compression spring is used in the casing to give an axial thrust to the pawl so that it maintains contact with the ratchet and shown in figure
- 29. SELF ADJUSTING ROLLER MECHANISM Problem due to no contact between roller and shaft • In previous structure, the actuator shaft was supported by the rollers mounted on the heliostat stand and the rotatable shaft due to which the actuation of the shaft faced following problems: • Insufficient contact between the actuator shaft and the rollers due to bend on the shaft. • Load on the motor due to insufficient roller contact. • The load of the actuator shaft on heliostat stand which cause the bending of the stand gave permanent deformation to the stand. • Due to this heliostat stand changed its original position and gave rise to tracking problems. • Less weld area on rotating shaft for heliostat stand. Solution • To increase the height of the rollers by welding the plates. • To change the load bearing structure of the shaft • Self-adjusting rollers to be used. • By replacing the actuating shaft.
- 30. IMPLEMENTATION OF MECHANISM • A c-clamp is to be welding to the rotating shaft. • The actuator is to be supported by the roller on the rotating shaft. • The load of the actuator is taken by the c clamp rather than the heliostat stand of the previous structure. • The guiding rollers are now placed in the c-clamp which eliminates the load on the heliostat stand resulting stable tracking of the system • The new dimension proposed of the actuator shaft are reduced and optimized. This gives adequate room (area) for the welding of the heliostat stand. Reducing deflection of the stand and increasing the structural integrity. • Bolt to be welded on the roller (no relative motion between the roller and the bolts). These are then mounted on the c-clamp with a spring placed in between the roller and the clamp. • The rollers are bolted with the nut on the c-clamp keeping adequate distance in between the roller and the clamp. • The spring placed in between roller and c-clamp continuously apply force on the roller to be in contact with the shaft. The spring with stiffness value 10,000 N/mm is selected. This allows the rollers to adjust the contact according to shaft surface. • This ensures that the contact between the shaft and the roller and reduces the friction and load on the stepper motor.
- 31. CAD MODEL AND ACTUAL IMPLEMENTATION
- 33. LOCATION OF HELIOSTAT ACTUATION PINS Problem • At the time of testing heliostat were not able to maintain focus of the reflected rays in the receiver it was found that after 1-2 hrs the heliostat were not able to maintain focus at receiver end resulting in improper tracking. Solution • With the geometry considered in Solid works the heliostats are deigned to focus all rays at the center of the receiver. • For the accurate locations of pins we will be assuming that the pin location for the center heliostat is correct and will be finding out the pin position relative to the central pin location. • For doing this we will be considering the movement of the sun for certain duration of time say 60 minutes. • In the 60 minutes the sun will travel an angle of 15 degrees. In order to maintain focus different heliostats will have to move different angles. • These angles can be found out from the geometry model and the pin location will be found out from the heliostat model. • The further calculations are performed on MS Excel.
- 34. PIN LOCATION GRAPHS 6.800 7.000 7.200 7.400 7.600 7.800 8.000 H1 H2 H3 H4 H5 H6 H7 H8 H9 at 50m T=60 Travel required at 50m T=60 Travel required 7.100 7.200 7.300 7.400 7.500 7.600 7.700 H1 H2 H3 H4 H5 H6 H7 H8 H9 T=120 Travel Required T=120 Travel Required Comparison of heliostat travel 44.800 44.850 44.900 44.950 45.000 45.050 H1 H2 H3 H4 H5 H6 H7 H8 H9 Travel Required Travel Required 282.5 282.6 282.7 282.8 282.9 283 283.1 283.2 283.3 283.4 283.5 1 2 3 4 5 6 7 8 9 Distance of Pin from Heliostat Pivot Travel required by heliostats Position of pins from heliostat pivot point
- 35. SELECTION OF DAMPING MATERIAL • Damping is the energy dissipation properties of a material or system under cyclical stress. • Damping materials work by changing the natural vibration frequency of the vibrating surface and thereby lowering radiated noise and increasing the transmission loss of the material. • Silicone is characterised by an excellent retention of many desirable properties over a wide range of temperatures. From indefinitely at -50°C to up to five years at 200°C, at moderate temperatures, silicone rubbers offer unlimited lifetime. • Silicone can sustain high and low temperatures significantly. • Silicone can be used indefinitely at 150 ’C with almost no change in its vibration isolation capabilities. It withstands use even at 200 ‘C and in some cases it can even sustain heat of 350 ‘C for short periods. • Therefore, it is suitable as a material for use in high temperature environments. Silicone Vs Rubbers
- 36. • It is observed that some rubbers will demonstrate a great change in modulus as they are subjected to repeated stress cycling. This is the "Mullins effect". • It is due to the rupture of filler-polymer physical bonds during flexing. These weak bonds re- form when the specimen is at rest for some time. • Silicone rubber is known for the retention of its properties. Its tensile strength is not particularly high but, compared to others, it is not very much affected by temperature. Comparison of silicone with different rubbers
- 39. CONCLUSION • Study of Solar Tracking Mechanism using Ganged Heliostats System was performed. • Testing of the system and rectification of manufacturing errors was done. • The following mechanical errors were observed and following changes were made : • Finite Element Analysis was performed on all over designed parts of the system with the aim of weight reduction. • To maintain focus of all nine heliostats, the torsional deflection of the rotatable shaft needs to be minimized. This can be done by Ratchet and Pawl Mechanism. Cad modeling and structural analysis has been performed and system is in ready to manufacture state. • The effects of inherent deflections were minimized by self adjusting rollers which ensure adequate contact of rollers and shaft thereby minimizing the load on the motor and heliostat stand. • In order to minimize the vibration in the system, silicone gel was chosen as an adhesive for the heliostats which also acts as a damping material thereby minimizing the vibrations. • The actuating pins needs to be accurately positioned for maintaining the continuous focus of sun rays. 2D analysis of solar geometry was performed for accurate positioning of pins.
- 40. • Due to axial tension of shaft occurred detachment of jaw coupling thereby selecting the rigid flange coupling as an alternative. • As the motor capacity was found insufficient, calculations were performed and hence motor of higher torque suitable to system was selected • With the incorporation of these changes, the functioning of the system will be efficient and more energy can be harnessed from radiant solar power energy.
- 41. REFERENCES 1. Patwardhan, 2011, ‘Solar central receiver system employing common positioning mechanism for heliostats’, United States Patent Application, Jan 2011. 2. Gadhe, Patwardhan, ‘A solar central receiver system’ utilizing ganged heliostats for harvesting solar energy’. 3. Patwardhan 2014, ‘Method and apparatus for orienting arrays of mechanically linked heliostats for focusing the incident sunlight on the stationary object’, United States Patent Application, Sep 2014. 4. International conference on concentrating solar power and chemical energy systems, SolarPACES 2014 – ‘Experimental validation of theoretical heliostat wind load’. 5. Bhandari V. B., Design of Machine Elements, 3rd Edition, McGraw Hill Education (India) Private Limited, 2010. 6. Website – ‘http://www.mysundial.ca/tsp/sun_charts.html’ 7. Quoc Pham, inventor; Esolar inc., assignee; Heliostat array layout for multi tower central receiver solar power plant, United States Patent Application, Feb 2014. 8. Website – ‘http://nise.res.in/’ 9. Website – ‘http://www.esolar.com/’, CSP technology. 10. R. B. Patil, Design of Machine elements – I, II; Techmax publication.