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Development of a Solar Cell and Environmental Characterization

1. attend E aa 50 APENAS ca enden 54 Appendix Electrical Design and Detail of Devices Used in the MASS 55 1 Schematic of Power Manager User interface Board 55 A 2 Connectors in Power Manager User interface Board 56 Microcontroller Battery Voltage Measuring System 56 A 4 Commercial Hardware used in the MASS System 58 A 5 Main Electronic components used in the Power Manager User interface Dodd ios ibtd t pn 60 Appendix B Electrical Design and Detail of Devices of the SCTU System 61 B 1 General Schematic of the Solar Cell Testing Unit SCTU 61 B 2 Connectors in Signal Conditioner Board esses 62 Interconnection of Solar Cells for Testing ees 62 B 4 Schematic of Signal Conditioner Board esse 64 B 5 Commercial Hardware used in the SCTU 65 B 6 Main Electronic Components used in the SCTU System 69 Appendix C Connections of MASS SCTU for Assembly in the Field 70 Appendix D Detailed pin out of MASS SCTU systems 74 D 1 Terminal blocks rack in the main enclosure
2. Figure B 7 Schematic of Signal Conditioner Board 64 65 B 5 Commercial Hardware used in the SCTU System Table B 3 Commercial hardware used in the SCTU system Block Device Main Characteristics ATJ Solar cell set 15x Emcore Advanced Triple Junction Solar Cells for Space Applications connected in series in a single solar panel InGaP InGaAs Ge Solar Cells with n on p polarity on 140 um Uniform Thickness Ge Substrate Fully space qualified with proven flight heritage in LEO and GEO environments Electrical Parameters at AMO 1353W M 2 at 28 C Vo 2 60V s J 17 1mA cm2 Vinp 2 30 Imp 16 2mA cm2 BOL efficiency at maximum power point 27 596 Silicon Solar cell set 3x Siemens 103mm standard single crystal silicon solar cells connected in series in a single solar panel Square silicon single crystal solar cell grown by the Czochralski method Electrical Parameters at Standard Test Conditions 1000W m 25 C and AM1 5 Vo 0 585V 3 46A Variable Load Executive Engineering EE30180A DC Electronic Load Adjustable and selectable quasi constant power constant current mode Thermal and over power protection Input Voltage 0 55V Input current adjustable 0 80 Amperes Maximum Power dissipation 300 Watts 66 Pan tilt unit Directed Perception Pan Tilt Unit Model PTU C46 70 Computer controlled RS
3. esses 74 D 2 Connections in Solar Controller eene 76 D 3 Connections in current measuring board secondary enclosure 76 D 4 Connections in Signal Conditioner Board sess 77 D 5 Connections in terminal blocks rack in the secondary enclosure 77 D 6 Connection of opto relays in main enclosure eese 78 D 7 Connection of solar cell testing sets 79 Appendix E Software specific Details olo encre eet taro erede 80 E 1 General Information about the processes see 80 E 2 Generated Data Piles AA pd beato ive des 80 LE Weather Datos sce dca eto nl ed o e nd de LAN 8l E4 Solar Cell Data e 81 E 5 Main programming code files ccc cccssscssssscesnsccsessnsessacceenseceenscessnnecs 82 E 6 About Log Files and Time Management see 84 Appendix F Implemented Protocol for PC Microcontroller Communication 85 F 1 Behavior with unknown messages and timeout sse 87 Appendix G Implemented User interface Menus eee 88 LIST OF TABLES Page Table 4 1 Main characteristics of the SCTU sensors connected to the general purpose data ds 31 Appendixes Table A 1 Commercial hardware used in the 5 58 Table A 2 Electronic components used in the Power Manager User i terface board end lt taa
4. Figure 3 2 MASS SCTU system installed in the field 3 1 4 Power Manager and User Interface System Modules The MASS includes a power manager system for power control and a user interface system for user interaction Although the two functions are not related both systems are controlled from a single microcontroller that independently manages both units The user interface includes an onboard mechanism for user control and monitoring The device incorporates a small LCD screen to display an ordered menu system for the user to perform routine tasks over the MASS or child experiments without using external tools The power manager globally controls the power budget of the MASS by switching devices On only when they are required to operate and switching the system Off if the battery voltage decreases below a configurable threshold The complete powering scheme is configured using the user interface system The user interface power manager systems is a relatively large system involving several algorithms and specific components The integrated system will be covered in detail in section 3 3 3 2 Software Core The software core defines the basic rules and programming code structure for all MASS related processes running on the main computer All MASS and child software which directly or indirectly uses one or more of the MASS modules must follow these rules in their programming code The MASS includes a core process whic
5. 5 Sub MEN SS Modules a at de toa la es id aa 5 3 1 1 Central Computer Module eo ore aeree i ee ae enn 6 3 1 2 Power Supply System 7 3 1 3 Mounting System Module cipe nnn dea ud pete eet 7 3 1 4 Power Manager and User Interface System Modules 8 O 9 3 3 Power Control and User Interface Systems oooooocccnoccccnonccononcconanacinnnccnn 11 3 3 1 PowerManager Systemie toroa dente dece uus 11 2 9 2 Usere Interface Syst m ini 13 3 3 3 User Interface amp Power Manager Software The Core Process 16 3 3 4 Microcontroller daria 18 4 Solar Cell Testing Unit SCTU eoe So eiit fu be AO AS aes 22 4l Objecuyex hn ta sd Ob ute iie p UU t 22 4 2 Implemented ld 23 4 2 1 Central Experimento iii iii 24 42 2 Pointing 28 2 2 ALY SEMIS OLS uo estesa utile vo oe wae LR 30 42 4 Physical Lay oU ostentat ig pe ituri oen dde a eR e UN 32 42 5 Control oos 34 A culpe EI D ane d me ILC 41 Sel Solar Cell Characterizaion niae lis 41 5 1 1 Current Voltage I V Curves eet 41 5 1 2 I V Curves during Different Times of the Day sess 43 321 9 SUMMA AC KING Syste cocer quse Spei temo buon ede evo E eE etae 44 5 1 4 Solar Spectrum Measurements essen eene enne 45 5 2 Weather iii ti 47 Concise tes 49
6. voltage 1 V voltage 2 V voltage 3 V templ C temp2 C Voltage x corresponds to the different voltage measuring signals in increasing voltage order being v3 the voltage across all the solar cells connected in series see Appendix D 7 Temp x corresponds to the temperature of the two thermocouples in the solar cell set Furthermore the last row in the data file includes the global irradiance in W m 2 measured during the execution of the experiment The parameter is repeated in the six different columns to help data processing E 5 Main programming code files The main programming code files written specifically for the MASS SCTU are discussed below General purpose libraries used in the system are omitted dataLogger h cc includes all functions that interact with the general purpose data logger Includes functions to download data read current weather read current date time server and for weather log file generation The 83 writeDataLogger FILE logFile function must be modified to change the format of output weather logs panelTest h c contains functions related to the AD DA board and temperature transmitter including functions to read the A D write the D A write the digital output and read the thermocouple inputs All these functions are used in readPanel cc pwrcomm h c contains all definitions and functions needed to achieve inter process communi
7. Experiments shown in this section were acquired during a single testing day on December 12 2004 in the region of Rancagua Chile The selected day was a typical summer day on the area sunny and completely cloudless 5 1 1 Current Voltage I V Curves One of the most distinctive characteristics of individual solar cell technologies is their current voltage I V curve This curve is obtained by varying the load in incremental steps constantly logging voltage and current values from open circuit to short circuit conditions as described in earlier sections Figure 5 1 contrasts the characteristic curves of ATJ and silicon solar cells during the maximum irradiance episode of the day in horizontal position showing relevant electrical parameters Results confirm that both solar technologies operate in distinct electrical ranges and present significant differences in performance Regarding data quality captured I V data from both solar cell sets lack of significant noise and are suitable for solar cell analysis 35 T T T Si Jsc 13 64 mA cm2 34 11 mA cm2 Vpmax 2020 mV 371 3 mV 12 31 mA cm2 29 99 mA cm2 as E _ Temp 53 7 C 5677 FF 77 74 61 7 Eff 23 6 10 6 Irradiance 1052 W m2 1052 W m2 T i Y BO ME DOTEM eis Voc 2345 mV 529 3 mV m a T T AlJiVcuve Jf SilV curve ATJ maximum powe
8. RELAY To Solar Experiment connection of switching relay Solar Panel Chooser brown Terminal Block B or C ICP Logger Green RS232 RS485 Converter TD A Temperature Logger DATA ICP Logger RS232 RS485 Converter TD B Yellow Temperature Logger DATA ICP Logger Red Terminal Block 12V Temperature Logger Vs ICP Logger Black Terminal Block B or C Temperature Logger GND G Terminal B or C equivalent to GND from Solar Charger Black from main cable from solar experiment 5V SV available from Power Supply Card PC 104 12V 12V available from Power Supply Card PC 104 Yellow from main cable from solar experiment 12V 12V available from Power Supply Card PC 104 Orange from main cable from solar experiment Digital Output Opto Isolator Field side Pin 7 DOO Channel A Analog Channel Solar Experiment Main Cable White Control Signal for the Variable Output VoO Load Analog Channel Solar Experiment Main Cable Green Input From External Current Input 0 Sensor Analog Channel Solar Experiment Main Cable Blue Input from Variable Load s Internal Input 1 Sensor Analog Channel Red Cable from Signal Conditioner Card Voltage reading of Panel 1 of Input 2 panels Analog Channel Green Cable from Signal Conditioner Card Voltage reading of Panel
9. Solar Cell Sets Input Revision Size Number D D Date 4 17 2005 Sheet of Hle CADocuments and Settings Avariable load scleBratwr Byly for document printing SCHDOC 5 4 6 Figure B 3 Schematic of the SCTU system Figure B 3 shows the schematic used to control the electronic controlled variable load from the MASS The diagram does not include details of the voltage monitoring signals which connect directly to the analog to digital converter of the MASS in the case of the silicon solar cells and through the signal conditioner board shown in Figure B 7 in the case of ATJ solar cells Different components shown in Figure B 3 are distributed between the primary and secondary electronic enclosures The electronic controlled variable load current sensor and switching relay are located in the secondary electronics enclosure in order to maintain cables connecting the testing solar cells and variable load the 62 shortest possible The opto isolator and voltage and current monitor signals are located in the main electronic enclosure interfacing with the MASS B 2 Connectors in Signal Conditioner Board ATJ voltage monitoring signals Figure B 4 Main connector in Signal Conditioner Board B 3 Interconnection of Solar Cells for Testing The ATJ solar cell set is built interconnecting in series fifteen Emcore Advanced Triple Junction solar cells The solar panel
10. spectrum since the atmosphere can unequally filter certain wavelengths Furthermore changes are also caused by variations in the temperature of the solar cell Varying I V curves may be corrected by temperature to make appropriate comparisons between experiments Correction parameters are provided by the manufacturer or can be determined by empirical analysis Correction by temperature is beyond the scope of this simplified analysis but the expected behavior is of a higher electrical performance with lower operating temperatures 5 1 3 Sun tracking system Figure 5 3 illustrates I V curves for both technologies which was obtained continually pointing the solar cells to the sun with the automatic sun 14 This approach considers that all the incident light to the surface is due to direct normal irradiance beam irradiance neglecting the influence of diffuse radiation reflections of scattering 45 tracking system of the SCTU During these experiments the cosine effect is cancelled since the incident sunrays are normal to the solar cells at all times Therefore observed changes along the day are attributed mainly by path variations of the incident sunlight through the atmosphere and changes in the operating temperatures of the solar cells An important improvement in performance can be observed related to Figure 5 2 specially during times of the day where the sun is far from the normal position when the cosine effect degradati
11. Figure D 8 Cable connections of the three opto relays of the system mounted in a 4 channel I O module rack 19 D 7 Connection of solar cell testing sets ATJ Set red E pd monton Sl S Ry green 9 N Signals Power Signal black 5 white red white black 1 Silicon Set Power SS Signal tk ARM i zzz A A red Voltage black 5 white Monitoring black 3 green Signals Figure D 9 Cable color code of ATJ and silicon solar cell sets 80 APPENDIXE SOFTWARE SPECIFIC DETAILS E 1 General Information about the processes The central computer of the system runs the MASS and SCTU processes under Redhat 7 3 The complete programming code of the software can be located in the hard drive at the following location home mwagner atacama src solarStation Code related to the MASS user interface and power manager systems can be found in the P C subdirectory The system runs two concurrent processes called pwrmngd MASS process and solarStation SCTU process Only the MASS process needs to be executed automatically running the child SCTU child process by forking procedures of Linux On the current setup the pwrmngd process is executed automatically on bootup by the rc local file Manual execution may be performed executing the following command usr sbin pwrmngd E 2 Generated Data Files The
12. Implemented user interface system ooooocnoccnocacooncnoncnannnona 14 Figure 3 5 Summary of implemented algorithm to perform an automatic shutdowar of the System eta oeil aan 18 Figure 3 6 Basic block diagram of the communication protocol between the computer and the microcontroller in the hardware context 20 Figure 4 1 General block diagram of SCTU system sess 22 Figure 4 2 Block diagram of SCTU and interaction with the MASS 23 Figure 4 3 Block diagram of the Central Experiment eee 25 Figure 4 4 ATJ solar cell set used in the SCTU embedded thermocouples are tia levee Eee UM eL IP LM Peas et eee 27 Figure 4 5 SCTU mobile platform pointing to the sun see 28 Figure 4 6 Top view diagram of the mechanical layout of SCTU mobile plat Oma a A ANC D M ID A EE 33 Figure 4 7 Main components of MASS SCTU mounted in the field 33 vil Figure 4 8 Layout of components in the Primary and Secondary Electronics dedu ones Sd eut Ee 34 Figure 4 9 Flowchart of the general software 36 Figure 4 10 Block diagram of processes and main functions running by the MASS and SC TU in the main computer ere ee aa 40 Figure 5 1 I V curve for ATJ and silicon solar cells during the maximum irradiance episode of the t
