Review on window-glazing technologies and future prospects

Abstract

Windows are one of the significant indicators of the energy efficiency of a building and have undergone extensive research since the last decades. This paper reviews the performance of various window technologies covering the physical and optical properties of traditional windows and advanced window technologies. In window technologies, one of the most critical parameters is its thermal transmittance value or also known as U-value. In this paper, we discuss the relationship between the physical and optical parameters of the different types of windows and its U-value. Additionally, this paper will also provide interested readers with a wide range of information, including the research gaps in window technologies. Among the main conclusions, we found that, although several advancements have been achieved in this field in the last decade, further research is needed to develop window technologies that not only have high insulating properties but also can generate power.

Full text

†Jorge Luis Aguilar-Santana, http://orcid.org/0000-0002-2507-7085
International Journal of Low-Carbon Technologies 2020, 15, 112–120
© The Author(s) 2019. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which
permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1093/ijlct/ctz032 Advance Access publication 5 December 2019 112
Review on window-glazing technologies and
future prospects
..............................................................................................................................................................
Jorge Luis Aguilar-Santana*,†, Hasila Jarimi, Mariana Velasco-Carrasco and Saa Riat
Department of Architecture and Built Environment, University of Nottingham, University
Park, Nottingham NG7 2RD, UK
............................................................................................................................................
Abstract
Windows are one of the signicant indicators of the energy eciency of a building and have undergone
extensive research since the last decades. This paper reviews the performance of various window technologies
covering the physical and optical properties of traditional windows and advanced window technologies. In
window technologies, one of the most critical parameters is its thermal transmittance value or also known
as U-value. In this paper, we discuss the relationship between the physical and optical parameters of the
dierent types of windows and its U-value. Additionally, this paper will also provide interested readers
with a wide range of information, including the research gaps in window technologies. Among the main
conclusions,wefoundthat,althoughseveraladvancementshavebeenachievedinthiseldinthelastdecade,
further research is needed to develop window technologies that not only have high insulating properties but
also can generate power.
Keywords: glazing technologies; vacuum glazing; U-value; optical properties
∗Corresponding author:
jorge.aguilarsantana
@nottingham.ac.uk Received 4 January 2019; revised 3 May 2019; editorial decision 9 May 2019; accepted 9 May 2019
................................................................................................................................................................................
1. INTRODUCTION
Energy consumption of buildings accounts for around 20–40%
of both commercial and residential sectors, impacting at least
on 30% of the global CO2accounted to developed countries
[1]. This is the result of the growth of energy use in emerging
economies related directly to the annual population expansion
estimated at 1.18% [2]. Achieving thermal comfort has proven to
be a complicated endeavour for locations with extreme climate
conditions, specially the electric load consumed in appliances to
maintain thermal comfort (Heating, Ventilation and Air Condi-
tioning (HVAC) systems).
This paper reviews the recent advancements in window tech-
nologies that can be categorised into static and dynamic windows.
Static windows (also considered as traditional) include passive
technologies that can improve heat and optical window perfor-
mance such as tinted glazing [3], low-E glazing [4], self-cleaning
glazing [5], anti-reective glass [6] and insulated glass [7]. Mean-
while,dynamicoractivewindowsincludetechnologiesthatutilise
internal interaction of materials to adapt or change to external
conditions; these include electrochromic glazing [8], photovoltaic
glazing [9][10], thermochromic glazing [11], gasochromic glaz-
ing [12] and liquid crystal glazing [13].
2. OPTICAL AND THERMAL PERFORMANCE
The important roles of windows in buildings are that, they provide
ventilation, daylighting, solar heat gain and aesthetics. In general,
the thermal and optical properties of a window can be presented
in terms of the following key parameters: U-value, Solar Heat
Gain Coecient (SHGC) and visible transmittance. The evalu-
ation the aforementioned parameters are governed by the three
well-known heat transfer mechanisms: conduction, convection
and radiation. In this section, we will discuss the key parameters
in detail.
2.1. U-value
Also known as the total heat transfer coecient or total thermal
transmittance, the U-value of a window is used to measure its
eectiveness as an insulator. Measured in W/m2K, the U-value
is evaluated based on the air to air heat transfer through the
window components (i.e. glazing, frame, the gap between the glass
panes (if any) and spacers) from or into the building based on
the ambient temperature dierence. As can be seen in Ta b le 1,
the incorporation of highly ecient windows to reduce the total
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A comprehensive state of the art analysis
Tab le 1. Average U-values in building components. Adapted from [14].
