Post on 12-Jul-2020
Adhesives in Photovoltaics
Dr. Hartmut Henneken Berlin, 23.11.2011
Scale-up Issues towards a 20 MW (250 m Rotor Blade Dimension) Wind Turbine…
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Photo from www.rechargenews.com
To compare dimensions: 20MW PV plant near Cagliari
Picture taken at ECN, Petten, NL
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Independent specialist for adhesive bonding technologies
headquarted in Switzerland (Sempach-Station).
Worldwide, the Group employs 328 persons at several
locations in Switzerland, Germany, France, and the
USA.
nolax belongs to the Collano Group
History and Key Figures
1947 Dr. Marcel Ebnöther establishes the adhesive company
Ebnöther AG in Olten/Switzerland
1997 50th anniversary, name change from Ebnöther AG to
Collano Ebnöther AG (and 2001 to Collano AG)
2008 Incorporation of the group companies:
nolax AG, Collano Adhesives AG, Collano Services AG
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
nolax Core Competencies R&D
Services
Adhesive evaluation
System development
Adhesive development
Technologies
Reactive systems
Hotmelts
Adhesive films
Water-based systems
The Collano group and especially nolax is involved in several commercial and research projects in the field of photovoltaics.
Adhesives Used in Photovoltaics
• Encapsulants Protection of solar cells from environment and
adhesive binding of all module components
• Framing adhesives Edge sealing of PV modules; connecting the module
with the frame
• Junction box adhesives Adhere the junction box to the module
• Back sheets Connecting different layers to each other
• Other (e.g. conductive adhesives, adhesives to connect
wiring, labels,…)
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
In this presentation, the encapsulants will be covered in detail.
Encapsulants…
• …are adhesives, that are playing an
important role in the PV module setup.
• … are connecting all interfaces of the
PV module to each other and have to
maintain good optical, mechanical and
electrical performance over decades of
operation.
• … are a key player in the lamination
process, which is besides the solar cell
production, significantly influencing
the final cost of the module.
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
J-Box
Frontsheet
Encapsulant
Backsheet
PV-film
Encapsulant
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Known Encapsulant Types
• Ethylene vinyl acetate copolymer (EVA)
• Siloxanes (PDMS)
• Plasticized polyvinyl butyral (PVB)
• Polyethylene ionomers
• Thermoplastic Polyolefins (TPO)
• Thermoplastic polyurethanes (TPU)
• UV curable high vinyl acetate containing EVA (EVM)
… other thermoplastic blockcopolymers
Encapsulant Structures
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
R
n m
n m
O ONa, Zn
RN O
O
H
n
n m
OO
O O OH
O
n m o
O
SiO
CH3
CH3
n
SiO
H3C
H3C
n
RN O
O
H
Si
CH3
H3C
m
EVA
TPO
Ionomers
PDMS TPU
PVB
… or combinations, e.g. PDMS and TPU blockcopolymers
Production of Thermoplastic Encapsulant
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Cast extrusion of encapsulants at nolax (Collano Services GmbH)in Buxtehude/ Germany
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
EVA Encapsulant
• The dominant encapsulant for c-Si PV today
• More than 25 years in the field, lots of reliability
data available
• Copolymer of ethylene and vinyl acetate (VA) with a
VA content of about 33 % by weight
• High VA content guarantees a greater than 90% light
transmission to the solar cells
• Must be cross-linked to seal the cells and prevent
flow/creep
• Issues with EVA degradation: generate acetic acid,
yellowing in the dark, residual peroxides decompose
into volatiles
PhenolicPhosphonite (0.1% to 0.2%)
Peroxide Decomposer/ Radical Scavenger
Encapsulant Example Formulation In general PV encapsulants are highly formulated
variations of the base resin. An example EVA
formulation for PV was published as followed (EVA
base resin, 96% to 98%):
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Photovoltaics International (9th Edition; August 2010; page 172)
Peroxide(1% to 2%) Crosslinker Benzoltriazole
(0.2% to 0.35%) UV Absorber
Hindered Amine Light Stabilizer (HALS) (0.1% to 0.2%)
Decomposes Peroxide Radicals
Trialkoxy Silane (0.2% to 1%)
Adhesion Promoter
Thermoset against Thermoplastic
Thermoplastic encapsulants:
• Potential to decrease cycle times
• Roll-to-Roll lamination possible
• Better reprocessing (e.g. for repairs)
• Easier to recycle
• Require higher process temperatures
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Thermoset encapsulants:
• Additional process time for curing
• No danger of creeping
• Lower process viscosity possible
• Shelf life restrictions
Thermoset against Thermoplastic
• Generally, most resins could be prepared as thermoset
or thermoplastic formulations.
