Southern University Southern University La ACES TeamLa ACES Team

EXCELLE ExperimentEXCELLE Experiment(Experiment For Solar Cell Efficiency)(Experiment For Solar Cell Efficiency)

Tannus Joubert, Kristen Hypolite, Kevin James, Tannus Joubert, Kristen Hypolite, Kevin James, Laquonda Johnson, Michael Johnson, Shanta Laquonda Johnson, Michael Johnson, Shanta

McKinzie, Leslie SanfordMcKinzie, Leslie Sanford

Preliminary Design Review (PDR)Preliminary Design Review (PDR) March 18, 2005March 18, 2005

Mission ObjectivesMission Objectives

Measure the light conversion efficiency Measure the light conversion efficiency Output of an assortment of solar cells Output of an assortment of solar cells

throughout various levels of the atmosphere throughout various levels of the atmosphere Results Results

– conclude whether future La ACES experiments conclude whether future La ACES experiments can be powered by the most efficient solar cells can be powered by the most efficient solar cells found found

SCIENCE GOALSSCIENCE GOALSUnderstandingUnderstanding

Solar Cell Efficiency Solar Cell Efficiency The Solar Spectrum The Solar Spectrum

– Its relation to the silicon solar cell material band Its relation to the silicon solar cell material band gap gap

Energy Energy PhotonsPhotons Wasted HeatWasted Heat

Types of solar cellsTypes of solar cells

MonocrystallineMonocrystalline– Made from pure silicon, most efficient Made from pure silicon, most efficient

(~24 % in the lab), but most expensive (~24 % in the lab), but most expensive since they are difficult to makesince they are difficult to make

Polycrystalline Polycrystalline – Less efficient (18 % in the lab) Less efficient (18 % in the lab)

AmorphousAmorphous– Least efficient (13%), used in watches, Least efficient (13%), used in watches,

calculatorscalculators

Technical GoalsTechnical Goals

Measure the light conversion efficiency that Measure the light conversion efficiency that solar cells solar cells – Research the condition the solar cells can Research the condition the solar cells can

withstand withstand – Find the position that the sun is at the time of Find the position that the sun is at the time of

launch and during launch to maximize the solar launch and during launch to maximize the solar power power

– Deal with the rotation that maybe encountered Deal with the rotation that maybe encountered by the cord being tangled by the cord being tangled

Payload DesignPayload Design

The payload will be surrounded with three The payload will be surrounded with three types of solar cells, so that energy types of solar cells, so that energy conversion efficiencies can be compared.conversion efficiencies can be compared.

DesignSubcategories: DesignSubcategories: SystemSystem ThermalThermal MechanicalMechanical ElectricalElectrical Software design Software design

Principle of OperationsPrinciple of Operations

N-Type

P-Type

_ _ _ _ _ _ _ _ _ _

+ + + + + ++ + + + ++ + + + + + +

Electric Field

Photon Path

I

Load

Power output

+

_

Vo

Possible challengesPossible challenges

Rotation effects- may be dealt with by measuring position Rotation effects- may be dealt with by measuring position of sun with respect to pay load of sun with respect to pay load

Ultra-violet radiation- Will it damage the cells or be Ultra-violet radiation- Will it damage the cells or be beneficial by providing more energy?beneficial by providing more energy?

Pendulum motion of package- will it interfere with our data?Pendulum motion of package- will it interfere with our data?

Launching at dawn – how to maximize sunlight intake due Launching at dawn – how to maximize sunlight intake due to low position of sun? to low position of sun?

System Interface ComponentsSystem Interface Components

Main System: Basic Stamp Processor

Subsystems: Solar cells User Interface Real Time Clock Analog-To-Digital Converter Memory Power System Reset Temperature Sensor

*Real Time Clock provides accurate date and time

Solar cells send the charge

through charge converter for

signal acquisition by

the multiplexer.

ADC converts analog to a readable digital signal

Memory must be

synchronized with the ADC to process the

data.

User interface (Laptop) will be used to upload and

download software and data.