Element U-value (W/m2K)
Floor 0.25
Roof 0.16
External wall 0.30
Windows 2. 00
Tab le 2. Typical U-values on dierent glazing types [16](Lolli&Ander-
sen, 2016).
Glass conguration U-value (W/m2K)
Uncoated single glass 6 mm 5.70
Uncoated double glass 12 mm cavity 2.80
Uncoated double glass 15 mm air cavity 1.40
Uncoated double glass 15 mm argon cavity 1.20
Uncoated triple glass 16 mm with argon 0.79
Uncoated double glass 22 mm monolithic aerogel 0.65
Uncoated double glass 33 mm granular aerogel 0.44
Figure 1. Heat transfer through double-glazing windows.
U-value of a building’s fabric will certainly improve the building’s
energy performance and occupants’ comfort [15].
Theheattransferthroughthewindowismainlyduetotheheat
conduction through the glass panes. Therefore, as summarised in
Table 2 , dierent conguration of glass panes (i.e. single-, double-,
or triple-glazed window), with and without low-emissivity coat-
ing, and with or without additional insulating materials between
the glass panes, results in dierent U-values. Other than the
glass panes, additional heat can also be conducted through the
window’s spacers and the frames. On the other hand, convection
and radiation occur specically in three places in multi-pane
windows: the interior and exterior surfaces of windows as well as
the internal cavities between glazing layers, as shown in Figure 1.
2.2. G-value
The SHGC, also described as G-value is the transmittance of
energy as a result of solar radiation; it is determined by the
solar transmittance/energy absorbed by window materials and
reemitted inwards [17]. This factor is used to quantify the solar
shading capabilities of these transparent components to the short-
wave radiation [18], and it is important for reducing the use of
Tab le 3. Overall relation of glazing thickness and heat transfer for Pilking-
ton OptioatTM clear.
Thickness mm U-value (W/m2K) G-value (SHGC) Visible transmittance (Tv)
2.0 5.8 0.89 0.91
4.0 5.8 0.87 0.90
6.0 5.7 0.82 0.88
8.0 5.6 0.80 0.87
10.0 5.6 0.77 0.87
12.0 5.5 0.74 0.85
19.0 5.3 0.66 0.81
heating loads in winter. Typical SHGC values range between 0.2
and 0.7 as presented in Figure 2.
2.3. Visible transmittance
This optical property comprises of the visible portion of the light
spectrum that passes through a given glazing material. It typically
ranges from 90% for clear glazing (see Figure 3) to 10% for highly
reective coated glazing. This factor is determined by the type of
the glazing, the number of panes and the presence of coatings
that can aect transparency [15]. A high visible transmittance
meansmoredaylightpresenceinagivenspaceandusually,a
reduction in electric lighting and heating loads. Typical double-
glazing windows show a visible transmittance of 78% and could
show further reductions if low-E coatings [19]andtintedlms
[20] are included in its composition.
3. STATIC GLAZING TECHNOLOGIES
This section reviews the static or traditional glazing technologies.
In recent years, the research on this type of glazing has been
focusing on enhancing the thermal and optical performances. The
glazing includes soda lime glass, multi-pane windows, laminated
glass, reective coatings, low-E coatings, suspended lms and
vacuum windows.
3.1. Glass thickness
For a single-glazed window, as summarised in Table 3 ,theinu-
ence of the glass thickness to its thermal performance was eval-
uated. A signicant reduction in the U-value of glass panes was
found for glass samples with thicknesses above 12 mm. However,
the reduction in the heat transfer comes with the penalty in the
visible transmittance and the overall weight of the window.
3.2. Multipane glazing
Double-glazed windows have been widely manufactured in the
UK since the last quarter of the 20th century [21]. They can
reduce energy consumption in buildings and improve the material
insulating properties, since the gap between panes is used as a
thermal barrier [22].TheimportanceofAguilar’sstudyliesinthe
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J. Luis et al.
Figure 2. Solar heat gain coecient of single glass for dierent tinting types.
Figure 3. Visible transmittance for dierent coatings in double-glazing units.
