The Advanced Photovoltaic Experiment was designed to generate laboratory reference standards as well as to explore the durability of a wide variety of space solar cells. In addition to the cells, it was equipped with an absolute cavity radiometer to measure solar intensity, a spectroradiometer to measure the spectral content of this radiation and a sun angle sensor. Data from the solar cells and various sensors was obtained on a daily basis during the first eleven months of the 69 month flight. In this paper pre-flight and post-flight laboratory measurements are compared with on-orbit calibration data. Pre-flight and post-flight calibration data of the cavity radiometer as well as on-orbit data demonstrated the accuracy and durability of the Eppley instrument flown on APEX

Brinker, David J.

Hickey, John R.

English

NASA Technical Reports Server

NASA Technical Memorandum 106828
/;4/" ,..;iC>
Final Results of the Advanced Photovoltaic
Experiment Flight Test
David J. Brinker
Lewis Research Center
Cleveland, Ohio
and
r
John R. Hickey
The Eppley Laboratory, Inc.
Newport, Rhode Island
Prepared for the
First World Conference on Photovoltaic Energy Conversion
cosponsored by IEEE, PVSEC-Japan, and PVSEC-Europe
Waikoloa, Hawaii, December 5-9, 1994
National Aeronautics and
Space Administration
(NASA-TM-lO_828) FINAL RESULTS
THE ADVANCED PHOTOVOLTAIC
EXPERIMENT FLIGHT TEST (NASA.
Lewis Research Center) 6 p
OF N95-18571
Unclas
G3/20 0035853
https://ntrs.nasa.gov/search.jsp?R=19950012156 2020-06-16T09:18:53+00:00Z
FINAL RESULTS OF THE ADVANCED PHOTOVOLTAIC
EXPERIMENT FLIGHT TEST
David J. Brinker and John R. Hickey*
NASA Lewis Research Center, Cleveland, Ohio 44135, USA
*The Eppley Laboratory, Inc., Newport, Rhode Island 02840, USA
ABSTRACT
The Advanced Photovoltaic Experiment was designed
to generate laboratory reference standards as well as to
explore the durability of a wide variety of space solar cells.
In addition to the cells, it was equipped with an absolute
cavity radiometer to measure solar intensity, a
spectroradiometer to measure the spectral content of this
radiation and a sun angle sensor. Data from the solar cells
and various sensors was obtained on a daily basis during
the first eleven months of the 69 month flight. In this
paper we compare pre-flight and post-flight laboratory
measurements with on-orbit calibration data. Pre-flight
and post-flight calibration data of the cavity radiometer as
well as on-orbit data demonstrated the accuracy and
durability of the Eppley instrument flown on APEX.
INTRODUCTION AND
EXPERIMENT DESCRIPTION
The Advanced Photovoltaic Experiment (APEX) is a
space flight test designed to provide reference cell
standards for laboratory photovoltaic performance
measurements as well as to investigate the solar
spectrum and the effect of long term exposure of solar
cells to the space environment. Toward this end, 155 solar
cells of the widest available variety of designs and
materials were incorporated into the experiment along with
sensors to measure total solar irradiance and sun angle.
Experimental measurements were made on a daily basis,
dependent upon the achievement of proper sun angles,
and recorded on an on-board magnetic tape recorder. The
experiment was designed around the original flight time of
one year, with battery capacity the principal lifetime
limiting factor. Useful data was, in fact, obtained for 325
days, at which time the voltage of the batteries supplying
the data acquisition system fell below the threshold
necessary for calibrated operation. Details of the design
and operation of APEX have been previously published
[1,2].
When the announcement of opportunity for LDEF
experiments was released in 1976, a launch in 1980 was
envisioned. As a result, the solar cell samples prepared
for APEX represented the state-of-the-art in space cell
technology as of 1979, as well as samples of cells in use
on a variety of satellites. A Shuttle-caused delay in the
launch of LDEF by several years provided both the
opportunity and necessity for updating the sample set, to
one including the most recent advances in technology.
