single axis solar tracker with out micro controller

documentation of solar tracker with out micro controller

1. 0

A
Project Report
On
SINGLE AXIS SOLAR TRACKER
Submitted in Partial Fulfillment of the Requirement for the Award of
Diploma
In
ELECTRICAL & ELECTRONICS ENGINEERING
2014-2015
GUIDE COPY
Submitted by
NAME OF THE STUDENT PIN.NO.
M.NARENDER 12253-EE-010
N.CHANDRASHEKAR REDDY 12253-EE-029
M.LAXMAN 12253-EE-016
M.D.ASIF 12253-EE-023
M.SANDEEP 12253-EE-017
K.ABHILASH 12253-EE-033
Under the guidance of
MR .K.DEVENDAR REDDY

2
nd
SHIFT POLYTECHNIC
VALLURUPALLI NAGESHWARA RAO VIGNANA JYOTHI INSTITUTE OF
ENGINEERING & TECHNOLOGY
(AN AUTONOMOUS INSTITUTE)
(Approved by AICTE, New Delhi and Govt. of T.S. & affiliated to JNTUH)
VignanaJyothi Nagar, Bachupally, Nizampet (S.O.) Hyderabad-500090. T.S. India.
Tel: [phone], Fax: [phone]
E-mail: [email protected], Website: www.vnrvjiet.ac.in

2. 1


2
nd
SHIFT POLYTECHNIC
VALLURUPALLI NAGESHWARA RAO VIGNANA JYOTHI INSTITUTE OF
ENGINEERING & TECHNOLOGY

(AN AUTONOMOUS INSTITUTE)
(Approved by AICTE, New Delhi and Govt. of T.S. & affiliated to JNTUH)
VignanaJyothi Nagar, Bachupally, Nizampet (S.O.) Hyderabad-500090. T.S. India.
Tel: [phone], Fax: [phone]
E-mail: [email protected], Website: www.vnrvjiet.ac.in
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
SINGLE AXIS SOLAR TRACKER
NAME OF THE STUDENT: PIN NO:
M.NARENDER 12253-EE-010
N.CHANDRASHEKAR REDDY 12253-EE-029
M.LAXMAN 12253-EE-016
M.D.ASIF 12253-EE-023
M.SANDEEP 12253-EE-017
K.ABHILASH 12253-EE-033

Internal guide: Mr.K.DEVENDAR REDDY

3. 2

2
nd
SHIFT POLYTECHNIC
VALLURUPALLI NAGESHWARA RAO VIGNANA JYOTHI INSTITUTE OF
ENGINEERING & TECHNOLOGY



DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
CERTIFICATE
This is to certify that the project entitled “SINGLE AXIS SOLAR TRACKER ” being submitted by
M.NARENDER 12253-EE-010
N.CHANDRASHEKAR REDDY 12253-EE-029
M.LAXMAN 12253-EE-016
M.D.ASIF 12253-EE-023
M.SANDEEP 12253-EE-017
K.ABHILASH 12253-EE-033
in partial fulfillment of the requirement for the Award of the DIPLOMA IN ELETRICAL &
ELECTRONICS ENGINEERING, SBTET , Hyderabad, is a record of the bonafide work carried out by
them under our guidance and supervision during the period 2014-2015.
The results presented in this thesis have been verified and are found to be satisfactory. The result
embodied in this project has not been submitted to any other university or institute for the award of
diploma.


Internal Guide Head of the Department
Mr.K.DEVENDER REDDY Dr. K.ANURADHA
LECTURER/VJP Professor & Head EEE Dept.
EEE Dept. EEE Dept.



External examiner

4. 3



ACKNOWLEDGEMENT

We avail the opportunity to thank the co-operative good will and support both moral and
technical extended by several individual out of which this prospect as involved.
We are expressing our sincere thanks to Mr.K.DEVENDER REDDY our project guide for her
valuable guidance and co-operation.
We cordially offer our boundless and profound sense of gratitude to Dr. Mrs. K.ANURADHA
head of the department of EEE, for her valuable suggestion and encouragement.
We express our sincere thanks to our beloved Dr. Mr. B.V.R. RAVI KUMAR vice principle of
polytechnic for his encouragement and course of study as well as the project work.
We are greatly indebted to Dr. C.D. NAIDU principle of the college for providing necessities to
complete this technical seminar work.
We are expressing our sincere thanks to Mr. K.RANJEETH KUMAR and Mr.
K.DEVENDER REDDY our project instructors for their guidance and co-operation.
We render our special thanks to each and every person who directly and indirectly helped us to
complete the project as grand success



Place: Hyderabad
Date: 01/04/2015

5. 4



2
nd
SHIFT POLYTECHNIC
VALLURUPALLI NAGESHWARA RAO VIGNANA JYOTHI INSTITUTE OF
ENGINEERING & TECHNOLOGY
DECLARATION

We do declare that the thesis work entitled “SINGLE AXIS SOLAR TRACKER ”
submitted in partial fulfillment of the requirement for the Award of the DIPLOMA IN ELETRICAL &
ELECTRONICS ENGINEERING, SBTET , Hyderabad,2
nd
SHIFT POLYTECHNIC
VallurupalliNageswaraRaoVignanaJyothi Institute of Engineering and Technology, is a bonafide
record of our own work carried out under the supervision of Mr.K.DEVENDER REDDY.
Also, we declare that the matter embodied in this thesis has not been submitted by me in full or
in any part thereof for the award of any degree/diploma of any other institution or university
previously



Place: Hyderabad
Date: 01/04/2015

6. 5

Contents

Chapter Page no

Title page i

Certificate ii
Acknowledgement iii
Declaration iv
List of figures and tables v
Abstract vi
1. Introduction 1
1.1. Overview 1
1.2. Solar power in india 3
1. India's largest photovoltaic (pv) power plants 3
1.3literature review 4
1.4 aim of the project 6
2. Solar radiation & photovoltaic 7
2.1 concepts on solar radiation 7
2.2 declination angle 7
2.3 hour angle 8
2.4 solar altitude (θz) 8
2.5 solar azimuth (θa) 9
2.6 insolation 9
2.7 projection effect 10
2.8 working of photovoltaics 10
3. Solar tracker 12
3.1 introduction 12
3.2 need for solar tracker 12
3.3 types of solar trackers 13
1.passive tracking systems 13

