Patent Description:
It is known in the technical sector of photovoltaic glass panes that these are generally formed by a sandwich structure comprising several layers superimposed in a thickness direction, said layers comprising a photovoltaic layer.

The photovoltaic layer generally has an active layer, for example comprising a plurality of photovoltaic cells, which is enclosed between two layers of transparent thermoplastic resin (usually polyvinyl butyral, PVB). The active layer has, combined therewith, on-board electronics and connection means such as cables and connectors for electrical connection and control of the photovoltaic active layer. Document <CIT> discloses a thin-film solar cell formed as a glazing pane according to the preamble of Claim <NUM>, having first and second planar glass substrates with a softening point over <NUM> in order to better withstand the high-temperature photovoltaic coating process for deposition of a photovoltaic coating interposed between the two planar glass substrates.

It is also known that photovoltaic glass panes or photovoltaic sandwich structures may be included in structural panels for buildings, in which case the photovoltaic structural panel overall must satisfy the mechanical requisites for making the panel classifiable as a structural safety panel, prescribed in the relevant standards, including in particular standard UNI <NUM>, and for which structural calculation models used by design engineers in the sector are known.

The structural photovoltaic panels therefore have the dual characteristic that they produce electric energy by means of the photovoltaic layer and act as an architectural building element.

In general there exist a plurality of standards relating to glass panes and glass panels, in particular relating to the material itself, to the modes of use and its performance features, including:.

Furthermore the certifications CEI EN <NUM> and CEI EN <NUM> are applicable for PVB laminated safety glass.

According to the present state of the art, in the sector in question, there does not exist a commercially available photovoltaic glass pane which has adequate fire-resistance properties for applications where fire-prevention is required.

Likewise, there does not exist in the technical sector a photovoltaic structural panel which has adequate fire-resistance properties for use in applications where fire-prevention is required. In particular there is no known photovoltaic structural panel which may be classified as E30 or E45 in accordance with the criteria defined by the standard UNI EN1363-<NUM> (<NUM>) relating to passive fire-resistant glass.

The technical problem which is posed therefore is that of providing a photovoltaic glass and/or structural photovoltaic panel with improved fire-resistance properties.

A particular object of the present invention is to provide a photovoltaic glass and/or structural photovoltaic panel, with improved structural strength and fire-resistance properties, in particular in relation to mechanical shocks during a fire.

In connection with this problem, it is also required that the glass or panel should have small dimensions (in particular as regards its thickness), be easy and inexpensive to produce and be able to be easily installed using normal standardized means.

These results are obtained according to the present invention by a laminated photovoltaic glass plane according to the characteristic features of Claim <NUM> and by a fire-resistant photovoltaic panel according to Claim <NUM>.

The present invention relates furthermore to a process according to claim for producing the photovoltaic structural glass pane and a structural element provided with the photovoltaic panel.

Further details may be obtained from the following description of non-limiting examples of embodiment of the subject of the present invention, provided with reference to the accompanying drawings, in which:.

With reference to <FIG>, an example of embodiment a photovoltaic laminated glass pane <NUM> according to the invention extends in a thickness direction Z-Z between a front side or sun side "S" and a rear side or inner side "I" and comprises a front glass sheet <NUM>, the front surface of which forms the sun side S which during use is exposed to the sun, a rear glass sheet <NUM> and at least one photovoltaic layer <NUM> arranged between the front glass sheet <NUM> and the rear glass sheet <NUM>.

With reference to <FIG>, the photovoltaic layer <NUM> has an active layer which is designed to be irradiated by solar energy and produce electric energy and which is enclosed between two layers <NUM> of transparent thermoplastic resin, preferably consisting of PVB. In particular, the active layer <NUM> comprises a plurality of photovoltaic cells <NUM>. The photovoltaic cells <NUM> may be made from crystalline silicon, with electrical interconnection means <NUM>, for example in the form of ribbons, in particular made of copper. It is understood that the photovoltaic layer <NUM> may also comprise a different number of layers of thermoplastic resin and/or a different active layer.

The interconnection means <NUM> may connect together a plurality of cells <NUM> and form output terminals 22a of the active layer for connection to/from the outside.

As shown, in preferred embodiments, the ribbons <NUM> may be arranged so as to form a plurality of terminals 22a arranged along the outer perimetral edge of the active layer, so as to provide connection terminals of the cells <NUM> with the outside for the active layer, emerging from the sandwich arrangement of the two PVB resin layers which encloses the active layer.

The active layer <NUM> has, combined therewith, on-board electronics <NUM> and connection means such as cables and connectors <NUM> for electrical connection and control of the photovoltaic active layer.

