Solar Oven Final Report
Solar Oven Final Report
University of Arizona Tucson, AZ, 85716
S.A.C.R.A.W Solar Oven Prepared for: Dr. Stanley Pau
Jack Speelman Rebecca Nelson Paola “Andy” Lopez Lorin Greenwood Stephanie Gilboy October 21st 2012
Figure 1: Shows the team members of Team S.A.C.R.A.W standing alongside the final solar oven on Solar Oven Testing Day.
Team S.A.C.R.A.W Solar Oven 2
Table of Contents
Cover 1 Table of Contents 2 Executive Summary 3 Introduction – Motivation/Background/Key Terms 4-5 – Criteria and Constraints 5-6 Main Body – Functional and Design Requirements 6-7 – Design Theory and System Model 7-10 – Design Description – Conceptual Design 11-13 – Design Description – Final Design 14-17 – Design Justification 17-18 – Evaluation of Results 18-19 – Test Procedure 19-20 Design Critique and Summary 20-22 Appendix – First Oven Spreadsheet Data and Design/Drawing 22-24 – Final Oven Spreadsheet Data and Design/Drawing 25-27 – References 28
Team S.A.C.R.A.W Solar Oven 3
Executive Summary
The objective of the solar oven project was to design, build, and test a productive solar oven that
could reach an interior temperature of 100˚C. This was obtained through converting solar energy,
also known as electromagnetic energy, into thermal energy. The first law of thermodynamics
was utilized by understanding that energy cannot be created or destroyed but could be
transformed and used to heat the interior of the oven.
Two solar ovens were constructed in order to fully maximize the temperature inside the oven
chamber. The first oven was used as a prototype and research tool in order to build an oven that
could reach the optimum temperature calculated. The initial oven was predicted at 170.26˚C but
only reached an interior temperature of 85.6˚C. This produced a preforming index number of
1.02 and a cost index of 6.05˚C/dollar. The improved oven had a predicted temperature of
176.58˚C using the ambient air temperature and solar density provided. The oven reached an
interior temperature of 99.6˚C. The performing index for the second oven was calculated to be
1.28 and a cost index of 4.34˚C/dollar.
Team S.A.C.R.A.W Solar Oven 4
Introduction
Motivation:
• Learn the concept of team work and how to work together with other people to
achieve a common goal
• Gain proficiency in Excel, Solid Works, and basic solar oven knowledge.
• Acquire knowledge of the transformation of solar energy to heat.
• Learn the basics of the design and construction process
Background:
The main goal of the solar oven project was to find out the best way to change solar
energy into thermal energy. To do this, teams needed to know the first law of thermodynamics.
The first law states that energy cannot be created or destroyed, but can be changed from one
form to another. In the Solar Oven Theory, the energy that is put into the oven should equal the
energy that comes out (Ein=Eout). Therefore, the solar energy in joules should equal the thermal
energy in joules. The oven does this by taking the energy from the sunlight and transferring it
into heat. Since the energy in equals the energy out it allows the equation stated above to be
true. Knowing that the power is equal allows Team S.A.C.R.A.W. to find the temperature of the
oven chamber.
Mathematics for the Solar Oven with Key Terms:
Predicted Temperature:
Team S.A.C.R.A.W Solar Oven 5
€
Tio = Tambient + IoAw ⋅ G⋅ τ
n ⋅ a Usb ⋅ Asb +Uw ⋅ Aw( )
Variables:
Tio =the temperature inside the cooking chamber
Tambient= the outdoor temperature on the day tested
G= the gain from the reflectors
Uw= the heat transfer coefficient of the window
Aw= the area of the window
Usb= the heat transfer coefficient of the sides and bottom of the cooking chamber
Asb= the total area of the sides and bottom of the cooking chamber
Constants:
a= absorption coefficient of the cavity walls
τ= the optical transmission coefficient of the cavity walls
Io= the incident solar power density
Performing Index:
Variables:
Tio =the temperature inside the cooking chamber
Tambient= the outdoor temperature on the day tested
Tpredicted= the predicted temperature of the oven
Cost= the amount of money and labor for the solar oven in dollars
(Source: “Solar Oven Basics” Engineering 102)
Team S.A.C.R.A.W Solar Oven 6
Criteria and Constraints:
• Cooking oven must be equal to 1000 cm3
o Length (L) and height (h) need to be a minimum of 5cm
• The cooking oven window needs to be a square (W=L)
• The oven must have access for a digital thermometer and have a rack to support a biscuit
• There must be two calculated Performing Index’s calculated PISTOD and PIcost
• The maximum M/L ratio is 3
• The minimum final oven temperature is 100ᵒ C
• Optimal final temperature is over 200ᵒ C
• Focusing lenses and parabolic designs are not allowed
(Source: Solar Oven Design Project and Report Guidelines)
Main Body
Functional and Design Requirements The overall purpose of constructing the solar oven is to convert the absorbed solar energy into
heat. Different requirements of the oven were given in order to fulfill the purpose of constructing
and designing the solar oven. Functional requirements of the oven are needed in order for the
oven to actual work. Functional Requirements for the project include:
• The oven chamber must reach a minimum temperature of at least 100 degrees Celsius.
