WO2012040778A1

WO2012040778A1 - Solar collector

Info

Publication number: WO2012040778A1
Application number: PCT/AU2011/001243
Authority: WO
Inventors: Norman Mills
Original assignee: Boss Polymer Technologies Pty Ltd
Priority date: 2010-09-27
Filing date: 2011-09-27
Publication date: 2012-04-05
Also published as: EP2622249A1; US20130186388A1; AU2011308081A1

Abstract

A solar collector for heating and transferring fluids, comprising an inlet manifold and an outlet manifold through which fluid is respectively transferred into and out of the solar collector; and 5 a plurality of polymer tubes each connected between the inlet and outlet manifolds, the polymer tubes having co-extruded concentric inner and outer tube layers, wherein the outer tube layer is composed of a harder polymer than the inner tube layer.

Description

SOLAR COLLECTOR

The present invention relates to a solar collector for use in a solar water heater, more particularly in heating pools or spas or for use in water heating applications such as domestic hot water services and horticultural applications, for example, for heating plant root soil.

BACKGROUND OF THE INVENTION

Various types of solar water heaters have been known for many years. In one particular type commonly used for pool or spa water heating, water is moved from a source (such as a pool or spa) into a solar collector (also known as a strip collector or a solar absorber), whereby solar radiation from the sun is absorbed by the solar collector and heats the water contained therein. The heated water is then returned back to the source in a closed circuit arrangement.

For domestic hot water applications the solar collector strip is generally contained within an enclosure beneath a clear panel such as tempered glass or plastic sheeting such a polycarbonate Corflute sheeting. The fluid to be heated is generally circulated within the system via convection (thermosiphon) or via a pump from either a hot water storage tank (direct system) or heat exchanger (indirect system) whereby solar radiation from the sun is absorbed by the solar collector and heats the circulating fluid contained therein in a closed circuit arrangement.

For horticultural applications, heated fluid, generally water, is circulated through the strip collector which is placed under or within a soil / plant root bed. The strip collector transfers heat from the circulating fluid within the tubes into the soil bed to encourage plant growth during colder months. The circulating fluid is usually heated by a boiler or other water heating appliance fuelled by fossil fuels or solar energy.

In other types of solar water heaters, a fluid other than water (such as ethylene glycol-based heat transfer fluids) is heated, and this fluid then transfers the heat therein to the water via a heat exchanger.

Solar collectors are often mounted on the roof of a house, garage or other structures facing the sun in order to obtain the maximum amount of solar radiation for that particular location.

The solar collector plays a vital part in the heating process as it transfers water and encourages it to be heated. One type of common solar collector is a single, black tube made of a material such as EPDM rubber, plasticised PVC, rigid polypropylene (PP) or rigid polyethylene (PE)(which can be either low density (LDPE) or high density (HDPE)) and which is approximately 2 centimetres in diameter or smaller.

Solar collector tubes may be rigid or flexible. Where the tube is rigid it may be placed on a roof as a coil. A number of rigid tubes which have been placed on the roof as a coil are connected to a manifold and are sufficiently long to create a coil large enough to cover a significant area upon which they are mounted. Another type of common solar collector includes multiple tubes such as those described above or straight tubes connected laterally via clips or a web.

There are a number of drawbacks with rigid tubes, including possessing little elasticity and unsatisfactory sealing properties, resulting in inadequate retention and sealing when installed onto a manifold barb. Generally the rigid tubes require special compression fittings to fix and seal the tube onto the barb, or alternatively, the manifold is over-moulded or welded onto the tubes in order to create a welded join at the interface to fix and seal the tube to the manifold, which can cause cracking and water leaks at the weld.

The drawbacks with flexible, plasticised or soft types of solar collectors are that the soft material cannot withstand the regular cycle of high pressure from the fluid therein followed by high vacuum pressure when the tube is drained of the fluid therein, and thus premature stress cracking can occur. Also, the material can deform easily, thus making installation and retention on the manifold difficult. An adhesive or a collar may be required to retain the tube on the manifold barbs. Release valves or other means of pressure release must be used to overcome the high pressures experienced in these types of solar collectors. Furthermore, the tubes can experience UV and chemical degradation over time, and can easily be damaged by pests or trampling by people during installation or maintenance.

Overall, these drawbacks result in a solar water heater that can be inefficient, costly and laborious to install and maintain, and susceptible to degradation and damage.

A solar collector is therefore required which can minimise or avoid these drawbacks.

SUMMARY OF THE INVENTION

According to the present invention there is provided a polymer tube for use in a solar collector for heating and transferring fluids, the tube having co-extruded concentric inner and outer tube layers, wherein the outer tube layer is composed of a harder polymer than the inner tube layer.