Figure 4. Glazing components for static windows.
modelling of four dierent congurations of double-glazing panes
on an air gap (using clear, absorbent, low-E and reective glass).
The study established that reective glass could save up to 72.9%
of energy consumption whilst having a median payback period of
8.75 years for hot and dry climates.
An air gap introduced between glass panes would act as the
thermal insulation layer, reducing heat transfer through the win-
dow components [23]. This also represents a 50% reduction in
heat losses when compared to single-glazing [24], with the advan-
tage of maintaining the visible transmittance and G-value at rela-
tively high level [20](seeFigure 4). Moreover, the heat transfer
rate a double-glazed window is 2.5 times lower than a single-
glazed window and hence reducing heat gain by about 50–67%
for warm climates [25].
3.3. Tinted glass
Tinting glazing panes help to retain material transparency from
the internal layer of the window, absorbing a portion of the
solar heat whilst blocking daylight [26]. Glass tinting involves the
addition of metallic components on the glass during the oating
process. This process reduces the window transmittance, visibility
and colour [27], maximising the absorption of solar energy to up
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A comprehensive state of the art analysis
Tab le 4. Tinted glass specications for various colours and thicknesses [27].
Colour Thickness mm U-value
(W/m2K)
G-value
(SHGC)
Visi bl e
transmittance
(Tv)
Bronze 4 5.8 0.68 0.60
6 5.7 0.60 0.49
8 5.6 0.53 0.40
10 5.6 0.48 0.33
Green 4 5.8 0.63 0.79
6 5.7 0.55 0.73
8 5.6 0.50 0.68
10 5.6 0.46 0.63
Grey 4 5.8 0.66 0.55
6 5.7 0.57 0.43
8 5.6 0.50 0.34
10 5.6 0.45 0.26
to 50% for single panes [20] whilst eectively reducing the solar
glare.
This absorption property on the glass can be adjusted to spec-
tral selectivity, meaning that the tinted glass pane can absorb the
near-infrared solar spectrum whilst transmitting solar daylight
only. Tabl e 4 summarises the tinted glass available in the market
based on their colour and thickness with the corresponding level
of transparency, insulation and heat gain coecients [27].
3.4. Low-emissivity coatings
Like a heat mirror, low-emissivity surface reects long infrared
wave. When applied in the internal surface of a window, the
glazing will allow visible light and short infrared to pass through
thewindow.However,itwillreecttheinteriorlongwaveinfrared
(heat energy), returning it back to the internal space. As a result,
the heat transfer between the inside and outside environments
is reduced and the insulating property of the window is
improved.
Low-emissivity (low-E) coated glass is manufactured with a
thin transparent coating made from metal oxide such as tin, silver
or zinc to reduce the emissivity of glass surfaces [28]. The man-
ufacturing of low-E coatings includes the sputtered and pyrolytic
methods [20]; the rst method includes the multi-layered coatings
of either metal (usually silver), oxide or nitrides deposited by
physical vapour sputtering, most commonly known as ‘so-coat
low-E’. Meanwhile, the pyrolytic technology includes tin-oxide
lmbondedtotheglassatthemoltenstate,inaprocesscalled
chemical molten deposition or ‘hard-coat low-E’ that results in
thicker coatings than the so-coat low-E.
Hard-coat low-E has reported savings of up to 13–17% com-
pared to so-coat low-E (8–10% respectively) and overall energy
savings for both heating and cooling loads as reported on as study
of Canadian dwellings [29]. Derived from the previous research,
the consideration of a hard-coat low-E solution would result in
improved performance for its utilisation in UK dwellings.
Similar to tinted glass, low-E coatings can be tailored to spe-
cicenergyspectrumsandwavelengthsinordertooptimisethe
Figure 5. Heat transfer, SHGC and visible transmittance adapted from Cardinal®
glass models.
cooling, heating and daylighting performance. A disadvantage
presented by low-E coatings [30] is that they can reduce the
solar heat gain to compensate any existent heating loads [31].
Nevertheless, the benecial reduction of glare and solar control
set these coatings as an option for emittance optimisation and
radiation control, as summarised in Figure 5.