13. transferring the data the computer is unable to determine in terms of its internal PC clock the exact time when the data was generated due to inexistent synchronization between clocks Exact synchronization between the PC and data logger is avoided due to its complex implementation specially for long periods of time As it is crucial that all data logged by the MASS SCTU systems is referred to a single clock the general purpose data logger is used additionally as a time server All logs are generated querying the data logger for the current time including logs related to the electrical data of the solar cell testing experiment The MASS software automatically transforms and logs the date format of the data logger in terms of standard Unix time elapsed number of seconds since 00 00 00 of January 1 1970 UTC time 85 APPENDIXF IMPLEMENTED PROTOCOL FOR PC MICROCONTROLLER COMMUNICATION The PC and the microcontroller communicate through a standard RS 232 serial line The PC works in a Connection Request Connected system having different options available according to its actual connection state The system will try to maintain a connected status during all the time possible The microcontroller does not specifically have a connected status but it defines its internal state according to the last command received from the PC and position of the relays opened closed Kinds of messages x represents a number between 0
14. 232 port Self calibration upon reset Power consumption can be controlled from host ASCII and binary command modes available DC input from unregulated source Constant current bipolar motor drives On the fly position and speed changes Pan 300 degrees of freedom Tilt 46 degrees of freedom bottom 31 degrees of freedom top Temperature logger ICP DAS Model CON I 7018 RS 485 interface Voltage current and thermocouple input Thermocouple Type J K T E R S B N C Channels 8 differential or 6 differential and 2 single ended by jumper select Accuracy 0 1 Sampling rate 10 Samples Second Power Consumption IW 67 General purpose data logger Pyranometer Campbell Scientific CR10X Kipp and Zonen CM3 Electrical Interfaces Analog Inputs 12 single ended or 6 differential individually configured Analog Outputs 3 switched active only during measurement 2 Pulse counters 3 Switched voltage excitations 8 control digital ports 1 Serial I O port 64Hz Scan rate 13 A D bits Stores 62000 data points non volatile 32 kilobytes available to run programs Electrical characteristics Input voltage 9 6 to 16V Current drain typical 1 3mA quiescent 13mA during processing and 46mA during analog measurement Thermopile pyranometer Measurement range 305 to 2800nm Maximum irradiance 2000W m Signal output 0 50mV Flat spec
15. AS VNNNS j AW AN AI SAS NN aA NNA INNI NK NSN NN NES SS SS USUS SS WN QQ KY KG KG NS NA NUN QNM MN NS SS NN SE SUS S VANAN VANA L SS SS SSS IN S Q SS SS NAN NA NSS SS eS eS D Panel 1 Temperature Measuring thermocouples As the SCTU is designed to characterize two different sets of solar cells Silicon Solar Cells Panel appropriate testing solar panel using a switching relay This relay is indirectly under equivalent electrical conditions the variable load is switched to connect to the controlled by a digital output of the MASS through a solid operation of the specific solar cells used including sufficient resolution points to generate complete I V curves open circuit to short circuit T3 Vb Va MASS A D inputs Relay bo gt gt PC controlled Control Signal from MASS Voltage Voltage dl 1 V V2 V3 Variable Load current sensor output to MASS Voltage Sensing Circuits From Si solar cells From ATJ solar cells Figure 4 3 Block diagram of the Central Experiment 26 b Current Measurement Current measurements of the solar cells are performed using a magneto resistive current sensor whose o
16. SCTU process generates several data files which are stored at the following location data weatherStation 2 n case of recompilation the pwrmngd file must be generated by a make install execution 8l Three subdirectories are available which store data on a daily basis dailyLogs stores tabulated weather text data files that can be directly imported to Matlab or Octave SolarPanels stores tabulated solar cell data from the SCTU which can be directly imported to Matlab or Octave Files are stored in the Automatic Data or in the Manual Data subdirectories depending if they were automatically generated or using the auxiliary process for manual control respectively All data captured on a single day is stored in a subdirectory containing the date in its name dailyPlots stores Octave executable scripts that automatically generate frequently required plots weather I V curves etc Plots are generated once all the weather data for a single day has been captured The data weatherStation directory additionally contains two files The usergnted m contains a filtered data set which was manually generated by the user after executing the appropriate option onh the user interface system The workLog dat file is a temporary file that stores weather data for the last ten days older data is automatically removed The workLog dat file is internally used by the system for automatically filtering data e g gener
17. Voltage monitoring signal black3 in solar panel White Analog Input 6 Voltage monitoring signal black5 in solar panel red Analog Input 7 Voltage monitoring signal in solar panel black Analog Ground Voltage monitoring ground in solar panel black1 1 Voltage monitoring ground in solar panel red 2 Voltage monitoring signal white black5 green black3 in solar panel Voltage monitoring signal in solar panel Voltage monitoring signal in solar panel 71 72 Shows the final internal wiring destination of the terminal block connection Connections such as A D and D A interface may be easily changed by modifying the programming code Values are shown as a reference and are current on the publication date Table C 6 Main connections in the main enclosure to install the MASS SCTU system in the field Terminal Connection 4 ATJ Power red V 5 ATJ Power white V 6 Silicon Power red V 7 Silicon Power white V 8 Signals red 4 coil 9 Signals brown coil 10 Signals blue variable load current signal 11 Signals white variable load control 12 Signals green current sensor signal 13 Signals yellow 12V 14 Signals orange 12V 15 Signals black logic ground 73 Table C 6 shows the cable connections needed in the secondary enclosure when installi
18. computer of SPICE is the standard for nearly all NASA planetary missions such as Galileo Clementine MGS Mars Odyssey Cassini NEAR DS 1 Stardust MER Deep Impact MRO and CONTOUR It will also be used on Mars Express in parallel with ESA standards and it could be used on ESA s Rosetta Japan s Nozomi or other foreign missions 30 the MASS as discussed in section 3 3 1 Dramatic power savings are introduced by the power manager when no experiments are performed e g after sunset Although the selected PTU requires initialization procedures to determine its absolute position each time it is powered it was empirically determined that better power efficiencies are obtained with numerous initializations on a day rather than continuous powering 4 2 3 Auxiliary Sensors The main objective of the auxiliary sensors is to capture data that characterizes the incident environment affecting the solar cell performance for the analysis of results All data is periodically captured and retransmitted for logging in the MASS Onboard measurements include solar spectrum irradiance total power per area environmental temperature relative humidity and wind speed The described system is implemented using a general purpose data logger which is operated through a RS 232 serial line from the MASS and a spectrophotometer operated through USB a General purpose data logger The general purpose data logger is a programmable device able to in
19. day This allows the batteries to be recharged avoiding endless cycles of powering up and down due to voltage variations caused by variations in the system load Figure 3 5 summarizes the implemented algorithm for the execution of shutdown procedures Configurable Thresholds All decision parameters such as limits of night day operations and voltage thresholds are configurable values which are stored in the microcontroller to be used by the core process in the computer This process polls for the stored values when needed according to the protocol detailed in Appendix F Therefore the user is able to dynamically update parameters using the user interface even when the computer has been powered down The implemented solution uses the advanced processing capacity of the computer to take all powering decisions but taking advantage of the features offered by the user interface as well Therefore the programming code must not be recompiled and there is no need to access files in the hard drive because all The scaled value is a reduced battery voltage that matches the ADC range of the microcontroller It is expressed in internal microcontroller counts which is proportional to the real voltage value 18 thresholds values are informed to the PC but not stored on it Therefore all the complexity of the power manager system relies on the PC and the PC only uses the microcontroller to perform simple user interface tasks Ev
20. external input Serial Board Connect Tech Inc Xtreme 104 Board provides 8 additional serial ports RS 232 and RS 422 or RS 485 interfaces are available jumper selectable 58 Power Board TRI M Model HE104 50W output 6V to 40V Input Range 5V 12V 12V regulated output Hard Drive Hitachi Travelstar 40GB Model IC25NO40ATCSO05 0 Solar Panels for 2 x Siemens SM55 solar Power modules 36 single crystalline Silicon solar cells per panel Weatherproof Maximum Power Rating 55W 5 1000W m 2 Short Circuit Current 3 45A Open circuit voltage 21 7V Bypass diodes for shading conditions Dimensions 1293 x 329 mm Solar Controller Morningstar Corporation Prostar 15 Charges batteries obtaining energy from solar panels Uses PWM techniques to operate solar panels in their maximum power point Supports different ranges of batteries and voltages 100 solid state Remote battery sense terminals Several electronic protections short circuit overload reverse current at night high voltage disconnect high temperature disconnect lighting and transient surge protection among others LCD display and LED to show status voltages and faults 59 60 A 5 Main Electronic components used in the Power Manager User interface Board Table A 2 Electronic components used in the Power Manager User interface board Block Device M
21. i 4L M A A d ED A L 1 1 1 0 5 10 15 20 0 5 10 15 20 Figure 5 5 Temperature amp Humidity weather plots Wind Speed for Oct 08 2004 Wind Speed m s 48 Polar plot of speed and direction of the wind Oct 18 2004 90 20 150 oe 30 S N pet 180 40 j N 210 J830 1 pa ue l z 240 300 270 Figure 5 6 Wind Speed amp Direction weather plots Insolation for Oct 08 2004 T 1000 800 600 Insolation W m 400 200 T T Figure 5 7 Solar Irradiance weather plot 49 6 CONCLUSIONS This document has proposed solutions to address the difficulties of performing experiments in isolation requiring external support The proposed system controls a solar cell testing unit that allows to characterize Advanced Triple Junction ATJ n p InGaP InGaAs Ge solar cells built for space applications on the earth in comparison to conventional silicon solar cell technologies The proposed solution allows to get a sets of data for solar cell characterization under a variety of external conditions including results that are relevant for both the electrical performance and mechanical weather requirements of the solar panels Two prototype versions of the system have been successfully tested during field operations of the Life in the Atacama project of Carnegie Mellon University
22. is arranged in three rows of five solar cells each Each row of solar cells provides a voltage output to monitor the voltage of each individual row The three voltage outputs are logged by the SCTU system through the analog to digital board of the main computer of the MASS Figure B 5 shows the connection scheme of the ATJ solar cell set The silicon solar cell set is built interconnecting in series three Siemens single crystal silicon solar cells Each individual solar cells provides an output to monitor the voltage of the individual cell The three voltage outputs are logged by 63 the SCTU system through the analog to digital board of the main computer of the MASS Figure B 6 shows the connection scheme of the silicon solar cell set QUAN ENS yo SSN BIN mE d ND Ea Essi Voltage Monitoring Signals Power Signal Figure B 5 Connection scheme of ATJ solar cell set used in the SCTU system a INIT Power Signal Voltage Monitoring Signals 7 g y Figure B 6 Connection scheme of silicon solar cell set used in the SCTU system B 4 Schematic of Signal Conditioner Board lt UIB TOP 1l oH Header 5 JPL Tile Sheet of TOROS Do Tue 5 ocumenis and Seting Buffer y filo de Dijo ie
23. is empirically determined for the specific set of solar cells that are being tested These parameters must be introduced in the programming code of the process As a consequence in the implemented SCTU silicon and ATJ solar cell sets have dedicated connectors that cannot be interchanged Furthermore the programming code will need modifications and recompilation if new solar cell sets with different electrical characteristics were incorporated to the system d Data processing The SCTU process incorporates data processing of the logged data ordering captured information Data is ordered on a daily basis generating separate files and directories for each day of experiments Weather data is logged in an independent text file each day incorporating data from all weather sensors in a single file Solar cell electrical data is logged in independent daily created directories storing in them all the multiple files generated during each experiment As the variable operates controlling current the short circuit condition is dependant on the characteristics of the solar cells used Each experiment of a particular set of solar cells pointing in a particular direction generates an independent text file log 38 execution All logs including weather data and solar cell data are tabulated text files that can be directly imported by Octave or Matlab software Furthermore the SCTU process automatically generates Octave plot scripts
24. on the overall solar cell performance SCTU Central Experiment Auxiliary Sensors Pointing System Spectrophotometer Variable Solar Test Cells Load Pyranometer Solar Cell Temperature Wind Sensors Ambient Humidity amp Temperature PTU Control Software Figure 4 1 General block diagram of the SCTU system 23 42 Implemented Solution Figure 4 1 shows a general block diagram of the SCTU The system is comprised of several units that perform specific independent tasks that aid the solar cell characterization The central experiment performs direct tests to the tested solar cells including an electrical characterization and solar cell temperature measurement the auxiliary sensors provide complementary environmental data that affect the performance of these devices the PTU pan tilt unit allows to change the incident position of the solar cells and the control software operates the complete system performing experiments capturing sensor data and orienting the solar cells appropriately The system is installed on the mounting system provided by the MASS not shown in Figure 4 1 which is analyzed in section 4 2 4 Electronic controlled Variable Load Voltage Level Conditioner Current Sensor Sensor Group of Testing Solar Cells RS 232 ports Thermo
