Solar Group Project Report

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Prepared for: Dr Senthilarasu Sundaram
Prepared by: Hakeem Buge, Chris Aoun & Hugo Tilmouth
8 December 2016
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Solar Powered Electronics Charging Station
CSMM427 SOLAR ENERGY RESEARCH & INNOVATION

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ABSTRACT
In this report, a polycrystalline-module is designed, fabricated and the corresponding analysis has been
completed to show its performance. The report includes an in depth analysis of the individual cell testing using
an I-V and an external quantum efficiency test (EQE) as well as the overall panel testing with comparisons to
industrial modules. Further studies have been completed on the thermal efficiency, Sylgard application,
soldering, component efficiencies, a resource analysis using PVSyst, gas strut calculations as well as user
testing to provide an all round evaluation of the project.
SPECS is designed for outdoor applications and specifically for UK parks. The module is highly effective at
charging a range of devices from mobile phones to tablets and a later iteration of the design can be scaled up
for commercial use across the globe.  
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TABLE OF CONTENTS
Abstract 3
Table of Contents 4
List Of Figures 6
List Of Tables 7
Aims and objectives 8
Objective 8
Goals 8
Introduction 9
Methods 10
System Design And Cad Drawings 10
Schematic Of Electronics 11
Analytical Calculations 12
Material Purchase List 13
Design Specification 14
Fabrications And Testing Methods 16
Results and Discussions 24
Soldering Review & Cell Breakages 24
Lab Testing Of Cell 24
Theoretical Maximum Calculations 31
Panel Testing 32
Comparison Between Theoretical, Actual & Industrial 36
Cell Thermal Efficiency Study 43
Individual Cell Function Test 44
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Sankey Diagram Of Energy Losses 47
Sylgard Application And Calculation 48
Use Of Acrylic Over Glass. 49
Efficiencies Of Components 51
Economics 53
Potential Sites For Placement Of Specs 56
Pvsyst Analysis 58
Gas Strut Calculations 64
Indoor Testing 65
Outdoor Testing 66
User Testing 67
Evaluation 68
Construction And Project 68
Evaluation Of Testing 69
Conclusion 70
Acknowledgement 71
Bibliography 72
Appendices 75
Sylgard® 184 Silicone Elastomer Properties 75
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LIST OF FIGURES
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LIST OF TABLES
insert when pdf 
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AIMS AND OBJECTIVES
OBJECTIVE
The objective of this project is to build and test the performance of a photovoltaic PV panel. The fabricated
panel consists of 36 monocrystalline solar cells. The performance of the fabricated solar panel will be
compared to that of a commercial solar panel of similar dimensions. Comparative performance analysis of the
IV Curve, Isc, Voc, Fill factor, Pmax and efﬁciency of the commercial and fabricated panels will be carried out.
This report outlines the methodology behind the construction of the panel and outlines the experiments and
results from the assessments carried out on an individual solar cell as well as the fabricated panel. The
fabrication of the solar panel required the soldering of electrical connections and encapsulation using Sylgard
within a glass casing. This document also discusses the design and application of the fabricated panel which
has as its objective to be utilised as a source of energy for small electronic devices.
GOALS
1. Optimally design a solar module for an appropriate application
2. Investigate a test cell’s performance to estimate the characteristics of the module
3. Construct the solar module
4. Test the solar module to verify earlier estimated power output and efﬁciency
5. Suggest reason for underperformance of the solar module
6. Compare module to industrial panels
7. Provide further analysis on various aspects of the design to gain a deeper understanding of performance
behaviour
8. To successfully charge multiply electronic devices
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INTRODUCTION
The initial idea of this project stems from the fact that even in the modern day and age, the electronic devices
regularly used on a day-to-day basis, such as mobile phones or tablets, consist of batteries that have
considerably low discharge times. The SPECS team wanted to create a system that would solve this issue
during a time when the electronic device would not be needed, for example, whilst taking a walk in the park or
undertaking recreational activities. Therefore, the result is to design a panel that would provide sufﬁcient energy
to charge the equivalent of four mobile phones at the same time and be portable to use in outdoor
applications. The structure will contain lockers to provide a space for the devices to be safely stored during the
period of charging. The idea was further pushed forward after completing some market research because
solar charging stations are not regularly used within the UK even though they would have a very useful
purpose during summer time.
The report will encompass the methods, results and discussion followed by a reﬂection section that evaluates
the project as a whole as well as ideas on how to commercially implement the system if it is to be taken to
large scale applications.
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METHODS
In this section of the report the methods used for fabricating the panel and the locker module are explained
and illustrations shown for the key steps. Justiﬁcation for each stage is also given.
SYSTEM DESIGN AND CAD DRAWINGS  
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Four individual lockers for storage of
phone while charging, each of these
will be lockable for security
36 cell poly crystalline
silicone cell array,
connected in series
Strong metal legs to
support the weight of
the panel and locker
module
20,000 mAh of battery storage comprising of
two 10,000 mAh external usb chargers
DC-DC converter to step
voltage down from panel to 5v
Partition to separate
the individual lockers
Ample space to store
p h o n e , t a b l e t o r
camera while charging Charging cable with
connections suitable
for all phones
Hinge to open panel lid
Figures 1, 2 and 3: CAD model of
SPECS

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SCHEMATIC OF ELECTRONICS 
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Figure 4: Schematic of the electronics in the project

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ANALYTICAL CALCULATIONS
There were some calculations that were required to be completed in order to gain a better understanding of
how to match the output and sizing of the panel.
The cell specifications are as follows:
Format : 125 mm x 125 mm +/- 0.5 mm, diagonal:165 mm
Thickness: 200 +/- 20 um
Front (-): Silicon nitride anti-reflecting coating, 1.5 mm wide front silver bus bars.
Back (+): Full aluminium back surface field, 2.5 mm wide (silver/aluminium) soldering pads.
Power: 2.8W
Efficiency: 17.6-17.8%
Vmp: 0.523 V
Imp: 5.215 A
Voc: 0.629 V
Isc: 5.585 A
Calculations based on a panel consisting of 36 cells:
Total cell coverage area of panel: 125mm * 125mm * 36 cells = 0.5625 m2 (0.75m x 0.75m)
Total power: 2.8W * 36 = 101 W
Total Vmp: 0.523 * 36 = 18.8 V
Total Imp: 5.215 A
Total Voc: 0.629 * 36 = 22.6 V
Total Isc: 5.585 A 
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MATERIAL PURCHASE LIST
Number Item Cost
1 36 x monocrystalline cells (150mm x 150mm approx.)
Supplied by university.
£0.00
2 Tabbing Wire – Supplied by university £0.00
3 Sylgard – Supplied by university £0.00
4 1 x standard wood sheet of top of box (£8) £8.00
5 Planks for frame of the box and compartments (£64.38) £64.38
6 Bottom mdf board (£11.44) £11.44
7 4 x stands (£12) optional £12.00
8 Large sheet of transparent acrylic (£10) £10.00
9 Sheet of glass( £5) £5.00
10 4 x Hinges (£5) £5.00
11 2 x Batteries (£26) £26.00
12 DC-DC Converter (£8) £8.00
13 Phone charging cables (£16) £16.00
14 Other costs (£15) £15.00
Total £180.82
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Table 1: Costings of the project