3.5. Anti-reective coatings
A modern technique to increase daylight transmittance uses anti-
reective coatings, which can increase the visible transmittance
up to 15% (from 0.74 to 0.89) in double pane windows. Low-E
coating using SnO2, demonstrating no impact in the overall U-
value factor and increasing the G-value by 7%. The use of this
technology helped to decrease the annual heating demand by 4%
[32]; a summary of the technical data presented on manufactured
products by IQ glass is illustrated in Tab l e 5 (IQ [33]).
3.6. Self-cleaning coatings
The eld of self-cleaning coatings uses the action of water as a
labour-saving method for the cleaning for glazing elements, and
it has been a technique used especially for those windows that
include a power generating solution, as photovoltaic panels.
Commercially self-cleaning coatings are constrained into two
main categories: hydrophobic and hydrophilic (as described in
Figure 6). In hydrophobic coatings, water droplets tend to roll
on the glass surface due to a high-static contact angle between
the surface and the water; this is achieved by means of moulded
polymers [34], waxes and chemical vapour deposition (CVD)
[35]. Meanwhile, hydrophilic coatings includes a thin transparent
layer of titanium dioxide (TiO2) to generate a static contact angle
of less than 90◦between the glass material and the water, which
chemically breaks down glazing dirt when exposed to light; this
behaviouronmaterialsisknownas‘photocatalysisprocess’[36]
[37].
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J. Luis et al.
Tab le 5. Anti-reectivewindowscurrentlyinthemarket,comparisonofopticalandthermalproperties.
Name Technology U-value (W/m2K) G-value (SHGC) Visible transmittance (Tv)
IQ anti-reective single glass SG/anti-reective low iron glass 5.80 0.90 0.98
IQ anti-reective double glass DG/anti-reective low iron glass/Ar-lled cavity/low-E coating 1.20 0.64 0.85
IQ anti-reective double glass DG/anti-reective low iron glass/Ar-lled cavity/solar control 1.20 0.48 0.85
Tab le 6. Triple-glazing heat transfer solar coecient and transmittance comparison for noble gas cavity llings.
Manufacturer Product U-value (W/m2K) Visible transm. (Tv)G-value (SHGC)
Modelling (Optitherm-Air) 4/12/4/12/4 air 0.90 0.58 0.34
Nippon Sheet Glass®Co. Pilkington 6/12/4/12/4 Ar 90% 0.70 0.73 0.61
Nippon Sheet Glass®Co. Pilkington 6/12/4/12/4 Kr 90% 0.60 0.73 0.61
Modelling (Optitherm-Xenon) 4/12/4/12/4 Xe 90% 0.53 0.58 0.34
Figure 6. Droplet angle comparison for untreated, hydrophobic, specially cleaned
and hydrophilic glass (Midtdal & Jelle, 2013).
3.7. Substitute gases
Awiderangeofgasesisusedforthedouble-glazingindustryto
ll the gap between glazing panes [24]. Noble (inert) gases are
usedextensivelybywindowcompaniesduetotheirresistance
to transmit heat and availability in nature. Xenon gas is the
most ecient of the solutions, but the scarcity of the material
makesitexpensivetomanufacture,whereaskryptongas(Ug-
value of 0.64 W/m2K) has a relatively medium-use due to its
improved performance but a higher price when compared to
argon solutions [14]. For multi-pane gas-insulated windows,
the double- and triple-glazed modules can achieve U-values
from 1.0 to 2.2.W/m2K, and 0.5–0.8 W/m2K, respectively [16],
a comprehensive summary of these technologies can be found
in Table 6 .
Previous experimentation and modelling have proven that
argon-lled solutions could reduce the window conductivity by
67% when compared to air-based mixtures [38]; their odourless
and non-toxic properties have made possible to incorporate
these technologies in residential households in colder regions
[39]. Krypton-based gap llings reduce the overall U-value by
17.18% from argon gaps in theoretical comparisons, although
itshighermanufacturingcosthaspositionedargonasamore
viable option for mass production. Alternatively, xenon gap ll
hasbeentestedasaninsulatingmaterial,reportingthelowest
U-values from them all (estimated at 0.28 W/m2K), although this
element faces a similar future as krypton, having more expen-
sive manufacturing costs than argon or krypton technologies
combined [15].
Multi-layered windows are recently seen as a technology suit-
able for replacing window glazing in historical buildings, where
the actual need for a thin and lightweight solution is required.
They represent an environmentally acceptable, non-degradable
and narrow solution that rarely presents condensation in the
middle gap during its lifecycle [24].