25. primary options and several submenus grouping related functions Child specific functions may be added as new options in existing groups or create complete new submenus Navigation is achieved 7 The firmware is written in a high level programming language C 15 in an analogue way to cellular telephone systems with cyclic menus Basic options of the MASS included in the user interface are the following Main Menu It cyclically displays user relevant data on the alphanumeric display including status of the system online permanent off back in X minutes during sleeping time system loading system boot failure or lost connection battery voltage and relevant values of child experiments This is the default state of the system when the interface has not been used in a predefined time Power Manager Menu Includes several submenus related to powering up and down the system Basic submenus are the following Turn the system permanently On or Off Starts or stops regular operations When turned On the system starts to monitor battery voltage and day night operation times Forced On Turns the system On with no experiments overriding day and night limits and low voltage conditions This option allows the user to get data from the PC during night operations when experiments are not needed switching the computer momentarily On This state must be manually executed to resume normal operat
26. process RS 232 Microcontroller Communication via IPC messages User generated manual commands User updateable configuration SCTU Main Process RS 232 NASA Spice Solar Library Switching of solar cells connecting variable load Output RS 232 40 PTU power opto relay PTU controller Opto relay and solar cell Switching relay Variable load control General 2 purpose data logger _Temperature Logger Ordered daily log files amp Octave script generation Solar cell voltage and current Figure 4 10 Block diagram of processes and main functions running by the MASS and SCTU in the main computer 41 5 RESULTS In order to demonstrate the capabilities of the system and validate the quality of its data the results of several automatically executed experiments are presented This section is only a brief summary of results obtained during the solar cell analysis and should not be used by themselves as concluding evidence about the performance of the tested solar cells Section 5 1 shows solar cell characterization results This includes I V curves for the ATJ and silicon solar cell sets and I V curve variation for ATJ solar cells along a single day In addition results of spectral measurements are illustrated Finally section 5 2 shows examples of automatically generated weather plots created by the MASS with SCTU data 5 1 Solar Cell Characterization
27. sistema sea f cilmente ampliable para proveer servicios similares a nuevos dispositivos que se requiera incorporar en el futuro El trabajo presentado en este documento fue desarrollado para entregar informaci n cient fica a las operaciones de terreno del proyecto NASA Life in the Atacama ejecutado por la Universidad de Carnegie Mellon en el desierto de Atacama Chile durante los afios 2003 2004 y 2005 ABSTRACT This work describes the methods and techniques used for the development of a multipurpose station to perform experiments in isolated places Its application in a system to characterize solar cells is presented where capturing of electrical and environmental data is required Obtained results allow to compare the performance of new and conventional photovoltaic devices and also to characterize the surrounding environment The implemented system incorporates two different solar cell technologies They are installed on a mobile platform capable of orienting their position arbitrarily and perform continuous sun tracking Voltage current and solar cell temperature data is logged together with relevant environmental information such as the incident solar spectrum total irradiance and weather variables The proposed solution is based on two complementary systems that interact between them It incorporates a specific device for solar cell characterization which interacts with a generic system that provides it with energy pro
28. the same queue and retrieves the message Sending and receiving processes need no synchronization between them being able to read or write the queue at any given moment A message in the queue will never interrupt the receiving process and will only be received when the queue is checked As a consequence if the sending process needs to be certain that the message was received a two way communication system with acknowledge and timeout must be programmed Running independent processes for each child experiment takes advantage of the multitasking capabilities of the Linux operating system and makes it possible to incorporate with ease new child experiments Routines that were originally written independently from the MASS may be easily incorporated as a new process to the system and only minor modifications are needed only when inter process communication is required in order to implement IPC messaging Hardware conflicts caused by two processes accessing a single piece of hardware is also solved using IPC message requests Only a single process directly accesses the device receiving IPC message requests from other processes to execute actions on their behalf Therefore in case several independent processes need to Unix System V Release 4 was developed by AT amp T Bell Laboratories incorporating message queues for interprocess communication IPC among other functionalities such as shared memory and semaphores 5 This solution
29. use analog outputs to operate the variable load and analog inputs to read current and voltage levels It additionally communicates with the core process of the MASS to receive user generated orders calibration parameters and powering down 35 requests It generates ordered logs with captured data and generates formatted scripts to create plots that need to be generated on a regular basis All instruments of the SCTU are operated on a sequential basis to prevent sharing conflicts on the main computer of the MASS Therefore only one Interrupt Request IRQ line is used to operate all RS 232 serial devices data logger temperature transmitter and PTU minimizing hardware occupation a General Operation of the software The child process runs a loop which periodically executes a set of experiments logging current voltage and temperature data for the complete range of operation of each set of solar cells in every predefined position Predefined positions are flat panel sun pointing and any other desired fixed position defined by the user Therefore during each loop the software powers up the PTU points the mobile platform to the first predefined position and controls the variable load to operate the first set of solar cells from open circuit to short circuit Once it has finished it switches the load to the second set of solar cells and repeats the experiment The PTU is sequentially pointed to each of the following pred
30. who trusted in me giving me the honor to participate in the Life in the Atacama project of Carnegie Mellon University representing our university During these two years I have received his unconditional support encouraging me to continue participating in the project and finish this work Undoubtedly it is thanks to him that now I have the opportunity to join the Robotics Institute of Carnegie Mellon University to continue my postgraduate studies Last but not least I have to thank the Life in the Atacama team and the Robotics Institute of Carnegie Mellon University who trusted in me providing all the necessary equipment for the development of this project I have to specially thank David Wettergreen Michael Wagner and James Teza I received from them all the support and technical advice that I could ever need for the development of this work They are the original creators of the idea of this project and undoubtedly many of the results obtained in this work have been their original thoughts 11 CONTENTS Page ACKNOWLEDGEMENTS ote eS did 11 ro tias vi IST FIGURES o e iet vii RESUMEN cosilla tad X ABSERAC D ode vagantes p m A e t C Mut xi 1 Background of ges ROM E PE ORO rei 1 2 OVERVIEW UT Oy a La a UR AE qu 2 2l Bi DO 3 3 Multipurpose Autonomous Solar Station
31. 01 PT5100 Series Data Sheet Texas Instruments Inc Emco04 EMCORE 2004 Advanced Triple Junction ATJ High Efficiency Solar Cells for Space Applications Product Brief Emcore Photovoltaics Siem94 SIEMENS 1994 High Efficiency Solar Electric Cells Siemens Solar Industries Exec03 EXECUTIVE ENGINEERING 2003 EE30180A DC Electronic Load 300 Watt Product Data Sheet and Installation Information Executive Engineering Inc Direc00 DIRECTED PERCEPTION 2000 Computer Controlled Pan Tilt Unit Model PTU User s Manual Version 1 14 Directed Perception Inc Camp01 CAMPBELL SCIENTIFIC 2001 CR10X Measurement and Control Module Operator s Manual Campbell Scientific Inc Camp02 CAMPBELL SCIENTIFIC 2002 CM3 Pyranometer Instruction Manual Campbell Scientific Inc Camp04 CAMPBELL SCIENTIFIC 2004 CS500 Temperature and Relative Humidity Probe Instruction Manual Campbell Scientific Inc Camp05 CAMPBELL SCIENTIFIC 2005 Wind Speed and Direction Sensor 05103 Product Brochure Campbell Scientific Inc Cam004 CAMPBELL SCIENTIFIC 2004 05103 05106 and 05305 R M Young Wind Monitors Instruction Manual Campbell Scientific Inc 32 Teza03 TEZA J and WAGNER M 2003 Insolation of the Atacama Desert Life in the Atacama Project Workshop Presentations July 28 Carnegie Mellon University Pittsburgh United States of America Sypr03 SYPRIS TEST AND MEASUREMENT 2003 F W Bell NT Series Magneto Resist
32. 1 2 Input 3 of ATJ panels Analog Channel Yellow Cable from Signal Conditioner Card Voltage reading of Panel 1 of Input 4 panels Analog Channel Silicon Panel Signal Cable Green Black 3 Input 5 Analog Channel Silicon Panel Signal Cable Whites Black 5 Input 6 Analog Channel Silicon Panel Signal Cable Red Input 7 Analog Ground Silicon Panel Signal Cable Black 1 G 75 Note Details marked in BOLD are connections that have to be made recurrently each time the Solar Station is installed Details not in bold are permanently connected and should remain untouched unless the weather station is disassembled completely D 2 Connections in Solar Controller Table D 8 Cable connections in solar controller From To Load Terminal Block B or C Load Terminal Block A Solar Terminal Block 1 Solar Terminal Block 4 Battery Terminal Block 8 Battery Terminal Block 5 Sense Short Circuit to Battery Sense Short Circuit to Battery D 3 Connections in current measuring board secondary enclosure Table D 9 cable connection in current sensor board Pin Connection 1 I Sensor Iout I Sensor lin Output I sensor Ground 12V Alaj wl N 12V 77 D 4 Connections in Signal Conditioner Board Table D 10 Cable connections in signal conditioner board ATJ voltage Connects monitor
33. 9 1x Informative deal with connection status of the PC 104 2x Synchronous commands from the PC to the PIC 3x Asynchronous commands from the PC to the PIC 4x Synchronous commands from the PIC to the PC 5x Asynchronous commands from the PIC to the PC All messages being communicated will have the following structure xxmmmm is the starting character for a message xx is the kind of message mmmm is the body of the message additional information being sent with kind of message Different kinds of data will be separated by a semicolon Different lengths are accepted but should be shorter than 100 characters ending character for delimiting the end of a message All possible messages are described in Table F 12 86 Table F 12 All possible messages in computer microcontroller communication protocol Message Description Informative 10 Connection Request from PC PC is not connected Will be sent every 5 seconds in case an ACK is not received NOTE PIC GOES TO MAIN MENU AUTOMATICALLY ACKIO ACK to 10 11 From the PC Should I turn on all the experiments ACK11 0 Answer to 11 no don t turn on experiments ACK11 1 Answer to 11 yes turn on experiments 12 From the PC What is the battery voltage limit ACKI2 XX Answer to 12 voltage in volts 100 no decimals included 13 From the PC What is the length of the night ACK13 XX Answer to 13 night length in
34. DC5 4000V ms optical isolation SV logic 5 60V ac output Current rating at 45 C 3A Switching Relay Potter amp Brumfield KUP 14D15 12 Basic enclosed relay 3C 3PDT contact arrangement 12Vpc coil input 10 Amps max Operational 3x ST Microelectronics TL062N 2 JFET input operational Amplifiers amplifiers per unit Wide common mode and differential voltage ranges Output short circuit protection Slew Rate 3 5V us typ These operational amplifiers are used in the signal conditioner board implementing a voltage follower in series with an active low pass filter in each unit 70 APPENDIX C CONNECTIONS OF MASS SCTU FOR ASSEMBLY IN THE FIELD Table C 5 shows the cable connections needed in the main enclosure when installing the system in the field Several cables enter the primary enclosure which are connected in one of the three connection locations available in the enclosure Table C 5 Main connections in the main enclosure to install the MASS SCTU system in the field Cable 0 Power Solar Panel 1 cable Connection Location A Wire connects in Cable 1 Power Solar Panel 2 cable terminal block rack Cable 2 Battery Cable Connection Location B Wire connects in signal Cable 3 From secondary enclosure conditioner board Cable 4 From temperature logger Connection Location C Wire connects in Cable 5 From silicon solar panel voltage general purpose data logger m
35. DERS A SHAW F SMITH T TEZA J TOMPKINS P URMSON C VERMA V WAGONNER A and WAGNER M 2003 Life in the Atacama Field Season 2003 Experiment Plans and Technical Results Robotics Institute Carnegie Mellon University Technical Report CMU RI TR 03 50 October 2003 Mars99 MARSHALL A D 1999 IPC Message Queues sys msg h Retrieved from nttp www cs cf ac uk Dave C node25 htm1 on December 1 2004 Nasa04 NASA 2004 Overview of Spice Navigation and Ancillary Information Facility NASA Retrieved from ftp naif jpl nasa gov pub naif toolkit docs Tutorials pdf individual docs 05 overview pdf on March 1 2005 Hopk04 HOPKINS S 2004 Analog Input Interfacing Considerations Diamond Systems Corporation Retrieved from http www diamondsystems com files binaries Analog Interfacing Co nsiderations ppF on March 1 2005 Pana02 PANASONIC 2002 Valve Regulated Lead Acid Batteries Individual Data Sheet Panasonic Corporation Diam03 DIAMOND 2003 Diamond MM 32 AT User Manual v2 64 Diamond Systems Corporation Conn04 CONNECT TECH 2004 Xtreme 104 User s Manual revision 0 05 Connect Tech Inc Siem98 SIEMENS 1998 Solar Module SM55 Product data sheet Siemens Solar Industries Morn01 MORNINGSTAR 2001 Prostar Solar Controller s Operator s Manual Morningstar Corporation 51 Micr01 MICROCHIP 2001 PIC16F87X Data Sheet Microchip Technology Inc Texa01 TEXAS INSTRUMENTS 20
