149
Increasing the efficiency of a solar oven
aBstract
e objective of this experiment was to design, build and
evaluate a solar oven that was both economically viable
and thermally ecient. In addition to the economic
objective, I sought to determine the best reector
angle for the solar cooker, by measuring the following
parameters: cooking power, eciency, and eectiveness.
Halogen lamps were used to simulate natural sunlight,
as the outdoor condition was too variable in the UK
to guarantee continued sunlight for 120 minutes in a
controlled fashion. e most eective reector angle i.e.
the reector angle with the greatest ability to convert
the solar insolation into thermal energy is the 60°C.
However, the data shows that the 70°C reector angle
produces the highest temperature consistently. Over the
series of dierent methods for evaluating the best reector
and angle, it would seem that a 70°C angle is consistently
highest in most of the test. With a reector angle of 70°C,
by 120 minutes, the solar oven was able to heat a pan of
water to 78°.
Keywords: solar, energy, oven, box, eciency, Global
Warming
resumen
El objetivo de esta investigación fue diseñar, construir y
evaluar un horno solar que fuera económicamente viable y
térmicamente eciente. Además del objetivo económico,
se buscó determinar el mejor ángulo de reector para
la cocina solar, midiendo los siguientes parámetros:
potencia de cocción, eciencia y efectividad. Se utilizaron
lámparas de halógeno para simular la luz solar natural, ya
que la condición al aire libre era demasiado variable en el
Reino Unido para garantizar la continuidad de la luz solar
durante 120 minutos de manera controlada. El ángulo
del reector que ofrece mayor capacidad para convertir la
insolación solar en energía térmica fue de 60 grados. Sin
embargo, los datos muestran que el ángulo del reector
de 70 °C produce una temperatura mayor y, a la vez,
constante. Con un ángulo de reector de 70 grados, por
120 minutos, el horno solar fue capaz de calentar una
cacerola con agua a 78°C.
Palabras clave: solar,energía, horno,caja,rendimiento,
calentamientoglobal
J T-R
1 University of Plymouth United
Kingdom
rowe@plymouyh.ac.uk
Aumentando la eciencia de un horno solar
Recibido: julio 11 de 2017 | Revisado: setiembre 16 de 2017 | Aceptado: octubre 14 de 2017
| C | L, | V. XX II | N. 24 | PP. - | - | | -
https://doi.org/10.24265/campus.2017.v22n24.01
150
| C | V. XXII | N. 24 | - | 2017 |
Introduction
e rst recorded design of a solar
oven was in 1767 by a Swiss naturalist
named Horace de Saussure. Most of his
experiments were not concerned with
solar ovens directly but with the nature
of solar energy (Arenas, 2007), he
managed to generate temperatures of
approximately 88 °C (Layton, 2017).
After this date, there were records from
1894 of the concept used by British
soldiers in India on-board boats on
long voyages, but these were mainly
isolated cases (ibid). It was not until
the 1950’ s that the concept became
formalised.
e inherent instability in oil prices
due to the complex and ad-hoc nature of
socio-economic and global politics has
left many people in developing nations to
choose between purchasing fuel and food
on a daily basis. is would be less of an
issue if it were not for the fact that globally
2.8 billion people live on less than $2 a
day (World Bank, 2001). e collection
of biomass (typically wood) for fuel is
contributing to increased desertication,
deforestation, soil erosion and depletion
of biodiversity in ecosystems (Bowman,
1985). Moreover, this practise promotes
the use of a resource that could otherwise
be utilised for building material or
fertilizer. In this regard, in relation to
deforestation Suharta, Seifert, and Sayigh
(2006) commented: rough the 1990s
the annual net loss [of forest] was 9
million hectares per year and down to 7.3
million ha/year between 2000 and 2005.
is gure in itself is striking, but is also
compounded by the fact that forests also
act as a carbon sink.
In the case where groups of people are
reliant on primary fuels such as rened
petrochemicals like propane, petrol etc.,
it is accelerating global warming and
restricting the conservation of primary
fuels for alternative uses such as making
plastics or other purposes. Taking this into
account, the rationale of this paper is that
some of the detrimental eects of burning
biofuels or rened petrochemicals can be
ameliorated by the use of inexpensive
solar technology. e use of a solar oven
can relieve or contribute to lessening the
time and eort needed to collect biomass
or other fuel, whilst also diminishing
the production of CO and CO
2
thus
reducing the impact on the environment.
If designed and built correctly, “It is
estimated that a solar cooker on average
would save 3.7 tonnes a year of CO
2
”
(Seifert, 1999), that would otherwise
be generated by burning biomass.
Solar ovens could also contribute to
pasteurising and purifying water sources
that are contaminated and undrinkable,
and so consequently oer additional
functionalities than heating.
As such, the use of carbon-based fuel
is becoming a large contributing factor
to the depletion and strain on global
fuel reserves. Solar ovens use no fossil
fuel; consequently, it is my contention
that they have a role to play in reducing
fuel poverty in developing nations and
reducing their dependence on inated
and erratically priced foreign fuel
imports. As global energy consumption
is forecast to in increase by 1.6% by the
International Energy Agency per annum
until 2030 (Aswathanarayana & Divi,
2009) and that global oil consumption
J T-R
150
| C | V. XXII | N. 24 | - | 2017 |
Introduction
e rst recorded design of a solar
oven was in 1767 by a Swiss naturalist
named Horace de Saussure. Most of his
experiments were not concerned with
solar ovens directly but with the nature
of solar energy (Arenas, 2007), he
managed to generate temperatures of
approximately 88 °C (Layton, 2017).
After this date, there were records from
1894 of the concept used by British
soldiers in India on-board boats on
long voyages, but these were mainly
isolated cases (ibid). It was not until
the 1950’ s that the concept became
formalised.
e inherent instability in oil prices
due to the complex and ad-hoc nature of
socio-economic and global politics has
left many people in developing nations to
choose between purchasing fuel and food
on a daily basis. is would be less of an
issue if it were not for the fact that globally
2.8 billion people live on less than $2 a
day (World Bank, 2001). e collection
of biomass (typically wood) for fuel is
contributing to increased desertication,
deforestation, soil erosion and depletion
of biodiversity in ecosystems (Bowman,
1985). Moreover, this practise promotes
the use of a resource that could otherwise
be utilised for building material or
fertilizer. In this regard, in relation to
deforestation Suharta, Seifert, and Sayigh
(2006) commented: rough the 1990s
the annual net loss [of forest] was 9
million hectares per year and down to 7.3
million ha/year between 2000 and 2005.
is gure in itself is striking, but is also
compounded by the fact that forests also
act as a carbon sink.
In the case where groups of people are
reliant on primary fuels such as rened
petrochemicals like propane, petrol etc.,
it is accelerating global warming and
restricting the conservation of primary
fuels for alternative uses such as making
plastics or other purposes. Taking this into
account, the rationale of this paper is that
some of the detrimental eects of burning
biofuels or rened petrochemicals can be
ameliorated by the use of inexpensive
solar technology. e use of a solar oven
can relieve or contribute to lessening the
time and eort needed to collect biomass
or other fuel, whilst also diminishing
the production of CO and CO
2
thus
reducing the impact on the environment.
If designed and built correctly, “It is
estimated that a solar cooker on average
would save 3.7 tonnes a year of CO
2
”
(Seifert, 1999), that would otherwise
be generated by burning biomass.
Solar ovens could also contribute to
pasteurising and purifying water sources
that are contaminated and undrinkable,
and so consequently oer additional
functionalities than heating.
As such, the use of carbon-based fuel
is becoming a large contributing factor
to the depletion and strain on global
fuel reserves. Solar ovens use no fossil
fuel; consequently, it is my contention
that they have a role to play in reducing
fuel poverty in developing nations and
reducing their dependence on inated
and erratically priced foreign fuel
imports. As global energy consumption
is forecast to in increase by 1.6% by the
International Energy Agency per annum
until 2030 (Aswathanarayana & Divi,
2009) and that global oil consumption
J T-R
151
| C | V. XXII | N. 24 | - | 2017 |
grew by 1.1% in 2007, or 1 million
barrels per day (b/d) slightly below the
10-year average (ibid). As such, the near
future is that fuel poverty will become a
standardised trend, so reducing fossil fuel
use and conserving land resources will
continue to be an important factor in
both developing and developed nations.
Due to this, there are a number of schemes
run by NGO’s trying to promote the use
of solar ovens.
erefore, to work towards improving
the eciency and diversication of these
devices, which would give more time
and freedom to people in developing
nations. Who are becoming increasingly
dependent on using fuel that is priced
beyond their economic abilities?
Additional, the assembly, dissemination
and use of solar cookers creates jobs and
would be upholding and promoting the
spirit of Article 12 of Kyoto Protocol in
poverty alleviation which states:
‾ To assist Non-Annex 1 countries
(developing countries) in achieving
sustainable development.
‾ To assist Annex 1 countries in
achieving their emission reduction
commitments. (Suharta, Seifert, and
Sayigh 2006)
e objective here was to design
and construct an economically viable
solar oven and evaluate the eect of
dierent external reector angles on the
eciency of the oven.
Solar Oven Design
Solar ovens are box-like structures
that concentrate natural sunlight using
reectors to heat water. Solar cookers are
a useful alternative to carbon fuel use, and
its eects on deforestation and climate
change. e ethos behind the design of
the solar oven is driven by the compromise
between economics and eciency.
us, to make the design of the product
sustainable and applicable for developing
nations we must employ Ockham’s razor:
‘Entities should not be multiplied
unnecessarily’ (Encyclopædia Britannica
2015)
A truncated pyramid design has been
chosen because it minimises the surface
area for thermal energy to dissipate,
whilst widening the aperture of the
glass window making a larger solar
interception area. Reducing the net heat
loss and increasing eciency (see Figures
below). e solar cooker will have a
relatively low height reducing heat loss
rising through conduction. e unit
will have reectors to channel the solar
energy towards the apex of the truncated
pyramid along its zenith angle. As the
unit was tested in controlled ambient
conditions, the wind load is no object
to stability consequently; the reectors
will be made large to channel as much
radiant energy as possible. e design
of the solar cooker can be found in the
scheme below.
I
152
Cubic Frame
Volume of a cube
Truncated pyramid Bird’s Eye View
Volume of a Truncated Pyramid
Where h = height of pyramid (0.4m)
a = top width of pyramid (0.2m)
b = bottom width of pyramid (0.5m)
cbaV
cube
a=0.5m
b=0.5m
c=0.5m
3
125.0
5.05.05.0
mV
V
cube
cube
m=meters
Cubic Frame
Volume of a cube
Truncated pyramid Bird’s Eye View
Volume of a Truncated Pyramid
Cubic Frame
Volume of a cube
Truncated pyramid Bird’s Eye View
Volume of a Truncated Pyramid
Where h = height of pyramid (0.4m)
a = top width of pyramid (0.2m)
b = bottom width of pyramid (0.5m)
cbaV
cube
a=0.5m
b=0.5m
c=0.5m
3
125.0
5.05.05.0
mV
V
cube
cube
m=meters
Where h = height of pyramid (0.4m)
a = top width of pyramid (0.2m)
b = bottom width of pyramid (0.5m)
3
22
22
1.0
3
3.0
)75.0(4.0
3
1
)25.01.04.0(4.0
3
1
)5.05.02.02.0(4.0
3
1
)(
3
1
mv
v
v
v
v
bbaahv
pyram
Inter volumetric space between cube and pyramid =
pyramcube
vv
3
int
25.0
1.0125.0
mv
vv
er
pyramcube
Full Design
Choice of Materials for Unit
The materials used should be cost-effective but also available in developing
nations and hence replaceable, non-toxic and economically viable. They should be
easy to repair and maintain. This is because the persons who would be the
J T-R
| C | V. XXII | N. 24 | - | 2017 |
152
Cubic Frame
Volume of a cube
Truncated pyramid Bird’s Eye View
Volume of a Truncated Pyramid
Where h = height of pyramid (0.4m)
a = top width of pyramid (0.2m)
b = bottom width of pyramid (0.5m)
cbaV
cube
a=0.5m
b=0.5m
c=0.5m
3
125.0
5.05.05.0
mV
V
cube
cube
m=meters
Cubic Frame
Volume of a cube
Truncated pyramid Bird’s Eye View
Volume of a Truncated Pyramid
Cubic Frame
Volume of a cube
Truncated pyramid Bird’s Eye View
Volume of a Truncated Pyramid
Where h = height of pyramid (0.4m)
a = top width of pyramid (0.2m)
b = bottom width of pyramid (0.5m)
cbaV
cube
a=0.5m
b=0.5m
c=0.5m
3
125.0
5.05.05.0
mV
V
cube
cube
m=meters
Where h = height of pyramid (0.4m)
a = top width of pyramid (0.2m)
b = bottom width of pyramid (0.5m)
3
22
22
1.0
3
3.0
)75.0(4.0
3
1
)25.01.04.0(4.0
3
1
)5.05.02.02.0(4.0
3
1
)(
3
1
mv
v
v
v
v
bbaahv
pyram
Inter volumetric space between cube and pyramid =
pyramcube
vv
3
int
25.0
1.0125.0
mv
vv
er
pyramcube
Full Design
Choice of Materials for Unit
The materials used should be cost-effective but also available in developing
nations and hence replaceable, non-toxic and economically viable. They should be
easy to repair and maintain. This is because the persons who would be the
J T-R
| C | V. XXII | N. 24 | - | 2017 |
153
Inter volumetric space between cube and pyramid =
Full Design
3
22
22
1.0
3
3.0
)75.0(4.0
3
1
)25.01.04.0(4.0
3
1
)5.05.02.02.0(4.0
3
1
)(
3
1
mv
v
v
v
v
bbaahv
pyram
Inter volumetric space between cube and pyramid =
pyramcube
vv
3
int
25.0
1.0125.0
mv
vv
er
pyramcube
Full Design
Choice of Materials for Unit
The materials used should be cost-effective but also available in developing
nations and hence replaceable, non-toxic and economically viable. They should be
easy to repair and maintain. This is because the persons who would be the
pyramcube
vv −
3
22
22
1.0
3
3.0
)75.0(4.0
3
1
)25.01.04.0(4.0
3
1
)5.05.02.02.0(4.0
3
1
)(
3
1
mv
v
v
v
v
bbaahv
pyram
Inter volumetric space between cube and pyramid =
pyramcube
vv
3
int
25.0
1.0125.0
mv
vv
er
pyramcube
Full Design
Choice of Materials for Unit
The materials used should be cost-effective but also available in developing
nations and hence replaceable, non-toxic and economically viable. They should be
easy to repair and maintain. This is because the persons who would be the
Choice of Materials for Unit
e materials used should be cost-
eective but also available in developing
nations and hence replaceable, non-toxic
and economically viable. ey should
be easy to repair and maintain. is is
because the persons who would be the
recipients of the unit would typically have
low per capita income and less facilities
and infrastructure than developed
nations. One of the contradictions of
solar ovens is that the people designed
to help cannot aord them. I have
attempted to overcome this, once more
by applying Ockham’s Razor.
