Multiple glazing

Abstract

Disclosed is a multiple glazing 100 with at least one glass pane 104, photovoltaic cell 102, and one insulating layer of inert gas 106 which may have a spacer bar full of silica desiccant. It may furt

Description

Field of the disclosure The present disclosure relates to a multiple glazing, and more particularly to a multiple glazing comprising a photovoltaic cell and a multiple glazing comprising vacuum-insulated glass units. Background to the Disclosure One way of improving the energy efficiency of buildings is to improve insulation, so that less heat is lost in winter, and demand for air conditioning is reduced in summer. Many windows are now double glazed, which conventionally refers to the use of two parallel panes of glass in a window, separated by a cavity, which may be generally filled with air or another gas. However, this only improves the insulation to some extent. Further layers of insulation, such as triple insulation, increase the thickness of the window considerably. Vacuum insulated glass is an alternative to conventional double glazing. Vacuum insulated glass refers to the use of two parallel panes of glass in a window, separated by a partial vacuum. Since the partial vacuum reduces convective and conductive heat transfer, these panels provide improved insulation. However, to support the panels against the pressure difference caused by the vacuum, vacuum-insulated glass panels require a plurality of pillars, bridging the gap between the two glass panels, in order to prevent the glass from caving in. Such pillars act as channels for heat transfer through the panels. Additionally, the increased heat transfer through the pillars, compared to the surrounding regions on each glass pane, means that the points where the pillars contact the glass pane are at a different temperature to the surrounding regions. This means that such regions will tend to form condensation on the pane facing a lower temperature area, resulting in circular regions of condensation surrounding each pillar. This is visually unappealing and reduces visibility through the window. Vacuum-insulated glass also has worse acoustic performance, since sound waves can travel through the pillars from one side of the glass to another. The physical contact between the two glass layers can also result in mechanical stresses, especially in the presence of a thermal gradient, which makes the glass vulnerable to breakage. Another way of improving the energy efficiency of buildings is to introduce renewable energy generation into the building. This may be done by introducing solar panels as part of a window. However, windows comprising such panels generally have poorer insulating properties. It is therefore desired to provide an improved multiple glazing. Summary of the Disclosure According to a first aspect of the present disclosure, there is described a multiple glazing, the multiple glazing comprising: at least one transparent layer; at least one photovoltaic cell; and at least one insulating layer comprising an inert gas. Preferably, the transparent layer(s), photovoltaic cell(s) and insulating layer(s) are arranged adjacently in the glazing. Preferably, the transparent layer(s) and photovoltaic cell(s) are attached together, for example as a laminate, and the insulating layer is arranged one on side of the laminate. The combination of an insulating layer comprising an inert gas with a photovoltaic cell allows the multiple glazing to provide benefits both in terms of insulation and in terms of energy generation, while still providing good acoustic insulation and mechanical properties. An inert gas layer also offers uniform internal support, reducing the risk of glass panel deformation or breakage due to external pressure differences, without the need for support pillars typically used in vacuum insulation which can create thermal bridging and reduce overall insulation efficiency. Inert gas also helps to distribute heat more evenly, mitigating thermal stress caused by temperature fluctuations from solar cell operation, which extends the lifespan of both the glass and the cell. Inert gas insulation is also simpler to manufacture and requires lower sealing demands, which reduces production complexity and maintenance costs. In some examples, the multiple glazing further comprises a mirror pane. This improves privacy of the multiple glazing by reducing visibility in one direction through the glazing. Preferably, a reflective surface of the mirror pane faces towards the photovoltaic cell. Advantageously, when the reflective surface faces the photovoltaic cell, this increases efficiency of energy generation by causing rays that have passed through the photovoltaic cell to be incident on the photovoltaic cell a second time, resulting in more sunlight being absorbed by the photovoltaic cell and so more electricity being generated. In some examples, the at least one photovoltaic cell comprises at least one bifacial photovoltaic cell. This allows the photovoltaic cell to generate electricity from light incident on either side, increasing the energy that may be generated from a given surface area of glazing. This is particularly advantageous when used with a mirror pane facing the bifacial photovoltaic cell, because this allows this reflected sunlight to be efficiently converted into electricity. In some examples, the multiple glazing is configured so that when in use in a window of a room, the photovoltaic