This is the minimum temperature that is needed to cook the biscuit inside the solar oven
chamber
Team S.A.C.R.A.W Solar Oven 7
• Using exactly four reflectors, sunlight needs to deflect into the Mylar windows at a
certain angle in order to achieve maximum temperature.
• Insulation is needed to surround the chamber to avoid loosing any form of heat.
• The four reflectors given need to be placed at a certain angle to not let any of the sunlight
be steered away from the Mylar window.
• An object or stand supporting the oven may be used in order to have the window be
exactly perpendicular to the sunlight. This way, all the sunlight can directly enter the
window.
Design requirements are given to avoid any advantage towards any oven. These requirements are
given in order for every oven to be at the same advantage. Design Requirements for the project
include:
• The oven chamber dimension should equal exactly 1000 cm3.
• Access to the inside of the solar oven should be fairly simple. Different methods to access
the oven include: lifting the top, door-opening mechanism, the sliding tray mechanism,
and many other methods.
• A hole or small opening for the thermometer to have access to the oven chamber
• The ratio of the reflectors and the width of the widow (M/L) should have a ratio of three
or less.
• The reflectors should be flat and straight; not parabolic. Having parabolic curves could
result in an explosion in the solar oven.
Design Theory and System Model
To conquer the solar oven, Team S.A.C.R.A.W. had to learn more about the theory
behind the solar oven. The knowledge learned can be implemented into constructing the most
Team S.A.C.R.A.W Solar Oven 8
efficient solar oven. The different dimensions of the oven are variables that affect how much
solar energy is converted heat inside the solar oven chamber. By knowing how these variables
affect the temperature allowed Team S.A.C.R.A.W. to reach optimum temperature inside the
oven. The equation predicting the temperature inside the chamber is:
Figure 2: Shows the equation to predict the temperature inside the solar oven chamber
In the equation above, the variables that have the most effect on the predicted temperature (Tio)
are the variables that are related to the dimensions of the solar oven chamber (Asb and Aw). Asb
represents the total surface areas of the side and bottoms of the solar oven chamber. Aw
represents the surface area of the window that heat is transferred through. Since a given
constraint of the oven is that the volume has to equal 1000 cm3, increasing the Aw would result in
decreasing the Asb. Since Aw appears in both the denominator and numerator in the equation,
increasing the value would have no affect in the Tio , but decreasing the Asb would result in a
higher Tio since the variable only appears in the denominator.
In the equation, G represents the gain of heat that the solar oven reflectors acquire. The
following equation is used to calculate the value of G:
Figure 3: Shows the equation to solve for G, and the variables that affect the value
As shown in Figure 3, the number of reflectors (represented by r) affects the overall gain.
Without any reflectors, the gain would equal just one. A higher M/L ratio for the oven would
also increase the gain value. The maximum value of M/L that is allowed is three, and as shown
€
Tio = Tambient + IoAw⋅ G⋅ τ
n⋅ a Usb⋅ Asb +Uw⋅ Aw( )
Team S.A.C.R.A.W Solar Oven 9
in Figure 3, the highest M/L would be most ideal. However, as shown in the table below, having
a higher M/L ratio results in a smaller alpha value.