The cell investigators were invited in mid-1982 to submit
new cells. Of the 136 calibration cells (120 Isc and 16 IV
cells), 69 were replaced. Many of those which were not
replaced were either standards previously calibrated by
other techniques or representative of cells in use on a
variety of satellites. These APEX solar cell investigators
and the number of cells each supplied are:
A.F. Wright Aeronautical Laboratory 8
Applied Solar Energy Corporation 14
COMSAT Laboratories 7
European Space Agency 9
Jet Propulsion Laboratory 34
NASA Lewis Research Center 56
NASA Marshall Space Flight Center 11
So!arex Corporation 7
Spectrolab, Inc. 9
Each group provided cells representative of
technologies which were either in development or
production. The experiment was designed to
accommodate a total of 155 such cells, including the
silicon cells which were employed as sensors for the
spectral radiometer portion of the experiment. All cells
were permanently mounted on aluminum plates with a
thermistor in contact with the rear of the cell. 139 cells
were designated as Isc cells, 120 to be calibrated as
reference standards and returned to the investigators,
eighteen for use as spectral radiometer sensors and one
as a night sensor to signal the data acquisition system
that conditions were correct for the requisite periodic
calibration of the cavity radiometer. For these cells, the
short-circuit current was converted to a voltage through
the use of a precision load resistor. In most cases a 0.1 _Q
value was used. The remaining sixteen cells were
designated IV cells, that is the entire current - voltage
characteristic was measured through the loading of the
cell by a series of five appropriately sized resistors.
At that time, only silicon cells were in production, with
the development of gallium arsenide in its early stages.
Thisis reflected in the distribution of these semiconductor
types in the APEX complement, which is summarized by
cell type and size below:
Si: 105 2x2cm GaAs: 10
21 2x4cm ..1.
2 5x5cm 11
15 5.9 x 5.9 cm
_...1. 6 x 6 cm (module)
144
2x2cm
1.3 x 1.6 cm
The cells were mounted on 127 aluminum plates of
twelve different sizes and configurations. 28 of the
mounts each held two 2 x 2 cm cells. Each mount was
equipped with a Yellow Springs Instruments Type 16429
thermistor (10,000 Q @ 25 °C). An additional thermistor
monitored the Eppley absolute cavity radiometer.
SENSOR RESU_S
A detailed examination and recalibration of the
various sensors and instruments on APEX was performed.
The Eppley Type HF absolute cavity radiometer was of
particular interest in that it is the only radiometer ever
retumed from an extended stay in space, it is identical to
an instrument that has provided over 12 years of data as
part of the Earth Radiation Budget experiment on Nimbus
7. After detailed examination at the Eppley Laboratories,
it was compared with standards at the World Radiation
Center in Davos, Switzerland [3]. As seen in Table I, the
69 months in-orbit had little effect on the radiometer. Its
sensitivity was essentially unchanged, as was the its
reflectance, in agreement with the results of visual
inspections.
A spectroradiometer was included in APEX to
measure the spectral content of the extraterrestrial
sunlight. After return, it was intended that the instrument
be used for calibration of laboratory solar simulators. The
spectroradiometer consisted of sixteen identical silicon
cells with narrow bandpass optical filters. The wavelength
Table I Cavity Radiometer Tests
-_ Post-Fliaht 6.%
Heater Resist.(Q) 152.2 152.2 0.00
Thermopile Res. (Q) 354.4 354.7 0.08
Power Sensitivity (V/W)
Atmosphere 0.02134 0.02084 -2.34
Vacuum 0.02592 0.02527 -2.51
Ratio, Vac/Atm 1.2146 1.2126 -0.16
Intercomparison with Wodd Radiation Reference
APEX Instrument 1.00069
Eppley Reference Instrument 1.00002
Reflectance Measurement
APEX Instrument 250-J:80ppm
New Eppley Cavity 270-J:80ppm
center of the filters ranged from 325 to 1100 nm, with the
last filter covering the infrared out to 2000 nm. Figure 1
compares values of solar irradiance from the APEX flight
data with the World Meteorological Organization (WMO)
25O0
2O0O
1500
o=
:: 1000
5O0
0
0 500 1000
Wavelength (nrn)
Fig. 1. APEX Spectroradiometer data compared with
WMO spectrum.
II
• _ _-- APEX F'cte_
I
1500
standard. A comparison of pre-flight and post-flight
transmittance of the first thirteen filters is seen in Figure 2.
