Portable Solar Tracker
Critical Design Review
Group 1
Summer 2010
Stephen Holman
Tri Bui
Christopher Davis
Tuyen Bui
Project Overview
• Design and optimize a solar energy collection, storage, and
distribution device
• The device will track the path of the sun
• Panel will be orthogonal to sun’s rays
• The device will have a user interface displaying useful
information
Goals and Objectives
•
•
•
•
•
•
•
High efficiency
Sustains on its own energy
Reliable operation
The best quality for the lowest cost
Durable
A user-friendly interface
Portable
Specifications
Dimensions:
Weight:
Avg. Collected
Voltage:
Voltage
Output:
Current
Output:
Power Output:
Temperature
Rating:
Efficiency
(Output/Input)
Life
Expectancy
Accuracy
S.I. Units
0.37m long x 0.203 m wide x
.508 m high
2.7 kg max
10.5-13 Volts DC
Imperial Units
14.5 in long x 8 in wide x
20 in high
≈ 6 lbs. max
-
5- 6 Volts DC
-
50-100 mA
-
.25 - .6 Watts
-10 °C to 50 °C
14 °F to 122 °F
10% minimum
(of the panel rating)
500
full charge/discharge cycles
±3° of the sun’s position
-
Components
Components
Part Name
Battery
Nickel Metal Hydride
LCD
HD44780
Motor
Hitec HS-322HD
Compass
HMC6352
Optics
Parabolic mirror
Solar panel
8V with 44 mA
Battery Monitor IC
DS2438
Switch
Pololu Switch
Reasons
•7.2 V
•Inexpensive
•Low power usage
•Minimal connections
•Fixed rotation servo
•Draws 7.4 mA at 4.8V sitting
idle
•Operation at 2.7V idle
•Easy Programmed and
operated by MCU with I2C
protocol
•Better concentration
•Good voltage
•Efficient battery
management
•Reduce power consumption
•Interrupts to display
Solar Panel
Since the main specification for this project is the optimization of output power of a
photovoltaic systems. What the aim of the solar tracker is to try to increase the
output power at least by 10%. The solar panel that is used in this project is:
•8 V 44 mA, .352W solar panel
•The current solar panel array in which
we will build is it is to have two of these
panel connect in series.
•There will be another configuration that
will be used is to have 4 in parallel.
The first configuration will provide 16 V with 88 mA, providing 1.408W.
As for the second configuration, it will provide 8 V with .176 mA and provides
1.408 W.
Solar
Solar
Panel
Panel
Cont’d
Since the main specification for this project is the optimization of output power of
a photovoltaic systems. What the aim of the solar tracker is to try to increase the
output power at least by 10%. The solar panel that will be used in this project will
This
be: is the current and voltage equation for a standard photovoltaic cell along with the
simple photovoltaic circuit model.
•.5 V 3.6A, 1.8W solar panel
•Optional panel is a 8V 44mA, .352 W
R1 = Series Resistor
The current solar panel array in which
R2 = Shunt Resistor
we will build is it is to have two of
D1 = Diode
these panel connect in series. This
array will have 1V with 3.6A. Using
the power equation P = VI, we have
In this equation, I is the output current. IL is the current produced by the photovoltaic cell.
3.6W. This will be plenty to supply the
That current is the short circuit current given by the manufacturer specification. ID is the
battery.
6”
diode current and ISH is the shunt resistance.
Also another option we are looking
into is have two types of panel. Each
ID can
describewill
by the
equation
of
thebe array
have
theirabove,
ownthe Schottkey diode equation.
function.
Solar Panel Cont’d
This is the energy conversion efficiency of the photovoltaic cells.
Pm is the power produced by the cell = .352W
E is the irradiance = 1000 W/m2
Ac is the area of the cell = .0381X..0762m = .0029 m2
So the efficiency for our single cell is = .1214
Which is approximately 12.14% ≈ 12%
=
This is the fill factor equation, which determines the ratio of the actual maximum power
to the theoretical power.
