IRJET- Dual Axis Parabolic Solar trough Collector's Performance Analysis ...
Final Year Project - 2012 Report
1. Design, Analysis and Fabrication of Solar Water
Heater with Solar Tracking
SESSION 2008-2012
PROJECT ADVISOR
PROF. DR SHAHID KHALIL
AUTHORS
Sheikh Haris Zia 08-ME-39
Ibrahim Azhar 08-ME-53
Ahmed Hilal Khan 08-ME-125
FACULTY OF MECHANICAL AND AERONAUTICAL ENGINEERING
UNIVERSITY OF ENGINEERING AND TECHNOLOGY,
TAXILA
2. Preface:
World is advancing very fast towards the renewable energy resources.
There are two big reasons behind this. Firstly the world is going to face
serious issues of oil and gas resources shortages in the later eras. Secondly
the renewable energy resources do not contribute in any running cost in any
project. They are one time investment projects.
Our beloved country is also facing economic recession and energy
crisis. That’s why it is much necessary that we should carefully think about it
and solve our issues by ourselves. Though it is much time consuming but we
should also kept in mind that we are not left with any other choice but to
produce by ourselves.
That’s why we think of such project which involves the use of
renewable energy resource. It basically uses the energy from the sun and
utilizes it to heat the water which is then stored and later on it can be utilized
when needed.
The first chapter of this book gives a brief introduction about various
renewable energy resources and the types of solar panels and concentrators
which are widely used in the world.
The second chapter constitutes the designing parameters along with
complete description on PRO/e, SOLIDWORKS, AUTOCAD and other
engineering software’s.
The third chapter is the analysis of the solar collector assembly. The
major portion of analysis constitutes the structural and thermal analysis on
ANSYS. This chapter also includes the CFD analysis of moving fluid on
FLUENT.
The fourth chapter is composed of step by step fabrication of different
parts and completes assembly. The thermal system assembly, the collector
and the transportation system.
The fifth chapter is the heat transfer analysis of the copper pipe from
surroundings. It also includes the effect of losses from the surroundings and
step by step calculations of various constants and non dimensional numbers.
3. Complete care and expertise has been devoted while writing this
report, with the aim to convey the reader the complete knowledge of solar
collector and other prospects. But to err is human, therefore the chances of
mistakes cannot be denied. We will be obliged to have any suggestions from
our readers.
Authors
4. Acknowledgments:
All praise to Almighty Allah who has given us knowledge and made us
human beings so that we can think and explore the universe. Blessings be
upon Prophet (PBUH) for they are the one who have conveyed to us the
message of God and thus showed us the right path.
Our parents are to be thanked for the affection and patience they have
showed during the project. And without their prayers this project couldn’t
have been completed.
Any student venture cannot be completed unless a competent and
affectionate teacher is here to guide them. Same is the case here; our advisor
Prof Dr. Shahid Khalil and Dr Masood-ur-Rehman has always been there to
guide us throughout the project. We express our deepest gratitude to them.
All the other faculty members, professors, lecturers and our beloved
friends are to be thanked for their continuous support. In other words we
thank all those whose names could not have been mentioned, but they
helped us in one way or the other during the project.
Authors
6. TABLE OF CONTENTS
Ch . No. Content Page
1. Introduction To Solar Energy 1
1.1. Introduction to Renewable Energies 2
1.1.1 Types of Renewable Energies 2
1.1.1.1 Wind Power 3
1.1.1.2 Biomass 3
1.1.1.3 Hydro Power 3
1.1.1.4 Geothermal Energy 4
1.1.1.4 Tidal Power 4
1.1.1.5 Solar Energy 5
1.2 Applications of Solar Technology 6
1.2.1 Architecture and Urban Planning 6
1.2.2 Agriculture and Horticulture 7
1.2.3 Solar Lighting 8
1.2.4 Solar Thermal 8
1.3 Solar Thermal Energy 9
1.3.1 Solar Thermal Collector 9
1.3.2 Types of Solar Collectors 9
1.3.2.1 Flat plate collectors 9
1.3.2.2 Evacuated tube collectors 12
1.3.2.3 Parabolic Trough 13
1.3.2.4 Parabolic Dish 14
1.4 Solar water heating 15
1.4.1 Types of solar water heating systems 15
2 Design of parabolic collector assembly 17
2.1 Working principle 18
2.2 Parabola Design 19
2.2.1 Parabola 19
2.2.2 Parabola Design Specifications 20
7. 2.2.2.1 Volume Calculation 21
2.2.3 Verification of Results 21
2.3 Parabolic Collector Design 23
2.3.1 Absorber / Receiver 23
2.3.2 Reflective material 25
2.3.3 Casing 26
2.3.4 Insulation Material 26
2.4 Parabolic Collector Design on Solid works 26
2.4.1 Motor – Gear Assembly 29
2.5 Optical design of parabolic collector 29
2.5.1 Concentration Ratio 30
2.5.2 Declination 30
2.5.3 Solar hour angle and sunset hour angle 31
2.5.4 Extraterrestrial radiation and clearness index 31
2.5.5 Tilted Irradiance 32
2.6 Optical Errors in the Design of Parabolic Trough Collector 33
2.6.1 Description of Optical Errors 34
2.6.2 Summary of Potential Errors 37
2.6.2.1 Potential errors in Materials 37
2.6.2.2 Potential errors in Manufacture and Assembly 37
2.6.2.3 Potential errors in Operation 38
3 Analysis of parabolic collector assembly 39
3.1 Units 40
3.2 Model (A4)/ Geometry 40
3.3 Coordinate Systems 42
3.4 Connections 42
3.5 Mesh 43
3.6 Static Structural (A5): 44
3.7 Solution (A6): 46
3.8 Material Data/ Structural Steel 51
8. 3.9 Units 52
3.10 Steady-State Thermal (A5) 52
3.11 Solution (A6): 56
3.12 CFD analysis of copper pipe on FLUENT 57
4 Fabrication of solar collector assembly 59
4.1 Fabrication of solar collector and assembly 60
4.1.1 Parts and their materials with dimensions 61
4.1.2 Complete steps 62
Making end semicircular plates 62
Supporting back: 62
Combining the end plates and the supporting back 63
Fixing the rubber pads 63
Making the base 64
Attaching the reflective plate 64
Inserting the absorbent pipe 65
Making the bush 65
Fabricating the axles 66
Fabricating the gear 67
The motor frame 67
4.1.3 Complete thermal system assembly 68
Hot Water Container 68
The pump 69
Solar Tracking System 70
12 VDC Motor 70
The Electronic Circuit 71
Light Dependent Resistances 71
IC (LM358P) 71
Resistances / Variable Resistances 72
Relay Switches 73
12VDC battery 73
9. 12VDC charger / power supply 73
The transportation system 74
The ball valve 74
T joint, sockets and nozzles 75
5 Heat transfer analysis of parabolic collector assembly 77
5.1 One-dimensional Energy balance model 78
5.1.1 Convection Heat Transfer between the HTF and the Absorber pipe 79
5.1.1.1 Turbulent Flow Case 80
5.1.2 Conduction heat transfer through the absorber wall 81
5.1.3 Heat transfer from the outer pipe surface to the atmosphere 82
5.1.3.1 Convection heat transfer 82
5.1.3.1.1 No Wind case 82
5.1.3.1.2 Wind case 84
5.1.3.2 Radiation heat transfer 84
10. TABLE OF FIGURES
Fig .
No.
Description Page
1. Introduction To Solar Energy 1
1.1. Direct solar water heating systems 16
2 Design of parabolic collector assembly 17
2.1 Concentrating Collector 18
2.2 Tracking the Sun 19
2.3 Parabola 19
2.9 Support Stand 27
2.10 Parabolic Trough with absorber pipe; Diameter of pipe 27
2.11 Collector with support stand 27
2.12 Gear 28
2.13 Gear Collector assembly 28
2.14 Assembly of Trough, stand and gear 28
2.15 Power window lifter motor 29
2.16 Description of Optical Errors 34
2.17 parabolic mirror surface 35
2.18
Ray traces of reflection from perfect and imperfect (random) mirror
surfaces
36
2.19
Representation of a mirror surface showing the difference between slope
errors and the mirror diffusivity.
37
3 Analysis of parabolic collector assembly 39
3.1 Model (A4) > Geometry > Figure 42
3.2 Model (A4) > Mesh > Figure 44
3.3 Model (A4) > Static Structural (A5) > Fixed Support > Figure 45
3.4 Model (A4) > Static Structural (A5) > Force > Figure 46
3.5
Model (A4) > Static Structural (A5) > Solution (A6) > Equivalent Elastic
Strain > Figure
47
3.6
Model (A4) > Static Structural (A5) > Solution (A6) > Maximum Shear
Elastic Strain > Figure
48
3.7
Model (A4) > Static Structural (A5) > Solution (A6) > Shear Elastic Strain >
Figure
48
3.8 Model (A4) > Static Structural (A5) > Solution (A6) > Equivalent Stress > 49
11. Figure
3.9
Model (A4) > Static Structural (A5) > Solution (A6) > Maximum Shear
Stress > Figure
49
3.10 Model (A4) > Static Structural (A5) > Solution (A6) > Shear Stress > Figure 50
3.11
Model (A4) > Static Structural (A5) > Solution (A6) > Total Deformation >
Figure
50
3.12 Model (A4) > Steady-State Thermal (A5) > Temperature 2 54
3.13 Model (A4) > Steady-State Thermal (A5) > Temperature 2 > Figure 54
3.14 Model (A4) > Steady-State Thermal (A5) > Radiation > Figure 55
3.15 Model (A4) > Steady-State Thermal (A5) > Heat Flow > Figure 55
3.16
Model (A4) > Steady-State Thermal (A5) > Solution (A6) > Temperature >
Figure 2
56
3.17 Contours of Static Temperature (K) 57
3.18 Contours of static pressure (Pascal) 58
4 Fabrication of solar collector assembly 59
4.1 The End Semicircular Plates 62
4.2 The Supporting Back 63
4.3 Combining End Plates and Back 63
4.4 Fixing the rubber pads 64
4.5 Making the base 64
4.6 Inserting the absorbent pipe 65
4.7 Making the bush 66
4.8 Fabricating the axles 66
4.8 Fabricating the gears 67
4.9 The motor frame 67
4.10 Complete Fabricated Solar Collector 68
4.11 Hot Water Container 69
4.12 12 VDC Motor 70
4.13 LDR 71
4.14 IC 72
4.15 Resistances / Variable Resistances 72
4.16 Relay Switches) 73
12. 4.17 12VDC battery 73
4.18 12VDC charger / power supply 74
4.19 Transportation System 74
4.20 The ball valve 75
4.21 T joint, sockets and nozzles 75
5 Heat transfer analysis of parabolic collector assembly 77
5.1
One dimensional study state energy balance for a cross section of Heat
collector element HCE
78
14. SOLAR ENERGY
1.1 Introduction to Renewable Energies
Renewable energy is energy which comes from natural resources such
as sunlight, wind, rain, tides, and geothermal heat, which are renewable(naturally
replenished). About 16% of global final energy consumption comes from renewables,
with 10% coming from traditional biomass, which is mainly used for heating, and
3.4% from hydroelectricity. New renewable (small hydro, modern biomass, wind,
solar, geothermal, and biofuels) accounted for another 3% and are growing very
rapidly. The share of renewables in electricity generation is around 19%, with 16% of
global electricity coming from hydroelectricity and 3% from new renewables.