According to the present invention there is also provided a solar collector for heating and transferring fluids, comprising an inlet manifold and an outlet manifold through which fluid is respectively transferred into and out of the solar collector; and a plurality of polymer tubes each connected between the inlet and outlet manifolds, the polymer tubes having co-extruded concentric inner and outer tube layers, wherein the outer tube layer is composed of a harder polymer than the inner tube layer.

The polymer tubes may be connected via a co-extruded web. The web may consist of multiple webs dispersed between the multiple tubes or one web with the multiple tubes connected to the one web.

In the above embodiments of a solar collector, the web may comprise the same material as the innermost soft layer or the outer harder layer. Alternatively, the web may be extruded between the polymer tubes from a separate web polymer, or the polymer tubes may be coated with a separate web polymer that also forms the web between the polymer tubes.

According to the present invention there is further provided a polymer tube for use in a solar collector for heating and transferring fluids, the tube having at least one tube layer and a co-extruded strip thereon, wherein the strip covers less than 100% of an outer surface of the tube layer, or wherein the main tube layer is visible.

According to the present invention there is also provided a polymer tube for use in a solar collector for heating and transferring fluids, the tube having co-extruded concentric inner and outer tube layers, wherein the outer tube layer is weldable.

In one embodiment the inner tube layer is made of a cross linked polymer.

There is also provided a solar collector for heating and transferring fluids, comprising an inlet manifold and an outlet manifold through which fluid is respectively transferred into and out of the solar collector; and

a plurality of polymer tubes as described above, each polymer tube welded to either the inlet manifold or outlet manifold, or to both.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments, incorporating all aspects of the invention, will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a solar collector in accordance with an embodiment of the invention; Figure 2a is a cross-sectional isometric view of the solar collector of Figure 1 ;

Figure 2b is a cross-sectional front view of the solar collector of Figure 1 ;

Figure 3a is an isometric view of the tubes of a solar collector in accordance with another embodiment of the invention;

Figure 3b is a cross-sectional front view of tubes of Figure 3a;

Figure 3c is a front sectional view of yet another embodiment of a solar collector;

Figure 3d is a front sectional view of yet another embodiment of a solar collector; Figure 3e is a front sectional view of still yet another embodiment of a solar collector;

Figure 4 illustrates a solar collector in accordance with Figure 3a when mounted on a roof;

Figure 5a is an isometric view of a solar collector in accordance with a further embodiment of the invention;

Figure 5b is a cross-sectional view of a solar collector of Figure 5a;

Figure 6 is an isometric view of a single solar collector tube;

Figure 7 is a cross-sectional view of a solar collector of Figure 6;

Figure 8 illustrates a variation of the solar collector of Figure 1 ;

Figure 9 illustrates the solar collector of Figure 6 in use attached to a manifold at both ends; and

Figure 10 illustrates the solar collector of Figure 6 attached to a manifold attached to a manifold at one end with the assistance of a collar.

Figure 1 1 is a cross-sectional view of a solar collector in accordance with another embodiment of the invention;

Figure 12 illustrates a solar collector in accordance with Figure 1 1 when mounted on a roof;

Figure 13 is a cross-sectional view of a solar collector in accordance with a further embodiment of the invention; and

Figure 14 illustrates a solar collector in accordance with Figure 13 when mounted on a roof.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 illustrates a solar collector in accordance with an embodiment of the invention. The solar collector 1 comprises an inlet manifold 8 and an outlet manifold 9 through which fluid is respectively transferred into and out of the solar collector, and a plurality of polymer tubes 2 with co-extruded and concentric inner and outer tube layers (4, 3 respectively). Each polymer tube 2 has at least two tube layers: an inner tube layer and an outer tube layer, although more than two layers are also contemplated further below.

The solar collector 1 is manufactured by a co-extrusion process. Co-extrusion is a well known technique in the art. The solar collector can be made to any length, width or depth depending on the particular application.

Co-extrusion is the process whereby two or more molten materials are combined in an extrusion die under pressure so as to create an extruded profile of two or more materials. The extruded profile is then either cooled (thermoplastic) or heated / vulcanised (thermoset) in order to set its shape. The process used to make the solar collector product of the present invention produces solar collectors possessing very high quality profiles at high line speeds, with minimal die deflection and low operating costs.

The solar collector may be a part of an open or closed fluid circuit/system for heating fluid in water heating applications such as domestic hot water services and horticultural applications, as well as pool and spa heating.

