The calibration of the direct conversion of solar energy through use of solar cells at high altitudes by balloon flight is reported. Twenty seven modules were carried to an altitude of 35.4 kilometers. Silicon cells are stable for long periods of time and can be used as standards. It is demonstrated that the cell mounting cavity may be either black or white with equal validity in setting solar simulators. The calibrated cells can be used as reference standards in simulator testing of cells and arrays

Seaman, C. H.

Weiss, R. S.

English

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JPL PUBLICATION 81-115
Rostaits of the 198,1 NASA./JPL
Balloon Flight Solar Cell
Calibration Program
C.H. Seaman
R.S. Weiss
(NASA-CE?-1b8442)
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January 15, 1982
`CV
NASA
National Aeronautics and
Space Administration
Jet Propulsion Laboratory
California Institite of Technology
Pasadena. California
L
i
JPL PLIKICATION 81-115
Results of the 1981 NASA/JPL
Balloon Flight Solar Cell
Calibration Program
C.H. Seaman
R.S. Weiss
January 15, 1982
RVSA
National Aeronautics and
Space Administration
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California
The research described in this public
Laboratory, California Institute of Te
Aeronautics and Space Administrati
VPREFACE
,he work described in this report was performed by the Control and Energy
Conversion Division of the Jet Propulsion Laboratory. The flight was conduc-
ted with the cooperation of the National Scientific Balloon Facility, located
in Palestine, Texas.
ABSTRACT
After an aborted launch on July 23 due to balloon failure during
inflation, the 1481 solar cell calibration balloon flight was successfully
completed on July 25, meeting all objectives of the program. Twenty-seven
modules were carried to an altitude of 35.4 kilometers. The calibrated cells
can now be used as reference standards in simulator testing of cells and
arrays.
tit
ACKNOWLEDGMENT
The authors wish to extend appreciation for the cooperation and support
provided by the entire staff of the National Scientific Balloon Facility.
Gratitude is also extended to assisting JPL personnel, especially B. E.
Anspaugh, for providing cell spectral response information and data reduction
assistance. The cooperation and patience extended by all participating
organizations are greatly appreciated.
iv
CONTENTS
I. INTRODUCTION -------------------------------------------------------- 1
II. PROCEDURE ----------------------------------------------------------- 1
III. SYSTEM DESCRIPTION -------------------------------------------------- 2
IV. DATA REDUCTION ------------------------------------------------------ 2
V. FILTERED CELLS ------------------------------------------------------ 6
VI. MODULE CAVITY SURFACE FINISH ---------------------------------------- 6
VII. MONITOR CELLS ------------------------------------------------------- 9
VIII. CONCLUSIONS --------------------------------------------------------- 9
REFERENCES------------------------•------------------------------
	 9
Tables
1. Cell Calibration Data ----------------------------------------------- 5
2. White-Black Ratio Versus Source ------------------------------------- 8
3. Repeatability of Standard Solar Cell BFS-17A ------------------------ 10
Figures
1. 1981 Solar Module Payload ------------------------------------------- 3
2. Balloon Mount -------------------------------------------------------- 3
3. Flight 1981 Altitude Versus Time ------------------------------------ 4
4. 1981 Module Location Chart ------------------------------------------ 6
