ABSTRACT
This project is aimed at designing, constructing and testing of a single axis,
variable speed passive solar tracking device. This is because all the solar
trackers in use in the country are mainly imported.
The design works on the principle that Freon – 12 (Dichloroflouromethane)
boils at very low temperatures i.e. somewhat lower than – 300 F (-34.44oC) thus
generating great pressures even with just a small quantity of it evaporating.
This pressure generated from the evaporation of some of the Freon – 12 tilts
the collector in the direction of the sun through a hydraulic cylinder pivoted to
the collector base.
The solar tracker was designed, constructed, and tested by mounting a solar
Photovoltaic (PV) module on the tracker and comparison of the power output of
the PV module on the tracker against that of a stationary PV module was made.
Results showed that the tracking panel had an average relative performance of
about 30% over the stationary module and a cost of over N40, 000.00 cheaper
than that of the imported one.
It was thus concluded that the project was a success because the relative
performance obtained is in agreement with reported performances of similar
tracking devices.
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TABLE OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vii
Table of content viii – xii
List of figures xiii – xiv
List of tables xiv
List of drawings xv
List of plates xvi
Symbols xvii – xviii
CHAPTER ONE
INTRODUCTION
1.1 Solar Energy ……………………………………….. 1
1.2 Solar Tracking ……………………………………… 2
1.3 Solar Collectors …………………………………….. 3
1.4 Solar Photovoltaic Cell …………………………… 4
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1.5 Solar Module ……………………………………… 5
1.6 Need for Tracking …………………………………. 5
1.7 The Aim of the Project ……………………………… 6
CHAPTER TWO
LITERATURE REVIEW
2.1 Solar Trackers ……………………………………… 7
2.2 Tracking Modes/ Geometries …………………….. 7
2.3 Previous Works on Solar Tracking systems …….. 9
2.4 Justification. ……………………………………….. 10
CHAPTER THREE
THEORY OF DESIGN AND DESIGN CALCULATIONS
3.1 Analysis of Tracking …………………………….. 11
3.1.1 Angle of Altitude ………………………………… 11
3.1.2 Angle of Slope …………………………………. 12
3.1.3 Angle of Incidence …………………………….. 12
3.1.4 Surface Azimuth Angle ……………………….. 13
3.1.5 Angle of Declination of the Sun ……………….. 13
3.1.6 Hour Angle ……………………………………. 14
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3.1.7 Total Solar Radiation on a Tilted Surface …… 14
3.2 Volume of Cylinder …………………………… 15
3.3 Pressure in a Cylinder ………………………… 15
3.4 Specific Gas Constant …………………………. 16
3.5 Ideal Gas Equation …………………………….. 16
3.6 Length of Throw Arm ………………………….. 17
3.7 Maximum Permissible Pressure in Refrigerant
Reservoir ……………………………………….. 17
3.8 Force on Hydraulic Cylinder ………………….. 18
3.9 Mass of Fluid …………………………………… 18
3.10 Design of Semi Tracking Variable Speed Solar
Tracking Device ………………………………… 18
3.11 Design Calculations ……………………………. 20
3.12 Length of Throw Arm …………………………. 31
3.13 Pressure Generated by Gas in Reservoir …….. 33
3.14 Altitude Angles at other Dates in the Year …… 33
3.15 Height of Shades Required for 21st September
And 21st March ……………………………….. 34
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CHAPTER FOUR
CONSTRUCTION OF SOLAR TRACKING DEVICE AND
MATERIAL SELECTION
4.1 Methodology …………………………………. 35
4.2 Description of Solar Tracking Device …….. 35
4.3 How the Solar Tracker Works …………….. 36
4.4 Specification of the Solar Tracking Device 38
4.4.1 The Refrigerant …………………………….. 38
4.4.2 The Frame …………………………………… 39
4.4.3 The Double Acting Hydraulic Cylinder …… 39
4.4.4 The Shades ………………………………….. 39
4.4.5 Refrigerant Hoses ……………………. 40
4.4.6 Valves ………………………………………… 40
4.4.7 Refrigerant Reservoir ………………………. 40
4.5 Material Selection and Manufacturing
Process ………………………………………. 40
4.5.1 Frame ………………………………………… 40
4.5.2 Double Acting Hydraulic Cylinder ………… 41
4.5.3 Shades ……………………………………….. 41
4.5.4 Refrigerant Hoses ……………………. 41
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4.5.5 Valves ……………………………………….. 41
4.5.6 Refrigerant …………………………………. 42
4.5.7 Refrigerant Reservoir ……………………… 43
CHAPTER FIVE
EXPERIMENTS AND RESULTS
5.1 Experimentation ……………………………. 44
5.2 Aim ………………………………………….. 44
5.3 Procedures ………………………………….. 44
5.4 Results ………………………………………. 46
5.5 Discussions ………………………………….. 54
5.6 Costing ………………………………………. 55
CHAPTER SIX
CONCLUSIONS AND RECOMMENDATIONS
Conclusion …………………………………………… 57
Recommendations ……………………………………. 57
REFERENCES ……………………………………….. 58
CHAPTER ONE
INTRODUCTION
1.1 SOLAR ENERGY
Solar energy is an important clean, cheap and abundantly available renewable
energy. The sun radiates heat and light. The heat and light received from the
sun support the environment on the earth through the following well-known
natural effects.