Equipment list
• Wood panel 2.6m
2
jigsaw, wood
glue, door knobs
• 6 non-ush hinges, power drill,
glass, wood and glass sealant
• Wood screws, baking foil, insulation,
hand saw, pan
Mass of water to be used in the
Solar Oven
In the paper Testing and Reporting
Solar Cooker Performance by the American
Society for Agricultural Engineers, based
on the test standards set at the ird
World Conference on Solar Cooking it
states in section 6.1 Loading, that:
“Cookers shall have 7,000 grams potable
water per square meter intercept area
distributed evenly between the cooking
vessels supplied with the cooker.” (ASAE,
2003, p. 3). is will serve as the basis for
calculations of the mass of water required
in testing the unit. e diagram below
illustrates the intercept area dimensions
of the unit and of an internal reector.
I
| C | V. XXII | N. 24 | - | 2017 |
154
recipients of the unit would typically have low per capita income and less facilities
and infrastructure than developed nations. One of the contradictions of solar ovens
is that the people designed to help cannot afford them. I have attempted to
overcome this, once more by applying Ockham’s Razor.
Equipment list
Wood panel 2.6m
2
jigsaw, wood glue, door knobs
6 non-flush hinges, power drill, glass, wood and glass sealant
Wood screws, baking foil, insulation, hand saw, pan
Mass of water to be used in the Solar Oven
In the paper Testing and Reporting Solar Cooker Performance by the American
Society for Agricultural Engineers, based on the test standards set at the Third
World Conference on Solar Cooking it states in section 6.1 Loading, that: “Cookers
shall have 7,000 grams potable water per square meter intercept area distributed
evenly between the cooking vessels supplied with the cooker.” (ASAE, 2003, p. 3).
This will serve as the basis for calculations of the mass of water required in testing
the unit. The diagram below illustrates the intercept area dimensions of the unit
and of an internal reflector.
Area of square intercept = 0.5m x 0.5m
Area = 0.25m
2
Area of internal reflector = (area of right angle triangle) x 2 + Area of rectangle
Area of Right angle triangle = 0.5 x (length x width)
= 0.5 x (0.15 x 0.20)
= 0.03 m
2
Multiplied by 2 = 0.06 m
2
Area of rectangle = 0.20 x 0.40
= 0.08 m
2
Area of square intercept = 0.5m x 0.5m = 0.25m
2
Area of internal reector = (area of right angle triangle) x 2 + Area of rectangle
Area of Right angle triangle = 0.5 x (length x width) = 0.03 m
2
Multiplied by 2 = 0.06 m
2
Area of rectangle = 0.20 x 0.40 = 0.08 m
2
Reector area = 0.14m
2
Intercept area = square intercept area – internal reector area
Intercept area = 0.11m
2
Calculation of Mass of Water
Mass of water = 0.77 kg/m
2
e area of the internal reector and
square intercept has been taken into
account because the standardised method
is based on the use of a square box cooker
without an internal reector. e exact
denition in the research literature of the
intercept area is “e sum of the [external]
reector and aperture areas projected onto
the plane perpendicular to direct beam
radiation” (ASAE, 2003, p. 2).
However,
in the experiment the parameter being
varied is that external reector angle,
which consequently changes the area of
the intercept area meaning that the mass
of water would have to vary with each
replicate. is would make the results of
each replicate incompatible with each other
when trying to analyse them, as the load
of water would change for each one. So
instead of taking into account the external
reector, the internal reector, which is
stationary has been considered instead.
However, the internal reector reduces
intercept area so instead of summing the
two values of the square aperture and
internal reector have been deducted in
calculating the mass of water required.
Unit Assembly Method
e wood for the exterior cubic frame
and truncated pyramid was purchased
based on the design plan area, which
was 1.5 m
2
. e wood intended is an
area of 2.6 m
2
allowing for errors in the
woods cutting if needed. Five squares of
dimension 0.5X0.5 m
2
were cut for the
cubic frame; the dimensions were pre-
marked out on the wood surface and cut
with a jigsaw. Followed by 4 truncated
triangles to the specication shown in
the design and a 0.20X0.20 cm square
for the truncated pyramid top, all cut
with a jigsaw and shaved to specication
if cutting was inaccurate. Following the
cutting four small non-ush hinges and
wood screws were used to construct the
truncated pyramid, hinging together the
J T-R
| C | V. XXII | N. 24 | - | 2017 |
154
recipients of the unit would typically have low per capita income and less facilities
and infrastructure than developed nations. One of the contradictions of solar ovens
is that the people designed to help cannot afford them. I have attempted to
overcome this, once more by applying Ockham’s Razor.
Equipment list
Wood panel 2.6m
2
jigsaw, wood glue, door knobs
6 non-flush hinges, power drill, glass, wood and glass sealant
Wood screws, baking foil, insulation, hand saw, pan
Mass of water to be used in the Solar Oven
In the paper Testing and Reporting Solar Cooker Performance by the American
Society for Agricultural Engineers, based on the test standards set at the Third
World Conference on Solar Cooking it states in section 6.1 Loading, that: “Cookers
shall have 7,000 grams potable water per square meter intercept area distributed
evenly between the cooking vessels supplied with the cooker.” (ASAE, 2003, p. 3).
This will serve as the basis for calculations of the mass of water required in testing
the unit. The diagram below illustrates the intercept area dimensions of the unit
and of an internal reflector.
Area of square intercept = 0.5m x 0.5m
Area = 0.25m
2
Area of internal reflector = (area of right angle triangle) x 2 + Area of rectangle
Area of Right angle triangle = 0.5 x (length x width)
= 0.5 x (0.15 x 0.20)
= 0.03 m
2
Multiplied by 2 = 0.06 m
2
Area of rectangle = 0.20 x 0.40
= 0.08 m
2
Area of square intercept = 0.5m x 0.5m = 0.25m
2
Area of internal reector = (area of right angle triangle) x 2 + Area of rectangle
Area of Right angle triangle = 0.5 x (length x width) = 0.03 m
2
Multiplied by 2 = 0.06 m
2
Area of rectangle = 0.20 x 0.40 = 0.08 m
2
Reector area = 0.14m
2
Intercept area = square intercept area – internal reector area
Intercept area = 0.11m
2
Calculation of Mass of Water
Mass of water = 0.77 kg/m
2
e area of the internal reector and
square intercept has been taken into
account because the standardised method
is based on the use of a square box cooker
without an internal reector. e exact
denition in the research literature of the
intercept area is “e sum of the [external]
reector and aperture areas projected onto
the plane perpendicular to direct beam
radiation” (ASAE, 2003, p. 2).
However,
in the experiment the parameter being
varied is that external reector angle,
which consequently changes the area of
the intercept area meaning that the mass
of water would have to vary with each
replicate. is would make the results of
each replicate incompatible with each other
when trying to analyse them, as the load
of water would change for each one. So
instead of taking into account the external
reector, the internal reector, which is
stationary has been considered instead.
However, the internal reector reduces
intercept area so instead of summing the
two values of the square aperture and
internal reector have been deducted in
calculating the mass of water required.
Unit Assembly Method
e wood for the exterior cubic frame
and truncated pyramid was purchased
based on the design plan area, which
was 1.5 m
2
. e wood intended is an
area of 2.6 m
2
allowing for errors in the
woods cutting if needed. Five squares of
dimension 0.5X0.5 m
2
were cut for the
cubic frame; the dimensions were pre-
marked out on the wood surface and cut
with a jigsaw. Followed by 4 truncated
triangles to the specication shown in
the design and a 0.20X0.20 cm square
for the truncated pyramid top, all cut
with a jigsaw and shaved to specication
if cutting was inaccurate. Following the
cutting four small non-ush hinges and
wood screws were used to construct the
truncated pyramid, hinging together the
J T-R
| C | V. XXII | N. 24 | - | 2017 |
155
four truncated triangles cut to their base.
eir sides were cut at a 45° angle so as
to ensure they form a square at their top
when raised together. After this, the ve
panels of the cubic frame were screwed
together using blocks joining two panels
together, a picture showing the blocks in
the unit is shown in Figure 2.
After this, the five panels of the cubic frame were screwed together using blocks
joining two panels together, a picture showing the blocks in the unit is shown in
Figure 2.
Figure 2. Joining blocks linking wood panels in the solar cooker
On the last panel to be assembled in the cubic frame, a door was made for an
entry hatch to introduce the pan of water, which was boiled. The size of the hatch
is determined from the width and height of the pan, making it possible to be taken
in and out with ease but not so large as to create unnecessary heat loss in the
unit. After all the five panels in the cubic frame were assembled, they were sealed
using a caulk sealant to reduce heat loss in the unit. The door in the truncated
pyramid to introduce the pan was cut next. Once the door was cut and assembled
the truncated pyramid was fitted inside the cube frame as shown in Figure 3.
Figure 3. Truncated pyramid inserted into main solar oven cube
Figure 2. Joining blocks linking wood panels in the solar
cooker
On the last panel to be assembled in the
cubic frame, a door was made for an
entry hatch to introduce the pan of water,
which was boiled. e size of the hatch is
determined from the width and height of
the pan, making it possible to be taken in
and out with ease but not so large as to
create unnecessary heat loss in the unit.
After all the ve panels in the cubic frame
were assembled, they were sealed using a
caulk sealant to reduce heat loss in the
unit. e door in the truncated pyramid
to introduce the pan was cut next. Once
the door was cut and assembled the
truncated pyramid was tted inside the
cube frame as shown in Figure 3.
After this, the five panels of the cubic frame were screwed together using blocks
joining two panels together, a picture showing the blocks in the unit is shown in
Figure 2.
Figure 2. Joining blocks linking wood panels in the solar cooker
On the last panel to be assembled in the cubic frame, a door was made for an
entry hatch to introduce the pan of water, which was boiled. The size of the hatch
is determined from the width and height of the pan, making it possible to be taken
in and out with ease but not so large as to create unnecessary heat loss in the
unit. After all the five panels in the cubic frame were assembled, they were sealed
using a caulk sealant to reduce heat loss in the unit. The door in the truncated
pyramid to introduce the pan was cut next. Once the door was cut and assembled
the truncated pyramid was fitted inside the cube frame as shown in Figure 3.
