Development of a Solar Fresnel Reflector and Its Tracking Stand Using Local Material

Manukaji John Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 5, Issue 1( Part 5), January 2015, pp.22-30
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Development of a Solar Fresnel Reflector and Its Tracking Stand
Using Local Material
Manukaji John
Solar Energy Research Centre Federal Polytechnic, Bida Niger State Nigeria
ABSTRACT
Solar collectors are the engines that drive all solar energy heating systems. Although solar heating collectors
have settled upon a few basic designs, they are still manufactured in an array of configurations.Solar collectors
are generally classified by the temperatures that can be produced under normal amounts of solar radiation. The
collector’s end-use application can be determined by their temperature classification such as Low-temperature
collectors, Medium-temperature collectors and High-temperature concentrators that track the sun and produces
the highest temperatures.Reflectorsthat are axially symmetrical and shaped like a parabola, has the property of
bringing parallel rays of light (such as sunlight) to a pointfocus and so any object that is located at its focus
receives highly concentrated sunlight, and therefore becomes very hot. This is the basis for the use of this kind
of reflector for high solar energy generation. Energy supply for domestic activities had been a major problem
faced by both rural and city dwellers for a long time now in Africa. It was therefore desirable to design and
construct a solar Fresnel reflector and a tracking stand that can be used to generate heat from the sun for
cooking, baking and distillation purposes. The reflector and the tracking stand designed and constructed was
able to concentrate solar energy within a regional diameter of 10cm and could be used to raise the temperature
of any object placed at its focal region. It was discovered that the heat generated is directly proportional to both
the perfection of the collector design, its construction, the quality of the reflectors e.g plain mirror, the area
exposed to the sun and the solar intensity of the day.
I. INTRODUCTION
Solar collectors are either non-concentrating or
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 light. Concentrating
collectors have a bigger interceptor than
absorber.Norton, Brian 2013
The classification of the collectors by their
effective end-use temperatures is a helpful method of
differentiation.
Flat plate solar collectors are the most common
for heating water and air in the home. The flat plate
solar collector is an insulated box with a plastic or
glass “lid” on top.
Solar collectors transform solar radiation into
heat and then transfer that heat to a medium (water,
solar fluid, or air). 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.
Concentrating solar collectors use mirrored
surfaces to concentrate the sun's energy on an
absorber called a receiver. Concentrating collectors
also achieve high temperatures, but unlike evacuated-
tube collectors, they can do so only when direct
sunlight is available.
Concentrating reflectors generate high
temperatures and cook quickly, but require frequent
adjustment. Reflectors that bring rays parallel to its
principal axis to point focus can be easily turned to
follow both the sun's daily motion and its seasonal
one. The cooking pot stays stationary at the focus. If
the paraboloidal reflector is axially symmetrical and
is made of material of uniform thickness, its centre of
mass coincides with its focus if the depth of the
reflector, measured along its axis of symmetry from
the vertex to the plane of the rim, is 1.8478 times its
focal length. The radius of the rim of the reflector is
2.7187 times the focal length. The angular radius of
the rim, as seen from the focal point, is 72.68
degrees.
If the reflector is aligned with its focal line
horizontal and east-west and is pointed so that its axis
of symmetry aims at the sun at noon, it will be tilted
up and down as the seasons progress. At the
equinoxes, no movement of the reflector is needed
during the day to track the sun.
Spherical reflectors operate much like
paraboloidal reflectors, such that the axis of
symmetry is pointed towards the sun so that light is
concentrated to a focus. However, the focus of a
spherical reflector will not be a point focus because it
suffers from a phenomenon known as spherical
aberration.
RESEARCH ARTICLE OPEN ACCESS