7. 6

Chapter Page no

2.active tracking systems 14
(a)single axis trackers 14
(b)dual axis trackers 15
4.components description 16
4.1passive device 16
4.2active devices 16
4.3resistor 16
1.types of resister 18
2. Resistor colour code 19
4.4 4.4variable resistors. 20
4.5 sensors 22
1.light dependent resistors (ldr) 22
2.working principle of ldr 22
4.5 motor driver l293d ic 23
1. H-bridge basics 23
2. Introduction to l293d ic 25
3. L293d connections 26
4. Working of l293d 27
5.truth table 27
6.voltage specification 28
4.6 voltage comparator lm1458 29
1.description 29
4.7 12v battery 31
4.8dc motors 32
1.motor specifications 32

8. 7




Chapter Page no
5.circuit and its working 34
5.1 how the solar tracker control circuit functions 34
5.2 advantages and disadvantages of a solar tracker system 35
1.advantages 35
2.disadvantages 36
5.3 future work 36
5.4 conclusion 37

9. 8

LIST OF FIGURES

Figures page no
 Fig. 1.1: sun path at latitude of 31
0
1
 Fig1. 2 :curve for the relationship between the 2
Solar radiation and the solar angle of incidence
 Fig 1.3:the average solar radiations receiver by
different regions in india 4
 Figure 2.1: the declination angles 8
 Figure 2.2:solar altitudes and azimuths typical
Behavior of sun path 9
 Fig 2.3: projection effect 10
 Figure 2.4: photovoltaic panel or array 11
 Figure 3.1: passive tracking system 14
 Figure 3.2: single axis solar tracker 14
 Figure3.3:dual axis solar tracking 15
 Fig 4.1: from top to bottom:
1
4
w,
1
2
w, and 1-w resistors 18
 Fig 4.2:different types of resistors 19
 Fig 4.3: fixed resistors 19
(a) Wire wound type 19
(b) Carbon film type 19
 Fig 4.4: color coding 20
 Fig 4.5: preset resistor 21
 Fig 4.6connection of preset 21
 Fig 4.7 ldr. 22
 Fig4.8 typical ldr resistance vs light intensity 23
 Fig 4.9:h-bridge 23
 Fig 4.10:switching of h-bridge 24
 Fig4.11:l293d 25
 Fig 4.12: l293d connections 27

10. 9

 Figure 4.13: to-99 package 30
 Figure 4.14: dual-in-line package 30
 Fig 4.15:12v battery 31
 Fig 4.16: dc motor: high torque mini12v dc motor 32
 Fig 4.17: dc motor 33
 Fig 5.1 single axis solar tracker circuit diagram 34
 Fig 5.2:solar tracker kit 36

LIST OF TABLES
Tables PAGE NO
 Table no-3.1: Direct power lost (%) due to misalignment (angle i) 13
 Table no:4.1: l293d TRUTH TABLE 28

11. 10

ABSTRACT

The project uses a solar panel coupled to a dc motor to track the Sun so that maximum
sun light is incident upon the panel at any given time of the day. This is better compared to light
sensing method that may not be accurate always for example during cloudy days.
With the impending scarcity of nonrenewable resources, people are considering to use
alternate sources of energy. From all other available resources sun energy is the most abundant
and it’s comparatively easy to convert it to electrical energy. Use of solar panel to convert sun’s
energy to electrical is very popular, but due to transition of the Sun from east to west the fixed
solar panel may be able to generate optimum energy. The proposed system solves the problem by
an arrangement for the solar panel to track the Sun.
This tracking movement is achieved by coupling a dc motor to the solar panel such that
the panel maintains its face always perpendicular to the Sun to generate maximum energy. This
is achieved by using a sensor circuit to deliver stepped pulses in periodical time intervals for the
dc motor to rotate the mounted panel as desired. The dc motor is driven by an interfacing IC as
the controller of a dc motor. The project is provided with a dummy solar panel which can be
used for demonstration purpose only.
Further the project can be enhanced by using RTC (Real Time Clock) to follow the Sun.
This helps in maintaining the required position of the panel even if the power is interrupted for
some time.

12. 11

CHAPTER- 1
INTRODUCTION

1.1 OVERVIEW
The world population is increasing day by day and the demand for energy is increasing
accordingly. Oil and coal as the main source of energy nowadays, is expected to end up from the
world during the recent century which explores a serious problem in providing the humanity
with an affordable and reliable source of energy. The need of the hour is renewable energy
resources with cheap running costs. Solar energy is considered as one of the main energy
resources in warm countries.



















Fig. 1.1: Sun path at latitude of 31
0

13. 12

In general, India has a relatively long sunny day to more than ten months and partly
cloudy sky for most of the days of the rest two months. This makes our country, especially the
desert sides in the west which include Rajasthan, Gujarat,
Madhya Pradesh etc. very rich is solar energy. Many projects have been done on using
photovoltaic cells in collecting solar radiation and converting it in to electrical energy but most
of these projects did not take in to account the difference of the sun angle of incidence by
installing the panels in a fixed orientation which influences very highly the solar energy
collected by the panel.
As we know that the angle of inclination ranges between -90
o
after sun rise and +90
o

before sun set passing with 0
o
at noon. This makes the collected solar radiation to be 0% at sun
rise and sun set and 100% at noon. This variation of solar radiations collection leads the
photovoltaic panel to lose more than 40% of the collected energy. Fig. 1.1 shows the yearly sun
path at the latitude of30
o
. From the figure 1.1, one can estimate the exact position of sun in every














Solar angle of incidence
Fig1. 2 :Curve for the relationship between the solar radiation and the solar angle of incidence.

14. 13

Month and at any time during the day. The position is decided by two angles in spherical
coordinates; the Altitude angle which is the angle of the sun in the vertical plane in which the
sun lies, and the Azimuth angle which represents the angle of the projected position of the sun in
the horizontal plane. These two angles will be discussed deeply later in this document. Fig. 1.2
shows a curve for the relationship between the solar radiation and the solar angle of incidence.
This figure shows that solar radiations falling on the solar array will be maximum when the
angle of incidence on the panel is 0
0
which means that the panel is perpendicular to the sun.