• Thermoplastic materials are better for R2R processes,
as junction boxes and connectors could be assembled
and reprocessed offline.
• Though thermoplastics do not need curing time, they
still need to melt, which can take some time,
depending on laminator setup and layer thicknesses.
• UV-curable resins are also available, they behave as
a thermoplastic during lamination and could be cured
in a second step.
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Requirements for Encapsulation
• Weatherability (UV, heat, moisture resistant)
• High transparency (over module life time)
• UV-stability, low yellowing
• Good adhesion (with all components)
• Barrier properties (water vapour, oxygen)
• Electric insulation
• Flexibility, no brittleness
• No creeping
• Cost efficiency, availability
• Low shrinkage
• Fit process
• Recyclability
• Flame retardant properties (e.g. for BIPV)
…
Water Ingress due to Diffusivity Rates into Different Encapsulants
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
M.D.Kempe, NREL, «Review of Polymer Use in Photovoltaics», Plastics in PV Conference, Philadelphia, USA, 20/09/2011
WVTR of some used frontsheet materials are relative high, NO barrier effect:
• ETFE 100 µm = 4 g m-2 d-1
• EVA 500 µm = 20 g m-2 d-1
Short term HF cycling (20 times IEC requirements ) shows that a-Si technology is very resistant to heat and moisture.
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Heat and Moisture Resistance
IEC Norm 10 cycles Humidity freeze
-40°C to 85°C, 85% Rh
Courtesy: Flexcell
Heat and Moisture Resistance
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Very long term HF cycling (> 100 x times IEC requirements !) shows a gradual power degradation due to mainly 3 phenomena:
Humidity freeze -40°C to 85°C, 85% Rh
Al corrosion from CH3COOH formation: it starts early but little affects the performance
Hydrolysis of PEN and cracking: only at very long exposure time (better than PET)
ITO discoloring and degradation
Courtesy: Flexcell
Transmission
to cells through 3.18 mm glass and 0.45 mm encapsulant
PDMS #1 94.8 ± 0.3%
PDMS #2 94.8 ± 0.3%
PVB 94.3 ± 0.4%
EVA 94.3 ± 0.4%
TPU 93.8 ± 0.3%
Ionomer#1 92.7 ± 0.4%
PDMS #3 92.1 ± 0.3%
Ionomer#2 88.7 ± 0.4%
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
M.D.Kempe, PVSC 37, Seattle, Washington, June 19-24, 2011
UV Stability
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
M.D.Kempe, NREL, «Review of Polymer Use in Photovoltaics», Plastics in PV Conference, Philadelphia, USA, 20/09/2011
Shrinkage
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
This example shows an ETFE/encapsulant/ETFE setup after vacuum lamination, but even these materials could be used to laminate wrinkle less modules by using appropriate laminator settings, even without applying vacuum.
Not only encapsulants, but also polymeric frontsheets, as well as backsheets can show significant shrinking.
No best Encapsulant for all Type of Modules
• Until 1995 PV modules had a more or less similar
setup
• Nowadays different types of solar cells are used or
developed, such as e.g. CIGS, CdTe, DSC, organic
solar cells,…
• There are many new back sheets available
• As front sheets not only glass but also polymers such
as ETFE, PVDF and PMMA are used
the interfaces that need to be connected/sealed have significantly increased
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Example: Back Sheet Types and Suppliers
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
2010: 17 suppliers offered 100 different back sheets; 2011: 22 suppliers offered already 112 types…
Source: K.Brust, Krempel GmbH, 5th SNEC, Shanghai, 2/2011; based on market survey Photon International 9/1010
Development of Solar Cell Technologies
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Source: Wikipedia «solar cells», scheme provided by NREL
Encapsulants Should be Selected According to the Specific Module Setup • CIGS cells are much more sensitive to moisture than c-Si
• C-Si wafers are much more sensitive to mechanical stress than
flexible amorphous Si cells
• Not every encapsulant is suitable for every front- or
backsheet (in terms of adhesion or process requirements)
• For R2R lamination thermoplastic encapsulants are better
suited, liquid 2-component systems are in this case difficult
to handle
• Maximum or minimum process temperatures and/or pressure
requirements must fit for all components
• Some materials are more tacky than others, which can be a
disadvantage, but sometimes also improving the handling
• Some encapsulants require vaccum lamination due to bubble
forming, other ones could be laminated at standard pressure
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
There Cannot be a Single Encapsulant for all Type of Modules
Just from the point of view of adhesion it is very
unlikely that one type of encapsulant is the best choice
(or even working) with every material combination.