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DESIGN SPECIFICATION
The solar module in this project is made of of 36 poly-crystaline cells, that are soldered together in a series
connection. These panels are first mounted on the MDF base of size 110cm x 110cm. This was chosen for its
ability to electrically insulate the cells and its ease of cutting and shape modification. This based then has a
3mm high boarder glued on top to create a space for the encapsulant to be spread without seeping out of the
sides. The encapsulent used is Sylgard 184 silicon elastomer, this is a highly transparent and insulating
material, and with a long curing time and viscous properties, it is able to fill open spaces automatically. Sylgard
also does not deform when exposed to heat while operating in the sun. On top of the encapsulent is a 3mm
acrylic sheet to prevent damage to the fragile cells. The series connection was completed using a copper
tabbing wire, with each module being soldered individually. The start and end connections were then drilled
though the wooden base and secured on the underside to allow connection to the electronic load devices.
Usually, to minimise losses due to resistance, tabbing wires are soldered to top or bottom of each module with
enough tabbing wire to connect to the next module. This arrangement can be seen in figure 5.
While starting the soldering process it was found that the panels would break under the weight of the long
tabbing wires (type A in figure 5). To avoid putting stress on the very delicate panels, short equal length,
tabbing wires protruding from both the top and bottom were soldered onto each cell (type B in figure 5). This
method can be seen in figure 5. This allows them to then be soldered to one another once installed onto the
full module, and more importantly prevent more cell breakage.
 
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Figure 5: Two types of tabbing wire methods

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The 36 cells were connected in series in arrangement show below in ﬁgure 6. When each cell was connected
in series the total circuit was then tested to ensure no cell was disconnected. To connect each line of 6 cells a
bus bar was soldered in reversing the direction and forming a zigzag shape for the cell arrangement.  
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Positive
Negative
Figure 6: Arrangement of the cells in the array

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FABRICATIONS AND TESTING METHODS
1. After purchasing the wood the ﬁrst step was to cut it to size using a circular saw. This was done with the
necessary safety precautions, using safety glasses and a dust mask.
2. As the wood was only half the width needed for the design, it was decided that two pieces should be
sandwiched together. The wood was then measured and drilled in to a precise depth.
3. The wood was then joined using dowel joints. It was also glued and then clamped together to make the
joint very strong. Then the gaps between the two pieces was ﬁlled with a mixture of wood glue and
sawdust. This would then be sanded down at a later date.  
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Stage 2Stage 1
Stage 3 Stage 3

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4. The front panel was then jigsawed to create the locker opening as shown below.
5. The frame was then doweled and glued together, before being clamped and left to dry over night. To add
additional strength 8 metal angle brackets were installed to ensure a 90 degree joint was maintained at
each corner.
6. The locker partitions were then made using a similar technique of dowel joints and wood glue.
7. The box was then assembled and a couple of pieces of wood drilled, screwed and glued in behind the
locker partitions so that they were secure, but could be removed at a later date to allow electronics to be
installed, and maintenance to be performed.  
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Stage 5Stage 4
Stage 6 Stage 7

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8. The solar cells arrived from China, and the soldering could begin. This involved cutting the tabbing wires
to the correct length, spreading flux on them, spreading flux on the cells and soldering the tabbing wires to
each side.
9. Once soldering was completed each cell was tested using the basic solar simulator in the renewable
energy laboratory to ensure that only the most efficient cells were chosen. The results from this testing can
found later in the report.
10. The image below shows the cells being numbered as they are individually tested.
11. The top wooden panel was then cut out to allow the solar cells to be installed on the surface. To prevent
the Sylgard from spilling out of the top surface, a 5mm border was glued to the surface. To guide the
placement of the cells a pencil guide was drawn onto the surface.  
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Stage 9Stage 8
Stage 10 Stage 11

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12. The soldering of the cells was completed in situ, on the wooden surface. After soldering each cell in series,
the entire chain of cells would best tested to ensure the last solder was completed properly.
13. At the end of each row the cells were connected via a bus bar to form a snake.
14. The next stage was to mix the Sylgard, this was measured and mixed in a 1:10 ratio of activator to carrier
ﬂuid. The Sylgard was the left to allow the air bubbles escape the liquid.  
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Stage 12Stage 12
Stage 13
Stage 14

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15. The Sylgard was then applied to all of the cells using a brush to carefully spread the liquid over the delicate
cells.
16. The top surface made from acrylic was then cut down to size using a jigsaw. We then polished the surface
to minimise the chance of air bubbles being trapped when placed onto the Sylgard.
17. The acrylic was then placed gently onto the top surface of the Sylgard and pressed to remove the air
bubbles.
18. Using the remaining acrylic, the locker doors were made, this was achieved by cutting them down to size,
attaching a small door handle and attaching a hinge. 
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Stage 16Stage 15
Stage 17
Stage 18

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19. Using reclaimed legs and bolts, a operation height system was constructed.
20. To achieve an antique look, a walnut coloured wood stain was applied to all of the wooden surfaces.
21. To make the top surface more tidy a frame was constructed to be attached on top of the acrylic. To
prevent shading a 45 degree was cut off the edge of the frames.
22. The edges were then cut down to the perfect size. 
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Stage 20Stage 19
Stage 21 Stage 22

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23. To attach the solar panel to the box a set of three hinges were installed. These were removable to allow
testing of the panel at a later date.
24. To prevent the hinge swinging open too much a string was installed.
25. The electronics were then installed inside the box. Leading from the solar panel were a positive and
negative connection, this went into a buck converter. This stepped the voltage down to 5v. This was then
split into two usb cables. These were then connected to two 10,000 mAh battery packs. These then had
two usb connections on each which had phone charging cables connected to each.
26. The phone charging cables had 4 different options for the different phones currently on the market.  
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Stage 24Stage 23
Stage 25 Stage 26

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27. It was decided that the best way to support the lid would be to install some gas struts to lift the solar
panel lid, and hold it in the 90 degree upwards position. After conducting online research it was found that
the geometry of these was more complicated than ﬁrst thought. A scale model of the gas strut was
therefore constructed to optimise the placement. More can be found in a later section of the report.
28. The gas struts were then installed according to the CAD model.
 