5. Black and White Cavity Modules -------------------------------------- 8
v
SECTION I
INTRODUCTION
The primary source of electrical power for unmanned space vehicles is
the direct conversion of a.olar energy through the use of solar cells. As ad-
vancing cell technology continues to modify the spectral response of solar
cells to utilize more of the sun's spectrum, designers of solar array_ must
have information detailing the impact of these modifications on cell conversion
efficiency to be able to confidently minimize the active cell area required
and, hence, the mass of the array structure.
Since laboratory simulation of extra-atmospheric solar radiation has
not been accomplished on a practical scale with sufficient fidelity, high
altitude exposure must be taken as the best representation of space itself.
While a theoretical prediction (Reference 1) and experimental evidence have
suggested that an altitude greater than 30 kilometers is sufficient to give
space equivalent calibration, the final decision as to an adequate altitude
must await the results of the space shuttle solar cell calibration experiment
scheduled for December 1982.
To reach and maintain the chosen altitude of 36 kilometers, the
calibration program makes use of balloons providea and launched by the
National Scientific Balloon Facility, Palestine, Texas.
SECTION II
PROCEDURF.
To insure electrical and mechanical compatibility with other comporvnts
of the flight system, the cells are mounted by the participants on JPL-supplied
standard modules according to directions in Reference 2, which details mater-
ials, techniques, and workmanship standards for assembly. The JPL standard
module is a machined copper block 3.7 cm x 4.8 cm x 0.3 cm thick, rimmed by
0.3 cm thick fiberglass, painted a high reflectance white, with insulated
solder posts and is permanently provided with a precision (0.1 percent, 20
ppm/ oC) load resistor appropriate for scaling the cell output to the tele-
metry constraints. This load resistor, 0.5 ohm for a 2 cm x 2 cm cell, for
example, also loads the cell in its short circuit current condition.
The mounted cells are then subjected to preflight measurements in the
JPL X25L solar simulator. This measurement, when compared to a postflight
measurement under the same conditions, may be used to detect cell damage or
instabilities.
Prior to shipment to the launch facility, the modules are mounted on
the sun tracker bed plate (Figure 1).
1
Upon arrival at the Palestine Facility, the tracker and module payload
are checked for proper operation, the data acquisition and Pulse Code Modula-
tion telemetry systems are calibrated. Mounting of the assembly onto the
balloon is then accomplished (Figure 2).
At operating altitude the sun tracker bed plate is held pointed at the
sun to within +1 deg. The response of each module, temperatures of represen-
tative modules, sun lock information, and system calibration voltages are
sampled twice each second and telemetercd to the ground station where they are
presented in teletype form for real-time assessment and are also recorded on
magnetic tape for later processing. Float altitude information is obtained
from data supplied by the balloon facility. A plot of altitude in kilometers
versus Central Daylight Time for the 081 flight is shown in Figure 3.
SECTION III
SYSTEM DESCRIPTION
A solar tracker mounted in a frame on top of the balloon carries the
module payload, while the transmitter of the data link is located in the lower
gondola along with batteries fjr power and ballast for balloon control. At