– Temperature balance on the earth
– Photosynthesis by biological plants, production of oxygen and organic
materials. Production of organic chemicals and biomass
– Wind due to unequal heating of water, land surfaces.
– Water cycle: Evaporation – Clouds – Rain – water – evaporation –
clouds – …
– Heating of ocean water: Ocean thermal energy (OTEC)
– Waves in Ocean: Ocean wave energy
– Tides in Ocean: Ocean tidal energy (due to gravitational forces._
The sun produces enormous amount of heat and light through sustained
nuclear fusion reactions. The solar energy received on earth and can be used for
heating and producing electrical energy.
The first person to use the sun’s energy on a large scale was Archimedes
who reportedly set fire to an attacking Roman fleet at Syracuse in 212BC. He
accomplished this by means of a burning glass composed of small square
mirrors moving everywhere upon hinges so as to reduce the Roman fleet to
ashes at a distance of a bowshot. Serious studies of the sun and its potentials
began in the 17th century when Galileo and Lavoiser utilized the sun in their
researches. By 1700 diamonds had been melted and by the early 1800s heat
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engines were operating with energy supplied by the sun. In the early twentieth
century, solar energy was used to power water distillation plants in Chile and
irrigation pumps in Egypt. (Kreider and Kreith, 1981).
About 170 trillion KW of solar energy are intercepted by the earth, an
amount which is 5000 times greater than the sum of all other energy inputs,
{Dickinson and Cheremisinoff, 1980). 30% of this amount is reflected back into
space as short wave radiation, 45% is absorbed by the atmosphere, the land
surface and oceans and it is converted to heat as the ambient surface
temperature of the planet. The remaining 25% powers the evaporation,
convection and precipitation cycles of the biosphere.
1.2 SOLAR TRACKING
Although it is abundant, solar energy impinging on the earth’s
atmosphere is relatively small due to attenuation, local weather phenomena and
air pollution. Also solar energy is received in cyclic, intermittent form with very
low power density from 0 to 1kW/m2. The direction of solar rays changes
during the day and with season. Solar energy received on ground level is
affected by atmospheric clarity, degree of latitude etc.
There is therefore a need to harness the cyclic and intermittent though
abundant solar energy. One way of doing this is using solar collectors.
Collectors are devices which absorbs and transfers the solar energy to heat
transport fluids. Solar Collectors could be flat plate, paraboloic trough,
Heliostat – reflector or Fresnel.
These collectors are usually operated in a fixed position oriented in a
north-south direction in the northern hemisphere titled at an angle
approximately equal to the latitude angle of that location. The collector
performance and efficiency are usually expressed in terms of solar energy
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incident on the collector. A method that has been receiving attention in recent
times for increasing the output of the collectors is that of making the collector
track the sun.
