WO 00/77860 (PCT/GB00/02159).

In WO 00/77860 we have disclosed a photovoltaic roof tile assembly which comprises a support framework for fixedly attaching to tile battens and a removable outer panel which is slideably mounted on the support framework. The outer panel comprises a transparent outer layer ? to enable solar radiation to reach the photovoltaic cells which are mounted beneath the outer layer, and an inner layer which slideably engages with the support framework. The support framework houses an electrical socket into which plugs, carried by the outer panel, engage on sliding the outer panel to a fully closed position.

In our earlier specification no. WO 00/77860 we disclose an electrical plug and socket connection between a slideable outer panel assembly which carries the photovoltaic cells, and a fixed support structure which carries a junction box for wiring which connects the tiles to an electrical output. In that arrangement the plug pins and socket bores extended parallel to the direction of sliding movement so that the connection was made automatically as the outer panel closely approached the fully closed position.

We have now realised that in certain circumstances it can be advantageous to arrange such a plug and socket connection such that the plug pins and socket bores extend substantially perpendicular to the plane of the tiles.

According to a first aspect of the invention a photovoltaic tile comprises a support structure adapted to be fixedly secured to a building framework (such as tile battens) and a removable outer panel assembly which substantially covers the support structure in the fully assembled position, of the outer panel assembly, the outer panel assembly incorporating photovoltaic cells which are connected to an electrical connector, the support structure mounting a junction box adapted to provide connections to electrical output leads, the junction box and the electrical connector of the outer panel being arranged to have a pin and socket connection with one another, the axes of the pins and socket bores of the connection being directed substantially perpendicular to the plane of the tile.

According to a second aspect of the invention there is provided a photovoltaic tile which is adapted to be fixedly secured to a building framework, the photovoltaic tile and the building framework being provided with respective components of a plug and socket arrangement, said components comprising at least one pin and at least one socket bore which is adapted to receive the at least one pin, and in an interconnected condition the axes of the pins and the socket bores being directed substantially perpendicular to the plane of the tile.

When a tile in accordance with the first and second aspects of the invention is used on a roof or floor, then the weight of the outer panel, and the transferred portion of the weight of an overlying tile will tend to hold the outer panel pressed downwardly against the support structure, thereby to assist in holding the plug and socket connection fully engaged.

In addition, fasteners accessible from above may be used to hold the connectors engaged, or a snap-fit arrangement may be provided for this purpose.

An advantage of such a pin and socket connection is that when the tile is used as wall cladding is it more difficult to facilitate safe sliding movement of an outer panel, and pivotal movement of the outer panel relative to the support may be preferable, this being facilitated by the pin, orientation.

The plug and socket connection/arrangement of the first and/or second aspects of the invention may be provided towards a margin of the panel/tile.

Typically, solar panels and tiles have been formed by sandwiching the photovoltaic elements between two flat surfaces (usually glass) and then attaching fixing and sealing systems (to effect sealing between one tile and another) to the underside of the laminated structure. Such arrangements are costly to produce, and reliability and long-term stability are not always good, and it is difficult to maintain water-and weather- proofing.

The prototype roof tiles which we constructed in accordance with WO 00/77860 utilised photovoltaic elements sandwiched between two glass sheets.

A third aspect of the invention enables a single glass sheet to be utilised to cover the photovoltaic elements, which may be mono-crystalline photovoltaic elements, thin-film photovoltaic elements, or other types.

For convenience, the inventive tiles will be considered as being on a sloping roof, and the terms'upper'and'lower'will relate to that situation, but it should be appreciated that the tiles may be used as wall or floor cladding, or on flat or curved roofs.

According to a third aspect of the invention, a photovoltaic tile comprises a support structure adapted to be fixedly secured to a building framework (such as a framework of tile battens) and a removable outer panel which substantially covers the support structure in the fully closed condition of, the outer panel, the outer panel assembly comprising a planar sheet of transparent material, preferably glass, which is sealably secured to a moulded base panel by sealing means which extends around photovoltaic elements, the base panel having a detachable connection with the support structure.

Advantageously use of a moulded base panel eliminates a large amount of cost and time during the production process. In one embodiment the moulded base panel is formed from a coloured plastics material whose colour is visible through the transparent panel and substantially corresponds with the colour of surrounding roof tiles.