The on-board electronics may comprise, for example, diodes housed inside containers <NUM>, for example made of ABS, and embedded in thermo-conductive, dielectric, adhesive silicone. Electronics <NUM> and cables <NUM> may be for example directly welded to the output ribbons 22a of the glass, the welds being for example insulated with silicone.

Advantageously, the active layer with connection terminals 22a and/or on-board connection electronics arranged along the perimetral edges allows the whole of the electrical/electronic connection part of the active layer <NUM> to be maintained inside a support frame of the glass pane <NUM>, as will become clearer below.

According to the invention, the front glass <NUM> is a heat-tempered glass with dilatometric softening point (for example measured in accordance with ASTM C338-<NUM> Standard Test Method for Softening Point) higher than or equal to <NUM>, preferably higher than <NUM>. Preferably, the softening point is also lower than <NUM>.

These softening point values are decidedly higher than those of standard glass used in the building industry (for example defined in UNI EN <NUM>) and it was surprisingly discovered that by using such a glass sheet as outer layer on the sun side it is possible to produce photovoltaic glass panes and photovoltaic structural panels with a surprising fire-resistance capacity.

Preferably, the front glass sheet <NUM> on the sun side has a fire resistance period of at least <NUM> minutes, namely it is classifiable as at least E30 according to the standard EN13501 (December <NUM>).

The front glass sheet <NUM> may be a borosilicate or alkaline earth silicate sheet. However such glass sheets are extremely costly and preferably the front glass sheet is made of soda-lime silicate glass in accordance with the standard EN <NUM> (December <NUM>).

Preferably the front sheet <NUM> comprises a percentage by weight of Na<NUM>O equal to between <NUM>% and <NUM>%, in particular less than or equal to <NUM>%, even more preferably less than or equal to <NUM>%. Owing to this characteristic feature the heat tempering may be increased and the softening point raised.

The percentage of aluminium oxide is preferably <NUM>% by weight, so as to provide the glass sheet <NUM> with a greater hydrolytic resistance.

A content of MgO greater than or equal to <NUM>% by weight may be chosen in order to improve the chemical resistance, while reducing the viscosity of the glass.

The outer glass sheet preferably has a very low percentage content of iron, less than or equal to <NUM>% by weight, which may contribute both towards raising the softening point and improving the transparency of the front glass <NUM>, thereby increasing the efficiency of the photovoltaic glass pane <NUM>.

The outer glass <NUM> may have very precise finishing of the edges, with micro-fissures smaller than <NUM>. For example, this may be obtained by means of super fine grain grinding (<50micro-m), in particular with a plurality of gradual grinding/polishing steps such as to avoid as far as possible the formation of micro-fractures. The material removed at each step must be preferably between <NUM> and a maximum of <NUM>.

In particular, the front glass sheet may have a round or flat, glossy, flush-ground perimetral edge.

As is known, the bottom cooling point, also called bottom relaxation limit" or "deformation point", represents the maximum operating temperature of a glass component. Above this limit temperature, the internal mechanical stresses are gradually reduced and the properties are modified permanently (but not irreversibly). The viscosity of the glass at the bottom softening point is by definition <NUM><NUM>,<NUM> Pa s.

The front glass sheet has preferably a bottom cooling point higher than or equal to <NUM>. This is advantageous in order to obtain optimum heat tempering. Optimum heat tempering allows a reduction in the incidence of micro-fissures along the edges of the glass sheet which may be the cause of spontaneous breakage in the case of fire stress. The possibility of greater tempering of the glass ensures a better stability in the event of fire.

In the event of a fire, the central part of the glass is more exposed and therefore hotter, while the edges are colder since they are protected by the door or window frame.

Owing to the use, in a photovoltaic glass pane, of a heat-tempered front glass sheet according to the invention, preferably with edges which are devoid of micro-fissures greater than <NUM>, it is possible to obtain a better resistance in the event of non-uniform distribution of the heat on the surface of the photovoltaic glass pane.

The front glass sheet may have a thickness, for example, less than or equal to <NUM>, in particular less or equal to <NUM> or <NUM>, more particularly less than or equal to <NUM>.

Preferably, the front glass sheet has a thickness greater than or equal to <NUM>, preferably greater than or equal to <NUM>.

The transparency of the front layer <NUM> is preferably greater than or equal to <NUM>%. In any case preferably the front glass sheet <NUM> is made of glass classified as being "super clear".

It is understood that the above preferred characteristics described may be combined all or partly by the design engineer so as to choose the front glass sheet <NUM> suitable for the design specifications, provided that it has overall the necessary fire-resistance characteristics.