cell is arranged between an interior of the room and the insulating layer. Positioning the photovoltaic cell in this way allows heat generated by the photovoltaic cell to be emitted into the room, resulting in the photovoltaic cell heating up the room. Advantageously, this means that the multiple glazing may be used to provide heat to a space in cold climates, rather than merely reducing heat loss from the space. Additionally, an indoor temperature may be more stable, so positioning a photovoltaic cell adjacent to an indoor space may ensure that the photovoltaic cell is held at temperatures close to optimal for operational efficiency. In some examples, the multiple glazing is configured so that when in use in a window of a room, the photovoltaic cell is separated from an interior of the room by the insulating layer. Positioning the photovoltaic cell in this way allows heat generated by the photovoltaic cell to be primarily radiated to the environment, as the insulating layer reduces transfer of this heat into the room. This improves performance in hot climates. In some examples, the at least one photovoltaic cell is a plurality of photovoltaic cells. Advantageously, providing a plurality of photovoltaic cells allows light that has passed through a first photovoltaic cell to be incident on a second photovoltaic cell, increasing the total electricity that may be generated for a given surface area by increasing the proportion of light that is converted into electricity. Preferably, the plurality of photovoltaic cells are separated by at least one insulation layer. Advantageously, this further improves both acoustic and thermal insulation provided by the multiple glazing. Preferably, the plurality of photovoltaic cells comprises a first photovoltaic cell with a first band gap, and a second photovoltaic cell with a second band gap, wherein the first band gap is greater than the second band gap, more preferably wherein, when in use in a window of a room, the second photovoltaic cell is arranged further towards to the interior of the room than the first photovoltaic cell. Such a setup allows light with a short wavelength (and therefore higher frequency and energy) to be absorbed by the first photovoltaic cell and converted into electricity at a higher voltage, while light with a longer wavelength (and therefore lower frequency and energy) which is unable to stimulate production of electricity in the first photovoltaic cell passes through and may be converted into electricity at a lower voltage by the second photovoltaic cell. Longer wavelength light may be attenuated less than the shorter wavelength light when passing through the layers of the glazing, so positioning the cell with the higher band gap in front of the cell with the lower band gap may improve efficiency. In some examples, the insulating layer comprises a spacer bar filled with silica desiccant. This prevents buildup of moisture, improving visibility through the multiple glazing and improving durability of the multiple glazing. In some examples, the multiple glazing comprises a vacuum insulated glazing unit. This may further increase the insulation afforded by the multiple glazing. Preferably, the vacuum insulated glazing unit is separated from the photovoltaic cell by a cavity. This increases audio insulation as well as reducing thermal transport and transfer of stresses through the glazing. More preferably, the cavity is filled with an inert gas. This allows the cavity to afford additional insulation, and increases the durability of the multiple glazing. Preferably, the inert gas is argon. In some examples, the at least one photovoltaic cell is partially transparent. This allows some light to pass through the multiple glazing, reducing lighting requirements when the multiple glazing is installed in a room, thereby additionally improving energy efficiency. Preferably, the at least one photovoltaic cell has a transparency in the range 10%-70%. This allows some sunlight to pass through while still providing some energy generation. In some examples, the photovoltaic cell comprises one of: a cadmium telluride cell; a copper indium gallium selenium cell; or a perovskite cell. ln some examples, the photovoltaic cell is bonded to the transparent layer. This may improve mechanical stability of the multiple glazing. Preferably, the photovoltaic cell is bonded to the transparent layer via a bonding layer comprising polyvinyl butyral and / or ethylene vinyl acetate. Preferably, edges of the photovoltaic cell are sealed using edge tape. The edge tape may be between the photovoltaic cell and transparent layer, or arranged to seal over the edges of the photovoltaic cell and transparent layer. In some examples, the multiple glazing further comprises a junction box. Preferably, the junction box is internal to the glazing. In some examples, the multiple glazing further comprises a low emissivity coating applied to a layer of the glazing, preferably applied to the at least one transparent layer, more preferably wherein the low emissivity coating is a silver coating. Advantageously, the low emissivity coating reflects radiation, particularly long-wave infrared radiation, reducing heat transfer through the multiple glazing by radiation. Most preferably, the multiple glazing comprises a plurality of low emissivity coatings applied to multiple layers of the glazing. This further reduces heat transfer through the multiple glazing by radiation. In some examples, the