In a further embodiment the moulded base comprises a moulded electrical terminal block which would both reduce the cost of assembly and increase greatly reliability and accuracy, such a base may comprise moulded-in electrical connectors.

The sealing means preferably comprises sealing areas which are preferably provided by an elastomeric sealing gasket which may be of circular cross-section and is preferably located in a channel provided in the upper surface of the base panel. The gasket may be replaced wholly, or in part, by adhesive jointing.

The transparent outer panel is preferably bonded to the base panel around the margin thereof so as to load the elastomeric seal, thereby to provide a long-term sealing action around the photovoltaic elements.

The photovoltaic elements are preferably accommodated in one or more recesses in the upper surface of the base panel.

The transparent sheet may be sealingly secured to the base panel by way of a portion of bonding material which during manufacture of a tile is positioned between the transparent sheet and the base panel. The bonding material is then heated, so that said bonding material bonds to both said transparent sheet and said base panel.

Such bonding material preferably sealingly secures the transparent sheet to the base layer. Advantageously such use of bonding material provides both a seal and a connection between the transparent sheet and the base panel, thus eliminating the need for sealing areas provided by elastomeric gasket means.

The bonding material preferably comprises a portion of a plastic sheet, and is most preferably a portion of an adhesive sheet. During manufacture the plastic sheet is sandwiched between the base panel and the transparent sheet, and then heated.

A fourth aspect of the invention is concerned with reducing the possibility of scratching of the upper surface of the transparent panel during sliding of the panel.

According to the fourth aspect of the invention a photovoltaic tile comprises a support structure adapted to be fixedly secured to a building framework (such as tile battens) and a removable outer panel assembly which substantially covers the support structure in the fully closed condition of the outer panel, the outer panel being slideable relative to the support structure from a fully closed position to a retracted position, the outer panel assembly comprising a planar sheet of transparent

material held captive to a base panel which has the slideable engagement with the support structure, the base panel being provided with an upstanding flange which lies against or adjacent to the upper edge of the transparent sheet, and protrudes above the level of the outer surface of, the transparent sheet, thereby to provide an engagement in use with the under-surface of an overlying tile.

The base panel may be moulded or formed from plastics, metal, ceramics, or other suitable material.

Thus, the upstanding flange, which may be continuous or discontinuous, will protect the upper surface of the transparent material from being scratched by the under-surface of an overlying tile when the outer panel is being slid from a fully closed position to a retracted position, or vice versa.

A fifth aspect of the invention relates to the provision of a sealing means between the lower edge of a photovoltaic tile and outer surface of an underlying tile.

In general roof tiles are not provided with elastomeric seals because they are generally narrow and rely on the shape of engagement between tiles, and on drip structures to direct water droplets down the roof. They are also commonly made from concrete materials which are generally not sympathetic to the dimensional detail needed for such seals.

Although it is common to seal the photovoltaic cells themselves against ingress of water, we consider it desirable to provide a resilient seal along the lower edge of a photovoltaic tile that overlaps another tile or tiles beneath it. This is because solar tiles are typically wider than conventional roof tiles or slates, and full contact along the length of the

lower edge is more difficult to achieve due to unevenness of the tiles if the fixing battens are uneven.

According to the fifth aspect of the invention a photovoltaic tile comprises a support structure adapted to be fixedly secured to a building framework (such as tile battens) and a removable outer panel assembly which substantially covers the support structure in the fully closed position of the outer panel assembly, the outer panel assembly being slideable relative to the support structure from a fully closed position to a retracted position, the outer panel being provided along the lower edge thereof with a downwardly directed flange, said flange, or the lower margin of the support structure, carrying an elastomeric blade seal which is adapted to seal in use against the upper surface of an underlying tile.

Preferably the blade seal is inclined inwardly of the lower margin of the tile.

In addition to the primary function of the blade seal to inhibit ingress of water, when the blade seal is carried by said flange, the blade seal can help to support the outer panel during sliding movement of the outer panel and prevent scratching to the glass surface on which it slides.

A sixth aspect of the invention is concerned with the provision of edge seals between a removable outer panel assembly and a fixed support structure.