Figure 3. Truncated pyramid inserted into main solar oven cube
Figure 3. Truncated pyramid inserted into main solar oven
cube
I
| C | V. XXII | N. 24 | - | 2017 |
e edges of the truncated pyramid
were cut and trimmed to the correct size to
t inside the cube frame using a handsaw
and plane for minor adjustments,
leaving a gap at the top for the pane of
glass. e four faces of the truncated
156
pyramid were coated in PVA glue and
baking foil attached to them acting as a
reective surface concentrating the solar
radiation onto the central cooking pot.
e insulation was tightly packed into
the 0.25m
3
inter-space gap between the
pyramid and the cubic frame. is was
to increase the heat retention of the unit
and secure the position of the inverted
truncated pyramid placed upon the
insulation. With this in place the glass
was sized, cut and tted into the top of
the unit and sealed in place with glass
sealant to reduce heat loss through the
top of unit. Next, the external reectors
were made from cardboard, PVA glue
and more baking foil in the same manner
as the internal reectors.
External Reector Design
From the research literature on the
international conventions for solar
cookers, found in Funk (2000) there
are no specications for the design of
the external reectors as such their
dimensions were based on a design made
by myself. e design of the external
reectors for the unit will mirror the
proportions of the internal reectors
in terms of height and smallest width.
e hypotenuse and largest width will
vary between replicates as reector angle
varies (Figure 4).
The edges of the truncated pyramid were cut and trimmed to the correct
size to fit inside the cube frame using a handsaw and plane for minor adjustments,
leaving a gap at the top for the pane of glass. The four faces of the truncated
pyramid were coated in PVA glue and baking foil attached to them acting as a
reflective surface concentrating the solar radiation onto the central cooking pot.
The insulation was tightly packed into the 0.25m
3
inter-space gap between the
pyramid and the cubic frame. This was to increase the heat retention of the unit
and secure the position of the inverted truncated pyramid placed upon the
insulation. With this in place the glass was sized, cut and fitted into the top of the
unit and sealed in place with glass sealant to reduce heat loss through the top of
unit. Next, the external reflectors were made from cardboard, PVA glue and more
baking foil in the same manner as the internal reflectors.
External Reflector Design
From the research literature on the international conventions for solar
cookers, found in Funk (2000) there are no specifications for the design of the
external reflectors as such their dimensions were based on a design made by
myself. The design of the external reflectors for the unit will mirror the proportions
of the internal reflectors in terms of height and smallest width. The hypotenuse and
largest width will vary between replicates as reflector angle varies (Figure 4).
Figure 4. The dimensions of an individual truncated pyramid
The external reflectors were made from cardboard and with baking foil
glued to them to create a reflective surface. Each replicate (i.e. per reflector angle)
had to have a different set of cardboards cut as the angle φ varies. The external
reflector will be the sum of four individual truncated triangles that will be attached
to together with duct tape to keep the specific angle required (φ) in place.
Figure 5. Schematic of external reflector dimensions and angles mounted on the unit
Figure 4. The dimensions of an individual
truncated pyramid
e external reectors were made from
cardboard and with baking foil glued to
them to create a reective surface. Each
replicate (i.e. per reector angle) had to
have a dierent set of cardboards cut as
the angle varies. e external reector will
be the sum of four individual truncated
triangles that will be attached to together
with duct tape to keep the specic angle
required (φ) in place.
Figure 5. Schematic of external reflector dimensions and angles mounted on the unit
The reflectors will also be held in place with string attached to alternate sides of
the cardboard frame, which can be adjusted if needed to alter the angles (Figure
5). The string will cause small amounts of shading from the light source in the
experiment but because the string is so thin, its effects will be minimal.
Project Limitations to en mass Dissemination and Use
There is an inherent lack of versatility in the design that I have produced
because it can only cook for a small number of people. Communal cooking and
larger families are more common in developing nations. So building a more
culturally relevant design is required. The design is only suitable for slow cooking
due to its thermodynamic inefficiencies and cannot compete with the convenience
of fast burning primary fuels. It can only be used efficiently in direct sunlight, and
requires continual realignment with the sun’s declination and ascension in the sky.
The reflectors on the unit are easily scratched which reduces the reflectivity and
effectiveness. The mass and dimensions of the design may be a deterrent to its
use as it is not easily mobile. There is an additional economic problem of replacing
the reflectors and other materials that break, which needs to be considered. This
comes with the limitation that in remote places the materials may not be able to be
obtained; even if this is possible, there may not be a person available with the
skills or knowledge to repair the unit. These additional costs could drive up the
price of the unit to comparable levels of purchasing fossil fuels making the whole
project redundant. Culturally there has been some documented resistance to solar
cookers, as they may be at odds with religious or cultural beliefs, and also involve
a change from traditional methods of cooking by the people using the unit (Coyle,
J T-R
| C | V. XXII | N. 24 | - | 2017 |
e reectors will also be held in
place with string attached to alternate
sides of the cardboard frame, which can
be adjusted if needed to alter the angles
(Figure 5). e string will cause small
amounts of shading from the light source
in the experiment but because the string
is so thin, its eects will be minimal.
156
pyramid were coated in PVA glue and
baking foil attached to them acting as a
reective surface concentrating the solar
radiation onto the central cooking pot.
e insulation was tightly packed into
the 0.25m
3
inter-space gap between the
pyramid and the cubic frame. is was
to increase the heat retention of the unit
and secure the position of the inverted
truncated pyramid placed upon the
insulation. With this in place the glass
was sized, cut and tted into the top of
the unit and sealed in place with glass
sealant to reduce heat loss through the
top of unit. Next, the external reectors
were made from cardboard, PVA glue
and more baking foil in the same manner
as the internal reectors.
External Reector Design
From the research literature on the
international conventions for solar
cookers, found in Funk (2000) there
are no specications for the design of
the external reectors as such their
dimensions were based on a design made
by myself. e design of the external
reectors for the unit will mirror the
proportions of the internal reectors
in terms of height and smallest width.
e hypotenuse and largest width will
vary between replicates as reector angle
varies (Figure 4).
The edges of the truncated pyramid were cut and trimmed to the correct
size to fit inside the cube frame using a handsaw and plane for minor adjustments,
leaving a gap at the top for the pane of glass. The four faces of the truncated
pyramid were coated in PVA glue and baking foil attached to them acting as a
reflective surface concentrating the solar radiation onto the central cooking pot.
The insulation was tightly packed into the 0.25m
3
inter-space gap between the
pyramid and the cubic frame. This was to increase the heat retention of the unit
and secure the position of the inverted truncated pyramid placed upon the
insulation. With this in place the glass was sized, cut and fitted into the top of the
unit and sealed in place with glass sealant to reduce heat loss through the top of
unit. Next, the external reflectors were made from cardboard, PVA glue and more
baking foil in the same manner as the internal reflectors.
External Reflector Design
From the research literature on the international conventions for solar
cookers, found in Funk (2000) there are no specifications for the design of the
external reflectors as such their dimensions were based on a design made by
myself. The design of the external reflectors for the unit will mirror the proportions
of the internal reflectors in terms of height and smallest width. The hypotenuse and
largest width will vary between replicates as reflector angle varies (Figure 4).
Figure 4. The dimensions of an individual truncated pyramid
The external reflectors were made from cardboard and with baking foil
glued to them to create a reflective surface. Each replicate (i.e. per reflector angle)
had to have a different set of cardboards cut as the angle φ varies. The external
reflector will be the sum of four individual truncated triangles that will be attached
to together with duct tape to keep the specific angle required (φ) in place.
Figure 5. Schematic of external reflector dimensions and angles mounted on the unit
Figure 4. The dimensions of an individual
truncated pyramid
e external reectors were made from
cardboard and with baking foil glued to
them to create a reective surface. Each
replicate (i.e. per reector angle) had to
have a dierent set of cardboards cut as
the angle varies. e external reector will
be the sum of four individual truncated
triangles that will be attached to together
with duct tape to keep the specic angle
required (φ) in place.
Figure 5. Schematic of external reflector dimensions and angles mounted on the unit
The reflectors will also be held in place with string attached to alternate sides of
the cardboard frame, which can be adjusted if needed to alter the angles (Figure
5). The string will cause small amounts of shading from the light source in the
experiment but because the string is so thin, its effects will be minimal.
Project Limitations to en mass Dissemination and Use
There is an inherent lack of versatility in the design that I have produced
because it can only cook for a small number of people. Communal cooking and
larger families are more common in developing nations. So building a more
culturally relevant design is required. The design is only suitable for slow cooking
due to its thermodynamic inefficiencies and cannot compete with the convenience
of fast burning primary fuels. It can only be used efficiently in direct sunlight, and
requires continual realignment with the sun’s declination and ascension in the sky.
The reflectors on the unit are easily scratched which reduces the reflectivity and
effectiveness. The mass and dimensions of the design may be a deterrent to its
use as it is not easily mobile. There is an additional economic problem of replacing
the reflectors and other materials that break, which needs to be considered. This
comes with the limitation that in remote places the materials may not be able to be
obtained; even if this is possible, there may not be a person available with the
skills or knowledge to repair the unit. These additional costs could drive up the
price of the unit to comparable levels of purchasing fossil fuels making the whole
project redundant. Culturally there has been some documented resistance to solar
cookers, as they may be at odds with religious or cultural beliefs, and also involve
a change from traditional methods of cooking by the people using the unit (Coyle,
J T-R
| C | V. XXII | N. 24 | - | 2017 |
e reectors will also be held in
place with string attached to alternate
sides of the cardboard frame, which can
be adjusted if needed to alter the angles
(Figure 5). e string will cause small
amounts of shading from the light source
in the experiment but because the string
is so thin, its eects will be minimal.
157
Project Limitations to en mass
Dissemination and Use
ere is an inherent lack of versatility in
the design that I have produced because it
can only cook for a small number of people.
Communal cooking and larger families are
more common in developing nations. So
building a more culturally relevant design
is required. e design is only suitable for
slow cooking due to its thermodynamic
ineciencies and cannot compete with the
convenience of fast burning primary fuels.
It can only be used eciently in direct
sunlight, and requires continual realignment
with the sun’s declination and ascension in
the sky. e reectors on the unit are easily
scratched which reduces the reectivity and
eectiveness. e mass and dimensions of
the design may be a deterrent to its use as it
is not easily mobile. ere is an additional
economic problem of replacing the reectors
and other materials that break, which needs
to be considered. is comes with the
limitation that in remote places the materials
may not be able to be obtained; even if this is
possible, there may not be a person available
with the skills or knowledge to repair the
unit. ese additional costs could drive up
the price of the unit to comparable levels
of purchasing fossil fuels making the whole
project redundant. Culturally there has been
some documented resistance to solar cookers,
as they may be at odds with religious or
cultural beliefs, and also involve a change
from traditional methods of cooking by the
people using the unit (Coyle, 2006). ere
is an onus to produce ovens that are socially
acceptable; this in itself is troublesome due to
variations in cultural preferences.
Data Analysis - Exergy and Energy
I have tried to make my data analysis
transparent so that it can be compared
with other projects. Consequently, I
have attempted to use analysis methods
in concordance with the standardised
testing procedures set out in the paper by
Ashok Kundapur et al of the International
Alternate Energy Trust, and Kalashree in
his paper, proposal for new world standard
for testing solar cookers, see Kundapur
and Sudhir (2009) which contains the
standardised nomenclature, analysis and
methodology for evaluating solar oven
eciency. Which in turn is a ratication
of the paper Evaluating the international
standard procedure for testing solar cookers
and reporting performance by Funk (2000)
which sets out the ground work for the need
for an international standardization of the
methodologies of solar oven eciency
analysis. e data analysis methodology
includes both exergy and energy analysis,
this is because measuring these quantities
gives results that are thermodynamically
and economically rational, meaningful
and practical (Öztürk, Öztekin &
Başçetinçelik, 2004, p. 1). In addition,
it gives an insight into the quality of the
thermal energy produced, whilst also
tting the ethos of this paper: economic
viability, and thermal eciency.
Experimental conditions in
accordance with Test Standards
Committee at the ird World
Conference on Solar Cooking
(Coimbatore, Tamil Nadu, India, 9
January 1997, see ASAE (1997))
Number of observations
For the purposes of plotting a linear
regression, there needs to be an adequate
number of observations, also to allow the
unit’s performance at dierence levels
to be calculated. In the ASAE paper
S580 Testing and Reporting Solar Cooker
I
| C | V. XXII | N. 24 | - | 2017 |
158
Performance it stipulates that there is
to be a minimum of 30 observations
(ASAE, 2003). e graphics here are
based on 105 observations and for ease
of calculations so will the measurements
of the solar oven be.
Ambient Temperature
e ambient temperature in which
the oven is tested needs to be below 35°C
and not uctuate over a range of 15°C
(Funk, 2000, p. 2).
Insolation
e insolation levels required to
validate the data obtained are to be
between the range of 450 to 1100 w/m
2
and should not vary more than 100 w/
m
2
in a 10 minute interval (Funk, 2000).
e insolation will be measured with a
pyranometer.
Temperature Measurement
e measurement of the water
load and ambient temperature is to be
conducted with a LOGIT thermocouple
(Funk, 2000).