Basic Stamp Processor is used to

control all data acquisition and

processing. Solar Cells

Charge Converter

Analog to Digital Converter

Basic Stamp Processor

Memory

Real TimeClock

System Reset

User Interface

MultiplexerTemperature

Sensor

Power

System Interface ComponentsSystem Interface Components

Electrical DesignElectrical Design

BalloonSat SystemBalloonSat System– 6V at 100mA6V at 100mA– 4 AA Li Batteries4 AA Li Batteries

Charge Controller/ConverterCharge Controller/Converter– Convert current coming from each cell into voltage Convert current coming from each cell into voltage – Convert excess voltage into heat, used to keep inside of Convert excess voltage into heat, used to keep inside of

box warm box warm – Voltage signal/readings to be passed through an 8 Voltage signal/readings to be passed through an 8

channel multiplexer channel multiplexer combine all the signals into one data stream combine all the signals into one data stream

Electrical Design cont’dElectrical Design cont’d

Onboard Temperature Reading Onboard Temperature Reading – Onboard ADC Onboard ADC – Voltage Regular Temperature ReadingVoltage Regular Temperature Reading– Operational AmplifierOperational Amplifier

BASIC STAMPBASIC STAMP– If memory is full Basic Stamp is able to turn itself off If memory is full Basic Stamp is able to turn itself off – Power supply regulator is already built into the circuit Power supply regulator is already built into the circuit

board board – LEDs will be used to confirm operations LEDs will be used to confirm operations

Electronic FlowchartElectronic Flowchart

SOLAR CELLS

CHARGE CONVERTER

MULTIPLEXER

ADC

RTC

BASIC STAMP

MEMORY

Thermal DesignThermal Design

Flying payload to the height of approximately Flying payload to the height of approximately 30km at the temperature of -6030km at the temperature of -60ooC.C.

Location Palestine, Texas.Location Palestine, Texas. Challenge is to design a payload to stay well Challenge is to design a payload to stay well

in the range of the operating condition of the in the range of the operating condition of the electronics.electronics.

Overheating of the solar cellOverheating of the solar cell

Payload Operating at -60 oC

Overheating of the Solar Cells

80oC

Overheating of Electronics

Thermal SchematicThermal Schematic

Solar cells cool by radiation

Mesh

Inner Temp maintained to within 5 - 6oC with induced convection with fan

Electronics generate heat

Air (R)

Solar Cells (R)

Mesh (INS) (C)

Foam Core (C, R)

Inside Payload (R) (CV)

Qcond

Spacer

Air flow (-60oC)

where R- radiation, C-conduction, CV-Convection, and INS – Insulation

RecommendationsRecommendations

Spacer-mesh combination to prevent Spacer-mesh combination to prevent scorching of foam corescorching of foam core

May rely of rotational effects to radiate heat May rely of rotational effects to radiate heat from the boxfrom the box

Test simulation will be done on electronic Test simulation will be done on electronic and payload system to determine possible and payload system to determine possible thermal effectsthermal effects

Mechanical Design Mechanical Design

1. Creating a payload of a low weight, high thermal stability, and a suitable degree impact resistance. Constructing a payload that will withstand such stresses is also a key factor in our design.

2. The method of attaching solar cells to the payload and interfacing them with the rest of the electronics.

3. Preflight worthiness test .

We will focus on :

Mechanical DesignMechanical Design

The box concept for now is simply rectangular payload with which consist of two modules:

1. Inner module

2. Outer module

Mechanical DesignMechanical Design

The functions of the outer module are:The functions of the outer module are:

1. To serve as a primary encase1. To serve as a primary encase for the second module.for the second module.

2. Provide a protective covering 2. Provide a protective covering against acceleration, deceleration,against acceleration, deceleration, shock, and impact.shock, and impact.

3. To provide a surface for the 3. To provide a surface for the

attachment of the solar cellsattachment of the solar cells

and framed mesh.and framed mesh.

4.4. To provide a barrier against theTo provide a barrier against the

cold temperatures experienced by the payload.cold temperatures experienced by the payload.

17 cm

18 cm

15.5 cm

Mechanical DesignMechanical Design

The functions of the inner module are:The functions of the inner module are:

1. To provide a containment for the electronics.

2. To hold the batteries.

3. To serve as a second line of defense against impact, shock and gravitational forces.

4. To help optimize the heat transfer of the payload.

14 cm

15 cm

6 cm

Mechanical Design Mechanical Design

•The solar cells will be mounted on a sheet of mesh framed with Popsicle sticks.

•The removable frame will then be attached to the payload by screwing the frame into half inch non-conducting standoffs that will already be attached to the box.