multiple glazing further comprises an ultraviolet light filter. This protects both inhabitants of a room and objects within the room from ultraviolet light, which otherwise may cause damage. The low emissivity coating may be arranged to reflect some light, such as certain wavelengths of light, back towards the photovoltaic cell. For example, coating may be arranged to reflect light from inside a room of a building to a photovoltaic cell arranged in the glazing further inward (i.e., further towards the interior of the room) than the low emissivity coating. This may increase the efficiency of electricity generation in the photovoltaic cell. In some examples, the at least one transparent layer is a glass layer, preferably a toughened glass layer and / or a laminated glass layer. Preferably, the at least one transparent layer is conductive and / or comprises a conductive coating. In other examples, the at least one transparent layer may comprise a plastic, such as acrylic, in which case a conductive coating map optionally be applied to the layer. In some examples, the multiple glazing comprises a plurality of transparent layers. In some examples, the multiple glazing further comprises an ethylene vinyl acetate film coating at least one external face of the multiple glazing. Ethylene vinyl acetate acts as a moisture barrier, so may be used to protect the multiple glazing from moisture. In some examples, the multiple glazing further comprises a further insulating layer, the further insulating layer comprising an inert gas. This further reduces heat and sound transfer through the multiple glazing. According to a second aspect of the present disclosure, there is described: a multiple glazing the glazing comprising: a first vacuum insulated glazing unit; a second vacuum insulated glazing unit; and an inert gas layer between the first and second vacuum insulated glazing units. Advantageously, the use of two vacuum insulated glazing units separated by an insulating layer means that the conventional drawbacks of vacuum insulation, namely condensation, thermal stresses, and thermal transfer through the pillars supporting the panes, are significantly reduced or avoided, as the insulation reduces the thermal gradients across each unit and so the thermal gradients between glass at pillar contact points and the surrounding glass are also reduced. In some examples, the glazing further comprises a photovoltaic cell. Any feature in one aspect of the disclosure may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory. It should also be appreciated that particular combinations of the various features described and defined in any aspects of the disclosure can be implemented and / or supplied and / or used independently. The disclosure extends to methods and / or apparatus substantially as herein described with reference to the accompanying drawings. The disclosure will now be described, by way of example, with reference to the accompanying drawings. Brief description of the drawings Figure 1 shows a first example multiple glazing; Figure 2 shows a second example multiple glazing; Figure 3 shows a third example multiple glazing; Figure 4 shows a fourth example multiple glazing; Figure 5 shows a fifth example multiple glazing; and Figure 6 shows a sixth example multiple glazing. Description of the preferred embodiments Referring to Figure 1, there is shown a first example multiple glazing 100. The multiple glazing 100 comprises a photovoltaic cell 102 and a transparent layer, which in this example is a glass pane 104. Between the photovoltaic cell and the pane 104 is an insulating layer 106. The insulating layer 106 comprises an inert gas, which fills a cavity formed between the photovoltaic cell and the pane. In use, light strikes the photovoltaic cell 102. At least a fraction of this incident light is converted into electricity. The insulating layer 106 reduces transfer of heat between a first side and a second side of the multiple glazing 100. Advantageously, the combination of insulation and a photovoltaic cell allows electricity to generated by the glazing, from solar energy, while also providing thermal insulation. Additionally, the use of an insulating layer comprising an inert gas results in better mechanical behaviour than if other insulating means were used, because the insulating layer acts as a buffer and prevents mechanical forces on the photovoltaic cell being transferred to, and so shattering, the pane, meaning that even if an impact shatters part of the multiple glazing, a window comprising the multiple glazing may remain sealed. The insulating layer also reduces localised thermal stresses at each layer in the multiple glazing, thereby reducing the likelihood of breakage of any of the layers of the glazing. In contrast to this, vacuum insulation requires internal support pillars bridging the cavity, which allows heat and stresses to travel through the pillars between the panels, increasing the likelihood of breakage of the glazing. The photovoltaic cell also provides partial shading due to absorption of some of incident sunlight, reducing overheating in summer. In some examples, the photovoltaic cell is supported by a further layer, preferably a further transparent layer such as a further pane of glass. In such examples, the photovoltaic cell is fixed to the pane by an interfacial layer, which may comprise ethylene vinyl acetate (EVA) and / or polyvinyl butyrate (PVB). EVA is preferred because