According to a sixth aspect of the invention a photovoltaic tile comprises a support structure adapted to be fixedly secured to a building framework (such as tile battens) and a removable outer panel assembly which substantially covers the support structure in the fully closed position of

the outer panel, the outer panel assembly having downwardly directed flanges at the opposite sides thereof, which flanges embrace respective outwardly facing side walls of side margins of the support structure, a respective elongate elastomeric seal being provided between the side, margin and the outer panel to provide edge seals along opposite sides of the assembled outer panel.

Preferably the elastomeric seals are mounted in respective longitudinal recesses in the upper faces of the side margins, and may be adhesively retained in the recesses, or the cross-sectional shape of the recesses and seals may be chosen such that the seals are held captive once they have been pressed into place.

Concern about the environment and the need to maximise the energy retention properties of roofing structures has led to the increasing use of loft insulation in both new roofs and those being refurbished. The solar tile of this invention having typically a glass surface will need to have protective packaging when delivered to site.

As a further feature of the invention, the packaging around the tile can of itself be a material suitable for use as a loft or wall insulation, thereby utilising the packaging and preventing it becoming site waste and, at the same time, improving the energy retaining properties of the building.

According to a seventh aspect of the invention there is provided a building tile provided in packaging, the packaging comprising building insulation material, the packaging being adapted to be secured to a building framework.

The packaging preferably comprises a central portion of building insulation material and a margin portion which is provided with adhesive.

The margin portion may be of increased flexibility with respect to the central portion. The packaging preferably comprises two margin portions which flank the central portion.

The packaging is preferably dimensioned to be wrapped around a roof tile so as to substantially enclose the tile.

The various aspects of the invention will now be further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic exploded perspective view of a photovoltaic tile in accordance with the invention, Figure 2 is a side-elevation, looking in the direction of the arrow A in Figure 1, of the slideable base panel, a portion of the glass panel being shown, Figure 3 is a perspective view of the assembled tile of Figure 1, Figure 4 is an enlarged perspective view of the lower left-hand corner of the panel of Figures 1 and 3, Figure 5 is a partial perspective view of a modified tile showing the outer panel in a retracted condition, the support framework being provided with edge seals, Figures 6,7 and 8 are enlarged perspective views of the lower left- hand corner of the support framework showing three seal configurations for use in the tile of Figure 5,

Figures 9,10 and 11 are partial end views of the flange provided on the slideable base panel, and showing three arrangements of sealing blade, Figure 12 is an end elevation of the bottom left-hand corner of a modified assembled tile, showing a sealing blade carried by the support framework, Figure 13 is an exploded partial view of the right-hand lower corner of the slideable panel structure showing a seal which surrounds the photovoltaic cells, Figure 14 is a partial view of the right-hand lower corner of the assembled slideable panel structure of Figure 13, Figure 15 is an enlarged section on the line 15-15 of Figure 14 showing the seal between the glass panel and the moulded base panel, Figure 16 is an end elevation of a further tile in accordance with the invention and shown in the assembled condition, Figure 17 is a view similar to Figure 16, with the base panel partially cutaway to show an electrical socket, the removable panel structure having been pivoted to a position in which the electrical plug and socket connection has been disconnected, Figures 18 to 21 show enlarged partial perspective views of the lower corners, broken away, of various modified upper panels,

Figures 22 and 23 are cross-sectional partial views of the lower margin of an assembled upper panel and base panel of the constructions of Figures 18 and 20 showing a fully bonded arrangement in Figure 22, and use of an elastomeric seal in Figure, 23, Figures 24 and 25 show views similar to Figure 22,23 for the upper panel of Figure 19, Figure 26 is a view similar to Figure 22 but for the upper panel of Figure 21, Figure 27 is a perspective view of a removable panel assembly of a further tile assembly in accordance with the invention, Figure 28 is a side elevation of the roof tile incorporating the removable panel assembly of Figure 27, Figure 29 is an enlarged side elevation of the removable panel of Figure 27, Figure 30 is a perspective view of an underclip for use in providing additional security to the tile assembly of Figure 1, Figure 31 is a perspective view of the keyhole slot in the support frame, Figure 32 is a perspective view showing the underclip in the fully assembled condition,

Figure 33 is a transverse cross-section through the root of the assembled clip of Figure 32, Figure 34 is a partial vertical cross-section of a sloping roof showing three arrangements for use of clips similar to that shown in Figure 30, Figure 35 shows a schematic perspective view of an inventive tile provided with packaging in accordance with the sixth aspect of the invention, Figure 36 shows a schematic perspective view of a portion of the packaging shown in Figure 35 which comprises building insulation material, Figure 37 shows the insulation portion of Figure 36 in situ between ceiling joists, Figure 38 shows a partial side elevation of photovoltaic tile arranged on a roof and being provided with electrical connection pins which are perpendicular to the tiles, Figure 39 is a schematic partial side elevation of the arrangement of Figure 38 on a larger scale, and Figure 40 is a partial side elevation of the arrangement of Figures 38 and 39 in which one of the tiles is being removed.