For the rays to be normal to the collector surface requires that the
collector follows the sun both in the east- west and in the north- south directions
continuously. This type of collector is known as the fully tracking collector. A
restricted form of tracking, called semi-tracking may however be obtained by
restricting the collector to rotate about a north – south axis, with the collector
inclined to the horizontal at an appropriate slope. Two cases may be
distinguished: one when the normal to the collector rotates at a uniform speed
of 150 per hour and the other when the normal to the collector is always in the
azimuthal plane. The later case, though better, requires that the collector be
rotated at rotational speeds which vary over the day. The last type of semi
tracking is by constraining the collector to rotate about a east – west axis, which
itself is inclined to the horizontal at an appropriate slope usually the latitude
angle of the location. This is usually done on a monthly basis.
1.3 SOLAR COLLECTORS
When sunlight strikes an object, a portion of the energy bounces off
(reflection). The remainder serves to increase its molecule activity causing a
corresponding rise in temperature.
The above discussion shows the relationship of sunlight to thermal
energy conversion process. The conversion takes place automatically on contact
between sunlight and a material. To be able to utilize the sunlight – to – thermal
phenomenon effectively requires a device capable of heating up efficiently, able
to transfer the collected heat to some kind of heat transfer fluid (either air or a
liquid) and be able to do this while exposed to outdoor weather conditions. The
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most popular device at present capable of fulfilling this is called a “flat – plate
collector”. All flat plate collectors have five basic components in common
namely:
a. The absorber surface
b. The heat transfer interface/fluid passage
c. The Glazing
d. The insulation and
e. The protective casing
Flat plate collectors could either be Liquid cooled or air cooled Flat plate
collectors. Water or a water/antifreeze solution is used predominantly as the
heat transfer (heat removing) Fluid in liquid cooled flat plate collectors. Non
toxic anti freezes and silicon based heat transfer fluids are also being developed
specifically for use in solar energy collection systems. Air cooled Flat plate
collectors use air as the heat transfer medium.
1.4 SOLAR PHOTOVOLTAIC CELLS
Photovoltaic (PV) is the direct conversion of sunlight to electricity
through photoelectric effect. The smallest unit of a solar electric device is the
solar cell. Solar cells are made of semi conductor material of which the
commonest is silicon. The silicon cell may be from monocrystaline,
polycrystalline or amorphous silicon. Monocrystaline refer to cells cut from
single crystal of Silicon while polycrystalline refers to cells made from many
crystals. Amorphous type cells are made from silicon that is not in crystalline
form. Instead silicon is deposited on the back of a glass or surface in very thin
layers. The surface is then scored to divide it into a number of cells and
electrical connections are added.
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Mono and poly crystalline silicon cells are silicon wafers sliced from
cylindrical silicon crystals using very precise saws. These wafers are then
chemically treated in furnaces to enhance their electrical properties, after which
an anti reflective coating is applied to the cell surface to help it absorb radiation
more effectively. Thin metal wires are soldered to the front of the cell. These
ribbons of metal on the cell act as the contact, whereas a solid layer of metal on
the back side of the cell acts as a negative contact.
1.5 SOLAR MODULE
Arrangement of solar cells wired in series sealed between glass and
plastic and supported inside a metal frame is called a solar cell module. A
standard module will produce 12 volt, 3.5 Amp at maximum power point.
While a solar array is a group of modules mounted together.
1.6 NEED FOR TRACKING
Tracking requires that the collectors receive sunshine early and late in the
day to be effective. At mid and high latitudes the summer gain is significantly
greater than the winter gain which typically is not more than 20%.(Paruleka and
Rao, 1999).
Solar tracking increases the amount of time solar collectors are oriented
towards the sun and therefore increase the solar collector output. Solar tracking
could to a lesser degree be used for control functions. In a situation where an
optical lens is to be used to track the sun’s movement, there would be a
reduction in the cost of the lens since the tracker allows the incident rays to
strike normal to the lens and therefore smaller lenses are required.
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1.7 THE AIM OF THE PROJECT
The aim of this research work is to design, construct and test a solar
energy tracking device to which a solar module can be incorporated.
The aim is to be achieved by the design of a single axis variable speed
passive solar tracking device after which construction of the tracker using the
design criteria would be undertaken.
A solar tracking device will maximize the amount of time the solar
module is oriented towards the sun thereby maximizing the energy output from
the solar module. It is also hoped that after the construction and
experimentation on the performance of the device, some useful information
would be gained which could lead to improvement on the design.
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