3.8. Vacuum glazing
The use of vacuum glazing is considered a very promising solution
to reduce the heat transfer via air conduction and convection
within the evacuated gap. This is due to the reduction in the
number of gas particles responsible for the heat transfer within
the evacuated gap.
Nowadays, the manufacturing industry is pursuing the devel-
opment of evacuated glazing [40][41]whichcanreportalower
U-value by reducing heat conduction through the support pillars.
Commercially available vacuum windows can achieve U-values as
low as 0.7 W/m2K (as included in Tab l e 7 ).
Heat transfer in vacuum glazing occurs by contact of the
support pillar array and edge sealing by means of conduction
(Figure 7); therefore, methods to include novel materials in these
components are tested in order to reduce these U-values in
windows [42].
Aerogel is a highly insulating material discovered early in the
year 1930 ([43]); it is a silica-based material composed of 4% silica
and96%air.Ithasafoam-likemolecularstructurethatentrapsair,
preventing heat convection existence whilst allowing a high light
transmittance. The use of this material in the window industry
has proven to reduce the heat transfer via conduction, reaching
U-values as low as 0.05 W/m2K[20]inthematerialproperties
solely [44].
4. DYNAMIC GLAZING TECHNOLOGIES
The dynamic window concept comprises module fenestrations
that integrate movable or switchable devices for shading and
energy harvesting (Figure 8). This includes variable optical and
thermal properties that in most cases are climate-dependant.
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A comprehensive state of the art analysis
Tab le 7. Sample comparison of vacuum-glazing windows commercially available (Pilkington-NSG, 2014) (NSG-Group, 2017).
Name Technolog y Thickness mm U-value (W/m2K) G-value (SHGC) Visible transmittance (Tv)
Pilkington SpaciaTM
(double glazing)
VDG with 0.2 mm pillars 6.2 1.4 0.66 0.76
Pilkington SpaciaTM
Shizuka (double g.)
VDG with laminated glass 9.2 1.4 0.61 0.73
Pilkington SpaciaTM
Shizuka Cool (double g.)
VDG with Ar interlayer
single low-E coating
6.2 1.0 0.49 0.7
Pilkington SpaciaTM 21
thermal control (triple g.)
VTGKrinterlayerdouble
low-E coating
18.2 0.9 0.58 0.64
Pilkington SpaciaTM 21
solarcontrol(tripleg.)
VTG Ar interlayer double
low-E coating
18.2 0.7 0.46 0.59
Figure 7. Typical vacuum-glazing components.
Figure 8. Thermochromic colour switching phases [45].
Tab le 8. The summary of electrochromic, photochromic, thermochromic and gasochromic windows.
Type Structure Behaviour U-value (W/m2K) Visible transmittance
(Tv)
G-value (SHGC) Comment
Electrochromic Liquid crystal droplets
in a conductive glass.
Requires constant
energy to maintain clear
state
0.86 [48]ReducesVtinresponse
to electric changes
Uses dynamic control Requires constant
energy to maintain a
clear state
Photochromic Polymeric matrixes Blocks sunlight in
response to the natural
light incidence
5.3–1.58
[Wu, et al., 2017].
Reduces Vt in the
response of Light
increase.
Darkens when exposed
to SHGC higher than
0.78
Blocks sunlight in
response to the natural
light incidence
Thermochromic Uses vanadium dioxide
to change the opacity
Polymer lm [45] - Reduces Vt When
exposed to higher
temperatures
-Polymerlm[45]
Gasochromic Uses Tungsten oxide
WO3in gas
encapsulated molecules
Regulates transparency
in variations to
temperature
- Reduces 5–6% in visible
transmittance [49].
- Regulates transparency
in variations to
temperature
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J. Luis et al.
Figure 9. Diagrams for triple glazing (b), double and triple glazing with PCM (a and c). Adapted from [Li, et al., 2018].
Figure 10. Diagram of c-Si Photovoltaic (PV) window model [Park, et al., 2010].
Some examples of these technologies are electrochromic and pho-
tochromic [Wu, et al., 2017], thermochromic as shown in Figure 8
[45][46], gasochromic, phase change materials and liquid crystal
devices [20][47]. Table 8 summarises the properties and charac-
teristics of some of the dynamic glazing windows.