As regards the rear glass sheet <NUM>, this is preferably a single-piece glass sheet. However, it could also be a laminated glass pane.

It is also envisaged that a plurality of rear glass sheets may be arranged between the active layer <NUM> and the inner side I.

The rear glass sheet may have a thickness, for example, less than or equal to <NUM>, in particular less or equal to <NUM> or <NUM>, more particularly less than or equal to <NUM>.

Preferably, the rear glass sheet has a thickness greater than or equal to <NUM>, preferably greater than or equal to <NUM>.

Depending on the design characteristics, the thickness of the rear sheet may be for example between <NUM> and <NUM>, preferably between <NUM> and <NUM> times the thickness of the front sheet. In some cases, however, it could also be greater than <NUM> times the thickness of the front glass sheet.

The glass <NUM> behind the cells is preferably a sheet of glass, in particular float glass, which has undergone heat hardening treatment. As is known, heat hardening is a heat treatment similar to tempering, but, unlike the latter, it involves gradual cooling of the glass sheet after it has been brought to a suitable temperature generally higher than or equal to <NUM>. Preferred methods and characteristics of heat hardening and of the heat-hardened glass are described in the standards UNI ENI <NUM>-<NUM>:<NUM> and UNI EN <NUM>-<NUM>:<NUM>.

This heat hardening characteristic provides the photovoltaic glass pane <NUM> with a greater structural strength and fire-resistance, also in conditions where the rear glass is broken, preventing the propagation of mechanical shocks to the front glass on the sun side and further reducing the risk of the known "bulge/sack effect" occurring.

The Applicant has in fact surprisingly discovered that a rear glass sheet which has been heat-hardened, rather than tempered, is preferable for use in a structural photovoltaic glass pane according to the present invention; a tempered glass sheet in fact breaks into small pieces, while a hardened glass sheet breaks into larger pieces and produces a mechanical shatter effect less intense than that produced by a tempered glass sheet.

Moreover, by laminating a hardened rear glass sheet with a tempered front glass sheet, in the event of breakage (of both of them), the "bulge/sack effect" does not occur.

It is therefore preferable that the rear glass sheet should have a softening point and/or a fire-resistance period which is less than that of the front glass sheet <NUM> on the sun side. It is even more preferable that the front glass sheet <NUM> should be the layer of the laminated photovoltaic glass pane <NUM> with the highest softening point and/or with the greatest fire-resistance period.

In fact, the delayed softening and/or greater fire-resistance period of the front sun-side layer <NUM> is such as to cause the collapse firstly of all the other inner layers which are not fire-resistant. The Applicant has surprisingly noted that, during a fire, the photovoltaic layer burns and becomes slippery (because it has liquefied) both owing to the cells and because of the presence of PVB. Also the one or more inner glass sheets <NUM> which form the photovoltaic sandwich arrangement may break on account of the high temperature during a fire. The breakage of one or more inner glass sheets may transmit to the front layer <NUM> mechanical shocks, but, because it has a higher softening point, the fire-resistant glass layer <NUM> does not break and allows all the other layers of the photovoltaic glass pane <NUM> to slide on top of the front glass layer <NUM>.

At the end of the first stage of a fire, the outer sun-side layer <NUM> is therefore the only one remaining and may assume a plastic behaviour so as not to allow smoke and flames to escape, without the need for any mechanical performance characteristic apart from a minimum self-supporting capacity.

Therefore, these characteristics are also able ensure a greater structural strength and fire-resistance, in particular in relation to mechanical shocks occurring during a fire.

The photovoltaic glass pane <NUM> is preferably a single laminated body obtained by means of lamination in an autoclave, or similar process where a plurality of layers are superimposed, heated and compressed in order to form a single laminated body.

A process according to the invention for producing the photovoltaic glass pane may comprise the following steps:.

The photovoltaic glass pane is therefore preferably laminated in an autoclave. Advantageously, the lamination operation which forms the sandwich structure may consist of a cycle which modulates pressure and temperature in a controlled manner, without any particular measures compared to those already used for the production of photovoltaic sandwich structures.

Following this operation the connection means and the on-board electronics may be applied to the active layer <NUM>, using techniques which are conventional per se.

The fire-resistant photovoltaic glass pane according to the present invention may be used to form a structural photovoltaic panel (i.e. a glass structural element for building use, with photovoltaic layer), for example for use in external architectural elements of a building.