Table 1: Shows the M/L ratio and the alpha and omega angle associated with each ratio
M/L α Ω 3 16.31° 106.31° 2 21.47° 111.47° 1 30° 120°
The alpha angle in the higher M/L ratio is smaller than the smallest M/L ratio, which is one.
However, when multiplying the M/L ratio by the sin (α), the highest value still comes out for the
M/L value that equals three. The highest M/L value is preferred for constructing the oven
because it will allow for the largest reflector gain for the oven.
Two values in the solar oven predicted temperature equation depend on the weather:
temperature (Tambient) and the solar irradiance of the sun (Io) at that time of day. If the
temperature outside is low, the Tambient will also be low, which would result in a lower Tio. If the
sky is cloudy and hardly any sunlight is penetrating through, the solar density will be low, which
would also result in a lower Tio. The weather is a major component in a higher Tio. Because
Arizona relatively tends to have high temperatures and large amounts of sunlight, both values
should be high.
Two other given constraints in the solar oven predicted temperature equation are τ
(optical transmission coefficient of window) and a (absorption coefficient of the cavity walls).
Team S.A.C.R.A.W wanted as much power to be absorbed into the solar oven chamber as
possible, which would result in a higher Tio To achieve such results, both τ and a have to be as
close to one as possible. The optical coefficient of the window depends on the type of window
material used. An ideal window material used for higher τ would have to be highly transparent
Team S.A.C.R.A.W Solar Oven 10
across the visible and near-infrared spectrum. The absorption coefficient of the cavity walls (a)
depends on the color used. The color black absorbs the highest amount of sunlight in comparison
with others colors, and thus has a higher absorption coefficient.
In the solar oven chamber predicted temperature equation, having a low U (overall heat
transfer coefficient) would result in a higher predicted temperature. The value of U is inversely
related to the thermal resistance to the flow of heat energy (R). The equation below shows the
relationship between both values:
Figures 4: Shows the relationship between the heat transfer coefficient and the thermal resistance
The equation shows that having multiple materials with higher thickness (x) and higher thermal
conductivity (k) values result in a higher R-value, which results in a lower U value. Having more
insulation materials (such as cardboard, foam, newspaper) decreases the overall heat transfer and
increases the Tio.
One of the main goals of Team S.A.C.R.A.W for constructing the solar oven chamber is
to have the actual temperature acquired equal to the predicted temperature calculated. However,
the task is nearly impossible. Different sources of error can prohibit Team S.A.C.R.A.W from
achieving the desired goal. One of the main errors is not having the dimensions of the solar oven
match up with the ones calculated. For example, if Team S.A.C.R.A.W calculated the area of the
window to be 0.02 m2 and instead constructed a window with an area of 0.018 m2, the result
would be an actual value of Tio that differs from the calculated Tio. Another source of error
includes the deterioration of the materials due to the heat. The materials to construct the oven
must be careful considered. If the materials used are not able to withstand the heat and melt, the
solar oven’s durability will also decrease.
Team S.A.C.R.A.W Solar Oven 11
Design Description – Conceptual Design
Figure 5: Shows the outer view of the first oven Figure 6: Shows the inside view (the insulation) of the first solar oven constructed
constructed.
The first goal for Team S.A.C.R.A.W was to generate a solar oven that met the minimum requirements given by the instructor. Since every solar oven group had two official
trials to test out the ovens, Team S.A.C.R.A.W.s’ main focus was to achieve the optimum
temperature possible with the given constraints. The variables in our oven focused around the
dimensions of the oven chamber. The following table lists the variables that were adjusted for the
first solar oven.
Table 2: Shows the design variables and measurements for the first solar oven constructed
Design Variables Measurements
Aw 0.01 m2
0.92
a 0.9
r 0.7
40
Usb 0.642192854
Asb 0.05 m2
Team S.A.C.R.A.W Solar Oven 12
Io 691 W/m2
40 degrees
Tambient 29.4 degrees Celsius
G 5.205335351
The materials that were given by the instructor to construct the oven include:
cardboard, Mylar sheets, black paper, scissors, and a thermometer. The cardboard given was
used to construct the four reflectors, the solar oven chamber, and the outer box where the solar
oven chamber and insulation was kept. Black Duct tape was used to connect the solar oven
chamber to the lid of the outer box. To get to the oven chamber, the reflectors and Mylar sheets
where lifted from a hole centered in the top lid. Inside the chamber, there was a rack that was
intended to hold to biscuit in place. To position the angle of the oven in order for the oven
chamber to absorb optimum heat, backpacks and notebooks were used.