1.2SOLAR POWER IN INDIA
In July 2009, India unveiled a US$19 billion plan to produce 20 GW (20,000MW) of
solar power by 2020. Under the plan, the use of solar-powered equipment and applications
would be made compulsory in all government buildings, as well as hospitals and hotels. On
November 18, 2009, it was reported that India was ready to launch its National Solar
Mission under the National Action Plan on Climate Change, with plans to generate 1,000
MW of power by 2013.
1. India's largest photovoltaic (PV) power plants
 Reliance Power Pokaran Solar PV Plant, Rajasthan, 40MW 02011-06 June 2011
Commissioning in March 2012
 AdaniBitta Solar Plant, Gujarat, 40MW 02011-06 June 2011 To be Completed
December 2011
 Moser Baer - Patan, Gujarat,30MW 02011-06 June 2011 Commissioned July
2011
 Azure Power - Sabarkantha, Gujarat, 10MW 02011-06 June 2011
Commissioned June 2011
 Green Infra Solar Energy Limited - Rajkot, Gujarat, 10M W 02011-11-29 November
29, 2 011 Commissioned November 2011

15. 14






















Fig 1.3:The average solar radiations receiver by different regions in India.
The daily average solar energy incident over India varies from 4 to 7 kWh/m
2

With about 1500–2000 sunshine hours per year (depending upon location), which is far more
than current total energy consumption. For example, assuming the efficiency of PV modules
were as low as 10%, this would still be a Thousand times greater than the domestic electricity
demand projected for 2015. Gujarat government has signed a MOU with Clinton Foundation to
build the world’s largest solar-power plant in the region. The 3,000-megawatt plant near the
border between India and Pakistan would be one of four planned by the initiative, a William J.
Clinton Foundation program to promote renewable energy. The other proposed sites are in
California, South Africa, and Australia.

16. 15

1.3LITERATURE REVIEW
Sun-synchronous navigation is related to moving the solar powered rover (robot) in such
a way that its solar panel always points toward the sun and which results into maximum battery
charging and hence the rover can work for long hours. The unique feature of this solar tracking
system is that instead of taking the earth as its reference, it takes the sun as a guiding source. Its
active sensors constantly monitor the sunlight and rotate the panel towards the direction where
the intensity of sunlight is maximum. The light dependent resistor’s do the job of sensing the
change in the position of the Sun. The control circuit does the job of fetching the input from the
sensor and gives command to the motor to run in order to tackle the change in the position of the
sun. By using this system the additional energy generated is around 25% to 30% with very less
consumption by the system itself. The paper gives the design and implementation of a fuzzy
logic computer controlled sun tracking system to enhance the power output of photo voltaic solar
panels. The tracking system was driven by two permanent magnet DC motors to provide motion
of the PV panels in two axis. The project describes the use of a microcontroller based design
methodology of an automatic solar tracker. Light dependent resistors are used as the sensors of
the solar tracker. The tracking system maximizes solar cell output by positioning a solar panel at
the point of maximum light intensity.
This paper describe the use of DC motors, special motors like stepper motors, servo
motors, real time actuators, to operate moving parts of the solar tracker. The system was
designed as the normal line of solar cell always move parallel to the rays of the sun. The Aim of
this project is to develop and implement a prototype of two-axis solar tracking system based on a
microcontroller. The parabolic reflector or parabolic dish is constructed around two feed
diameter to capture the sun’s energy. The focus of the parabolic reflector is pointed to a small
area to get extremely high temperature. The temperature at the focus of the parabolic reflector is
measured with temperature probes. This auto-tracking system is controlled with two 12V, 6W
DC gear box motors. The five light sensors (LDR) are used to track the sun and to start the
operation (Day/Night operation). The paper adopts the PWM DC motor controller. It is capable
of archiving the timeliness, reliability and stability of motor speed control, which is difficult to
implement in traditional analog controller. The project concentrates on the design and control of
dual axis orientation system for the photovoltaic solar panels. The orientation system
calculations are based on astronomical data and the system is assumed to be valid for any region

17. 16

with small modifications. The system is designed to control the Altitude angle in the vertical
plane as well as the Azimuth angle in the horizontal plane of the photovoltaic panel workspace.
And this system is expected to save more than 40% of the total energy of the panels by keeping
the panel’s face perpendicular to the sun. In the previous solutions, each tracking direction is
controlled by using a Sun sensor made by a pair of phototransistors. The single matrix Sun
sensor (MSS) controls both axes of the tracking system. The inspiration for the MSS is the
antique solar clock. MSS comprises 8 photo resistors and a cylinder The difference between a
shaded photo resistor cell and a lighted cell is recognized using an electronic circuit and
corresponding output voltage signals are given to the DC motors which will move the array
toward sun. In order to improve the solar tracking accuracy, the author comes up with combining
program control and sensor control. Program control includes calendar-check tracking and the
local longitude, latitude and time, to calculate the solar altitude and solar azimuth by SCM
(single-chip microcomputer), servo motor is used to adjust the attitude of the solar panel. Sensor
control is that sunray is detected by photoelectric detector and then the changed signal is
transmitted to control step motor to adjust the attitude of the solar. The paper discusses the
technology options, their current status and opportunities and challenges in developing solar
thermal power plants in the context of India. The National Solar Mission is a major initiative of
the Government of India and State Governments to promote ecologically sustainable growth
while addressing India’s energy security challenge. It will also constitute a major contribution by
India to the global effort to meet the challenges of climate change.

1.4 AIM OF THE PROJECT
The aim of the project is to keep the solar photovoltaic panel perpendicular to the sun
throughout the year in order to make it more efficient. The dual axis solar photovoltaic panel
takes astronomical data as reference and the tracking system has the capability to always point
the solar array toward the sun and can be installed in various regions with minor modifications.
The vertical and horizontal motion of the panel is obtained by taking altitude angle and azimuth
angle as reference. The fuzzy controller has been used to control the position of DC motors. The
mathematical simulation control of dual axis solar tracking system ensures the point to point
motion of the DC motors while tracking the sun.

18. 17

CHAPTER-2
SOLAR RADIATION & PHOTOVOLTA IC

2.1 CONCEPTS ON SOLAR RADIATION
Before talking about the solar tracking systems, we will review some basic concepts
concerning solar radiation and mention some important values to better understand the results of
this work.
The sun, at an estimated temperature of 5800 K, emits high amounts of energy in the form
of radiation, which reaches the planets of the solar system. Sunlight has two components, the
direct beam and diffuse beam. Direct radiation (also called beam radiation) is the solar radiation
of the sun that has not been scattered (causes shadow). Direct beam carries about 90% of the
solar energy, and the "diffuse sunlight" that carries the remainder. The diffuse portion is the blue
sky on a clear day and increases as a proportion on cloudy days. The diffuse radiation is the sun
radiation that has been scattered (complete radiation on cloudy days). Reflected radiation is the
incident radiation (beam and diffuse) that has been reflected by the earth. The sum of beams,
diffuse and reflected radiation is considered as the global radiation on a surface. As the majority
of the energy is in the direct beam, maximizing collection requires the sun to be visible to the
panels as long as possible.