•By mounting the solar cells on this structure, the heat that will dissipate from the solar cells will be able to flow freely away from the payload.

Back view of framed mesh. Front view of framed mesh.

Non-conducting standoff

Mechanical Design Mechanical Design

Weight Budget of the Pay Load:Weight Budget of the Pay Load:

Weight limit: 500 g

• Balloon Sat:

0.5g x 3 x 4 = 6.00 g

63.55 g

• One monocrysitaline solar cell:

• Batteries: 8.3 x 4 = 33.3 g

• Inter and outer modules: 160 g+ 262.85 g500 g - =

< 237.15 g237.15 g• Frame

• Mesh

• Standoffs

Futuristic Payload DevelopmentFuturistic Payload Development

Charge Converter SystemCharge Converter System Control Solar SystemControl Solar System

– CircuitCircuit Mechanical SystemsMechanical Systems

– ScrewsScrews Thermal Control SystemThermal Control System

– Too Hot???Too Hot??? Finishing SoftwareFinishing Software Build PrototypeBuild Prototype

– Find circuits that work interface with softwareFind circuits that work interface with software

Payload Construction PlanPayload Construction Plan

Electronics- planning, development, and Electronics- planning, development, and implementationimplementation

Mechanical and thermal- Planning, Mechanical and thermal- Planning, development and implementationdevelopment and implementation

Software systemsSoftware systems DocumentationsDocumentations Flight ImplementationFlight Implementation

Electronics Mechanical Thermal Software Integration Flight

BalloonSat

Basic Stamp

ADC Converter

Multiplexer

Sensors

Interfaces

Foam Core

Inner Module

Outer Module

Spacers

Mesh

Solar cells

Electronics

Modules

Solar cells

Mesh

Foam Core

ADC program

Sensors

Basic Stamp

Control

Interfaces

Electronics

Mechanical

Thermal

Software

Interfaces

BalloonSat

Basic Stamp

ADC Converter

Multiplexer

Sensors

Interfaces

Hardware FabricationHardware Fabrication

Solar CellsSolar Cells– Testing Testing – Framework Framework

Charge Converter Circuitry (Separate Boards)Charge Converter Circuitry (Separate Boards)– CircuitryCircuitry– MultiplexerMultiplexer

Box StructureBox Structure– Shock and Thermal TestingShock and Thermal Testing– Drop TestDrop Test

Battery (Power System)Battery (Power System)– LocationLocation– Interfacing to Whatever Needs PowerInterfacing to Whatever Needs Power

Integration PlanIntegration Plan

To test the connections between electronics To test the connections between electronics and software.and software.

Stabilize Power ConnectionStabilize Power Connection

Ensure that the Mechanical structure is able Ensure that the Mechanical structure is able to hold the batteries, boards, and other to hold the batteries, boards, and other system ancillaries.system ancillaries.

Take Thermal Test to ensure that Take Thermal Test to ensure that components are working properly due components are working properly due changes in temperature.changes in temperature.

Software Implementation and Software Implementation and VerificationVerification

The Software designed will calculate and The Software designed will calculate and measure the current and voltage output by measure the current and voltage output by the cells and store the data the cells and store the data

The software will decide from which set of The software will decide from which set of cells the signal is being read, and process cells the signal is being read, and process each accordingly. The software will be used each accordingly. The software will be used to calculate voltage and power produced by to calculate voltage and power produced by the cells as a function of altitude. the cells as a function of altitude.

ADC

Inputs the Data

SolarCell

Identifier

1Not 1

2

Reads the ADC value

Reads the ADC value

Calculates the

Voltage

SolarCell

Identifier

SolarCell

Identifier

3

Stores into Memory

End

Time Stamp

Function

After completion of flight, memory is downloaded to obtain data and for the analysis of results.

TemperatureNot T

Not 2

Reads the ADC value

T

Flight Certification TestingFlight Certification Testing Upon the completion of the total payload, we will start flight certification Upon the completion of the total payload, we will start flight certification

testing. We will do both testing. We will do both temperaturetemperature and and shock testingshock testing. .

Temperature testing of the payloadTemperature testing of the payload : : We will place the payload in a ice chest which will contain dry ice and We will place the payload in a ice chest which will contain dry ice and

run the electronics as if in actual flight. run the electronics as if in actual flight.