completion of the experiment, the upper payload and lower gondola are returned
by parachutes and recovered. A more complete description of the system, in-
cluding the sun tracker, can be found in Reference 3.
SECTION IV
DATA REDUCTION
The raw data as taken from the magnetic tape is corrected for
temperature and sun-Earth distance according to the formula (Reference 4):
V28,1 - VT,R (R2 ) - a(T-28)
where
VTR = measured module output voltage at temperature T and distance R
R = sun-Earth distance in astronomical units
a - module output temperature coefficient (supplied by participant)
T - module temperature in oC
2
ew ^
	 1
ORIGINAL PAGE
BLAC K AND WHITE PHOTOGRAPH
r	 •
Figure 1.	 1981 Solar Module Payload
Figure 1.	 balloon Mount
3
CENTRAL DAYLIGHT TIME
AN [
n
Is
DI00
Figure 3. Flight 1981 Altitude Versus Time
The calibration value is taken to be the average of 200 consecutive
data points taken around the time of solar noon after indicated temperature
stability.
The flight data were thus reduced, and modules with their data and
calibration values were returned to the participants. This information is
collected in Table 1. The placement of modules on the field of the tracker
bed for the 1981 flight is shown in Figure 4.
A detailed discussion of data reduction and an analysis of system error
may be found in Reference 3.
4
The error in the calibration values due tc
scattering by the residual atmosphere at float al
less than 0.2 percent (Reference 1).
Table 1. Cell Calibration Data
RALL OON FLIGHT 81 . 1	 OATI 7-2s.al ALTITUDE 311.60	 KM Rvel.O1s6S
CHANNEL MODULE ORGANIZATION TEMP.	 INTENSITY STANDARD AMO.><OLAR	 81 04. COMPARI5ON.SOLA11 CnMMENTS
NUMBER NUMSER CODE ADJ. AVERAGE DEVIATION 1	 Au g 26 DIG.0 SI MULATOR 0 FLT
Pkj-FLT 006.OLT PRE-FLT FLIGHT
v6. vs.
POf-FLT PRE.FLT
( P E RCENT) (PERCENT)
1 51.001 JPL 45.2s .06675 06.80 84.10 ..43 .113 97 AL SGMN6
2 010110 HUGHES 70.99 .011502 69.70 69.30 ..117 1.86 K1
3 al-lei 7114 64.82 .07495 SI.so 03.60 .12 1.76 OLK-01
4 01.002 JPL 67.10 .06473 86.00 85.110 ..SO 1.24 97 wH WHO
s 61.132 "UGHfs 60.42 .06223 76.40 16.40 .00 41.26 K4 1/4
0 61.161 MSFC 77.76 .064ss 7A.90 77.00 .2.41 .1.41 06.061 666CM
7 76.001 JPL 67.06 .as*10 60.70 68.70 .00 .1.22
8 PI-103 TRw 76.45 .06125 16.70 76.40 .13 .32 K8F.02
9 81.134 HUGHES 27.16 .07914 22.40 22.70 ..64 21.32 SoONMNP 004
10 61.104 low 76.53 .06416 76.&C 76.60 .26 .17 SSF.03
11 81 . 003 JPL 111.511 .07710 76.20 75.00 •1.117 ..86 KC 394 a 86
12 V3•102 JOL 67.06 .06172 60.40 64.60 .29 -.64
11 81.146 wC 70.67 .06234 74.20 74.20 .1.26 .119 M4.063 666CM
14 74.2es JPL 69.99 .07070 S1.&O 41.S0 .11 2.97
111 0l -Ios Tow 71.54 .0646, 73.40 73. 4 0 .00 .14 6811.02
16 .1.004 JPL 77.511 .04504 77.00 76. 4 0 ..26 .72 K4 lip s K a6
11 61.136 HUGHES 22.36 .01100 26.40 20.90 .00 7.06 f0eowwwP ago
1s 41.106 Too 73.72 .06407 71.90 73.80 ..14 ..25 S8R.63
19 1FS-l7. JPL 60.01 .06167 60.110 66.110 .00 -.71 MONITOR
20 41.107 Tow 79.03 .04199 1A.80 78.00 .00 .24 SPa10.02
21 11.138 HUGHES 23.15 .06601 22.60 22.20 •1.77 2,45 3110.7410MNMP
22 .1.006 JOL 72.49 .06798 72.10 72.20 .14 .so NO 00F
21 81.160 711M 79.11 .06492 19.00 79.00 .o0 .14 66194.03
24 73.143 Jot 66.03 •OS610 67.70 67.70 .00 -1.24
is 10-li0 HUGHES 94.82 .011830 93.70 93.50 ..21 1.20 KT
26 P1-142 Tow 011.09 .6111141 63.00 64.00 .24 1.114 OL4.02
27 81.041 JPL 81.46 .00313 46.84 68.60 .00 .79 (.*TI $8F
39 10O•MV 103.256 .11S0615 .00 .80 .00 .00
40 64 -MV 62.926 .066s1 Co. .00 .06 .00
41 so-MV 51.906 .06494 .00 .00 .00 .00
42 e.MV .406 .08040 .00 .00 .00 .90
6 INDICATES CHANNEL FO& WHICH NO TEMPERATURE COEFFICIENT was PROVI M.
AVERAGE TINPERATUOE (OEG.C)
	