Renewable energy flows involve natural phenomena such
as sunlight, wind, tides, plant growth, and geothermal heat, as the International
Energy Agency explains:
Renewable energy is derived from natural processes that are replenished
constantly. In its various forms, it derives directly from the sun, or from heat
generated deep within the earth. Included in the definition is electricity and heat
generated from solar, wind, ocean, hydropower, biomass, geothermal resources,
and biofuels and hydrogen derived from renewable resources.
Renewable energy replaces conventional fuels in four distinct areas:
1. Electricity generation
2. Hot water/space heating
3. Motor fuels
4. Rural (off-grid) energy services
1.1.1 Types of Renewable Energies
Renewable energy is becoming more and more prevalent around the
world, but it is still not the dominant energy resource.
With so much dependency placed upon our natural resources to produce our
much needed energy, scientists have been evaluating and producing renewable
energy as an alternative to traditional energy sources. Renewable energy is energy
that can be reproduced in a short period of time. The most prevalent forms of
renewable energy are solar, wind, biomass, hydro power, geothermal and biofuels.
o Wind power
o Biomass
o Geothermal
o Wave
o Tidal power
o Hydro power
15. o Solar power
1.1.1.1 Wind Power
Wind power is the conversion of wind
energy into a useful form of energy, such as
using: wind turbines to make electricity, windmills for
mechanical power, wind pumps for water
pumping or drainage, or sails to propel ships.
Wind power, as an alternative to fossil fuels, is
plentiful, renewable, widely distributed, clean,
produces no greenhouse gas emissions during
operation and uses little land. Any effects on the environment are generally less
problematic than those from other power sources. As of 2010 wind energy
production was over 2.5% of worldwide power, growing at more than 25% per
annum. The overall cost per unit of energy produced is similar to the cost for new
coal and natural gas installations. Although wind power is a popular form of energy
generation, the construction of wind farms is not universally welcomed.
1.1.1.2 Biomass
Biomass, as a renewable energy source, is biological material from living, or
recently living organisms. As an energy source, biomass can either be used directly,
or converted into other energy products such as biofuel.
In the first sense, biomass is plant matter used to generate electricity with
steam turbines & gasifiers or produce heat, usually by direct combustion. Examples
include forest residues (such as dead trees, branches and tree stumps), yard
clippings, wood chips and even municipal solid waste. In the second sense, biomass
includes plant or animal matter that can be converted into fibers or other
industrial chemicals, including biofuels. Industrial biomass can be grown from
numerous types of plants,
includingmiscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane,
and a variety of tree species, ranging
from eucalyptus to oil palm (palm oil).
1.1.1.3 Hydro Power
Hydro energy is derived from the movement
of water. One form of hydro power is generated
through the movement of water through turbines,
such as water running through turbines in a Dam.
Hydro power is considered a renewable energy
source as the water is continuously cycled back
through the plant or into nature.
The cost of hydroelectricity is relatively low, making it a competitive source of
renewable electricity. The average cost of electricity from a hydro plant larger than
16. 10 megawatts is 3 to 5 U.S. cents per kilowatt-hour. Hydro is also a flexible source of
electricity since plants can be ramped up and down very quickly to adapt to changing
energy demands. However, damming interrupts the flow of rivers and can harm local
ecosystems, and building large dams and reservoirs often involves displacing people
and wildlife. Once a hydroelectric complex is constructed, the project produces no
direct waste, and has a considerably lower output level of the greenhouse
gas carbon dioxide (CO2) than fossil fuel powered energy plants.
1.1.1.4 Geothermal Energy
Geothermal energy is thermal
energy generated and stored in the Earth.
Thermal energy is the energy that
determines the temperature of matter.
Earth's geothermal energy originates from
the original formation of the planet (20%)
and from radioactive decay of minerals
(80%).The geothermal gradient, which is
the difference in temperature between the
core of the planet and its surface, drives a
continuous conduction of thermal energy in the form of heat from the core to the
surface. The adjective geothermal originates from the Greek roots γη (ge), meaning
earth, and θερμος (thermos), meaning hot.
Geothermal power is cost effective, reliable, sustainable, and environmentally
friendly, but has historically been limited to areas near tectonic plate boundaries.
Recent technological advances have dramatically expanded the range and size of
viable resources, especially for applications such as home heating, opening a
potential for widespread exploitation. Geothermal wells release greenhouse gases
trapped deep within the earth, but these emissions are much lower per energy unit
than those of fossil fuels. As a result, geothermal power has the potential to help
mitigate global warming if widely deployed in place of fossil fuels.
1.1.1.4 Tidal Power
Tidal power, also called tidal energy, is a
form of hydropower that converts the energy
of tides into useful forms of power - mainly
electricity.Although not yet widely used; tidal power
has potential for future electricity generation. Tides
are more predictable than wind energy and solar
power. Among sources of renewable energy, tidal
power has traditionally suffered from relatively high
cost and limited availability of sites with sufficiently
high tidal ranges or flow velocities, thus constricting its total availability. However,
17. many recent technological developments and improvements, both in design
(e.g. dynamic tidal power, tidal lagoons) and turbine technology (e.g. new axial
turbines, cross flow turbines), indicate that the total availability of tidal power may be
much higher than previously assumed, and that economic and environmental costs
may be brought down to competitive levels.
1.1.1.5 Solar Energy
Solar energy, radiant light and heat from
the sun, has been harnessed by humans
since ancient times using a range of ever-
evolving technologies. Solar energy technologies
include solar heating, solar photovoltaics, solar
thermal electricity and solar architecture, which
can make considerable contributions to solving
some of the most urgent problems the world now
faces.
Solar technologies are broadly
characterized as either passive solar or active solar depending on the way they
capture, convert and distribute solar energy. Active solar techniques include the use
of photovoltaic panels and solar thermal collectors to harness the energy. Passive
solar techniques include orienting a building to the Sun, selecting materials with
favorable thermal mass or light dispersing properties, and designing spaces
that naturally circulate air.
In 2011, the International Energy Agency said that "the development of
affordable, inexhaustible and clean solar energy technologies will have huge longer-
term benefits. It will increase countries’ energy security through reliance on an
indigenous, inexhaustible and mostly import-independent resource,
enhance sustainability, reduce pollution, lower the costs of mitigating climate
change, and keep fossil fuel prices lower than otherwise. These advantages are
global. Hence the additional costs of the incentives for early deployment should be
considered learning investments; they must be wisely spent and need to be widely
shared".
The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation)
at the upper atmosphere. Approximately 30% is reflected back to space while the
rest is absorbed by clouds, oceans and
land masses. The spectrum of solar light
at the Earth's surface is mostly spread
across thevisible and near-
infrared ranges with a small part in
the near-ultraviolet.
Earth's land surface, oceans and
atmosphere absorb solar radiation, and this
18. raises their temperature. Warm air containing evaporated water from the oceans
rises, causing atmospheric circulation or convection. When the air reaches a high
altitude, where the temperature is low, water vapor condenses into clouds, which
rain onto the Earth's surface, completing the water cycle. The latent heat of water
condensation amplifies convection, producing atmospheric phenomena such
as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land
masses keeps the surface at an average temperature of
14 °C. By photosynthesis green plants convert solar energy into chemical energy,
which produces food, wood and the biomass from which fossil fuels are derived.
The total solar energy absorbed by Earth's atmosphere, oceans and land
masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more
energy in one hour than the world used in one year. Photosynthesis captures
approximately 3,000 EJ per year in biomass. The amount of solar energy reaching
the surface of the planet is so vast that in one year it is about twice as much as will
ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural
gas, and mined uranium combined.
Solar energy can be harnessed in different levels around the world.
Depending on a geographical location the closer to the equator the more "potential"
solar energy is available.
1.2 Applications of Solar Technology
Solar energy refers primarily to the use of solar radiation for practical ends.
However, all renewable energies, other than geothermal and tidal, derive their
energy from the sun.
Solar technologies are broadly characterized as either passive or active
depending on the way they capture, convert and distribute sunlight. Active solar
techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful
outputs. Passive solar techniques include selecting materials with favorable thermal
properties, designing spaces that naturally circulate air, and referencing the position
of a building to the Sun. Active solar technologies increase the supply of energy and
are considered supply side technologies, while passive solar technologies reduce
the need for alternate resources and are generally considered demand side
technologies.
1.2.1 Architecture and Urban Planning
Sunlight has influenced building design since the beginning of architectural
history. Advanced solar architecture and urban planning methods were first
employed by the Greeks and Chinese, who oriented their buildings toward the south
to provide light and warmth.
The common features of passive solar architecture are orientation relative to
the Sun, compact proportion (a low surface area to volume ratio), selective shading
(overhangs) and thermal mass. When these features are tailored to the local climate
19. and environment they can produce well-lit spaces that stay in a comfortable
temperature range. Socrates' Megaron House is a classic example of passive solar
design. The most recent approaches to solar design use computer modeling tying
together solar lighting, heating and ventilation systems in an integrated solar
design package. Active solar equipment such as pumps, fans and switchable
windows can complement passive design and improve system performance.
Urban heat islands (UHI) are metropolitan areas with higher temperatures
than that of the surrounding environment. The higher temperatures are a result of
increased absorption of the Solar light by urban materials such as asphalt and
concrete, which have lower albedos and higher heat capacities than those in the
natural environment. A straightforward method of counteracting the UHI effect is to
paint buildings and roads white and plant trees. Using these methods, a hypothetical
"cool communities" program in Los Angeles has projected that urban temperatures
could be reduced by approximately 3 °C at an estimated cost of US$1 billion, giving
estimated total annual benefits of US$530 million from reduced air-conditioning costs
and healthcare savings.
1.2.2 Agriculture and Horticulture
Agriculture and horticulture seek to optimize the capture of solar energy in
order to optimize the productivity of plants. Techniques such as timed planting
cycles, tailored row orientation, staggered heights between rows and the mixing of
plant varieties can improve crop yields. While sunlight is generally considered a
plentiful resource, the exceptions highlight the importance of solar energy to
agriculture. During the short growing seasons of the Little Ice Age, French
and English farmers employed fruit walls to maximize the collection of solar energy.
These walls acted as thermal masses and accelerated ripening by keeping plants
warm. Early fruit walls were built perpendicular to the ground and facing south, but
over time, sloping walls were developed to make better use of sunlight. In
1699, Nicolas Fatio de Duillier even suggested using a tracking mechanism which
could pivot to follow the Sun. Applications of solar energy in agriculture aside from
growing crops include pumping water, drying crops, brooding chicks and drying
chicken manure. More recently the technology has been embraced by vinters, who
use the energy generated by solar panels to power grape presses.