Shock Testing of the payload: To test the durability of the payload. We will drop the payload (about To test the durability of the payload. We will drop the payload (about

10ft) to make sure the electronics are safely contained and will good 10ft) to make sure the electronics are safely contained and will good conditions to take post-flight measurementsconditions to take post-flight measurements. .

We will analyze the data for both test and make the necessary We will analyze the data for both test and make the necessary changes needed for a successful flight mission.changes needed for a successful flight mission.

Mission Operations

*Synchronize our Real Time Clock with the Global Positioning System

*Erase all test data before flight

Launch Requirements

*Synchronize RTC with GPS. *Computer to communicate with

the Basic Stamp.

Flight Requirements and Operations

*Flight duration of approximately 4 hours*Reach approximately 100,000 before

falling *Temperatures ranges from -60 to 85

degrees Celsius.*Ascent of balloon is expected to be

smooth*Turbulence is expected during the fall.

Data Acquisition and Analysis Plan

Data to be collected:*Charge from solar cells*Product of current and voltage

will allow us to compute the power output by each cell group.

*Temperature inside the payload*Time stamp generated RTC

*All data will be stored on board using EEPROM memory.

Data needed:GPS system data: Longitude, Latitude, Altitude.This data will be gathered after the flight. The data will then be

correlated to the data collected on the payload.

Organization and ResponsibilitiesOrganization and Responsibilities

La Aces Program Office

Team Leader(T. Joubert)

PayloadDesign

Data Analysis(L. Johnson)

Project Management(T. Joubert)

MechanicalDesign

(L. Sanford )Documentation

ThermalDesign

(M. Johnson)

ElectricalDesign

(S. McKinzie )

Software Design

(T. Joubert )

SystemDesign

(K. James )Calibrations

Parts/Budget Flight Data Analysis

Scheduling(K. Hypolite)

Results

Interface ControlInterface Control

Electronic Interfaces(System) Need to know much voltage is coming in various components.Circuits needs to checked for connections to software and system components

Thermal InterfacesDepends on the mechanical design for cooling of solar cells, temperature inside the box.All electronic components on the payload will need to endure extreme temperature changes

Mechanical InterfacesNeeds to be able supply an adequate amount of space for all components. Materials used in construction depend on thermal testing.To provide a suitable degree of impact resistance.

System DesignNeeds to be able to communicate with all components.

Interface Control

Software Interfaces(Electronic) Needs to know when to read data; how often to read data.

Master ScheduleMaster ScheduleActivity Start Finish

Mission Objectives/Project Management 2/28/2005 3/9/2005

Payload Design 3/2/2005 4/12/2005

Payload Development 3/9/2005 4/12/2005

Payload Construction Plan 3/9/2005 3/9/2005

Master Budget/ PDR 3/10/2005 3/13/2005

Submit Complete PDR 3/17/2005 3/17/2005

Preliminary Design Review 3/18/2005 3/18/2005

Spring Break 3/21/2005 3/29/2005

Submit Complete CDR 4/12/2005 4/12/2005

Critical Design Review 4/15/2005 4/15/2005

Flight Readiness Review

5/23/2005 5/24/2005

Launch Trip 5/22/2005 5/26/2005

Work Break Down ScheduleWork Break Down Schedule

Time ScheduleTime Schedule MilestonesMilestones

BudgetBudgetName Vendor Source Delivery

TimeQty Part No. Price per

quantityPrice

Solar Cells Radio Shack Went tostore

In Stock 6 276-124 10.00 10.0010.00

Multiplexer Digi-Key TBD TBD TBD

Glue TBD TBD

EEPROM Digi-Key Catalog 1 week 1 AT27BV256-12JC-ND

2.32 2.322.32

Batteries RadioShack Went toStore

In Stock 1 4 AA 3.99 3.993.99

Foamcore ACESProgram

In Stock 1

ADC Digi-Key CatalogCatalog TBD TBD

Popsickles Wal-Mart TBD 100 TBD

Standoffs Digi-Key Catalog 1 week 10 1902ck-nd $5.24 5.245.24

Construction Tools

ACESProgram

In Stock

Total So Far $21.55$21.55

RISK MANAGEMENTRISK MANAGEMENTLevels of RiskLevels of Risk

HighHigh

MediumMedium

LowLow

Transfer of ResponsibilityTransfer of Responsibility