Title of Invention

A FORMULATION FOR ENCAPSULATION OF PHOTOVALTAIC (PV) MODULES

Abstract A formulation for encapsulation of photovoltaic (PV) modules comprising Ethylene vinyl acetate (EVA), a cross linker, an UV stabilizer, a bonding agent and an antioxidant such as herein described, said cross linker being present in 1 to 2 parts by weight based on 100 parts by weight of EVA, said UV stabilizer being present in 0.1 to 0.3 parts by weight based on 100 parts by weight of EVA, said bonding agent being present in a proportion of 0.25 to 1.0 parts by weight based on 100 parts by weight of EVA and said antioxidant is present in 0.1 to 0.3 parts by weight, based on 100 parts by weight of EVA.
Full Text FIELD OF THE INVENTION:
This invention relates to a formulation for the encapsulation material for
amorphous silicon and crystalline silicon photovoltaic (PV) modules or for that
matter, PV modules, in general, and a process for the preparation thereof.
This invention further relates to an ethylene vinyl acetate (EVA) formulation,
which exhibits properties equivalent to commercially available EVA and to
photovoltaic (PV) modules using the formulation as an encapsulation material.
BACKGROUND OF THE INVENTION:
The overall performance and efficiency of PV module in converting the
incident solar energy into electrical power depends upon environmental
factors such as, environmental temperature & humidity fluctuations, incident
UV radiations, atmospheric gases and pollutants, the diurnal and annual
thermal cycles. In addition to these detrimental environmental elements, a
variety of other factors, such as rain, hail, dust, wind, thermal expansion
mismatches, condensation and evaporation of water, may further reduce the
performance of the module. In order to maintain long-term performance &
reliability of the PV modules, it needs protection by some suitable
encapsulation materials. The encapsulant must exhibit long term weathering
stability, so that the solar cells in an encapsulated module could also exhibit
long term weathering stability to five reliable performance of the PV system.
Further for PV modules to become economically competitive in terrestrial
power generation market, the PV modules must undergo a substantial cost
reduction. The reduction in cost of encapsulation material in PV module will
help realize low cost PV modules.
OBJECTS OF THE INVENTION:
It is therefore an object of this invention to provide a formulation for the
encapsulation material (EVA) for photovoltaic modules, which uses
environment friendly process.
It is a further object of this invention to provide a formulation for the
encapsulation material for photovoltaic modules, which is cost-effective.
BRIEF DESCRIPTION OF THE INVENTION:
Thus, according to this invention, a formulation and process for the
encapsulation material of photovoltaic modules is provided.
In accordance with this invention, a formulation is provided for EVA
encapsulation material for PV module using indigenous low cost EVA resin in
granular, form. EVA granules of EXXON MOBIL make (type 2825) or NOCIL
make having 28% VA content have been used in the formulation. Constituents
of EVA formulation including additives for use in PV module encapsulation
have been optimized.
The additives used are cross linker, UV stabilizer, a bonding agent, and an
antioxidant.
The cross linker is selected from compounds such asi,Ljpersol 101, Luperox
101 (2,5 dimethyl-2,5-di-t-butyl peroxy hexane) of Elf Atofina Peroxides India
Ltd, Chennai and Lupersol 231 ( 1, 1-di-(t-butylperoxy)-3,3,5-
trimethylcyclohexane), Lupersol TBEC ( 0,0,-t-butyl-0-(2-ethylhexyl) mono-
peroxy-carbonate) and is used in 1 to 2^parts by weight The UV stabiliser is
selected from compounds such as Tinuvin 327 (2(2'-hydroxy-3',5'-di-t-butyl
phenyl)-5 chlorobenzotriazole) of Ciba Geigy Corp., USA, Hillite-77 [Bis
(2,2,6,6-tetramethyl-4-piperidinyl) sebacate) of High Polymer Lab (HPL),
FaridabedJinuvin 770 (4(2,2',6,6'-tetramethyi) piperidinyi)sebacate), CyasorbUV
531 ( 2-hydroxy-4-octyloxy benzophenone), Irganox 1076 (Octadecyl 3(3,5 di,
tert, butyl,4 hydroxy phenyl)-propionate)and UV absorbers such as(Pheny!
salicylate), (Resorcinol monob«nzoate)f{2-Hydroxy-4-mtthoxyb«nzoph«nonf),
(2,2'-Dihydroxy-4- methoxybenzophenone), (2-(2-hydroxyphenyl)-benzotriazole),
(l^^-Tris-fZ^ydroxyphenyO-friazineXe^B^khbro-S^O-dephenyttrwphenoxa-
ztne). The UV stabilizer is used in a proportion of 0.1 to 0.3 parts by weight. The
bonding agtnt may be an organo silane such as A-174 (y-methacryioxy propyi
trimethoxysilane) of Union Carbide, USA, or Z-6030 of Dow Corning, USA or
Dynasylan Memo(3Hrimethoxy silylpropyl methacrylate) of Degussa Germany, Hi
0.25 to 1.0 parts by weight. The antktxident may be a compound such as Kinox-
10 (Tetrakis [methylene-(3,5-di t-buty 1-4-hydrocinnamate)m«than*] of HPL,UV
absorbers, such as (Phenyi salicyiate), (Resorcinol monobenzoate),(2-Hydroxy-
4- methoxybenzopherwne)/(2^'-Dihydroxy^^etr»xybenzophenone)/ (2-(2-
hydroxyphenyl)-benzotriaioie)f (l,3,5-Tris-(2-hydroxyph*nyl)-tria2in«),(6/13-
dtch(ro-3,10-dtph«nyltriaph«nodioxizint), and issued in 0.1 to 0.3 parts by
weight.
According to an embodiment of this invention is provided a process for
manufacturing EVA sheets for encapsulation of photovoltaic module comprising
preparing a mixture of cross-linker, UV stabilizer, bonding agent and anttoxidant
in a solvent, coating the ethylene vinyl acetate granules with said mixture,
followed by melt extrusion of the mixture, to obtain the EVA sheets.
According to a further embodiment of this invention is provided an encapsulated
photovoltaic module comprising a string of silicon cell overlaid by a glass and
having on its undersurface the EVA sheets made from a said formulation
comprising EVA, cross linker,11V stabilizer and antioxidant and followed by a layer
of Tedlar or equivalent laminate as the back sheet.
The invention will now be explained in greater detail with the help of the
following non-limiting example.
Typical exampls of formulation: 100 grams, Luperox 101:1.5
gram , Dynasylan Memo: 0.3 gram, Hillite-77 : 0.1 gram, Kinox -10:0.2 gram
were mixed and the EVA sheets were extruded in a commercial sheet extrusion
machine. The sample PV modules of large area were prepared and subjected to
hot water soak test, thermal cycling and outdoor exposure. Further, the