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
1. Frame 2. Junction box 3. Connectors and PV wire 4. Backsheet 5. Back encapsulant 6. Solar cell 7. Front encapsulant 8. Front sheet 9. Glass
Source: SBM Solar
Organic solar module ©Fraunhofer ISE
Adhesive Testing
• Very small changes in formulation can have large
effects on adhesive performance.
• The same applies for changes in surface chemistry of
the substrates.
• It is very difficult to predict adhesion in detail,
usually it is necessary to do intensive testing.
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Adhesive Screening Example
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
This graph shows a part of a large adhesive screening of base resins (different types/ grades/formulations) laminated on PVDF front sheet film. Generally more polar formulations perform better, but even within one resin, there are very good as well as very bad results found!
Adhesive Strength
• There is no official standard available yet, that describes what adhesive strength would be required for any of the interfaces!
• Some manufacturers use values in the range of 5-10 N/mm peel strength, others are working with 1 N/mm…
• Important is that no delamination occurs during module lifetime, as in this case e.g. humidity could accumulate in cavities and induce rapid corrosion.
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Module Lifetime (1)
Solar panels should have a guaranteed performance of 20-
30 years, but manufacturers are facing difficulties
to do it. It is hardly possible to predict the real
effects of outdoor exposure on modern at high
efficiencies operating modules by doing indoor
exposure or ageing test.
There are a lot of standard test procedures that need to
be passed in order to get a certified module, but a
discussion would be to much for this presentation.
Tests include Heat-Freeze Cycles, Damp-Heat Tests, Hail
Testing, Flash Tests, Thermal aging tests,…
…
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Module Lifetime (2)
Even though it is a wishful thinking that modules still deliver 80% or more power after 25 years, it is in my opinion maybe not really necessary: Research progress and costs might be reasons that people would like to replace even working modules after 15 years with modern types…
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
www.pvgum.eu
nolax is Taking Part in the EU-Projekt PV-GUM
Bitumen: > 50% of all flat roofs in Europe
Goal:
• 10m x 1.2m bituminous PV membrane
• Production by Roll-to-roll process
EU FP-7 cost shared project:
• 01.11.2010 – 31.10.2013
• Consortium: 9 partners
• Total budget 11 M€, EU subsidy 6.2 M€
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
nolax is Taking Part in the EU-Projekt PV-GUM
www.pvgum.eu
R2R Lamination of Flexible Solar Cells
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
The main scope of the PV-GUM project is to
fully integrate flexible thin film PV
modules in the bitumen-based roofing
membrane. A roll-to-roll process and new
equipment is being developed to encapsulate
the solar cell directly on the roofing
membrane.
During this project e.g. Meyer Machines GmbH
had build a prototype vacuum laminator that
is capable to do R2R laminations (no
pictures shown, the photograph shows the R2R
lamination using a non-vacuum setup) and
nolax has gained a lot of experience in
continuous and batch lamination.
Production and application
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Adhesion Testing for Batch and Roll Lamination
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
T2 = T1 + 20°C; HS (High speed) = 6x LS (Low Speed); “+O”: add. heating without pressure WI: Water Immersion at 80°C ST: Special surface treatment of ETFE (standard is the commercially available (also surface treated) material)
Conclusions
• Adhesives are used in many parts of solar modules
• Encapsulation is one of the key adhesive applications
• Many different encapsulants are nowadays available
• Different modules and lamination procedures might require different encapsulants the formerly exclusively used EVA could be NOT suitable in some cases
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
www.nolax.com |Adhesives in Photovoltaics | Berlin 23.11.2011
Thank you for your attention.