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Stage 28Stage 27
Stage 25 Stage 26

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RESULTS AND DISCUSSIONS
SOLDERING REVIEW & CELL BREAKAGES
At first there were several cells that were used to practice the soldering technique before starting the
production of the soldering for the cells that were to be used on the panel. It is important to take good practice
soldering because solar cell substrates are extremely delicate. The quality of the soldering process has a direct
influence on the series resistance of the photovoltaic module. Using a suitable ribbon thickness and also
monitoring how well the solder has been applied is very important in order to maintain constant performance if
this kind of project were to be implemented on a larger scale. Although if SPECS is to be pushed forward
further, it would be much preferable and efficient to implement the use of automatic machines that can provide
a constant soldering process so that series resistance can become negligible.
The manual process of soldering a solar cell requires a certain amount of pressure to be exerted which can
result in micro-cracks forming and propagating within the substrate. The formation of micro-cracks occurred
several times during the soldering process which were later followed by the complete breakage of the cells.
Several others were broken during the management, transportation and testing of the cells. Despite this, there
were 36 solar cells that were successfully soldered and ready to be implemented within the panel. However,
whilst the cells had been soldered and kept in storage with clear indications that they should not be touched,
the cells were moved by some people working in the lab, resulting in the further breakages of 6 more.
Fortunately as there were 4 unsoldered cells spare, it only left the panel with 2 cells short and hence only a
reduced output of approximately 4W.
LAB TESTING OF CELL
I-V Test
As shown in figure 7, one of the solar cells was selected to be tested through a solar simulator which can
provide various levels of solar radiation but the test had to be at standard conditions: solar irradiance of 1 sun
(1000W/m2), air temperature of 25 degrees celsius and an air mass of 1.5 (AM1.5) spectrum (admin, 2013).
This test is to determine the exact open circuit voltage and short circuit current after the soldering as this
would have changed from the cell specifications due to soldering or perhaps micro-cracks as previously
mentioned. The results of the lab testing are presented in figure 7 below.
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Power[W]
Figure 7: I-V curve showing the changes due to temperature effects Source: (Instruments, 2008)

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Figure 7 shows an I-V curve along with the related results that were generated by putting the cell through the
solar simulator. The short circuit current and the open circuit voltage are slightly less than the specified rated
values of the cell. One factor would be due to the soldering process but also it is important to note that the
actual measuring temperature is at 28.7 degrees celsius which is above the standard testing conditions and
therefore the extra heating would have a significant affect on these values. Whilst the blue coloured graph
represents the I-V curve, the green coloured graph is a representation of the power output for the given
voltages and currents.
Despite the fact that the Voc and Isc are the highest values at 0.59V and 5.4A respectively, the overall power at
both these values is 0W. Whereas the Vmp and Imp represent the values of voltage and current where the
maximum power occurs and this is highlighted on the graph by the point at the peak of the green parabola.
The maximum power given by the result of the test is rated at 1.686W which is comparatively lower than the
rated. A good indicator to be looking at is the fill factor (FF) which, in this case, has been measured to be at
0.526. A simple way of describing the fill factor is as a measure of the quality of the solar cell where the closer
it is to 1, the better the quality. In more technical terms, it is the ratio of the maximum power to the theoretical
power and it can be calculated through the equation (Instruments, 2008):
"
Therefore for this cell;
In order to analyse the potential causes of this value for the fill factor, the theory of I-V characterisation should
be studied.
I-V Characterisation
A good way to model a photovoltaic cell is a current source connected in parallel with a diode. Without any
incoming solar radiation (light), the cell simply acts as a diode. As the light intensity increases, current gets
generated by the cell and the Isc is dependant upon the value of that light intensity. Isc also occurs at the
beginning of a forward-bias sweep (When the positive terminal of the battery is connected to the p-type
material and the negative terminal of the battery is connected to the n-type material (Washington (2016)) and
FF =
Imp ×Vmp
Isc ×Voc
FF =
4.519 × 0.373
5.417 × 0.592
= 0.526
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for this project, if the soldering was done perfectly, there were no micro cracks and the cell was considered as
an ideal cell; this maximum current value would be equivalent to the total current produced in the solar cell by
the means of photon excitation.
The crystals within the poly-crystalline structure of the cells that were used in this project, as previously stated,
are very sensitive to temperature. It was observed that in the testing condition, the cell temperature was at
28.7 degrees celsius. So how much of an effect does this have on the I-V characterisation for the cell?
The follow ﬁgure shows exactly how much affect a temperature differential from the standard conditions can
have on the cell performance:
Figure 8 shows that both the Voc and the Isc are affected by a temperature increase but in opposite directions
where the Isc increases and the Voc decreases. A more interesting point to consider is the rate at which the
variation occurs. The change in Voc is 10 times more than that of the Isc per degree celsius. This would
provide a good explanation as to why the test results were slightly different to those of the cell speciﬁcation.
The following table compares the two results:
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Figure 8: I-V curve showing the changes due to temperature effects Source: (Instruments, 2008)

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The results show that in all cases the lab test values are lower than those on the specification but it is clear
that the voltage is affected more heavily than the currents. Although the previous table 2 shows that the Isc
should increase, the fact that it has decreased practically provides evidence that this could be due to external
issues such as the soldering or micro-cracks. Considering the temperature difference of 3.7 degrees Celsius,
between the standard conditions and test conditions, using the rate suggested in 8 (0.5%/degree Celsius) the
total Voc loss would be:
0.5% * 3.7 degrees celsius = 1.85% loss of Voc, as a result of the elevated temperature of the cell.
In this case the Voc has dropped by 5.9% ; (0.592/0.629)*100
Overall, this suggests that although there is a 1.85% loss from the temperature differential, there is also a 4%
loss attributed to those previously suggested external factors.
External Quantum Efficiency (EQE) Test
The second lab test that was performed on the cell was the external quantum efficiency test. A solar cell's
quantum efficiency can be defined as the amount of current a cell will produce when irradiated by photons of a
current wavelength (PVEd, 2014). However there are two different types of quantum efficiencies: Internal and
external (IQE & EQE). The latter can be defined as the ratio of the number of charge carriers collected by the
solar cell to the number of photons of a given energy shining on the cell from the outside (incident photons)
(PVEd, 2014). The IQE is fundamentally the same however it takes into account the photons are actually
absorbed into the cell as well as those that are shining from the outside. In order to calculate the IQE, the EQE
must be calculated first and once this is found, the data can be combined with the transmissivity and
reflectivity, however due to the lack of lab instruments to measure these values, a test was only run on the
EQE.  
Cell Specifications Lab Cell Testing
Open Circuit Voltage (Voc) 0.629 V 0.592 V
Short Circuit Current (Isc) 5.585 A 5.417 A
Maximum Voltage (Vmp) 0.523 V 0.373 V
Maximum Current (Imp) 5.215 A 4.519 A
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Table 2: Comparison between the cell specifications and the results from the lab cell testing

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A formula for the EQE can be expressed as:
"
The following figures represent the test result from the EQE readings. There have been two different tests taken
because the first one shows a test taken without calibrating the system meaning that the impurities in the air
were not taken into account. Therefore, a calibrated cell was used where all the parameters were known and
once all these values were run through the machine, the second test can then be made to produce a much
smoother curve and also one that does not have any anomalous results as shown in figure 9.
The test was ran for the wavelengths between 400 nm and 1000 nm going up in intervals of 5 nm so that the
results are spread out and as accurate as possible. Generally for the modern solar cells, they do not operate
outside these wavelengths (ultraviolet and infrared) are either filtered out or absorbed by the cell, which would
cause it to heat up, thus decrease its efficiency. In both cases, there positive results where the average
efficiency is approximately 90%. The peak efficiency point (93%) occurs at a wavelength of 605 nm according
to the second improved test whilst the lowest point (73.5%) occurs at 1000 nm. However, this is a relatively
good result and it is close to the ideal shape which would be a square shaped graph. The range that has been
used represents the top of that square and it is clear that they are relatively in a straight line as the values are
fairly constant throughout the test. The possible reason for the reduction and not achieving 100% is because
of the recombination effects where the electrons cannot move into an external circuit.
EQE =
electrons/sec
photons/sec
=
current/(charge of one electron)
(total power of photons)/(energy of one photon)
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Figure 9: Testing the cell for its EQE