Pm is the power produced by the cell = .352 W
Voc is the open circuit voltage = 8 V
Isc is the short circuit current = 44 mA (Values varies under certain conditions)
Our FF = 1, a typical commercial cell is > .7
Results
Time
Voltage (V)
Current (mA)
Current (mA)
Power (W)
8
6.15
6.75
8:15
6.33
6.76
8:30
6.48
27.16
0.175997
6.8
74.8
0.50864
8:50
6.52
33.4
0.217768
6.77
78
0.52806
9:10
6.58
40.8
0.268464
6.66
82.6
0.550116
9:30
6.6
40.6
0.26796
6.7
81.3
0.54471
9:50
6.7
53.5
0.35845
6.76
83.4
0.563784
10:10
6.59
65.2
0.429668
6.67
88
0.58696
10:30
6.68
75.1
0.501668
6.62
93.6
0.619632
10:50
6.6
76.2
0.50292
6.63
93.4
0.619242
11:10
6.67
79.6
0.530932
6.58
93.6
0.615888
11:30
6.62
80.8
0.534896
6.6
91
0.6006
12:50
6.64
100.5
0.66732
6.63
102.6
0.680238
1:50
6.78
92
0.62376
6.65
93
0.61845
Fixed
Power (W)
Voltage (V)
Tracking
Results
Power Comparsion Between Fixed
and Tracking
0.6
Fixed Power
0.4
Tracker Power
0.2
0
8:
30
9:
10
9:
50
10
:3
0
11
:1
0
12
:5
0
Power (W)
0.8
Time
Results
In the morning, there is a 12% increase in efficiency.
At mid-morning, there is a 6% increase in efficiency.
Since, the sun’s rays is starting to become orthogonal to the panel
As for noon, the efficiency are roughly the same.
At this time both fixed and tracking panel are orthogonal to the sun’s rays.
Solar Panel Cont’d
The following figure describes the effects of temperature on a
photovoltaic cells.
Provided by Squirmymchphee
Solar Panel Cont’d
Other ways to improve the optimization of photovoltaic cells is to account for the rise
in temperature of the cells.
Possible Solution:
•Usage of a heat sink
•Usage of water
•Either submerge the panel in a water solution.
•Another method is the use a water system
•Then there is the use of fan(s), the solar panel or the battery will help in powering
the fan so that it can help reduce the temperature across the panel.
Optical Configuration
Perhaps the most important aspect of the Portable Solar Tracker is
the optical configuration. The purpose of the optical configuration is
to increase the performance of the photovoltaic cells by increasing
the amount of light that is received.
Factors taken into consideration:
• Size
• Shape
• Weight
• Material Reflectivity
• Durability
• Heat Concentration
Mirrors
Mirrors
Plane
Parabolic
Trough
Simple
Available
Simple
Easy to control
Single or Dual-Axis
Bulky/Less portable
Foldable for a more
compact frame
Bulky/ Less Portable
Single –Axis
Less reflected light
rays received
Complicated
frame/Motor System
Simple Motor System
Least amount of
Heat concentration
on Cells
Higher Heat
Concentration on
Cells
Not easily Available
Reflectivity
The reflectivity of material is the amount of incident radiation
reflected by a particular surface. Different materials are being
considered including mirrors and aluminum foil among others.
To maximize reflectivity the
material has to exhibit specular
reflection. Specular reflection is
best explained by the law of
reflection which states that the
incoming light and the reflected
light have the same angle with
respect to the normal of the
surface.
Optical Configuration
The optical configuration that was chosen was a trough shape
reflective material called Mylar placed onto a lightweight wire
mesh. The trough shape was chosen because it could be made
relatively cheap and efficient because it was easily modifiable to
adjust the focal point to the location needed.
Optical Configuration
Why A Trough Mirror?
• No clear cut difference in
Parabolic mirror over Trough or
Plane mirror design
• Easy to fabricate/purchase
• Allows for more incident light
to be reflected
• Cheap
• Lightweight
Why not use a Lens?
Two different lens types were
tested while investigating optical
configurations. Both magnifying
and Fresnel lenses reduced or had
no effect on power output of the
solar panels. In addition the lenses
focused too much light onto the
photovoltaic cells which thus began
to damage the panels and reduce
their efficiency.
Battery Options
The battery will be a critical element of the device and will need
to satisfy the established goals.
Type
Pros
Cons
Lithium-ion
High energy capacity, lightweight, low self-discharge,
handles overcharge well
Expensive, thermal runaway,
explosive, needs protection
circuitry
Nickel-Metal
Hydride
Good energy capacity, reasonable High self-discharge, sensitive to
W/kg, constant voltage output
overcharge damage, needs
protection circuitry
Lead-Acid
Very durable, least susceptible to
degradation due to multiple
cycles
Low energy density, heavy mass,
lead is toxic
Selected Battery
•
•
•
•
Ni-MH is the battery used for this project.
7.2V 3300mAh from RadioShack (See Figure)
Purchased for about 1/3 the price of similar Li-ion packages
It is powerful, but the main concern will be lifespan.
Battery Charging Method
•
•
The battery will be charged using a –∆V sensor fast charge method
In this method: Charge voltage increases to
peak, then falls to a voltage where
charge is terminated.
• This retains 100% charge capacity
• Operates in 0-40°C temperatures
• This method can be moderated
by a microcontroller algorithm controlling a switch
Provide by SBS organization.
Battery Protection
Circuit to the right provides basic
reverse current protection with a
MOSFET and Schottkey diode.
