The document discusses challenges for glass and encapsulation in bifacial BIPV modules. It notes that bifacial modules require double glass laminates for the rear-facing solar cells. Thin float glass alone may not meet regulations for facade/roof glazing due to limited strength as laminated glass. Safety performance of common PV encapsulants like EVA and TPO are insufficient for laminated safety glass standards, while PVB, ionomer and TPU encapsulants can meet these standards, especially when combined with heat-strengthened or tempered glass. Future BIPV market development may focus on glass and encapsulant materials that best fulfill glazing safety and security performance requirements.

1. Bifacial BIPV
Challenges for glass and
encapsulation
Bernd Koll/ Kuraray Europe GmbH
Bifi PV Workshop, Chambery May 26/27, 2014

2. Content
5/27/2014 2
BIPV basics
Challenges for BIPV module glass
Challenges for BIPV module encapsulation
Glass and encapsulants for laminated PV safety glass
Summary

3. Which will be the preferred (bifacial ) PV solar panel in
about 25 years from now?
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Version A „Standard size“
OR
Version B „Custom Size/BIPV“

4. 5/27/2014 4
BIPV basics

5. Building Integrated Photovoltaic (BIPV)
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6. Why BIPV – now?
Transition from niche to mass market
 Changing economic drivers
 Establishing new PV supply chain
 New also bifacial cell concepts
 New PV products/solutions
 Significant cost reductions
 Multiple product benefits
 Growing awareness
 Proven test/case studies
5/27/2014 6

7.  New design/aesthetics and
architectural solutions
 Higher functionality of glazing
beside safety, security, sound,
shading...
 Large building area with PV =
excellent energy balance
(cost saving)
 PV module has function of
„electrical power producing
glass pane“
Building Integrated Photovoltaic benefits

8. Integration of BIPV in building process
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Synergy between Glass and PV industry
=> Team-up of PV company with supplier of glazing building
products
Glass production
Glass processing
Static engineering
Building standards
and codes
Cell production
Standard module
production
Long term module
reliability
IEC certification

9. 5/27/2014 9
Challenges for BIPV module glass

10. PV glass developments for standard PV modules
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 Current PV cover/back glass standard is 3.2 mm
low-iron tempered or heat strengthened
 Target : panel with 2x 2mm glass based has similar
mechanical strength than panel with 2x 3 mm glass
 AR coated front glass improves module efficiency
 Better performance of G/G modules in extreme
(desert or tropical) climate
 Tempering or heat strengthening of 2 mm glass
improves mechanical performance and minimises
deflection by static/dynamic load
 G/G panels have much better fire resistance
 Thin and stable G/G panels can be also frameless
 But: 2 mm ultra clear glass is not cheaper than 3 or
4 mm glass and not easy in glass processing

11. Glass for architectural glazings
 Standard architectural glass thickness is from 4 mm
up to 25 mm float/annealed glass
 In some cases also 3 mm float glass is used (double
or triple Insulating Glass Units)
 Standard clear glass is preferred, but also low iron
glass is used (~ 1/3 of glass consumption)
 Tempered (TG) or heat strengthened (HSG) glass
improves glazing stability
 Laminated glass consists of minimum 2 x 3 mm
float glass and 0.38 mm interlayer
 Laminated glass has to fulfil several (EU) safety
glazing norms, regulations and building codes
 G/G solar panels are generally not regulated
according to EU glazing standards and need
therefore (national) building products approval
5/27/2014 11

12. 5/27/2014 12
Challenges for BIPV module encapsulation

13. PV module encapsulant properties
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 Mechanical protection (by adapted
module component adhesion)
 Optical coupling of glass/front sheet
to solar cell
 Physical protection (weathering-
induced, environmental damage)
 Electrical insulation
 No corrosion/PID of module
components (Long-term reliability)
 Low thermal conductivity
 Control, reduce or eliminate moisture
ingress

14. 5/27/2014 14
Encapsulant materials
Thermoplastics
(not cross-linkable)
Elastomers/Thermoset
(cross-linkable)
Polyvinyl butyral (PVB)
Thermoplastic
Polyurethane (TPU)
Ionomer
Modified Poly-Olefines
(TPO, EPDM...)
Ethylen Vinyl Acetate
(EVA)
Polyurethane cast resins
(TPU)
Polyacrylate cast resins
Silicones (2K)

15. (Bifacial) module encapsulants
 Encapsulant film market is dominated by
(thermoset) EVA film, global market share > 90%
 EVA is partly replaced by Thermoplastic Polyolefin
TPO (reasons: price, PID and corrosion resistance )
 Both EVA and TPO are used for solar panel mass
production (standard 60 or 72 cells module)
 Other encapsulants are Polysilicone, Ionomer and
PVB which are used mainly for niche application
(also for BIPV)
 Encapsulant type use beside material costs is
influenced by module production size, throughput,
standard module size and lamination tools
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16. 5/27/2014 16
Glass and encapsulants for laminated PV safety glass