formulation was improved for EVA transmission and UV stabilization. The sheet
making process used in the present invention is melt-....................................
extrusion/casting in ontrast to solution casting In.the prior art. For dissolving
the resin, solution-casting method needs lot of solvent (e.g., Tetra Hydro
Furan) involving cost and subsequent drying operation that creates
environmental problems. THF solvent is used to coat EVA resin with a thin
layer of additives.
The EVA formulation so developed was tested for various functional
properties. These properties were found to be equivalent to those of the
commercially available EVA material and the results are illustrated with the
help of the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1. Schematic (not to actual scale) of the PV modules (1a amorphous
silicon, 1b. Crystalline silicon) showing EVA encapsulation material.
Fig 2. is a graph exhibiting out door performance of medium efficiency (6% as
produced modules) 1'x3' double junction amorphous silicon (a-Si) modules
encapsulated with the said low cost EVA formulation, over a period of nearly
three years. One of the graphs shows a module encapsulated with
commercially available EVA as reference (#27B86). The figure shows that
both the modules (encapsulated with reference and new EVA) exhibit similar
performance pattern over three years of out door exposure. This indicates that
the said EVA formulation meets the functional requirements and hence is
equivalent to commercially available EVA in the present context.
Fig 3. is a graph exhibiting out door performance of high efficiency (7% as
produced modules) 1' x 3' double junction amorphous silicon (a-Si) modules
encapsulated with the said low cost EVA formulation. This is shown to
indicate the repeatability of out door performance of 1' x 3' double junction
amorphous silicon (a-Si) modules encapsulated with the said low-cost EVA
formulation at a later date.
Fig 4. is a graph exhibiting performance stabilization of 1'x3' double junction
amorphous silicon (a-Si) modules encapsulated with the said low cost EVA
formulation after 20 cycles of water boiling/soaking, each for 8 hrs boiling and
16 hrs soaking. The observed degradation is within the acceptable limit of 5%.
Fig 5. is a graph exhibiting performance stabilization of 1' x 3' double junction
amorphous silicon (a-Si) modules encapsulated with the said low cost EVA
formulation after 10 cycles each of oven heating at 85 C for 15 min. The
observed degradation is within the acceptable limit of 5%.
Table 1. gives the details of the properties of the EVA formulation relevant to
encapsulation of PV modules. The properties are equivalent to EVA available
commercially.
The details of the material properties and their comparison with that of the
reference formulation are given in Table 1.
Further the EVA material was evaluated with PV modules as end use
requirement for laminating properties. For evaluation of EVA material various
configurations like glass/EVA/poly vinyl fluoride (PVF), PVF/EVA were
prepared in a vacuum laminator with a microprocessor controller, using
programmed temperature-time-pressure profiles. The typical lamination
temperature was 110-120°C for 5-10 minutes followed by curing at about
150°C for 20 minutes. The samples used for various tests like peel strength,
gel content, water vapour transmission and mechanical properties etc are
given in Table 1.
Differential Scanning Calorimetry (DSC) was used to obtain melting point of
the EVA before cross-linking. Ninety-degree peel method was used to find
peel strength at glass/EVA interface using custom made test set up. THF
solvent was used to dissolve stabilizers and uncured EVA from the cross-
linked EVA. The gel content was determined from the ratio of the weights of
cross-linked portion of the film to the total weight of the film before dissolving
the uncured portion of film.
Using laboratory scale samples of EVA, a few modules of 1x3 sq ft were
laminated & subjected to out door exposure test and preliminary thermal
cycling and water boiling test. Outdoor exposure test on these modules have
shown performance stabilizing characteristics equivalent to modules
encapsulated with commercially available EVA. The degradation behaviour of
the PV module power out put is given in Figures 2 through 5 under various
tests conditions and varying initial out put power values.
The EVA formulation has been used to laminate PV modules for exposure to
out door environmental conditions. The electrical performance stabilization
properties of the a-Si PV modules using said EVA formulation, during out door
exposure for last three years, was found to be equivalent to those with
commercially available EVA material.
The estimated cost of the said EVA material is reduced by 43% compared to
that of the imported EVA sheets used commercially.
WE CLAIMS
1. A formulation for encapsulation of photovoltaic (PV) modules comprising
Ethylene vinyl acetate (EVA), a cross linker, an UV stabilizer, a bonding agent
and an antioxidant such as herein described, said cross linker being present in 1
to 2 parts by weight based on 100 parts by weight of EVA, said UV stabilizer
being presenting 0.1 to 0.3 parts by weight based on 100 parts b weight of EVA
said bonding agent being present in a proportion of 0.25 to 1.0 parts by weight
based on 100 parts by weight of EVA and said antioxidant is present in 0.1 to 0.3
parts by weight, based on 100 parts by weight of EVA.
2. The formulation as claimed in claim 1 wherein said EVA is in the form of
granules having 28% vinyl acetate content.
3. The formulation as claimed in claim 1, wherein said cross linker is selected
from compound such as Uipersol 101 or Luperox 101 (2,5-dimethyl-2,5-di-t-
butyl peroxy hexane), Lupersol 231 (1, 1-di (t-butylperoxy)-3, 3, 5-
trimethykyclohexane, Lupersol TBEC (0,0, ¦*- butyl-0-(2-ethylhexyl) mono-
peroxy-carbonate), and is used in 1 to 2 parts by weight.
4. The formulation as claimed in claim 1, wherein said UV stabilizer is selected
from Tinuvin 327 (2(2'-hydroxy-3r, 5'-di-t-butyl phenyl)-5-chtorobenzotriazole) of
Ciba Geigy Corp, USA, HHtite- 77 [Bis (2,2,6,6-tetramethyH-piperidinyl)
sebacate) of High Polymer Lab (HPL), Faridabad, Tinuvin 770 (4 (2,2' 6,6'-
tetramethyl piperidinyl) sebacate Cyasorb UV 531 (2-hydroxy-4-octyloxy
benzophenone), Irganox 1076 (Octadecyl 3(3,5 di, tert, butyl), (4-hydroxy