36. OHMOBy FARBEN y OTECSH 25539 E B o Qa UTSA 1 2 E e ga 21218181 ale pP da 3 E al a g B 3 E B AE i i 3 A 2 E soso EB EE RD ES 8 PICIGFS77A Backight ON OFF signal PT5102 2V Jes E our GND 220uF 42 tao IGND Pa Figure A 1 Schematic of Power Manager User interface Board 56 A 2 Connectors in Power Manager User interface Board Keypad connector 12V Output Battery input 24V RS 232 Interface to PC PC relay control LCD screen contrast adjust Voltage Reference adjust 11 1 Cielo Battery voltage divider adjust LCD screen backlight adjust x T LCD screen connector Figure A 2 Interface connectors in Power Manager User interface Board A 3 Microcontroller Battery Voltage Measuring System The Power Manager system uses the
37. PONTIFICIA UNIVERSIDAD CATOLICA DE CHILE 220 ESCUELA DE INGENIERIA DEVELOPMENT OF A SOLAR CELL AND ENVIRONMENTAL CHARACTERIZATION SYSTEM FOR ISOLATED LOCATIONS FRANCISCO JAVIER CALDER N PERALTA Memoria para optar al t tulo de Ingeniero Civil Electricista Profesor Supervisor ANDR S GUESALAGA MEISSNER Santiago de Chile 2005 PONTIFICIA UNIVERSIDAD CATOLICA DE CHILE ESCUELA DE INGENIERIA Departamento de Ingenier a El ctrica LAN ERS X A UN La 1N LATIFI T Y OF CHE DEVELOPMENT OF A SOLAR CELL AND ENVIRONMENTAL CHARACTERIZATION SYSTEM FOR ISOLATED LOCATIONS FRANCISCO JAVIER CALDERON PERALTA Memoria presentada a la Comisi n integrada por los profesores ANDR S GUESALAGA MEISSNER JUAN DIXON ROJAS LVARO SOTO ARRIAZA Para completar las exigencias del t tulo de Ingeniero Civil Electricista Santiago de Chile 2005 ACKNOWLEDGEMENTS I would like to express my gratitude to Allan L ders classmate and friend with whom we participated in the Life in the Atacama project representing Pontificia Universidad Cat lica de Chile This work is the result of many hours of discussions as part of our long run teamwork to complete our respective theses Both complementary works are the result of a common goal which was to accurately characterize new ATJ solar technologies This made us work together on both of our theses I have to specially thank my advisor Andr s Guesalaga
38. ach individual technology are mainly observed in the current values being the open circuit voltage almost stationary along the day Current Density mA cm2 ON Voltage V Figure 5 2 I V curves of ATJ and silicon solar cells in horizontal position during the testing day Maximum power points are marked with an asterisk 44 As stated above an important cause for curve changes during the day is the variation of the sun incident radiation angle which is explained by the cosine effect This effect states that for a surface located on a fixed position on earth the amount of incident sunrays will vary along the day due to variations of the exposed area to the solar rays The maximum amount of incident radiation on the fixed surface will occur when the incident sunrays strike perpendicular to the fixed surface This occurs because during these episodes the parallel incident sunrays see the largest surface Changes during the day are also caused by the atmosphere because the path length of the incident radiation varies with the position of the sun Normal incident sunrays to the surface of the earth cross a smaller section of the atmosphere resulting in less attenuation Conversely when the path of the sunrays is largest the attenuating effect of the atmosphere on the sunrays increases resulting in a lower irradiance These path length differences may also cause variations in the solar
39. ain Characteristics Microcontroller PIC16F877 High performance RISC CPU CMOS FLASH based 8 bit microcontroller 256 Bytes of EEPROM data memory 368 bytes of data memory RAM 8 channels of 10 bit Analog to Digital A D converter Interrupt capabilities Universal Synchronous Asynchronous Receiver Transmitter USART SCI with 9 bit address detection 2 additional timers User display DMC 16202NY LY AGE LCD Display 16x2 with Backlight User keypad Storm GS040203 4 key keypad Polymer casing keytops with configurable keytop graphics Voltage Texas Instruments PT5101 5V and 1 A Positive Step down Regulation PT5102 12V Integrated Switching Regulator 90 efficiency Laser trimmed output voltage Output current limiting Thermal shutdown protection Input voltage range 9 38V PT5101 16 38V PT5102 Output current 0 1 61 APPENDIXB ELECTRICAL DESIGN AND DETAIL OF DEVICES OF THE SCTU SYSTEM B 1 General Schematic of the Solar Cell Testing Unit SCTU 1 2 3 4 3 6 JP4 Input from A Variable Load D A bo id uU A 10 Load Control j v 1 ud 1 B4 A Pl E son Co n 2 4 A Es 2 JP2 Control Signal Ul DSS Input KI Current Sensor 4 lout Tin 1 ga 4s ess E 12V Current Output Silicon solar cells 3
40. analog to digital converter from the PIC microcontroller to read the battery voltage value as described in the main section of this document The PC shutdowns itself if the read voltage decreases below a threshold defined by the user The microcontroller reads a raw voltage value between 0 and 1024 value which is proportional to the input voltage The value in The analog to digital conversion is based on 10 bits Therefore 2 1024 discrete levels can be read by the microcontroller 57 volts can be determined knowing the exact voltage of the Zener reference adjustable using a potentiometer on the power manager board and the resistor values of the voltage divider used to match the battery voltage to the voltage operation levels of the microcontroller The core process of the MASS in the main computer reads the raw voltage value obtained by the microcontroller and converts it to volts The value in volts in retransmitted back to the microcontroller as text according to the protocol shown in Appendix F to be shown to the user on the LCD display Although this system reduces processing requirements to the microcontroller the user interface is not able to show a value in volts when the system loses the processing power of the main computer of the MASS night operations and low battery voltage operations As an alternative during these operation conditions the user interface shows the raw voltage value on the user screen in the fo
41. at is not expected in the actual state from the PC PC if unexpected command is received returns to not connected connection request status If 100 characters are received with no and ff data is assumed as erroneous and returns to the not connected state Each sent message has a timeout IM and repeats it every x seconds if no acknowledge is received 88 APPENDIX G IMPLEMENTED USER INTERFACE MENUS MAIN Shows current weather conditions amp battery voltage GENERATE PLOTS POWER CONFIGURE MANAGER Battery Voltage limits for turning system on off For Today Length of the night Minutes to turn PC back on Last 24 hours Start of the night time when to turn PC off PTU Orientation Last X hours X chosen by user PTU Slip Is Solar Experiment Connected Figure G 10 Implemented menus in user interface system Turn ON OFF 104 and all experiments Turn ON PC 104 with no experiments to download data at Shut Down PC now turn it back on tomorrow Point PTU to the sun
42. ation of usergnted m but may also be used by the user for simplifying manual multiple day data processing procedures E 3 Weather Data Weather log data is written on a single daily file with the following format 101 year day of year Unix time insol W m tot energy kJ 0 0 102 year day of year Unix time wind m s wind m s wind d1 wind d2 103 year day of year Unix time temp C humidity 0 0 E 4 Solar Cell Data Solar cell data files include relevant information in the filename for file ordering The file format is the following n type position time log 82 n increasing sequential number indicating the experiment of the day type defines the solar panel used for the experiment ATJ or Si position indicates the desired orientation of the solar cells in the format of a sequential position number defined in the programming code May be 10 11 in predefined positions or iSun sun oriented time time of the day in HH MM format Additionally relevant parameters related to the execution of the experiment are included as a header in the text file Captured data is preceded by a Jo sign ignored comments for Matlab Octave Parameters include the real orientation of the solar cells desired orientation in degrees and settle measuring time among other relevant factors Captured data is logged with the following format current A
43. atmosphere eventually filters relevant wavelengths to one of the junctions the performance of the whole solar cell may be degraded due to its serial configuration Therefore spectral differences in space and in the atmosphere may be used to analyze the obtained results The system developed for this work uses a spectrophotometer which is powered and operated through a USB interface It uses a closed proprietary communication protocol so its operation is restricted to the software provided by the manufacturer It has two independent channels master and slave which together cover a spectral range from 200 to 1100nm Although the spectrometer does not cover the complete spectral range used by ATJ solar cells 300 to 1900nm approximately it includes the part with the highest irradiances visible region 4 2 4 Physical Layout All devices related to the SCTU are installed using the mounting system module provided by the MASS Sensors and solar cells for testing are mounted on the PTU located on the top of the MASS tripod see Figure 4 6 Most of the electronics within the SCTU including the signal conditioner board PTU controller and general purpose data logger are mounted in the MASS electronics enclosure A SCTU specific secondary electronics enclosure was installed on top of the tripod in order to place the variable load as close as possible to the test solar cells This minimizes cable length requirements of the solar cell variable load cir
44. cation IPC messages used by the SCTU solarStation process readPanel h cc contains all constants and functions needed to capture the electrical data related with the solar cell testing experiment It controls the variable load captures current and voltage data and generates log files The writePanelData FILE logFile RADIANS ptuPan RADIANS ptuTilt must be modified in order to change the format of output weather logs The h file contains important definitions related to settle times voltage divider scaling factors calibration factors for current measurement and operation range of the variable load for each set of solar cells solarStation cc contains the main function of the SCTU solarStation and NASA SPICE related functions needed to track the sun solarStationPTU h cc defines SolarStationPTU class which encapsulates the functionality of the Directed Perception PTU 46 70 on which the testing solar cell sets and spectrophotometer are mounted weatherStationSerialPorts h defines serial ports used by MASS SCTU systems PIC src prococol h Cc contains functions related with the communication protocol between the MASS pwrmngd process and the PIC microcontroller It includes functions called on a recurrent basis including the connection procedure reading values stored in the EEPROM memory of the Code written by Michael Wagner Senior Research Program
45. ce of an uncertainty factor the MASS tries to reduce the power consumption of devices whenever possible in order to prevent potential power outages The MASS is designed to use its components in an energy efficient way in order to provide services to child experiments at any time of the day Its ability to The incorporation of higher capacity batteries or larger solar panels is discarded in order to keep a portable and reduced sized system 12 switch Off selected devices introduces important energy savings specially when high consuming devices with short duty cycles are switched Off e g the pan tilt unit in the SCTU Additionally it optionally incorporates the concept of night operations when no experiments and no user monitoring are required during predefined times of the day During these episodes it makes a controlled shutdown of the main computer of the MASS reducing power consumption to the minimum and only switching it back On during day operations when experiments are needed Furthermore the system incorporates continuous battery state monitoring capabilities performing a controlled shutdown of the computer when battery voltage levels drop below a user defined threshold All components from the MASS and child experiments are grouped either as devices that need permanent power or devices whose power supply can be interrupted Permanently powered components should be extremely low consumers with requirements
46. cessing power physical support and user interface in the field As a consequence of this generic approach the system can be easily expanded to provide analogue services to new devices that need to be incorporated in the future The described system was developed to provide relevant scientific data for field operations of the NASA funded Life in the Atacama project performed by Carnegie Mellon University in the Atacama desert Chile during years 2003 2004 and 2005 xi 1 BACKGROUND OF THE PROJECT This document is developed as part of the NASA funded Life in the Atacama project executed by Carnegie Mellon University with the collaboration of Pontificia Universidad Cat lica de Chile among other institutions The Life in the Atacama project seeks to develop technology in support of robotic astrobiology for NASA while conducting useful Earth science in the Atacama Desert of northern Chile Wett03 The final objective is to create technology relevant to the exploration of Mars in the form of an autonomous rover capable of traversing extremely long distances finding basic forms of life without direct human intervention This technical report covers all details related to the construction of a solar powered and autonomous station for testing which provides complementary engineering and scientific data for rover operations during field experiments The main objectives of the station are 1 to characterize the electrical performance o
47. couple Temperature Transmitter Variation of position Data Logger Spectrophotometer PTU Pyranometer Wind Sensor Temperature amp Humidity Sensor Control Signal Test Signal Mechanical Figure 4 2 Block diagram of the SCTU and interaction with the MASS 24 Figure 4 2 shows an electrical block diagram of the implemented SCTU interacting with the MASS does not include interface with power manager and user interface systems Current and voltage signals are logged in the MASS after they have been conditioned to match its electrical input specifications when needed The SCTU is controlled by a child experiment process running on the main computer of the MASS Auxiliary data is captured by a spectrophotometer and a general purpose data logger 4 2 1 Central Experiment As mentioned above the central experiment performs direct tests to the solar cells including an electrical characterization and measurement of the solar cell temperature The electrical characterization determines current voltage I V curves under variations of its load in incremental steps These curves are characteristic to the specific solar cell technology used The implemented system allows to test two independent sets of solar cells which are analyzed on a consecutive basis The same load and current voltage sensors are switched to the appropriate solar cell set when performing tests Therefore comparative results are obtained because both ex