Greenhouses convert solar light to heat, enabling year-round production and
the growth (in enclosed environments) of specialty crops and other plants not
naturally suited to the local climate. Primitive greenhouses were first used during
Roman times to produce cucumbers year-round for the Roman emperor Tiberius.
The first modern greenhouses were built in Europe in the 16th century to keep exotic
plants brought back from explorations abroad. Greenhouses remain an important
part of horticulture today, and plastic transparent materials have also been used to
similar effect in polytonal and row covers.
20. 1.2.3 Solar Lighting
The history of lighting is dominated by the use of natural light. The Romans
recognized a right to light as early as the 6th century and English law echoed these
judgments with the Prescription Act of 1832. In the 20th century
artificial lighting became the main source of interior illumination but day lighting
techniques and hybrid solar lighting solutions are ways to reduce energy
consumption.
Day lighting systems collect and distribute sunlight to provide interior
illumination. This passive technology directly offsets energy use by replacing artificial
lighting, and indirectly offsets non-solar energy use by reducing the need for air-
conditioning. Although difficult to quantify, the use of natural lighting also offers
physiological and psychological benefits compared to artificial lighting. Day lighting
design implies careful selection of window types, sizes and orientation; exterior
shading devices may be considered as well. Individual features include saw tooth
roofs, clerestory windows, light shelves, skylights and light tubes. They may be
incorporated into existing structures, but are most effective when integrated into
a solar design package that accounts for factors such as glare, heat flux and time-of-
use. When day lighting features are properly implemented they can reduce lighting-
related energy requirements by 25%.
Hybrid solar lighting is an active solar method of providing interior illumination.
HSL systems collect sunlight using focusing mirrors that track the Sun and
use optical fibers to transmit it inside the building to supplement conventional
lighting. In single-story applications these systems are able to transmit 50% of the
direct sunlight received.
Solar lights that charge during the day and light up at dusk are a common
sight along walkways. Solar-charged lanterns have become popular in developing
countries where they provide a safer and cheaper alternative to kerosene lamps.
Although daylight saving time is promoted as a way to use sunlight to save
energy, recent research has been limited and reports contradictory results: several
studies report savings, but just as many suggest no effect or even a net loss,
particularly when gasoline consumption is taken into account. Electricity use is
greatly affected by geography, climate and economics, making it hard to generalize
from single studies.
1.2.4 Solar Thermal
Solar thermal technologies can be used for
water heating
space heating
space cooling
Process heat generation
21. 1.3 Solar Thermal Energy
Solar thermal energy (STE) is an innovative technology for harnessing solar
energy for thermal energy (heat). Solar thermal collectors are classified by the
United States Energy Information Administration as low-, medium-, or high-
temperature collectors. Low-temperature collectors are flat plates generally used to
heat swimming pools. Medium-temperature collectors are also usually flat plates but
are used for heating water or air for residential and commercial use. High-
temperature collectors concentrate sunlight using mirrors or lenses and are generally
used for electric power production. STE is different from and much more efficient
than photovoltaics, which converts solar energy directly into electricity. While existing
generation facilities provide only 600 megawatts of solar thermal power worldwide in
October 2009, plants for an additional 400 megawatts are under construction and
development is underway for concentrated solar power projects totalling 14,000
megawatts.
1.3.1 Solar Thermal Collector
A solar thermal collector is a solar collector designed to
collect heat by absorbing sunlight. The term is applied to solar hot water panels, but
may also be used to denote more complex installations such as solar parabolic, solar
trough and solar towers or simpler installations such as solar air heat. The more
complex collectors are generally used in solar power plants where solar heat is used
to generate electricity by heating water to produce steam which drives
a turbine connected to an electrical generator. The simpler collectors are typically
used for supplemental space heating in residential and commercial buildings. A
collector is a device for converting the energy in solar radiation into a more usable or
storable form. The energy in sunlight is in the form of electromagnetic radiation from
the infrared (long) to the ultraviolet (short) wavelengths. The solar energy striking the
Earth's surface depends on weather conditions, as well as location and orientation of
the surface, but overall, it averages about 1,000 watts per square meter under clear
skies with the surface directly perpendicular to the sun's rays.
1.3.2 Types of Solar Collectors
Solar collectors fall into two general categories: non-concentrating and
concentrating. In the non-concentrating type, the collector area (i.e., the area that
intercepts the solar radiation) is the same as the absorber area (i.e., the area
absorbing the radiation). In these types the whole solar panel absorbs the light.
Flat-plate and evacuated-tube solar collectors are used to collect heat for space
heating, domestic hot water or cooling with an
absorption chiller.
1.3.2.1 Flat plate collectors
Flat-plate collectors, developed by Hottel and
Whillier in the 1950s, are the most common type. They
22. consist of (1) a dark flat-plate absorber of solar energy, (2) a transparent cover that
allows solar energy to pass through but reduces heat losses, (3) a heat-transport
fluid (air, antifreeze or water) to remove heat from the absorber, and (4) a heat
insulating backing. The absorber consists of a thin absorber sheet (of thermally
stable polymers, aluminum, steel or copper, to which a matte black or selective
coating is applied) often backed by a grid or coil of fluid tubing placed in an insulated
casing with a glass or polycarbonate cover. In water heat panels, fluid is usually
circulated through tubing to transfer heat from the absorber to an insulated water
tank. This may be achieved directly or through a heat exchanger. Most air heat
fabricators and some water heat manufacturers have a completely flooded absorber
consisting of two sheets of metal which the fluid passes between. Because the heat
exchange area is greater they may be marginally more efficient than traditional
absorbers.
Sunlight passes through the glazing and strikes the absorber plate, which
heats up, changing solar energy into heat energy. The heat is transferred to liquid
passing through pipes attached to the absorber plate. Absorber plates are commonly
painted with "selective coatings," which absorb and retain heat better than ordinary
black paint. Absorber plates are usually made of metal—typically copper or
aluminum—because the metal is a good heat conductor. Copper is more expensive,
but is a better conductor and less prone to corrosion than aluminum. In locations with
average available solar energy, flat plate collectors are sized approximately one-half-
to one-square foot per gallon of one-day's hot water use.
There is a number of absorber piping configurations:
harp — traditional design with bottom pipe risers and top collection pipe, used in
low pressure thermosyphon and pumped systems
serpentine — one continuous S that maximizes temperature but not total energy
yield in variable flow systems, used in compact solar domestic hot water only
systems (no space heating role)
Completely flooded absorber consisting of two sheets of metal stamped to
produce a circulation zone.
Boundary layer absorber collectors consisting of several layers of transparent
and opaque sheets that enable absorption in a boundary layer. Because the
solar energy is absorbed in the boundary layer, the heat conversion may be more
efficient than for collectors where absorbed heat is conducted through a material
before the heat is accumulated in a circulating liquid.
As an alternative to metal collectors, new polymer flat plate collectors are now
being produced in Europe. These may be wholly polymer, or they may include metal
plates in front of freeze-tolerant water channels made of silicone rubber. Polymers,
being flexible and therefore freeze-tolerant, are able to contain plain water instead of
antifreeze, so that they may be plumbed directly into existing water tanks instead of
needing to use heat exchangers which lower efficiency. By dispensing with a heat
23. exchanger in these flat plate panels, temperatures need not be quite so high for the
circulation system to be switched on, so such direct circulation panels, whether
polymer or otherwise, can be more efficient, particularly at low light levels.
Some early selectively coated polymer collectors suffered from overheating
when insulated, as stagnation temperatures can exceed the melting point of the
polymer. For example, the melting point of polypropylene is 160 °C (320 °F), while
the stagnation temperature of insulated thermal collectors can exceed 180
°C (356 °F) if control strategies are not used. For this reason polypropylene is not
often used in glazed selectively coated solar collectors. Increasingly polymers such
as high temperate silicones (which melt at over 250 °C (482 °F)) are being used.
Some non polypropylene polymer based glazed solar collectors are matte black
coated rather than selectively coated to reduce the stagnation temperature to 150
°C (302 °F) or less.
In areas where freezing is a possibility, freeze-tolerance (the capability to
freeze repeatedly without cracking) can be achieved by the use of flexible polymers.
Silicone rubber pipes have been used for this purpose in UK since 1999.
Conventional metal collectors are vulnerable to damage from freezing, so if they are
water filled they must be carefully plumbed so they completely drain down using
gravity before freezing is expected, so that they do not crack. Many metal collectors
are installed as part of a sealed heat exchanger system. Rather than having the
potable water flow directly through the collectors, a mixture of water and antifreeze
such as propylene glycol (which is used in the food industry) is used as a heat
exchange fluid to protect against freeze damage down to a locally determined risk
temperature that depends on the proportion of propylene glycol in the mixture. The
use of glycol lowers the water's heat carrying capacity marginally, while the addition
of an extra heat exchanger may lower system performance at low light levels.
A pool or unglazed collector is a simple form of flat-plate collector without a
transparent cover. Typically polypropylene or EPDM rubber or silicone rubber is
used as an absorber. Used for pool heating it can work quite well when the desired
output temperature is near the ambient temperature (that is, when it is warm
outside). As the ambient temperature gets cooler, these collectors become less
effective.
Most flat plate collectors have a life expectancy of over 25 years.
Applications: The main use of this technology is in residential buildings where the
demand for hot water has a large impact on energy bills. This generally means a
situation with a large family, or a situation in which the hot water demand is
excessive due to frequent laundry washing. Commercial applications include
Laundromats, car washes, military laundry facilities and eating establishments. The
technology can also be used for space heating if the building is located off-grid or if
utility power is subject to frequent outages. Solar water heating systems are most
likely to be cost effective for facilities with water heating systems that are expensive
24. to operate, or with operations such as laundries or kitchens that require large
quantities of hot water.
Unglazed liquid collectors are commonly used to heat water for swimming
pools. Because these collectors need not withstand high temperatures, they can use
less expensive materials such as plastic or rubber. They also do not require freeze-
proofing because swimming pools are generally used only in warm weather or can
be drained easily during cold weather.
While solar collectors are most cost-effective in sunny, temperate areas, they can
be cost effective virtually anywhere in the country so should be considered.
1.3.2.2 Evacuated tube collectors
Most (if not all) vacuum tube collectors use heat pipes for their core instead of
passing liquid directly through them. Evacuated heat pipe tubes (EHPTs) are
composed of multiple evacuated glass tubes each containing an absorber plate
fused to a heat pipe. The heat from the hot end of the heat pipes is transferred to the
transfer fluid (water or an antifreeze mix—typically propylene glycol) of a domestic
hot water or hydronic space heating system in a heat exchanger called a "manifold".
The manifold is wrapped in insulation and covered by a sheet metal or plastic case
to protect it from the elements.