The drastic change in transmittance in many filters is
clearly seen, although there was no major shift in
wavelength band. This degradation was, of course,
unexpected and has made the instrument unsuitable for
further use in the laboratory. An explanation of the effect
or its probable cause has not been forthcoming from the
filter manufacturer [4].
i i/  iliii j i
o
275 325 375 425 475 525 575 625 675 725 73'5 825 875 925 975
WA_'_ (rrnl
Fig. 2. Pre- and post-flight transmittance of UV-Visible
filters.
SOLARCELLRESULTS
Theoverallconditionof the cellsamplesetwas
excellent.AcontaminatingfilmseenovermuchofLDEF
waspresenttoa varyingdegreeonAPEX,thethickness
of the layerdependentuponlocation.No lossof cell
coverglass nor significant changes in color or appearance
was observed. Several of the cells were cratered from
microometeoroid and/or debris impacts, with the range of
damage spanning from microscopic craters in the
coverglass surface to penetration of the coverglass and
cell and cratering of the underlying aluminum mounting
plate. However, even the few cells in which the cratering
extended into the solar cell itself, or caused a crack in the
coverglass and cell, electrical continuity was maintained.
Loss in current proportional to the damage area and
decrease in fill factor due to cell cracking was observed.
The electrical leads from the mounting plate feedthrough
to the cell front and rear contacts were found to open in six
cells. A silver ribbon of about 3 mil thickness was used for
these cells. Where the flat portion of the ribbon faced the
ram direction, the ribbon was severely eroded, creating an
open circuit. In most cases the ribbon twisted through 90 °
at the feedthrough so that the narrow (3 mil) edge faced
the ram direction; here the silver ribbon remained intact.
Examination of the flight data indicates that the erosion
did not occur to any extent that would affect cell
performance during the data recording portion of the flight,
the first eleven months. Post-flight performance testing of
these cells was accomplished by direct probing of the cell
contacts, no significant change from pre-flight
performance was seen.
The first post-flight electrical test performed was
measurement of the short-circuit current utilizing the
precision load resistor mounted on each cell for the flight.
The resistors were soldered to the cell mounting plate
electrical feedthroughs on the underside of the cell
mounting plates. These measurements, as well as
subsequent current-voltage (I-V) tests, were carried out in
the Solar Cell Evaluation Laboratory at Lewis Research
Center using a Spectrolab X-25L solar simulator. This
simulator employs a short-arc xenon lamp as the light
source and provides uniform, collimated illumination. The
intensity of the simulator was set using an aircraft
calibrated silicon standard which is identical to the
standard used at Eppley Laboratory for pre-flight testing,
where a xenon arc lamp simulator was also utilized. Cell
temperature was monitored using the flight thermistors.
One thermistor was found to be open. An examination of
the flight data showed abnormal readings from it,
indicating that the failure occurred before launch. With
this sole exception, all of the thermistors functioned
properly, providing values in close agreement with a
temperature sensor used in controlling the laboratory test
fixture. The short-circuit current values obtained in these
test are useful in comparison with both pre-flight
performance and flight data. The values obtained were in
most cases in good agreement with pre-flight values, with
the exception of those cells without a coverglass.
Upon completion of the measurement of short-circuit
current, the load resistor was removed from the circuit by
cutting one of its two leads. If LDEF had been retrieved on
schedule and the value of the cells as calibration
standards was retained, the load resistors could not have
been removed. However, the absence of data from the
last five years on-orbit negates their usefulness as
standards. The complete I-V characteristic of all cells
were then measured at 25 °C and recorded. Table II
compares flight data with pre- and post-flight simulator
data for a small representative sampling of the silicon
cells. All data presented here is corrected to 25 °C and
one AM0 sun (136.7 mW/cm2). All of these cells are n-p
type, as were most of the silicon cells flown. Also included
is the value of short-circuit current as measured on-orbit.