17. Laminated modules for BIPV roof application
 Have to be laminated safety glass
with high performance
 Reason: no splinter loss in case of
destruction
 Also high post-breakage behaviour
(public traffic areas)
 Regulated in international building
codes and safety regulations
 Static load stable (e.g. snow load)
 Safety requirements regulated by
ball drop test acc. to standards EN
12543-4 and DIN 52338
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18. Minimum requirement for laminated (BIPV) safety glass
 Ball drop test with 1 kg steel ball according to EN
12543-4 and DIN 52338
 Minimum LSG glass/encapsulant make-up:
2 x 3 mm float and 0.4 mm film
 Falling height is 4.0 m
 Test at room temperature (23°C)
 Test is passed, if steel ball does not fall through
the glass samples (3 test pieces)
 Test fulfilled with the encapsulants: PVB,
Ionomer, TPU
 Test not fulfilled with the encapsulants: EVA,
Polyolefines TPO, Silicones, cast resins
 Conclusion: main PV module encapsulants like
EVA and TPO have low safety performance
5/27/2014 18
Above test passed, below not passed

19. Fall preventing glazing
 Have to consist of laminated
safety glass (LSG with PVB
interlayer)
 Reason: no glass splinter loss in
case of destruction
 High residual strength
 Mandatory near to public traffic
way
 Germany: Technical Rule for fall
preventing glazing (TRAV, valid
since 2003)
 Safety requirements according
to pendulum impact test acc. to
standard EN 12600 (class 1B1)
BIPV module for facade elements

20. Pendulum impact test standard EN 12600
 Twin tyre 50 kg
 Testing (laminated) glass size 896 x 1938 mm
 Test with 3 falling heights:
- Class 1B1 1200 mm (100 % impact energy)
- Class 2B2 450 mm ( 40 % impact energy)
- Class 3B3 190 mm ( 15 % impact energy)
 Determination of minimum glass thickness at first with
laminates made of float glass
 Class 1B1 safely reached with PVB and make-up 33.2 and
44.2 (2 = 0.76 mm PVB)
 TG and HSG offer more reserve to pass the requested
safety class compared to float glass of same thickness
 Glass lower than 3 mm is currently not regulated to EU
building regulations/codes, same as LSG made of float
glass or HSG/TG (HSG= heat strengthened glass, TG =
tempered glass)
5/27/2014 20

21. Pendulum impact test results EN 12600
LSG with 2x2 mm HSG or 2x3 float/0.9-1.0 mm film
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Film type HSG 2 mm float HSG 2 mm cast float 3 mm
EVA
(Architectural)
2B2 2B2 2B2
EVA (Solar) 2B2 2B2 2B2
Polyolefine TPO 1 1B1*narrow 2B2 2B2
Polyolefine TPO 2 1B1*narrow 1B1*narrow 2B2
Ionomer 1B1 1B1 1B1
Silicone 2B2 2B2 2B2
Polyurethane TPU 1B1 1B1 1B1
PVB 1B1 1B1 1B1

22. Pendulum impact test comparison PVB/EVA
LSG made of 2 x 3 mm float glass, class 1B1 (1200 mm)
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PVB 1.00 mm, 1B1 passed EVA 0.95 mm, 1B1 not passed

23. BIPV Insulating Glass Unit (IGU) with bifacial cells
 Integration of bifacial solar panel in double
or triple IGU unit possible
 bifacial panel is inner pane for higher
module efficiency
 can be combined with different features
like:
 coated glass for heat absorption
 colours/printing for window design
 acoustic interlayer (preferred PVB) for
sound damping
 specific safety or security properties by
improved glass/interlayer combinations for
both facade and roof glazings
5/27/2014 23

24. Buildings account for almost half of global CO2 emission. Yet there is
enough building surface to generate all our electricity needs
 Still in infancy – less than 2% PV market share
 Globally installed BIPV modules 2013: ~400 MW
 Higher value/margins worth $5 bn in 2016
Constrained by:
 Varying module certification and building standards
 Different installation skills/processes
 Lack of suitable products/supply chain
 No mass production/custom size
 New cell concepts like bifacial need 2 glass panes
 Facade and roof glazing PV elements require valid
safety & security standards safely fulfilled by PVB,
Ionomer and TPU encapsulant combined with
float/heat strengthened/tempered glass
5/27/2014 24
BIPV market as a chance for high performance encapsulants

25. 5/27/2014 25
Summary

26. Challenges for Bifacial BIPV glass/encapsulants
 Bifacial PV modules need double glass laminates
 Thin (< 3mm) float glass is limited to be used in
facade/roof glazing due to non regulation and
limited laminated glass strength
 Extra clear thin glass still is more expensive than
thicker glass, capacity still limited
 Chances for thin glass laminates in IGU glazing due
to high transparency and low weight
 Safety performance of PV encapsulants is not
unique with thin glass elements in LSG norms
 PVB, Ionomer and TPU outperform other encap
materials which are used in PV panel mass
production
 Future BIPV market will focus on glass and
encapsulants which have best glazing standard
performance
5/27/2014 26

27. Thank you for your kind attention!
Your questions,please!
Photo: „The brain“ with courtesy of Ertex Solar, Austria5/27/2014 27