The vacuum that surrounds the outside of the tube greatly reduces convection
and conduction heat loss to the outside, therefore achieving greater efficiency than
flat-plate collectors, especially in colder conditions. This advantage is largely lost in
warmer climates, except in those cases where very hot water is desirable, for
example commercial process water. The high temperatures that can occur may
require special system design to avoid or mitigate overheating conditions. Some
evacuated tubes (glass-metal) are made with one layer of glass that fuses to the
heat pipe at the upper end and encloses the heat pipe and absorber in the vacuum.
Others (glass-glass) are made with a double layer of glass fused together at one or
both ends with a vacuum between the layers (like a vacuum bottle or flask) with the
absorber and heat pipe contained at normal atmospheric pressure. Glass-glass
tubes have a highly reliable vacuum seal but the two layers of glass reduce the light
that reaches the absorber and there is some possibility that moisture will enter the
non-evacuated area of the tube and cause absorber corrosion. Glass-metal tubes
allow more light to reach the absorber and protect the absorber and heat pipe
(contained in the vacuum) from corrosion even if they are made from dissimilar
materials (see galvanic corrosion).
The gaps between the tubes may allow for snow to fall through the collector,
minimizing the loss of production in some snowy conditions, though the lack of
radiated heat from the tubes can also prevent effective shedding of accumulated
snow.
25. 1.3.2.3 Parabolic Trough
This type of collector is generally used in solar power plants. A trough-
shaped parabolic reflector is used to concentrate sunlight on an insulated tube
(Dewar tube) or heat pipe, placed at the focal point, containing coolant which
transfers heat from the collectors to the boilers in the power station.
Parabolic-trough collectors use curved mirrors to focus sunlight on a dark-
surfaced tube running the length of the trough. A mixture of water and fluids that
transfer heat is pumped through the tube. The fluids absorb solar heat and reach
temperatures up to 299C (570oF). The hot water is sent to a thermal storage tank,
or the steam is directed through a turbine to generate electricity. Parabolic-trough
collectors provide hot water and/or electricity for industrial and commercial buildings.
Parabolic-trough collectors use only direct radiation, and even though they use
tracking systems to keep them facing the sun, they are most effective where there
are good solar resources. Parabolic-trough collectors are more efficient for large
facilities that require hot water around the clock. They also require large areas for
installation, yet they offset the need for conventional energy and provide energy
savings and environmental benefits.
Parabolic-trough solar water heating is a well-
proven technology that directly substitutes renewable
energy for conventional energy in water heating.
Parabolic-trough Collectors can also drive absorption
cooling systems or other equipment that runs off a
Thermal load. There is considerable potential for
using these technologies at federal facilities in the
southwestern United States or other areas with high
direct-beam solar radiation. Facilities such as jails,
hospitals, and barracks that consistently use large
volumes of hot water are particularly good
candidates. Use of parabolic-trough systems help
federal facilities comply with executive order 12902's
directive to reduce energy use by 30% by 2005 and
advance other efforts to get the federal government
to set a good example in energy use reduction, such
as the 1997 million solar roofs initiative. This Federal
Technology Alert (FTA) from the Federal Energy
Management Program (FEMP) is one of a series on
new energy-efficiency and renewable energy
technologies. It describes the technology of
parabolic-trough solar water-heating and absorption-
cooling systems, the situations in which parabolic-
trough systems are likely to be cost effective, and
considerations in selecting and designing a system. This FTA also explains Energy
26. Savings Performance Contracting (ESPC), a method for financing Federal facility
energy conservation and renewable energy projects. ESPC is available for parabolic-
trough systems and offers many important advantages. Parabolic-trough collectors
use mirrored surfaces curved in a linearly extended parabolic shape to focus sunlight
on a dark-surfaced absorber tube running the length of the trough. A mixture of water
and antifreeze or other heat transfer fluid is pumped through the absorber tube to
pick up the solar heat, and then through heat exchangers to heat potable water or a
thermal storage tank. Because the trough mirrors will reflect only direct-beam
sunlight, parabolic-trough systems use single-axis tracking systems to keep them
facing the sun.
Application: Use of parabolic-trough systems is more limited by geography and
system size than are other types of solar water heating, but where parabolic troughs
are usable they often have very attractive economics. As concentrating systems,
parabolic troughs use only direct radiation, so are less effective where skies are
cloudy and much more likely to be effective in areas such as the Southwestern
United States that have good solar resources dominated by direct-beam sunlight. It
is also more cost effective to build large systems that will be used on a continuous
basis. Parabolic-trough solar water heating (and air-conditioning) is therefore most
effective for large, 7-days-a- week, domestic hot-water users, such as Federal
hospitals, prisons, or barracks. (For most situations, about 500 gallons per day of hot
water use is a minimum for a viable parabolic-trough system.) Troughs also work
well for district space or water heating systems serving multiple buildings from a
central steam or hot-water plant. The cost of the collector system is a main economic
factor, but as with any capital-intensive energy conservation or renewable energy
installation, the critical factor is likely to be current cost of energy. Facilities that pay
high utility rates for conventional water heating will always be the best prospects for
cost-effective parabolic-trough solar water heating or air-conditioning.
1.3.2.4 Parabolic Dish
It is the most powerful type of collector. One or
more parabolic dishes concentrate solar energy at a
single focal point, similar to a reflecting
telescope which focuses starlight, or to a dish
antenna used to focus radio waves. This geometry
may be used in solar furnaces and solar power plants.
There are two key phenomena to understand in
order to comprehend the design of a parabolic dish. One is that the shape of a
parabola is defined such that incoming rays which are parallel to the dish's axis will
be reflected toward the focus, no matter where on the dish they arrive. The second
key is that the light rays from the sun arriving at the Earth's surface are almost
27. completely parallel. So if the dish can be aligned with its axis pointing at the sun,
almost all of the incoming radiation will be reflected towards the focal point of the
dish—most losses are due to imperfections in the parabolic shape and imperfect
reflection.
Losses due to atmosphere between the dish and its focal point are minimal,
as the dish is generally designed specifically to be small enough that this factor is
insignificant on a clear, sunny day. Compare this though with some other designs,
and you will see that this could be an important factor, and if the local weather is
hazy, or foggy, it may reduce the efficiency of a parabolic dish significantly.
In dish Stirling power plant designs, a Stirling engine coupled to a dynamo, is
placed at the focus of the dish, which absorbs the heat of the incident solar radiation,
and converts it into electricity.
1.4 Solar water heating
Solar water heating (SWH) or solar hot water (SHW) systems comprise
several innovations and many mature renewable energy technologies that have
been well established for many years. SWH has been widely used in Greece,
Cyprus, Turkey, Israel, Australia, Japan, Austria and China.
In a "close-coupled" SWH system the storage tank is horizontally mounted
immediately above the solar collectors on the roof. No pumping is required as the hot
water naturally rises into the tank through thermosiphon flow. In a "pump-circulated"
system the storage tank is ground- or floor-mounted and is below the level of the
collectors; a circulating pump moves water or heat transfer fluid between the tank
and the collectors.
SWH systems are designed to deliver hot water for most of the year.
However, in winter there sometimes may not be sufficient solar heat gain to deliver
sufficient hot water. In this case a gas or electric booster is normally used to heat the
water.
1.4.1 Types of solar water heating systems
Solar water heaters can be either
Active
Passive.
An active system uses an electric pump to circulate the heat-transfer fluid; a passive
system has no pump. The amount of hot water a solar water heater produces
depends on the type and size of the system, the amount of sun available at the site,
proper installation, and the tilt angle and orientation of the collectors.
28. Fig 1.1 (Direct solar water heating systems. (A) Passive; (B) active)
Solar water heaters are also characterized as
Open Loop (also called "direct")
Closed Loop (also called "indirect").
An open-loop system circulates household (potable) water through the collector.
A closed-loop system uses a heat-transfer fluid (water or diluted antifreeze, for
example) to collect heat and a heat exchanger to transfer the heat to household
water.
30. There are two key phenomena to understand in order to comprehend the
design of a parabolic trough collector. One is that the shape of a parabola is defined
such that incoming rays which are parallel to the collector's axis will be reflected
toward the focus, no matter where on the collector they arrive. The second key is
that the light rays from the sun arriving at the Earth's surface are almost completely
parallel. So if the collector can be aligned with its axis pointing at the sun, almost all
of the incoming radiation will be reflected towards the focal point of the collector—
most losses are due to imperfections in the parabolic shape and imperfect reflection.
2.1 Working principle
The reflecting surface of parabolic trough collectors, also called linear imaging
concentrators, has a parabolic cross section. The curve of a parabola is such that
light travelling parallel to the axis of a parabolic mirror will be reflected to a single
focal point from any place along the curve. Because the sun is so far away, all direct
solar beams (i.e., excluding diffuse) are essentially parallel so if the parabola is
facing the sun, the sunlight is concentrated at the focal point. A parabolic trough
extends the parabolic shape to three dimensions along a single direction, creating a
focal line along which the absorber tube is run.
Fig 2.1 Concentrating Collector
Parabolic trough collectors—like other solar concentrating systems—have to track the sun.
The troughs are normally designed to track the sun along one axis oriented in the north-south
or east-west direction. As parabolic troughs use only direct radiation, cloudy skies become a
more critical factor than when using flat-plate collectors, which can also use diffuse sunlight.
Periodic cleaning of mirrors also is essential to assure an adequate parabolic trough field
performance.
31. Fig 2.2 Tracking the Sun
2.2 Parabola Design
2.2.1 Parabola
A parabola is basically a
conic section, created from the
intersection of a right circular
conical surface and a plane
parallel to a generating straight line
of that surface. Another way to
generate a parabola is to examine
a point (the focus) and a line (the
directrix) on a plane. The locus of
points in that plane that are
equidistant from both the line and
point is a parabola.
The line perpendicular to the directrix and passing through the focus (that is,
the line that splits the parabola through the middle) is called the "axis of symmetry".
The point on the axis of symmetry that intersects the parabola is called the "vertex",
and it is the point where the curvature is greatest. Parabolas can open up, down, left,
right, or in some other arbitrary direction. Any parabola can be repositioned and
rescaled to fit exactly on any other parabola — that is, all parabolas are similar.
The parabola has many important applications, from automobile headlight
reflectors to the design of ballistic missiles. They are frequently used in physics,
engineering, and many other areas.
Fig 2.3 Parabola
32. 2.2.2 Parabola Design Specifications
The parabola designed for the collector has the following specifications:
Diameter (d) 2 ft
Depth (a) 0.54 ft
Linear Diameter 2.34 ft
The focus can be determined as:
F = 1/4a
F = 1/4 * 0.54 = 0.46 ft
Focal / Diameter 0.23
Area 3.14 sq ft.