it has higher transparency and better weather resistance than PVB. The photovoltaic cell may be sealed to the further layer using edge tape. Using edge tape to seal edges of the structure improves adhesion between layers, preventing moisture or air from infiltrating the structure, as well as being more flexible than layers such as glass. The flexibility of edge tape allows it to absorb thermal stresses due to mismatches in coefficients of thermal expansion between the photovoltaic cell and other layers, such as glass. Edge tape may comprise EVA and / or PVB. In such examples, the further pane is preferably 3.2 mm thick, and the interfacial layer is preferably 1.52 mm thick. Advantageously, the interfacial layer may hold the further pane of glass together in the case of an impact, preventing shards of the further pane from being scattered outwards. This reduces likelihood of injury due to the further pane of glass. In some examples, the insulating layer is 16 mm thick. In some examples, the photovoltaic cell is 3.2 mm thick. In some examples, the transparent layer is 5 mm thick. In some examples, the transparent layer and / or the further layer may be toughened glass. In some examples, the transparent layer and / or the further layer may be float glass, preferably laminated float glass. Advantageously, laminating float glass reduces safety risks on breakage of the glass by holding fragments together, reducing the spread of shards of glass through the environment. Additionally, the use of two glass panes provides extra strength and structural support, enhancing overall stability, safety, and sound insulation. In some examples, the pane comprises a low emissivity coating, preferably a single silver coating. Low emissivity coatings primarily reflect long-wave infrared radiation, but also partially reflect short-wave radiation. When in use, if the low emissivity coating is positioned facing into a room, it reflects some of the heat radiation back into the room. Since indoor radiation is primarily long-wave infrared radiation, low emissivity coatings advantageously further improve heat retention of the glazing. If the low emissivity coating is positioned facing out of a room, it reflects some of the incoming solar radiation, as although this is primarily short-wave radiation, the coating still has some reflectivity at these wavelengths, so still provides some improvement to insulation of a room from outside heat. A low emissivity coating may therefore be positioned facing inwards when used in colder climates, and facing outwards when used in warmer climates. While in the above example, the pane 104 is made of glass, in other examples the pane 104 and / or the further pane may be made of another transparent material, such as acrylic or polycarbonate. Where the photovoltaic cell is made of cadmium telluride, the substrate must be conductive in order for the cell to function properly. As a result, where cadmium telluride is used, the pane 104 may be made of conductive glass or may comprise a conductive layer at the interface between the pane and the photovoltaic cell. For example, the pane may be made of non-conductive glass or polycarbonate, and may comprise a conductive coating. Conductive glass is generally preferable to a non-conductive material with a conductive coating, as the conductive coating often negatively impacts transparency and durability. Referring to Figure 2, there is shown a second example multiple glazing 200. The multiple glazing comprises a first photovoltaic cell 202, a first interfacial layer 204, a first transparent layer 206, a second transparent layer 208, a second interfacial layer 212, a second photovoltaic cell 214, an insulating layer 216, and a mirror pane 218. The insulating layer 216 comprises a spacer bar 222. Both the first transparent layer 206 and second transparent layer 208 in this example are formed as transparent panes, such as panes of glass. The first photovoltaic cell 202 is fixed to the first pane 206 via the first interfacial layer 204. The second photovoltaic cell 214 is fixed to the second pane 208 via the second interfacial layer 212. The insulating layer 216 is formed between the second photovoltaic cell 214 and the mirror pane 218. The spacer bar 222 extends across the insulating layer 216 from the second photovoltaic cell 214 to the mirror pane 218. When in use, incident light first hits the first photovoltaic cell. This photovoltaic cell is supported by the first pane. A fraction of the light is absorbed by the first photovoltaic cell with the remainder passing through the first photovoltaic cell, through the first interfacial layer and first pane (which are each at least substantially transparent), and through the second pane and second interfacial layer (both of which are also at least substantially transparent) to the second photovoltaic cell. The second photovoltaic cell also absorbs a fraction of the light incident upon it, with the remainder passing through the second photovoltaic cell, through the insulating layer 216, to the mirror pane. The mirror pane reflects a fraction of the light, while the remaining light passes through the mirror pane. Advantageously, the use of a mirror pane both provides privacy for occupants of a building where the glazing is installed, and improves the efficiency of the photovoltaic cells, as the photovoltaic cells each receive light on both a front surface (from the incident sunlight) and a back surface (reflected