In the solar collector illustrated in Figure 1 , the inlet and outlet manifolds 8, 9 are in turn connected to inlet and outlet pipes (not shown) through which fluid, typically water, is pumped through the solar collector then on to the desired heating application. The manifolds 8, 9 may be traditionally positioned in a solar collector circuit, namely at opposite ends of tubes laid out straight. Alternatively, the inlet and outlet manifolds may lie alongside each other with the polymer tubes bent in a return U-shape to connect to each manifold. Still alternatively, one end of the polymer tubes could be connected to one of the inlet or outlet manifold, while the other end of each tube is connected to a connecting/intermediate manifold. Still another alternative is to form the inlet and outlet manifolds in a single manifold containing an internal partition wall that divides the manifold into an inlet part and an outlet part.

In a first embodiment of a solar collector tube described herein the outer tube layer 3 is made of a harder polymer than the inner layer 4. This combination allows the solar collector polymer tube to absorb and transfer solar radiation to fluid inside the tubes with superior performance to that of known solar collectors while also ensuring product longevity.

The hardness of the outer layer 3 means it is able to withstand damage to the tube's integrity as a result of weight or sharp impact by various means such as humans, animals, or weather conditions, like storms, hail or projectiles.

With the material of the inner tube layer 4 being softer than the outer tube layer, it is more easily deformable and offers more friction so to be able to grip onto a manifold barb (not shown) used in connecting the polymer tubes to the inlet and outlet manifolds. The material of the inner tube layer 4 allows the polymer tube 2 to deform and securely grip the barbs of a manifold while still providing good sealing on the barb and good barb retention under pressure.

In a second embodiment of a solar collector polymer tube described herein, the tube comprises at least two concentric and co-extruded tube layers where the inner tube is made of a cross-linked polymer and the outer layer is weldable. This version allows for each tube to be connected to a manifold by welding (typically in the factory) rather than by assembly onto a barb. The outer tube layer is fusable so that it can be welded to the manifold material by way of heat or sonic welding, over-moulding or other known polymer fusion techniques.

In the embodiment shown in Figure 2b, the polymer tubes 2 are connected laterally via a web 5. Fluid, typically water, flows through a central bore 6 (see Figures 2a and 2b) in each co-extruded tube 2 and circulates within a closed or open solar collecting system to distribute heated fluid. In this embodiment, the web 5 connecting the tubes is a continuous hard, rigid web the same length as the tubes. The width of the web can be smaller, equal to or greater than the diameter of the tubes. The web may have a line of thinning, or other tearable feature, to promote tearing to allow an installer to quickly and easily adjust the width of tubes to the desired length of manifold. Furthermore, tearing along the webs also allows the installer to separate the tubes from the webs for a sufficient distance (for example, approximately 100 mm) to enable the individual tubes to be connected onto a corresponding manifold barb, which is set a fixed distance apart from the next barb. This can be done on- site and without the need for any special skills or equipment. The web may be scored, perforated or broken in sections to assist tearing of the web, and the web may be perforated to assist with roof drainage and roof retention.

The web may alternatively be a soft, pliable web so that it is flexible and hence the distance between the tubes is flexible to allow for easier attachment of tubes to the barbs regardless of misaligned separation between the barbs and the tubes. This flexibility in the web could also make possible the automated/mechanised assembly of tubes onto barbs. The web can be a plasticised material that possess elastic properties combined with good UV and weathering resistance.

Web 5 is co-extruded with the solar collector polymer tubes. The web may be co- extruded in the same material as the inner tube 4, as shown in Figure 2c, or the material of the outer tube 3, as shown in Figure 2e. In either case, the web is joined to the outer surface of the outer tube layer 4. Alternatively, the web may comprise a different material to either the inner or outer tubes and/or may be formed from a full or partial third tube layer co- extruded around the outer layer. This embodiment is illustrated in Figure 2d which shows a co-extruded partial layer that appears as a strip 1 1 , or slat, over the outer layer. This third material may be chosen to be softer or harder than the inner and outer layers as desired, but in one embodiment could be soft and tactile to assist with grip when assembling the tubes onto barbs (manually or mechanically), and/or may appear a different colour, as discussed in more detail below.

The number of tubes present in solar collector 1 can vary to suit the particular application. A solar collector can contain 1 to 1000 tubes, or more, where the number of tubes is largely dependent on the size of the solar collector, the diameter of the tubes and the spacing therebetween. In terms of size, the area covered by a solar collector in heating of domestic swimming pools or hot water supplies, could be between 20 to 40 square metres, but for larger commercial applications the area covered by the solar collector can be 100 square metres or more.

For example, the present solar collector could be provided in the form of a flexible mat-type system where the tubes connected by webbing could cover an area of 2 metres x 13 metres, with the supply and return manifolds traversing the 2 metre width. The average number of tubes connected along the 2 metre long manifold system for in this example could range between 140 to 220 tubes, again depending on spacing between the tubes and tube size.

It is understood, however, that the dimensional area, set-up and tube size/spacing of the configuration of this example can vary considerably from installation to installation. Accordingly, it is open to provide solar collectors with a wide range of different numbers of tubes.

Where multiple tubes are used, the tube number may range between 2 to 50 tubes, and more particularly, 4 to 20 tubes, or 4 to 8 or 8 to 16 tubes. Alternatively, the system may incorporate the use of single tubes that are not joined by a web.

The width of the solar collector 1 will depend on the diameter of the tube 2, the width of the web 5 and the number of tubes 2 present. Thus the width of the solar collector 1 can vary greatly. In one embodiment suitable for domestic solar pool systems, the width of the solar collector can range from 100 millimetres to 300 millimetres wide, or even more such as 1000 millimetres, and comprise 4 to 20 tubes. For example, the solar collector 1 can be 170 millimetres wide with 8 to 16 tubes, or 100 millimetres wide with 4 to 8 tubes, or 300 millimetres wide with 20 to 32 tubes.

Although the polymer tube(s) 2 depicted in the Figures are circular in shape, it is to be understood that the tube(s) 2 may be of any suitable shape, including oval, "D" shaped, triangular, square (with or without radial corners), rectangular (with or without radial corners) or oblong. Barb manifold solar collector tubes

Figures 2a, 2b, 2c, 2d, 3c and 3d more clearly illustrate an embodiment of the solar collector 1 that comprises a harder outer tube layer 3 and a softer inner tube layer 4.

Outer Tube Layer

The outer tube layer 3 is made of one or more materials that is able to absorb solar radiation to heat the fluid inside the tube. The material also preferably exhibits good UV (ultraviolet) and weathering resistance and other desirable properties required for an outer surface, such as a suitable Dyne level for roof glue adhesion and suitable tension set. In the embodiment that includes a full or partial third layer, that third layer would possess and exhibit similar UV and weathering resistance.

Furthermore, the material of the outer tube layer 3 is preferably not easily deformable at an elevated temperature and/or under high vacuum pressures created during drain down of fluid in the collector and/or expandable under high fluid pressures inside the tube. Instead the outer tube layer 3 exhibits some rigidity to maintain its integrity and retention on a barb on a manifold.

Suitable materials for the outer tube layer 3 include polymeric materials such as thermoset or thermoplastic.

Examples of thermoset materials include thermoset elastomers, such as EPDM and silicone rubber.

Examples of thermoplastic materials include thermoplastic elastomers, rubbers or alloys. One type of suitable thermoplastic material is a thermoplastic polymer such as polyvinylchloride (PVC) or modified or unmodified plasticised PVC. Other suitable materials include thermoplastic elastomers (TPE), such as thermoset rubbers. Thermoplastic elastomers include materials such as thermoplastic vulcanizates (TPV), styrene block copolymers such as styrene-ethylbutylene-styrene (SEBS) and polyolefin elastomers (POE). Thermoset elastomers include EPDM and silicone rubber. Other possible thermoplastic materials include crosslinked (XL) or non-crosslinked polyolefins such as polypropylene (PP), polyethylene ((PE), including LDPE and HDPE) and their alloys.

'Alloy' means any blend of two or more compatible materials to form a composite polymer. For example, Santoprene® is a thermoplastic elastomeric alloy of EPDM rubber and polypropylene.

Examples of other suitable materials are moisture curable, silane grafted high density polyethylene XL-HDPE or moisture curable, silane grafted polyolefin elastomer XL- POE, Santoprene® rubber (a TPV), plasticised PVC and/or nitrile modified plasticised PVC.

The hardness of outer tube layer 3 will generally be in the range of 45 Shore A to 90 Shore D and preferably within the range of 80 Shore A to 50 Shore D. However, a hardness outside of this range may be acceptable depending on the particular application.

The outer tube layer 3 can be of any colour. In one embodiment, the colour of outer tube layer 3 and optionally web 5 is black. In other embodiments, outer tube layer 3 and optionally web 5 is entirely red, blue, or another colour such that the solar collector blends into its surroundings. In yet another embodiment, outer tube layer 3 and optionally web 5 is multicoloured. By 'multi-coloured', it is meant that the outer tube layer 3 and optionally web 5 is/are two or more different colours, preferably in solid blocks, i.e. no mixing or swirling of the colours is present. It can be appreciated that the first colour may coat one quarter of the outer tube layer 3, and the second colour may coat the remaining three quarters of the outer tube layer 3. Web 5 may be coloured in a similar manner as outer tube layer 3. Alternatively, the first colour may coat one half (for example the top half) of the outer tube layer 3 and optionally web 5, and the second colour may coat the other half (for example the bottom half) of the outer tube layer 3 and optionally web 5.

Figures 3a and 3b specifically illustrate embodiments of solar collector tubes 2, where the outer tube layer 3 and web 5 are multi-coloured, and are namely made up of two colours, 3a and 3b. This multi-coloured feature enables one colour to be visible when the solar collector 1 is mounted at a particular angle on a surface, such as a sloping roof, and the other colour to not be visible or to be visible to a lesser extent at the same angle.

Figure 4 illustrates one example where the solar collector 1 of Figure 3a with inlet and outlet manifolds 8 at both ends of polymer tubes 2 is mounted on a roof 14, whereby one colour 3a is visible to a person P standing on the ground and the other colour 3b is not.

This multi-coloured feature of outer tube layer 3 and optionally web 5 has both aesthetic and functional advantages. Specifically, one colour may be chosen for its aesthetic value and the other colour may be chosen for its heat absorbance capabilities. For example, as shown in Figure 4, one half of the upper tube surface (i.e. 25% of the total tube surface) of the outer tube layer 3 may be orange coloured 3a to suit a terracotta tiled roof while the other half of the upper tube surface of the outer tube layer 3 and the web 5 may be black 3b. The black top tube surface and web 5 serve to maximise the amount of solar radiation absorbed due to it being in alignment with the sun's trajectory. Ideally the bottom tube surface (not shown) 3b would also be black to maximise the heat absorption due to convection from the underlying roof surface material e.g. terracotta tiles. Therefore the solar collector 1 is designed to absorb the maximum amount of solar radiation possible whilst exhibiting a visually pleasing colour.

Inner Tube layer

The inner tube layer 4 transfers the solar radiation absorbed by the outer tube layer 3 to the fluid in the tube. The material of the inner tube layer 4 is softer, more easily deformable and offers more friction when in contact with a barb than the material of the outer tube layer 3. Thus the material of the inner tube layer 4 is able to deform and securely grip the barbs of a manifold. In combination with the harder outer tube layer 3 which surrounds and shrinks around the softer inner tube layer 4, a fluid-tight seal is created which resists against fluid pressure in the tube and thereby retains and seals the solar collector on the barb.

The material of the inner tube layer 4 preferably efficiently transfers the UV radiation absorbed by the harder outer tube layer 3 to the fluid for efficient heating.

The material of the inner tube layer 4 is preferably chemical resistant. This is relevant where the solar collector 1 is to be used to heat and transfer a fluid which contains chemicals, such as chlorine, that can degrade the tube material over time.

Suitable materials for the inner tube layer include the same group of materials as those discussed above in respect of the outer tube layer and include polymeric materials such as thermoset materials and thermoplastic materials. Once again an example of a thermoset material is thermoset elastomers such as EPDM and silicone rubber. Similar to above, examples of thermoplastic materials include thermoplastic elastomers, thermoplastic rubbers and thermoplastic alloys.

One type of suitable thermoplastic material is a thermoplastic polymer such as polyvinylchloride (PVC) or modified or unmodified plasticised PVC. Other suitable materials include thermoplastic rubbers (also known as thermoplastic elastomers (TPE)).

Thermoplastic rubbers include materials such as thermoplastic vulcanizates (TPV), styrene block copolymers such as styrene-ethylbutylene-styrene (SEBS) and polyolefin elastomers (POE). Other possible thermoplastic materials include crosslinked or non-crosslinked polyolefins, such as polypropylene (PP), polyethylene ((PE), including LDPE and HDPE) and their alloys.

Examples of more suitable materials includes an olefin block copolymer (a OBC), moisture curable, silane grafted olefin block copolymer (a XL-OBC), Santoprene® rubber (a TPV), plasticised PVC and/or nitrile modified plasticised PVC.

The hardness of inner tube layer 4 will generally be in the range of 10 Shore A to 90 Shore A and preferably within the range of 30 Shore A to 60 Shore A, with a relative hardness that is not more than that of the outer tube layer 3. The material of inner tube layer 4 preferably avoids or substantially reduces flex fatigue, possesses the appropriate friction co-efficient for secure barb grip, and has the appropriate softness for barb locking and sealing.

Inner tube layer 4 has a diameter that efficiently transfers heat to the fluid carried therein and effectively transfers fluid through the solar collecting system. Generally, the smaller the diameter of inner tube layer 4 (and hence the co-extruded outer tube layer 3), the greater the amount of tube surface area that contacts the fluid, and therefore the greater - l i the transfer of heat to the fluid. In general, the internal diameter of inner tube layer 4 can range from 3 millimetres to 20, 25, 30 or more millimetres.