The loss in voltage and current in the unglassed cells
(cells ISC 63 and ISC 83) was consistent with the proton
radiation flux of the 250 nm, 28° inclination orbit. The
variation in pre-flight to post-flight Isc for the last four cells
of Table II is typical of the entire cells set; the variation
Cell Numl_r Descri0tion
ISC 63 NA-10 Solarex, BSR/BSF
ISC 83 B-21R LeRC Aircraft Standard
ISC 86 B2SOF COMSAT, Intelsat 5
ISC 95 M-5 ASEC, Large Area W//A
ISC 112 B-2R COMSAT Blue Response
ISC 114 B-4R COMSAT Non-Reflecting
Table II Silicon Cell Results
Coverolass
No Cover
No Cover
6 rail Fused Silica
6 railFused Silica
30 mil V-groove
12 mil Fused Silica
Short-Circuit Current (mA)
Pre-Fliaht F_JLght Post-Flight
146.9 144.6 133.5
(AVoc = - 65 mV)
150.1 152.0 145.4
(AVoc = - 46 mV)
288.2 300.9 292.3
1199.0 881.3 1195.0
160.0 178.6 163.7
193.1 202.7 189.3
' iL¸ ,
was within about :P.2% It is believed that this variation was
due to inherent differences is the LeRC simulator and data
acquisition system used for post-flight testing and those
at Eppley Labs used for pre-flight testing. Pre-flight
testing was not performed at LeRC as it was expected that
the APEX cells would be used as calibrated reference
cells; the evolution of the experiment into a long term
durability test was neither expected nor ever
contemplated. The I-V characteristic of 16 cells was
measured by first recording the open-circuit voltage and
then switching in five load resistors and recording cell
current and voltage for each. The excellent agreement of
the on-orbit I-V data (black squares) with the post-flight
laboratory data of a Solar Maximum Mission cell in shown
(Figure 3).
2OO
160
E.
(._ 8O
Fig. 3.
; NaT B-II. I_. e -t6o.S2 m/k
Ve¢ .-E/9.S mY
_C_II :/HO4 _ =-14:LS,m,_
:4 _1. ¢m. Vmi¢ _ 4;PJL1 mV
Tem_eralu_ : _L_ ¢wJ C Pmlz. E4LQ5 ¢ltW
/w Mast, Zero FJ:. =73.1
Fde N,lme : IV|7_11 _ e 12.4%
,.,.,, .... | ......... _ ........ L ........ i ....... J ......... i ......... t,.
ir
, I ,,, I f ,r - f .... f
.1 .2 .1 .4 ,-S ,6 .7
VCLTAGE (vo¢_)
I-V curve of Solar Maximum Mission cell.
A summary of results from GaAs cells is shown in
Table III. Of the eleven GaAs cells flown, ten were made
by Hughes Research Laboratory using liquid phase
epitaxy, the only type of GaAs cells then available. These
cells had junction depths of either 0.35 pm or 0.50 p.m and
were flown with either a 12 mil fused silica coverglass or
unglassed. The performance degradation, particularly in
open-circuit voltage, of the uncovered cells is consistent
with the known radiation characteristics of these cells and
the mostly proton flux of the orbit. The eleventh GaAs cell
was a metal-oxide-semiconductor design which was under
study at that time as a low fabrication cost alternative to
epitaxial growth for III-V compounds. It has a very thick
coverglass of unknown thickness and material and
degraded significantly in short-circuit current. The
accuracy of the pre-flight Isc value is suspect.
Detailed discussion of other cells in the set,
particularly those which sustained physical damage from
micrometeoroids/debris, can be found in ref. 2 and 5.
CONCLUSION
The solar cells and sensors flown on APEX survived
well their nearly six years in low earth orbit. Post-flight
testing of the Eppley cavity radiometer shows that it is
essential unchanged from its pre-flight condition. The
solar cell set survived equally well, with no evidence of
electrical or physical changes except in those cases
where debris or micrometeoroids cratered the cells. Pre-
flight and post-flight performance measurements are in
good agreement.
REFERENCES
1. Brinker, D.J.; Hart, R.E. and Hickey, J.R., 21st IEEE
PVSC, 1990, pp 1213-1218.
, Brinker, D.J.; Hickey, J.R. and Scheiman, D.A., 1st
LDEF Post-Retrieval Symposium, June 1991, NASA
CP 3134, pp 1395-1404.
3. Hickey, J.R., 1st LDEF Post-Retrieval Symposium,
June 1991, NASA CP 3134, pp 1493-1510.