The equation for the parabola is:
y = a x2 + b x + c
The coefficients describing this parabola are:
a = 0.5434
b = 0
c = 0
The equation of this parabola is:
y = 0.5434 x2
Since the vertex of the parabola is at origin, the standard equation of parabola
is:
(X +0)^2 = 1.84(Y +0)
33. The graph of the parabola is shown:
2.2.2.1 Volume Calculation
The volume of the parabola is one-half the area of the circular opening times
the depth, written mathematically as:
Volume = ( π * (d/2)2 * a ) / 2
The volume for this parabola is:
Volume = ( π * (2/2)2 * 0.54 ) / 2
Volume = 0.85 cubic ft
2.2.3 Verification of Results
The results obtained above are verified by using the software Parabolic
Collector 2.0 which is a very helpful tool in determining the focal length and other
0
0.1
0.2
0.3
0.4
0.5
0.6
-1.5 -1 -0.5 0 0.5 1 1.5
Yaxis
X axis
34. important parameters of the parabola. This Freeware program is written to help
students design solar collector or wifi projects using parabolic reflectors. Whether it
is required for improving the signal strength of wifi antenna, or designing a satellite
antenna or solar trough, this program calculates the focal length and (x, y)
coordinates for a parabola of any diameter and depth. It can help us determine what
size and shape to make the parabola very quickly.
Once the diameter and depth of the parabola is known, the program
automatically calculates the focal length, focal to diameter ratio, the area of the
parabola and also the volume of the parabolic curve. It also plots the approximate
graph of the parabolic equation and by navigating through the menu command list
the equations of the parabola and volume of the parabolic curve.
35. 2.3 Parabolic Collector Design
Once the parabola of the collector has been designed, the collector assembly
can now be designed. The main components of the collector assembly are:
1. Absorber / Receiver
2. Reflective material
3. Casing
4. Insulation material
5. Collector frame support
2.3.1. Absorber / Receiver
The parabolic trough linear receiver, also called a heat collection element
(HCE), is one of the primary reasons for the high efficiency of parabolic trough
collector design. The receiver is provided with a special solar-selective absorber
surface. Located at the mirror focal line of the parabola, the receiver heats a special
heat transfer fluid as it circulates through the receiver tube.
The selective coating on the steel tube has good solar absorptance and a low
thermal emittance for reducing thermal radiation losses. The main design
parameters for the parabolic receivers are:
Receiver reliability
Optical and thermal performance
The lifetime of receivers.
The materials suitable for parabolic trough collectors are:
i. Steel
ii. Aluminium
iii. Copper
Design Property
Thermal Conductivity
Thermal conductivity, k is the property of a material's ability to conduct heat. It
appears primarily in Fourier's Law for heat conduction.
Q = - kA ΔT / Δx
36. Heat transfer across materials of high thermal conductivity occurs at a higher
rate than across materials of low thermal conductivity. Correspondingly materials of
high thermal conductivity are widely used in heat sink applications and materials of
low thermal conductivity are used as thermal insulation. Thermal conductivity of
materials is temperature dependent. The reciprocal of thermal conductivity is thermal
resistivity.
Absorber Material Thermal Conductivity
Steel 50
Aluminium 210
Copper 380
Material Selected: Copper
Absorber coating
The absorber coating has the task of absorbing as much of the incident
sunlight as possible and converting it to heat. This applies regardless of the collector
application! In the "thermal" range of the spectrum, i.e. in the infrared, it is important
that as little energy be emitted as possible.
Absorptance
Solar Absorptance is the measure of proportion of solar radiation a body
absorbs. The higher the SA, the more energy will be absorbed. Energy that is
reflected returns through the atmosphere to space. Energy that is absorbed is
emitted by radiation and convection from all surfaces.
Absorbance is a quantitative measure expressed as a logarithmic ratio
between the radiation falling upon a material and the radiation transmitted through a
material.
α = ln (I0 / I1)
where I1 is the intensity of the radiation (light) that has passed through the
material (transmitted radiation),
and I0 is the intensity of the radiation before it passes through the material
(incident radiation).
Absorber coatings with high absorptance α in the solar spectral range (0.3 -
2.5 µm) and simultaneously a low emittance ε in the wavelength range 2.5 - 50µm
are termed "selective coatings". Absorber coatings are divided into the following
classes:
Selective coating: 0 ≤ ε < 0.2, α > 0.9
Partially selective coating: 0.2 ≤ ε < 0.5, α >0.9
Non selective coating: 0.5 ≤ ε < 1.0, α >0.9
37. For regions with high solar radiation like Pakistan, non-selective coatings
might be adequate.
Coating Selected: Partially selective coating with black paint.
2.3.2 Reflective material
The most obvious features of the parabolic trough solar collector are its
parabolic-shaped mirrors or reflectors. The mirrors are curved in the shape of a
parabola, which allows them to concentrate the sun's direct beam radiation on the
linear receiver. The reflective material should possess high reflectivity and low
emissivity.
Emissivity
The emissivity of a material (usually written ε or e) is the relative ability of its
surface to emit energy by radiation. It is the ratio of energy radiated by a particular
material to energy radiated by a black body at the same temperature. A true black
body would have an ε = 1 while any real object would have ε < 1. Emissivity is a
dimensionless quantity.
Material Emissivity Coefficient
Aluminium Commercial sheet 0.09
Aluminium Rough 0.07
Stainless steel, polished 0.075
Reflectivity
Reflectivity is the fraction of incident radiation reflected by a surface. It is
given as percentage.
Material Reflectivity
Aluminium Commercial sheet 91 %
Aluminium Rough 93 %
Stainless steel, polished 92.5 %
Reflective Material Selected: Stainless steel, polished.
38. 2.3.3 Casing
To support the main parabolic trough surface consisting of receiver and the
reflective sheet, steel sheets are used as casing. The casing is then supported by
the steel stand.
2.3.4 Insulation Material
Mineral wool and glass wool are often used as insulating material. Before a
mineral wool product is incorporated, its outgassing must be investigated.
Condensed outgassing products from the binder material of mineral wool can lead to
precipitates on the transparent cover, if it is not counteracted. If polyurethane or
polystyrol foam is used, it must always be protected against high temperatures by a
covering layer. It has to be taken into consideration, that the stagnation temperatures
of good selective coated collectors can reach temperatures as high as 200°C. Even
simple collectors with black painted absorbers reach stagnation temperatures of
about 140°C. The backside insulation of the collector has to resist these
temperatures.
Insulating
Material
Maximum
allowable
temperature
( 0C )
Density
Kg/m3
Conductivity
( W/mK at 200C)
Mineral wool >200 60 – 200 0.040
Glass wool > 200 30 – 100 0.040
Polyurethane foam <130 30 – 80 0.030
Polystyrol foam <80 30 - 50 0.034
Insulation Material Selected: Glass wool
2.4 Parabolic Collector Design on Solidworks
After selecting the appropriate materials and determining the exact
dimensions of all the components of the collector assembly, it is then modeled on the
3D solid modeling software Solidworks 2011. Following are the images of different
components of the assembly modeled on Solidworks 2011.
39. Fig 2.9 Support Stand
Fig 2.10 Parabolic Trough with absorber pipe; Diameter of pipe: 0.75 inch, material:
Copper
Fig 2.11 Collector with support stand.
40. Fig 2.12 Gear; No. of Teeth: 41
Fig 2.13 Gear Collector assembly
Fig 2.14 Assembly of Trough, stand and gear
41. 2.4.1 Motor – Gear Assembly
The motor used is a power window
lifter DC motor provided with a small gear fixed
to it. The motor has the following
specifications:
Voltage: 12V DC
RPM: 84 free
Torque: 10.4 Nm
The gear of the motor is meshed with the gear provided to the collector
assembly. The RPM of the collector gear can be calculated as follows:
No. of teeth of motor gear: T1 = 8
No. of teeth of collector gear: T2 = 41
Gear Ratio = Distance moved by Driver / Distance moved by Driven
= 41 / 8 = 5.125
RPM of motor: N1 = 84
T1 / T2 = N2 / N1
N2 = ( T1 / T2 ) * N1
N2 = ( 8 / 41 ) * 84
N2 = 16.4 RPM
2.5 Optical design of parabolic collector
When designing a parabolic trough type solar collector, it is essential to take
into account the optical factors in addition to the thermal factors. The optical design
parameters include:
1. Concentration ratio
2. Declination
3. Solar Hour angle and Sunset Hour angle
4. Extraterrestrial radiation and clearness index
Fig 2.15 Power window lifter motor
42. 5. Tilted Irradiance
2.5.1 Concentration Ratio
The concentration ratio of a parabolic trough collector is defined as the ratio of
the collector aperture area to the total area of the absorber / receiver tube.
C = Aa / Ar
Usual values of the concentration ratios are about 20 although the maximum
theoretical value of the concentration ratio is in the order of 70. High concentration
ratios are associated to high working temperatures.
The collector aperture area Aa is given by:
Aa = la * l
Where Ia is the width of the parabola = 2 ft = 0.6096 m
I is the length of the collector = 6 ft = 1.8288 m
Aa = 2 * 6 = 12 ft2 = 1.1484 m2
The total area of the absorber tube Ar is given by:
Ar = πdo * I
Where do is the outer diameter of the absorber pipe = 0.75 inch = 0.01905 m
Ar = πdo * I = 0.1094 m2
C = Aa / Ar
The concentration ratio C can now be calculated as:
C = 1.1484 / 0.01905 = 60.283
2.5.2 Declination
The declination is the angular position of the sun at solar noon, with respect to
the plane of the equator. Its value in degrees is given by Cooper’s equation:
δ = 23.45 sin ( 2π (284 + n) / 365 )
where n is the day of year (i.e. n =1 for January 1, n =32 for February 1, etc.).
Declination varies between -23.45° on December 21 and +23.45° on June 21. For
July 4th, n = 186; So δ = 22.80.
43. 2.5.3 Solar hour angle and sunset hour angle
The solar hour angle is the angular displacement of the sun east or west of
the local meridian; morning negative, afternoon positive. The solar hour angle is
equal to zero at solar noon and varies by 15 degrees per hour from solar noon. For
example at 7 a.m. (solar time2) the solar hour angle is equal to –75° (7 a.m. is five
hours from noon; five times 15 is equal to 75, with a negative sign because it is
morning).
The sunset hour angle ωs is the solar hour angle corresponding to the time
when the sun sets. It is given by the following equation:
Cos ωs = - Tan ψ * Tan δ
where δ is the declination and ψ is the latitude of the site, specified by the
user. The latitude of Rawalpindi is 33.6000° N.
Cos ωs = - Tan 33.6 * Tan 22.80
Cos ωs = - 0.279
ωs = 106.20
2.5.4 Extraterrestrial radiation and clearness index
Solar radiation outside the earth’s atmosphere is called extraterrestrial
radiation. Daily extraterrestrial radiation on a horizontal surface, H0 , can be
computed for the day of year n from the following equation:
where Gsc is the solar constant equal to 1,367 W/m2, and all other variables
have the same meaning as before.
H0 = 37614267.52 * 0.967 * ( 0.7374 + 22.7744 )
H0 = 8.55 x 108 W/m2
Before reaching the surface of the earth, radiation from the sun is attenuated
by the atmosphere and the clouds. The ratio of solar radiation at the surface of the
44. earth to extraterrestrial radiation is called the clearness index. Thus the monthly
average clearness index, K T , is defined as:
KT = H /H0
where H is the monthly average daily solar radiation on a horizontal surface
and H0 is the monthly average extraterrestrial daily solar radiation on a horizontal
surface.