48. cuit minimizing undesired inductive noise and resistive losses 33 Test Panel 1 Si Spectrophotometer Support Plate Mobile Platform Temperature Transmitter Test Panel 2 ATJ Advanced Triple Junction Solar Test Panel Emcore Thermocouples Figure 4 6 Top view diagram of the mechanical layout of SCTU mobile platform Wind Sensor Secondary Electronics Enclosure Primary Electronics Enclosure Figure 4 7 Main components of the MASS SCTU mounted in the field 34 Figure 4 7 shows the mounting scheme of the SCTU devices Figure 4 8 shows the layout of components of the SCTU in the primary and secondary electronics enclosure Primarv Electronics Enclosure Secondarv Electronics Enclosure PTU Controller MN _ Variable a ME Load Relay switches solar cell Sets Protectio n Fuses Generic Data Current Conditioner Sensor Figure 4 8 Layout of components in the Primary and Secondary Electronics Enclosure 4 2 5 Control Software The SCTU is operated by a single independent process running on the main computer of the MASS It operates the general purpose data logger temperature transmitter PTU controller and central experiment using the features of the MASS The process uses RS 232 serial interfaces for communications digital outputs to switch to the appropriate solar cell set and to power down the PTU when not in
49. daa seca tasto naan 60 Table B 3 Commercial hardware used in the SCTU 65 Table B 4 Main electronic components used in the SCTU system 69 Table C 5 Main connections in the main enclosure to install the MASS SETU system qm the field eel 70 Table C 6 Main connections in the main enclosure to install the MASS SCTU systenran the Held tops nda gelb ta ta does 72 Table D 7 Connected devices per terminal blocks in main enclosure 74 Table D 8 Cable connections in solar controller eene 76 Table D 9 cable connection in current sensor board see 76 Table D 10 Cable connections in signal conditioner board 77 Table D 11 Cable connections in terminal blocks of the secondary enclosure 77 Table F 12 All possible messages in computer microcontroller communication protocol 22 seen et epica tn sobran 86 vi LIST OF FIGURES Page Figure 2 1 Block diagram of the Mt 4 Figure 3 1 Internal structure of the MASS interacting with child EXPENSAS 5 Figure 3 2 MASS SCTU system installed in the field sess 8 Figure 3 3 Simplified power control diagram of devices whose power can bedterrupled secos i Er ooh aute ute tiq I 13 Figure 3 4
50. efined positions repeating equivalent experiments for each orientation for both solar cell sets A summary of this procedure is shown in Figure 4 9 Once finished the PTU is finally powered down until the next set of experiments is performed 19 Octave is a free software written under the terms of the GNU General Public License GPL by John W Eaton and others The software is a high level language primarily intended for numerical computations with capabilities similar to Mathworks Matlab 36 The photo Mobile platform is Both panels are tested spectra is pointed to a curves temperatures System Starts Je manually predefined position and insolation are i acquired using the PTU acquired and saved Are all the predefined positions reviewed Waits a predefined amount of time and restarts Figure 4 9 Flowchart of the general software operation Part of the power manager execution of the MASS is performed in the child experiment powering up and down the PTU This is done for simplicity purposes since the child process is the only program requiring to control the power of the PTU Alternatively control of power could have been integrated to the rest of the power manager being controlled by the core process and receiving powering requests from the child experiment through IPC messages This solution was avoided because it introduces additional complexity to the syst
51. electrical and environmental data The MASS is a solar powered and general purpose system designed to provide power processing capacity user interface and physical support to one or more child experiments for long periods of time in isolated places It offers hardware and software to control child experiments by capturing filtering and displaying obtained results Additionally it provides power to devices through a power manager system with energy saving capabilities The system is capable of switching Off selected components when they are not in use and also to monitor the available energy in the system batteries If there is no remaining energy in the system it performs a controlled emergency shutdown maintaining the computer Off until the system batteries have been recharged Furthermore the MASS includes an onboard user interface composed by an alphanumeric display and keypad to manually execute commands change crucial execution parameters and monitor measured variables without using external devices All MASS characteristics are discussed in Chapter 3 1 Child experiments are defined as electronic systems that need to be externally powered and controlled e g data logging systems A controlled shutdown takes into account the hardware and software context exiting software routines and even closing the complete operating system when necessary prior to hardware disconnection This is done to maintain the integrity of the
52. em without major benefits b Integration with the MASS The SCTU takes advantage of the features of the MASS designed for child experiments Relevant configuration parameters that are subject to frequent changes are stored in the EEPROM memory of the microcontroller including geographical location latitude and longitude and correction values for the PTU orientation Additionally the user can generate manual commands through the user interface including sun pointing at any moment and the suspension of the solar cell experiment therefore only logging weather data acting as a weather station The user can also read the latest weather data available on the user display according to the current data logged by the process of the SCTU All functionality offered by the 37 MASS is achieved by communicating with the core process of the MASS via IPC messages as described on earlier sections c Software of the electronically controlled load As discussed in section 4 2 1 in order to control the variable load a voltage control signal must be generated in incremental steps in order to vary the solar cell operation from open circuit to short circuit This is achieved by the SCTU using the D A converter of the MASS The process logs only data points that provide valuable information i e points which are obtained until the short circuit condition is reached The control range used for each set of solar cells from open circuit to short circuit
53. ent End of Day Event Battery Low during Operations or Battery Low night operations during day operations No action Actions no devices available to power 1 Core process detects event down 2 Core process calculates remaining time until the start of day operations and publishes it to the microcontroller Core process halts the computer Microcontroller disconnects the PC operations has elapsed Microcontroller turns the PC back on when time until start of day Figure 3 5 Summary of implemented algorithm to perform an automatic shutdown of the system iv Communication with the microcontroller The core process periodically communicates with the microcontroller using a custom protocol designed for the MASS The protocol is comprised of computer generated synchronous messages and microcontroller generated asynchronous messages Only synchronous messages are acknowledged where the microcontroller sends relevant parameters to the core process as an answer to the original message Details of the protocol are described in Appendix F A general description of the protocol is covered in section 3 3 4 subsection c 3 3 4 Microcontroller The microcontroller that manages the power manager and user interface systems is a low power device that operates continually having power requirements that are negligible compared to the total capacity of the batteries Due to its 19 extremely low power consumption it should opera
54. esting day atra aeos epe vex 42 Figure 5 2 I V curves of ATJ and silicon solar cells in horizontal position during the testing day Maximum power points are marked with an asterisk oo teftes tete P EE DU e TER Ae INE E re DO ve deeem iUe 43 Figure 5 3 I V curves for the solar cells pointing to the sun along the day Maximum power points are marked by an asterisk sess 45 Figure 5 4 Sunlight spectrum during different times of the day 46 Figure 5 5 Temperature amp Humidity weather plots eee 47 Figure 5 6 Wind Speed amp Direction weather plots esee 48 Figure 5 7 Solar Irradiance weather plot eee 48 Appendixes Figure A 1 Schematic of Power Manager User interface Board 55 Figure A 2 Interface connectors in Power Manager User interface Board 56 Figure B 3 Schematic of SCTU system eese 61 Figure B 4 Main connector in Signal Conditioner Board sss 62 viii Figure B 5 Connection scheme of ATJ solar cell set used in the SCTU O Figure B 6 Connection scheme of silicon solar cell set used in the SCTU SSA at Figure B 7 Schematic of Signal Conditioner Board ess Figure D 8 Cable connections of the three opto relays of the system mounted in a 4 channel I O
55. f Advanced Triple Junction ATJ n p InGaP InGaAs Ge solar cells built for space applications in relation to standard silicon solar cell technology 11 to provide tools for weather characterization during field operations providing relevant data for solar cell analysis rover operation and scientific investigation and iii to be easily upgradeable to add new experiments or additional weather sensors in the future The developed system was built and tested during field rover operations of years 2003 and 2004 in the Atacama desert near the cities of Iquique and Antofagasta Chile The final version of the autonomous station is completed to operate during the upcoming field season of 2005 The project was financed by the Robotics Institute of Carnegie Mellon University CMU being developed by students of the Electrical Engineering Department of Pontificia Universidad Cat lica de Chile PUC under supervision of professors of PUC and faculty of CMU 2 OVERVIEW OF SYSTEM System requirements detailed in Chapter 1 are accomplished by the development of two independent and interacting systems the Multipurpose Autonomous Solar Station MASS and the Solar Cell Testing Unit SCTU The MASS is designed as a general purpose device which provides basic services to child experiments needing to operate in stand alone mode It interacts with the SCTU which is a child experiment capable of characterizing multiple solar cell technologies by capturing
56. file system The SCTU is a group of several independent logging tools that provide complementary information to characterize solar cells Its objective is to analyze the performance of standard silicon solar cells compared to the newly commercially available Advanced Triple Junction ATJ n p InGaP InGaAs Ge solar cells under equivalent environmental conditions It continually logs current voltage data I V curves for the complete operation range and logs other possibly efficiency correlated values such as temperature of the solar panels irradiance solar spectrum and weather data All measurements are captured during different times of the day with the cells positioned to different orientations fixed positions and continuous sun tracking The results of the SCTU provide relevant electrical data to compare new and old solar cell technologies and data to quantify the benefits of a sun tracking mobile system Details of the SCTU including individual experiments and captured variables are discussed in Chapter 4 2 1 Block Diagram The MASS and SCTU systems contain several controllers instruments sensors and actuators which are integrated to accomplish all of its requirements Figure 2 1 shows the modules and interfaces that form the MASS and SCTU systems including the control interface and power lines of the most relevant power consuming devices A complete description of the elements shown will be covered in detail in this document Po
57. gging capacity input and output of analog and digital interfaces physical storage space and user interface Individual modules are composed by one or more hardware units and include a control software when applicable As this report mainly intends to document the most relevant concepts and techniques used in the implementation of a MASS system details of specific components used will be omitted in the main sections of this report only generic characteristics of the selected devices will be mentioned Details of specific brands and characteristics of used devices are included in Appendix A 3 1 1 Central Computer Module The central computer module is based on a high performance x86 CPU using the PC 104 form factor The PC 104 format was chosen due to its small sized and stackable architecture which allows to add new hardware boards in a space efficient way The computer uses a laptop type 3 5 hard drive and runs Redhat Linux operating system Linux was chosen given its proved stability solid networking capabilities and simple programming tools The system provides processing and storage capacity to child experiments as well as to the power manager user interface module Therefore the main computer module of the MASS can be used to control child experiments and also to log and process their captured data In order to achieve the generic and expandable objectives of the MASS the PC 104 standard stack was expanded with additional boa
58. h manages the user interface power manager module by handling user input and executing power schemes details of the core process are covered in section 3 3 3 This is a crucial software for the operation of the MASS and must run at all times while the computer is powered This process must be the only entity that directly communicates with the microcontroller In the case of child experiments in general terms the main computer must run at least n independent processes for n implemented experiments Frequently these processes need to communicate with other child processes to exchange relevant data e g configuration parameters or with the core process to execute MASS specific actions e g external user requests Methods such as the use of files or 3 A process is referred in this document as an entity capable of executing a given piece of code that has its own execution stack its own set of memory pages its own file descriptors table and a unique process ID 10 direct memory access to share information between processes are discarded because of speed limitations and sharing conflicts among other potential problems The software core states that inter process communication must be achieved using System V IPC messages Two or more processes can exchange information if they access a common system message queue The sending process places a message onto a queue through a message passing module Then the receiving process accesses