4.1. PCM windows
Phase change materials [Li, et al., 2018] are substances that can
absorb store and release energy from surrounding materials; their
use in reducing heat transfer in windows plays an important role
as described by its structure included in Figure 9.Recentstudies
show that double-glazing window with PCM llings can help to
reduce solar heat gains in buildings whilst increasing up to 3.0◦C
the temperature on the window interior surface [Li, et al., 2018].
4.2. Building Integrated Photovoltaics (BIPV)
Windows with integrated solar photovoltaic modules face the
challenge of maintaining a high electricity yield, without com-
promising the visible transmittance of glass [50]. Therefore, most
of the novel developments in PV glazing are limited to the semi-
transparent PV cells (as presented in Figure 10). Dye-sensitised
solar cells (DSSC) are conductive glazing materials that include a
TiO2lm that is capable to reach an average energy eciency of
16–20% [51]. Recent technologies on windows are aimed to har-
vest solar energy for electricity conversion, becoming an attractive
option for its lower environmental impact, cost reduction and
eective land use.
Manufacturing energy ecient windows according to local
energy codes require the improvement of U-value factors on all
external glazing units, as well as cost, weight and dimensions.
Finally, a market-based summary on fenestration technologies is
presented in Figure 11,focusingontheU-values based on the
data presented by major international window companies. The
important reduction achieved by substitute gases, electrochromic
and vacuum glazing windows is remarkable and mainly driven
from their eort to reduce the heat transfer by conduction and
radiation in the glazing samples.
5. CONCLUSIONS
This review comprises of a detailed study of commercially avail-
able window products that were assessed based on the window’s
heat transfer, visible transmittance and SHGC. From the literature
review, the following conclusions can be drawn:
•Energy loss through the building envelope is directly linked
to the interaction of exterior surfaces to the environment.
Traditional windows are manufactured with materials of high
heat transfer rate, and their U-values are particularly high in
comparison to other elements (walls, roofs and oors). Present
and future researches are focused on reducing heat transfer
on fenestration elements by the use of static and dynamic
technologies.
•Increasingthewindowpanethicknesshasnoprotableimpact
on reducing the U-valueofwindowsasitmakesthesamples
extremely heavy and bulky. Tinted windows have a similar
inuence on heat transfer, aecting only the visible transmit-
tance and solar heat transfer coecient when used as a stand-
alone solution.
•Window coatings, on the other hand, are eective solutions to
reduce the impact of SHGC in buildings. An example of this
is the use of low-E, anti-reective and self-cleaning coatings,
which can reduce the SHGC factor to 0.48 (for low-E) without
having a signicant repercussion in the glazing transparency.
•Gas-lled cavities can reduce signicantly the U-value of win-
dows (by −22.2% with argon, −33.3% using krypton and
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A comprehensive state of the art analysis
Figure 11. Average U-value comparison according to commercially published reports (IQ [33]) [39].
−41.1 for xenon, respectively), in comparison to air-lled
cavity values (0.62 W/m2K).
•Amongst the compared window technologies, multi-pane
glazing can signicantly reduce the heat transfer on windows
(double, triple and vacuum windows). Nevertheless, vacuum
glazing with 0.7 W/m2K can reduce the U-value by almost 42%
when compared against standard double glazing with argon
lling (1.2 W/m2K). This eectively improves the insulating
characteristics of the nowadays widely used double-glazing
technology.
•Although dynamic windows can provide control on visible
transmittance and heat transfer of windows; manufacturing
processes, material availability and climatic conditions are to
be considered when selecting the most appropriate solution for
each scenario.
•Vacuum glazing provides a high-performance solution to
reduce the heat transfer on windows by eectively reducing the
thermal conduction and convection within the window gap.
Favourable conditions for this technology to be developed in
coming years are predicted from this review.
•Building integrated photovoltaic modules are a promising
and attractive solution to energy harvesting, providing lower
impactsonthewindowlifecycleandincreasingitsoutputyield.
•From the review, we may conclude that vacuum-glazing tech-
nologies with aerogel applications could appear in the market
in the coming years, as stated by Cuce [15] when the challenges
on the materials strength and stability are overcome. Similarly,
the use of semi-transparent crystalline PV modules integrated
into window prototypes may be considered as a method to
achieve net zero carbon buildings for future fenestrations.
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