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During the day the sun has different positions.
For low concentration systems tracking can be
avoided, butfor higher concentrations, however, if the
mirrors or lenses do not move, then the focus of the
mirrors or lenses changes and so tracking must be
carried out from time to time. The tracking system
increases the cost and complexity of a collector. With
this in mind, different designs can be distinguished in
how they concentrate the light and track the position
of the sun.
Solar reflectors and collectors use a renewable and
non- polluting type of energy source. They reflect and
collect an energy that is so decentralized that every
home can utilize it as desired. The techniques of
construction are simple. It involves only the initial
capital cost and does not attract any recurrent cost.
Under initial review, it was discovered that on an
average sunny day including the periods of cloud cover,
the reflectors and collectors, collect enough energy
from the sun that are equivalent to the energy supplied
by conventional energy sources. Finally, its use will
eventually reduce the family energy costs by reducing
the amount spent on purchase of conventional fuels.
Many solar reflectors have already been developed
world wide.
The performance of both types hadbeen reported in
the literature, but the results of these designs were not
based on comparative analysis. The performance of any
solar reflector improves if the collector efficiency is
increased. Therefore the efficiency of the collector
should be maximized if such a step does not
significantly increase the reflector and collector cost.
The variables affecting reflector and collector
efficiency fall into several groups.
1. Operating conditions (Insolation, tracking mode,
operating temperature, flow rate, wind speed and
other general weather conditions)
2. Properties of materials (reflectance, absorbtance,
and transmittance)
3. Receiver type (absorber shape, evacuated or non-
evacuated) and
4 Concentrator geometry (concentration ratio and
rim angle)
Because operating conditions may vary from
installation to installation, relative comparism between
existing reflectors may be difficult to achieve.
Comparatively, literature showed that the parabolic-
shaped-collectorgenerated the highest temperature than
any other reflector developed in modern times. This is
because it produces a point focus while others
generated a regional focus. However the production of
electroplated parabolic and Fresnel collectors requires a
sophisticated and costly fabrication process that is not
readily available in most developing countries. This
project therefore also aims at developing a collector
that has similar performance characteristics like the
conventional concentrating reflectors. It will be
constructed using local materials and constructional
techniques that are affordable by rural African dwellers.
II. DESIGN ANALYSIS
Many potential applications of solar heat require
higher temperature than those achievable by the best
flat plate collectors.
A concentrating collector comprises a receiver
where the radiation is absorbed and converted to some
other energy forms. A concentrator is the optical
system that directs beam radiation onto the receiver.
Therefore it is usually necessary to continually move
the concentrator so that it faces the solar beam.
The smooth optical surface of a reflector or lens
can be broken into segments, a trick invented by
Fresnel. Optically a Fresnel mirror can approximate a
focusing parabola. The effective aperture is obtained
by multiplying the total area of the Fresnel mirror by a
ground cover factor. Values of the factor between 0.3
and 0.6 are practical for Fresnel reflectorsDuffie and
Bechman, 1974.
The aperture of the system Aa is the projected area
of the concentrator, facing the beam. The concentration
ratio is the ratio of the area of aperture to the area of the
receiver.
CR = Aa/Ar
The individual plane or curved segments are each
designed to reflect radiation to the receiver. The
advantage of the system is in its lack of appreciable
dimension in the direction normal to the radiation
which may permit easy fabrication. A disadvantage
lies in the lost area between the segments near the rim
of the assembly.Duffie and Bechman, 1974
CONDUCTION: For the non-uniform flux
distribution of the radiation on the absorber’s surface,
substantial temperature gradients may exist across the
absorber’s surface and due to high surface temperature
of the absorber, the conduction losses through the
support structure may also be significant.
CONVECTION: Since the focal point of Fresnel
reflectors are located outside the reflectors, placing the
absorber in an open sunny location usually exposes it to
cooling breeze: This increases the convective losses
through forced convection by wind. The analysis of
this loss will be complex since the wind speed changes
from time to time. To reduce loss of heat from the
absorber by forced convection from wind which
severely limits the performance, the absorbermay be
sheltered on all sides except the top and bottom with a
wooden box. This will now reduce the analysis to free
convection by the air in the gap between the absorber
and casing.
RADIATION: Solar radiation arrives on the earth’s
surface at a maximum flux density of about 1 kW/m2
in
a wave length band between 0.3 and 2.5m. This is

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called short wave radiation and includes the visible
spectrum. Holman 1963.
Radiation losses are to the sky and or the
environmental. Solar collectors absorb radiation at
wavelengths around 0.5m and emit radiation at
wavelengths around 10mHolman1963.
The rate of radiation heat transfer between two
surfaces also depends upon their geometric
configuration and relationships. The influence of
geometry in radiation heat transfer can be expressed in
terms of the radiation shape factor between any two
surfaces 1 and 2.
III. DESIGN SPECIFICATION AND
CONSTRUCTIONAL DETAILS
MATERIAL SELECTION
The selection of materials for engineering design
and construction varies directly, with the type of
design, the aims and objectives of the design, the
function of each material and inversely with the cost
of the material, availability of the material,
processing of the material and maintenance.
Some of these factors have direct bearing with
the dimensions of the material, and the various ways
of joining the elements of the system. Others affect
the configuration of the total system and its usage.
The nature of the constructional problems, its
economics, the facilities and equipment available and
working methods play a key role in selection
exercises.
The solar Fresnel reflector being designed is
composed of two major parts
(1) The Fresnel reflector
(2) The tracking stand.
Table1: Materials Used For The Fresnel Reflector
S/No DESCRIPTION DIMENTION m QTY
1 Plywood 1.22x2.44x0.019 2
2 Plywood 1.22x2.44x0.0125 1
3 Galvanized iron sheet 1.22x2.44x.0.00055 2
4 Plain Mirror 0.42x1.22x0.003 4
5 Wood screws 0.04 1pkt
6 Nails 0.0125 0.5kg
7 Evostic 4litres
8 Oxblood paint 4litres
The construction of the Fresnel reflector was
made up of five stages.
STAGE 1 PRODUCTION OF THE
TEMPLATE
In constructing the Fresnel reflector, a template
was produced. The procedure used
in producing the Fresnel template was as follows.
1. A reference base line was drawn on a cardboard
paper.
2. A principal axis perpendicular to the base line
was drawn
3. A convenient focal distance was chosen along
the principal axis (45cm was chosen in this
Design)
4. A convenient focal width parallel to the base line
at the point of focus was marked A and B.
(10cm was chosen in this design)
5. It was assumed that the first direct ray from the
sun passed through the point B, parallel to the
principal axis and met the base line at C. That
incident ray was marked i1
6. At point C, a reflected ray r1 was drawn to pass
through the focal width at point A.
7. The angle BCA was bisected and the normal to
the incident and reflected rays was drawn to pass
it. The normal was n1.
8. At point C, a line p1 perpendicular to the normal
was drawn.
9. A line parallel to r1 was drawn to pass through
point B and meet the perpendicular line from C.
This line torched the base line at D.
10. Another assumed incident ray i2 parallel to the
first incident ray i1 was drawn to meet the base
line at D.
11. At D a reflected ray r2 was drawn to pass through
point A on the focal width. The ray r2 met the
perpendicular line from C at E. The point CE
was then the length of the mirror segment as well
as the slanting height of the Frustum that was to
be developed.
12. The angle between i2 and r2 was bisected and
normal n2 was drawn to pass through it.
13. A line perpendicular to n2 was drawn to produce
the second segment of the template.
14. Processes 9 to 11 were repeated each time until a
template equal in length to the radius of the

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circle derived from the collector area calculated
was achieved. In this case, the length was 47
cm. The ray diagram described in 1 to 14 above
is shown in figure 1 and the template in figure 2.
Figure 1 Ray diagram used for the development of template
Figure 2 the developed template.
The diagram in fig 2 was cut out from the
cardboard and transferred to the 21 mm thick
plywood. Twenty four of these shapes were
produced.
STAGE TWO: DEVELOPMENT AND
PRODUCTION OF THE FRUSTUM RINGS.
1. The vertical and horizontal components of each
template segment with reference to the base line
and the principal axis were determined. These
points were indicated as shown in fig 3.
Fig 3 Ray diagram for the development of the
Frustum ring.
VE was d2
Oc was a1
O1V was A1
O1C was b1
O1E was B1
CE was d1
The completed image of fig 3 is shown in fig 4
Fig 4. Complete image of Fig 3
Note that
d2 = radius of the big cone
a1 = radius of the small cone
B1 = Slant height of the big cone
b1 = slant height of the small cone
d1 = slant height of the Frustum
The Frustum ring was developed by performing the
following operation.
(1) Half of the drawing in fig 4 was produced
(2) With d2 as radius and V as centre, an arc was
constructed from point E to meet the extended line
O1V at F.