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Figure 10: EQE Test Results without reference cell
Figure 11: EQE Test Results with reference cell

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THEORETICAL MAXIMUM CALCULATIONS
The following are the analytical calculations from the beginning of the report that represent the ideal case
where all the cells are at their speciﬁcation. However, this is impossible even in industry as when the cells are
connected together, there are always losses due to the wiring. This is especially the case because all 36 cells
are connected in series and the wiring losses occur most when there is a long and thin wire (which is the case
for a solar panel) because the resistance will be increased signiﬁcantly.
Calculations based on a panel consisting of 36 cells:
Total cell coverage area of panel: 125mm * 125mm * 36 cells = 0.5625 m2 (0.75m x 0.75m)
Total power: 2.8W * 36 = 101 W
Total Vmp: 0.523 * 36 = 18.8 V
Total Imp: 5.215 A
Total Voc: 0.629 * 36 = 22.6 V
Total Isc: 5.585 A
Now that the cell testing has been completed, a new theoretical maximum can be found from the following
calculations:
Total power: 1.686W * 36 = 60.7 W
Total Vmp: 0.373 * 36 = 13.4 V
Total Imp: 4.519 A
Total Voc: 0.592 * 36 = 21.3 V
Total Isc: 5.417 A
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PANEL TESTING
The Simulator
The panel was taken for testing under a different simulator which is required to be a larger size due to the
larger panel. The simulator that was used to test the cell was the WACOM simulator which can only measure a
total area of 210mm x 210mm (WACOM, 2015). Therefore, the Pasan Sunsim Solar module tester was used
for the testing of the panel as it can measure modules up to 2m x 2m. This module tester is the first of its kind
in the UK having an A+A+A+ certification meaning that it is twice as good as the best class A solar simulators
from the IEC ranks (WACOM, 2015). This technology has been designed to not only test silicon-based
modules (which were used for this project) but also new technologies such as thin-films.
This solar simulator is an indoor device which provides illumination that is very similar to that of the sun at
standard conditions. The advantage of using an indoor facility is that all the variables can be controlled to
provide accurate testing of the overall performance of the panel.
Accuracy is very important for module producers as these small details can determine whether the company
could make profit or loss especially if this was to be done on a large scale. Although this project only consists
of 1 module, it is an advantage to have such precise results so that a conclusion can be drawn on how to
make improvements for the future.
Testing
The test was undertaken in a dark room that had to be completely closed off from external light so that there
are no extra influences on the panel performance. In order for the program to run, certain parameters had to
be pre-entered into the system so that the simulator can make the correct calculations. These parameters
included: Total cell area, number of cells, cell open circuit voltage (Voc) and cell short circuit current (Isc).
The first test that was run was under the standard conditions of 1000W/m2, 25 degrees celsius and an air
mass 1.5 spectrum. The results for this simulation are as follows:
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Performance measurement
PASAN Tester
DUT area
Cells in parallel
156.25
Manufacturer Type Poly
Serial number
Single cell area 12100.0cm² cm²
unknown
1Cells in series
'''36-SERIES'''111
36
Configuration Module
Operator SAV Pasan
PASAN Tester version R2.3.4 / PBV100 0.0.0
Measurement 2016/11/30 11.24.15
MC Irradiance Channel 1
Serial number 123456
Sensitivity 131.684 mV/(kW/m²)Temperature 0.0 %/°C
2016/11/30 2/1
Direct Irradiance Channel 1
Compensated Temperature 25.0 °C Fill factor 60.115576 %
Compensated Irradiance 1.0 kW/m² Cell efficiency 5.432454 %
DUT temperature 24.104035 °C DUT efficiency 2.525418 %
Monitor cell temperature 24.104035 °C
Gavg 1.021 kW/m²
GstdDev 0.001 kW/m²
Regression linear for Voc 23.997 V
Linear regression Isc 2.12 A
Regression linear for serial 6.881 Ω
Regression linear for Shunt 32.04 Ω
Maximum power 30.558 W
Voltage at Maximum power 17.115 V
Current at Maximum power 1.79 A
Figure 12: Panel testing results for 1000W/m2 simulation

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Performance measurement
PASAN Tester
DUT area
Cells in parallel
121.68
Manufacturer Type Poly
Serial number
Single cell area 100000.0cm² cm²
unknown
1Cells in series
0.8kw
27
Configuration Module
Operator SAV Pasan
PASAN Tester version R2.3.4 / PBV100 0.0.0
Measurement 2016/11/30 11.26.01
MC Irradiance Channel 1
Serial number 123456
Sensitivity 131.684 mV/(kW/m²)Temperature 0.0 %/°C
2016/11/30 2/1
Direct Irradiance Channel 1
Compensated Temperature 25.0 °C Fill factor 74.541762 %
Compensated Irradiance 0.8 kW/m² Cell efficiency 9.275625 %
DUT temperature 24.014824 °C DUT efficiency 0.304738 %
Monitor cell temperature 24.014824 °C
Gavg 0.811 kW/m²
GstdDev 0.0 kW/m²
Regression linear for Voc 18.772 V
Linear regression Isc 1.74 A
Regression linear for serial 0.68 Ω
Regression linear for Shunt 42.36 Ω
Maximum power 24.379 W
Voltage at Maximum power 17.016 V
Current at Maximum power 1.43 A
Figure 13: Panel testing results for 800 W/m2 simulation

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The results from the first test lower value of the power (at 30.558W) than what was calculated to be the
theoretical value (60.7W). This is approximately shown with the fill factor calculation that shows a value of 60%.
The conditions this time were at standard temperature and irradiance therefore this was not a factor in the
results. The efficiency values have been shown to be very low, much lower than expectations. By looking into
this more deeply it seems that the major issue with the power generation is the fact that the current at the
maximum power is much lower than expected with a value of only 1.79A. The potential reasons for this could
be due to the fact that the soldering was not done to the best standard, or the fact that there had been certain
cell breakages throughout the panel during the Sylgard application process but also losses due to the
formation of the bubbles from the Sylgard.
The majority of the current losses can be attributed to micro-cracks and even larger cracks within the cells
because the cracks result in a much increased rate of recombination which, in turn, creates a higher resistance
thus reducing the current. A report by J. I. van Mölken et al (2012), states that the micro-cracks have a direct
negative effect on both the Isc and the efficiency of the cell. The micro cracks would have been a result of the
manual soldering process which require stress to be applied but also the fact that the bus bars are taken
through very fast temperature changes which change the shape of the tabbing wire and therefore form micro-
cracks within the substrate.
The efficiency can be also related to the fact that the incorrect pre defined area for the program was used. The
area was used (as shown in figure 13) is at 1.21 m2 which is, in fact, the total area of the panel including its
border, spacings and edges. Therefore if the simulator is taking into account a larger catchment area then
there actually is, the performance related to that catchment area will be minimised in comparison to what the
actual performance should be. For example, in this case, the catchment area is 1.2 m2 and it is only producing
30W therefore the efficiency would be calculated to be much lower than if the correct solar area was used
which is 0.5625 m2. This perhaps represents the largest loss of efficiency. This is further evident because the
collection area for the second test (above) was mistakenly inputted at a value that is an order of 10 higher than
it should be. The efficiency in the second test is much less than that of the first test therefore the area definitely
plays a big factor in determining the overall efficiency of the module. A study conducted by the National
Renewable Energy Laboratory (NREL), states that 'the area definitions used by the PV community can account
for large differences (over 100%) in the efficiency between various groups' (Emery, 2010).
Also, the inputted values for the Voc and the Isc were those of the cell specification rather than what was
measured for the independent cell. As the specification values are higher than the actual measured, the
program would make calculations based on the fact that the module should perform better than it actually did.
Overall, there were certainly issues with cell breakages, Slygard and soldering however, the main source of
under-performance is a result of the input parameters into the program.  
!35