Data analysis methodology
Cooking Power
is value is an indicator of the level
of performance of the cooker, but is not
an absolute guarantee (Funk, 2000). It
corresponds to the ability of the oven to
raise the temperature of a given mass of
water within a 10 minute time interval
(Funk 2000). e equation below is used
to calculate the Cooking Power in Watts,
once more taken from ASAE (2003):
Standardised Cooking Power
is parameter is used as a method
of standardisation for the sake of
comparing data of other tests conducted
in dierent latitudes and times (ibid).
e values of the insolation is normalised
by multiplying the cooking power ( )
by 700 w/m
2
and dividing by the average
insolation over the given interval of 600
seconds (10 minutes), hence it represents
the cooking power per second (Kundapur
& Sudhir, 2009).
(ASAE, 2003)
Nomenclature
- Standardized Cooking Power in Watts
- Cooking Power over the 600 second
interval in watts
- Average Insolation value over the 600
seconds interval in watts
Energy Input of the Cooker
is gure is simply a product of the
average solar insolation and the aperture
area of the solar cooker. Moreover, it is
used in calculating the eciency of the
solar oven (Kundapur &
Sudhir, 2009)
Eciency
e eciency calculation is a function of
the oven’s power in terms of the energy
input into the oven. It is a dimensionless
measurement expressed in percentage the
Ambient Temperature
The ambient temperature in which the oven is tested needs to be below 35°C and
not fluctuate over a range of 15°C (Funk, 2000, p. 2).
Insolation
The insolation levels required to validate the data obtained are to be between the
range of 450 w/m
2
to 1100 w/m
2
and should not vary more than 100 w/m
2
in a 10
minute interval (Funk, 2000). The insolation will be measured with a pyranometer.
Temperature Measurement
The measurement of the water load and ambient temperature is to be conducted
with a LOGIT thermocouple (Funk, 2000).
Data analysis methodology
Cooking Power
This value is an indicator of the level of performance of the cooker, but is not an
absolute guarantee (Funk, 2000). It corresponds to the ability of the oven to raise
the temperature of a given mass of water within a 10 minute time interval (Funk
2000). The equation below is used to calculate the Cooking Power in Watts, once
more taken from ASAE (2003):
21
()
600
v
i
T T MC
P
Standardised Cooking Power
This parameter is used as a method of standardisation for the sake of
comparing data of other tests conducted in different latitudes and times (ibid). The
values of the insolation is normalised by multiplying the cooking power (
i
P
) by 700
w/m
2
and dividing by the average insolation over the given interval of 600 seconds
Nomenclature
Where
i
P
-cookingpowerinWatts
2
T
-Finalwatertemperature°c
1
T
-Initialwatertemperature°c
M
-MassofwaterinKg
-Specificheatcapacityofwater(4186
J/[kg·K])
Ambient Temperature
The ambient temperature in which the oven is tested needs to be below 35°C and
not fluctuate over a range of 15°C (Funk, 2000, p. 2).
Insolation
The insolation levels required to validate the data obtained are to be between the
range of 450 w/m
2
to 1100 w/m
2
and should not vary more than 100 w/m
2
in a 10
minute interval (Funk, 2000). The insolation will be measured with a pyranometer.
Temperature Measurement
The measurement of the water load and ambient temperature is to be conducted
with a LOGIT thermocouple (Funk, 2000).
Data analysis methodology
Cooking Power
This value is an indicator of the level of performance of the cooker, but is not an
absolute guarantee (Funk, 2000). It corresponds to the ability of the oven to raise
the temperature of a given mass of water within a 10 minute time interval (Funk
2000). The equation below is used to calculate the Cooking Power in Watts, once
more taken from ASAE (2003):
21
()
600
v
i
T T MC
P
Standardised Cooking Power
This parameter is used as a method of standardisation for the sake of
comparing data of other tests conducted in different latitudes and times (ibid). The
values of the insolation is normalised by multiplying the cooking power (
i
P
) by 700
w/m
2
and dividing by the average insolation over the given interval of 600 seconds
Nomenclature
Where
i
P
-cookingpowerinWatts
2
T
-Finalwatertemperature°c
1
T
-Initialwatertemperature°c
M
-MassofwaterinKg
-Specificheatcapacityofwater(4186
J/[kg·K])
P
s
= P
i
(700/I
i
)
P
s
P
i
I
i
P
i
(10 minutes), hence it represents the cooking power per second (Kundapur &
Sudhir, 2009).
(700 / )
si i
PP I
(ASAE, 2003)
Nomenclature
s
P
- Standardized Cooking Power in Watts
i
P
- Cooking Power over the 600 second interval in watts
i
I
- Average Insolation value over the 600 seconds interval in watts
Energy Input of the Cooker
This figure is simply a product of the average solar insolation and the aperture
area of the solar cooker. Moreover, it is used in calculating the efficiency of the
solar oven
i aw sc
E IA
(Kundapur & Sudhir, 2009)
Efficiency
The efficiency calculation is
a function of the oven’s
power in terms of the
energy input into the oven.
It is a dimensionless
measurement expressed in
percentage the equation
(Kundapur & Sudhir, 2009),
where:
21
0
w pw
t
sc aw
mC T T
AI t
Exergy
The concept of exergy is roughly equated with the term available work
(Coatanéa, Kuuva, Makkonnen, Saarelainen & Castillòn-Solano, 2006, p. 83) it
“represents quantitatively the ‘useful’ energy or the ability to do work-the work
content of a great variety of streams (mass, heat, work) that flow through the
system” (Dincer & Cengel, 2001, p. 130). The term is difficult to define because it
is dependent upon the environment in which it is used (Demirel, 2002, p. 111). It
Nomenclature
-Efficiencyin%
w
m
-MassofwaterinKg
pw
C
-Specificheatcapacityofwater(4186J/[kg·K])
2
T
-Finalwatertemperaturein°c
1
T
-Initialwatertemperaturein°c
sc
A
-Apertureareaofthesolarcookerinm
2
0
t
aw
I
-IntegralofAverageinsolationovertime-period
t
-Differenceintemperatureambientandwater
temperaturein°c
t-Timebetweeneachinterval
J T-R
| C | V. XXII | N. 24 | - | 2017 |
158
Performance it stipulates that there is
to be a minimum of 30 observations
(ASAE, 2003). e graphics here are
based on 105 observations and for ease
of calculations so will the measurements
of the solar oven be.
Ambient Temperature
e ambient temperature in which
the oven is tested needs to be below 35°C
and not uctuate over a range of 15°C
(Funk, 2000, p. 2).
Insolation
e insolation levels required to
validate the data obtained are to be
between the range of 450 to 1100 w/m
2
and should not vary more than 100 w/
m
2
in a 10 minute interval (Funk, 2000).
e insolation will be measured with a
pyranometer.
Temperature Measurement
e measurement of the water
load and ambient temperature is to be
conducted with a LOGIT thermocouple
(Funk, 2000).
Data analysis methodology
Cooking Power
is value is an indicator of the level
of performance of the cooker, but is not
an absolute guarantee (Funk, 2000). It
corresponds to the ability of the oven to
raise the temperature of a given mass of
water within a 10 minute time interval
(Funk 2000). e equation below is used
to calculate the Cooking Power in Watts,
once more taken from ASAE (2003):
Standardised Cooking Power
is parameter is used as a method
of standardisation for the sake of
comparing data of other tests conducted
in dierent latitudes and times (ibid).
e values of the insolation is normalised
by multiplying the cooking power ( )
by 700 w/m
2
and dividing by the average
insolation over the given interval of 600
seconds (10 minutes), hence it represents
the cooking power per second (Kundapur
& Sudhir, 2009).
(ASAE, 2003)
Nomenclature
- Standardized Cooking Power in Watts
- Cooking Power over the 600 second
interval in watts
- Average Insolation value over the 600
seconds interval in watts
Energy Input of the Cooker
is gure is simply a product of the
average solar insolation and the aperture
area of the solar cooker. Moreover, it is
used in calculating the eciency of the
solar oven (Kundapur &
Sudhir, 2009)
Eciency
e eciency calculation is a function of
the oven’s power in terms of the energy
input into the oven. It is a dimensionless
measurement expressed in percentage the
Ambient Temperature
The ambient temperature in which the oven is tested needs to be below 35°C and
not fluctuate over a range of 15°C (Funk, 2000, p. 2).
Insolation
The insolation levels required to validate the data obtained are to be between the
range of 450 w/m
2
to 1100 w/m
2
and should not vary more than 100 w/m
2
in a 10
minute interval (Funk, 2000). The insolation will be measured with a pyranometer.
Temperature Measurement
The measurement of the water load and ambient temperature is to be conducted
with a LOGIT thermocouple (Funk, 2000).
Data analysis methodology
Cooking Power
This value is an indicator of the level of performance of the cooker, but is not an
absolute guarantee (Funk, 2000). It corresponds to the ability of the oven to raise
the temperature of a given mass of water within a 10 minute time interval (Funk
2000). The equation below is used to calculate the Cooking Power in Watts, once
more taken from ASAE (2003):
21
()
600
v
i
T T MC
P
Standardised Cooking Power
This parameter is used as a method of standardisation for the sake of
comparing data of other tests conducted in different latitudes and times (ibid). The
values of the insolation is normalised by multiplying the cooking power (
i
P
) by 700
w/m
2
and dividing by the average insolation over the given interval of 600 seconds
Nomenclature
Where
i
P
-cookingpowerinWatts
2
T
-Finalwatertemperature°c
1
T
-Initialwatertemperature°c
M
-MassofwaterinKg
-Specificheatcapacityofwater(4186
J/[kg·K])
Ambient Temperature
The ambient temperature in which the oven is tested needs to be below 35°C and
not fluctuate over a range of 15°C (Funk, 2000, p. 2).
Insolation
The insolation levels required to validate the data obtained are to be between the
range of 450 w/m
2
to 1100 w/m
2
and should not vary more than 100 w/m
2
in a 10
minute interval (Funk, 2000). The insolation will be measured with a pyranometer.
Temperature Measurement
The measurement of the water load and ambient temperature is to be conducted
with a LOGIT thermocouple (Funk, 2000).
Data analysis methodology
Cooking Power
This value is an indicator of the level of performance of the cooker, but is not an
absolute guarantee (Funk, 2000). It corresponds to the ability of the oven to raise
the temperature of a given mass of water within a 10 minute time interval (Funk
2000). The equation below is used to calculate the Cooking Power in Watts, once
more taken from ASAE (2003):
21
()
600
v
i
T T MC
P
Standardised Cooking Power
This parameter is used as a method of standardisation for the sake of
comparing data of other tests conducted in different latitudes and times (ibid). The
values of the insolation is normalised by multiplying the cooking power (
i
P
) by 700
w/m
2
and dividing by the average insolation over the given interval of 600 seconds
Nomenclature
Where
i
P
-cookingpowerinWatts
2
T
-Finalwatertemperature°c
1
T
-Initialwatertemperature°c
M
-MassofwaterinKg
-Specificheatcapacityofwater(4186
J/[kg·K])
P
s
= P
i
(700/I
i
)
P
s
P
i
I
i
P
i
(10 minutes), hence it represents the cooking power per second (Kundapur &
Sudhir, 2009).
(700 / )
si i
PP I
(ASAE, 2003)
Nomenclature
s
P
- Standardized Cooking Power in Watts
i
P
- Cooking Power over the 600 second interval in watts
i
I
- Average Insolation value over the 600 seconds interval in watts
Energy Input of the Cooker
This figure is simply a product of the average solar insolation and the aperture
area of the solar cooker. Moreover, it is used in calculating the efficiency of the
solar oven
i aw sc
E IA
(Kundapur & Sudhir, 2009)
Efficiency
The efficiency calculation is
a function of the oven’s
power in terms of the
energy input into the oven.
It is a dimensionless
measurement expressed in
percentage the equation
(Kundapur & Sudhir, 2009),
where:
21
0
w pw
t
sc aw
mC T T
AI t
Exergy
The concept of exergy is roughly equated with the term available work
(Coatanéa, Kuuva, Makkonnen, Saarelainen & Castillòn-Solano, 2006, p. 83) it
“represents quantitatively the ‘useful’ energy or the ability to do work-the work
content of a great variety of streams (mass, heat, work) that flow through the
system” (Dincer & Cengel, 2001, p. 130). The term is difficult to define because it
is dependent upon the environment in which it is used (Demirel, 2002, p. 111). It
Nomenclature
-Efficiencyin%
w
m
-MassofwaterinKg
pw
C
-Specificheatcapacityofwater(4186J/[kg·K])
2
T
-Finalwatertemperaturein°c
1
T
-Initialwatertemperaturein°c
sc
A
-Apertureareaofthesolarcookerinm
2
0
t
aw
I
-IntegralofAverageinsolationovertime-period
t
-Differenceintemperatureambientandwater
temperaturein°c
t-Timebetweeneachinterval
J T-R
| C | V. XXII | N. 24 | - | 2017 |
159
equation (Kundapur & Sudhir, 2009),
where:
(10 minutes), hence it represents the cooking power per second (Kundapur &
Sudhir, 2009).