pheny!)- propionate) and UV absorbers such as Phenyl saHcylate, Resorcino!
monobenzoate, 2- Hydroxy-4-methoxybenzoprwnorM^'-Dihydiroxy^-
methoxybenzophenone/2(2-hydroxyphenyl)-ben20trlazole, 1, 3, S-Trte (2-
hydroxyphenyl) - triazine, 6,13 -dlchbro-3,10-diphenyltriaphenodbxa7ine.
5. Tta formulation as claimed in claim 1 wherein said bonding agtnt is an
organosilane or methacrylate such as A-174 (r-methacryloxy propyi
trlmethoxysHane, z- 6030 and Dynasyian Memo (3-trimethoxy silytpropyi
mtthacrylate.
6. The formulation as claimed in claim l,wherein said bonding agent is an
organosilane.
7. The formulation as claimed in clam 1 wherein said antioxidants are selected
from compounds such as UV absorbers, such as Phenyl, salkyiate
Resorcinol monobenzoate, 24lydroxy-4-fnethoxybenzophtnone, 2,2r-Dihydroxy-
4-methoxy-benzophenone, 2-(2-hydroxyphenyl)-benzotriazole, 1, 3, 5-Tris-(2-
hydroxyphenyI)-triaz(06,6,13-dichlof0-3,10-diphenyltriaphenodioxazfne, N^phenyl-
p-oaphthylamine, 4,4'-Dioctyldiphtnylamine, N,N'- Diphtnyl-p-
phenylenediamine^N^N'-D-p-naphthyl-p-phGnylenediamine.