Two Mylar sheets were used and were on top of one another. They were placed
directly above the solar oven chamber and were connected to the reflectors. Having more Mylar
sheets minimized heat losses through the window, while still allowing solar energy to be
transmitted into the oven chamber.
Four reflectors were used and were covered with aluminum foil. Aluminum foil was
used because the material is low-cost and effective. Despite trying to have a smooth aluminum
foil covering the reflectors, Team S.A.C.R.A.W had to take into account the wrinkled sheets,
which affects the overall temperature inside the oven. The shape of the four reflectors was a
trapezoid, and to keep things simple, the height of each reflector was 30 cm. Having a trapezoid
shape for the reflectors allowed no gaps between the reflectors, a problem that would arise if
rectangular reflectors were used. The base of the reflectors was 10 cm wide, conforming to the
Team S.A.C.R.A.W Solar Oven 13
dimensions of the width of the mylar windows. In order to maintain a M/L ratio of 3 or less, the
area of the window had to be 10 cm by 10 cm. To keep with the constraint of having a solar oven
chamber with a volume of 1000 cm3, the solar oven ended up being a cube.
To maximize insulation, Team S.A.C.R.A.W built a huge outer oven to store all of
the insulation. The dimensions of the outer box were 0.62×0.62×0.1 all measured in meters.
However, the insulation material used – newspaper and printer paper – was all wrinkled up and
was not arranged in an organized matter (as shown in Figure 4). However, having high
insulation, allowed for a higher Uxb value, which increases the Tio value overall. Also, to not let
any heat escape the sides of the oven, the thermometer was placed inside the oven. Having that
particular setup prevents obstruction of window and loss of heat through mylar window.
To obtain the dimensions for the oven, Team S.A.C.R.A.W worked from the inside
out, starting with the dimension of the solar oven chamber. To keep things simple, the solar oven
chamber was made into a cube, and from those dimensions, the height of the reflectors was
determined. Having a maximum volume of 1000 cm3 and a M/L ratio of less than three put a
constraint on the oven since it prohibited from further increasing the height of the reflector.
Team S.A.C.R.A.W Solar Oven 14
Design Description – Final Design
Figure 7: Shows the construction of the new reflectors Figure 8: Shows the side view of the for the final oven final solar oven on Solar Oven Testing Day
The first solar oven testing allowed Team S.A.C.R.A.W to see what adjustments were
needed for the second oven. Needless to say, many adjustments were done. A new goal was
created – to reach the minimum temperature required, which was 100 degrees Celsius. Also, the
group strived to try to achieve a higher Performance index by reducing the total materials used,
thus reducing the total performing index. To decrease the cost without falling under the
minimum temperature required (100 degrees Celsius), Team S.A.C.R.A.W. took the following
steps: create a smaller insulation box, create smaller and more efficient reflectors, and improve
the design of cooking chamber in order to maximize the total volume. The following variables in
the table below show the values used to calculate the predicted temperature
Table 3: Shows the list of variables used to predict the temperature inside the oven chamber.
Design Variables Measurements
Aw 0.013225 m2
0.92
a 0.9
Team S.A.C.R.A.W Solar Oven 15
40
Usb 0.642192854
Asb 0.0219206522 m2
Io 619 W/m2
40 degrees
Tambient 29.4 degrees Celsius
G 5.205335351
Somehow, the first solar oven had dimensions that did not match up with the dimensions
that Team S.A.C.R.A.W. calculated. The group that dissected the oven noticed that the alpha
angle did not match up with the value that Team S.A.C.R.A.W had calculated. The angle value
that Team S.A.C.R.A.W that used based off of the M/L value, which was equal to three. The
group that dissected Team S.A.C.R.A.W.s’ oven measured out the angle to be 15.687 degrees.
The angle that Team S.A.C.R.A.W. calculated based off the M/L ratio was 16.31. Also, the M/L
ratio (that the group who dissected Team S.A.C.R.A.Ws’ oven measured out) was higher than
three. Knowing that these dimensions were inaccurate from the proposed dimensions given by
Team S.A.C.R.A.W, Team S.A.C.R.A.W focused more on accurately measuring out the
dimensions of the oven and making sure that all of the dimensions calculated for the oven
matched up to the actual oven.