(700 / )
si i
PP I
(ASAE, 2003)
Nomenclature
s
P
- Standardized Cooking Power in Watts
i
P
- Cooking Power over the 600 second interval in watts
i
I
- Average Insolation value over the 600 seconds interval in watts
Energy Input of the Cooker
This figure is simply a product of the average solar insolation and the aperture
area of the solar cooker. Moreover, it is used in calculating the efficiency of the
solar oven
i aw sc
E IA
(Kundapur & Sudhir, 2009)
Efficiency
The efficiency calculation is
a function of the oven’s
power in terms of the
energy input into the oven.
It is a dimensionless
measurement expressed in
percentage the equation
(Kundapur & Sudhir, 2009),
where:
21
0
w pw
t
sc aw
mC T T
AI t
Exergy
The concept of exergy is roughly equated with the term available work
(Coatanéa, Kuuva, Makkonnen, Saarelainen & Castillòn-Solano, 2006, p. 83) it
“represents quantitatively the ‘useful’ energy or the ability to do work-the work
content of a great variety of streams (mass, heat, work) that flow through the
system” (Dincer & Cengel, 2001, p. 130). The term is difficult to define because it
is dependent upon the environment in which it is used (Demirel, 2002, p. 111). It
Nomenclature
-Efficiencyin%
w
m
-MassofwaterinKg
pw
C
-Specificheatcapacityofwater(4186J/[kg·K])
2
T
-Finalwatertemperaturein°c
1
T
-Initialwatertemperaturein°c
sc
A
-Apertureareaofthesolarcookerinm
2
0
t
aw
I
-IntegralofAverageinsolationovertime-period
t
-Differenceintemperatureambientandwater
temperaturein°c
t-Timebetweeneachinterval
(10 minutes), hence it represents the cooking power per second (Kundapur &
Sudhir, 2009).
(700 / )
si i
PP I
(ASAE, 2003)
Nomenclature
s
P
- Standardized Cooking Power in Watts
i
P
- Cooking Power over the 600 second interval in watts
i
I
- Average Insolation value over the 600 seconds interval in watts
Energy Input of the Cooker
This figure is simply a product of the average solar insolation and the aperture
area of the solar cooker. Moreover, it is used in calculating the efficiency of the
solar oven
i aw sc
E IA
(Kundapur & Sudhir, 2009)
Efficiency
The efficiency calculation is
a function of the oven’s
power in terms of the
energy input into the oven.
It is a dimensionless
measurement expressed in
percentage the equation
(Kundapur & Sudhir, 2009),
where:
21
0
w pw
t
sc aw
mC T T
AI t
Exergy
The concept of exergy is roughly equated with the term available work
(Coatanéa, Kuuva, Makkonnen, Saarelainen & Castillòn-Solano, 2006, p. 83) it
“represents quantitatively the ‘useful’ energy or the ability to do work-the work
content of a great variety of streams (mass, heat, work) that flow through the
system” (Dincer & Cengel, 2001, p. 130). The term is difficult to define because it
is dependent upon the environment in which it is used (Demirel, 2002, p. 111). It
Nomenclature
-Efficiencyin%
w
m
-MassofwaterinKg
pw
C
-Specificheatcapacityofwater(4186J/[kg·K])
2
T
-Finalwatertemperaturein°c
1
T
-Initialwatertemperaturein°c
sc
A
-Apertureareaofthesolarcookerinm
2
0
t
aw
I
-IntegralofAverageinsolationovertime-
period
t
-Differenceintemperatureambientandwater
temperaturein°c
t-Timebetweeneachinterval
Exergy
e concept of exergy is roughly
equated with the term available work
(Coatanéa, Kuuva, Makkonnen,
Saarelainen & Castillòn-Solano, 2006, p.
83) it represents quantitatively the useful
energy or the ability to do work-the
work content of a great variety of streams
(mass, heat, work) that ow through the
system (Dincer & Cengel, 2001, p. 130).
e term is dicult to dene because it
is dependent upon the environment in
which it is used (Demirel, 2002, p. 111). It
suces to say it is a method for analysing
the eciency of energy resources use in a
system. e form of the equations used
to determine exergy are based on using
the exergy factor denoted here as r. e
exergy factor is used when determining
exergy content due to the transfer of
thermal energy between two thermal
reservoirs (Kundapur & Sudhir, 2009). It
is eectively the ratio between the exergy
and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
suffices to say it is a method for analysing the efficiency of energy resources use
in a system. The form of the equations used to determine exergy are based on
using the exergy factor denoted here as r. The exergy factor is used when
determining exergy content due to the transfer of thermal energy between two
thermal reservoirs (Kundapur & Sudhir, 2009). It is effectively the ratio between
the exergy and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
Effectiveness
The effectiveness of the cooker is in this case meant to illustrate the ability
of the unit to convert the solar insolation entering it into thermal energy (Kundapur
& Sudhir, 2009). This value is expressed as a percentage, and as before with the
efficiency value it is normalised to a standard insolation value to give it more
meaningful application.
0
aw r
II
I
(ibid)
Where
r aw
I rI
Nomenclature
r
-ExergyFactordimensionlesscoefficient
0
T
-Ambienttemperaturein°c
w
T
-Changeinwatertemperatureover600
secondtimeintervalin°c
1w
T
-Initialwatertemperatureof600seconds
intervalin°c
Nomenclature
-EffectivenessinPercent
aw
I
-AverageInsolationvalueinw/m
2
0
I
-Averagetheoreticalinsolation700w/m
2
suffices to say it is a method for analysing the efficiency of energy resources use
in a system. The form of the equations used to determine exergy are based on
using the exergy factor denoted here as r. The exergy factor is used when
determining exergy content due to the transfer of thermal energy between two
thermal reservoirs (Kundapur & Sudhir, 2009). It is effectively the ratio between
the exergy and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
Effectiveness
The effectiveness of the cooker is in this case meant to illustrate the ability
of the unit to convert the solar insolation entering it into thermal energy (Kundapur
& Sudhir, 2009). This value is expressed as a percentage, and as before with the
efficiency value it is normalised to a standard insolation value to give it more
meaningful application.
0
aw r
II
I
(ibid)
Where
r aw
I rI
Nomenclature
r
-ExergyFactordimensionlesscoefficient
0
T
-Ambienttemperaturein°c
w
T
-Changeinwatertemperatureover600
secondtimeintervalin°c
1w
T
-Initialwatertemperatureof600seconds
intervalin°c
Nomenclature
-EffectivenessinPercent
aw
I
-AverageInsolationvalueinw/m
2
0
I
-Averagetheoreticalinsolation700w/m
2
suffices to say it is a method for analysing the efficiency of energy resources use
in a system. The form of the equations used to determine exergy are based on
using the exergy factor denoted here as r. The exergy factor is used when
determining exergy content due to the transfer of thermal energy between two
thermal reservoirs (Kundapur & Sudhir, 2009). It is effectively the ratio between
the exergy and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
Effectiveness
The effectiveness of the cooker is in this case meant to illustrate the ability
of the unit to convert the solar insolation entering it into thermal energy (Kundapur
& Sudhir, 2009). This value is expressed as a percentage, and as before with the
efficiency value it is normalised to a standard insolation value to give it more
meaningful application.
0
aw r
II
I
(ibid)
Where
r aw
I rI
Nomenclature
r
-ExergyFactordimensionlesscoefficient
0
T
-Ambienttemperaturein°c
w
T
-Changeinwatertemperatureover600
secondtimeintervalin°c
1w
T
-Initialwatertemperatureof600seconds
intervalin°c
Nomenclature
-EffectivenessinPercent
aw
I
-AverageInsolationvalueinw/m
2
0
I
-Averagetheoreticalinsolation700w/m
2
Eectiveness
e eectiveness of the cooker
is in this case meant to illustrate the
ability of the unit to convert the solar
insolation entering it into thermal energy
(Kundapur & Sudhir, 2009). is value
is expressed as a percentage, and as before
with the eciency value it is normalised
to a standard insolation value to give it
more meaningful application.
Where
I
| C | V. XXII | N. 24 | - | 2017 |
suffices to say it is a method for analysing the efficiency of energy resources use
in a system. The form of the equations used to determine exergy are based on
using the exergy factor denoted here as r. The exergy factor is used when
determining exergy content due to the transfer of thermal energy between two
thermal reservoirs (Kundapur & Sudhir, 2009). It is effectively the ratio between
the exergy and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
Effectiveness
The effectiveness of the cooker is in this case meant to illustrate the ability
of the unit to convert the solar insolation entering it into thermal energy (Kundapur
& Sudhir, 2009). This value is expressed as a percentage, and as before with the
efficiency value it is normalised to a standard insolation value to give it more
meaningful application.
0
aw r
II
I
(ibid)
Where
r aw
I rI
Nomenclature
r
-ExergyFactordimensionlesscoefficient
0
T
-Ambienttemperaturein°c
w
T
-Changeinwatertemperatureover600
secondtimeintervalin°c
1w
T
-Initialwatertemperatureof600seconds
intervalin°c
Nomenclature
-EffectivenessinPercent
aw
I
-AverageInsolationvalueinw/m
2
0
I
-Averagetheoreticalinsolation700w/m
2
suffices to say it is a method for analysing the efficiency of energy resources use
in a system. The form of the equations used to determine exergy are based on
using the exergy factor denoted here as r. The exergy factor is used when
determining exergy content due to the transfer of thermal energy between two
thermal reservoirs (Kundapur & Sudhir, 2009). It is effectively the ratio between
the exergy and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
Effectiveness
The effectiveness of the cooker is in this case meant to illustrate the ability
of the unit to convert the solar insolation entering it into thermal energy (Kundapur
& Sudhir, 2009). This value is expressed as a percentage, and as before with the
efficiency value it is normalised to a standard insolation value to give it more
meaningful application.
0
aw r
II
I
(ibid)
Where
r aw
I rI
Nomenclature
r
-ExergyFactordimensionlesscoefficient
0
T
-Ambienttemperaturein°c
w
T
-Changeinwatertemperatureover600
secondtimeintervalin°c
1w
T
-Initialwatertemperatureof600seconds
intervalin°c
Nomenclature
-EffectivenessinPercent
aw
I
-AverageInsolationvalueinw/m
2
0
I
-Averagetheoreticalinsolation700w/m
2
suffices to say it is a method for analysing the efficiency of energy resources use
in a system. The form of the equations used to determine exergy are based on
using the exergy factor denoted here as r. The exergy factor is used when
determining exergy content due to the transfer of thermal energy between two
thermal reservoirs (Kundapur & Sudhir, 2009). It is effectively the ratio between
the exergy and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
Effectiveness
The effectiveness of the cooker is in this case meant to illustrate the ability
of the unit to convert the solar insolation entering it into thermal energy (Kundapur
& Sudhir, 2009). This value is expressed as a percentage, and as before with the
efficiency value it is normalised to a standard insolation value to give it more
meaningful application.
0
aw r
II
I
(ibid)
Where
r aw
I rI
Nomenclature
r
-ExergyFactordimensionlesscoefficient
0
T
-Ambienttemperaturein°c
w
T
-Changeinwatertemperatureover600
secondtimeintervalin°c
1w
T
-Initialwatertemperatureof600seconds
intervalin°c
Nomenclature
-EffectivenessinPercent
aw
I
-AverageInsolationvalueinw/m
2
0
I
-Averagetheoreticalinsolation700w/m
2
160
Total Costing of the Solar Oven
e costs for all the raw materials
of the solar were documented. ese
values have been summed to give a total
cost for building the unit. For example,
the total cost of wood for the unit is £
23.21including taxes. It was estimated
that the area of wood used divided by
the area wood purchased, that 80 % of
the original piece costing £23.21 had
been utilised. Multiplying £23.21 by
0.80% gives a value of £ 18.57, the
same approach was taken to the other
materials, all results can be found in the
table below.