by the mirror pane). The reflection of some of the incident light from the environment off the mirror pane and back into the environment means that anyone attempting to see into an inside space through the glazing will see primarily their own reflection, as long as more light is being absorbed or reflected by the glazing than is passing through the glazing from the inside space. In some examples, the first pane and the second pane may be laminated together. Advantageously, the panes thereby provide each other with structural support, improving the strength of the glazing and enhancing its stability. In other examples, the first pane and the second pane may be spaced apart, with the space between them being filled with an inert gas or a vacuum. This may improve the thermal and acoustic insulation of the glazing. The spacer bar may comprise silica desiccant to prevent moisture buildup in the insulating layer, which could cause undesirable condensation on the inside of the glazing to occur. In some examples, the first pane and / orthe second pane comprise float glass. In some examples, the first interfacial layer and / orthe second interfacial layer comprise polyvinyl butyrate. In some examples, the first interfacial layer and / or the second interfacial layer comprise ethylene vinyl acetate. In some examples, the insulating layer comprises argon. In some examples, the first and / orthe second photovoltaic cell is a cadmium telluride cell. In some examples, the mirror pane comprises toughened glass. The toughened glass may be coated to provide a reflective surface. In some examples, the first photovoltaic cell and the second photovoltaic cells have different band gaps. Advantageously, this allows a greater proportion of energy to be recovered from incident sunlight. Preferably, the first photovoltaic cell has a greater band gap than the second photovoltaic cell. When the multiple glazing is positioned so that the first photovoltaic cell is outward facing from a building, light is first incident on the first photovoltaic cell. Light whose wavelength is lower than the band gap passes through the first photovoltaic cell and is incident on the second photovoltaic cell. A higher band gap means that a greater voltage is generated across the photovoltaic cell, and so less energy is lost as heat from photons with higher energy than the band gap than would be lost by a photovoltaic cell with a smaller band gap. The provision of a second photovoltaic cell with a smaller band gap means that photons that pass through the first photovoltaic cell because their energy is insufficient for the first band gap may be absorbed by the second photovoltaic cell if their energy exceeds that required by the band gap of the second photovoltaic cell. In some examples, the first and second photovoltaic cells have a thickness of 3.2 mm. In some examples, the first and second panes have a thickness of 3.2 mm. In some examples, the first and second interfacial layers each have a thickness of 0.76 mm. In some examples, the insulating layer has a thickness of 8 mm. In some examples, the mirror pane has a thickness of 5 mm. In examples, the multiple glazing has a total thickness of 27.32 mm. In some examples, the multiple glazing has a weight of 46.5 kg / m2. In such a design, the second example multiple glazing may be capable of generating 100-120 kWh per square meter annually, with a light transmission percentage of 14 LT%, and a heat transmission g-value of 5%. Referring to Figure 3, there is shown a third example multiple glazing 300. The multiple glazing comprises a first photovoltaic cell 302, a first interfacial layer 304, a first transparent layer 306, a second transparent layer 308, a second interfacial layer 312, a second photovoltaic cell 314, a first insulating layer 316, a mirror pane 318, a second insulating layer 320, and a third pane 326. The first insulating layer 316 comprises a first spacer bar 322. The second insulating layer 320 comprises a second spacer bar 324. Again, the first transparent layer 306 and second transparent layer 308 in this example are formed as transparent panes, such as panes of glass. The first photovoltaic cell 302 is fixed to the first pane 306 via the first interfacial layer 304. The second photovoltaic cell 314 is fixed to the second pane 308 via the second interfacial layer 312. The first insulating layer 316 is formed between the second photovoltaic cell 314 and the mirror pane 318. The second insulating layer 320 is formed between the mirror pane 318 and the third pane 326. The first spacer bar 322 extends across the first insulating layer 316. The second spacer bar extends across the second insulating layer 320. Similarly to the second example multiple glazing, the third example multiple glazing provides privacy and enhanced power generation due to the combination of the mirror pane and the photovoltaic cells. Advantageously, the third example multiple glazing comprises an additional insulating layer. This further improves the insulating properties of the glazing. In some examples, the first pane and second pane may be separated, and an insulating layer may be provided between the first and second panes. For example, a vacuum or an inert gas may be provided between the first and second panes. In some examples, the third example multiple glazing may comprise a low-emissivity coating, such as a single silver layer, coated on one of the panes. In some examples, the first and second