2.2 Declination Angle
The declination of the sun is the angle between the equator and a line drawn from the
centre of the Earth to the centre of the sun. The declination is maximum (23.45
0
) on the
summer/winter (in India 21 June and 22 December) The declination angle, denoted by δ, varies
seasonally due to the tilt of the Earth on its axis of rotation and the rotation of the Earth around
the sun. If the Earth were not tilted on its axis of rotation, the declination would always be 0°.
However, the Earth is tilted by 23.45° and the declination angle varies plus or minus this
amount. Only at the spring and fall equinoxes is the declination angle equal to 0°.

19. 18
















Figure 2.1: The Declination Angles

2.3 Hour Angle
The Hour Angle is the angular distance that the earth has rotated in a day. It is equal to 15
degrees multiplied by the number of hours from local solar noon. This is based on the nominal
time, 24 hours, required for the earth to rotate once i.e. 360 degrees.
Solar hour angle is zero when sun is straight over head, negative before noon, and positive
after noon.(here noon means 12.00 hour)

2.4 Solar Altitude (θz)
The solar altitude is the vertical angle between the horizontal and the line connecting to
the sun. At sunset/sunrise altitude is 0 and is 90 degrees when the sun is at the zenith. The
altitude relates to the latitude of the site, the declination angle and the hour angle.

20. 19









Figure 2.2:Solar altitudes and azimuths typical behavior of sun path

2.5 Solar Azimuth (θA)
The azimuth angle is the angle within the horizontal plane measured from true South or
North. The azimuth angle is measured clockwise from the zero azimuth. For example, if you're
in the Northern Hemisphere and the zero azimuth is set to South, the azimuth angle value will be
negative before solar noon, and positive after solar noon.

2.6 INSOLATION
Insolation is a measure of solar radiation energy received on a given surface area and
recorded during a given time. It is also called solar irradiation and expressed as hourly
irradiation if recorded during an hour, daily irradiation if recorded during a day, for example.
The unit recommended by the World Meteorological Organization is MJ/m
2
(mega joules per
square meter) or J/cm
2
( joules per square centimeter).Practitioners in the business of solar energy
may use the unit Wh/m
2
(watt-hours per square meter). If this energy is divided by the recording
time in hours, it is then a density of power called irradiance, expressed in W/m
2
(watts per square
meter). Over the course of a year the average solar radiation arriving at the top of the Earth's
atmosphere at any point in time is roughly 1366 watts per square meter. The Sun's rays are
attenuated as they pass through the atmosphere, thus reducing the irradiance at the Earth's
surface to approximately 1000 W m
−2
for a surface perpendicular to the Sun's rays at sea level on
a clear day. The insolation of the sun can also be expressed in Suns, where one Sun equals 1000
W/m
2
.

21. 20

2.7 PROJECTION EFFECT
The insolation into a surface is largest when the surface directly faces the Sun. As the
angle increases between the direction at a right angle to the surface and the direction of the rays
of sunlight, the insolation is reduced in proportion to cosine of the angle; see effect of sun angle
on climate.
This 'projection effect' is the main reason why the Polar Regions are much colder than
equatorial regions on Earth. On an annual average the poles receive less insolation than does the
equator, because at the poles the Earth's surface are angled away from the Sun.


FIG 2.3: Projection effect
Figure 2.3One beam one mile wide shines on the ground at a 90° angle, and another at a 30°
angle. The one at a shallower angle distributes the same amount of light energy over twice as
much area.

2.8 WORKING OF PHOTOVOLTAICS
Photo voltaics are the direct conversion of light into electricity at the atomic level. Some
materials exhibit a property known as the photoelectric effect that causes them to absorb photons
of light and release electrons. When these free electrons are captured, an electric current results

22. 21

that can be used as electricity. A solar cell (also called photovoltaic cell or photoelectric cell) is a
solid state electrical device that converts the energy of light directly into electricity by the
photovoltaic effect. Crystalline silicon PV cells are the most common photovoltaic cells in use
today.
A number of solar cells electrically connected to each other and mounted in a support
structure or frame are called a photovoltaic module. Modules are designed to supply electricity at
a certain voltage, such as a common 12 volts system. The current produced is directly dependent
on how much light strikes the module. Multiple modules can be wired together to form an array.
In general, the larger the area of a module or array, the more electricity will be produced.
Photovoltaic modules and arrays produce direct-current (DC) electricity. They can be connected
in both series and parallel electrical arrangements to produce any required voltage and current
combination.


















Figure 2.4: Photovoltaic panel or array

23. 22

CHAPTER-3
SOLAR TRACKER

3.1 INTRODUCTION
Solar Tracker is a Device which follows the movement of the sun as it rotates from the east
to the west every day. The main function of all tracking systems is to provide one or two degrees
of freedom in movement. Trackers are used to keep solar collectors/solar panels oriented directly
towards the sun as it moves through the sky every day. Using solar trackers increases the amount
of solar energy which is received by the solar energy collector and improves the energy output of
the heat/electricity which is generated. Solar trackers can increase the output of solar panels by
20-30% which improves the economics of the solar panel project.

3.2 NEED FOR SOLAR TRACKER
The sun travels through 360 degrees east-west a day, but from the perspective of any fixed
location the visible portion is 180 degrees during a 1/2 day period. Local horizon effects reduce
this somewhat, making the effective motion about 150 degrees. A solar panel in a fixed
orientation between the dawn and sunset extremes will see a motion of 75 degrees on either side,
and thus, according to the table above, will lose 75% of the energy in the morning and evening.
Rotating the panels to the east and west can help recapture these losses. A tracker rotating in the
east-west direction is known as a single-axis tracker.
The sun also moves through 46 degrees north-south over the period of a year. The same set
of panels set at the midpoint between the two local extremes will thus see the sun move 23
degrees on either side, causing losses of 8.3% A tracker that accounts for both the daily and
seasonal motions is known as a dual axis tracker.
The energy contributed by the direct beam drops off with the cosine of the angle between the
incoming light and the panel. The table no. 2.1 shows the Direct power lost (%) due to
misalignment (angle i).