With reference to Figures 1 and 3, a photovoltaic roof tile 1 comprises a removable outer panel assembly 2 slideably mounted on a support structure in the form of a support framework 3 which is provided with

various fixing holes 4 for securing the support framework 3 to roofing tile battens (or to an equivalent building framework when the tiles are to be used as a wall or floor cladding).

The outer panel assembly 2 comprises a planar glass, or similar transparent material, outer layer 5, a moulded plastics or formed base panel 6 and an array 7 of photovoltaic elements which may be mono- crystalline, thin-film or other types of photovoltaic elements.

The base panel 6 comprises an essentially flat plate 8 formed with shallow recesses 9 of complementary shape to that of the photovoltaic element array to accommodate the photovoltaic element array when the glass panel 5 is lying on the upper surface of flat plate 8.

Base panel 6 is formed along the upper edge with an upstanding flange 10, and along the lower edge with a downwardly directed flange 11.

The upstanding flange 10 forms a location abutment for the upper edge 12 of the glass panel 5. Importantly the height of the flange 10 is made sufficiently high to protrude above the outer surface of glass 5, as shown at 13 in Figure 2, to provide some protection against scratching of the upper surface of glass 5 during sliding of the removable panel assembly. The protruding edge 13 of flange 10 will engage with the underside of an overlying tile to hold the overlying tile clear of the glass surface at that point.

As shown in Figure 1 and 2, the underside of the plate 8 integrally supports a junction box 14 furnished with projecting pins 15 which are adapted to connect with respective sockets 16 provided on a further junction box integral with the support framework 3. A hole 17 in plate 8

enables leads from the photovoltaic array 7 to be fed into the junction box 14 for connection to the pins 15. The junction box of the support structure 3 enables connections to be made to the power take-off circuitry.

The flange 11 provides a stop to determine the fully closed position of the slideable outer panel assembly, the flange 11 abutting with the lower frame member 18 of the support framework.

A pair of angled feet 18'extend downwards from opposite side margins of the base panel 6 and are receivable in the enlarged portions of respective keyhole slots 19 in the opposite sides of the support framework, for retaining the outer panel captive to the support framework 3 when the slideable panel assembly is moved back to bring flange 11 into abutment with the lower frame member 18, or forwards to gain access to electrical sockets 16.

As shown in Figure 1, the left hand margin of the support framework is provided with a corrugated upper surface 20, and the right hand margin of the base panel 6 is formed on the underside thereof with complementary corrugations 21, of known configuration, which mate with corrugations on adjacent tile margins to resist water ingress.

In the modification of Figure 5 the support framework 3 is provided with a pair of grooves 22 (only the left-hand one shown in Figure 5), which are positioned outside keyhole slots 19 and carry respective elastomeric seals 23 for sealing the side margins 22'of the framework 3 to the slideable outer panel 2.

In Figure 6 the seal 23 is of circular cross-section. Figure 7 shows a modified seal 23'in the form of a blade 23a, and Figure 8 shows a

seal 23b of square cross-section. The seal 23 effects a sealing action with the underside of the margin of the plate 8, the margin of the base panel 6 being formed with downwardly directed side flanges 24 which embrace the sidewall 25 of the respective support framework 3.

Figures 9 to 11 show various forms of elastomeric seal fast with the flange 11 of the slideable outer panel assembly 2 and which engage with the outer surface of the glass panel of an underlying tile to effect a seal against ingress of water.

In Figure 10 the elastomeric seal 26 is of blade form and is secured in a slot 27 provided in the inwardly-angled free end 28 of flange 11. The seal 26 thereby extends at an acute angle to the surface of glass 5 and is directed generally inwardly of the lower margin of the tile.