K T values depend on the location and the time of year considered; they are
usually between 0.3 (for very overcast climates) and 0.8 (for very sunny locations).
We have assumed the value of KT to be 0.72.
2.5.5 Tilted Irradiance
Solar radiation in the plane of the solar collector is required to estimate the
efficiency of the collector and the actual amount of solar energy collected. The Liu
and Jordan’s isotropic diffuse algorithm to compute monthly average radiation in the
plane of the collector, HT :
The first term on the right-hand side of this equation represents solar radiation
coming directly from the sun. It is the product of monthly average beam radiation Hb
times a purely geometrical factor, Rb, which depends only on collector orientation,
site latitude, and time of year. The second term represents the contribution of
monthly average diffuse radiation, Hd, which depends on the slope of the collector, β.
The last term represents reflection of radiation on the ground in front of the collector,
and depends on the slope of the collector and on ground reflectivity, ρg. This latter
value is assumed to be equal to 0.2 when the monthly average temperature is above
0°C and 0.7 when it is below -5°C; and to vary linearly with temperature between
these two thresholds.
Monthly average daily diffuse radiation is calculated from global radiation
through the following formulae:
for values of the sunset hour angle ωs less than 81.4°:
45. for values of the sunset hour angle ωs greater than 81.4°:
Since our calculated value for ωs is 106.2 and KT = 0.72, we will apply the
second formula to determine the monthly average daily diffuse radiation:
Hd / H = 0.232
Hd = 1.43 x 108 W/m2
The monthly average daily beam radiation Hb is simply computed from:
Hb = H – Hd
Hb = 4.73 X 108 W/m2
2.6 Optical Errors in the Design of Parabolic Trough Collector
The upper limit to the concentration that a parabolic trough can achieve is set
by the sun's width. In practice, however, the average concentration ratio of a trough
is degraded to values much below this upper limit due to:
apparent changes in sun's width and incidence angle effects;
physical properties of the materials used in receiver and reflector
construction;
Imperfections (or errors) that may result from poor manufacture and/or
assembly, imperfect tracking of the sun, and poor operating
procedures.
Proper identification of all the factors that affect the optical performance and
hence precise knowledge of their effects are vital for the successful design and
dimensioning of the trough.
46. 2.6.1 Description of Optical Errors
Fig 2.16 Description of Optical Errors
Figure 2.16 presents a schematic representation of various types of potential
errors that may be encountered in parabolic troughs. These can be listed as:
errors associated with the reflecting surface.
mislocation of the receiver with the effective focus of the reflecting
surface.
and misalignment of the collector aperture with respect to the sun (e.g.,
tracking errors).
First, the errors associated with the reflecting surface are considered. As a
hypothetical example, the reflecting surface of the trough is assumed to be
composed of a thin sheet of material, one surface of which is reflective. When this
sheet is attached to its supporting structure (ribs), various distortions occur in the
47. surface. The resulting surface has a wavy pattern and in general the mean surface
obtained by averaging out the waves also may differ from the ideal (desired) surface.
Finally, the reflecting surface may have a small scale structure consisting of a grainy
texture plus a striation pattern. All these factors will contribute to the blurring of the
concentrated image at the receiver. However, they can be characterized as three
basically independent modes of reflector error.
Fig 2.17 Schematic representation of parabolic mirror surface showing the difference
between slope errors and reflector profile errors
As shown in Figure 2.17, the actual mean surface deviates from the ideal in
such a way as to displace the effective focus. A local slope error primarily dependent
on the deviation of the actual wavy surface from its mean contributes a deflection
which approximates twice the angular deviation between the actual surface from the
mean as is shown in Figure 2.18. Finally, small-scale structure consisting of a grainy
texture can be characterized as a material property, namely, nonspecularity
(diffusivity) of the reflective material.
Fig 2.17 illustrates the difference between slope errors and reflector profile
errors, and Figure 2.18 illustrated the difference between slope errors and mirror
diffusivity.
48. Fig 2.18 Ray traces of reflection from perfect and imperfect (random) mirror surfaces
showing perfectly reflected central ray Sn and imperfectly reflected central ray S’
n
Two additional sources of error are those associated with the alignment and
positioning of the receiver with respect to the expected focus and with the tracking
accuracy of the collector drive system. As shown in Figure 2.16 at any given time the
center of the absorber tube may be positioned at a distance away from the effective
focus of the reflector due to:
errors in positioning the receiver tube during assembly;
change in the effective focus of the reflector during operation;
thermal growth and expansion of the receiver and its insulation during
operation;
sagging of the receiver between supports which themselves are elastic and
will be distorted by thermal gradients.
Furthermore, at a given time, the projected central ray from the sun
may strike the reflector aperture plane at an angle (instead of striking the plane
perpendicularly). This will be due to the rotation of the vertex-to-focus axis of the
49. reflector during assembly or instantaneous misalignment of the reflector with the
sun (tracking errors).
Fig 2.19 Schematic representation of a mirror surface showing the difference between
slope errors and the mirror diffusivity.
2.6.2 Summary of Potential Errors
2.6.2.1 Potential errors in Materials
Nonspecularity (diffusivity) of the reflective material.
2.6.2.2 Potential errors in Manufacture and Assembly
Local slope errors (surface waviness) of the reflector that may result from
distortion of its surface during manufacture, Profile errors: Average shape of
the reflector (obtained by averaging the local slope errors or waves) may differ
from a parabola. This may be due for example to distortions during
manufacture and/or assembly. (It may also develop after collector has been in
operation over a period of time.)
Misalignment of the reflector during assembly. That is, reflector may be
rotated (or twisted) about the vertex-to-focus axis during assembly (see
Figure 2.16).
50. Mislocation of the receiver tube. The receiver tube may be misaligned with
respect to the effective focus of the reflector during manufacture and/or
assembly (Figure 2.16)
2.6.2.3 Potential errors in Operation
Tracker epuipment may cause tracking bias/error due to its poor quality or
tracking biases may develop after the collectors have been in operation for
some time.
Profile errors may develop or increase due to wind loading, temperature
effects, etc., during operation.
Nonspecularity (or diffusivity) of the reflective surface may increase with
time, due to weathering or accumulated dust on reflector.
Misalignment of the receiver with the effective focus may develop during
operation due to one or a combination of the following:
o sagging or buckling of the receiver tube because of thermal
expansion (if insufficient thermal expansion tolerance exists in the
design);
o permanent expansion of the receiver as a result of thermal cycling
over a period of time;
o change in location of the effective focus, due for example to
increased profile errors in the reflector.
52. Analysis Of Solar Collector On ANSYS 12
3.1 Units:
TABLE 3.1
Unit System Metric (m, kg, N, s, V, A) Degrees rad/s Celsius
Angle Degrees
Rotational Velocity rad/s
Temperature Celsius
3.2 Model (A4)/ Geometry:
TABLE 3.2
Model (A4) > Geometry
Object Name Geometry
State Fully Defined
Definition
Source C:UsersibbiDesktopNew folder (2)final collector.SLDASM
Type Solid Works
Length Unit Meters
Element Control Program Controlled
Display Style Part Color
Bounding Box
Length X 2.0469 m
Length Y 0.61504 m
Length Z 0.67477 m
Properties
53. Volume 3.3587e-002 m³
Mass 27.66 kg
Scale Factor Value 1.
Statistics
Bodies 3
Active Bodies 3
Nodes 26023
Elements 9837
Mesh Metric None
TABLE 3.3
Model (A4) > Geometry > Parts
Object Name stand-1 collector-1 gear-2
State Meshed
Graphics Properties
Visible Yes
Transparency 1
Definition
Suppressed No
Stiffness Behavior Flexible
Coordinate System Default Coordinate System
Reference Temperature By Environment
Material
Assignment Structural Steel
Nonlinear Effects Yes
Thermal Strain Effects Yes
Bounding Box
Length X 2.0193 m 2.0467 m 1.3208e-002 m
Length Y 0.4511 m 0.32743 m 0.10965 m
Length Z 0.4064 m 0.67477 m 0.10971 m
Properties
Volume 9.9908e-003 m³ 2.3517e-002 m³ 7.992e-005 m³
Mass 8.57 kg 18.85 kg 0.235 kg
Centroid X -0.19468 m -0.19401 m -1.2253 m
Centroid Y -0.18647 m 0.18382 m 0.16103 m
Centroid Z 0.26227 m 0.26672 m 0.26227 m
Statistics
Nodes 1116 15124 9783
Elements 472 7633 1732
54. Mesh Metric None
FIGURE 3.1
Model (A4) > Geometry > Figure
3.3 Coordinate Systems:
TABLE 3.4
Model (A4) > Coordinate Systems > Coordinate System
Object Name Global Coordinate System
State Fully Defined
Definition
Type Cartesian
Ansys System Number 0.
Origin
Origin X 0. m
Origin Y 0. m
Origin Z 0. m
3.4 Connections:
TABLE 3.5
Model (A4) > Connections
Object Name Connections
State Fully Defined
Transparency
Enabled Yes
55. TABLE 3.6
Model (A4) > Connections > Contact Regions
Object Name Contact Region Contact Region 2
State Fully Defined
Scope
Scoping Method Geometry Selection
Contact 2 Faces 1 Face
Target 2 Faces 1 Face
Contact Bodies stand-1 collector-1
Target Bodies collector-1 gear-2
Definition
Type Bonded
Scope Mode Automatic
Behavior Symmetric
Suppressed No
3.5 Mesh:
TABLE 3.7
Model (A4) > Mesh
Object Name Mesh
State Solved
Defaults
Physics Preference Mechanical
Relevance 0
Sizing
Use Advanced Size Function Off
Element Size Default
Initial Size Seed Active Assembly
Smoothing Medium
Transition Fast
Minimum Edge Length 1.778e-003 m
Statistics
Nodes 26023
Elements 9837
Mesh Metric None
56. FIGURE 3.2
Model (A4) > Mesh > Figure
3.6 Static Structural (A5):
TABLE 3.8
Model (A4) > Analysis
Object Name Static Structural (A5)
State Solved
Definition
Physics Type Structural
Analysis Type Static Structural
Solver Target ANSYS Mechanical
Options
Environment Temperature 22. °C
Generate Input Only No
TABLE 3.9
Model (A4) > Static Structural (A5) > Loads
Object Name Fixed Support Force
State Fully Defined
Scope
Scoping Method Geometry Selection
Geometry 2 Faces 1 Face
57. Definition
Type Fixed Support Force
Suppressed No
Define By Vector
Magnitude 200. N (ramped)
Direction Defined
FIGURE 3.3
Model (A4) > Static Structural (A5) > Fixed Support > Figure
58. FIGURE 3.4
Model (A4) > Static Structural (A5) > Force > Figure
3.7 Solution (A6):
TABLE 3.10
Model (A4) > Static Structural (A5) > Solution
Object Name Solution (A6)
State Solved
Adaptive Mesh Refinement
Max Refinement Loops 1.
