bifacial BIPV: challenges for glass and encapsulation

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

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