Provided by Texas Instruments
The figure on the left is the
diagram of the battery protection
circuit implemented on the PCB to
protect against overcharging the
battery.
Microcontroller
For this project, the MCU of choice is the Atmel atmega168 Microcontroller.
•20 I/O pins
•Of the 20, 6 are analog pins
•14 digital pins
•Of the 14, 6 are PWM pins
•Can supply components up to 5 V
•Operating voltage of 2.7-5.5V
•Has lower power consumption mode
Microcontroller Cont’d
Microcontroller Cont’d
To connect the pin outs for the various
components are :
•LCD requires 6 digital pins
•Servo require 1 digital (PWM) pin
each
•Photoresister requires 1 analog pin
each (4 Photoresister)
•Compass requires 2 analog pins
•Battery monitoring requires 1 digital
pin
•REED relay requires 1 digital pin
•Pololu switch requires 2 digital pins
Motors
Before the selection of a motor could be done, initial research into
servo motors and DC motors was conducted.
Servo Motor
DC Motor
Low Power Consumption
Greater Torque/Speed
Low Price
Requires Motor Controller
Simple 3 Wire Interface
Higher Power Consumption
Low Torque/Speed
Greater Complexity
Motors
A servo motor was chosen for the reasons listed below:
• Low Cost ($9.99)
• Low Power Consumption (0.036 W)
• Ease of use/Familiarity
Because the Solar Tracker follows the sun across the sky gradually
over the course of a day, speed was not taken into consideration.
Torque on the other hand was, but because of the portability of the
Solar Tracker weight of the optical configuration was determined
low enough for a servo motor to handle.
Servo Motors
Once a Servo motor was chosen, a fixed rotation servo was
compared against a continuous rotation servo. Continuous rotation
was not required because the sun is never visible for over 180º at
ground level.
Name
HS-322HD
S9405
S3001
Torque
@4.8V3.0kg.cm
@6.0V3.7kg.cm
@4.8V5.8kg.cm
@6.0V7.2kg.cm
Speed
@4.8V0.19sec/60º
@6.0V0.15sec/60º
@4.8V0.13sec/60º
@6.0V0.11sec/60º
Additional
Idle Current Draw
@4.8V - 7.4mA
@6.0V - 7.7mA
180º Range
Temp Range -4º - 140º F
Coreless Motor
Weight - 55g
Available
Yes
Price
$9.99
Yes
$64.99
@4.8V2.4kg.cm
@6.0V3.0kg.cm
@4.8V0.28sec/60º
@6.0V0.22sec/60º
Temp Range -4º - 140º F
Single Ball Bearing
Weight - 44g
Yes
$16.49
Compass
A feature of the Portable Solar Tracker is an electronic compass
which will allow the user to determine the current direction the base
is facing via the LCD Display.
The factors that were important when selecting a compass were:
• Low power consumption
• Modes of operation (Standby)
• Reliability
• Price
HMC 6352
The HMC 6352 is the compass chosen for use with this project.
Name
Axis
Additional
Available
Price
HMC6352
Operating
Voltage
2.7V - 5.2V
Dual Axis
Yes
$34.95
HM55B
3.0V - 6.7V
Dual Axis
Yes
$29.99
HMC5843
2.5V - 3.3V
3- Axis
Heading
Repeatability - 1º
Heading
Resolution - 0.5º
3 Modes of
Operation
Standby Mode
1 µA Current
Draw in Standby
Voltage Regulator
5 Different
Operating Modes
I2C
551SparkFun
$49.95
Displaying
To represent the information to the user, an LCD with HD44780
controller is used.
Features
• 16x2 characters
• 5x8 dot matrix
• Operates at 2.7 to 5.5V
• 8 or 4-bit interface
4-bit interface is
used to save I/O pins.
Displaying
The Pololu switch is used to help display information on the LCD
screen.
Once the button is press the following information will be
Displayed
• Battery life
•Battery Voltage
• Load current
• Temperature
• Directional Heading
Output
USB female adapter
To power handheld
devices such as cell
phone, Mp3 player, and
camera.
Output
To replicate a USB charger, the Data + and Data – pins must
produce 2.5V and 2V, respectively.
Battery Monitoring
Specifications of the monitoring system
• Battery life
• Charging and discharging state
• Sleep mode
• Overcharge protection
Maxim DS2438 battery monitoring IC
• 1-wire interface
• Temperature sensor
• End-of –charge and
discharge detection
• Measure Voltage
• Measure current
through sense resistor
Provided by Maxim-IC Co.
1-Wire Bus System
Allows the microcontroller
and the device to
communicate with a single
connection. When idle the
wire is resistively pulled up
to a high state.
Communicating by
using a controlled lowduration time pulse.