24. 23

Misalignment (angle i ) Direct power lost (%)=1-cos(i)

0
0
0

1
0
.015

3
0
.14

8
0
1

23.4
0
8.3

30
0
13.4

45
0
30

75
0
>75


Table no-3.1: Direct power lost (%) due to misalignment (angle i)

3.3 TYPES OF SOLAR TRACKERS
There are two types of tracking sytems they are
 Passive tracking
 Active tracking
1.PASSIVE TRACKING SYSTEMS
The passive tracking system realizes the movement of the system by utilizing a low
boiling point liquid. This liquid is vaporized by the added heat of the sun and the center of mass
is shifted leading to that the system finds the new equilibrium position.

25. 24







Figure 3.1: Passive tracking system

2.ACTIVE TRACKING SYSTEMS
The two basic types of active solar tracker are single-axis and double-axis.
(a)Single axis trackers
The single axis tracking systems realizes the movement of either elevation or azimuth for a solar
power system. Which one of these movements is desired, depends on the technology used on the
tracker as well as the space that it is mounted on. For example the parabolic through systems
utilize the azimuthally tracking whereas the many rooftop PV-systems utilize elevation tracking
because of the lack of space. A single-axis tracker can only pivot in one plane – either
horizontally or vertically. This makes it less complicated and generally cheaper than a two-axis
tracker, but also less effective at harvesting the total solar energy available at a site. Trackers use
motors and gear trains to direct the tracker as commanded by a controller responding to the solar
direction. Since the motors consume energy, one wants to use them only as necessary.
Single axis trackers have one degree of freedom that acts as an axis of rotation. There are several
common implementations of single axis trackers. These include horizontal single axis trackers
(HSAT) and vertical single axis trackers (VSAT).

Figure 3.2: Single axis solar tracker

26. 25

A horizontal-axis tracker consists of a long horizontal tube to which solar modules are
attached. The tube is aligned in a north-south direction, is supported on bearings mounted on
pylons or frames, and rotates slowly on its axis to follow the sun's motion across the sky. This
kind of tracker is most effective at equatorial latitudes where the sun is more or less overhead at
noon. In general, it is effective wherever the solar path is high in the sky for substantial parts of
the year, but for this very reason, does not perform well at higher latitudes. For higher latitude, a
vertical-axis tracker is better suited. This works well wherever t he sun is typically lower in the
sky and, at least in the summer months, the days are long.
(b)Dual Axis Trackers
Dual axis trackers as shown in the figure 2.6 have two degrees of freedom that act as
axes of rotation. Double-axis solar trackers, as the same suggest, can rotate simultaneously in
horizontal and vertical directions, and s o are able to point exactly at the sun at all times in any
location.
Dual axis tracking systems realize movement both along the elevation- and azimuthally
axes. These tracking systems naturally provide the best performance, given that the components
have high enough accuracy as well.











Figure 3.3:Dual axis solar tracking

27. 26

CHAPTER- 4
Components Description

When a beginner to electronics first looks at a circuit board full of components is often
overwhelmed. In these next few sections we will help you to identify some of the simple
components. Then you should be able to call them resistors and transistors instead.
Electronic component are classed into either being Passive devices or Active devices.

4.1Passive Device
A Passive Device is one that contributes no power gain (amplification) to a circuit or
system. It has not control action and does not require any input other than a signal to perform its
function. In other words, “the components with no brains” Examples are Resistors, Capacitors
and Inductors

4.2Active Devices
Active Devices are components that are capable of controlling voltages or currents and can
create a switching action in the circuit. In other words, “Devices with smarts” Examples are
Diodes, Transistors and integrated circuits. Most active components are semiconductors.

4.3Resistor
A resistor is a component of a circuit that resists the flow of electrical current. It has two
terminals across which electricity must pass, and it is designed to drop the voltage of the current
as it flows from one terminal to the other. Resistors are primarily used to create and maintain
known safe currents within electrical components. Resistance is measured in ohms, after Ohm's
law. This law states that electrical resistance is equal to the drop in voltage across the terminals
of the resistor divided by the current being applied. A high ohm rating indicates a high resistance
to current. This rating can be written in a number of different ways - for example, 81R represents
81 ohms, while 81K represents 81,000 ohms. Materials in general have a characteristic behavior
of opposing the flow of electric charge. This opposition is due to the collisions between electrons

28. 27

that make up the materials. This physical property, or ability to resist current, is known as
resistance and is represented by the symbol R. Resistance is expressed in ohms which is
symbolized by the capital Greek letter omega.
The resistance of any material is dictated by four factors:
 Material property-each material will oppose the flow of current differently.
 Length-the longer the length, the more is the probability of collisions and, hence, the
larger the resistance.
 Cross-sectional area-the larger the area A, the easier it becomes for electrons to flow and,
hence, the lower the resistance.
 Temperature-typically, for metals, as temperature increases, the resistance increases.
The amount of resistance offered by a resistor is determined by its physical construction. A
carbon composition resistor has resistive carbon packed into a ceramic cylinder, while a carbon
film resistor consists of a similar ceramic tube, but has conductive carbon film wrapped around
the outside. Metal film or metal oxide resistors are made much the same way, but with metal
instead of carbon. A wire wound resistor, made with metal wire wrapped around clay, plastic, or
fibre glass tubing, offers resistance at higher power levels. Those used for applications that must
withstand high temperatures are typically made of materials such as cermets, a ceramic-metal
composite, or tantalum, a rare metal, so that they can endure the heat. Resistors are coated with
paint or enamel, or covered in moulded plastic to protect them. Because they are often too small
to be written on, a standardized colour-coding system is used to identify them. The first three
colours represent ohm value, and a fourth indicates the tolerance, or how close by percentage the
resistor is to its ohm value. This is important for two reasons: the nature of its construction is
imprecise, and if used above its maximum current, the value can change or the unit itself can
burn up. The circuit element used to model the current-resisting behavior of a material is the
resistor. For the purpose of constructing circuits, resistors shown in Figure 4.22 are usually made
from metallic alloys and carbon compounds. The resistor is the simplest passive element.