Table 1
Total cost of the unit’s construction
Material Base Final
Cost £ Cost £
Wood 23.21 18.57
Screws 1 1
Handles 1.25 1.25
Foil 1 1
Glue 2.2 2.2
caulk 1 1
Glass 25 6.25
TOTAL £
£31.27
Table 2
Comparison of prices of various solar ovens available
J T-R
| C | V. XXII | N. 24 | - | 2017 |
e total cost of the unit is £31.27,
in terms of the wages of a person in a
developing country this a still a very large
sum of money. However, solar ovens
tend to be purchased and distributed by
NGO’s more often than by individuals.
e cost of the oven is evaluated by
comparing it to other solar ovens available
on the market, with due relevance to
their size. A table of these results is found
below
Model Price $ Price £ size compared to Unit (approx)
R4S3LDB3 24.90 17.14 smaller
SR-GS4702 37.13 25.53 smaller
My Solar oven 45.53 31.27 50 x 50 x 50 cm
WW63711M00 52.95 36.45 25 x 64 x 64 cm
Solar Furnace 89.95 61.92 30 cm diameter
Hot Pot Simple Solar Cooker 99.00 68.14 40 x 40 x 27 cm
Lehmans deluxe sun oven 249.00 171.39 same size
SKU# SunOven001 254.95 175.49 60 x 60 x 38 cm
Global Sun Oven 255.00 175.52 48 X 30 CM
All the prices and data of the solar
ovens models was taken from a Google
product price comparison search for solar
oven, see Google (2017). All prices are
converted to US dollars, as the USA is the
main manufacturer of ovens. Dimension
are given where found in the literature of
the dierent solar ovens, otherwise size is
estimated compared to the solar oven I
have designed. To give a reference point,
the size of my solar oven unit is 50x50x50
cm
3
. Table 2 has been ordered in terms
of price from lowest to highest. Given
the prices and sizes of the other models
available. I feel that the solar oven that
I have designed remains economically
competitive.
160
Total Costing of the Solar Oven
e costs for all the raw materials
of the solar were documented. ese
values have been summed to give a total
cost for building the unit. For example,
the total cost of wood for the unit is £
23.21including taxes. It was estimated
that the area of wood used divided by
the area wood purchased, that 80 % of
the original piece costing £23.21 had
been utilised. Multiplying £23.21 by
0.80% gives a value of £ 18.57, the
same approach was taken to the other
materials, all results can be found in the
table below.
Table 1
Total cost of the unit’s construction
Material Base Final
Cost £ Cost £
Wood 23.21 18.57
Screws 1 1
Handles 1.25 1.25
Foil 1 1
Glue 2.2 2.2
caulk 1 1
Glass 25 6.25
TOTAL £ £31.27
Table 2
Comparison of prices of various solar ovens available
J T-R
| C | V. XXII | N. 24 | - | 2017 |
e total cost of the unit is £31.27,
in terms of the wages of a person in a
developing country this a still a very large
sum of money. However, solar ovens
tend to be purchased and distributed by
NGO’s more often than by individuals.
e cost of the oven is evaluated by
comparing it to other solar ovens available
on the market, with due relevance to
their size. A table of these results is found
below
Model Price $ Price £ size compared to Unit (approx)
R4S3LDB3 24.90 17.14 smaller
SR-GS4702 37.13 25.53 smaller
My Solar oven 45.53 31.27 50 x 50 x 50 cm
WW63711M00 52.95 36.45 25 x 64 x 64 cm
Solar Furnace 89.95 61.92 30 cm diameter
Hot Pot Simple Solar Cooker 99.00 68.14 40 x 40 x 27 cm
Lehmans deluxe sun oven 249.00 171.39 same size
SKU# SunOven001 254.95 175.49 60 x 60 x 38 cm
Global Sun Oven 255.00 175.52 48 X 30 CM
All the prices and data of the solar
ovens models was taken from a Google
product price comparison search for solar
oven, see Google (2017). All prices are
converted to US dollars, as the USA is the
main manufacturer of ovens. Dimension
are given where found in the literature of
the dierent solar ovens, otherwise size is
estimated compared to the solar oven I
have designed. To give a reference point,
the size of my solar oven unit is 50x50x50
cm
3
. Table 2 has been ordered in terms
of price from lowest to highest. Given
the prices and sizes of the other models
available. I feel that the solar oven that
I have designed remains economically
competitive.
161
Results and Discussion
All the prices and data of the solar ovens models was taken from a Google
product price comparison search for solar oven, see Google (2017). All prices are
converted to US dollars, as the USA is the main manufacturer of ovens.
Dimension are given where found in the literature of the different solar ovens,
otherwise size is estimated compared to the solar oven I have designed. To give a
reference point, the size of my solar oven unit is 50x50x50 cm
3
. Table 2 has been
ordered in terms of price from lowest to highest. Given the prices and sizes of the
other models available. I feel that the solar oven that I have designed remains
economically competitive.
Results
Temperature Difference Vs Adjusted Cooking Power
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60
Temperature Difference C
Adjusted Cooking Power
Watts
lid on 0 degrees
lid off 0 degrees
30 degrees
40 degrees
50 degrees
70 degrees
60 degrees
Effectiveness
0
20
40
60
80
100
120
0
8
16
24
32
40
48
56
64
72
80
88
96
104
112
120
128
Time Minutes
Effectiveness %
lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
All the prices and data of the solar ovens models was taken from a Google
product price comparison search for solar oven, see Google (2017). All prices are
converted to US dollars, as the USA is the main manufacturer of ovens.
Dimension are given where found in the literature of the different solar ovens,
otherwise size is estimated compared to the solar oven I have designed. To give a
reference point, the size of my solar oven unit is 50x50x50 cm
3
. Table 2 has been
ordered in terms of price from lowest to highest. Given the prices and sizes of the
other models available. I feel that the solar oven that I have designed remains
economically competitive.
Results
Temperature Difference Vs Adjusted Cooking Power
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60
Temperature Difference C
Adjusted Cooking Power
Watts
lid on 0 degrees
lid off 0 degrees
30 degrees
40 degrees
50 degrees
70 degrees
60 degrees
Effectiveness
0
20
40
60
80
100
120
0
8
16
24
32
40
48
56
64
72
80
88
96
104
112
120
128
Time Minutes
Effectiveness %
lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Efficiency
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120
Time minutes
Efficiency %
lid on 0 deg
lif off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Temperature Vs Time
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120 140
Time Minutes
Temperature C
Lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Analysis of Results
In the ASAE paper Testing and Reporting Solar Cooker Performance it outlines a
parameter of Single Measure of Performance based on the standardised cooking
power rating of each test (ASAE, 2003). The value of the standardised cooking
power is computed at a temperature difference of 50°c. Using a linear regression
method on the data of the power curve shown below, an excel spreadsheet can
produce an equation for each set of data.
Temperature Difference Vs Adjusted Cooking Power
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60
Temperature Difference C
Adjusted Cooking Power
Watts
lid on 0 degrees
lid off 0 degrees
30 degrees
40 degrees
50 degrees
70 degrees
60 degrees
Increasing the efficiency of a solar oven
| Campus | V. XXII | No. 24 | julio-diciembre | 2017 |
Efficiency
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120
Time minutes
Efficiency %
lid on 0 deg
lif off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Temperature Vs Time
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120 140
Time Minutes
Temperature C
Lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Analysis of Results
In the ASAE paper Testing and Reporting Solar Cooker Performance it outlines a
parameter of Single Measure of Performance based on the standardised cooking
power rating of each test (ASAE, 2003). The value of the standardised cooking
power is computed at a temperature difference of 50°c. Using a linear regression
method on the data of the power curve shown below, an excel spreadsheet can
produce an equation for each set of data.
Temperature Difference Vs Adjusted Cooking Power
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60
Temperature Difference C
Adjusted Cooking Power
Watts
lid on 0 degrees
lid off 0 degrees
30 degrees
40 degrees
50 degrees
70 degrees
60 degrees
162
In the ASAE paper Testing and
Reporting Solar Cooker Performance it
outlines a parameter of Single Measure
of Performance based on the standardised
cooking power rating of each test (ASAE,
2003). e value of the standardised
cooking power is computed at a
temperature dierence of 50°C. Using a
linear regression method on the data of
the power curve shown below, an excel
spreadsheet can produce an equation for
each set of data.
Efficiency
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120
Time minutes
Efficiency %
lid on 0 deg
lif off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Temperature Vs Time
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120 140
Time Minutes
Temperature C
Lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Analysis of Results
In the ASAE paper Testing and Reporting Solar Cooker Performance it outlines a
parameter of Single Measure of Performance based on the standardised cooking
power rating of each test (ASAE, 2003). The value of the standardised cooking
power is computed at a temperature difference of 50°c. Using a linear regression
method on the data of the power curve shown below, an excel spreadsheet can
produce an equation for each set of data.
Temperature Difference Vs Adjusted Cooking Power
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60
Temperature Difference C
Adjusted Cooking Power
Watts
lid on 0 degrees
lid off 0 degrees
30 degrees
40 degrees
50 degrees
70 degrees
60 degrees
Figure 5. Temperature dierence vs adjusted cooking power
Because the equation is based on linear
regression, it has the form y =mx +c, for
example the equation generated for a 50°
angle reector is:
Where y is the adjusted as power in
Watts, with this equation we use a value
of x of 50°c to generate a value for the
single measure of performance for each
reector angle. Another parameter that
was generated for each replicate was
the coecient of determination r
2
.e
coecient of determination is described
Figure 5. Temperature difference vs adjusted cooking power
Because the equation is based on linear regression, it has the form y =mx +c, for
example the equation generated for a 50° angle reflector is:
Where Y is the adjusted as power in Watts, with this equation we use a value of x
of 50°c to generate a value for the single measure of performance for each
reflector angle. Another parameter that was generated for each replicate was the
coefficient of determination r
2
.The coefficient of determination is described as the
total variation in n observed values of the dependent variable that is explained by
the simple linear regression model. The higher the value of r
2
, the better fit the
model (Pennsylvania State University, 2017). To validate the results taken the
value of r
2
must be above 0.75 (ASAE, 2003).
The value of r
2
is calculated by the
excel
spreadsheet based on the linear regression line. The table below is a
summary of these parameters for the different reflector angles.
Table 3
The single measure of performance and r2 values of each replicate
The negative values of the single measure of performance are a result of
their values being based on the linear regression equation not the exact equation
of the data obtained. The exact equation in some cases not having a completely
linear relationship whereas the regression method does, causing a potential to
obtain negative results. The measure of performance is based up standardised
cooking power values and as such represents the cooking power per second
(Kundapur & Sudhir, 2009). The table shows that as the reflector angle increases
the so does the performance of the solar oven. In addition, it demonstrates that all
as the total variation in n observed
values of the dependent variable that is
explained by the simple linear regression
model. e higher the value of r
2
, the
better t the model (Pennsylvania State
University, 2017). To validate the results
taken the value of r
2
must be above
0.75 (ASAE, 2003).
e value of r
2
is
calculated by the excel
spreadsheet based
on the linear regression line. e table
below is a summary of these parameters
for the dierent reector angles.
J T-R
| C | V. XXII | N. 24 | - | 2017 |
Table 3
The single measure of performance and r
2
values of each replicate
Angle of Reflector Single Measure of Performance Watts Coeffucient of determination r
2
0 (without lid) 6.453 0.946
0 (with lid) -0.552 0.971
30 -0.698 0.971
40 1.390 0.949
50 2.759 0.946
60 2.238 0.948
70 4.676 0.961
162
In the ASAE paper Testing and
Reporting Solar Cooker Performance it
outlines a parameter of Single Measure
of Performance based on the standardised
cooking power rating of each test (ASAE,
2003). e value of the standardised
cooking power is computed at a
temperature dierence of 50°C. Using a
linear regression method on the data of
the power curve shown below, an excel
spreadsheet can produce an equation for
each set of data.
Efficiency
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120
Time minutes
Efficiency %
lid on 0 deg
lif off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Temperature Vs Time
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120 140
Time Minutes
Temperature C
Lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Analysis of Results
In the ASAE paper Testing and Reporting Solar Cooker Performance it outlines a
parameter of Single Measure of Performance based on the standardised cooking
power rating of each test (ASAE, 2003). The value of the standardised cooking
power is computed at a temperature difference of 50°c. Using a linear regression
method on the data of the power curve shown below, an excel spreadsheet can
produce an equation for each set of data.
Temperature Difference Vs Adjusted Cooking Power
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60
Temperature Difference C
Adjusted Cooking Power
Watts
lid on 0 degrees
lid off 0 degrees
30 degrees
40 degrees
50 degrees
70 degrees
60 degrees
Figure 5. Temperature dierence vs adjusted cooking power
Because the equation is based on linear
regression, it has the form y =mx +c, for
example the equation generated for a 50°
angle reector is:
Where y is the adjusted as power in
Watts, with this equation we use a value
of x of 50°c to generate a value for the
single measure of performance for each
reector angle. Another parameter that
was generated for each replicate was
the coecient of determination r
2
.e
coecient of determination is described
Figure 5. Temperature difference vs adjusted cooking power
Because the equation is based on linear regression, it has the form y =mx +c, for
example the equation generated for a 50° angle reflector is:
Where Y is the adjusted as power in Watts, with this equation we use a value of x
of 50°c to generate a value for the single measure of performance for each
reflector angle. Another parameter that was generated for each replicate was the
coefficient of determination r
2
.The coefficient of determination is described as the
total variation in n observed values of the dependent variable that is explained by
the simple linear regression model. The higher the value of r
2
, the better fit the
model (Pennsylvania State University, 2017). To validate the results taken the
value of r
2
must be above 0.75 (ASAE, 2003).