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COMPARISON BETWEEN THEORETICAL, ACTUAL & INDUSTRIAL
The following tables speciﬁcations (electrical and mechanical) of four different industrial panels that all have 36
cells and all of different power ratings.
!36
Figure 14: Source: (Admin, 2010)

!
!37
Tables 3: Compares the values of specs with the values for industrial panels
Figure 15: Source: (Admin, 2010)
The table and graphs below present the comparison of all these industrial panels with the SPECS module.

!
!38
Figure 16: Compares the STC Power of SPECS and industrial panels
Figure 17: Compares the STC Power rating per unit area of SPECS and
industrial panels

!
!39
Figure 19: Compares the Isc of SPECS and industrial panels
Figure 18: Compares the Imp of SPECS and industrial panels

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!40
Figure 21: Compares the Voc of SPECS and industrial panels
Figure 20: Compares the Vmp of SPECS and industrial panels

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Comparison Discussion
Firstly, although all panels have the same number of cells (36), they all have individual characteristics due to
other variable factors. The first of which is the power at standard conditions (figure 16). These values have a
range from 30W up to 130W which shows the real variability that can occur between the cells and
manufacturers. These can perhaps be attributed to the area of each cell therefore a more accurate
representation is the STC power per unit area (W/m2) as shown in figure 17. In this figure it can be seen that a
lot of the values are relatively close to each other except for the actual SPECS result which lies at 58.2 W/m2.
The reasons for this were discussed previously but an important thing to note is that in an ideal (theoretical)
scenario, the SPECS would perform very close to the manufacturer's level. Currently, with the issues and
breakages, the SPECS module performs an approximate 50% worse than an industrial model of the same size
but with improvements it could possibly reach a level that is only 10% less than that of the manufacturers.
The next variables to consider are the current (Isc and Imp) - figures 18 & 19. Both graphs same trend where
the better rated modules have better currents. Whilst the SPECS module only produces an Imp value of
1.79A, the next module (KE45) only produces a marginally larger 2.55A. However, the highest performing
!41
Figure 22: Compares the peak efficiency of SPECS and industrial panels

!
module produces a total of 7.47A at the maximum power point so it is definitely a big factor in the overall
performance.
The maximum power voltage proved to be very similar throughout all the panels and therefore this value can
be regarded as not having an effect on the overall output of the module. The Voc also follows the same trend
but this time the Voc of the SPECS module is the highest at 24V whilst the average for the others is
approximately 21.7V so the variation is still small. For the industrial panels, it is most likely an advantage to
have the lower Voc because when a lot of these panels are connected in series, the total overall voltage will
rapidly rise and it may become difficult to match this voltage with that of charge controllers, for example. On
the other hand as SPECS is designed for a stand alone purpose, there is no need for controllers and therefore
this Voc value is good for the application.
Finally, the last graph (figure 22) shows the variability within the peak efficiencies and this is where the industrial
panels differ the most from SPECS. The panels average at 13% efficiency whilst the SPECS only has
approximately 3% but as was discussed earlier, despite the soldering, breakages and Sylgard, the main reason
for this large difference is the fact that the testing parameters were incorrect. If this was corrected, the SPECS
module could see the efficiency rise significantly making it approximately 7% which is still less than that of the
industrial panels but it would provide a much better performance. So it is important to consider that the
SPECS panel performs better than the test results show but there is a certain room for improvement which will
be discussed in the evaluation section of the report.
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CELL THERMAL EFFICIENCY STUDY
In order to determine the thermal efficiency of the
cells a data logging micro controller was
constructed. This was achieved by using an Arduino
micro controller and a temperature probe. The
Arduino was then connected to a laptop that plotted
its temperature at 1 second intervals. This data was
combined with readings from the multimeter to
produce the data shown in figure 25. This shows
that voltage is inversely proportional to temperature.  
!43
Figure 26: Shows the effect of heat on the cells voltage
Figure 23, 24 and 25:
testing apparatus and
testing methods for the
thermal efficiency study.

!
INDIVIDUAL CELL FUNCTION TEST
Every cell that was used in the creation of the panel was tested individually to see if it functioned according to
manufacturers specifications. At the time of testing there were 41 cells available some of which had
considerably low voltage readings. All cells were tested in the lab using a basic continuous solar simulator that
emitted 1 sun on each cell with the objective of selecting the best 36 cells for the panel construction. 1 sun is
typically defined as the nominal full sunlight intensity on a bright clear day on Earth, which measures 1000 W/
m2.
The figure below shows the maximum and minimum (after 25 seconds of exposure in the simulator) voltage
reading of each tested cell. The yellow line is the open circuit voltage, which is the maximum voltage a cell can
produce under no load. All initial voltage readings were below the rated Voc. which is expected due to micro-
cracks and other minor miscellaneous imperfections, the stabilised voltage reading after 25 seconds shows a
11.3% drop from the initial Voc reading. This difference was accredited to heat generated efficiency losses
caused by solar simulator. This drop in production is to be expected in real life applications on a sunny day. All
solar cells functioned, but out of the 41 cells available the 5 cells with the lowest Voc and Stabilised readings
were discarded and not used towards the construction of the panel. 
!44
Figure 27: Range of different voltages at max and min, also showing the cut
off point and the expected value.
VoltageReading
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Cell Number
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42
Max Voltage Reading
Min Voltage Reading
Lowest
acceptable
value
Expected value

!
Cell
Number
Max V. Reading Min V. Reading Percentage Drop
Between
Readings
1 0.592 0.514 13.34
2 0.499 0.462 7.41
3 0.57 0.512 10.18
4 0.601 0.535 10.98
5 0.582 0.521 10.48
6 0.578 0.522 9.69
7 0.604 0.523 13.41
8 0.606 0.518 14.52
9 0.599 0.54 9.85
10 0.608 0.542 10.86
11 0.578 0.543 6.06
12 0.612 0.521 14.87
13 0.589 0.543 7.81
14 0.598 0.567 5.18
15 0.602 0.552 8.31
16 0.587 0.553 5.79
17 0.603 0.557 7.63
18 0.603 0.551 8.62
19 0.608 0.581 4.44
20 0.589 0.539 8.49
21 0.608 0.552 9.21
!45
Table 4 Part 1: Cell numbers and the voltage readings for each
The table below shows the results from each individual cells testing.