A formulation for encapsulation of photovoltaic (PV) modules comprising
Ethylene vinyl acetate (EVA), a cross linker, an UV stabilizer, a bonding agent
and an antioxidant such as herein described, said cross linker being present in 1
to 2 parts by weight based on 100 parts by weight of EVA, said UV stabilizer
being present in 0.1 to 0.3 parts by weight based on 100 parts by weight of EVA,
said bonding agent being present in a proportion of 0.25 to 1.0 parts by weight
based on 100 parts by weight of EVA and said antioxidant is present in 0.1 to
0.3 parts by weight, based on 100 parts by weight of EVA.

Documents:

00256-kol-2005-claims-1.1.pdf

00256-kol-2005-claims.pdf

00256-kol-2005-correspondence-1.1.pdf

00256-kol-2005-correspondence-1.2.pdf

00256-kol-2005-correspondence.pdf

00256-kol-2005-description(complete)-1.1.pdf

00256-kol-2005-description(complete).pdf

00256-kol-2005-description(provisional).pdf

00256-kol-2005-drawings-1.1.pdf

00256-kol-2005-drawings.pdf

00256-kol-2005-form-1.pdf

00256-kol-2005-form-18.pdf

00256-kol-2005-form-2-1.1.pdf

00256-kol-2005-form-2-1.2.pdf

00256-kol-2005-form-2.pdf

00256-kol-2005-form-3.pdf

00256-kol-2005-form-5.pdf

256-KOL-2005-FORM-27-1.1.pdf

256-KOL-2005-FORM-27.pdf

256-kol-2005-granted-abstract.pdf

256-kol-2005-granted-claims.pdf

256-kol-2005-granted-correspondence.pdf

256-kol-2005-granted-description (complete).pdf

256-kol-2005-granted-drawings.pdf

256-kol-2005-granted-examination report.pdf

256-kol-2005-granted-form 1.pdf

256-kol-2005-granted-form 18.pdf

256-kol-2005-granted-form 2.pdf

256-kol-2005-granted-form 3.pdf

256-kol-2005-granted-form 5.pdf

256-kol-2005-granted-gpa.pdf

256-kol-2005-granted-reply to examination report.pdf

256-kol-2005-granted-specification.pdf


Patent Number 238373
Indian Patent Application Number 256/KOL/2005
PG Journal Number 06/2010
Publication Date 05-Feb-2010
Grant Date 03-Feb-2010
Date of Filing 31-Mar-2005
Name of Patentee BHARAT HEAVY ELECTRICALS LIMITED
Applicant Address REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJBLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA
Inventors:
# Inventor's Name Inventor's Address
1 S.BHATTACHARYA BHEL-ASSCP,C/O-BHEL HOUSE,SIRI FORT,NEW DELHI-110049
2 B.PRASAD BHEL-ASSCP, C/O BHEL HOUSE, SIRI FORT, NEW DELHI-110049
3 S. BHATTACHARYA BHEL-ASSCP,C/O-BHEL HOUSE,SIRI FORT,NEW DELHI-110049
4 S R REDDY BHEL-ASSCP,C/O-BHEL HOUSE,SIRI FORT,NEW DELHI-110049
5 NAGENDER SINGH BHEL-ASSCP,C/O-BHEL HOUSE,SIRI FORT,NEW DELHI-110049
6 DR.VEENA CHOUDHARY CENTER FOR POLYMER SCIENCE&ENGINEERING,IIT DELHI,HAUZ KHAS,NEW DELHI-110016
PCT International Classification Number C08K 5/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA