Speakers whose topics relate to the reliability physics of solar arrays are listed and their topics briefly reviewed. Nine reports are reviewed ranging in subjects from studies of photothermal degradation in encapsulants and polymerizable ultraviolet stabilizers to interface bonding stability to electrochemical degradation of photovoltaic modules

Cuddihy, E. F.

Ross, R. G., Jr.

English

NASA Technical Reports Server

Technical Sessions 
RELIABILITY PHYSICS 
Edward F. Cuddihy and 
Ronald G. Ross, Jr., Chairmen 
Rclnty H. Liung of JPL reported on Studie.3 of Rotothermal Degradation in 
Encapsulants. The fundamental mechanisms and associated reaction kinetics of 
the thermal and photothermal yellowing of EVA are described. EVAwill yellow 
dvring dark-oven aging at elevated temperatures, and will also yellow in the 
presence of UV. But the UV will induce a partial photobleaching of the thermal 
yellowing. Ilecacse the  kinetic^ of the thermal yellowing, CV yellowing, and 
UV bleaching are different, the overall yellocing of CVA is not eimplv related 
to UV intensity and tem2ereture. The work described seeks r3 derive the 
overall reaction kinetics of EVA yellowing as part of the development of a 
life-prediction methodology. 
C.C-  Gonzalez and R.G. Ross, Jr., of JPL reported on Predicting 
Photothermal Field Performance. A preliminary kiuet ics mode 1 of EVA yellowing 
was generated from the fundaments1 work described in the previous prwsntacion. 
Using this model and SOLMET weather data, predictions of the level of weather- 
induced yellowing ic EVA from 30 years of simulated outdoor exposure in Photnix 
were generated. Yellawing of EVA results in optical absorption of transmitted 
sunlight, thereby reducing the power output of solar cells encapulsated in EVA. 
This preliminary work indicated power losses amounting to near 3.5% for ground- 
mounted arrays, and power losses approaching 7.9X for roof-mounted arrays, 
which typically operate st higher temperatures than ground-mounted arrays. 
J. Suillet af YJniversity of Toronto rep~rted on Micromolecular Modeling. 
'Ibis contract work seeks to dzvelop a reaction-kinetics-based model of the 
overall photodegradation process experienced by encapsulatants in an outdoor 
wearher envi.ronment. Inasmrwh as well over 50 individual reaction mechanisms 
have been identified, part of this work is to develop a computer ahility to 
solve all of the rection kinetic equations simultaneously for life-prediction 
purposes, aid for chemical infomation related to the selection of the most 
effective stabilizing additives for weather-sensitive encapwlants such as EVA. 
l%e computerized model indicates that s combination of s UV absorber and a 
hindered amine light stabilizer (RALS) wculd be ail effective stabilizing system. 
P. Gomez, S.K. Fu, and 0. Vogl of the Polytechnic Institute of ! k w  York 
rep~rted on Po1ym;rizable Ultraviolet Stabilizers. Pclytechnic Institute of 
New York carries aut chemical synthesis of advanced polymeric and reactive 
stabilization additives for polymeric materials, such as EVA. These additives, 
such as protective UV-absorbing sgents , are resistant to high-tempera.tare 
physical losses. The latest deve1opme:;ts in this area were presented" 
P. Will ;s ot Springhorn Laboratortes , Inc., reported on Encapsulated 
Materials Research. Springbwn Laboratories updated its continding work on 
long-lif?, weather-stable encapsulation materials f ~ r  photovoltaic modu1.e~. 
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The program emphasis at Springborn has shif ted from material development and 
identification to life-assesssent experiments, and to the identification 
and/or development of stabilization additives for encapsulation materials. 
Two items of signif icauce were presented: ( 1  preliminaty experimental testing 
is supporting the combination of a UV absother and HALS as an effective 
stabilization system, as theoretically derived at the University of Toronto, 
! and ( 2 )  the significant usefulness of the outdoor heating racks (called OPTS 
in the Springbmn presentationj as an acceleratzd weathering technique. 
J. Koenig of Case Western Reserve University reported on EVA-Glass 
> Interface Bond Stability. Koenig and Boerio (see below) have developed the 
technology to investigate a chemically bonde! interfact for direct acquisition 
of chemical infornation on both bonding and aging mechanisms. The technology 
is based on Fourier transform infrared techniques (FTIRJ. Koenig presented 
F T I R  spectra of the bonded interface between EVA and glass, which had been 
hydrolytically aged for at least cne week in 80°C water. The early results 
indicate strong possibil.ities for a long-term weather-stable interfacial 
bocl. R.e EVA-glass primer system is the one developed by Dow "orning Corp. 
for FSA, of which experimental quantities can be obtained from Springborn 
Laboratories under the designation A-11861. 
J. Boerio of  the University of Cincinnati reported on Interface Bonding 
Stability. Boerio's efforts are identical with those of Koenig, except that 
the emphasis of his study is on po?ymers and metals, such as EVA and 
aluminum. ahese i~te~facial cheaistries can be quite distinct from those 
between EVA and glass, for example. Recently Dow Corning observed that EVA 
bonds strongly to aluminized back surfaces of solar cells, when using the 
standard A-11862 EVA-glass primer system. Ordinarily EVA bonds weakly to 
aluminum fail or sheet stock, using the same primer, and therefore this 
observation with the s ~ l a r  cells was not expected. Eoerio described his 
examination of the alumLnized back surface using SEM and EDS, and reported his 
initial findings that the back surface appears to be a mixture of aluminum and 
silicon. If it can be assumed that the silicon may be present as an oxide or 
hydroxide, then perhaps the back surface has glass-like chemistry, which would 
help to explain the Dow Corning obszrvation. If true, the self-priming EVA 
being developed jointly by Dow Corning and Springbor;~ for glass would also 
work with solar cells. More work in this area is planned. 
G.R. Mon of JPL reported 09 Topics in Electrochemical %gradation of 
Photovoltaic Modcles. Various topics related to the potential for electro- 
chemical degradation of photovoltaic modules during 30 years of service in the 
natural outdoor weatherir.g envi rcnment were presented. These included ( 1)  the 
relationehip betweer, leakage curient and electrochemical degradation, with 
emphasis on the elforts of positive and negative polgrity, and tho dependency 
of temperature and humidity; (2) a discussion of leakage current ;esponee 
mechaaisms, ard ( 3 )  consideratione related to laboratory rimlation of outdoor 
behavior to derive ac:.leration factors for aodule life   re diction, and module 
qualification rests related to electrochem!cal susceptibility. 
J. Orehotsky of Wilkes College reparted on Polymer-Water Interaction 
Strtdies. Electrochemical susceptibility requires absorption of water by the 
encapsulation pottants, such as EVA and PVB. A new contract activity has been 
initided at Wilkes College to determine experimenta.lly the magnitude6 arid 
RELIABILITY PHYSICS 
r a t e s  of t h e  absorp t ion  and desorp t ion  of atmospheric water vapor by p o t t a n t  
m a t e r i a l s .  7hi.a s tudy inc ludes  the  dependency on magnitude and change r a t e  of 
temperature and r e l a t i v e  humidity.  Zhe d i s c u s s i o n  inc1v;ded t h e  background f o r  
the  e x p e r i s e n t a l  s t u d i e s ,  d e t a i l s  of  the  exper imenta l  t - v h n i q u e s ,  and 
p re l iminary  e x p e ~ i m e n t a l  d a t a  r e l a t e d  t o  (1) water absorp t ion  and d e s o r p t i c s  
k i n e t i c s  i n  EVA and PVB, ( 2 )  humidity dependence of e l e c t r i c a l  p r o p z r t i e ~  oL 
EVA and PVB, and ( 3 )  in f luence  of p l a s t i c i z e r  i n  PVB on water absorp t ion  and 
e l e c t r i c a l  p r o p e r t i e s  . 


Reliability physics

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