The value of r
2
is calculated by the
excel
spreadsheet based on the linear regression line. The table below is a
summary of these parameters for the different reflector angles.
Table 3
The single measure of performance and r2 values of each replicate
The negative values of the single measure of performance are a result of
their values being based on the linear regression equation not the exact equation
of the data obtained. The exact equation in some cases not having a completely
linear relationship whereas the regression method does, causing a potential to
obtain negative results. The measure of performance is based up standardised
cooking power values and as such represents the cooking power per second
(Kundapur & Sudhir, 2009). The table shows that as the reflector angle increases
the so does the performance of the solar oven. In addition, it demonstrates that all
as the total variation in n observed
values of the dependent variable that is
explained by the simple linear regression
model. e higher the value of r
2
, the
better t the model (Pennsylvania State
University, 2017). To validate the results
taken the value of r
2
must be above
0.75 (ASAE, 2003).
e value of r
2
is
calculated by the excel
spreadsheet based
on the linear regression line. e table
below is a summary of these parameters
for the dierent reector angles.
J T-R
| C | V. XXII | N. 24 | - | 2017 |
Table 3
The single measure of performance and r
2
values of each replicate
Angle of Reflector Single Measure of Performance Watts Coeffucient of determination r
2
0 (without lid) 6.453 0.946
0 (with lid) -0.552 0.971
30 -0.698 0.971
40 1.390 0.949
50 2.759 0.946
60 2.238 0.948
70 4.676 0.961
163
e negative values of the single
measure of performance are a result of
their values being based on the linear
regression equation not the exact equation
of the data obtained. e exact equation
in some cases not having a completely
linear relationship whereas the regression
method does, causing a potential to
obtain negative results. e measure of
performance is based up standardised
cooking power values and as such
represents the cooking power per second
(Kundapur & Sudhir, 2009). e table
shows that as the reector angle increases
the so does the performance of the solar
oven. In addition, it demonstrates that all
values of the coecient of determination
are about 0.95, the lowest being 0.9466.
e highest value of the single measure
of performance occurred at a 70-degree
reector angle.
Eectiveness
is single measure of performance is
not the only parameter for evaluating the
solar cooker’s performance. For example,
there is also a measure of eectiveness,
which is based upon the ability of the unit
to convert the solar insolation entering
it into thermal energy (Kundapur &
Sudhir, 2009). e Figure 6 details the
eectiveness of each reector angle
throughout the period of the experiment.
values of the coefficient of determination are about 0.95, the lowest being 0.9466.
The highest value of the single measure of performance occurred at a 70-degree
reflector angle.
Effectiveness
This single measure of performance is not the only parameter for evaluating
the solar cooker’s performance. For example, there is also a measure of
effectiveness, which is based upon the ability of the unit to convert the solar
insolation entering it into thermal energy (Kundapur & Sudhir, 2009). The graph
below details the effectiveness of each reflector angle throughout the period of the
experiment.
Effectiveness
0
20
40
60
80
100
120
0
8
16
24
32
40
48
56
64
72
80
88
96
104
112
120
128
Time Minutes
Effectiveness %
lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Figure 6. The effectiveness off each reflector angle against tim
The graph illustrates the most effective reflector angle occurs at 60
degrees, the other reflector angles have a similar level of effectiveness. The best
behind 60 degrees is a 70-degree angle. The effectiveness of each replicate
oscillates throughout the experiment at 60 degrees it oscillates between 85 % and
95 %, the equation for the measuring the effectiveness is:
0
aw r
II
I
Where
Figure 6. e eectiveness o each reector angle against tim
I
| C | V. XXII | N. 24 | - | 2017 |
e graph illustrates the most eective
reector angle occurs at 60 degrees, the
other reector angles have a similar level of
eectiveness. e best behind 60 degrees
is a 70-degree angle. e eectiveness
of each replicate oscillates throughout
the experiment at 60 degrees it oscillates
between 85 % and 95 %, the equation
for the measuring the eectiveness is:
Where
suffices to say it is a method for analysing the efficiency of energy resources use
in a system. The form of the equations used to determine exergy are based on
using the exergy factor denoted here as r. The exergy factor is used when
determining exergy content due to the transfer of thermal energy between two
thermal reservoirs (Kundapur & Sudhir, 2009). It is effectively the ratio between
the exergy and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
Effectiveness
The effectiveness of the cooker is in this case meant to illustrate the ability
of the unit to convert the solar insolation entering it into thermal energy (Kundapur
& Sudhir, 2009). This value is expressed as a percentage, and as before with the
efficiency value it is normalised to a standard insolation value to give it more
meaningful application.
0
aw r
II
I
(ibid)
Where
r aw
I rI
Nomenclature
r
-ExergyFactordimensionlesscoefficient
0
T
-Ambienttemperaturein°c
w
T
-Changeinwatertemperatureover600
secondtimeintervalin°c
1w
T
-Initialwatertemperatureof600seconds
intervalin°c
Nomenclature
-EffectivenessinPercent
aw
I
-AverageInsolationvalueinw/m
2
0
I
-Averagetheoreticalinsolation700w/m
2
suffices to say it is a method for analysing the efficiency of energy resources use
in a system. The form of the equations used to determine exergy are based on
using the exergy factor denoted here as r. The exergy factor is used when
determining exergy content due to the transfer of thermal energy between two
thermal reservoirs (Kundapur & Sudhir, 2009). It is effectively the ratio between
the exergy and enthalpy of the resource. See below:
Simplifying to:
(Kundapur & Sudhir, 2009)
Effectiveness
The effectiveness of the cooker is in this case meant to illustrate the ability
of the unit to convert the solar insolation entering it into thermal energy (Kundapur
& Sudhir, 2009). This value is expressed as a percentage, and as before with the
efficiency value it is normalised to a standard insolation value to give it more
meaningful application.
0
aw r
II
I
(ibid)
Where
r aw
I rI
Nomenclature
r
-ExergyFactordimensionlesscoefficient
0
T
-Ambienttemperaturein°c
w
T
-Changeinwatertemperatureover600
secondtimeintervalin°c
1w
T
-Initialwatertemperatureof600seconds
intervalin°c
Nomenclature
-EffectivenessinPercent
aw
I
-AverageInsolationvalueinw/m
2
0
I
-Averagetheoreticalinsolation700w/m
2
e letter I standing for insolation
in various forms, as such it can be seen
that the eectiveness is dependant upon
the insolation levels. As these insolation
levels oscillate, it causes the eectiveness
to oscillate as well.
Eciency
Another measure of the solar oven’s
performance is its eciency. e
eciency is dened in this context as a
function of the energy input to the oven
in terms of the oven aperture area and
164
r aw
I rI
The letter I standing for insolation in various forms, as such it can be seen that the
effectiveness is dependant upon the insolation levels. As these insolation levels
oscillate, it causes the effectiveness to oscillate as well.
Efficiency
Another measure of the solar oven’s performance is its efficiency. The efficiency is
defined in this context as a function of the energy input to the oven in terms of the
oven aperture area and insolation levels. It is a dimensionless measurement
expressed in percent. The graph below shows the efficiency of the different
reflector angles tested.
Efficiency
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120
Time minutes
Efficiency %
lid on 0 deg
lif off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Figure 7. Time Vs Efficiency at Different Reflector Angles
As the time in minutes progresses the efficiency decreases at an exponential rate,
having initially very high levels efficiencies but declining rapidly. All the replicates
by approximately 30 minutes into the experiment had 10% efficiency or less. The
angle that is most efficient varies at different time points in the experiment. For the
first 40 minutes, the 40-degree angle reflector is most efficient, followed closely by
the 70-degree angle reflector. After approximately 50 minutes, the baseline
replicate conducted without a reflector and the saucepan lid on became the most
efficient. Indicating that the lidded pot retains efficiency better than the replicates
without a lid as the temperature increases with time.
insolation levels. It is a dimensionless
measurement expressed in percent. e
As the time in minutes progresses the
eciency decreases at an exponential rate,
having initially very high levels eciencies
but declining rapidly. All the replicates by
approximately 30 minutes into the experi-
ment had 10% eciency or less. e angle
that is most ecient varies at dierent time
points in the experiment. For the rst 40
minutes, the 40 degree angle reector is
most ecient, followed closely by the 70
degree angle reector. After approximately
50 minutes, the baseline replicate conduct-
ed without a reector and the saucepan lid
on became the most ecient. Indicating
that the lidded pot retains eciency better
than the replicates without a lid as the tem-
perature increases with time.
Temperature generated
Purely in terms of the kinetic energy
of the water, the temperature prole of
each replicates gives an indication of its
performance. e graph below shows the
temperature variation with time of the
dierent replicates.
Figure 8. e Temperature Variation with Time of the Dierent Reector Angles
Temperature generated
Purely in terms of the kinetic energy of the water, the temperature profile of each
replicates gives an indication of its performance. The graph below shows the
temperature variation with time of the different replicates.
Temperature Vs Time
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120 140
Time Minutes
Temperature C
Lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Figure 8. The Temperature Variation with Time of the Different Reflector Angles
The 70-degree reflector angle gave the highest temperature of all the replicates,
followed by the 60-degree reflector angle. The replicate conducted with the pan lid
kept on showed linear curve than the replicate with the lid off the pan. Its
characteristics are linear, it achieved the higher temperatures slower, and its final
temperature in comparison is higher than the other replicates except 70 degrees
and equal to the 60-degree replicate. With are reflector angle of 70 degrees, by
120 minutes, the solar oven was able to heat the pan of water to 78 degrees
Celsius.
Corrigenda for Adjusting Transmittance of Halogen Light Source Compared to
Sun light
I used halogen lights to simulate sunlight in this experiment. The spectra of natural
and artificial halogen light and their characteristics are not uniform. To take this
into account of the results analysed they shall be contrasted to illustrate the
differences between the sources. This is also important to the application of the
J T-R
| C | V. XXII | N. 24 | - | 2017 |
Figure 7 shows the eciency of the
dierent reector angles tested.
Figure 7. Time Vs Eciency at Dierent Reector Angles
164
r aw
I rI
The letter I standing for insolation in various forms, as such it can be seen that the
effectiveness is dependant upon the insolation levels. As these insolation levels
oscillate, it causes the effectiveness to oscillate as well.
Efficiency
Another measure of the solar oven’s performance is its efficiency. The efficiency is
defined in this context as a function of the energy input to the oven in terms of the
oven aperture area and insolation levels. It is a dimensionless measurement
expressed in percent. The graph below shows the efficiency of the different
reflector angles tested.
Efficiency
0
10
20
30
40
50
60
70
80
90
0 20 40 60 80 100 120
Time minutes
Efficiency %
lid on 0 deg
lif off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Figure 7. Time Vs Efficiency at Different Reflector Angles
As the time in minutes progresses the efficiency decreases at an exponential rate,
having initially very high levels efficiencies but declining rapidly. All the replicates
by approximately 30 minutes into the experiment had 10% efficiency or less. The
angle that is most efficient varies at different time points in the experiment. For the
first 40 minutes, the 40-degree angle reflector is most efficient, followed closely by
the 70-degree angle reflector. After approximately 50 minutes, the baseline
replicate conducted without a reflector and the saucepan lid on became the most
efficient. Indicating that the lidded pot retains efficiency better than the replicates
without a lid as the temperature increases with time.
insolation levels. It is a dimensionless
measurement expressed in percent. e
As the time in minutes progresses the
eciency decreases at an exponential rate,
having initially very high levels eciencies
but declining rapidly. All the replicates by
approximately 30 minutes into the experi-
ment had 10% eciency or less. e angle
that is most ecient varies at dierent time
points in the experiment. For the rst 40
minutes, the 40 degree angle reector is
most ecient, followed closely by the 70
degree angle reector. After approximately
50 minutes, the baseline replicate conduct-
ed without a reector and the saucepan lid
on became the most ecient. Indicating
that the lidded pot retains eciency better
than the replicates without a lid as the tem-
perature increases with time.
Temperature generated
Purely in terms of the kinetic energy
of the water, the temperature prole of
each replicates gives an indication of its
performance. e graph below shows the
temperature variation with time of the
dierent replicates.
Figure 8. e Temperature Variation with Time of the Dierent Reector Angles
Temperature generated
Purely in terms of the kinetic energy of the water, the temperature profile of each
replicates gives an indication of its performance. The graph below shows the
temperature variation with time of the different replicates.
Temperature Vs Time
0
10
20
30
40
50
60
70
80
0 20 40 60 80 100 120 140
Time Minutes
Temperature C
Lid on 0 deg
lid off 0 deg
30 deg
40 deg
50 deg
70 deg
60 deg
Figure 8. The Temperature Variation with Time of the Different Reflector Angles
The 70-degree reflector angle gave the highest temperature of all the replicates,
followed by the 60-degree reflector angle. The replicate conducted with the pan lid
kept on showed linear curve than the replicate with the lid off the pan. Its
characteristics are linear, it achieved the higher temperatures slower, and its final
temperature in comparison is higher than the other replicates except 70 degrees
and equal to the 60-degree replicate. With are reflector angle of 70 degrees, by
120 minutes, the solar oven was able to heat the pan of water to 78 degrees
Celsius.