. Hickey, J.R.; Brinker, D.J. and Jenkins, P.P., 2nd
LDEF Post-Retrieval Symposium", June 1992, NASA
CP-3194, pp. 1375-1388.
. Brinker, D.J.; Hickey, J.R. and Scheiman, D.A., 2nd
LDEF Post-Retrieval Symposium, June 1992, NASA
CP-3194, pp. 1291-1302.
Cell Number DescriDtior I
ISC71 NB-15L Hughes, Dj=0.5wn
ISC 76 NB-29R HRL, Dj = 0.5 I_m
ISC 77 NB-29L HRL, Dj = 0.35 I_m
ISC 111 A-2 JPL, AMOS
Table III Gallium Arsenide Cell Results
Coverolass
12 rail Fused Silica
No Cover
No Cover
Unknown
Short-Circuit Current (mA)
Pre-Fliaht J_l.t Post-Fliaht
122.5 116.1 108.0
(AVoc = + 10 mV)
117.2 111.6 95.5
(AVoc = - 65 mV)
117.3 113.1 93.6
(AVoc = - 85 mV)
17.6 33.6 22.0
4

Form Approved
REPORT DOCUMENTATION PAGE OMBNo. 0704-0188
Public.reporting burden, for this.collection of information is estimatedto average 1 hour per response, including the time for reviewing instructions, searching existing data sources,
ga!.nenng an.d .mamtalmng the ,,claraneeded, and completing and reviewtng the collection of information. Send comments regarding this burden estimate or any other aspect of th s
colLeclion ol mtormation, inc=uoing suggestions for reoucing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson
Davis Highway, Suite 1204, Arlington, VA 222024302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.
1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED
January 1995 Technical Memorandum
4. TITLE AND SUBTITLE 5. FUNDING NUMBERS
Final Results of the Advanced Photovoltaic Experiment Flight Test
6. AUTHOR(S)
David J. Brinker and John R. Hickey
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
WU-233-01-0A
8. PERFORMING ORGANIZATION
REPORT NUMBER
E-9377
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
NASA TM- 106828
11. SUPPLEMENTARY NOTES
Prepared for the First World Conference on Photovoltaic Energy Conversion cosponsored b ¢IEEE, PVSEC-Japan, and PVSEC-Europe,
Waikoloa, Hawaii, December 5-9, 1994. David J. Brinker, NASA Lewis Research Center and John R. Hiekey, The Eppley Laboratory,
Inc., Newport, Rhode Island 02840. Responsible person, David J. Brirtker, organization code 5410, (216) 433-2236.
12a. DISTRIBUTION/AVAILABILITY STATEMENT
Unclassified -Unlimited
Subject Category 20
This publication is available from the NASA Center for Aerospace Information, (301) 621-0390.
12b. DISTRIBUTION CODE
13. ABSTRACT (Maximum 200 words)
The Advanced Photovoltaic Experiment was designed to generate laboratory reference standards as well as to explore the
durability of a wide variety of space solar cells. In addition to the cells, it was equipped with an absolute cavity radiom-
eter to measure solar intensity, a spectroradiometer to measure the spectral content of this radiation and a sun angle
sensor. Data from the solar cells and various sensors was obtained on a daily basis during the first eleven months of the 69
month flight. In this paper we compare pre-flight and post-flight laboratory measurements with on-orbit calibration data.
Pre-flight and post-flight calibration data of the cavity radiometer as well as on-orbit data demonstrated the accuracy and
durability of the Eppley instrument flown on APEX.
14. SUBJECT TERMS
LDEF; Space solar cell flight test
17. SECURITY CLASSIFICATION
OF REPORT
Unclassified
NSN 7540-01-280-5500
18. SECURFrY CLASSIFICATION
OF THIS PAGE
Unclassified
19. SECURITYCLASSIFICATION
OF ABSTRACT
Unclassified
15. NUMBER OF PAGES
6
16. PRICE CODE
A02
20. LIMITATION OF ABSTRACT
Standard Form 298 (Rev. 2-89)
Prescribed by ANSI Std. Z39-18
298-102


Final Results of the Advanced Photovoltaic Experiment Flight Test

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server