With reference to <FIG>, an example of a fire-resistant photovoltaic panel according to the present invention is in the form of a double-glazed unit <NUM> comprising an outer glass pane <NUM> formed by a photovoltaic laminated glass pane according to the present invention which during use is arranged facing the outside and exposed to the sun, and an inner glass pane <NUM>. The outer glass pane <NUM> on the sun side and the inner glass pane <NUM> are joined together along the perimeter with the arrangement, between them, of a spacing frame-piece or channel <NUM>, for example made of profiled metal or plastic, so as to form a cavity <NUM>, or insulating chamber, designed to contain dehydrated air or gas (usually argon or krypton). The spacing channel <NUM> is in particular structured so as to be able to house salts 141a designed to keep the air inside the insulating chamber <NUM> dehydrated. As shown, a layer of sealing material <NUM> may be arranged perimetrally around the channel <NUM>. The sealing material <NUM> is preferably a glass/glass structural silicone (e.g. Dow Corning <NUM>), in particular with at least <NUM> depth. The weight and volume of the sealing material <NUM> preferably is not more than <NUM>% of the photovoltaic panel.

The channel <NUM> is preferably made of stainless steel, for example Cromatech Plus Inox (Rolltech). In the event of a fire, this embodiment helps keep the panel in place, preventing it from collapsing inwards, since it has a greater heat resistance, this being preferable to a "controlled" breakage which is normally used for this type of double-glazed unit.

The inner glass pane <NUM> is preferably a (pre-)laminated glass pane in which one or more layers of transparent thermoplastic resin are arranged between two or more glass sheets, in particular a laminated safety glass pane in accordance with the standard UNI EN ISO12543 and/or CEI EN <NUM>, which is able to retain the fragments in the event of breakage.

The inner glass pane <NUM> may be for example a <NUM> pre-laminated glass pane, but it will be clear to the person skilled in the art that other structural and/or pre-laminated glass panes may be used in the panel <NUM> according to the invention.

In <FIG>, the photovoltaic structural panel <NUM> according to the present invention is shown retained by glass-fastener means <NUM> in the form of pressers <NUM> connected by tie-bolts <NUM>. Preferably, a respective heat-expanding - in particular graphite-based - seal <NUM> is arranged between the pressers <NUM> and the panel.

As shown, the pressers <NUM> act on the inner surface and on the sun-side outer surface of the panel <NUM>, overlapping them by a certain overlapping distance d1 measured from the outer perimetral edge of the respective inner or outer glass pane of the structural panel.

This overlapping distance d1 is preferably, at least on the front side "S" smaller than or equal to <NUM>.

Preferably also, the distance between the side of the channel <NUM> on the inside of the chamber <NUM> and the perimetral edge of the panel is less than or equal to <NUM> and/or substantially equal to this distance d1.

This feature advantageously ensures that the heat produced by combustion is distributed more uniformly without giving rise to "cold" zones which may trigger the breakage of the front layer <NUM>.

The panel according to the present invention may include further insulating chambers and further glass panes, provided that the fire-resistant laminated glass pane according to the present invention is the outermost one overall.

A fire-resistant photovoltaic panel <NUM> according to the present invention may be joined to a frame designed to be fixed to a wall, in particular an outer wall of a building, so as to form an architectural element and in particular continuous façade element, a roofing or a window.

The frame may be of any known type for use as a window or door frame in continuous façade elements, for example a fire-breaker window or door frame used for passive continuous facades with steel uprights and cross-pieces, comprising supports for the panel and presser-type glass fasteners joined to the uprights and cross-pieces. The connection means and on-board electronics of the photovoltaic panel may be housed inside the frame, so as not to affect the impermeability thereof.

With reference to <FIG> an example of embodiment of a continuous façade element, such as a structural double-glazed unit, which includes a photovoltaic panel <NUM> according to the present invention mounted on a frame designed to be fixed to a wall W, in particular an outer wall of a building, is now described.

In the example shown, the frame comprises a structure <NUM>, with uprights and cross-pieces, designed to be rigidly joined to the wall. The glass-fastener means <NUM> are designed to be joined to the frame and to retain or support the photovoltaic panel <NUM> according to the invention on the uprights and cross-pieces, in particular by means of presser elements <NUM>. Swelling seals <NUM>, in particular graphite-based, for example of the type comprising a double row of heat-expanding graphite-based tape, are preferably arranged between the pressers <NUM> and the panel.

Means <NUM> for fixing the frame to the wall comprise, for example, a plurality of angle brackets <NUM>, one side of which is designed to be fixed by means of anchoring plugs <NUM> to the wall and the other side of which is designed to be rigidly connected to the structure <NUM> of the frame.

A cover comprising one or more closing cases <NUM> is designed to be retained by the glass-fastener means <NUM> on the outer side of the window or door frame and fixed to the wall W by suitable fixing means <NUM>.