Refinement Depth 2.
TABLE 3.11
Model (A4) > Static Structural (A5) > Solution (A6) > Solution Information
Object Name Solution Information
State Solved
Solution Information
Solution Output Solver Output
Newton-Raphson Residuals 0
Update Interval 2.5 s
Display Points All
59. TABLE 3.12
Model (A4) > Static Structural (A5) > Solution (A6) > Results
Object
Name
Equivalent
Elastic Strain
Maximum
Shear Elastic
Strain
Shear
Elastic
Strain
Equivalent
Stress
Maximum
Shear Stress
State Solved
Results
Minimum
1.9412e-014
m/m
2.7186e-014
m/m
-2.3019e-
006 m/m
3.8823e-003
Pa
2.0913e-003
Pa
Maximum
3.3139e-006
m/m
4.9714e-006
m/m
2.4393e-
006 m/m
6.6279e+005
Pa
3.8241e+005
Pa
Minimum
Occurs On
stand-1 collector-1 stand-1
Maximum
Occurs On
gear-2 collector-1 gear-2
FIGURE 3.5
Model (A4) > Static Structural (A5) > Solution (A6) > Equivalent Elastic Strain > Figure
62. TABLE 3.13
Model (A4) > Static Structural (A5) > Solution (A6) > Results
Object Name Shear Stress Total Deformation
State Solved
Results
Minimum -1.7707e+005 Pa 0. m
Maximum 1.8764e+005 Pa 5.0477e-006 m
Minimum Occurs On collector-1 stand-1
Maximum Occurs On collector-1
FIGURE 3.10
Model (A4) > Static Structural (A5) > Solution (A6) > Shear Stress > Figure
FIGURE 3.11
Model (A4) > Static Structural (A5) > Solution (A6) > Total Deformation > Figure
63. 3.8 Material Data/ Structural Steel:
TABLE 3.14
Density 7850 kg m^-3
Coefficient of Thermal Expansion 1.2e-005 C^-1
Specific Heat 434 J kg^-1 C^-1
Thermal Conductivity 60.5 W m^-1 C^-1
Resistivity 1.7e-007 ohm m
Compressive Ultimate Strength Pa 0
Compressive Yield Strength Pa 2.5e+008
Tensile Yield Strength Pa 2.5e+008
Tensile Ultimate Strength Pa 4.6e+008
Relative Permeability 10000
Young's Modulus Pa 2.e+011
Poisson's Ratio 0.3
TABLE 3.15
Structural Steel > Strain-Life Parameters
Strength
Coefficient
Pa
Strength
Exponent
Ductility
Coefficient
Ductility
Exponent
Cyclic
Strength
Coefficient
Pa
Cyclic Strain
Hardening
Exponent
9.2e+008 -0.106 0.213 -0.47 1.e+009 0.2
64. Thermal Analysis Of Solar Collector In ANSYS 12
3.9 Units:
TABLE 3.16
Unit System Metric (m, kg, N, s, V, A) Degrees rad/s Celsius
Angle Degrees
Rotational
Velocity
rad/s
Temperature Celsius
3.10 Steady-State Thermal (A5):
TABLE 3.17
Model (A4) > Analysis
Object Name Steady-State Thermal (A5)
State Solved
Definition
Physics Type Thermal
Analysis Type Steady-State
Solver Target ANSYS Mechanical
Options
Generate Input
Only
No
65. TABLE 3.18
Model (A4) > Steady-State Thermal (A5) > Initial Condition
Object Name Initial Temperature
State Fully Defined
Definition
Initial Temperature Uniform Temperature
Initial Temperature
Value
22. °C
TABLE 3.19
Model (A4) > Steady-State Thermal (A5) > Loads
Object Name Convection Temperature 2 Radiation Heat Flow
State Fully Defined
Scope
Scoping Method Geometry Selection
Geometry 1 Face
Definition
Type Convection Temperature Radiation Heat Flow
Film Coefficient
56. W/m²·°C
(ramped)
Ambient
Temperature
22. °C (ramped)
22. °C
(ramped)
Suppressed No
Magnitude
100. °C
(ramped)
34. W
(ramped)
Correlation To Ambient
Emissivity
1. (step
applied)
Define As Heat Flow
TABLE 3.20
Model (A4) > Steady-State Thermal (A5) > Convection
Steps
Time
[s]
Convection Coefficient
[W/m²·°C]
Temperature [°C]
1
0. 0.
22.
1. 56.
66. FIGURE 3.12
Model (A4) > Steady-State Thermal (A5) > Temperature 2
FIGURE 3.13
Model (A4) > Steady-State Thermal (A5) > Temperature 2 > Figure
68. 3.11 Solution (A6):
TABLE 3.21
Model (A4) > Steady-State Thermal (A5) > Solution (A6) > Results
Object Name Temperature
State Solved
Scope
Scoping Method Geometry Selection
Geometry All Bodies
Definition
Type Temperature
By Time
Display Time Last
Calculate Time History Yes
Identifier
Results
Minimum 26.212 °C
Maximum 101.1 °C
Minimum Occurs On collector-1
Maximum Occurs On collector-1
FIGURE 3.16
Model (A4) > Steady-State Thermal (A5) > Solution (A6) > Temperature > Figure 2
72. 4.1 Fabrication of solar collector and assembly
This chapter is a description of a method to produce a closed parabolic trough
Solar energy collector. What is described here is basically a manual method to make
high efficiency solar collectors against very low cost, which is particularly suited for
teaching, research or demonstration purposes. But it is hard for a manually made
collector to match the efficiency, lifetime and water tightness standard of an industrial
Product using the same method. It will also cost more than the industrial collector.
What is described here is basically a manual method to make high efficiency
solar collectors against very low cost, which is particularly suited for teaching,
research or demonstration purposes. But it is hard for a manually made collector to
match the efficiency, lifetime and water tightness standard of an industrial product
using the same method. It will also cost more than the industrial collector.
There are two known methods to form a cylindrical parabolic trough collector:
1. Forming a curved plate material under high temperature.
2. Adding pre-formed ribs at the back of a flat reflective plate, then force the
plate to follow the curve of the ribs.
Both methods are expensive, and both have difficulties to reach a high
precision. Our method uses the natural elastic deformation of a planar plate to
form a curved surface close to a parabolic cylinder, and then redress the
approximation error of this surface, again using elasticity. As it is easier to get
higher precision by natural elastic deformation, this method has the following
advantages.
1. Simplicity and low cost.
It is actually the only known method for home making high performance
parabolic trough solar collectors without any special tools. Not only the
production cost drops to far blow the other manufacturing methods of
parabolic troughs, but also it makes the solar energy collecting cost
substantially lower than any fossil fuel. The economic and social signification
of the method may be huge.
2. Better performance and quality of the product.
The fundamental characteristics of the performance of a parabolic
trough solar collector are its concentration ratio and its optical efficiency.
Today, the concentration ratio of a parabolic trough collector of width between
1m and 2m is limited to about 50 times under industrial manufacturing
conditions and with high cost, while our method can achieve an effective and
73. efficient concentration ratio of over 80 times for a manually made parabolic
trough of width less than 1m, together with a higher efficiency.
First we will consider the fabrication of collector and then we will move on to
the assembly.
4.1.1 Parts and their materials with dimensions
It is very necessary to accurately design the solar collector and the assembly
before fabricating it. That’s why different designing and simulations soft wares have
been used and employed to obtain an optimal and effective design as described in
the previous chapters. These soft wares include Pro/Engineer, Auto CAD, Solid
Works, ANSYS, FLUENT. It is not just an experiment to just fabricate the model of
the collector with some lump sump dimensions. We have to find the optimal and
economical solution while designing and fabricating any engineering project. All the
factors must be considered properly such as the dimensions, the optimal cost, the
performance etc, and the best and optimal solution is always a compromise between
these factors. Sometimes the desired performance is not achieved so we have to
increase the scale of our project but cost increases drastically while doing so and the
project becomes uneconomical from financial point of view, and sometimes
controlling the cost results in a very small scale project. So it is always a compromise
between all these factors to affectively design and fabricate any engineering project.
Plus we also have to consider the different types of materials available in the market
and selection of the best possible material from a list of different available materials
that serves it purpose the best. The different types of materials used according to
their purpose, functions along with their accurate dimensions are as under:
DESCRIPTION
Quantity
Material
Dimension
Supporting plate
01 Steel plate 6 ft * 2.5 ft (18
gage)
Front reflective plate
01 Polished
Stainless steel
plate
6 ft * 2.5 ft
(18 gage)
Insulating material 01 sheet Glass wool 6 ft * 2.5 ft
Supporting pads 02 Rubber 2.5 ft * 0.167 ft
( 1 inch thick)
End semi-circular plates 02 Steel plate (18
gage)
2.5 ft long
Focal height
(0.6 ft)
74. Absorbent pipe 01 Copper 7 ft long
And 0.75 inch
in diameter
Hollow pipe for base 01 Steel pipe 3 inch * 1 inch
cross sectional
pipe (10 ft long)
Bearings 02 Roller steel
bearings
15 mm
Axles 02 Steel 16 mm
Gears 01 Steel
Motor frame (L shaped strips) 02 Cast iron 3 inch * 1 inch
Bushings 02 Cast iron 30mm
Screws 7-8
dozen
Steel As per
requirement
Nut and bolts 02 Steel As per
requirement
Table 4.1 (Materials and Dimensions of the Parts)
4.1.2 Complete steps:
1. Making end semicircular plates
The semicircular plates are cut from the steel sheet by setting
the width 2 ft and the focal height 0.5 ft and setting the height with
some tolerance of about 0.2 ft i.e. the net becomes 0.7 ft.
Figure 4.1(The End Semicircular Plates)
2. Supporting back:
75. The back is a flat plate of steel sheet and it must be bent in its
moving direction and not in the transversal direction. The supporting
back sheet is cut from a standard sheet of dimension 4 ft * 8 ft
available in the market. The desired dimension (6 ft * 2.5 ft) is cut from
an iron cutter and it is then bend in the moving direction to form the
supporting back.
Figure 4.2 (The Supporting Back)
3. Combining the end plates and the supporting back :
The end semicircular plates and the supporting plate are then
screwed at the ends after proper bending and the resulting assembly is
as under.
Figure 4.3 (Combining End Plates and Back)
4. Fixing the rubber pads:
Two rubber pads are attached at equal distance along the length
wise of the collector. These rubber pads serve their purpose in
separating the two sheets i.e. the back sheet and the front reflexive
sheet and they also provide a thickness between the two plates so that
the insulating material glass wool may be added between the two
76. plates. The glass wool helps in decreasing the heat transfer from the
backside so that thermal efficiency of the solar collector may be
enhanced.
