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Bifacial BIPV
Challenges for glass and
encapsulation
Bernd Koll/ Kuraray Europe GmbH
Bifi PV Workshop, Chambery May 26/27, 2014
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
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“
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BIPV basics
Building Integrated Photovoltaic (BIPV)
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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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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
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
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Challenges for BIPV module glass
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
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 ironglass is used (~ 1/3 of glass consumption)
Tempered (TG) or heat strengthened (HSG) glassimproves 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) safetyglazing norms, regulations and building codes
G/G solar panels are generally not regulatedaccording to EU glazing standards and needtherefore (national) building products approval
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Challenges for BIPV module encapsulation
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
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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)
(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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Glass and encapsulants for laminated PV safety glass
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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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
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
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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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
Pendulum impact test comparison PVB/EVALSG 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
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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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 withfloat/heat strengthened/tempered glass
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BIPV market as a chance for high performance encapsulants
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Summary
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 andlimited laminated glass strength
Extra clear thin glass still is more expensive thanthicker 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 encapmaterials which are used in PV panel massproduction
Future BIPV market will focus on glass andencapsulants which have best glazing standardperformance
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Thank you for your kind attention!
Your questions,please!
Photo: „The brain“ with courtesy of Ertex Solar, Austria5/27/2014 27