Instead of constructing a cubic oven chamber, a rectangular-shaped oven was generated.
Team S.A.C.R.A.W decreased the height of the oven chamber to increase the area of the top and
bottom sides of the oven chamber. Since the width and length of the Mylar sheets are correlated
with the dimensions of the top lid of the chamber oven, the area of the window also increased by
making the oven chamber rectangular. The length of the square Mylar sheet for the new oven
Team S.A.C.R.A.W Solar Oven 16
was determined to be 11.5 cm, which also increased the height of the trapezoidal reflectors to
34.5 cm (to keep in with the M/L ratio of 3).
During the trial for the first solar oven, Team S.A.C.R.A.W noted that tape used did not
properly hold the oven in its place. A new brand of tape was bought, Gorilla duct-tape, which
withstood the heat and did not melt or peel off when exposed to the sun. Although it increased
the Performance Index cost since it was more expensive than the previous adhesive, this new
duct-tape improved structural rigidity and high-temperature performance. The duct-tape was
applied along the sides and corners of any joint component of the oven, which resulted in a
stronger structure and prohibited any air from escaping.
Instead of using wrinkled up newspaper and printer paper for insulation, Polyurethane
insulation foam was used. This foam did a better job of trapping heat and hardly left any room
for letting heat escape. The foam also had greater thickness than the newspaper and higher
thermal conductivity, thus increasing the resistance to escaping heat. However, it was discovered
afterwards that the foam expanded during testing. This increased the dimensions of the outer box
and may have possibly decreased the volume of the solar oven chamber.
The last improvement done on the final solar oven would be the dimensions of the
reflectors. Since the alpha angle was off in the first solar oven, a protractor was used to insure
that the angle matches to the one calculated by Team S.A.C.R.A.W. These new reflectors were
longer, were angled correctly to match the alpha angle calculated (16.31 degrees Celsius), and
had a higher reflectivity (aluminum foil was much smoother). Also to avoid loosing more heat,
the chambers’ sides were still connected with the reflectors when they were cut out. This way,
instead of loosing heat between the gaps of the reflectors and chamber, hardly any heat would be
lost. To have access to the insides of the chamber, the chamber and reflectors were lifted (since
Team S.A.C.R.A.W Solar Oven 17
they were connected). The Mylar sheets were placed from the top and were put at the bottom of
the reflectors. The cut out of the Mylar sheets had a slightly larger area than the window
dimensions, allowing the extra surface area on the Mylar sheets to connect the mylar window to
the top of the solar chamber (area where the solar chamber and reflectors meet).
Much more care and accuracy was placed into constructing the final oven in comparison
with the first oven. Also, to absorb more heat, the inside solar chamber was painted black. Black
is known to absorb the most amount of heat in comparison with other colors. Team
S.A.C.R.A.W also made the outer chamber more aesthetically pleasing by decorating it with red
paint.
Design Justification
To keep the first solar oven simple, Team S.A.C.R.A.W. made the solar oven chamber,
the basis for the construction of the oven, a cube. Team S.A.C.R.A.W.s’ main focus was on
simplicity and the performance of the oven, thus generating an oven with large reflectors and a
cubic solar oven chamber. With those factors in mind, Team S.A.C.R.A.W designed the oven
and constructed the oven based on those parameters. An example of a performance-orientated
component of the oven was the insulation. Team S.A.C.R.A.W decided to use as much insulation
as possible to achieve optimum temperature and a greater performance overall. Unfortunately,
having more insulation in the outer box chamber resulted in more material usage and more open
space for heat to escape (a factor that was not thought of until the day of solar oven testing). In
addition, the size of the reflectors was maximized in relations with the width of the window
(M/L = 3). Both actions were done without a thought about the performance index cost.
