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~~ Lf-f'/r /x/ -."/)i. dvq- i *& ,'** 9 7y9B JPL Publication 87-23 DOEIJPL-1012-126 Distribution Category UC-63b Concentrator Hot-Spot Testing \ Phase I Final Report i I C .C. Gonzalez R.S. Sugimura May 15, 1987 Prepared for Sandia National Laboratories U.S. Department of Energy Through an Agreement with National Aeronautics and Space Administration by Jet Propulsion Laboratory California Institute of Technology Pasadena, California (NASA-CE- 181322) CCBCENTRAICG HCI-SPOT N87-24C28 IESTILG, EBASE 1 Eioal Bekort (Jet Excpalsicn LaL,) 28 F Avail: hlIS HC AC3/H€ AC1 CSCL 10B Unclas G3/44 0097498

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  • ~~

    Lf-f'/r / x / -."/)i. dvq- i *&

    , ' * * 9 7 y 9 B JPL Publication 87-23 DOEIJPL-1012-126

    Distribution Category UC-63b

    Concentrator Hot-Spot Testing \ Phase I Final Report

    i

    I

    C .C. Gonzalez R.S. Sugimura

    May 15, 1987

    Prepared for Sandia National Laboratories U.S. Department of Energy Through an Agreement with National Aeronautics and Space Administration

    by Jet Propulsion Laboratory California Institute of Technology Pasadena, California

    (NASA-CE- 181322) C C B C E N T R A I C G HCI-SPOT N87-24C28 I E S T I L G , E B A S E 1 E i o a l Bekort ( J e t E x c p a l s i c n LaL,) 28 F A v a i l : hlIS HC AC3/H A C 1 CSCL 10B Unclas

    G3/44 0097498

  • JPL Publication 87-23 DOEIJPL-1012-126 Distribution Category UC-63b

    Concentrator Hot-Spot Testing Phase I Final Report

    C . C . Gonzalez R.S. Sugimura

    May 15, 1987

    Prepared for Sandia National Laboratories U.S. Department of Energy Through an Agreement with National Aeronautics and Space Administration

    Jet Propulsion Laboratory California Institute of Technology Pasadena, California

    by

  • Prepared by the Jet Propulsion Laboratory, California Institute of Technology, for the U.S. Department of Energy through an agreement with the National Aeronautics and Space Administration.

    This work reported here was sponsored by Sandia National Laboratories of the U.S. Department of Energy and is part of the Photovoltaic Energy Systems Program.

    This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com- pleteness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

    Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

    This publication reports on work performed under NASA Task RE-152, Amend- ment 420, SNLA Nos. 04-4848 and 02-2047.

  • ABSTRACT

    Results of a study to determine the hot-spot susceptibility of concentrator cells, to provide a hot-spot qualification test for concentrator modules, and to provide guidelines for reducing hot-spot susceptibility are presented. voltaic module when the short-circuit current of a cell is lower than the string operating current forcing the cell into reverse bias with a concurrent power dissipation.

    Hot-spot heating occurs in a photo-

    Although the basis for the concentrator-module hot-spot qualification test is the test developed for flat-plate modules, issues, such as providing cell illumination, introduce additional complexities into the testing procedure.

    The same general guide1 ines apply for protecting concentrator modules from hot-spot stressing as apply to flat-plate modules. Therefere, recemmendatc!ns are made e!? the numtser e f h v n x r -J r --- dindes required per given number of series cells per module or source circuit. In addition, a new method for determining the cell temperature in the laboratory or in the field is discussed.

    i i i

  • ACKNOWLEDGMENT

    The authors thank Elizabeth Richards, Rob Barlow, Alex Maish, and Charles S t i l lwe l l of Sandia National Laboratories f o r providing infor - mation and module components used in the work reported herein, and f o r making valuable suggestions on the content of t h i s report . thank Ron Ross of the Je t Propulsion Laboratory (JPL) f o r many useful discussions and suggestions during the performance of the research reported upon, and f o r valuable suggestions on the content of t h i s report . Finally, we thank Elizabeth J e t t e r of JPL f o r s e t t i n g up equipment, and performing much of the t e s t i n g and data reduction, and Scot t Leland and Otto Whitte of JPL f o r ass i s tance in making and modi- fying tes t equipment and preparation of t e s t samples.

    We a l so

    iv

  • GLOSSARY

    Back-bias voltage Voltage applied across a ce l l in the negative direct ion.

    Bypass diode Diode t h a t i s connected in paral le l across a group of ser ies c e l l s (or paral le l groups o f ser ies c e l l s ) so t h a t i t conducts only when the voltage across the c e l l s i s in the reverse direct ion.

    Cel l /heat sink assembly

    Cell attached t o a heat sink (as in a module) removed from the module s t ruc ture and without concentrating opt ics .