AT FLOAT	 ALTITUDE 4	 52.41
5
/i-143
MSFC
/1-001 E0/1-101
HESTRW
 /;1 	 SUN
,J 	 (De 	 10	 11	 C^	 1,1
7", 1	 11-107	 8I.134	 /1-IW	 81-002
	
T7S-
JIL	 TIN	 MUGNES	 TRW	 1 ►L	 JFL	 11-146
N&K
7M20b	 11 - 1 OS	 /1-004	 /i-176	 11-106	 IFS17A
1► l	 TRW	 JIL	 MUGA$	 TRW	 1►l
11	 IS	 16	 17	 1/	 19
^^ 21 ® ^ (:^ ^ ze ^il
TI
/1-107 /i-17t /1 -006 t1-10/ 77-Iq 7/-110 /i-io2 BI -006
TRW IIUGKS JIl TRW JK INJGIIES TRW JIl
0 INDICATES CHANNEL NUMIER
TI	 STD CELL @)
T2 TRACK11 ELIC. 4
TS STD CELL Cis)
T4 STD CELL
TS VOLTAGE REF /OX 47
Figure 4. 1981 Module Location Chart
SECTION V
FILTERED CELLS
The relationship of the spectral irradiance of simulated sunlight
sources to the AMO solar spectral irradiance is an important factor in the
design and fabrication of cells and panels, since it directly impacts the
predictions of performance in the space environment.
To facilitate the monitoring of the spectral irradiance of simulators,
three modules of this 'light were assembled with permanently bonded band pass
filters of selected center wavelengths (Reference S). With these and similar
modules from previous flights, a family of AMO calibrated spectral samplings
characterizing a simulator's spectral irradiance can be quickly and easily
performed.
SECTION VI
MODULE CAVITY SURFACE FINISH
Questions have recently surfaced as to the effect of reflections within
the white painted module cavity on the cell calibration value and the
resultant effect on the setting of a solar simulator using these cells. Would
a black painted cavity be more appropriate? Experiments with several
6
simulators of ra:ious radiation angular subtense ( 0.5 to 4.j deg) have
demonstrated thar a cell mounted in a white painted cavity will in fact show a
calibration !-slue about 2 percent greater than a cell mounted in a black
painted cavity. However, these same experiments have also show •. that this
measured difference is not a function of course angular subtense ( at least
over the angular range of 0.5 to 4.5 deg), ar.i, hence, calls in either black
or white cavities should " see" the simulators ( a:^gles of 0.5 to 4.5 deg) in
the same way they "saw" the sun (angle 0.5 deg) in the original calibration.
Therefore, setting of the simuiacuc should not be dependent upon the cavity
finish of the calibrated cell as long as that cavity finish is not altered
from the calibrat i on condition.
These laboratory experiments were extended by including two matched
Fairs of cells on this 1981 calibration flight, one of each pair being mounted
In a white painted cavity, the other in a black. See Figure 5 for a
representative pair.
Cells 81 -001 and 81-002 are each K7, are from the same production run,
and have the same absolute spectral response. Cell 81-001 is mounted in a
black painted cavity, cell 81-002 in a white.
Cells 81-003 and 81-004 are each K4-3/4, are from the same production
run, and have the same absolute spectral response. Cell 81-003 is mounted in
a black painted cavity, cell 81-004 in a white.
The flight calibration values are:
81-002 - 87.10 mV
81-001 - 85.25 mV
81-004 - 77.55 mV
81-003 - 75.55 mV
The ratios of the flight calibration values are:
81-OUL;81-001 - 1.022
81-004/81-003 - 1.027
These cell pairs were then measured in four simulators (LAPSS, ACC302,
X25, and X25L of angular subtense 0.5, 1.5, 4. 0, and 4.5 deg, respectively)*
according to the following scheme. Each simulator was adjusted to the
calibration value of one cell of a pair ( say, the white painted one), and the
output of the second of that pair was then measured. The results, sho+'., es