29. 28




Fig 4.1: from top to bottom:
1
4
W,
1
2
W, and 1-W resistors

1.TYPES OF RESISTER
Different types of resistors have been created to meet different requirements. Some resistors
are shown in Figure 4.23. The primary functions of resistors are to limit current, divide voltage
and dissipate heat. A resistor is either fixed or variable. Most resistors are of the fixed type that is
their resistance remains constant. The two common types of fixed resistors wire wound and
composition are shown in Figure 4.24. Wire wound resistors are used when there is a need to
dissipate a large amount of heat while the composition resistors are used when large resistance is
needed.

30. 29



Fig 4.2:Different types of resistors



(a) (b)

Fig 4.3: Fixed resistors: (a) wire wound type (b) Carbon film type
2. RESISTOR COLOUR COD E
Some resistors are physically large enough to have their values printed on them. Other
resistors are too small to have their values printed on them. For such small resistors color coding
provides a way of determining the value of resistance. As shown in Figure 4.25 the color coding
consists of three, four, or five bands of color around the resistor.

31. 30


Fig 4.4: Color coding

The first three bands specify the value of the resistance. Bands A and B represent the first and
second digits of the resistance value and C is usually given as a power of 10 as shown in figure
4.25. If present the fourth band D indicates the tolerance percentage. For example a 5 percent
tolerance indicates that the actual value of the resistance is within ± 5 of the color-coded value.
When the fourth band is absent, the tolerance is taken by default to be ± 20 percent. The fifth
band E, if present is used to indicate a reliability factor which is a Statistical indication of the
expected number of components that will fail to have the indicated resistance after working for
1,000 hours. As shown in Figure 4.25 the statement “Big Boys Race Our Young Girls, But
Violet Generally Wins” can serve as a memory aid in remembering the color code.

4.4 Variable resistors.
Presets and potentiometers are commonly used types of variable resistors. These are mostly
used for voltage division and setting the sensitivity of sensors. These have a sliding contact or
wiper which can be rotated with the help of a screw driver to change the resistance value. In the
linear type, the change in resistance is linear as the wiper rotates. In the logarithmic type, the
resistance changes exponentially as the wiper slides. The value is meant to be set correctly when
installed in some device, and is not adjusted by the device's user.

32. 31



Fig 4.5: Preset Resistor

The variable may have three tabs where the middle tab is the wiper. If all the three tabs are
used, it behaves as a voltage divider. If only wiper tab is used along with another tab, it becomes
a variable resistor or rheostat. If only the side tabs are used, then it behaves as a fixed resistor.
These are mostly used for tuning, voltage division and adjusting sensitivity of sensors.
The variable can have one or two switches in-built where the resistor operates for the ON
state of the switch(s). Such resistors were mostly used for volume control in older TV and radio
circuits. There may also be four-tab variables where the fourth lead is for feedback signal and
placed near the first tab. Wire wound variable resistors are used for very precise control of
resistance. The wiper may also be rotary (as in most presets), sliding or disc shaped (as used in
pocket radios for volume control).


Fig 4.6connection of preset

33. 32

4.4 Sensors
A sensor is a device that measures a physical quantity and converts it into a signal which
can be read by an observer or by an instrument.

1.Light dependent resistors (LDR):
LDRs have cadmium sulfide zigzag tack whose resistance decreases as the light intensity
incident on it increases. In the absence of light, its resistance is in mega ohms but on the
application of light, the resistance falls drastically. These resistors are used in many consumer
items such as camera light meters, street lights, clock radios, alarms, and outdoor clocks.


Fig 4.7 ldr
Also, LDR’s are less sensitive than photo diodes and photo transistor
2.Working Principle of LDR
A light dependent resistor works on the principle of photo conductivity. Photo conductivity
is an optical phenomenon in which the materials conductivity (Hence resistivity) reduces when
light is absorbed by the material.

34. 33

An LDR is usually made of a semiconductor material (Normally Silicon) doped with a
small percentage of a valency 5 material (commonly Arsenic), to make it an "N" material.
The photons of the light affecting the LDR, charge the electrons of the doped material so that
they can easily be dislodged by any electrical charges thus allowing the current to flow more
easily. The increase of current flow for the same PD proves that the resistance of the device has
been reduced by the increase of light.
Variation in resistance with changing light intensity

FIG4.8 Typical LDR resistance vs light intensity

4.5 MOTOR DRIVER L293D IC
1. H-bridge basics
Generally, even the simplest robot requires a motor to rotate a wheel
or performs particular action. Since motors require more current then the
microcontroller pin can typically generate, you need some type of a switch
(Transistors, MOSFET, Relay etc.,) which can accept a small current,
amplify it and generate a larger current, which further drives a motor. This
entire process is done by what is known as a motor driver.
FIG 4.9:H-BRIDGE

35. 34

Motor driver is basically a current amplifier which takes a low-current signal from the
microcontroller and gives out a proportionally higher current signal which can control and drive
a motor. In most cases, a transistor can act as a switch and perform this task which drives the
motor in a single direction.Turning a motor ON and OFF requires only one switch to control a
single motor in a single direction. What if you want your motor to reverse its direction? The
simple answer is to reverse its polarity. This can be achieved by using four switches that are
arranged in an intelligent manner such that the circuit not only drives the motor, but also controls
its direction. Out of many, one of the most common and clever design a H-bridge circuit where
transistors are arranged in a shape that resembles the English alphabet "H".
As you can see in the image, the circuit has four switches A, B, C and D. Turning these
switches ON and OFF can drive a motor in different ways.
 Turning on Switches A and D makes the motor rotate clockwise
 Turning on Switches B and C makes the motor rotate anti-clockwise
 Turning on Switches A and B will stop the motor (Brakes)
 Turning off all the switches gives the motor a free wheel drive
 Lastly turning on A & C at the same time or B & D at the same time shorts your entire
circuit. So, do not attempt this.