Outermost tube layer

As discussed above, a third layer, or more layers, may coat varying fractions of outer tube layer 3 and optionally web 5.

Figures 3c, 3d and 3e illustrate a variation on the coloured stripe co-extruded as part of the outer layer as described above and shown in Figures 3a and 3b. In the embodiments of 3c to 3e, a third layer, and namely a contrasting coloured strip 1 1 , is co- extruded over the outer layer 3 and in this case constitutes an outermost layer. As illustrated, strip 1 1 is co-extruded to only extend partially around the outer tube 3, although the degree of coverage can vary according to desire and application but will usually be less than 100% coverage on the outer tube periphery. If the strip 1 1 is to function as described above in relation to figures 3a and 3b to appear a certain colour (or blend/camouflage with the surface it is mounted on), then the strip will typically cover about 25%-75%, or in terms of degrees of coverage around the outer tube, 90°-270 °, of the outer surface. In a more specific embodiment the coverage of the strip could be closer to 50%, namely 180 °.

This embodiment is useful to provide versatility in an application where, for example, one side of a solar collector tube has a co-extruded strip (about 50%) in a first colour, while the other side has either a second co-extruded strip in a second colour or the exposed part of the outer tube that is not covered by the strip is provided in a second colour. The first colour could be red terracotta, while the second colour could be green, both colours being popular colours of roofs. A user could then choose which side of the solar collector tubes to lay exposed, and depending on the colour of the roof onto which the solar collector is to be laid. Furthermore, a distributor or retailer need only stock one type of product for two applications because the product can be laid in two different orientations (upside down from each other) to achieve two different effects, namely two different colours exposed to view.

The outermost tube layer 1 1 , aside from optionally being a different colour to the outer tube layer, may also comprise other characteristics. For example, the material of the outermost tube layer may be weldable to enable fusion to the manifold. Further, the material may be soft to give a tactile feel and promote grip to enable easier assembly onto a barb.

It is also understood that an outermost layer 1 1 may be co-extruded to cover 100% or the outer tube layer 3 and thereby constitute a full, third outermost tube layer. Further partial or full layers may even be co-extruded on top thereof.

A similar variation to that shown in Figures 3a and 3b is shown in Figure 1 1 , where the solar collector 1 comprises a plurality of polymer tubes 2 with co-extruded inner and outer tube layers (4, 3) connected laterally via a web 5. Fluid, typically water, flows through a central bore 6 in each co-extruded tube 2 and circulates within a closed or open solar collecting system to distribute heated fluid. A strip 1 1 is additionally applied over outer tube layer 3. As implied above, 'strip' means that less than 100% of outer tube layer 3 is extruded with a coloured material, while the outermost layer may additionally comprise full, 100% coverage.

The 'strip' in one version preferably covers less than 75%, and more preferably between 0.1 to 50%, of outer tube layer 3, to achieve a quarter coloured look. In the embodiment shown in Figure 1 1 , approximately 25% of the outer surface of tube layer 3 is covered by strip 1 1. In other words, some of the outer tube layer 3 will be visible so that the 'strip' does not necessarily cover the whole surface of the outer layer.

In another version the strip can cover preferably around 25% and 75% of the outer layer, and closer to 50%, namely 40% to 60%.

Optionally, and in addition, a part of or all of web 5 may also be provided with an extruded strip.

The strip is intended to provide the same aesthetic and functional advantages as the multicoloured outer layer described above under outer tube layer for the solar collector shown in Figures 3a, 3b and 4. Specifically, the strip 1 1 may be chosen for its aesthetic value and the outer tube layer 3 may be chosen for its heat absorbance capabilities.

Other variations

Figures 5a and 5b show another embodiment of the present invention, wherein inner tube layer 4 contains a spiralled projection 7 running along the length of its central bore 6. The spiralled projection 7 may be made out of the same or a different material as the inner tube layer 4. Furthermore, the spiralled projection 7 may be made integral or separate to the inner tube layer 4. Typically, the spiralled projection 7 is extruded with the tube 2.

More particularly, the spiralled projection 7 may be produced as an internal spiral on a single polymer extrusion without the need for co-extrusion.

Spiralled projection 7 serves to increase the turbulence of the fluid to be heated as it passes through the tube 2, thus facilitating transfer of heat into the fluid more efficiently.

Figures 6 and 7 illustrate a solar collector in accordance with another embodiment of the invention. The solar collector 1 comprises a single tube 2 with co-extruded inner and outer tube layers (4, 3). A single tube may be used on its own or in combination with additional single tubes that are separately attached to a manifold without the use of a web. The single tube may be obtained by separation from a plurality of tubes connected together by web(s) 5, as described above. Outer layer 3 has a hardness that is greater than inner tube layer 4 similar to the earlier embodiments described above.