!
Cell
Number
Max V. Reading Min V. Reading Percentage Drop
Between
Readings
22 0.589 0.542 7.98
23 0.4930 0.468 5.07
24 0.603 0.547 9.29
25 0.602 0.55 8.64
26 0.578 0.533 7.79
27 0.602 0.54 10.30
28 0.613 0.542 11.58
29 0.594 0.538 9.43
30 0.167 0.11 34.13
31 0.599 0.529 11.69
32 0.621 0.532 14.33
33 0.612 0.513 16.18
34 0.618 0.515 16.67
35 0.612 0.534 12.75
36 0.454 0.41 9.69
37 0.617 0.529 14.26
38 0.625 0.549 12.16
39 0.410 0.384 6.34
40 0.62 0.53 14.52
41 0.617 0.55 10.86
!46
Table 4 Part 2: Cell numbers and the voltage readings for each

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SANKEY DIAGRAM OF ENERGY LOSSES
The sankey diagram below shows the percentage of losses in each stage of transmission, starting from the
solar radiation on the panels through to the received energy in the charging devices.This diagram shows that
the majority of the losses in the system are inquired from the solar panel and not within the unit, therefore the
majority of efﬁciency losses in the are beyond control in the assembly stage. 
!47
Figure 28: Sankey diagram of energy losses through the system
07/12/2016, 14:54H8gL9sU46vxoAAAAAElFTkSuQmCC 600×800 pixels
Panel
90%

!
SYLGARD APPLICATION AND CALCULATION
The importance of correct module encapsulation can not be overstated, it is needed for the protection of the
PV cells from exterior damage and for electrical insulation to minimize losses. 1.1kg of Sylgard was made
available for this purpose.
Sylgard 184 silicone elastomer is a transparent encapsulate with good flame resistance and an intrinsic
dielectric strength of 19kV/mm. The dielectric strength of an insulating material is the maximum electric field
that a pure material can withstand under ideal conditions without experiencing failure of its insulating
properties. Practical dielectric strength decreases with increased sample thickness. For this reason, when
applying Sylgard the objective was to evenly spread a thin layer that would completely cover the module area.
The plan was to rest the PV modules, against the acrylic cover and insulate the rear, the negative contact area
of the module. This was in order to make the best of the amount of Sylgard. The procedure was proposed by
supervising PhD student Hassan Baig.
Ideally for a 1m2 module area, the maximum thickness of Sylgard required would be 1.07mm. The calculation
is defined below. For a hand made assembly, it would be nearly impossible to efficiently regulate the thickness
by eye, so in order to meet the requirements of the thinnest possible layer of Sylgard was poured.
Unfortunately the distribution was not shared as evenly as anticipated, because some of the Sylgard seeped
into the front of some cells and got trapped between the front of the cells and the acrylic, reducing the amount
of encapsulate available for the encapsulation of the rear. This caused visible air bubbles within the structure.
CALCULATION:
We know
Amount of Sylgard required = Sylgard density x module area x required thickness
Therefore:
Required thickness = Amount of Sylgard / (Sylgard density x module area)
!48

!
We know the amount of Sylgard available is 1.1kg
Density: 1030
Module area : 1m2
So:
Required thickness = 1100g/ (1030 x 1000 x 1) = 1.067mm
(In this case required thickness is max possible thickness)
USE OF ACRYLIC OVER GLASS.
A rigid outer transparent layer of protection is usually placed at the uppermost layer of the module, allowing
light to pass through to the cells all the while ensuring its protection from damage and water. In most
assemblies, glass sheets are used to cover the cells. In this assembly an acrylic sheet was used instead.
Acrylic sheets have numerous advantages over glass in this application, some of which include:
• Transparent acrylic glass transmits up to 92% of visible light where as glass transmits 80-90% depending
on the manufacturer. (White, 2015)
• Acrylic has a high impact strength which makes it more shatter resistant than glass, improving the safety
figures
• Acrylic has a high thermal efficiency, which can be beneficial for the cells, reducing the heat gain on the cells
from the sun's radiations
• Acrylic is easier to transport and more easier to assemble.
• Acrylic is significantly cheaper than glass.
Acrylic also has some disadvantages, which include
• It is softer than glass and can be scratched much easier than glass, in this assembly scratching is very
plausible because the panel is not elevated beyond the reach of users.
!49

!
• Acrylic can warp when overheated, in this assembly the risk of warping has been mitigated, having used
wood, a material with low thermal conductivity, in the rear of the panel as an insulator the risk of overheating
is significantly reduced.
• An untreated acrylic is susceptible to tarnishing with exposure to sunlight.
Acrylic was chosen over glass because it is fit for function in this assembly, the decision was further
encouraged by financial and structural incentives of it being cheaper and more malleable than glass. But for
future purposes hardened glass would be worth considering because it us less susceptible to scratches and
will also be resistant to shattering.
!50

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EFFICIENCIES OF COMPONENTS
Energy loss is an unavoidable part of energy conversion systems. A 100% efficient system is not achievable,
but well-designed power systems can achieve remarkable efficiencies, approaching percentages in the mid to
high 90s. This section will analyse the efficiency of each component, with the objective of answering the
questions, how much of the generated electricity is utilised, how much is wasted and what could be done to
improve efficiencies.
Efficiency of the panel
The calculated device under test efficiency result of the panel is misleading, in the test the area of the panel
considered is not the actual panel area but rather the panel frame, which includes the spaces in between each
cell and the edge of the frame, giving the area of 1.25m^2 where as the total cell area 0.56m^2. This
significant increase in considered area is the reason for a low panel DUT efficiency of 2.5% but under
reevaluation the expected efficiency is expected to be closer to 10%.
Efficiency loss due to copper wire
The power losses due to the internal resistance in the 1mm copper wire will be calculated below:
Formula for Power loss calculation: Imp^2*Rwire
The wire resistance R, is calculated using the formula information from an American Wire Gauge (AWG) chart.
(School of science, 2011) The chart says that 1mm diameter copper wire is equivalent to 18 AWG, using
this information we find the resistance per metre of 18 AWG copper wire to be 20.9 ohms per km (Newton,
1999) We can calculate the resistance of the wire R, by multiplying the length of the wire by the resistance per
meter.
The length L: 4.14m (the longer the wire, the greater its resistance)
Rwire = 0.004km x 20.9 = 0.083 ohms
The value of Rwire was confirmed using an online calculator provided by CIRRIC systems which gave Rwire to
be 0.087ohms. (Ellsworth, 2015). For the sake of this calculation we will use the calculated Rwire value of
0.083ohms.
The power loss: Imp^2 x Rwire = 4.52^2 x 0.083 = 1.71W
The theoretical power of the module is 60.7W. The power loss from the wire is 1.71W, this equates to a
negligible power reduction, bringing the actual power to 97.2% of the original theoretical power.
!51

