Design of Mechanism for Solar Tracking to generate concentrated Solar Power.

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.

24. THE MECHANISM
Pawl
Casing
Ratchet
Spring

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

28. IMPLEMENTATION IN ASSEMBLY

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

37. Heliostat Backbone

38. Heliostat Backbone Frame

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.