Figure 8 illustrates a variation of the solar collector of Figure 1. Specifically, in this embodiment the web 5 is wider than that illustrated in Figure 1 and demonstrates that the web between tubes 2 can be as short or as wide as is desired and/or required by the application.

Figure 9 illustrates the web-less, single solar collector of Figure 6 in use.

In both Figures 8 and 9, the two open ends of the solar collector 1 are attached to barbs (not shown) protruding from a manifold 8. However, as discussed further below under "Weldable Solar Collector Tubes", the tube(s) may be directly welded onto the manifold rather than being pushed onto barbs.

As explained above, the properties of the inner and outer tube layer materials enable the solar collector to resist the normal operational pressures and temperatures experienced by the solar collector in order to retain it on, and create a fluid-tight seal with, the barb. However, in some circumstances, a collar may still be used to enhance the seal, as illustrated in Figure 10. Figure 10 illustrates the single tube of Figure 6 (obtained by separation from a plurality of tubes along the web to obtain a single tube) attached to a manifold 8 with the assistance of a collar 10.

The web 5 may be a continuous web the same length as the tubes, or a broken or perforated web that can be torn as already described above. The width of the web, the number of tubes present in solar collector and thus the width of the solar collector can be as already described above. The shape of the polymer tube(s) 2 can also be of any shape as already described above. The polymer tube(s) can also contain a spiralled projection as already described above.

Figure 12 illustrates one example where solar collector 1 of Figure 1 1 is attached to a manifold 8 at both ends and mounted on a roof 14, whereby strip 1 1 is visible to a person P standing on the ground and the outer tube layer 3 is not. Strip 1 1 covers one half of the top of outer tube layer 3 (i.e. 25% of the total outer tube layer 3) and, for example, may be grey to suit a cement tiled roof while the other half of the top of outer tube layer 3 (not covered by strip 1 1 ) and web 5 may be black. The colour black maximises the amount of solar radiation absorbed by the outer layer and web because these are intended to be laid in alignment with the sun's trajectory. Ideally the bottom outer tube surface (not shown) would also be black to maximise the heat absorption due to convection from the underlying roof surface material e.g. cement tiles. Therefore the solar collector 1 is designed to absorb the maximum amount of solar radiation possible whilst exhibiting a visually pleasing colour. The strip material may be any of the materials already mentioned above for the outer tube layer 3 or inner tube layer 4, or may be a combination thereof, with the same physical characteristics and desirable characteristics already mentioned for these materials.

The strip may be of any thickness. It is envisaged that the thickness is up to 0.2 millimetres; however other thicknesses depending on the particular requirements of the application can be used. In most cases, the strip is of such a thickness that it does not substantially affect the properties of outer tube layer 3 or the solar collector 1 as a whole.

Another embodiment of the present invention is shown in Figure 13. This embodiment is a variation of the embodiments described above. In this embodiment, outer tube layer 3 exists only in part and also defines differently coloured strip 1 1.

Figure 13 shows solar collector 1 comprising a plurality of polymer tubes 2 with co- extruded main tube layers 12 connected laterally via a web 5. Fluid, typically water, flows through a central bore 6 in each co-extruded tube 2 and circulates within a closed or open solar collecting system to distribute heated fluid. Strip 1 1 , which in this embodiment forms a partial outer layer, is additionally applied over main tube layer 12. By 'strip', it is meant as above that less than 100% of main tube layer 12 and/or web 5 is extruded with a coloured material to form the strip. Depending on application, this could be between 25% and 75%, or alternatively between 0.1 % and 50%, of main tube layer 12 and/or web 5 is extruded with a coloured material. In the embodiment of Figure 13 strip 1 1 is illustrated as covering approximately 25% of the outer surface of the main tube layer 12.

The web 5 may be a continuous web the same length as the tubes, or may be readily torn by providing a broken or perforated web as already described above. The width of the web, the number of tubes present in solar collector and thus the width of the solar collector can be as already described above. The shape of the polymer tube(s) 2 can also be of any shape as already described above. The shape of the polymer tube(s) 2 can also be of any shape as already described above. The polymer tube(s) can also contain a spiralled projection as already described above.

The strip is intended to provide the same aesthetic and functional advantages as the multicoloured outer tube described above for the solar collector shown in Figures 3a, 3b and 4. Specifically, the strip 1 1 may be chosen for its aesthetic value and the main tube layer 12 may be chosen for its heat absorbance capabilities.