photovoltaic cells have a thickness of 3.2 mm. In some examples, the first and second panes have a thickness of 3.2 mm. In some examples, the first and second interfacial layers have a thickness of 1.52 mm. In some examples, the first insulating layer has a thickness of 12 mm. In some examples, the mirror pane has a thickness of 2 mm. In some examples, the second insulating layer has a thickness of 12 mm. In some examples, the third pane has a thickness of 4 mm. In some examples, the third pane comprises toughened glass. In some examples, the multiple glazing has a total thickness of 41.84 mm. In such a design, the third example multiple glazing may be capable of generating 100-120 kWh per square meter annually, with a light transmission percentage of 10 LT%, and a heat transmission g-value of 4%. Referring to Figure 4, there is shown a fourth example multiple glazing 400. The multiple glazing comprises a first transparent layer 402, a second transparent layer 404, a vacuum 406, an insulating layer 408, a photovoltaic cell 412, an interfacial layer 414, and a third transparent layer 416. A spacer 422 is provided within the insulating layer 408. Again, the first transparent layer 402, second transparent layer 404, and third transparent layer 416 in this example are formed as transparent panes, such as panes of glass. The first pane 402 and second pane 404 are separated by the vacuum 406, which fills a cavity defined by the first and second panes. The insulating layer 408 comprises an inert gas, which fills a cavity defined by the second pane 404 and the photovoltaic cell 412. The photovoltaic cell 412 is attached via the interfacial layer 414 to the third pane 416, which provides it with structural support. The spacer 422 spans the insulating layer 408 and provides structural support to the cavity. The spacer bar may also comprise silica desiccant to prevent moisture buildup within the insulating layer. In a first method of use, the multiple glazing 400 may be installed in a building so that the first pane is adjacent an outside of the building, while the third pane is adjacent an inside of the building. In this configuration, there is no insulation between the photovoltaic cell and the inside of the building. This means that energy absorbed by the photovoltaic cell in the form of heat is emitted both towards the inside of the building and towards the first and second panes. Since there is an insulating layer between the photovoltaic cell and the second pane, and a vacuum provided between the first and second layers, transfer of heat by convection and conduction away from the photovoltaic cell and through the glazing is limited. Transfer of heat by convection and conduction towards the inside of the building is less restricted, and so more heat is transferred into the building via conductive contact with air inside the building, and convection of the air inside the building, than is transferred out of the building. This results in such a glazing not merely insulating a room from colder surroundings, but actively heating the room to above the temperature of the surroundings, all while generating electricity. In a second method of use, the multiple glazing 400 may be installed in a building so that the first pane is adjacent an inside of the building, while the third pane is adjacent an outside of the building. In this configuration, insulation is provided between the photovoltaic cell and the inside of the building. As a result, the glazing insulates the building both from its surroundings and the photovoltaic cell, meaning that heat generated by the photovoltaic cell during summer will primarily transferred to the surroundings. Such a glazing may be desirable where the temperature in summer is likely to exceed a desired temperature of the inside of the building. In examples, the first pane and / or the second pane comprise toughened glass. In examples, the first pane and / or the second pane are ultra-clear glass. In examples, the interfacial layer comprises polyvinyl butyrate. In examples, the first pane and second pane are 5 mm thick. In examples, the vacuum is 0.3 mm thick. In examples, the insulating layer is 10 mm thick. In examples, the photovoltaic cell is 3.2 mm thick. In examples, the interfacial layer is 1.52 mm thick. In examples, the third pane is 3.2 mm thick. In examples, the total thickness of the multiple glazing is 28.22 mm. While in Figure 4, the third pane is shown facing outwards from the glazing, in alternative embodiments the third pane and the photovoltaic cell may be reversed, so that the photovoltaic cell is facing outwards from the glazing. This may be particularly suitable for the first method of use, as sunlight is then incident directly on the cell rather than being transmitted through the supporting pane and interfacial layer. Referring to Figure 5, there is shown a fifth example multiple glazing 500. The multiple glazing 500 comprises a photovoltaic cell 502, an interfacial layer 504, a first transparent layer 506, a first insulating layer 508, a second transparent layer 512, a second insulating layer 514, and a third transparent layer 516. The first insulating layer 508 comprises a first spacer bar 522. The second insulating layer 514 comprises a second spacer bar 524. Again, the first transparent layer 506 and second transparent layer 512 and third transparent layer 516 in this example are formed as transparent panes, such as panes of glass. The photovoltaic