ratios, and the percent difference from the solar calibration ratios are given
in Table 2.
These results are in agreement with the previous experiments
demonstrating the validity of either cavity condition for a standard cell.
*Large Area Pulsed ` )1ar Simulator tLAPSS), X25, and X25L, Spectrolab, Inc;
ACC302, Aerospace Control Corporation.
7
0, a - U	 A
t
Oft GINAL PAGE
FLACK AND WHITE PHOTOf`?gPtA
Table 2. White-Black Ratio Versus Source
Cell
Pair X25 X25L ACC302 tAPSS
SOn
(CALIB)
81-002
$I -^6I
1.022 1.021 1.024 1.021 1.022
A% vs Sun C -0.10 +0.20 -0.10 -
81-004 1.029 1.024 1.027 1.028 1.027
81-003
Op vs Sun +0.19 -0.29 0 +0.10 -
Figure 5. Black and White Cavity Modules
8
Several standard modules have been flown repeatedly over the 19-year
period of calibration flights. The record of the one with the longest his-
tory, BFS-17A, appears in Table 3. This data shows a standard deviation of
0.39 percent and a maximum deviation of 0.92 percent from the mean.
In addition, the uniformity of the solar irradiance (i.e., no spurious
reflections, shadowing) ov%.r the field of the modules has been demonstrated
since the local ton of this module was changed in that field from flight to
flight.
SECTION VIII
CONCLUSIONS
As emphasized by the history of repeatability of cell BFS-17A, via,
+1 p,arcent (see Table 3), silicon cells, when properly cared for, are stable
Tar lone periods of time and may be used as standards with confidence.
It has peen demonstrated that the cell mounting cavity may be either
black or white with equal validity in setting solar simulators.
REFERENCES
Seaman, C. H., and Weiss, R. S., Results of the 1979 NASA/JPL
Balloon Flight Solar Cell Calibration Program, JPL Publication
80-31, Jet Propulsion Laboratory, Pasadena, CA, May 1, 1980.
2. Greenwood, R. F., "Solar Cell Nodules Balloon Flight Standard,
Fabrication of," Procedure No. EP504443, Revision C, Jet Propulsion
Laboratory, Pasadena, CA, June 11, 1974 (JPL Internal Document).
3. Yasui, R. K., and Greenwood, R. F., Results of the 1973 NASA/JPL
Balloon Flight Solar Cell Calibration Program, Technical Report
32-1600, Jet Propulsion Laboratory, Pasadena, CA, November 1, 1975.
4. Solar Cell Array Design Handbook, JPL SP 43-38, Vol. 1, p. 3.6-2,
Jet Propulsion Laboratory, Pasadena, CA, 1976.
5. Goodelle, G.e., et al., Simulator Spectral Characterization Using
Balloon Calibrated Solar Cells with arrow Bond Pass Filters,
Proceedings Fifteenth IEEE Photovoltaic Specialists Conference,
1981.
9
Table 3. Repeatability of Standard Solar Cell BFS-17A
(33 Flights over a 19-Year Period)
Flight date Output, mV Flight data Output, mV
9/5/63 b0.07 8/5/70 60.32
8/3/64 60.43 4/5/74 60.37
8/8/64 60.17 4/23/74 60.37
7/28/65 59.90 5/8/74 60.36
8/9/65 59.90 10/12/74 60.80
8/13/65 59.93 10/24/74 60.56
7/29/65 60.67 6/6/75 60.20
8/4/66 60.25 6/27/75 60.21
8/12/66 60.15 6/10/77 60.35
8/26/66 60.02 8/11/77 60.46
7/14/67 60.06 7/20/78 60.49
7/25/67 60.02 8/8/79 60.14
8/4/67 59.83 7/24/80 60.05
8/10/67 60.02 7/25/81 60.07
7/19/68 60.31
7/29/68 60.20
8/26/69 60 .37 Mean 60.25
9/8/69 60.17 Std.	 Deviation 0.24
7/28/70 60.42 Maximum deviation 0.55
Each data point is an average of 20 to 30 points per flight for
period 9/5/63 to 8/5/70.
For flights on 4/5/74 through 1/1/75 each data point is an average
of 100 or more flight data points.
For flights starting in September 1975, each data point !s in average
of 200 data points.
10
	
N&U in C^" LA CAW


Results of the 1981 NASA/JPL balloon flight solar cell calibration program

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