Team S.A.C.R.A.W Solar Oven 18
Once the oven was tested and dissected by another team, Team S.A.C.R.A.W noticed that
keeping the oven simple was not a method to achieve maximum performance. The overuse of
materials and lack of accuracy of the dimensions made the performance index relatively low. As
a result, the oven had the lowest temperature acquired out of all the other ovens in the class. For
the second oven, the team decided to replace many materials with more durable options and
made sure that the oven matched the dimensions that were calculated. Less cardboard was used
on the solar chamber and outer chamber, and also, different insulation was used. However, to
obtain a higher temperature, the size of the reflectors was increased. Increasing reflector size
resulted in a higher area of window and a lower surface area of the sides and bottom of the
chamber. The outer chamber box was decreased to reduce the insulation and the new insulation,
foam, did a better job of not letting heat escape than the newspaper and printer paper. The
performance index cost reduced with the usage of less material for the first oven. Also, the
overall performing index of the new solar oven was higher than the first solar oven.
Evaluation of Results
Due to the cloudy day and lack of sunlight, the final test did not yield results consistent
with the teams’ expectations and did not verify the final design process. The solar power density
given before the Solar Oven Throw down did not match up with the actual solar density value of
the weather. The result caused the predicted temperature calculated beforehand to be much
higher than the one actually calculated on that day (calculated to be around 109 degrees). The
temperature of the final oven was 99.6 degrees Celsius with a performing index of 1.28. The
predicted temperature of the oven on that day was calculated to be 176.58 degrees Celsius. The
large difference in predicted and actual temperature resulted in a lower performing index.
Team S.A.C.R.A.W Solar Oven 19
However, the main focus for the second design of the solar oven was to improve on the
performing index and durability of the oven. The first oven had a performing index of 1.02, a
predicted temperature of 170.26 degrees Celsius, and an actual temperature of 85.8 degrees
Celsius. No issues regarding the weather occurred on the first solar oven trial day – the day was
filled with sunlight and heat. Although the final oven did not reach the desired 100 degree
Celsius temperature, the final oven had a greater performance and better durability than the first
oven, which was the overall goal for Team S.A.C.R.A.W.
Test Procedure
Table 4: Shows the values measured in both ovens.
Value Measured First Oven Second Oven
Predicted Temperature (Tio) 170. 26 degrees Celsius 176.58 degrees Celsius
Actual Temperature Acquired 85.8 degrees Celsius 99.6 degrees Celsius
Performing Index 1.02 1,23
Performing Cost 6.05 degrees Celsius/dollar 4.34 degrees Celsius/dollar
As shown in Table 4, the measured values are much smaller than the predicted values. For the
first oven, Team S.A.C.R.A.W. identified that the result of disagreement between the predicted
and actual temperature value was because of the lack of accuracy done on the dimensions of the
oven. The angles of the reflectors were not measured accurately – the angles were just assumed
to be correct based off of the dimensions of the reflectors. Also, the insulation was not tightly
packed together; instead there were many openings for heat escape through. For the second oven,
more accuracy was placed on the dimensions of the oven. Also, a different material was used for
Team S.A.C.R.A.W Solar Oven 20
the insulation. However, the reason for the vast difference in degree of the predicted and actual
temperature was because of the weather. The weather on solar oven testing day was much cooler
than predicted. Also, not that much sunlight was penetrating through the clouds, resulting in a
lower solar irradiance value (I0)). The change in weather is out of Team S.A.C.R.A.Ws’ control,
thus no conclusion can be made on what improvements could have been done for the final oven
aside from testing it on a different day that includes more sunlight and less clouds.
Design Critique and Summary
Team S.A.C.R.A.W.’s objective was to build a solar oven that met the constraints and
performed at optimum temperature. The team needed to build the oven at a low cost but still able
to withstand the high temperatures made on the day of testing. Teamwork, collaboration, and
attention to detail were implemented to produce an oven that had the potential to reach 176.58°
C. During construction of the first and second oven, the team realized many areas of
improvement that would raise the temperature of their oven and produce a more efficient
product. For example, in the first oven constructed, a flimsy duct tape was used to hold together
the corners of the exterior of the oven. When the first oven was tested, the tape could not
withstand the high temperatures and the adhesives began to fall apart. Because of the error, gaps
began to form around the exterior oven, which allowed heat to escape. To prevent this from
happening again, the second oven was constructed with a heavy-duty black duct tape that was
able to withstand much higher temperatures than what could be reached with the solar oven. If
Team S.A.C.R.A.W Solar Oven 21
another oven was to be built, it should be constructed with the heat resistant tape to minimize the
heat loss. Another area that needed improvement from the first oven to the second was the angle of
the reflectors relative to the oven container. Precise measurements needed to be done in order to
have the optimal angle that would allow the most solar light to be reflected into the cooking
chamber. To fix this problem, S.A.C.R.A.W. used a more accurate protractor and ruler when
measuring the reflectors for the second oven. This way the angle was accurate and allowed the
most light to be reflected into the cooking chamber. If this oven was to be reconstructed it is
recommended that an emphasis is put on the measurement of the angles because this has a direct
impact on the amount of light reflected into the cooking chamber. The more light reflected into
the cooking chamber, the higher the temperature will reach.