Logic 1 transmits as a
short pulse and logic 0
transmits as a long
pulse.
Provided by Maxim-IC Co.
Battery Monitoring Circuit
Method of Tracking
Photoresistor is a device that changes its resistance depending on
the amount of light exerted on it.
Provided by Perkin Elmer inc.
As the level of brightness increases, the resistance decreases.
Method of Tracking
The position of the sun can be determined by differentiating the
voltage drop across the two photoresistors. The voltage vaules are
quantized by the Arduino’s A/D converter.
Method of Tracking
To find the photoresistor that has high sensitivity, each one is
measured for its responsiveness to the change in position of
the sun.
Interfacing with the
Microcontroller
Interfacing of
components used in this
project is displayed to
the right. The
microcontroller is the
heart of the device.
•LCD
•Compass
•IC’s
•Servo motors
•Battery
•Solar panel
Interfacing Circuitry
Interfacing Circuitry
Interfacing Circuitry
Interfacing Circuitry
Interfacing Circuitry
Programming
The Arduino microcontroller is programmed in it’s own Arduino
programming environment. The language is based on C and C++.
There are three main parts Arduino programs are divided up into:
Structure (if, for, do while, etc…), Values (constants and variables),
and Functions. There are also many libraries to control components
such as Servos, LCD displays, and EEPROM.
Programming Flow Chart
Programming Samples
voltagearray[x] = MeasADC(_1W_Pin, V_AD);
for(i = x; i > 0; i--)
{
if(voltagearray[i] < voltagearray[i-1])
dropping++;
temparray[y] = MeasTemperature_2438(_1W_Pin);
for(j = y; j > 0; j--)
{
if(temparray[j] > pow(voltagearray[j-1], 1.25))
rising++;
if(dropping >= 3 || rising >= 3)
digitalWrite(relaypin, LOW);
}
}
Battery Protection
Void Photocheck1 ( )
{
if (photo1 < photo2)
{
if (timeelapsed < 10000)
{
rotateXservo (10)
}
else if (timeelapsed < 150000)
{
rotateXservo (15)
}
else
{
}
}
}
Photoresistor Comparison
Mechanical Structure
The picture shown is a representation of the mechanical structure that is used in this
project. The trough system will be setup as depicted in the picture shown. Motors will be
attached on the side of the trough so that it can rotate 180 degree across the sky, as well
as a servo on the base to move it left and right. All of the components will be placed
within the enclosure. The enclosure will be a box with dimension 14.5 in long X 8 in
wide X 20 in high and is made from acrylic.
Milestones
Milestones
Budget
Initial Estimated Budget
Solar Panels:
$50
Battery:
$50
Microcontroller:
$50
Motors:
$30
LCD Display:
$30
Optics (Mirrors and Lenses):
$40
Frame Components:
$50
Cooling System:
$30
Miscellaneous Components:
Total:
_______$70_______
$400
Budget
Current Expenditures (as of 7/31/10)
Solar Panels:
$150
Battery:
$22
Microcontroller:
$37
Motors:
$50
LCD Display:
$8
Optics (Mirrors and Lenses):
$16
Frame Components:
$129
Miscellaneous Components:
Total:
_______$133_______
$545
Manufacturability
This project can be reproduce with the following amount
Solar Panels:
$120
Battery:
$22
Microcontroller:
$4
Motors:
$20
LCD Display:
$8
Optics (Mirrors and Lenses):
$16
Frame Components:
$60
Miscellaneous Components:
Total:
_______$30_______
$280
Progress
Progress
Research
Design
Part Acquisition
Progress
Prototyping
Testing
Overall
0
20
40
60
80
100
Work Distribution
Chris
Tuyen
Stephen
Tri
Circuit Design
-
X
X
-
Programming
Architecture
-
X
X
X
Mechanical
Design
X
X
X
X
Optical Design
X
-
-
-
X
X
PCB Fab.
Work hours Distribution
Chris
Tuyen
Stephen
Tri
Total
Circuit
Design
30
40
40
20
130
Programming
Architecture
10
50
50
10
120
Mechanical
Design
35
35
35
35
140
Optical
Design
15
5
15
10
45
PCB Fab.
30
5
35
20
90
Misc.
20
20
20
20
80
Approximated
Challenges
1. Power
2. Panel Configuration
1. 12 parallel -> MCU
2. 4 – 2 set in series then in parallel -> Battery/Output
3. Compass readings distorted by wire mesh/metal screw
and washers
1. Compass calibration
4. Replacement servo
1. Original motor burnout
Future Improvements
1.
2.
3.
4.
5.
6.
7.
More precise values for photoresistors
More efficient solar panel
Bigger tracker
More efficient concentrator
Plastic screws
Weight reduction
Heat dissipation system
Questions