59. hours MW 3 5 FL M du J Master Channel W nm m2 hv a T 18 18 hours f s g 0 TM 0 5 0 Mg p 200 30 400 500 600 700 800 900 1000 Wavelength nm Figure 5 4 Sunlight spectrum during different times of the day 47 5 2 Weather Reports As earlier discussed the SCTU generates daily weather plots from sensors logging the environmental temperature humidity wind speed direction and total solar irradiance This section shows automatically generated plots with the system installed in Mina El Guanaco in the Atacama desert Chile on October 18 2004 Obtained values are shown in Figure 5 5 Figure 5 6 and Figure 5 7 They appear concordant to expected values contour and magnitude and lack of significant noise Therefore these values are suitable for solar cell and environmental characterization considering that the instruments have been calibrated by the manufacturer Temperature for Oct 08 2004 Relative Humidity for Oct 08 2004 1 1 dI 1 1 1 1 1 18 L LLEMND L Li 4 A ee 20 4 AMI 5 16 ee ERI Wo x owe 3 ANE NET 3 EL de ap 3 Qe s PEE EE gt a 1 1 1 d 5 15 c DNE Er E g 12 hal eed M MA 2 S D NN CREER F i i Ji g gt E mE NX P EL via E HN cR M DE C e Luc sessi Ae 1 1 1 L A
60. in the Atacama desert in Chile They have been operated for two independent one month periods with successful results The final version of the system has been tested in the area of Rancagua Chile capturing relevant data for an uninterrupted two month period The system has been completed to operate uninterruptedly during the three month long field operations of Life in the Atacama during year 2005 This document has intended to cover all technical details of the implemented solution serving the purpose of a technical manual but also has intended to propose generic solutions to common problems of devices needing to operate autonomously and unattended The development of a power manager system is proposed providing hardware and software tools to minimize the power consumption of experiments that are performed in isolation Additionally a generic and expandable user interface is proposed automating commonly user required tasks that allow to perform these actions without requiring additional hardware tools Future work in the system shown in this document is completely opened to serve multiple purposes from being just an autonomous weather station incorporating additional relevant sensors precipitation barometric pressure and leaf wetness among others to incorporating completely new child system using the MASS to receive complete support 50 REFERENCES Wett03 WETTERGREEN D CABROL N CALDER N F DEANS M JONAK D L
61. ing cable to black 1 1 red 2 white black 5 3 green black 3 4 D 5 Connections in terminal blocks rack in the secondary enclosure Table D 11 Cable connections in terminal blocks of the secondary enclosure Pin Connection 1 NC 2 NC INC 4 V ATJ Panels 5 Common V for ATJ amp Si Panels 6 V Si Panels 7 Common V for amp Si Panels 8 Relay Control V Coil Red 9 Relay Control V Coil Brown 10 Output from internal I sensor included in Variable Load Blue 11 Control Signal for Variable Load White 12 Output from external I sensor Green 13 12V Yellow 14 12V Orange 15 Logical Ground Black 78 D 6 Connection of opto relays in main enclosure The three opto relays located in the main enclosure PC power PTU power and solar panel control are installed in a 4 channel I O module rack Figure D 8 shows the connection scheme of interface with the rest of the system 24V PT from Solar 12V Charger from PC 104 24V PWR to PC 104 3 2 10A 24V PWR s to PTU 1A 12V PWR 7 8 9 to RELAY ypass switc Sl E ELD Solar Exp Ju 2 2 2 2 NIC 3 3 3 4 4 4 0 2 3 CONTROL 2 8 9 Control from D 5 V in Digital Channel A bit 0 from Powe Control from D Manager Digital Channel A bit 4 PC Control from PIC 5V from AD DA
62. interaction capabilities between the user and the MASS by including a small alphanumeric display and keypad onboard The user can execute actions on the MASS or can indirectly access any of the child experiments using IPC messages Figure 3 4 shows the user interface system keypad and user display implemented for this work The user interface is completely operated by the microcontroller and communicates with the core process of the MASS when needed The device displays relevant data on the user display receives user input from the keypad and stores relevant execution values in its internal EEPROM memory Additionally the microcontroller may be indirectly used by child experiments through the core 14 process to store internal values display local data on the user screen and for the user to perform manual requests e g data processing on the experiment Figure 3 4 Implemented user interface system Child specific values may be stored in the EEPROM of the microcontroller to avoid recompilations during routine changes or calibration These parameters can be modified using the user interface even when the main computer is powered down Therefore all values can be updated without requiring external hardware e g keyboard monitor external computer etc when operating in the field To implement all this child specific functionality in the microcontroller its firmware must be updated The interface system includes menus with
63. ions Turn the system Off for today This option turns the system immediately Off turning it back On tomorrow morning according to the predefined schedule This function is useful when experiments are not required for the current conditions e g bad weather or when irradiance conditions are poor for battery charge setting the system in a charging state to prevent emergency shutdowns in the future Additionally this option can be used to exit from the Forced On state engaging the scheduling system again Configure Menu Includes several submenus related to the storage of relevant parameters in the EEPROM memory of the microcontroller Basic stored parameters are low battery voltage threshold for turning the system Off time 16 of the day when night operations start and total length in minutes of night operations The specific implemented menu system used for the MASS SCTU in this work is exposed in Appendix G including specific options for the SCTU child experiment 3 3 3 User Interface amp Power Manager Software The Core Process The core process running on the PC is crucial for the operation of the power manager and user interface systems of the microcontroller The core process acts as the coordinating unit between the microcontroller and the rest of the system being the only process that directly communicates with it It generates scheduled or emergency shutdowns powers down devices that are n
64. is analogue to the system used by the core process where it is the only entity that directly communicates with the microcontroller 11 access a single piece of hardware a dedicated server process for the hardware is implemented Then this is the only process that directly communicates with the shared device providing services to other processes through IPC messages to control the hardware This implemented solution avoids the need of a synchronizing unit to handle hardware access The system developed in this work runs a single child process to handle the complete SCTU child experiment This process controls several external components such as data logging systems and testing units and also communicates with the core process to exchange data with the user interface system The SCTU process is analyzed in detail in chapter 4 3 3 Power Control and User Interface Systems Sections 3 3 1 and 3 3 2 presents specific characteristics of the power manager and user interface systems Finally sections 3 3 3 and 3 3 4 discusses all shared elements microcontroller and operating software of both systems 3 3 1 Power Manager System The MASS system is designed to operate continuously providing energy and services to child experiments at all times As a solar powered system the daily amount of energy available is variable and depends on the sun power available and also in the size and efficiency of the power solar panels Due to the existen
65. ive Current Sensors for Peak Currents up to 150A Sypris Test and Measurement Inc Opto204 OPTO 22 2004 G4 Digital DC Output Data Sheet Opto 22 Inc Gray05 GRAYHILL 2005 Grayhill Output Modules Product Brochure Grayhill Inc Icpd04 ICP DAS 2004 I 7017 I 7018 I 7019 M 7017 M 7018 and M 7019 Series User s Manual revision B1 3 ICP DAS Inc Tyco03 TYCO 2003 KU Series P amp B Catalog 1308242 Tyco Electronics Newm95 NEWMARCH J 1995 Inter Process Communication Unix API Retrieved from http pandonia canberra edu au OS 19_1 html December 1 2004 Cani02 CANISIUS COLLEGE 2002 Interprocess communication in UNIX Computer Science Department Canisius College Retrieved from http www cs canisius edu PL TUTORIALS C ADVANCED ipc on December 1 2004 Cani85 CANISIUS COLLEGE 1985 Concurrent Programming in C Under the UNIX Operating System Computer Science Department Canisius College Retrieved from http www cs canisius edu PL TUTORIALS C ADVANCED ipc on December 1 2004 Kort04 KORTESMAA T 2004 Multi Process Programming and Inter Process Communications IPC Retrieved from http users evitech fi tk rtp multi process html on December 1 2004 53 APPENDIXES 54 55 APPENDIX A ELECTRICAL DESIGN AND DETAIL OF DEVICES USED IN THE MASS A l Schematic of Power Manager User interface Board i E Sheet CiDocuments and Settings Power Managed S
66. mer from the Robotics Institute of Carnegie Mellon University member of the Life in the Atacama team P P P 84 microcontroller checking user generated commands checking battery voltage checking current time related to the power off schedule and performing shutdown procedures IC src pwrcomm h c contains all definitions and functions needed to achieve inter process communication IPC messages used by the MASS pwrmngd process IC src pwrmngd h c contains the main function of the MASS pwrmngd process It executes the SCTU solarStation process by fork procedures of Linux and implements the complete communication protocol with the PIC microcontroller IC src solarControl c contains all functions needed for the manual operation of the solar experiment Compilation generates an independent executable file in the PIC bin subdirectory which allows the user to orient the solar panels and perform the solar experiment through a prompt automatic execution is suspended The generated program does not access the hardware directly instead it generates IPC messages indirectly performing actions in the solarStation process E 6 About Log Files and Time Management The general purpose data logger permanently logs weather data in its internal memory adding a timestamp of its internal clock When the PC is online all information stored in the data logger is transferred to the computer When
67. minutes 14 From the PC At what time does the night start ACK14 HH MM Answer to 14 hours amp minutes 15 From the PC What is the PTU Orientation ACK15 XX Answer to 15 PTU Orientation in degrees 100 16 From the PC What is the PTU Slip ACK16 XX Answer to 16 PTU Orientation in degrees 100 17 From the PC What is the Latitude ACK17 XX Answer to 17 Latitude 100 18 From the PC What is the Longitude ACK18 XX Answer to 18 Longitude 100 19 From the PC PC was turned on normally ACK19 0 Answer to 19 No it was turned at night ACK19 1 Answer to 19 Yes From PC to 20x From the PC Temperature is being sent C 100 no decimals RANGE 99 99 PIC to 99 99 C 21x From the PC Relative Humidity is being sent 100 no decimals Limit 100 00 22x From the PC W m 2 is being sent 10 no decimals LIMIT 3276 7 W m 2 23 From PC Wind m s is being sent 100 no decimals Limit 327 67 m s 87 24 From the PC Leaf sensor measurement is being sent 10 no decimals LIMIT 100 0 25xit From the PC Informing battery level in Volts 100 this is the same measurement received from the PIC but transformed into Volts according to voltage divider and supply voltage LIMIT 99 99 V ACK2x V From the PIC Informing actual battery level This message will be sent as an answer to any 2x message V in ticks between 0 1024 30x Auto shutdown request
68. module rack eee Figure D 9 Cable color code of ATJ and silicon solar cell Figure G 10 Implemented menus in user interface system eee 1X RESUMEN Este documento describe el disefio y desarrollo de una estaci n multiprop sito para la realizaci n de experimentos en lugares aislados Se presenta su aplicaci n a un sistema para caracterizar celdas solares adonde se requiere capturar datos el ctricos y ambientales Esto permite evaluar el desempefio de nuevos dispositivos fotovoltaicos respecto a tecnolog as convencionales y a la vez hacer un an lisis ambiental del entorno El sistema implementado incluye dos tipos de celdas solares de prueba sobre un sistema m vil capaz de orientarlas a posiciones arbitrarias incluyendo la localizaci n continua del sol Se captura informaci n de sus caracter sticas de corriente voltaje y sus temperaturas a lo largo del d a adem s de informaci n ambiental incluyendo el espectro solar incidente la irradianza total y variables meteorol gicas La soluci n propuesta est basada en dos sistemas complementarios que interact an entre s Se incorpora un sistema espec fico para la caracterizaci n de celdas solares el cual interact a con un dispositivo gen rico que le provee de energ a capacidad de procesamiento soporte f sico e interfaz con el usuario en terreno Este disefio gen rico permite que el
69. ng the SCTU system in the field Three cables enter the secondary enclosure named as ATJ Power power signal from ATJ solar cell set Silicon Power power signal from silicon solar cell set and Signals signals and power for from the main enclosure 74 APPENDIXD DETAILED PIN OUT OF MASS SCTU SYSTEMS The following tables shows every connection between devices in the complete MASS SCTU system These tables are provided for reference purposes only and should not be changed for regular operations unless a severe electronic redesign is being made or for fault detection D 1 Terminal blocks rack in the main enclosure All cables connected to individual blocks are shown below Table D 7 Connected devices per terminal blocks in main enclosure Block Number Detail of Connected Devices 1 Solar Panel 1 Power Supply Solar Solar Charger 2 Solar Panel 1 Power Supply Terminal Block 3 3 Solar Panel 2 Power Supply Terminal Block 2 4 Solar Panel 2 Power Supply Solar Solar Charger 5 GND for Power Manager Card Battery Solar Charger Terminal Block 6 6 Battery Terminal Block 5 7 Battery Terminal Block 8 8 24V for Power Manager Card Battery Solar Charger Terminal Block 7 RELAY Solar Experiment connection of switching relay Solar Panel Chooser red SS Relay Rack Opto 22 Field Connection 7
70. ntroller in order to confirm that the system is operating normally Heartbeat messages must be received from the core process on a regular basis containing new or else redundant data if there is no new relevant information available Lack of regular communications causes the microcontroller to assume communication problems and display a lost connection message on the user screen All synchronous messages are answered with relevant data to the core process e g battery voltage answer to requests etc 21 In parallel the user interface can generate microcontroller transmitted asynchronous messages as a result of user requests These messages are transferred to the core process when needed and they are not acknowledged 4 SOLAR CELL TESTING UNIT SCTU 4 1 Objective 22 The objective of the Solar Cell Testing Unit SCTU is to accurately characterize solar cells when operating on the earth providing tools for a comparative analysis between new and conventional photovoltaic technologies The system makes an electrical characterization of the solar cells and provides data to determine other relevant parameters such as efficiency fill factor spectral response and temperature sensitivity among others Furthermore the system can vary the orientation of the solar cells fixed positions and sun orientation to quantify the benefits of a sun tracking system and to analyze the influence of the incident radiation angle