The insulating material is a large component of how much heat will be retained and how
much will be lost through the walls of the oven. In the first oven, the team used crumpled up
newspaper and printer paper to insulate the cooking chamber. While the crumpled up paper took
up a lot of room, there was a lot of room for the air to move around between the pieces of paper.
The conductive heat loss was maximized because the molecules had a lot of air to move around
in and therefore they did not hold very much heat. For the second oven constructed, insulating
foam was used inside the oven. The foam sealed all of the edges of the oven to heat was not lost
through those and it also reduced the movement of air inside the chamber. The heat stayed
localized to the chamber instead of freely moving about the oven and escaping. This was
essential for the oven built by S.A.C.R.A.W. because on the day of testing it was very cloudy out
and the ambient air temperature and the incident solar density were not very high. This meant
that the oven only increased temperature when there was direct sunlight. The data oscillated
Team S.A.C.R.A.W Solar Oven 22
because every time the sun would go behind the clouds, the temperature would drop slowly and
when the sun would come back out, the temperature would shoot up. Because of the foam
insulation and the minimal amount of heat escaping the oven, S.A.C.R.A.W.’s oven was able to
maintain a temperature higher than the ambient air temperature when the sun was behind the
clouds so when it did come out and provide direct sunlight, the temperature was able to start at a
higher initial temperature and rise from there. If there had been direct sunlight on the day of
testing, the oven would be considered a viable cooking unit that could be used if desired to cook
food for consumption. Appendix
First Oven Spreadsheet Data and Drawing
Figure 9: Shows the drawing and dimensions for the first solar oven.
Team S.A.C.R.A.W Solar Oven 23
Table 5: Shows the value of each variable and their value. It also states the variables’ units and description
Variable Value Units Description Io 619 watts/m2 (solar power density)
τ 0.92 (transmissivity for single layer of mylar)
a 0.9 (absorptivity of oven chamber and contents)
r 0.7 (reflectivity of Al foil) Tambient 29.4 C ambient temperature L 0.1 m length of oven window
h 0.1 m height of oven chamber n 2 # of layers of mylar M 0.3 m length of reflectors Aw 0.01 m2 area of the window
Asb 0.05 m2 area of the sides and bottom
Vchamber 0.00099981 m3 volume of the oven chamber
M/L 3 ratio of reflector length to oven window length
Usb 0.642192854 heat transfer coefficient of the chamber
α 0.284602961 angle of the reflectors with respect to the Sun’s rays
G 5.205335351 gain from reflectors Table 7: Shows the dimensions of the oven
Table 6: Shows the materials used for insulation
Wall Element Thickness (m)
Thermal Conductivity (watts/m-C)
Inner cardboard wall x1 0.003 k1 0.064 Insulation (wadded newspaper) x2 0.18 k2 0.123 Outer cardboard wall x3 0.003 k3 0.064
Dimension Length (m) Length of window 0.1 Width of window 0.1 Length of oven 0.6096 Width of oven 0.6096 Height of oven 0.1524 Length of chamber 0.1 Width of chamber 0.1 Height of chamber 0.1 Reflector length 0.3
Team S.A.C.R.A.W Solar Oven 24
Tio Uw(single) Uw(double) Table Combo 1
10.1 4.9 66 225.319429 13.9 6.7 93 179.723146 18.7 9 121 145.571651 24.3 11.7 149 121.231541 31.6 15.2 177 101.530964 40.1 19.4 204 87.1142525
Value Measured First Oven Predicted Temperature (Tio)