Figure 11 shows a modified seal 26'of blade form which clasps the angled free end 28 of flange 11.

In Figure 9 the free end 29 of the portion 28 of the flange 11 has been moulded as a soft plastics edge to the flange 11.

Figures 13 to 15 show how the glass panel 5 can be sealed to the base panel around the array of photovoltaic elements by the provision of an elastomeric seal 30 located in a recess 31 which surrounds the photovoltaic array. As shown in Figure 15 the glass panel 5 is urged towards the base panel 6 so as to deform the seal 30, and the panel 5 is then bonded to the base panel 6 by suitable bonded connections, which may be spaced-apart connections.

Figures 16 and 17 show an embodiment of the invention in which the tile assembly comprises a support framework 43 for attachment to battens

which may be roofing battens or battens provided on a vertical wall. A removable upper panel 46 is provided on the underside thereof with a junction box 54 to connect with leads to the photovoltaic array, not shown, housed beneath a transparent outer surface 45 of the removable panel assembly 46. The junction box 54 has electrical pins 55 adapted to be received in a socket 56 carried by the support framework 43, the axes of the pins 55 and socket boxes extending substantially normal to the plane of the assembled tile. One or more of the pin and socket pairs could be reversed if desired.

As shown, the pin and socket connection 55,56 is provided adjacent to the lower margin of the tile to enable the outer panel assembly 46 to be pivoted about the upper end in order to disconnect the connection 55,56, thereby enabling the removable panel assembly 46 to be removed by a sliding action. To facilitate such pivoting the angled feet 58, which correspond to feet 18, are provided adjacent to the upper end of the outer panel assembly 46.

As shown in Figures 16 and 17 the tile assembly is normally held closed by retaining screws 60 which are captive to a flange 61 on the lower edge of the removable outer panel assembly 46. These screws 60 may be mounted perpendicular to surface 45, or inclined at an angle to permit release if the tiles abut each other (such as in wall cladding).

Figure 12 shows a blade seal 62 which is suitable for use with a tile assembly of the kind shown in Figures 16 and 17, and in Figures 1 and 2, the seal being carried by the support panel 43, for engagement with the glass 45 of the underlying tile.

With reference to Figures 38 and 39 there is shown a partial view of photovoltaic tiles 91 which are supported on roof battens 95 on a roof 96.

Each tile 91 is provided with two electrical connection pins 97 which are adapted to be received by two sockets 98. The pins 97 are connected to an array of photovoltaic cells in each respective tile, and said pins being provided towards a margin of each tile. The pins 97 of each tile 91 extend in a direction which is substantially perpendicular to the plane of the tile.

In situ, the pins are received by the respective bores of the sockets 98, which sockets are mounted on a respective bracket 93 and an end portion of the bracket 93 being positioned between a batten 95 and an adjacent tile. The bracket 93 is attached to the batten by way of one or more screws (not shown). Electrical wires 99 extend from the sockets 98 to suitable circuitry (not shown).

With reference to Figure 40, in order to remove a tile from the roof it is simply necessary to pivot the tile generally upwardly and so disengage the pins 97 from the sockets 98.

The tiles 91 may be essentially very similar to the tiles previously shown and described (save for the different position of the connection pins).

Figures 18 to 26 show various modified arrangements for assisting in preventing water ingress to the photovoltaic elements. In these embodiments the upper panel 5 has been provided with marginal flanges 5a and 5b, extending along the side margins and bottom margin respectively of the panel 5. Such flanged upper panels may be produced in various ways such as a combination of glass and plastics, as a layered composite or sandwich for example, where a glass sheet provides a flat surface, and the plastic is bonded or moulded to create the flange/s.

In the construction of Figures 18 and 22 the flanges 5a and 5b are each provided with a respective return flange 5d, whereas in Figure 19 there are no such return flanges, and in Figure 20 there is a single return flange 19 along the lower flange 5b.

The upper panel 5 of the constructions of Figures 18 and 20 may be slid into position on the base panel 6, which is formed with a corresponding undercut or undercuts 5e, whereas in the construction of Figure 19 the panel 5 can be directly placed over the base panel 6. In the case of the construction of Figure 20 the flange 5d may be hooked into the corresponding undercut 5e, and the panel 5 may then be pivoted downwards into the assembled position.