71. on is stronger Current Density mA cm2 Figure 5 3 I V curves for the solar cells pointing to the sun along the day Maximum power points are marked by an asterisk 5 1 4 Solar Spectrum Measurements The spectrum of the incident radiation is crucial for the analysis of solar cells Solar cell performance is dependant on the presence of specific bands of the spectrum so its values are an important performance variable to consider in the analysis 46 The spectrophotometer used by the SCTU generates a text file with the number of counts for each wavelength slot This data must be corrected and calibrated obtaining the power density versus wavelength and area The nm m device includes two channels the Master Channel covering the UV and visible ranges and the Slave channel covering the near infrared segment Several spectral measurements were performed during the testing day Figure 5 4 shows two solar spectra measurements corrected and calibrated at different times of the day in horizontal position The obtained curve is similar to theoretical expected values observing the maximum power per wavelengths near the maximum insolation episode No important local differences besides amplitude can be distinguished between measurements along the day Sun Light spectra at 13 51 PM vs 18 18 hours horizontal position 5 T T T T T T T Slave Channel 13 51
72. onitoring Cable 6 From ATJ solar panel voltage monitoring Cable 7 Cable from pyranometer Cable 8 Cable from anemometer Cable 9 Cable from temperature and humidity sensor Cable Wire in Connects to Connection Final electrical Cable location Connection in MASS or in primary SCTU hardware 0 1 2 3 4 516 7 8 9 enclosure A B C X 1 X Solar Controller X 2 X Power Solar Panel 2 series connection X 3 X Power Solar Panel 1 series connection X 4 X Solar Controller X 6 X Solar Controller Battery and power manager board X 7 X Solar Controller Batter 4 and power manager board X red Relay X Switching relay in SCTU coil Brown Relay Switching relay in SCTU coil white Analog Output Electronic controlled Vo0 variable load control signal green Analog Input 0 Current sensor output signal blue Analog Input 1 Electronic controlled variable load internal current sensor output not used Black G Ground for secondary enclosure yellow 12V 12V for secondary enclosure orange 12V 12V for secondary enclosure green ICP Logger Temperature transmitter green data yellow ICP Logger Temperature transmitter yellow data red ICP Logger red Temperature transmitter Vs black ICP Logger Temperature data black transmitter Gnd Green Analog Input 5
73. ot in use provides child experiments with execution parameters stored in the microcontroller publishes relevant user values on the onboard display and executes manual requests upon user request 1 Scheduled Shutdowns During scheduled shutdowns the core process generates an auto shutdown procedure in order to save energy These procedures are executed at predefined times of the day relying on the microcontroller to be powered back On The algorithm defines day and night operations which are arbitrary times of the day defined by the user During night operations no power controlled experiments are executed and no external information is displayed on the user screen because the computer is powered off The PC is automatically turned back on by the microcontroller at the beginning of day operations according to a configurable time determined by the core process before the computer was halted 17 ii Emergency Shutdowns Emergency shutdowns are also computer generated halt requests but they are a consequence of the detection of a potential power problem The core process periodically receives scaled battery voltage information from the microcontroller and generates an auto shutdown procedure if its levels decrease below a configurable threshold This mechanism prevents a deep discharge of the batteries and an abrupt drop of power When an emergency shutdown is generated all day operations are cancelled until the following
74. ower requirements of the experiments and devices used in this work two 1293 x 329mm commercial silicon solar panels were used together with two 12V lead acid batteries connected in series The selected solar controller includes the adequate pre programmed charging cycle for the batteries 3 1 3 Mounting System Module The system includes a weatherproof UV stabilized enclosure to mount electronic components It is installed on a tripod providing mechanical support to the complete system and physical storage space for MASS related and external components It offers connection with the exterior in order to interface with sensors and to receive solar power input A modified weather station enclosure was used in this work to benefit from its incorporated capacity to keep the components protected from sunlight dust and moist Built as a white fiberglass reinforced enclosure it is designed to reflect the solar radiation therefore maintaining a relatively moderate internal temperature when exposed to the sun Modifications include a hinge based second floor to provide additional space for electronic components and also weatherproof ducts to communicate with the exterior The enclosure was mounted on a standard three meter tall galvanized steel weather station tripod as shown in Figure 3 2 Child experiment sensors are intended to be mounted on the top of the tripod in order to minimize external effects caused by factors such as people and shadows
75. ows the main electrical characteristics of sensors used by the SCTU that are connected to the general purpose data logger Table 4 1 Main characteristics of the SCTU sensors connected to the general purpose data logger Sensor Main Characteristics Pyranometer Flat spectral response for the full solar spectrum Spectral Response Waveband 305 2800nm Maximum Irradiance 2000 W Operating Temperature 40 to 80 C Wind Monitor Measures wind speed amp direction Range of operation speed 0 60 m s Accuracy speed 0 3m s Range of operation direction 355 electrical Accuracy direction 3 Temperature amp Temperature Range 40 C to 60 C Relative Humidity Expected error lt 0 6 C for 0 35 C range Sensor Relative Humidity Range 0 to 100 Typical long term stability lt 1 RH per year 32 b Spectrophotometer The spectrophotometer allows to analyze the performance of the solar cell sets capturing the incident solar spectrum The device is mounted on the same mobile plate of the testing solar cells controlled by the PTU in order to capture the exact incident solar radiation of the panels The spectrophotometer was incorporated mainly to analyze the performance of ATJ solar cells when comparing results to existing studies in space ATJ solar cells are constructed including three junctions in series optimized to capture specific parts of the spectrum If the
76. peration is based on the anisotropic magneto resistive AMR effect The output of the sensor is a voltage proportional to the measured current The output voltage range meets the electrical standards of the analog input of the MASS so it can be directly connected to that system Electrically the current sensor is connected in series with the variable load see Figure 4 3 being switched by the same relay connecting both solar cell sets Therefore a single sensor for current measurement is used allowing to get comparable current measurements and thus avoiding potential differences between sensors c Voltage Measurement The voltage measurement electrical implementation is specific for the particular set of solar cells that are being tested which is dependant on the expected history maximum output voltage of the solar cells Sensed voltages should never exceed the electrical limits of the A D converter of the MASS Higher expected voltages occur during high irradiance episodes during open circuit conditions In the case of the silicon solar cell sets used the open circuit voltages will never exceed the maximum voltage accepted by the analog input of the MASS Due to its low impedance the voltage signal is directly connected to the analog input of the MASS Conversely ATJ solar cells are expected to operate at higher voltages and lower currents than silicon solar cells due to its construction characteristics Open circuit voltages reg
77. periments are performed under equivalent conditions The system developed in this work includes a set of silicon solar cells conventional technology and a set of the newly commercially available Advanced Triple Junction ATJ n p InGaP InGaAs Ge solar cells traditionally used on satellites A general implementation scheme of the system is shown in Figure 4 3 a Load control A single electronically controlled load is connected to the set of solar cells to be tested The device acts as a current regulator forcing the current to be proportional to a voltage signal controlled by the MASS If the solar panels cannot deliver the demanded current the load acts as a short circuit The control software must be appropriately designed so that the variable load covers the complete range of 25 V2 Panel 2 ATJ Solar Cells Panel state opto relay temperature transmitter to MASS SS X SS SSSS SSSS Us WN ASS SS SS A SJ VC SSS XA SJ SI se K amp S VI X SI SI ES BSS ESSE XX ASS ASS SOC SO Ys 24 MLE 777 7 ES MLE 73 yy Wh 7 yy A 7 ni Si E ees ST S SS SS N SSN SN NN NAN NENNEN NEN WENNEN SES ERES NES NES SN W A SS S S KS XA SIA amp SS C WSN GN SGV GSE GS CS SS S SS WS ASS ASS AS KG NNN NA
78. pointing system is to characterize testing solar cells under different external conditions The solar cells and complementary instruments are mounted on a pan tilt unit PTU that can vary its orientation from horizontal to sun pointing or any fixed orientation at any given moment a picture of the mobile platform is shown in Figure 4 5 This mechanism provides the tools to quantify the power benefits of implementing a sun tracking system for applications such as robots It may be additionally used to determine the influence of the incident sun angle over the efficiency of the solar cells due to reflections and varying path lengths on each semiconductor caused by changes in the angle of the incident light Figure 4 5 SCTU mobile platform pointing to the sun The main component of the solar tracking system is its operation software Sun position is analytically determined knowing the geographical location latitude and longitude and day and time of the year This has economic advantages over sun locating sensors but requires precision when installing the device in order to get proper orientation 20 Sun tracking software uses the SPICE library written by NASA SPICE system is used as the mechanism for capturing archiving and disseminating a variety of ancillary and engineering information needed by scientists involved in mission design observation planning science data analysis and visualization and correlation of data between mul
79. r point T Si maximum power point Current Density mA cm2 Voltage V Figure 5 1 I V curve for ATJ and silicon solar cells during the maximum irradiance episode of the testing day ATJ solar cells operate at a higher voltage and lower current levels than silicon solar cells ATJ technology demonstrates a noticeably higher conversion efficiency than silicon solar cells obtaining a 23 696 compared to the 10 696 of the silicon technology While the ATJ curve has a more squared shape sharp corner the silicon curve is rounder what is reflected on a higher fill factor FF of the ATJ technology 15 The conversion efficiency parameter indicates the percentage of incident solar power that the solar cell converts into electrical power 42 43 5 1 2 I V Curves during Different Times of the Day The I V curves presented in section 5 1 1 only reflect the performance of the solar cells during a particular instant of the day I V curves vary significantly during the day mainly because of variations in the sun radiation angle cosine effect influence of the atmosphere changes in the relative position of the earth respect to the sun and variations in solar cell temperature Varying curves during the testing day for the horizontal position are shown in Figure 5 2 ATJ and silicon technologies maintain significant differences in their electrical operating ranges Variations of I V curves along the day for e
80. rds to include various widely used analog and digital input output I O interfaces Basic PC 104 interfaces were extended with an analog digital A D input output board and with a multiserial RS232 RS422 485 communications board The specific characteristics of the selected boards are an A D interface with 32 analog inputs 4 analog outputs and 24 shared digital I O and a multiserial board providing 8 additional serial ports Considering the existence of a USB interface in the motherboard the system provides child systems with most of standard interfaces available 3 1 2 Power Supply System Module The MASS provides power to its internal components as well as to child experiments It offers several voltage outputs which may be uninterrupted for low consuming devices or relay controlled for devices with high power requirements or with short duty cycles The system obtains its power from a group of solar panels The excess energy charges a set of batteries which power the system when there is no enough solar energy available A solar controller is included which automatically manages the energy available giving an optimal charging cycle to the batteries and also maintaining the power solar panels working at their maximum efficiency point by using pulse width modulation switching techniques The solar charger additionally protects the batteries from deep discharge disconnecting them when a low voltage threshold is reached Given the p
81. rmat X 1024 where X is the raw voltage During night operations and low voltage battery conditions the system is assumed to be unmonitored and battery voltage should not be needed by the user on regular operations Anyway during these conditions the user can alternatively read the battery voltage from the included display of the solar controller 4 Commercial Hardware used in MASS System Table A 1 Commercial hardware used in the MASS Block Device Main Characteristics Batteries 2 x Panasonic valve regulated lead acid batteries Model LC X1220P Nominal voltage 12V each Nominal voltage 20Ah each Note both batteries are connected in series in the MASS PC 104 stack Main CPU Board Pentium III Processor Diamond Model MM 32 AT Kontron model MOPSIcd7 256Mb RAM 2 serial ports parallel port USB 10 100 Base TX Ethernet Onboard VGA interface Analog Digital Analog Inputs Digital Analog Board 32single ended 16 differential or 16SE 8DI o Current configuration 32 single ended inputs 16 bits A D resolution Bipolar or unipolar 10V maximum detectable input several input ranges Maximum recommended impedance to input 2000 Analog Outputs 4 channels 12 bit resolution several ranges available maximum output 10V Digital I O 24 programmable I O Other features 2x 32 bit down counter 1x 16 bit down counter Clock 10Mhz internal or