Fig 4.10:switching of h-bridge

36. 35

H-bridges can be built from scratch using relays, mosfets, field effect transistors (FET), bi-
polar junction transistors (BJT), etc. But if your current requirement is not too high and all you
need is a single package which does the job of driving a small DC motor in two directions, then
all you need is a L293D IC. This single inexpensive package can interface not one, but two DC
motors. L293, L293B and few other versions also does the same job, but pick the L293D version
as this one has an inbuilt fly back diode which protects the driving transistors from voltage
spikes that occur when the motor coil is turned off.
2.Introduction to L293D IC
L293D IC generally comes as a standard 16-pin DIP (dual-in line
package). This motor driver IC can simultaneously control two small
motors in either direction; forward and reverse with just 4 microcontroller
pins (if you do not use enable pins). Some of the features (and drawbacks)
of this IC are:
 Output current capability is limited to 600mA per channel Fig4.11:l293d
with peak output current limited to 1.2A (non-repetitive). This means you cannot drive
bigger motors with this IC. However, most small motors used in hobby robotics should
work. If you are unsure whether the IC can handle a particular motor, connect the IC to
its circuit and run the motor with your finger on the IC. If it gets really hot, then beware...
Also note the words "non-repetitive"; if the current output repeatedly reaches 1.2A, it
might destroy the drive transistors.
 Supply voltage can be as large as 36 Volts. This means you do not have to worry much
about voltage regulation.
 L293D has an enable facility which helps you enable the IC output pins. If an enable pin
is set to logic high, then state of the inputs match the state of the outputs. If you pull this
low, then the outputs will be turned off regardless of the input states
 The datasheet also mentions an "over temperature protection" built into the IC. This
means an internal sensor senses its internal temperature and stops driving the motors if
the temperature crosses a set point

37. 36

 Another major feature of L293D is its internal clamp diodes. This flyback diode helps
protect the driver IC from voltage spikes that occur when the motor coil is turned on and
off (mostly when turned off)
 The logical low in the IC is set to 1.5V. This means the pin is set high only if the voltage
across the pin crosses 1.5V which makes it suitable for use in high frequency applications
like switching applications (up to 5KHz)
 Lastly, this integrated circuit not only drives DC motors, but can also be used to drive
relay solenoids, stepper motors etc.
3.L293D Connections
The circuit shown to the right is the most basic implementation of L293D IC. There are 16
pins sticking out of this IC and we have to understand the functionality of each pin before
implementing this in a circuit.
 Pin1 and Pin9 are "Enable" pins. They should be connected to +5V for the drivers to
function. If they pulled low (GND), then the outputs will be turned off regardless of the
input states, stopping the motors. If you have two spare pins in your microcontroller,
connect these pins to the microcontroller, or just connect them to regulated positive 5
Volts.
 Pin4, Pin5, Pin12 and Pin13 are ground pins which should ideally be connected to
microcontroller's ground.
 Pin2, Pin7, Pin10 and Pin15 are logic input pins. These are control pins which should be
connected to microcontroller pins. Pin2 and Pin7 control the first motor (left); Pin10 and
Pin15 control the second motor(right).
 Pin3, Pin6, Pin11, and Pin14 are output pins. Tie Pin3 and Pin6 to the first motor, Pin11
and Pin14 to second motor
 Pin16 powers the IC and it should be connected to regulated +5Volts
 Pin8 powers the two motors and should be connected to positive lead of a secondary
battery. As per the datasheet, supply voltage can be as high as 36 Volts.

38. 37










Fig 4.12: l293d connections
4.Working of L293D
There are 4 input pins for this l293d, pin 2,7 on the left and pin 15 ,10 on the right as shown
on the pin diagrams Left input pins will regulate the rotation of motor connected across
. left side and right input for motor on the right hand side. The motors are rotated on the basis of
the inputs provided across the input pins as LOGIC 0 or LOGIC 1. In simple you need to provide
Logic 0 or 1 across the input pins for rotating the motor.
5.Truth table: I have shown you where to connect the motors, battery and the microcontroller.
But how do we control the direction of these motors? Let us take an example Suppose you need
to control the left motor which is connected to Pin3 (O1) and Pin6 (O2). As mentioned above,
we require three pins to control this motor - Pin1 (E1), Pin2 (I1) and Pin7 (I2). Here is the truth
table representing the functionality of this motor driver.

39. 38

Pin 1 Pin 2 Pin 7 Function
High High Low Turn Anti-clockwise (Reverse)
High Low High Turn clockwise (Forward)
High High High Stop
High Low Low Stop
Low X X Stop
High ~+5V, Low ~0V, X= Either high or low (don't care)
Table no:4.1: l293d TRUTH TABLE
In the above truth table you can observe that if Pin1 (E1) is low then the motor stops,
irrespective of the states on Pin2 and Pin7. Hence it is essential to hold E1 high for the driver
to function, or simply connect enable pins to positive 5 volts.With Pin1 high, if Pin2 is set
high and Pin7 are pulled low then current flows from Pin2 to Pin7 driving the motor in anti-
clockwise direction, If the states of Pin2 and Pin7 are flipped, then current flows from Pin7 to
Pin2 driving the motor in clockwise direction.The above concept holds true for other side of
the IC too. Connect your motor to Pin11 and Pin14; Pin10 and Pin15 are input pins, and Pin9
(E2) enables the driver.
6.Voltage Specification: VCC is the voltage that it needs for its own internal operation 5v;
L293D will not use this voltage for driving the motor. For driving the motors it has a separate
provision to provide motor supply VSS (V supply). L293d will use this to drive the motor. It
means if you want to operate a motor at 9V then you need to provide a Supply of 9V across VSS
Motor supply. The maximum voltage for VSS motor supply is 36V. It can supply a max current
of 600mA per channel Since it can drive motors Up to 36v hence you can drive pretty big motors
with this l293d. VCC pin 16 is the voltage for its own internal Operation. The maximum voltage
ranges from 5v and up to 36v.

40. 39

TIP: Don’t Exceed the V max Voltage of 36 volts or it will cause damage.
Features
 Featuring Unit rode L293 and L293D Products Now From Texas Instruments
 Wide Supply-Voltage Range: 4.5 V to 36 V
 Separate Input-Logic Supply
 Internal ESD Protection
 Thermal Shutdown
 High-Noise-Immunity Inputs
 Output Current 1 A Per Channel (600mA for L293D)
 Peak Output Current 2 A Per Channel (1.2 A for L293D)
 Output Clamp Diodes for Inductive Transient Suppression (L293D)
4.6VOLTAGE COMPARATOR Lm1458
1.Description
The LM1458 and the LM1558 are general purpose dual operational amplifiers. The two
amplifiers share a common bias network and power supply leads. Otherwise, their operation is
completely independent.
The LM1458 is identical to the LM1558 except that the LM1458 has its specifications
guaranteed over the temperature range from 0°C to +70°C instead of −55°C to +125°C.