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(3) With F as centre and same radius, the previous
arc was cut at G.
(4) With E as centre and same radius the previous
arc was cut at H.
(5) With centre O1, and radius B1 an arc was
produced starting from E to point J
(6) With O1, as centre and b1 as radius another arc
was produced starting from C to point k
(7) With FG as length 13 points were marked off on
the EJ arc.
(8) The points O1L and O1J were joined.
The above construction was drawn to scale and
when it was exploded gave the first Frustum ring of the
first segment of the template. The diagrams produced
are in fig 4 and fig5. The other Frustum rings for the
other segments of the template were produced
following the same steps.
Fig 5 Frustum ring
Figure 5
The full scale dimension of the Frustum ring was now
cut out from the 0.55 mm thick
galvanized iron sheet.
STAGE THREE: PRODUCTION OF THE
TRAPEZOIDAL SHAPED MIRROR TABLETS.
The circumference of the outer edges of the first
Frustum is C1 = 2d2
The circumference of the inner edges of the first
Frustum is C2 = 2a1
C1 was divided into twenty four equal parts and C2
was divided into twenty four equal parts and the two
divisions formed the two parallel sides of the
trapezoidal mirror tablets. The height of the mirror
tablet was B1 - b1 each. The other Frustums were
also developed. The first two Frustums were divided
into 24 each to form the dimension of the mirror
tables while the other three Frustums were divided
into 48 each to form the dimensions of the mirror
tablets.
The mirror tablets are shown below in fig 6
Fig 6 mirror tablets
STAGE FOUR: PRODUCTION OF THE BASE
PLATE
A circular disc with a diameter equal to the
diameter of the circular area calculated was cut out
from the 21 mm thick plywood.
Figure 7
STAGE FIVE: ASSEMBLING
The twenty four templates were fixed round the
surface of the circular disc with the aid of the 40 mm
wood screws. Each Frustum ring was nailed into
position at the right template segment with the aid of
the 15 mm nails. The mirror tablets were glued onto
the surface of the Frustum rings with the aid of evostic
as shown below

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.
Figure 8
THE TRACKING STAND
Table .2 MATERIALS USED FOR THE TRACKING STAND
S/No DESCRIPTION DIMENTION M QTY
1 Galvanized hollow pipe 0 0.05x 3.66 1
2 Galvanized hollow pipe 0 0.45 x 3.66 1
3 Bolts and nuts 0 0.01 x 0.04 8
4 Mild steel flat bar 0.005 x 0.05 x 3.66 1
5 Mild steel angle iron 0.002 x 0.025 x 3.66 1
6 Welding electrode 1pkt
7 Wire mesh 0.35 x 0.35 x 0.002 1
The pipes and flat bars were cut into appropriate dimensions and were joined together to produce the structure
in fig 9.

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Figure 9
The assembly drawing of the FRESNEL collector with the tracking stand is in fig10.

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Figure 10
IV. PERFORMANCE TEST
The Fresnel reflector mounted on its tracking stand
was positioned outside in the north-south direction to
facilitate an east-west tracking of the sun: The reflector
was adjusted by changing the position of the chain at 15
minutes time intervals for altitudinal changes in the
sun’s position. The azimuthal changes were
compensated for by rotating the stand. A black painted
aluminumdisc15cm in diameter and 1cm thickness was
placed at the focal point. Thermocouple wires were
attached to the Aluminum disc.AComark digital
thermometer was used for the readout. The reflector
was able to raise the temperature of the aluminum disc
to an average of 300o
C
V. DISCUSSION
A critical analysis of the results derived with the
aluminum disc showed that the reflector was able to
raise the temperature of the disc to an average
temperature of 300o
C. It was also able to boil 3kg of
water within an average time of 30 minutes for tests
carried out between 10.00 am and 1.00 pm. For tests
carried out between 12 pm and 3 pm an average water
boiling time of 24-28 minutes were recorded. The
difference in the boiling time could be traced to the fact
that solar intensity is normally higher during the
afternoons than in the mornings. This therefore shows
that the temperature generated with the Fresnel
reflector is directly related to the weather condition of
the time and day of testing.
VI. RECOMMENDATION FOR
FURTHER WORKS
Since the performance of the reflector is strictly
connected to the weather more efficient reflectors that
can produce higher temperature should be developed
and used. The fragile mirrors used as reflectors should
be replaced with developed flat sheets electroplated
with shinning surfaces. Automatic tracking mechanism
should also be developed and incorporated to make the
tracking less labour intensive.
VII. CONCLUSION
From the results obtained when the reflector was
used, it performed satisfactorily and did not deviate
much from the initial assumption made during the
designing stage. The reflector uses an energy that has
been generally accepted as the most promising,
renewable and non-polluting type of energy. The
reflector can also be produced using local materials and
does not involve complex constructional techniques.
The energy it uses is so decentralized that any user can

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use it without having to transport it to the sight of use.
The energy it uses is also free. Since its performance
isfavourable, it should be used for cooking in Africa.
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[4.] Halacy Beth and Dan (1978): The Solar
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Development of a Solar Fresnel Reflector and Its Tracking Stand Using Local Material

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