    Cell junction Temperature of ce l l a t a par t icu lar temperature location in the junction.

    Dark (reverse voltage) The term "dark" re fers t o an I-V curve taken 1 - V curve in room-ambient l i gh t .

    IR camera Camera sensit ive t o infrared radation and producing electr ical signals t h a t can be converted t o a black-and white video image with a grey scale proportional t o the temperature of an emitting surface.

    NOCT Nominal operating cel l temperature.

    Reverse q u a d r a n t Refers t o t h e current-voltage charac te r i s t ics o f a solar cell when i t i s operating with current in the posi t ive direct ion and with negative voltage across the c e l l .

    Reverse-breakdown Reverse voltage where ce l l passes an unlimited voltage amount o f current.

    Reverse voltage Cell voltage i n the negative direct ion.

    Type A ce l l

    Type B ce l l

    Cell whose reverse voltage i s limited by the number of ce l l s in se r ies with the c e l l .

    Cell whose reverse voltage i s limited by the breakdown voltage of the c e l l .

    V

  • CONTENTS

    I . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 1 A . OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . 1 B . HOT-SPOT HEATING FUNDAMENTALS . . . . . . . . . . . . . . 1

    I1 . TEST IMPLEMENTATION AND RESULTS . . . . . . . . . . . . . . . 5 A . CHARACTERIZATION OF INTERSOL CELLS . . . . . . . . . . . 5 B . HOT-SPOT TESTING . . . . . . . . . . . . . . . . . . . . 6

    I11 . HOT-SPOT QUALIFICATION TEST DEVELOPMENT . . . . . . . . . . . 15 IV . CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . . . . . . . . 17 II n r r r n rwr rr V . nLr LnLiiLLa . . . . . . . . . . . . . . . . . . . . . . . . . 13 APPENDIX: TEST PROCEDURE FOR CONCENTRATOR-MODULE HOT-SPOT TEST . A-1 F i q I! r e E

    1 . Visualization of Hot-Spot Cell Heating for High-Shunt- Resistance Cell . . . . . . . . . . . . . . . . . . . . . . . 3

    2 . Visualization of Hot-Spot Cell Heating for Low-Shunt- Resistance Cell . . . . . . . . . . . . . . . . . . . . . . . 3

    3 . Intersol Module Receiver Assembly . . . . . . . . . . . . . . 5 4 . Typical Concentrator Cell Reverse-Quadrant I-V Curves for

    Various Illumination Levels . . . . . . . . . . . . . . . . . 6 5 . Modified Spectrolab XT-10 Steady-State Solar Simulator . . . 7 6 . Fresnel Lens and Receiver Assembly . . . . . . . . . . . . . 8 7 . Cell Temperature Versus Junction Voltage and Current . . . . 9 8 . Test Setup for Hot-Spot Testing of Receiver Assembly . . . . 11 9 . Test Setup for Hot-Spot Testing of Concentrator Modules . . . 12 10 . IR Camera Video Image o f Cell Hot Spot . . . . . . . . . . . 13 11 . Cell Temperature Versus Power Dissipated for Various Test

    Configurations . . . . . . . . . . . . . . . . . . . . . . . 14 12 . Cell Hot-Spot Temperature Increase Above Operating

    Temperature Versus Number o f Cells per Bypass Diode . . . . . 14 vi i

  • SECTION I

    INTRODUCTION

    A. OBJECTIVES

    The objective of this study was t o develop an understanding of the hot-spot susceptibility levels of concentrator modules, to define a qualification test for quantifying the hot-spot endurance of concentra- tor modules, and to provide guidelines for improving their endurance.

    The study centered on the exploratory testing o f an Intersol second-generation, point-focus module (Serial Number 1069). This module has 14 cells (0.89-inch-square) in series, each attached to an aluminum heat sink, and has a geometric concentration of 84, achieved with planar Fresnel lenses. A single bypass diode is externally mounted across the modules terminals.

    Meeting the above objectives involved conducting a variety o f research activities as described in this report. These included:

    (1) Characterizing the reverse-quadrant I-V curves of the Intersol cell s .

    (2) Quantifying the hot-spot heating characteristics of the Intersol cells and module.

    (3 ) Generating a draft hot-spot test procedure for concentrator modules.

    (4) Developing illumination sources to allow operating the modules in the laboratory environment under simulated steady- state field conditions.

    (5) Developing techniques for accurately measuring cell temper- atures including localized hot spots.

    B. HOT-SPOT HEATING FUNDAMENTALS

    Hot-spot heating is caused when the short-circuit current level o f an individual cell or group of cells in an array circuit is reduced below the module operating current level. The reduced short-circuit current fault condition can be the result of a variety of causes in- cluding nonuniform illumination (local shadowing or rnistracking), or individual cell degradation d