cell 502 is attached to the first pane 506 via the interfacial layer 504. The first pane 506 and the second pane 512 define walls of the first insulating layer 508, which is a cavity comprising an inert gas. The second pane and the third pane similarly define the walls of the second insulating layer 514, which is also a cavity comprising an inert gas. The first spacer bar 522 and the second spacer bar 524 span the first and second insulating layers respectively. In use, the first and second insulating layers are positioned facing inwards towards an inside of a building in order to insulate the inside of the building from both its surroundings and from the photovoltaic cell. This improves the energy efficiency of the building, as the glazing provides both insulation and a source ofclean energy generation. In examples, the interfacial layer may comprise polyvinyl butyrate. In examples, the spacer bar may comprise silica desiccant to prevent moisture buildup within the insulating layers. In examples, the photovoltaic cell may be a cadmium telluride cell of 3.2 mm thickness. In examples, the interfacial layer may be 1.52 mm thick. In examples, the first pane may be float glass and may be 3.2 mm thick. In examples, the first insulating layer and second insulating layer may be 12 mm thick. In examples, the insulating layers may comprise argon. In examples, the second pane may be 4 mm thick. In examples, the second pane may be float glass. In examples, the third pane may be 4 mm thick. In examples, the third pane may be float glass. In examples, the third pane may comprise a low emissivity coating, such as silver. Referring to Figure 6, there is shown a sixth example multiple glazing. The glazing comprises a first vacuum-insulated glass (VIG) unit 610, and a second VIG unit 620, separated by an insulating layer 630. The insulating layer may be filled with an inert gas, such as argon. The first VIG unit comprises a first glass pane 612 and a second glass pane 614. These panes define a first cavity 616, which contains a vacuum. The second VIG unit comprises a third glass pane 622 and a fourth glass pane 624. These panes define a second cavity 626, which contains a vacuum. The cavity 630 comprises a spacer bar 632, which extends between the first and second VIG units. In other examples, the glass panes may be replaced by another transparent layer, such as a clear plastic layer, such as an acrylic layer. In use, the combination of the two VIG units with an insulating layer results in improved insulating properties. The increase in insulation reduces any temperature gradient between pillars on the VIG panes, which therefore reduces preferential buildup of condensation around the pillars, which improves visibility through the glazing. Additionally, the reduced temperature gradient between pillars results in reduced thermal stresses through the VIG unit. In examples, the multiple glazing further comprises a low emissivity coating, preferably a low emissivity coating within each of the VIG units. In examples, the low emissivity coating is a two-layer double silver coating. In examples, each VIG unit comprises a pair of 5 mm thick panes of glass. In examples, the vacuum enclosed by each VIG unit is 0.3 mm in depth. In examples, the cavity has a depth of 8 mm. In examples, the cavity comprises a spacer bar filled with silica desiccant to prevent buildup of moisture inside the pane. Advantageously, such dimensions allow the multiple glazing to fit within a standard window frame, while still providing significantly improved insulation. In examples a multiple glazing with the above proportions provides a light transmission of 46%, and a heat transmission g-value of 18%, with an acoustic reduction of 45 decibels. Alternatives and modifications It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention. For example, any of the example multiple glazings comprising a photovoltaic cell may further comprise a junction box, which may be positioned on any side of the glazing. In examples, the photovoltaic cell or photovoltaic cells comprise a cadmium telluride photovoltaic cell. Advantageously, cadmium telluride cells maintain good operating efficiency even at higher temperatures, meaning that the cells can be used without a cooling or heating means in a variety of weather conditions, without sacrificing performance. However in other examples, the photovoltaic cells may alternatively or additionally comprise a perovskite photovoltaic cell, or a copper indium gallium selenium (CIGS) cell. In some examples, a UV filter is additionally provided. For example, a titanium dioxide nanocoating may be provided on the outer surface of the glazing, which is capable of filtering 99% of UV rays. Features described in the context of any one of the example multiple glazings may be equally applied to another example multiple glazing. For example, additional insulating layers and / or vacuum-insulated glass units may be provided within any of the example multiple glazings. Similarly, low emissivity coatings may be provided over different layers and / or additional layers of each example multiple glazing. Any of the transparent layers described in any of the examples may be formed of any transparent material. In some examples the transparent layers may be panes of glass, but alternative transparent materials may be used instead such as sheets of clear acrylic or even coloured acrylic. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