41. 40

Connection Diagram








Features
 No Frequency Compensation Required
 Short-Circuit Protection
 Wide Common-Mode and Differential Voltage Ranges
 Low-Power Consumption
 8-Lead TO-99 and 8-Lead PDIP
 No Latch Up When Input Common Mode Range is Exceeded









Figure 4.13: TO-99 Package Figure 4.14:. Dual-In-Line Package
( Top View) ( Top View)

42. 41


4.7 12V BATTERTY
A battery is a device that can create electricity using a chemical reaction. It converts energy
stored in molecules inside the battery into electricity. They produce direct current (DC)
electricity(electricity that flows in one direction, and does not switch back and forth).

Fig 4.15:12v battery
Using the electricity from an outlet in a house or building is cheaper and uses less energy, but a
battery can provide electricity in areas that do not have electric power distribution. It is also
useful for things that moved around and cords would get in the way.

43. 42

4.8Dc motors
Motor is use to drive the Solar Tracker to the best angle of exposure of light. For this
section, we are using A DC Geared motor These are very commonly used in robotics. DC
motors can rotate in both directions depending upon the polarity of current through the motor.
These motors have free running torque and current ideally zero. These motors have high speed
which can be reduced with the help of gears and traded off for torque. Speed Control of DC
motors is done through Pulse Width Modulation techniques, i.e. sending the current in
intermittent bursts. PWM can be generated by 555timer IC with adjusted duty cycle. Varying
current through the motor varies the torque.















Fig 4.16: DC Motor: High Torque Mini 12V DC Gear Motor, 200 rpm

44. 43

1.Motor Specifications

 Voltage: 12.0VDC
 Output Speed: 200 +/- 10% RPM
 No-Load output current: =< 50mA
 Rotation Output: CW / CCW
 Noise: No Gear Noise
 Stall output: : Slip Gear, Broken Gear is no allowed
 Output shaft of the axial clearance: =< 0.1 ~ 0.3mm, Horizontal clearance
requirement =< 0.05











Fig 4.17: dc motor

45. 44

Chapter 5
CIRCUIT AND ITS WORKING
5.1 Circuit diagram

Fig 5.1 single axis solar tracker circuit dia gram
5.2 HOW THE SOLAR TRACKER CONTROL CIRCUIT FUNCTIONS
A careful investigation of the circuit shown in the diagram reveals that the whole
configuration is actually very simple and straightforward. Here a single IC1458 is utilized for the
required operations.
The op amps are primarily wired to form a kind of window comparator, responsible for
activating their outputs whenever their inputs waver or drift out of the predetermined window,
set by the relevant pots.
Two LDRs are connected to the inputs of the op amps for sensing the light levels. As long
as the lights over the two LDRs are uniform, the outputs of the op amp remain deactivated.

However the moment one of the LDRs senses a different magnitude of light over it (which may
happen due to the changing position of the sun) the balance over the input of the op amp shift

46. 45

toward one direction, immediately making the relevant op amps output go high. This high output
instantly activates the MOTOR DRIVE (IC293D), which in turn rotates the connected motor in a
set direction, such that the panel rotates and adjusts its alignment with the sun rays until uniform
amount of light is restored over the relevant set of LDRs. Once the light level over the relevant
LDR sets is restored, the opamps again become dormant and switch off their outputs and also the
motor.
The above sequence keeps on happening for the whole day, in steps, as the sun alters its
position and the above mechanism keeps shifting in accordance to the suns position. It should be
noted that two sets of the above explained circuit assemblies will be required for controlling the
dual actions or simply to make the above discussed dual tracker solar system mechanism.

5.3 Advantages and Disadvantages of a Solar Tracker System
Solar trackers are rising in popularity, but not everyone understands the complete benefits
and potential drawbacks of the system. Solar panel tracking solutions are a type of device that
host mounted photovoltaic panels, which use the sun to generate electricity. Stationary mounts,
which hold these panels in a fixed position, can have their productivity compromised when the
sun passes to a less-than-optimal angle. Compensating for this, solar trackers automatically move
to “track” the progress of the sun across the sky, thereby maximizing output.
It’s a fantastic system for energy output, but there are a few considerations to bear in mind before
pursuing one for your jobsite.
1.Advantages
 Solar trackers generate more electricity than their stationary counterparts due to an
increased direct exposure to solar rays.
 There are many different kinds of solar tracker, such as single-axis and dual-axis
trackers, which can help you find the perfect fit for your unique jobsite. Installation
size, local weather, degree of latitude, and electrical requirements are all important
considerations that can influence the type of solar tracker that’s best for you.
 Solar trackers generate more electricity in roughly the same amount of space needed
for fixed tilt systems, making them ideal optimizing land usage.

47. 46

2.Disadvantages
 Solar trackers are slightly more expensive than their stationary counterparts, due to the
more complex technology and moving parts necessary for their operation.
 Some ongoing maintenance is generally required, though the quality of the solar tracker
can play a role in how much and how often this maintenance is needed.
Overall, solar trackers are highly efficient installations, and are a great fit for many smaller
jobsites. If you’re interested in learning more about solar trackers or how a solar tracker system
could work on your jobsite, be sure to contact us for more information!
5.3 Future Work
The goals of this project were purposely kept within what was believed to be attainable
within the allotted timeline. As such, many improvements can be made upon this initial design.
That being said, it is felt that this design represents a functioning miniature scale model which
could be replicated to a much larger scale. The following recommendations are provided as ideas
for future expansion of this project:
 Increase the sensitivity and accuracy of tracking by using a different light sensor. A
phototransistor with an amplification circuit would provide improved resolution and
better tracking accuracy/precision.
 Utilize a dual-axis design versus a single-axis to increase tracking accuracy.


FIG 5.2:solar tracker kit

48. 47

5.4 Conclusion
From the design of experimental set up of a Solar Tracking System Using dc Motor If we
compare Tracking by the use of LDR with Fixed Solar Panel System we found that the efficiency
of Solar Tracking System is improved by 30-45% and it was found that all the parts of the
experimental setup are giving good results. The required Power is used to run the motor by using
a 12v battery. Moreover, this tracking system does track the sun in a continuous manner. And
this system is more efficient and cost effective in long run. From the results it is found that, by
automatic tracking system, there is 30 % gain in increase of efficiency when compared with non-
tracking system. The solar tracker can be still enhanced additional features like rain protection
and wind protection which can be done as future work.