Title:
Enhanced Efficiency Solar Energy
Concentrator – Final Report
Date:
February 9, 2016
Authors:
Vasisht, Abhinov --abhinov@uvic.ca
Keating, Erin --ekeating@uvic.ca
Laver, Cliff – lavercliff@hotmail.com
Hoffman, Roderick --rhoffman@uvic.ca
Rahimi, Shayan -- shayanr@gmail.com
Supervisor: Dr. Reuven Gordon
1
Table of Contents
Enhanced Efficiency Solar Energy Concentrator – Final Report ................................................................... 1
Table of Contents ...................................................................................................................................... 2
Summary ....................................................................................................................................................... 3
Introduction .................................................................................................................................................. 4
Overview ....................................................................................................................................................... 5
Solar Concentrator ................................................................................................................................ 5
Sun Tracking System ............................................................................................................................. 6
Problems ............................................................................................................................................... 6
Objective ....................................................................................................................................................... 7
Design Parameters ................................................................................................................................ 7
DESIGN .......................................................................................................................................................... 8
Filter ...................................................................................................................................................... 8
Concentrator ......................................................................................................................................... 9
Energy Storage .................................................................................................................................... 14
Tracking ............................................................................................................................................... 15
Results ......................................................................................................................................................... 20
Analysis ....................................................................................................................................................... 22
Cost Analysis ....................................................................................................................................... 22
Theoretical .......................................................................................................................................... 23
Actual .................................................................................................................................................. 23
Conclusion ................................................................................................................................................... 24
Additional Remarks ............................................................................................................................. 24
References .................................................................................................................................................. 25
Appendix A .................................................................................................................................................. 26
2
Summary
The objective of this project is to increase efficiency and generate high output power of a silicon-based
solar energy system with minimal extra costs. Thus, an infrared filter along with a solar concentrator
and a solar tracker are the major design components of the project. The purpose of a solar concentrator
is to focus a larger area of sunlight directly onto solar cells, thereby increasing the amount of available
light. The concentration of light therefore increases the output power from the photovoltaic effect of
the solar array. This is a cost-efficient way to increase the amount of available light for a solar array.
The purpose of a solar tracker is to follow the sun throughout the day to get the maximum available
sunlight. The overview section of this report explains solar trackers in detail.
The concentrator increases the temperature of the solar cells over time until the temperature goes
beyond operating temperature, thus reducing the efficiency of the solar array. In the operating
temperature range, there is a peak power output point which corresponds to a specific temperature of
the solar cells. For this project, the solar array power output is maximal at a temperature of 35 degrees
Celsius. As the temperature of the solar cells continues to increase, the solar array output power
decreases. Therefore, the system requires a technique to keep the solar cells at the temperature which
maximizes output power. A color camera film filter is used to block out unwanted wavelengths which
lead to temperature increases of the solar array. The filter keeps the solar array at a constant
temperature to maintain a maximum output power level. The film filter is successful in limiting the
temperature of the solar cells in the operating temperature range, allowing the solar array to operate
close to the optimal temperature. However, the film also blocks a portion of useable wavelengths for
the solar cells, thus reducing the overall output power of the system.
The cost analysis section of this report does not support any evidence that a solar concentrator and
optical filter system is economically feasible. Although the price of the filter is significantly lower than
the cost of the solar array, the total cost of the system is actually quite expensive and only increases the
payback time for the entire system.
3
Introduction
Today’s energy consumption heavily relies on the burning of fossil fuels which create CO2 emissions, a
problematic greenhouse gas. The need to develop clean energy is a hot topic for geologists, engineers,
economists and politicians to resolve. Renewable energy sources offer possibilities to resolve issues
concerning the environment and the growing energy demand. Solar energy is one example of a
renewable energy source by which solar cells convert sunlight into electricity via a photovoltaic effect
that occurs within the solar cell structure. There are pros and cons for all renewable energy systems
including solar energy systems.
A much debated topic of solar systems is cost effectiveness. Conventional systems are popular because
of the cheapness, availability and overall energy output suppliers are able to harness and deliver to
consumers. If it would be possible to harness the same amount of energy as a conventional system
using solar arrays while remaining at a similar cost, then there would be no debate. Extra expenses are
always an issue when adapting new systems due to the need to create new infrastructure and new
manufacturing costs. However, the market for creating high-grade silicon is decreasing, suggesting that
the cost of solar energy systems that use silicon based photovoltaic cells should follow. Marketers
foresee that within 7 to 10 years it is possible that the cost of generating solar energy could be at par
with conventional systems in locations with high solar insolation and high utility costs. Currently,
consumers in most locations rely on government subsidies to keep solar systems economical.
Another major issue which makes solar energy systems less attractive than conventional systems is that
the power generated by solar systems simply will not supply total energy demand. It is estimated by
McKinsey and Company that “(solar energy) represents only 1.5 to 3 percent of global electricity output”
whereas fossil fuels amount to over 30 percent. Thus, there is a need to develop technology to reduce
carbon emissions as well as a need to develop more efficient products that will result in higher yield of
energy generation.
The need to increase efficiency of silicon based solar energy systems has led to the development of this
project. The idea originates from the project supervisor Dr. Reuven Gordon, an expert in photonics.
This group is given the task of investigating a cheap technique that could help boost the efficiency of a
silicon solar array, given that a solar array is placed in front of a solar concentrator. Before describing
the details of the project objectives, a brief technical overview of how solar concentration works is
explained in the next section of this report.
4
Overview
Solar Concentrator
The solar concentrator is a configuration that uses lenses or mirrors to focus a larger area of sunlight to
a smaller area where a solar array is mounted. The purpose of using a solar concentrator is to reduce
cost by substituting a larger area of cheaper material (like a mirror) for the more expensive material (i.e.
silicon solar array). The solar array can then be greatly reduced in area and produce an equivalent
amount of energy as a large stand-alone solar array. Diagram 1.1.1 below outlines a typical
construction:
Diagram 1.1.1: A typical solar concentrator configuration.
Diagram 1.1.1 shows light being reflected from a concave parabolic mirror which focuses on another
mirror which then reflects the light through an aperture of the main mirror. This type of configuration is
called the Cassegrain mirror configuration and is commonly found in telescopes used for astronomy.
The light that passes through the aperture is passed through a prism which separates the wavelengths
of light on to different paths. This is called beam splitting. After the light has been separated, each
wavelength will enter a different material which will be absorbed for various applications. Generally,
silicon solar arrays absorb infrared (IR) wavelengths.
5
Sun Tracking System
Another important design feature of a solar concentrator is the ability to track the sun. Diagram 1.2.1
below demonstrates the principal of solar tracking which aids explaining the importance of this feature:
Diagram 1.2.1: Sunlight entering the atmosphere at different angles.
Diagram 1.2.1 shows how sunlight enters the atmosphere at different angles from the ground’s surface.
If sunlight shines directly perpendicular (90 degrees) onto a surface, the energy at the surface will be
more intense than if sunlight shines from an acute angle. A solar concentrator that tracks sunlight will
ensure that the surface of the reflective mirror is always perpendicular to the sunlight, which leads to
more power generation and hence, more produced energy. We can prove this by using some very
simple algebra and keeping in mind the angles of incidence shown in Diagram 1.2. If the intensity of
sunlight irradiance is labelled Em (Watts per meter squared) then the power received at the surface is
Em
where θ is the angle between the surface and the sun. It can be shown that the maximum
power received occurs when θ is 90 degrees.
Problems
As one might expect, the focused light from a concentrator can rapidly heat a surface. This is analogous
to using a magnified glass to burn holes in paper. If a solar array is placed at the focal point of a
concentrator, then the temperature of the solar cells will rise above normal operating temperature and
the efficiency of the solar energy productivity will drop. Because of this, a device is required that will
allow productive light to strike the solar array, but will prevent other wavelengths from heating up the
array.
In summary, the use of a solar concentrator reduces the cost of expensive materials, while the use of a
tracking system optimizes the amount of energy production as the Sun moves over the surface of the
Earth. An optical filtering device is necessary to prevent overheating of the solar array.
6
Objective
The primary objective of this project is to design, implement and analyze a filter that will prevent the
temperature of the solar array from rising above operating temperatures and generate stable energy
from the solar arrays. The analysis section includes maximum temperatures reached, power output
from the solar array, cost effectiveness and implementation problems. Other objectives include
designing a cost-efficient concentrator and tracking mechanism. An additional project feature includes a
system of storing energy from the solar array and using the system to provide energy to an electrical
load.
Design Parameters
Silicon has a band gap of 1.1-1.3eV which corresponds to a material that produces electricity when
exposed to light with about 950nm to 1200nm. Shorter wavelengths will penetrate the silicon and
increase the temperature of the system. As can be seen from diagram 2.1.1 below, sunlight radiates at a
large range of wavelengths with various intensities.
Diagram 2.1.1: Solar irradiance versus wavelength
It is clear that infrared (IR) light from the sun must pass through a filter but shorter wavelengths should
not pass the filter in order to prevent heating of the solar array. Therefore, this project requires a filter
to block visible light which will in turn prevent overheating of the silicon solar array.
7
DESIGN
Filter
A simple way to create an IR filter is to use color camera film. The photograph shown below in diagram
3.1.1 was taken using a digital camera and an IR lens.
Diagram 3.1.1: Infrared photograph of a tree.
Clearly, this looks like no ordinary tree. IR filters used in photography generally pass 700nm to 900nm
wavelengths. This range of wavelength is the near-infrared spectrum. Using this principal and applying
it to the project objective, a cheap IR filter is made using camera film. For about $10 CAD a roll, a cheap
filter is made by exposing and developing color film, and then simply tailoring the film to align in front of
a solar array. The developed film will allow infrared light to pass but will block shorter wavelengths. The
concept for this filter takes use of the fact that negatives block light wavelengths that are represented
on prints. Therefore, if the color camera film is exposed to white light, the developed negatives will
mostly block white light from the concentrator and allow IR to pass through to the solar array. Hence,
the filter prevents temperature increases and maintains energy production.
8
Concentrator
The concentrator can be easily assembled with some equipment commonly found around the house or
easily purchased at any local hardware store. Although there are many configurations of a solar
concentrator, this group chose a simple strategy. The materials used are: a satellite dish, reflective
aluminum tape, balsa wood, steel supports, and a lazy-susan base structure. Diagram 3.2.1 provides a
visual for the design of the concentrator.
Diagram 3.2.1: Solar concentrator base construction.
The main reflector of the satellite dish is used to provide the shape of the parabolic reflector. By simply
applying aluminum foil tape, the surface reflects light with a reflectivity of about 85%. The convenience
of using the satellite dish is that it offers a mechanical structure to work with. The arm provides a
perfect placement for the solar array where sunlight is focused after being reflected from the parabolic
dish. The base of the satellite dish also mounts easily to the wood frame turn table.
9
Some additions were made to the satellite dish structure. Diagram 2.2.2 and 2.2.3 show the importance
of these additions.
Diagram 3.2.2: Arm fixture support for solar array.
The support shown in the diagram above was made using a length of ½ inch steel bar, some balsa wood
and a few bolts, screws and nuts. It is an important feature for this project to allow the solar array and
filter to be moved away from the focal point and closer to the reflecting dish in order to prevent the
filter from melting when sunlight is being reflected on to the solar array. This support can be adjusted
towards or away from the parabolic reflector by simply moving the steel bar along the long metal bolt
until a desired position is found, and then fixing it in place. The balsa wood holds in its frame the solar
array, which is covered by the camera film filter.
10
Diagram 3.2.3: Back side arm lever.
The addition of a steel bar lever allows the tracker’s circuit to control the satellite dish’s reflective
surface so that it points in various vertical directions. A 12 volt DC motor feeds a line of string to the end
of the arm lever seen taped down with black duct tape. Pulling the lever down moves the reflective
surface upward to face the sky, whereas loosening the string allows the front reflective surface to drop
down and face the horizon. It should be noted that the concentrator is at rest when the reflective
surface faces the horizon. It requires work from the motor to hold the satellite dish so that the
reflective surface is facing upwards.
11
Diagrams 3.2.4 and 3.2.5 illustrate how the solar array is placed in a support structure. The camera film
filter can easily move away from or over the solar array. The reason for moving the camera film away
from the solar array is purely for analytical reasons when measuring the difference between the power
outputs of the solar array with a filter and without.
Diagram 3.2.4: Solar array placement with lens flipped down.
The wood frame is bolted to a steel bar which has a drilled hole at the back allowing the steel to mount
on the front of the satellite dish. The wood frame has a gap which allows the solar array to slide into
place on the frame and also allows wind to pass behind the array for cooling purposes. Two small
hinges at the base of the wood frame are used to hold the filter in place and allow a flipping movement
for the filter to cover the solar array or move out of the way of incoming light. Electrical leads protrude
from either side of the solar array which are inputs to an energy storage circuit.
12
Diagram 3.2.5: Solar array structure mounted before the parabolic reflector.
The picture shows how the whole wood and metal frame are mounted in front of the parabolic
reflector. Notice the angle at which the solar array faces. As mentioned earlier in this report, the
satellite dish offers the convenience of an existing structure for mounting the solar array in place. The
solar array faces at an angle where most of the light is reflected nearly perpendicular to the surface of
the filter and array. This optimizes the amount of energy harnessed from the incident light from the
reflector. The steel bar is adjustable along a steel bolt. The adjustments are made to strategically find a
position where focused light will illuminate the solar array but will also have a broad enough
circumference so that the filter will not melt. The optimal point is where the filter placed 15cm in front
of the focal point.
13
Energy Storage
All energy systems require the use or storage of the energy produced. The circuit schematic shown in
diagram 3.3.1 will aid the reader with the following explanation of how the solar cells generate energy
and store charge in a 1500 Farad ultracapacitor. Note that this circuit is a practical storage unit for solar
energy systems the ultracapacitors charge efficiently. Also ultracapacitors have practical use in the
automotive industry as they discharge quickly to accelerate hybrid vehicles. Therefore this section of
the project demonstrates how a solar array station for hybrid vehicles that make frequent stops, such as
electric buses, could use this technology to charge up the vehicles ultracapacitors which allow
acceleration of the vehicle after leaving the stop.
Diagram 3.3.1: Circuit schematic for the charging of a 1500F ultracapacitor.
This solar light circuit has two parts. The first is a charge controller section which keeps the solar panel
from overcharging the ultracapacitor. Basically, it consists of a PNP power transistor which draws
current from the solar panels whenever the ultracapacitor voltage is over about 2.6 volts. The 4040
precision Zener will conduct current if the voltage across it (Vz) exceeds 2.5 volts. It is in series with a
Schottky diode type 1N5819. The Schottky diode has a forward conduction (Vf) of about .1 volts. So if
the voltage across the two diodes is 2.6 volts or more, they will conduct. They are in series with the base
of the TIP30 PNP power transistor. If current flows out of its base, more current will flow from its
emitter to its collector. It takes about .6 volts (Vbe) from its emitter to base for current to flow out of
the base. So if the voltage from the emitter to ground (Vbe+Vf +Vz) is over 3.2 volts, current will flow
out of the TIP30 base, and it will be turned on. When that happens, enough current from the solar
panels will flow through the TIP30 to reduce the panel output voltage to 3.2 volts.
14
There is a 1N4004 silicon diode in series with the output of the panel where it goes to the
ultracapacitor. Since the forward voltage of a silicon diode is about .6 volts, the output of the panels
after the 1N4004 will be limited to 3.2V-.6V=2.6V. The ultracapacitor is rated at 2.7V, so the voltage on it
will never exceed its rating.
The second part of the circuit consists of a white LED with integrated voltage boost circuit and a photo
switch circuit to turn on the LED when in the dark. The boost circuit allows the LED to operate at any
voltage between about .8V and 3.5V.
The switch circuit consists of a 2N5818 NPN transistor in series with the LED. The base of the 2N5818 is
connected to the + terminal of the ultracapacitor through a 7.5K resistor. It is also connected to the terminal through a photocell light sensor. When the photocell is exposed to light, its resistance
decreases. So in the light, the base of the 2N5818 is pulled to -, and the transistor is off. When the
photocell is in darkness, its resistance increases, and the 7.5K resistor pulls the base to + and turns on
the transistor, thus turning on the light.
Tracking
One way to locate a light source is to use two optical sensors placed a small distance apart. One optical
sensor is used to track horizontal movements of light and another sensor tracks vertical movements. A
simple optical sensor can be made using an LED pair along with some standard electronic components.
The LEDs generate various currents dependent on the amount of light emitted onto it. In our design, the
LED pairs are placed a small distance apart on the same axis. The tracking circuit amplifies the difference
in current between each LED. The output of the amplifier goes to the input of 2 relay circuits. The
output of the relay circuits connects to a 12 volt DC motor which mechanically adjust the position of the
solar concentrator. When the two LEDs produce equal current, the amplifier does not have a differential
output and therefore the relay circuits do not have output. The motor will not move and the dish is
correctly facing the sun.
Diagrams 3.4.1, 3.4.2, 3.4.3, 3.4.4 depict the sensors circuits, horizontal DC motor, vertical DC motor and
circuit supply respectively.
15
Diagram 3.4.1: Optical sensor circuits for horizontal and vertical positioning.
Some play of mounting the sensors was done in order to find an appropriate position so that the sensors
hold the solar concentrator position steady when most of the reflected light strikes the solar array. As
can be seen some double sided tape is added below the sensors to give lift of the vertical axis sensors.
Also notice that black electrical tape is added to prevent any loose contacts from shorting on the back
side of the circuit boards. The grey wires seen in this photo are the supply voltage (12V) to the sensors
and the brown wires relay to the DC motors. Each LED acts as a current source to the base junction of a
Darlington pair current amplifier. The output of the amplifier is one input to differential amplifier stage
which differentiates between each LED current. When one LED produces more current than another,
the DC motor repositions the solar concentrator in the direction so that the less producing current LED
moves closer to the other LED position.
See Appendix A for the full tracker schematic.
16
Diagram 3.4.2: Vertical positioning DC motor.
This design is simple in that it requires common household items, is easy to assemble and is a strong and
durable mechanical implementation of controlling the vertical positioning of the solar concentrator. A
spool of thread is fitted over a cylindrical shaft. A line of rope is threaded through the side of the spool
and the spool is held by the motor. When the motor turns the spool, the rope feeds or pulls on the back
of the antenna structure as was demonstrated in diagram 3.2.3. When the motor pulls in the line of
rope, the antenna is moved back so that the face of the parabolic reflector is pointing to the sky. When
the motor feeds the rope, the weight of the antenna allows the reflector to face the horizon.
Notice in the left side of diagram 3.4.2 there are 2 black switch diodes. These diodes are used for
position error checking. In the case that an interfering light source causes the optical sensors circuit to
move the motor in a certain direction that is beyond mechanical limitations (i.e. the motor pulls the
rope until it snaps as the concentrator can no longer move further back) the diodes are strategically
placed to trip the connection and stop motor movement.
17
Diagram 3.4.3: Horizontal positioning DC motor.
The horizontal movement is also a simple mechanical implementation. The circular wooden lazy Susan
easily rotates about the center. With the addition of the motor holding a fringed wheel and soft
gripping tape added to the edge of the lazy Susan, a low slip contact is made between the motor and the
rotating frame. Since the tracking in the horizontal position will only follow the sun for a 180 degree
movement, 2 more switched diodes (not shown here) are added to the lazy Susan at quarter circle
positions relative to the front of the rotating board. These switches will ensure that movement does not
follow ambiguous light in the horizontal direction when the sun is down.
18
Diagram 3.4.4: 12 Volt supply to optical sensor circuits.
Not much explanation is needed here but it will be mentioned now that the motors typically draw 90mA
of current at 12 volts when repositioning the solar concentrator.
19
Results
Diagram 4.1.1: Temperature effects on the solar array without a filter.
The three figures above show temperature effects on the solar array performance as light is
concentrated without the use of a filter. The power output increases as temperature increases until a
maximum power output at approximately 35 ⁰C is reached. As the temperature increases further, the
output power decreases sharply. After roughly five minutes the solar array reaches 65 ⁰C.
20
Diagram 4.1.2: Temperature effects on solar array with a filter.
The results shown above are encouraging as the filter limits the temperature of solar cells allowing it to
operate closer to the maximum temperature output range of approximately 35 ⁰C. The problem with
this specific filter is that the film appears to blocks a portion of the useable light as the overall power of
the system is only .18 Watts but without the filter the output power is 0.4 Watts. The use of the filter
more than halves the output power.
As a portion of the useable light is blocked, less power is produced from the cell. This clearly is not a
desired scenario. An alternative filter, such as glass specifically designed to block out only the visible
light, may prove to be a more viable option. The glass filter may also allow more power generation with
the use of other photovoltaic cells to harness other wavelengths. However, the cost of glass filter is
significantly greater than the film filter and therefore this may not be a cost effective solution.
The use of the filter during a five minutes period resulted in the solar array temperature reaching only
27 ⁰C.
21
Analysis
The solar array must operate with maximum efficiency. In general, the results show that when the
temperature of the solar array rises, the efficiency of the system reduces. To maximize the efficiency of
the system, operating temperature must be 35 ⁰C. AT 35 ⁰C, the cell operates at a stable high efficiency
and as the temperature rises above 35⁰C, the power output starts to drop sharply.
The solar array configuration without the use of a filter shows that with light concentrating over a five
minute time frame the temperature of the cells increase to 65⁰C. At this temperature the power output
is very low. The solar array configuration with the use of a filter limits the solar array temperature to
30⁰C over any length of time. Using a camera film filter works in reducing the cell temperature to about
30⁰C over a long period; however the film filter also blocked some of the useful wavelengths required by
the solar cell to produce power. Therefore the total power produced by the system using a filter is less
than a system without a filter, however over the course of an entire day, the energy produced by a
system with the use of a filter will not only be greater but will also be stable.
Thus a filter that limits the surface temperature as well as blocks unwanted wavelengths will
significantly improve the efficiency of the overall system.
Cost Analysis
This section determines the total production cost of one unit and determines the time of payback for a
system putting electricity back on the grid.
Materials
Item
Aluminum Foil Tape
Rope
Screws, steel bolt, steel bar, washers
Satellite Dish
More nuts, bolts
Color Camera Film (developed for free)
Poster Board
Relay Circuit
Miscellaneous Cost
Motors and sensors
Ultracapacitor and Solar Circuit
Lazy Susan
Electrical Tape
Speaker Wires
Soldering Wire
Price ($ CAD)
7.49
1.2
27.56
33.59
6.6
9.06
15.67
2.78
33.51
101.5
82
15
1.5
2.5
8
22
The total cost of materials for one unit is therefore: $ 347.96
With the information above, an estimate is established for a typical large scale system. This analysis is
for a typical cost for 1 unit.
With the assumption that the parabolic antenna is approximately rectangular in area we get an
approximate area of Area of antenna = 0.9*0.6m2 = 0.54m2.
Payback Period
This section of the analysis deals with losses of energy, production of energy and prices of energy
sellable back to the grid.
Theoretical
Typical direct sunlight carries approximately 1000W/m2/hour of light energy. Of this approximately
1/10 of the energy can be harnessed by PV cells. With the area of the parabolic antenna above, this
gives a maximum of 0.54*1000/10 Watts/hour = 54 Watts/hour. Note that this is the maximum amount
of energy that this system is capable of harnessing assuming no losses.
A typical efficiency for a solar cell is about 25%, and a typical reflectivity for the 1.1eV to 1.3 eV waves
from aluminum are about 90 to 95% reflected.
So a typical value of harnessed energy for this system comes out to be:
54*.25*.9 = 12.15 Watts/hour (minimum).
A typical location will get about 5 hours of direct sunlight each day. This amounts to an average of
22.17kWh of energy annually. With the cost of energy being approximately $0.05/kWh USD, the
payback for a system is:
Payback Period = 347.96/( 22.17x0.05) ≈ 314 years.
Note that this is only a theoretical value. The actual energy produced by the system using a filter is
analyzed below.
Actual
The results shown in figures 4-7 representing the system using the filter. The annual energy production
and payback time for the real system is calculated:
Energy (Watt-hours) =Power (Watts)*3600(seconds/hour)
= (0.00018 kilowatts)* 5 hours/day*365 days/year = 0.3285 kilowatt hours/ year.
23
The ratio of the expected hourly energy to the actual produced energy is 0.0061. This means that the
real system produces 0.61% of the energy than what is expected. This number seems very low so it is
possible that some of the assumptions made to create a theoretical value are fundamentally incorrect.
The true payback time is then calculated to be 21,184 years!
The addition of a simple filter adds a cost of $9.06 CAD. The ratio of the total cost to the filter cost is
2.6%.
The ratio of the cost of the solar array to the total cost of the system is 23.6%.
The ratio of the cost of the solar array to the cost of the filter is 11.05%.
Conclusion
This group concludes that as the temperature of solar cells increase, the power output increases to a
maximum limit, which occurs at about 35 degrees Celsius and after this point the power starts to drop
and the cell is no longer efficiently producing electricity. Therefore, the temperature of the solar array
must be limited to maximize energy production.
To prevent the solar cell from overheating, a filter is needed to block the unwanted wavelengths. The
filter therefore limits the temperature of the solar array. The film filter is successful in limiting the
temperature of the solar array and is cost effective. The price of the filter amounts to 2.6% of the
overall cost of the system and is relatively cheap to the cost of the solar array at 11.05%. In conclusion
the addition of camera film used as an optical filter is indeed economically feasible, however its
performance reduces the overall energy production of the system so to make the project unrealistic.
Without the use of a filter, the power output from this system more than doubles so long even at the
most inefficient temperatures. Although the addition of the film allows the solar cell to operate close to
the maximum efficiency level, the film also blocks a portion of the required wavelengths for the solar
cell. As a portion of the useable light is blocked, the solar cell produces less power than is available,
however the filter stabilizes temperatures of the solar array.
The cost analysis section of this report shows that the system realized by this group is not worth
developing further. Although the price of the filter is significantly lower than the cost of the solar array,
the total cost of the system is actually quite expensive and only increases the payback time for the
entire system.
Additional Remarks
To improve the efficiency, a glass filter can be specifically designed to filter out the unwanted
wavelengths which cause the temperature to rise. However, these glass filters cost significantly more
than the film filters and thus may not be economically viable.
24
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http://en.wikipedia.org/wiki/Cassegrain_reflector
[4]COVALENT Clear view to Solar. Retrieved March 9, 2010, from
http://www.covalentsolar.com/Technology
[5]Monocrystalline Silicon. Retrieved March 10, 2010, from
http://www.cogeneration.net/monocrystalline_silicon.htm
[6]Concave mirrors. Retrieved March 20, 2010, from
http://www.thorlabs.com/newGroupPage9.cfm?objectGroup_id=1161
[7] Photovoltaic System Economics. Retrieved March 2, 2010, from
http://www.infinitepower.org/calc_pv.htm
[8] Images Scientific Instruments. Solar Cells. Retrieved March 12, 2010,
from http://www.imagesco.com/solar/solar-cells.html
[9] Solar Power. Retrieved March 1, 2010, from http://www.solar4power.com/solar-power-basics.html
25
Appendix A
Tracker circuit diagrams:
26