Advantageously, the cases may be made of stainless steel and filled with an insulating filler material <NUM>, in particular rock wool.

The part of the case <NUM> subject to the action of the clamping pressers <NUM> is preferably filled with calcium silicate 182a.

Air-tight seals optionally provided with a water-tight sealing lip, preferably of the non-combustible type, may be arranged between the frame and the panel <NUM>.

The continuous façade element of Example <NUM> is composed of the following:.

Inside the aforementioned front and rear glass panes there are <NUM> PVB solar sheets, <NUM> each, which enclose crystalline silicon photovoltaic cells;.

The panel had an overall thickness of <NUM>, a height of <NUM> and a length of <NUM>.

The fire resistance of the panel in Example <NUM> was tested in accordance with the standard UNI EN <NUM>-<NUM>: <NUM> (para.

The frame with panel was fixed to an opening in a wall of a closed furnace by means of eight angle brackets welded to the frame and secured to the wall by means of steel anchoring plugs; a combustion apparatus was ignited inside the closed furnace so as to generate a flame only on the inner side of the panel, and the panel mounted on the frame was exposed to rising temperatures in accordance with the heating curve of the cited standard UNI EN <NUM>-<NUM>, up to a temperature of <NUM>. After <NUM> minutes the furnace was switched off because of external problems due to the irradiation in the surrounding environment.

The results of test are described in Table <NUM>.

The results of the integrity tests carried out on samples of the panel following the initial test are shown in Table <NUM>.

As can be seen, the panel retained its structural integrity and its sealed condition for <NUM> minutes and maintained these characteristics also during the subsequent cooling step.

The panel in Example <NUM> was also found to have, following the laboratory test, the following characteristics:.

It is therefore clear how the photovoltaic glass pane according to the present invention is fire-resistant without the need for surface coatings which would limit its ease of handling and adversely affect the economic viability of the design.

The laminated glass pane and the photovoltaic panel according to the present invention can be classified as at least E30 and as belonging to the A1 fire reaction class, in accordance with the Decision <NUM>/<NUM>/EC, being therefore suitable as building products to be used in works for which the requisite of safety in the event of fire is prescribed.

The photovoltaic glass pane according to the present invention is such as to render the autoclave lamination cycles sustainable without the front glass on the sun side reacting to heat or needing special modifications to this type of process.

With the photovoltaic glass pane according to the present invention it is possible to provide photovoltaic structural panels with improved fire resistance, while maintaining the characteristic of structural safety glass.

In preferred embodiments, it is possible to use a front glass pane with the transparency of "low iron" glass also known as "extra-clear" glass, which is particularly advantageous as sun-side glass for a photovoltaic panel. Thus, the improved fire resistance is accompanied by an optimal electrical yield of the panel.

Since the sun-side front glass is tempered glass, it is possible to form the photovoltaic glass panes or panels according to the invention while maintaining the mechanical strength of tempered glass, without the need for substantial changes to the structural calculation models currently used by design engineers in the sector.

With the photovoltaic glass pane according to the present invention it is possible to avoid the propagation of mechanical shocks to the outer sun-side glass during combustion. Preferably, the rear glass is a sheet of glass which has undergone heat hardening treatment which, as a whole, provides the photovoltaic glass pane with additional structural strength even under breakage conditions and makes it possible to avoid the well-known "bulge/sack effect".

With the photovoltaic panel according to the invention the heat generated by the combustion may be uniformly distributed without creating "cold" zones that could trigger the breakage of the outer sun-side glass E30/E45.

The panel according to the invention does not need altimetric valves to dispose of the overpressure inside the insulating chamber during heating by combustion inside the room.

Claim 1:
Photovoltaic laminated glass pane (<NUM>) extending in a direction of thickness (Z-Z) between a front side or sun side (S) and a rear side (I) and comprising a plurality of superimposed layers in said direction of thickness, said layers comprising a front glass sheet (<NUM>), the front surface of which forms the sun side (S), a rear glass sheet (<NUM>) and at least one photovoltaic layer (<NUM>) arranged between the front glass sheet (<NUM>) and the rear glass sheet (<NUM>), wherein the photovoltaic layer (<NUM>) has an active layer designed to be irradiated by solar energy and to produce electric energy and wherein the front glass sheet (<NUM>) is made of a heat-tempered glass with a dilatometric softening point higher than or equal to <NUM>, preferably higher than <NUM>;
characterized in that the rear glass sheet (<NUM>) is a sheet of glass which has undergone heat hardening treatment and/or has a softening point and/or fire resistance period less than that of the front glass sheet (<NUM>) on the sun side.