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Efficiency losses from DC/DC Converter
An ideal DC/DC converter would have 100% efficiency, operate over arbitrary input and output voltage ranges,
and supply arbitrary currents to the load. Realistically, DC/DC converters common in battery-driven, portable,
and other high-efficiency systems such as the SPECS, can deliver efficiencies greater than 95% while
boosting, reducing, or inverting supply voltages. Resistance in the power source is one of the most important
factors that can limit efficiency, in this section we analyse the convertors efficiency loss. Lin, W. (2013)
The system will always have substantial loading, either when charging mobile devices directly or charging the
batteries for later use, this means the DC/DC converter will always be under substantial load and will work
within high efficiencies. For this DC/DC converter the data sheet says it has an efficiency of 96%.
Efficiency losses in battery
Lithium-ion batteries are most commonly valued for their light weight, small size and long life cycles when
compared to traditional lead acid batteries. Lithium-ion deep cycle batteries give long operational time if you
require a battery that gives you more operational time, and was the best battery fit to purpose for this task.
A lead acid battery’s internal resistance becomes higher the deeper it is discharged. Therefore the charging
algorithm is designed to slowly charge the battery at lower voltage levels. Conversely, the constant current
algorithm of lithium batteries is preferable due to the high efficiency and low internal resistance. That means
you are able to charge at a much higher rate. In turn, reducing downtime and increasing operational time.
Rechargeable lithium-ion batteries have an efficiency of 99% and offer a much higher usable capacity at the
same Amp hour rating than lead batteries (Hecimovich, 2015).
!52

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ECONOMICS
This section discusses and analyses the financials involved with the project. It will consider the cost of
assembly and the financial savings made by the project.
The cost of electricity is used in this economic study is SSE's 11.47 pence per kWh (UKPower, 2016). In this
study we assume that mobile devices (phones, tablets & kindles) can be continuously charged for a total of 6
hours a day from the batteries, this is based on the battery specifications. An iphone 6 requires 2 hours to
charge from 10% to 100% (Apple, 2015). For this study we assume that the unit charges continoulsy for 5
hours a day everyday with no down time that comes down to 1825 hours of charging per annum for each
compartment. The entire unit is able to charge 4 devices simoutaniously which equates to 7300 hours of
charge per annum by the station. We also know that most phone chargers consume anywhere between 2-6
watts to charge, iphone chargers consume 5.1 watts while charging (Bonnington, 2013)
Calculating the amount of kWh used per annum by the unit to charge devices will give the amount of energy
saved by the device, this value will be converted to monetary terms using the cost of electricity.
7300 hours x 0.0051kW = 37.2kwh
The cost of electricity equates to the multiplication of the unit price of electricity by the amount of electricity
being used.
37.2kWh x 11.47
37.2kWh x 11.47p = 426.6p
It will take 43 years to pay back the assembly cost. The assembly cost is different from the total from the
material cost list. The assembly cost consists of all purchased materials, as well as the cost of Sylgard and the
panels.
Sylgard: £30;
36 solar cells: £56.2
Bringing the total assembly cost to £267.02
The solar cells have a life span of 20 years, meaning the system will never make a payback based on
electricity savings. To compensate for this deficit a payment for service system is proposed.
In this proposed system each user will be charged a 10p fee for the service. It is assumed that the payment
will be for a single charge to maximum device battery level, assuming it is charging an iphone from 10%-100%
which will take two hours. So we assume that the payment of 10p for every two hour of use.
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!
Dividing the number of hours the system charges per annum for (7300 hours) by the number of hours it takes
to charge a phone, (2 hours) gives the number of charges the system will make per annum. This comes down
to 3650 charges per annum across all 4 compartments. Multiplying the number of charges by £0.1 (10p) will
give the amount of money generated if the system was used contioniously. This comes down to £365 per
annum. Realistically the system will not be used continuously, a realistic usage factor must be adopted.
Factors such as seasonal variation, area population density will affect the rate of use, to compensate for this
the usage factor of 0.2 was adopted.
A similar analysis was made considering a 20p charge
Based on these systems the ﬁnancial reviews below were made.
 
!54
Figure 29: 10p charge Figure 30: 20p charge

!
A comparison of the two cash ﬂow models shows that having a 10p charge will have a payback after the 4th
year of installation and generate a revenue of £1119.98 at the end of its 20-year life time. Where as a 20p
charge will have a payback after its 2nd year of installation and generate a revenue of £2506.98.
 
!55
Figure31:CashFlowModel

!
POTENTIAL SITES FOR PLACEMENT OF SPECS
The SPECS team have identiﬁed 4 different sites that would be appropriate for the installation of the unit,
around the University of Exeter, Penryn Campus, Cornwall. These were based on a range of factors listed
below.
Site Reasoning for choice
1 This site is based in the middle of the student village, with a space used in the summer for
socialising and BBQing, the students could charge their phones while relaxing in the sun.
2 This site is adjacent to the university outdoor games area, allowing users of the facility to
charge their devices while completing recreational activities.
3 This site located outside the Stannary, the part of the campus with the highest human
trafﬁc. This would allow the highest number of people to use SPECS and promote
sustainability with the student population.
4 This site is outside the ESI, the leading solar research and innovation centre in the UK.
Displaying SPECS here would be a very prestigious opportunity for the team.
!56
Table 5: Chosen sites and the reasoning behind the site choices
Figure 32: Chosen sites

!
 
!57
Site 1:
Glasney Student Village recreational area
Site 2:
MUGA sports ground
Site 3:
Stannary and Library Entrance
Site 4:
ESI Entrance
Figure 33, 34, 35 and 36: Site photos of the proposed
sites at Penryn Campus

!
PVSYST ANALYSIS
Using the potential sites that have been allocated on campus, a PVSyst analysis took place to determine the
overall incoming solar radiation and the total energy output from the panel. 
!58
Figure 37: Solar radiation monthly data for Penryn Campus, UK

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!60
Figure 39: Simulation report page 1

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!61

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!62

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!63

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GAS STRUT CALCULATIONS
While constructing the solar panel it was decided
that to better explain how the panel worked, the
inside electronics would be labelled and a poster
would be displayed on the bottom of the panel lid.
To allow the lid to operate easily and safely a
variety of different devices were investigated.
Initially a string was installed to hold the lid as a
120 degree angle. This proved to be quite
precarious and was discarded. Another idea was
for the use of a hanging stick, similar to that of a
cars front bonnet was suggested, but was also rejected.
The chosen method was to use two 100Nm gas struts. This value was chosen by measuring the force needed
to open the lid with a 50-500Nm gauge. The value recorded was 80Nm per side but 100Nm was chosen to
ensure that the lid would be held securely.
Through research it was found the the geometry of the gas strut was very important to gain the
greatest leverage and allow the lid to move freely. Therefore to optimise the placement of the strut,
a solidworks model was created to model the strut and its movement. An animation of the struts
movement can be found by using the link at the side of the document.
After this was tested and analysed, the geometry measurements were taken and used for installing
the real gas struts on the device. Due to the careful measurement, planning and testing they worked
perfectly in the ﬁrst attempt of installation.  
!64
goo.gl/nZQ3cA
Figure 43: 3D model of hinge structure
Figure 44, 45 and 46: Animation of the gas strut moving

!
INDOOR TESTING
Before testing the rig outside it was important to check that the panel was connected correctly and producing
electricity. This was achieved by using a multimeter connected to the panel, and a high powered light. The light
proved to be enough to power the panels. The next stage was to connected the dc-dc converter and connect
a usb charger for a mobile phone. This also worked perfectly and while testing 4 phones were connected
directly to the panel and all were successfully charged at the same time.  
!65
Images of indoor
testing.

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OUTDOOR TESTING
 
!66
https://goo.gl/43uorn
Before testing the unit on the public, it was important it worked
reliably. The team tested the unit outside the laboratory for 6 hrs
monitoring the status of charging in two test devices throughout.
This test proved very successful and the panel managed to
continue charging even in the shade. This made the team conﬁdent
to proceed to user testing. The QR code and link lead to a video
showing the panel being testing outside.
Figure 50, 51 and 52: Images of outdoor
testing.