82. ssages executing actions upon request IPC messages used for communication between the main and auxiliary processes constitute an independent queue that has no relation with IPC communication between the core process of the MASS and the rest of the child processes In order to interrupt the execution of automatic solar cell experiments during manual operations the auxiliary process generates an IPC flag upon execution Once this flag is set the main SCTU process only operates under requests 39 from the auxiliary process until this flag is removed when the process is exited Therefore it is important to exit the auxiliary process properly by using the included interface in order to remove the execution flag and resume automatic operations f Implemented MASS SCTU processes Figure 4 10 shows a general block scheme describing the main tasks performed by the running process of the MASS and SCTU systems Inter process communication and hardware management of external devices are also included Blocks shown within individual processes only describe actions of the process and do not necessarily constitute the exact structure of the programming code Blocks within the same process may achieve intercommunication that is not shown in Figure 4 10 implementing them as individual or common programming functions of the process SCTU Auxiliary Process User Requests e Point toa predefined 7 position Make solar experiment Inter
83. te for weeks with the energy in the batteries even during low power episodes due to its capacity to disconnect high consuming devices before the battery voltage levels decrease to critical values For the power manager system the microcontroller acts as a passive unit most of the time acting only upon orders received from the core process of the computer In the case of the user interface the system is autonomously executed allowing the user to navigate through an ordered menu system and store relevant values without requiring additional processing capacity a Voltage Monitoring Voltage monitoring is executed by the microcontroller which constantly reads the battery voltage using its internal analog to digital converter ADC The captured voltage is a scaled value of the real battery voltage that matches the range of the ADC The scaled value is obtained from an adjustable high impedance voltage divider potentiometer The ADC uses an external voltage reference to perform the analog to digital conversion thus minimizing erroneous readings such as those generated by a fluctuating power supply The external reference is composed by a Zener diode and a potentiometer to adapt the breaking voltage of the diode b Time Monitoring The time monitoring system is used to measure time accurately while the main computer is down Time measurement is needed in order to systematically switch On and Off the main computer at predefined times of
84. terface with an enormous variety of sensors for different purposes Its interface offers analog inputs pulse counters switched voltage excitations and digital ports The system runs user programs built with a proprietary programming language being able to scan measurements at independent intervals and make more complex operations such as averaging of measurements and raw data conversion to units It offers data storage capabilities being capable of operating for long periods of time without communication with the MASS It logs the data from the pyranometer wind sensor and temperature relative humidity sensor periodically transferring data to the MASS during day operations New sensors may be easily incorporated by modifying its internal user program The general purpose data logger is an extremely low power consumer negligible compared to the total capacity of the batteries so the system is powered directly from the batteries of the MASS with no power control Therefore the system continually logs data from its sensors even during night operations This allows to 3l permanently log weather variables even when the MASS is powered down allowing to characterize the surrounding environment Deep discharge of the battery is unlikely to occur because according to electrical specifications they should provide the data logger with enough power for days even when the MASS was powered down due to low voltage conditions Table 4 1 sh
85. that are negligible compared to the total capacity of the batteries of the system Devices such as the microcontroller or weather loggers that need to capture data continually fall under this category All other components including most child experiments must be considered as devices whose power must be controlled Figure 3 3 shows a simplified power scheme of devices whose power can be interrupted As the experiments are assumed to be controlled by the main computer direct power control from the microcontroller over the experiments is not required since the PC is the core of their execution Therefore the microcontroller only controls the power state of the computer Devices that need permanent power are fed using switching power supplies directly connected to the batteries These regulators are characterized to be extremely efficient guaranteeing that only a reduced amount of power will be lost in dc to dc voltage conversions Devices whose power is controlled by the microcontroller or by the PC are managed by opto isolated solid state relays SSRs Therefore power control of high consuming components is achieved by generating standard TTL digital control signals 13 Battery Levels Voltage Reference Microcontroller always on Experiment 1 Experiment 2 Figure 3 3 Simplified power control diagram of devices whose power can be interrupted 3 3 2 User Interface System The user interface system provides direct
86. that generate commonly used graphs on a daily basis Generated plots include weather graphs the current voltage curve highlighting the maximum power point and any other custom relevant variable defined by the user Weather plots are generated with one day of delay generating scripts for the previous day when the SCTU process is ran for the first time on the day this is when the complete data for the previous day becomes available e Auxiliary process for manual operation The software of the SCTU includes an auxiliary and optional process independent from the main process of the SCTU previously described in order to manually operate the SCTU devices This auxiliary process must be manually executed by the user by logging into the main computer of the MASS directly or through network access Once the process is executed the user gains direct control over the SCTU being able to point the solar cells at arbitrary positions and to execute experiments at any given moment This manual execution is useful when the user wants to perform the experiments at precise intervals with particular external conditions and to take external manual measurements such as the spectrum for certain precise orientations In order to prevent sharing conflicts between the main SCTU and auxiliary processes only the primary process directly accesses the hardware of the SCTU The auxiliary process generates requests which are received by the main process using IPC me
87. the day To achieve this precision requirement an auxiliary low frequency crystal clock was enabled in the microcontroller in addition to the high frequency crystal used for the main clock The low frequency crystal overflows a counter in an exact number of seconds generating an interrupt where precise time operations may be performed 20 c Firmware of the Microcontroller The firmware of the microcontroller is one of the most relevant components of the MASS system being the nucleus of the user interface and power manager systems The microcontroller achieves these tasks running a single routine based on interruptions Communication with the central computer is achieved through a standard RS 232 serial port from the microcontroller using the custom built protocol described in Appendix F A general overview of the protocol in the context of the hardware is shown in Figure 3 6 Synchronous Messages 1 Heartbeat info PC Q Acknowledge info Microcontroller Asynchronous Messages User Requests User Interface Figure 3 6 Basic block diagram of the communication protocol between the computer and the microcontroller in the hardware context All synchronous messages are computer generated requests directed to the microcontroller to perform relevant tasks e g data to display on the user screen power down requests etc These messages also act as heartbeats or keep alive messages to the microco
88. tiple instruments SPICE ancillary data includes spacecraft trajectory target body ephemerides target size shape orientation spacecraft orientation instrument mounting and field of view geometry and commands and events associated with the conduct of a mission By providing SPICE with the current geographic location and current date and time the SCTU is able to get the position of the sun at any given moment The implemented system in this document uses a commercial PTU device based on a stepper motor The pan tilt unit includes a PTU controller which is operated using a standard RS 232 serial line of the MASS The PTU has a freedom of 300 pan 46 tilt bottom and 31 tilt top The pan range allows to track the sun during daylight but the tilt range may be a limiting factor on certain locations during specific times of the day The SCTU was built to operate in the latitudes ranging from the Atacama desert to Rancagua Chile where the sun is positioned in the range of the PTU during all the relevant high irradiance times of the day for the complete year The selected PTU is a big power consumer what is mainly caused by the controller servoing the PTU to maintain the desired position Therefore the PTU was integrated to the power manager system of the MASS only being powered during experiment execution when repositioning of the solar cells is required Powering of the device is achieved using an opto relay SSR controlled by the main
89. tral response of the full solar spectrum range Temperature and Relative Humidity Sensor Campbell Scientific CS500 L Contains a Platinum Resistance Temperature detector PRT and a Vaisala INTERCAP capacitive relative humidity sensor Temperature measurement range 40 to 60 C Temperature Output signal 0 to IV Relative Humidity measurement range 0 to100 68 Wind Monitor R M Young 05103 Measures wind speed and direction Wind speed range 0 60m s 0 3m s accuracy Wind speed range 0 360 mechanical 355 electrical 4 3 accuracy Power switched excitation provided by the data logger Spectrophotometer Ocean Optics SD2000 Two independent channels master and slave Spectral Range 200 to 850nm master channel 520 1100nm slave channel Cosine corrector disks both channels 69 Main Electronic Components used in the SCTU System Table B 4 Main electronic components used in the SCTU system Block Device Main Characteristics Current Sensor F W Bell NT 5 Primary nominal current lpn 5A Measurement Range 0 to 15A for 3 seconds Output voltage at I 4 2 5V Linearity 0 25 Opto relays for control of PC power and PTU power 2x Grayhill 70G ODC5 4000V ms optical isolation SV a logic 3 60V ac output Current rating at 45 C 3A PC controlled opto relay solar cells Opto 22 Model G40
90. turn back on tomorrow to be used when turning off at night in X minutes If x 1 do not turn on again Limit 999 minutes 31x Auto shutdown request PIC decides when to turn system on again low battery limit Message should include for how much more time it should monitor the batteries If that time occurs delay turning on for tomorrow NOT USED From PIC to SOx Shut down PC now X 1 to turn back on tomorrow X 0 turning off is forever PC 51 Command was removed NOT USED 52 Shut down solar experiment now for today 53 Point to the sun to manually take spectrophotometry 54xit Generate plots now for x hours If X 1 generate plots for today 55 User has updated configuration values stored in the so PC should ask for these values again F 1 Behavior with unknown messages and timeouts Microcontroller Only answers to known commands ignoring unknown messages If 100 continuous characters are received without and the received message is discarded and waits for a new message If no messages are received from the PC in 10 seconds assumes communication problems and displays an error on the LCD screen User generated messages asynchronous messages don t have a timeout nor expect an acknowledge The PIC does not know the connection state of the PC connected connection request and will always answer to ANY command received even if it is a command th
91. ularly exceed the maximum voltage limit allowed by the analog input of the MASS In order to decrease this input voltage a high impedance voltage divider is implemented obtaining a scaled value with negligible power losses This high impedance voltage divider exceeds the maximum input impedance recommended for the analog input of the MASS Therefore a voltage follower is also included in order to decrease the input impedance observed by the MASS 27 Additionally a low pass active filter was also incorporated to remove eventual electric noise in the signal Voltage divider low pass filter and voltage follower are grouped and built together in a signal conditioner board d Solar Cell Temperature Each set of solar cells includes two K type thermocouples located in two different locations of the solar panel as seen in Figure 4 4 for the ATJ solar panel location is analogous for the silicon solar panel To determine the temperature of the solar cell sets a temperature transmitter to interface with the thermocouples is used The transmitter is programmed to operate with the specific kind of thermocouple providing a calibrated output temperature upon request from the central computer of the MASS The device digitally transmits the temperature values from the four thermocouples Figure 4 4 solar cell set used in the SCTU embedded thermocouples are shown 28 4 2 2 Pointing System The objective of the
92. wer Solar Panels Hard Disk PC 104 Spectrophotometer DAC ADC DIO Board Central Computer Voltage Current Variable Solar Panels Signal gt Power Figure 2 1 Block diagram of the system 3 MULTIPURPOSE AUTONOMOUS SOLAR STATION MASS As discussed in Chapter 2 the MASS includes several hardware and software components that provide services to child experiments These components are grouped into modules or hardware software units which are available to child experiments as independent units to perform specific functions as shown in Figure 3 1 The MASS additionally defines a software core which delineates all the basic rules for the software running on the MASS All programs including internal module software and external child experiment software must follow these rules in order to avoid potential conflicts Software Core r Main Power Manager o Child Computer User Interface Experiments Modules 4 PC 104 Microcontroller Mounting Power Supply System System Figure 3 1 Internal structure of the MASS interacting with child experiments 3 1 MASS Modules As shown in Figure 3 1 the MASS includes a main computer module power manager user interface module mounting module and power supply system module They provide child experiments with controlled power when available advanced processing capacity lo

Development of a Solar Cell and Environmental Characterization

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