1. A multiple glazing, the multiple glazing comprising:at least one transparent layer;at least one photovoltaic cell; andat least one insulating layer comprising an inert gas.

2. The multiple glazing of claim 1, further comprising a mirror pane.

3. The multiple glazing of claim 2, wherein a reflective surface of the mirror pane faces towards the photovoltaic cell.

4. The multiple glazing of any of claims 1 to 3, wherein the at least one photovoltaic cell comprises at least one bifacial photovoltaic cell.

5. The multiple glazing of any preceding claim, wherein the multiple glazing is configured so that when in use in a window of a room, the photovoltaic cell is arranged between an interior of the room and the insulating layer.

6. The multiple glazing of any of claims 1 to 4, wherein the multiple glazing is configured so that when in use in a window of a room, the photovoltaic cell is separated from an interior of the room by the insulating layer.

7. The multiple glazing of any preceding claim, wherein the at least one photovoltaic cell is a plurality of photovoltaic cells.

8. The multiple glazing of claim 7, wherein the plurality of photovoltaic cells are separated by at least one insulation layer.

9. The multiple glazing of claim 7 or 8, wherein the plurality of photovoltaic cells comprises a first photovoltaic cell with a first band gap, and a second photovoltaic cell with a second band gap, wherein the first band gap is greater than the second band gap, preferably wherein, when in use in a window of a room, the second photovoltaic cell is arranged further towards to the interior of the room than the first photovoltaic cell.

10. The multiple glazing of any preceding claim, wherein the insulating layer comprises a spacer bar filled with silica desiccant.

11. The multiple glazing of any preceding claim, wherein the multiple glazing comprises a vacuum insulated glazing unit.

12. The multiple glazing of claim 11, wherein the vacuum insulated glazing unit is separated from the photovoltaic cell by a cavity, preferably wherein the cavity is filled with an inert gas, preferably argon.

13. The multiple glazing of any preceding claim, wherein the at least one photovoltaic cell is partially transparent, preferably wherein the at least one photovoltaic cell has a transparency in the range 10%-70%.

14. The multiple glazing of any preceding claim, wherein the photovoltaic cell comprises one of: a cadmium telluride cell; a copper indium gallium selenium cell; or a perovskite cell.

15. The multiple glazing of any preceding claim, wherein the photovoltaic cell is bonded to the transparent layer.

16. The multiple glazing of claim 15, wherein the photovoltaic cell is bonded to the transparent layer via a bonding layer comprising polyvinyl butyral and / or ethylene vinyl acetate.

17. The multiple glazing of any preceding claim, further comprising a junction box, wherein the junction box is internal to the glazing.

18. The multiple glazing of any preceding claim, further comprising a low emissivity coating applied to a layer of the glazing, preferably applied to the at least one transparent layer, more preferably wherein the low emissivity coating is a silver coating, most preferably comprising multiple low emissivity coatings applied to multiple layers of the glazing.

19. The multiple glazing of any preceding claim, further comprising an ultraviolet light filter.

20. The multiple glazing of any preceding claim, wherein the at least one transparent layer is aglass layer, preferably a toughened glass layer and / or a laminated glass layer.

21. The multiple glazing of any preceding claim, comprising a plurality of transparent layers.

22. The multiple glazing of any preceding claim, further comprising an ethylene vinyl acetate filmcoating at least one external face of the multiple glazing.

23. The multiple glazing of any preceding claim, comprising a further insulating layer, the further insulating layer comprising an inert gas.

24. A multiple glazing, the glazing comprising:5 a first vacuum insulated glazing unit;a second vacuum insulated glazing unit; andan inert gas layer between the first and second vacuum insulated glazing units.

25. The multiple glazing of claim 24, wherein the glazing further comprises a photovoltaic cell.s

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