!
USER TESTING
To test the ease of use of the device we tested the rig on several students from the university. With no
instruction they operated and understood the device. This was a great success and proved that the design
was user friendly. After each student ﬁnished using the device we asked for feedback. The feedback can be
seen below:
“The rig is very simple to use and great as it doesn't use energy from the grid” Tom
“I like that rig is easy to understand, it would be good as an educational tool in schools” Bruce
This feedback was useful and positive towards the project.  
!67
Images of user testing.

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EVALUATION
CONSTRUCTION AND PROJECT
Despite this project being a great success and the goals being achieved, there are parts of the project that
would be completed in a different manner if completed again. This section of the report will discuss these
points.
While the lockers for the phones are adequate for use on a university campus, the lack of locks means that it
could not be installed in a public area, due to the ease of theft. It would therefore be recommended for a future
project to install locks on each individual lockers.
Similarly with the lockers, in a future model it would be recommended that more lockers be installed, than the
four that were chosen for this design, as the panel could power many more devices, and this would allow
more users to benefit from the technology.
While completing the Sylgard application to the cells it was found to be difficult due to the large size of the
panel and the lack of prior knowledge of the behaviour of the Sylgard polymer. In future it would be
recommended that the Sylgard should be applied to the base of the panel, to create a perfectly flat surface to
place the cells on, then the cells be installed, then a layer of Sylgard be poured over the cells, and while curing
the entire panel placed on a vibrating table for 48 hrs.
The soldering process also turned out to be a difficult part of the project, due to the highly fragile nature of the
cells, several cells were broken while starting the soldering process. With a future project, the advice would be
to anticipate just how fragile the cells and treat them with more caution from the start.
The soldering process which in this project was efficient and accurate when compared to other manual
soldering techniques, in a commercial version of this project the soldering could be improved with the use of
an automatic soldering machine.
On a similar topic, when the cells were soldered they were left on the laboratory, and moved by a staff member
not familiar with their fragile nature. This unfortunately resulted in several more cells being broken and many
others developing micro-fractures.
The panel on this project was very effective despite being angled at 0 degrees at all times. It would be much
more efficient for the panel to be angled at a 40 degree angle. It would also be more effective to develop a
tracking panel system. This could be the work completed by a future research group.
The method for attaching the cells together was decided due to the fragile nature of the cells, allowing a large
amount of space between cells and around the boarder, and with more practise a higher cell density could be
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achieved. This would significantly increase the power generation to size of panel, making it more economically
efficient as well as improving the DUT efficiency.
The cells chosen for this project were silicon poly-crystiline cells used had a factory efficiency of 17.7%,
although that is high it would be possible to invest in higher efficiency cells to produce more power. This option
could be investigated for a future project.
As investigated in the section above, the acrylic used in this project was untreated and therefore would
discolour with use over time. It would therefore be suggested in a future project to use either treated acrylic or
a sheet of glass. The addition of glass would potentially make the project less safe. An option of tempered or
plastic laminated glass should also be explored.
As shown in the section investigating the thermal efficiency of the cells , the efficiency does drop while the
panels heat up. The current predict does not include a heat sink to pull the heat away from the panels. It would
therefore be suggested for a future project to implement a heat sink, to prevent these efficiency losses.
Due to the nature of this project, time was limited and certain aspects could not be fully investigated. The
development of a battery controller is one of these parts. This would improve the delivery of power to the
charging devices and improve how the rig handles the incoming energy deciding automatically whether to
store or charge a device.
The buck converter used was taken from an car battery supplier, and only starts working when the cell starts
producing more than 8v, this could be switched out for an optimised buck converter to start working at a lower
voltage and with higher efficiency of conversion.
To allow the rig to me moved more easily, the project recommends that some coasters or wheels be installed
on the base of the legs. This would allow the rig to be installed and moved around more easily. This opens up
applications for festivals allowing the rigs to be brought onto sites quickly and removed with ease.
EVALUATION OF TESTING
Perhaps the largest factor that caused an under achievement in the efficiency performance of the panel was
the testing process. Although the ideal conditions were used alongside a well-established solar simulator, the
input testing parameters were incorrect. If the testing process were to be re-taken in the future, it would be
ensured that the exact parameters for the sizing of the system were entered into the program so that an
accurate efficiency can be determined.
As for the cell testing, the temperature conditions were higher than the standard conditions and in the future,
the cell testing would take place at exactly 25 degrees celsius so that the cell can be tested at its optimal
performance.  
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CONCLUSION
Overall, the project can be seen as a very successful because despite all of the difficulties, the panel is fit for
the purpose and it can charge multiple electronic devices simultaneously. Those difficulties came from
soldering, cell breakages, Sylgard application and bubble formation. The cell performed relatively well under
the I-V testing with results similar to those in the specification and it performed with an average of 92%
efficiency in the EQE test. The module testing should have been repeated with the correct input parameters
however due to time constraints this was not possible however, the important thing that was found was that
the panel was generating power and even under the conditions of 800W/m2. Once compared to the industrial
panels of the same size, it proved to be under performing however those reasons were attributed mainly to the
cell breakages and the fact that the soldering had been completed manually, increasing the wire resistance.
The voltage seemed to be very similar to that of the commercial panels and the main reason for the lower
power output is a result of the reduced current in comparison.
The poly-crystalline panels have proven to be working however due to their senesitivity within a stand alone
structure, there are increased chances of breakages throughout their lifetime. Therefore there is a possibility of
also implementing third-generation solar cells into the system as they are rapidly developing to become more
space efficient but these technologies will need to be explored further before becoming available commercially.
In conclusion, this panel has proven to provide enough power to successfully charge numerous electronic
devices throughout the day and the hope for the future is that the principle of this idea can be expanded,
improved and implemented on a larger scale throughout the UK.
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ACKNOWLEDGEMENT
This project was partially ﬁnancially supported by Exeter University. We thank our colleagues from the ESI who
provided insight and expertise that greatly assisted the research, although they may not agree with all of the
interpretations/conclusions of this paper.
We would also like to show our gratitude to the Brian, the lab supervisor for sharing his pearls of wisdom with
us during the course of this research, and we thank the students that tested and gave comments on the
ﬁnished product.
Katie Shanks provided guidance on the individual cell testing and we are grateful for her help as well as Dr.
Hasan Baig and Prabhu Selvaraj who provided great help with the soldering and Sylgard application.
Finally we are immensely grateful to Dr Senthilarasu Sundaram and Prof. Tapas Kumar Mallick for their
organisation of this module and their support and feedback throughout the project, although any errors are our
own and should not tarnish the reputations of these esteemed persons. 
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APPENDICES
SYLGARD® 184 SILICONE ELASTOMER PROPERTIES
Property Unit Result
Ratio - 1:10
Colour - Colourless
Viscosity (Base) cP 5100
Viscosity (Mixed) cP 3500
Thermal Conductivity btu/hr ft oF 0.15
Cure Time at 25oC hours 48
Refractive Index @ 589 nm 1.4118
Refractive Index @ 632.8 nm 1.4225
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Figure 56: Properties of Sygard 184

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