The top panel 5 of the construction of Figure 19 is secured in use to the base panel 6 by a suitable bonding process, which can also be arranged to effect a seal along at least three margins of the panel 5.

Figures 23 and 25 show the use of an elastomeric seal 30 similar to that of Figure 15.

Figures 21 and 26 show flanges 5a and 5b formed with an integral rib 5f of rounded cross-sectional profile adapted to snap into a groove 5g of complementary profile provided in the outwardly facing surface of the base panel 6. If desired, the flanges 5a and 5b in Figure 21 could continue along the upper margin of the panel 5, to effect a snap-fit with the base panel 6 along all four margins of the panels 5,6.

When an elastomeric seal 30 has been provided, the panels 5 and 6 are preferably also bonded to each other so as to retain the seal 30 in position, but the bonding need not also provide a seal along the entire periphery.

Figure 27 shows the removable panel assembly of a tile in which the upper panel 5 is provided with a downturned flange 5b and return flange 5d along the lower margin only. As shown in Figure 28 and 29, the flanges 56 and 11 running along the bottom edge of the removable panel assembly 5,6 provide good protection against ingress of water running down a sloping roof.

With reference to Figure 1 and 31, the side margins of the support frame 3 are advantageously provided with a lower keyhole slot 70 for the optional use of an underclip 71 shown in Figure 30. Such an underclip is used in high wind areas to stop tiles'fluttering'and lifting in high winds.

The clip 71 of Figure 30 comprises a root 72 in the form of an upper rectangular platform 73 of larger dimensions than the enlarged portion 74 of the keyhole slot 70, as indicated in broken outline in Figure 31, a lower rectangular enlargement 75 of complementary dimensions to that of portion 74, so as to be capable of passing through the slot portion 74, and a neck 78 connecting platform 73 and enlargement 75, the neck 78 having a transverse dimension corresponding to the width of the elongate part 77 of slot 70, so as to be slideable along slot 77, by means of a screwdriver blade engaged in recess 79 in platform 73.

The clip 71 comprises a curved clip arm 80 depending from root 72 and of smaller transverse dimensions than slot portion 74 to enable the clip arm to be inserted through slot portion 74 to bring the clip arm substantially to an operative position prior to engagement at the root 72 in slot portion 74, and sliding of the clip along slot 77.

Figure 34 shows in the left hand part, such a clip in an assembled condition with the hooked end 81 engaging around a roof batten 82. The middle and right clips of Figure 34 have different shapes of clip arms to

provide different engagements to retain the tile assembly carrying the clip.

It will be appreciated that the clip 71 can be assembled into position from above the support structure 3, prior to assembly of the removable panel assembly to the structure 3.

With reference to Figure 35, an inventive roof tile 1 may be provided in packaging which is longitudinally wrapped around the tile and which packaging comprises a insulation portion 85 and an integral backing sheet 89. The portion 85 and the sheet 89 are both of substantially oblong- rectangular shape and whose width and length are greater than those of tile 1. So for example the packaging for a single tile with dimensions of 410mm x 735mm would be approximately 1470mm long and 410mm wide.

The insulation portion 85 comprises longitudinal margins 86, the lowermost surfaces of which are provided with self-adhesive (tacky) strips 88 along them. Located substantially centrally of the insulation portion 85 there is provided a portion of building insulation material 87.

The insulation material typically comprises a glass fibre material. The undersides of the end margins 91 are also provided with adhesive strips (not referenced) During transportation the self-adhesive strips 88 adhere to opposing surfaces of the backing sheet 89 so as to enclose the tile 1.

Although Figure 35 shows insulation material on one side of the tile in what may be termed the transportation condition, the packaging may more typically consist of an extended length of the insulation portion 85 which is long enough to be wrapped around the tile.

In use the packaging is peeled open on site (as shown by the arrow in Figure 35). The insulation portion 85 is then inserted between ceiling joists 90 (see Figure 37). The self-adhesive strips are pressed against (or on) the joists to provide a seal for the insulation portion and hence improve the insulation properties. Advantageously, the use of self- adhesive eliminates the need for other fixings such as metal staples when the tiles are wrapped prior to transportation.

Since surfaces of end margins of the insulation portion 85 are also provided with self-adhesive adjacent lengths of insulation can be adhered to each other, thus effectively providing a continuous length of insulation.