Corrigenda for Adjusting Transmittance of Halogen Light Source Compared to
Sun light
I used halogen lights to simulate sunlight in this experiment. The spectra of natural
and artificial halogen light and their characteristics are not uniform. To take this
into account of the results analysed they shall be contrasted to illustrate the
differences between the sources. This is also important to the application of the
J T-R
| C | V. XXII | N. 24 | - | 2017 |
Figure 7 shows the eciency of the
dierent reector angles tested.
Figure 7. Time Vs Eciency at Dierent Reector Angles
165
e 70 degree reector angle gave the
highest temperature of all the replicates,
followed by the 60 degree reector angle.
e replicate conducted with the pan
lid kept on showed linear curve than
the replicate with the lid o the pan. Its
characteristics are linear, it achieved the
higher temperatures slower, and its nal
temperature in comparison is higher than
the other replicates except 70 degrees and
equal to the 60-degree replicate. With
are reector angle of 70 degrees, by 120
minutes, the solar oven was able to heat
the pan of water to 78 degrees Celsius.
Corrigenda for Adjusting
Transmittance of Halogen Light
Source Compared to Sun light
I used halogen lights to simulate
sunlight in this experiment. e
spectra of natural and articial halogen
light and their characteristics are not
uniform. To take this into account of the
results analysed they shall be contrasted
to illustrate the dierences between
the sources. is is also important to
the application of the unit, as it was
designed to be used in a real life, natural
light situation not under articial
sources. e temperature at which a
black body radiator that has been heated
corresponds to the light colour of a source
is the colour temperature of that source
(Colsmann et al., 2011). is quantity
can be used to determine the level of
irradiance of a light source. e table
below shows the colour temperature of
dierent light sources, both articial
and natural in Kelvin.
Table 4
The value of colour temperature in Kelvin of different light sources, all data sourced and
adapted from Davidson (2015)
Natural Light Colour Temperature Articial Light Colour Temperature
Source (K) kelvins Source (K) Kelvins
Sky Light 12000 -18000 500 Watt Tungsten lamp 3200
Overcast Sky light 7000 200 Watt Lamp 2980
Midday Sun Summer 5000-7000 100 Watt lamp 2900
Midday Sun Winter 5500-6000 75 Watt Lamp 2820
Average Midday light 5400 40 Watt Lamp 2650
Northern Hemisphere Gas Light 2000 - 2000
Sunrise, Sunset 3000 Candle Light 2900
I
| C | V. XXII | N. 24 | - | 2017 |
We know that as the temperature
colour (T
F
) increases at a given wavelength
the relative intensity of the light source
increases.(Ibid)
As halogen, lamps and other forms of
articial lighting have lower temperature
values. ey consequently will have less
intensity than if the unit was tested in
direct sunlight. Sunlight’s wavelength
falls within the visible light spectrum of
400-760 nm, were as the wavelength of
halogen lamps is further into the Infrared
spectrum.
As shown by the emission spectrum
of varioces light sources (Roberts 2012)
is an issue that needs to be considered as,
the levels of transmittance of light (and
energy) through the glass at the top of
the oven alters with the wavelength of
the light.
166
Figure 9. e transmittance of Soda-lime glass at specic
wave lengths, from Schaeer et al. (2015 )
As halogen, lamps and other forms of artificial lighting have lower temperature
values. They consequently will have less intensity than if the unit was tested in
direct sunlight. Sunlight’s wavelength falls within the visible light spectrum of 400-
760 nm, were as the wavelength of halogen lamps is further into the Infrared
spectrum, as shown below.
Figure 10. Emission Spectra of Various light sources, modified from Roberts (2012)
As shown by the spectrum above. This is an issue that needs to be considered as,
the levels of transmittance of light (and energy) through the glass at the top of the
oven alters with the wavelength of the light.
Figure 11. The transmittance of Soda-lime glass at specific wave lengths, from Schaeffer et al.
(2015 )
e plot of Soda-lime glass wavelength
against transmission illustrates that
higher levels of transmission into the
solar oven occur at the lower levels of
the visible light spectrum, i.e. between
approximately 450 nm and 650 nm.
e level of transmission decreases as the
wavelength progresses into the infrared
wavelength of the spectrum. From this,
it can be concluded that the performance
of the solar oven using a halogen lamp in
place of natural direct sun light will be
slightly lower.
The plot of Soda-lime glass wavelength against transmission illustrates that higher
levels of transmission into the solar oven occur at the lower levels of the visible
light spectrum, i.e. between approximately 450 nm and 650 nm. The level of
transmission decreases as the wavelength progresses into the infrared
wavelength of the spectrum. From this, it can be concluded that the performance
of the solar oven using a halogen lamp in place of natural direct sun light will be
slightly lower.
Figure 12. Transpose of graphs of the spectral data and transmittance of different forms light
source at a given wavelengths
.
Above the figures have been approximately transposed to illustrate that although
there will be a reduction in transmittance to the solar cooker using halogen light
sources it is only a few percent and as such will not cause major issues to apply
the results of the research to real life applications.
Conclusion
I feel that the solar oven that I have designed is economical given the prices
and sizes of the other models available to be purchased. Whilst still being durable
enough to last for a long time, as such I feel that it meets the requirements I had
set initially for the project, the main drawback being its size and weight making it
less portable. The reflector angle that is most effective at increasing the efficiency
of the solar oven is partly dependant on what definition of efficiency is applied. The
reflector angle with the greatest ability to convert the solar insolation into thermal
energy (termed effectiveness).
It is not the same as the reflector and angle that caused the solar oven to
retain the thermal energy over the given aperture area and time period of 600
seconds (termed efficiency here). The most effective reflector angle i.e. the
Figure 10. Transpose of graphs of the spectral data and transmittance of dierent
forms light source at a given wavelengths.
Above the gures have been approximately
transposed to illustrate that although
there will be a reduction in transmittance
to the solar cooker using halogen light
sources it is only a few percent and as
such will not cause major issues to apply
the results of the research to real life
applications.
J T-R
| C | V. XXII | N. 24 | - | 2017 |
166
Figure 9. e transmittance of Soda-lime glass at specic
wave lengths, from Schaeer et al. (2015 )
As halogen, lamps and other forms of artificial lighting have lower temperature
values. They consequently will have less intensity than if the unit was tested in
direct sunlight. Sunlight’s wavelength falls within the visible light spectrum of 400-
760 nm, were as the wavelength of halogen lamps is further into the Infrared
spectrum, as shown below.
Figure 10. Emission Spectra of Various light sources, modified from Roberts (2012)
As shown by the spectrum above. This is an issue that needs to be considered as,
the levels of transmittance of light (and energy) through the glass at the top of the
oven alters with the wavelength of the light.
Figure 11. The transmittance of Soda-lime glass at specific wave lengths, from Schaeffer et al.
(2015 )
e plot of Soda-lime glass wavelength
against transmission illustrates that
higher levels of transmission into the
solar oven occur at the lower levels of
the visible light spectrum, i.e. between
approximately 450 nm and 650 nm.
e level of transmission decreases as the
wavelength progresses into the infrared
wavelength of the spectrum. From this,
it can be concluded that the performance
of the solar oven using a halogen lamp in
place of natural direct sun light will be
slightly lower.
The plot of Soda-lime glass wavelength against transmission illustrates that higher
levels of transmission into the solar oven occur at the lower levels of the visible
light spectrum, i.e. between approximately 450 nm and 650 nm. The level of
transmission decreases as the wavelength progresses into the infrared
wavelength of the spectrum. From this, it can be concluded that the performance
of the solar oven using a halogen lamp in place of natural direct sun light will be
slightly lower.
Figure 12. Transpose of graphs of the spectral data and transmittance of different forms light
source at a given wavelengths
.
Above the figures have been approximately transposed to illustrate that although
there will be a reduction in transmittance to the solar cooker using halogen light
sources it is only a few percent and as such will not cause major issues to apply
the results of the research to real life applications.
Conclusion
I feel that the solar oven that I have designed is economical given the prices
and sizes of the other models available to be purchased. Whilst still being durable
enough to last for a long time, as such I feel that it meets the requirements I had
set initially for the project, the main drawback being its size and weight making it
less portable. The reflector angle that is most effective at increasing the efficiency
of the solar oven is partly dependant on what definition of efficiency is applied. The
reflector angle with the greatest ability to convert the solar insolation into thermal
energy (termed effectiveness).
It is not the same as the reflector and angle that caused the solar oven to
retain the thermal energy over the given aperture area and time period of 600
seconds (termed efficiency here). The most effective reflector angle i.e. the
Figure 10. Transpose of graphs of the spectral data and transmittance of dierent
forms light source at a given wavelengths.
Above the gures have been approximately
transposed to illustrate that although
there will be a reduction in transmittance
to the solar cooker using halogen light
sources it is only a few percent and as
such will not cause major issues to apply
the results of the research to real life
applications.
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| C | V. XXII | N. 24 | - | 2017 |
Conclusion
I feel that the solar oven that I have
designed is economical given the prices
and sizes of the other models available to
be purchased. Whilst still being durable
enough to last for a long time, as such
I feel that it meets the requirements I
had set initially for the project, the main
drawback being its size and weight making
it less portable. e reector angle that is
most eective at increasing the eciency
of the solar oven is partly dependant on
what denition of eciency is applied.
e reector angle with the greatest
ability to convert the solar insolation into
thermal energy (termed eectiveness).
It is not the same as the reector and
angle that caused the solar oven to retain
the thermal energy over the given aperture
area and time period of 600 seconds
(termed eciency here). e most
eective reector angle i.e. the reector
angle with the greatest ability to convert
the solar insolation into thermal energy
is the 60 degrees reector. It would seem
that at this angle the greatest amount of
solar insolation is concentrated on the
cooking pot itself. Causing the greatest
conversion of insolation to thermal
energy, the angles below and above
60 degrees causes the insolation to be
focused above or below the pot, making
them less eective.
e most ecient reector angle
occurs at 40 degrees followed closely by
70 degrees, but this is only true for the
rst 40 minutes of cooking time. After
this point, the replicates conducted
with the lid on the pot and no reector
becomes the most ecient. Similar results
are obtained for the adjusted power-
rating curve of the dierent reector
angles, 70 degrees having the highest
power rating followed by 40 degrees.
Also as with the eciency ratings the
replicate conducted with the lid on the
pot and no reector started with a lower
power rating than the other replicates
but towards the end of the experiment
it exceed them. e temperature prole
of the all the replicates shows that the
70 degree reector angle produces the
highest temperature consistently. After
18 minutes into the experiment, the 70
degree reector produces the highest
temperature of all replicates until the end
of the experiment, followed closely by the
60 degrees reector angle. Over the series
of dierent methods for evaluating the
best reector and angle, it would seem
that a 70 degree angle is consistently
highest in most of the tests. Ideally, then,
if cost were less of an obstacle, a simple
motor could be tter that adjusted the
angle of the reectors at dierent periods
to maximise cooking power or eciency.
However, this is not within the remit of
the experiment as it stands.
Excluding economics and durability,
the most important characteristic
of the oven for its use in developing
nations would be achieving the highest
temperature in the quickest time,
reducing the waiting time to cook a meal
or pasteurise water. However, this may
vary on the preference of the individual
and culture and circumstances involved.
Considering this, I feel a reector angle
of 70 degrees is in general the best
option for the solar oven of box design
as it is one of the most consistently high-
ranking angles in each performance
evaluation test. e analysis for adjusting
the results for natural light showed that
168
the dierence between the results would
have been minimal, in the region of a few
percent. As such I feel that my results are
comparable to the use of the solar oven
in natural sun light and do not need to
be adjusted. If more time and resources
were available additional tests that could
be carried out, include running repeat
tests of each reector angle to validate
the results obtained initially, as well as
increasing the number of angles tested.
e unit could be tested outdoors to
demonstrate and contrast the dierences
between the controlled conditions and
the actual application of the unit. It could
also be tested in dierent seasons or on a
monthly basis to demonstrate how the
performance varies throughout the year.
In conclusion, I have achieved my
objectives of designing a solar oven that
is a compromise between economics and
eciency enough to be disseminated
with moderate success, and also nding
the optimum reector angle for it, which
is 70 degrees.
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the dierence between the results would
have been minimal, in the region of a few
percent. As such I feel that my results are
comparable to the use of the solar oven
in natural sun light and do not need to
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tests of each reector angle to validate
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monthly basis to demonstrate how the
performance varies throughout the year.
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objectives of designing a solar oven that
is a compromise between economics and
eciency enough to be disseminated
with moderate success, and also nding
the optimum reector angle for it, which
is 70 degrees.
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World Conference on Solar Cook-
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