Figure 4.4 (Fixing the rubber pads)
5. Making the base :
The base of this collector is made from the hollow steel pipe of
cross section 3 inch * 1 inch. The pipe is cut to form a T shaped vertical
stand and the assembly is so welded that two verticals stands are
welded by a horizontal bar to form a complete and rigid base.
Figure 4.5 (Making the base)
6. Attaching the reflective plate:
Polished stainless steel plate available in the size of 8 ft *4 ft is
cut to the right dimension. The plate will be bended to form the
reflective surface. The first thing to do is to determine the direction of
the plate used to make the back. The production of a flat plate, either of
plastics or of metal, is done either by extrusion or by rolling. We call the
direction of the die or the roller the transversal direction of the plate,
and the direction of the output of the plate the moving direction. The
crucial point is to avoid bending the back in the transversal direction,
because the plate is usually less uniform in that direction, with more
inherent curvature, internal stress and variations of thickness. This will
lower the optical precision of the back, and add to redressing difficulty.
77. So the correct method is to bend the sheet in the moving direction and
its edges are flanged so that they may be screwed to the supporting
plates with steel screws. The holes are drilled along the length wise
and width wise of the flange and the two plates are fixed together.
7. Inserting the absorbent pipe:
The copper pipe of diameter ¾ inch and 7 ft in length is purchased
from the market and it is then inserted at the focal point which comes at a
height of 0.43 ft. a point from the base of parabola is marked at 0.43ft
vertically. A hole of app ¾ inches is drilled at this point. Then the copper
pipe is passed through the two drilled holes. Moreover two conical shapes
cups are cut and riveted at the ends so in order to fix the pipe properly .At
one side of the pipe a valve is attached for controlling the flow. The other
side serves as an inlet.
Figure 4.6 (Inserting the absorbent pipe)
8. Making the bush:
The bush is made from a cylindrical thick cast iron pipe. The
bush are first cut from the cylinder according to the right dimensions
approximately 1 inch wide, then the bushes are properly machined and
faced to give a better outlook. The internal dia of bushes is set by
reaming the internal diameter of the cylinder; this diameter is set
according to the accurate dimensions of the bearings. The internal
diameter of bush is kept smaller than the bearing external diameter so
that the bearing may be fitted in the bushing by the PRESS FIT. The
bearings are purchased from the market according to the dia of the
axle whose fabrication is considered in the later section. Moreover the
bearing is approximately 15mm inner diameter and this bearing is
press fitted in the bush. Thus two bushes containing the two bearings
78. are fabricated. These bushes are then welded to the steel pipe so that
an axle may be passed from the hole.
Figure 4.7 (Making the bush)
9. Fabricating the axles:
Two shaft / axles are cut from a steel rod by a power hacksaw
as per our dimensions the outer diameter of the axles are machined
according to the right dimensions and the inner diameter of the bearing
is slightly kept less than the outer diameter of shaft so that the shaft
may be press fitted in the bearing. On both the side of the axles the
threads are cut so that the inner side of the axle may be screwed in the
collector frame and a nut is tightened on the other side.
The other axle is fabricated just in the same way but it is slightly
large because a gear has to be mounted on this side. Again the gear is
also designed and fabricated in such a way so that gaer may be press
fitted on the axle / shaft.
Figure 4.8 (Fabricating the axles)
79. 10. Fabricating the gear :
The gear is designed and then it is fabricated on the milling
machine. After proper indexing the teeth of the gear and the pitch is set
and gear is cut on the milling machine. The gear is made from steel
plate approximately 10 mm thick. After proper designing and fabricating
the gear is mounted on the shaft as described.
Figure 4.8 (Fabricating the gears)
11. The motor frame:
The motor frame is made from two cast iron strips by welding them
together and three holes are drilled on the strips so that motor may be
fixed at these holes through nuts and bolts. Then the whole assembly is
welded to the collector base pipe so that the two gears i.e the small motor
gear and the fabricated gear may properly mesh into each other to work
properly.
Figure 4.9 (The motor frame)
The complete fabricated solar collector is shown in the following image.
80. Figure 4.10 (Complete Fabricated Solar Collector)
4.1.3 Complete thermal system assembly
The complete thermal system assembly consists of the following parts:
Solar collector
Hot water container
Pump
Motor
Electronic circuit for solar tracking
12 VDC battery
12V / 7amp power supply for charging
Piping systems
Valves
The complete fabrication of solar collector has been described. Now we shall
move onto the next level, the fabrication of other parts and the assembling of
complete system.
Hot Water Container:
The hot water container is fabricated from 20 gage steel sheet .It is a
cylindrical container of capacity 10 liter. It contains an output nozzle and an input
nozzle. The flow from the output nozzle can be controlled from a valve (1/2 inch dia).
The container has a cover of same diameter as of the cylinder at the top. The top
cover contains a hole in it so that the output pipe of the pump can be passed through
it. The pump for recirculation of water is immersed at the bottom of container so that
it sucks water from the base and re-circulates it at the inlet of solar collector. The
recirculation is performed in case if the water is not heated enough at our desired
temperature. The hot water container is completely insulated so that the losses
during the heat transfer may be reduced to minimum level. The insulation is provided
81. with a double sheet of JUMBOLON. The sheet is pasted over the cylinder with sticky
SAMAD BOND.
Figure 4.11 (Hot Water Container)
The pump:
The pump is a small unit applied for the recirculation of water from the hot
water container to the solar collector so that the water may be passed again and
again to the absorber pipe of solar collector until it becomes hot and our desired hot
temperature may be achieved. For this purpose we looked for a small pump which
can perform this function and we purchased the fish aquarium pump with a
discharge of 1600 lit / hr and a head of 1.5 meter. The pump is to be immersed in
water in the container. At the base it sucks the water and through a rubber pipe
attached at its outlet, it transports it to the inlet of solar collector. The inlet, outlet and
pump images are shown in the following figures.
82. Solar Tracking System:
In order to automate the system, we designed a complete solar tracking
system so that it work in such a way that it sense the light intensity or the sun
intensity and rotates the solar collector in that direction. In this way the parabolic
trough will remain exactly in front of the solar intensity and the system can work all
day from morning through evening. So in order to complete the solar tracking
phenomena we designed and purchased the following parts.
12 VDC Motor
Electronic circuit
1. Light dependent resistances (sensors)
2. Integrated circuit (LM398P)
3. Resistances
4. Variable resistances
5. Relay switches
6. Battery 12VDC / 7 amp
7. Power supply 12 VDC / 7 amps.
o 12 VDC Motor:
A DC motor is used to rotate the parabolic trough on the axles through
bearings. The motor employed here is 12 VDC / 7 amps. This motor is basically used
in the car door to operate the power window mirrors automatically. But it can serve
its purpose to rotate a parabolic trough if the load is applied on the bearings through
axles. On the shaft of the motor a small gear having 6 teeth is mounted. So a bigger
gear is designed and mounted on the axle shaft. This bigger gear completely
meshes in the teeth of smaller gear and when the motor rotates it will ultimately
rotate the collector by transmitting the power through smaller gear to the bigger gear.
The bigger will also serve another function – it will reduce the rpm of the motor due
to its greater pitch circle diameter and large number of teeth. The motor is shown in
the following figure.
Figure 4.12 (12 VDC Motor)
83. o The Electronic Circuit:
The complete electronic circuit is designed and fabricated on the printed
circuit board and Vero board. The electronic circuit basically exploits the use of two
LDRs as sensors and an IC as a comparator. By comparing the light intensity at the
two LDR, whenever there is a light intensity difference it basically compares through
the IC and generates an output pulse which drives the motor and the trough is
rotated.
Light Dependent Resistances (LDR)
A photo resistor or LDR is a resistor whose resistance decreases with
increasing incident light intensity; in other words, it exhibits photoconductivity.
A photo resistor is made of a high resistance semiconductor. If light falling
on the device is of high enough frequency, photons absorbed by the
semiconductor give bound electrons enough energy to jump into the conduction
band. The resulting free electron (and its hole partner) conduct electricity, thereby
lowering resistance.
The light dependent resistance is an electronic device which basically
works on the light intensity difference. In our system two LDRs are used as a
sensor. The LDR are attached at the parabolic trough reflective plate at two
different locations. If a light intensity at one LDR is greater than the other i.e one
LDR is exposed to more light as compared to the other. Then the motor will rotate
the collector by comparing through the IC. The placement of LDR is very
important and has to be placed accurately at the trough where it serves its
purpose the best.
Figure 4.13 (LDR)
IC (LM358P)
An integrated circuit or monolithic integrated circuit (also referred to
as IC, chip, or microchip) is an electronic circuit manufactured by lithography, or
the patterned diffusion of trace elements into the surface of a
thin substrate of semiconductor material. Additional materials are deposited and
patterned to form interconnections between semiconductor devices.
84. This IC basically serves as a comparator. It has total eight legs. It basically
receives the signal or pulse from the sensors and it transmits the pulse to the
relay switches which in turn rotate the motor by generating a 12 VDC pulse. This
IC is shown in the following figure.
Figure 4.14 (IC)
Resistances / Variable Resistances:
A resistor is a passive two-terminal electrical component that
implements electrical resistance as a circuit element. The current through a
resistor is in direct proportion to the voltage across the resistor's terminals. Thus,
the ratio of the voltage applied across a resistor's terminals to the intensity of
current through the circuit is called resistance. This relation is represented
by Ohm's law:
The variable resistances are employed in the circuit so that the
resistances at various branches may be varied and achieved as per our
requirement.
The color code carbon resistances are employed of various ohms as per
the circuit diagrams to complete the circuit.
Figure 4.15 (Resistances / Variable Resistances)
85. Relay Switches:
The relay switch is an electronic component whose basic function is to
increase the mill volts pulses into higher volts so that they can be fed to the
battery at the operating battery / power supply voltage. In our circuit we have
employed four relays and they are attached as per circuit diagram on the printed
circuit board.
Figure 4.16 (Relay Switches)
12VDC battery:
A power supply battery of 12VDC and 07 amps is purchased to run the
motor. The battery is lithium ions alkaline battery. The battery can be used whole
day once fully charged because it has to perform very less operation and it has to
rotate the trough only when needed.
Figure 4.17 (12VDC battery)
12VDC charger / power supply:
A charger or the power supply has been purchased to charge the battery
during night hours so that it can perform its function all day long. The power supply is
operated at 220volts and its output is 12VDC and 07 amps.
The complete system is controlled by different valves and flow lines. The
water is stored in a hot water container so that it can be utilized when we want to do
so and the next reason for storing the water is so that it can be re-circulated over and
over again until it becomes hot at our desired temperature.
86. Figure 4.18 (12VDC charger / power supply)
The flow diagram of transportation system of cold water as well as hot water
is shown in figure.
Figure 4.19 (Transportation System)
Now we will discuss the fabrication of transport and piping system.
The transportation system:
The piping system consists of different ball valve and rubber tubing for
complete transportation of water.
o The ball valve:
The ball valve used in our case is of 1inch dia , brass cross section valve.
The ball valves are easily available in market in various sizes. Two ball valves are