170. 26 degrees Celsius
Actual Temperature Acquired
85.8 degrees Celsius
Performing Index 1.02 Cost Index 6.05 degrees
Celsius/dollar
Component Amount Cost ($)
Total Cost for Component ($)
Grand Cost ($)
Reflectors $0.31 $1.25 $1.25 Interior Chamber
$0.40 $0.40 $1.59
Exterior Chamber
$1.94 $1.94 $3.73
Mylar Sheets $0.25 $0.50 With Reflectors
Duct Tape $0.50 $0.50 $8.73 Paper $0.03 $0.03 With interior
chamber Newspaper $0.00 $0.00 $8.73 Grand Total $8.73
Table 8: Shows the heat transfer values for the windows
Table 9: Final Results for the First Oven
Table 10: Shows the breakdown of costs for the first oven
Figure 10: Shows the graph and equations of line used to predict the temperature of the fist oven
Team S.A.C.R.A.W Solar Oven 25
Second Oven Spreadsheet Data and Drawing
Figure 11: shows the drawing and dimensions for the final oven
Team S.A.C.R.A.W Solar Oven 26
Table 11: Shows the values for the variables used to predict the Tio for the second oven Variable Combo 1 Units Description Io 619 watts/m2 (solar power density)
τ 0.92 (transmissivity for single layer of mylar)
a 0.9 (absorptivity of oven chamber and contents)
r 0.7 (reflectivity of Al foil) Tambient 29.4 C ambient temperature L 0.115 M length of oven window
h 0.115 M height of oven chamber n 2 # of layers of mylar M 0.345 M length of reflectors Aw 0.013225 m2 area of the window
Asb 0.048001 m2 area of the sides and bottom
Vchamber 0.00099981 m3 volume of the oven chamber
M/L 3 ratio of reflector length to oven window length
Usb 0.642192854 heat transfer coefficient of the chamber
α 0.284602961 angle of the reflectors with respect to the Sun’s rays
G 5.205335351 gain from reflectors Table 12: Shows the values for the insulation used. Table 13: Shows the dimensions of the oven
Wall Element Thickness (m)
Thermal Conductivity (watts/m-C)
Inner cardboard wall x1 0.003 k1 0.064 Insulation foam x2 0.0925 k2 0.21 Outer cardboard x3 0.003 k3 0.064
Dimension Length (m) Length of Window 0.115 Width of Window 0.115 Length of oven 0.3 Width of oven 0.3 Height of oven 0.197 Length of Chamber
0.115
Width of Chamber 0.115 Height of Chamber 0.0756 Reflector Length 0.345
Team S.A.C.R.A.W Solar Oven 27
Table #16: Shows the breakdown of costs for the final oven
Tio Uw(single) Uw(double) Table Combo 1
10.1 4.9 66 358.947717 13.9 6.7 93 285.790364 18.7 9 121 229.865253 24.3 11.7 149 189.399928 31.6 15.2 177 156.270352 40.1 19.4 204 131.809152
Value Measured Second Oven Predicted Temperature (Tio)
176.58 degrees Celsius
Actual Temperature Acquired
99.6 degrees Celsius
Performing Index 1,23 Cost Index 4.34 degrees
Celsius/dollar
Component Amount Cost $
Total Cost for Component $
Grand Cost $
Reflectors $0.43 $1.72 $1.72 Interior Chamber
$0.05 $0.05 $1.77
Exterior Chamber
$0.71 $0.71 $2.48
Mylar Sheets $0.25 $0.50 With Reflectors Duct Tape $5.00 $5.00 $7.48 Foam $5.00 $7.50 $14.98 Grand Total $14.98
Figure 12: Shows the graph and equation of lines used to determine the predicted temperature for the final oven
Table 14: Shows the heat transfer values for the windows Table 15: Shows the final results for the final oven.
Team S.A.C.R.A.W Solar Oven 28
References References from Solar Oven Handout
“Solar Oven Basics” University of Arizona. Engineering 102. 2012
Shawyer, Michael and Avilio F. Medina Pizzali. “FAO Fisheries Technical Paper 436: The use
of ice on small fishing vessels.” FAO Corporate Document Repository. Food and
Agriculture Organization of the United Nations. Rome. 2003. Web. 13 Oct. 2012.