Figure 14 illustrates one example where solar collector 1 of Figure 13 is attached to a manifold 8 at both ends and mounted on a roof 14, whereby strip 1 1 is visible to a person P standing on the ground and the main tube layer 12 is not. Strip 1 1 covers one half of the top of main tube layer 12 (i.e. 25% of the total tube layer 12). Strip 1 1 may be coloured to suit the colour of the roof on which the solar collector is laid, while the other half of the top of main tube layer 12 not covered by strip 1 1 , and web 5, may be black to maximise the amount of solar radiation absorbed by it due to it being in alignment with the sun's trajectory. The bottom of the main tube surface (not shown) could be black to maximise the heat absorption due to convection from the underlying roof surface material e.g. cement or terracotta tiles. Alternatively, the bottom of the main tube surface could be another desirable colour to have exposed to view so that an option is provided to flip the tubes around to choose and expose the desired tube colour. The solar collector 1 is designed to absorb the maximum amount of solar radiation possible whilst exhibiting a visually pleasing colour.

In a preferred embodiment, strip 1 1 is coloured and matches the colour of the surrounding surface from the viewpoint of a person standing at a position P whilst allowing for the maximum amount of heat possible to be absorbed by the main tube layer 12 by being black in colour.

The strip material may be any of the materials already mentioned above for the outer tube layer 3 or inner tube layer 4, or may be a combination thereof, with the same physical characteristics and desirable characteristics already mentioned for these materials.

The strip may be of any thickness. It is envisaged that the thickness is up to 0.2 millimetres; however other thicknesses depending on the particular requirements of the application can be used. In most cases, the strip is of such a thickness that it does not substantially affect the properties of tube layer 12 or the solar collector 1 as a whole.

As described above, the polymer tube(s) depicted in the Figures are circular in shape, but may be of any suitable shape, including oval, "D" shaped, triangular, square (with or without radial corners), rectangular (with or without radial corners) or oblong. Installation and/or maintenance of the solar collector of the present invention which possess a harder outer tube and a softer inner tube is made more simple than currently available solar collectors. To install, each end of a tube on the solar collector is forced onto a barb protruding from an end manifold located at both ends of the tube. The interconnected tubes and manifolds create a fluid circuit which fluid flows through within a closed or open fluid circuit. The harder outer tube layer of the solar collector of the present invention is not easily distortable itself, and surrounds and maintains a compressive force around the softer inner tube layer, thus preventing the softer inner tube layer from distorting and expanding off the manifold barb. The harder outer tube layer can also withstand higher fluid and vacuum pressures than the inner tube layer's softer material, and therefore resists expansion, contraction or failure of the tubes due to high positive and negative pressures. This also creates a fluid-tight seal with the barb. The softer inner tube layer is made of a material which is more easily deformable than the harder outer tube layer and offers more friction when in contact with a barb than the harder outer tube layer, thus the softer inner tube layer can grip and seal on the barb securely. These characteristics also serve to retain the solar collector on the barbs of the manifold and create a fluid-tight seal on the barb. Previously it was necessary to apply adhesives and/or collars to the solar collector in order to securely attach it to a barb due to normal operational fluid pressures and at elevated temperatures. The solar collector of the present invention reduces or even eliminates the use of adhesives and/or collars. However, as illustrated in Figure 10, a collar may still be used in some circumstances.

Where there is no distinct 'inner' and Outer' tube layers present, such as the main tube layer embodiment shown in Figures 13 and 14, it is to be understood that the main tube layer 2 may be manufactured from a single material that possess a combination of characteristics possessed by the inner and/or outer tube layers. However, a collar or an adhesive may still be used in some circumstances.

Weldable solar collector tubes

In the second main embodiment of the solar collector tube the outer tube layer is made of a material that is weldable to the manifold while the inner tube layer is made of a cross linked polymer that exhibits good mechanical (namely, physical) properties at elevated temperatures, good heat transfer properties, minimal thermal expansion, and able to withstand elevated positive or negative pressures at extremes of temperatures without deforming, cracking or splitting or other damage. In this embodiment the material of the inner tube may be the same hardness, or harder than that of the outer tube, or vice versa.

In instances where the inner tube layer is harder than the outer tube layer, it is the inner tube layer that provides rigidity and strength to the weldable solar collector while the outer tube layer is non-rigid, or softer, to minimise cracking at the weld.

An example of a suitable inner tube material for use in this embodiment is a moisture curable, silane grafted high density polyethylene XL-HDPE. Other examples of suitable materials are shown in Table 1 below.

Examples of a suitable outer tube materials are PP, PE, POE or HDPE. Other examples of suitable materials are shown in Table 1 .

The weldable solar collector tubes may also comprise the same features described above and below in relation to the web, namely flexible or rigid or tearable, and in relation to the 'stripe', which can similarly be co-extruded to extend partially around the outer tube and less than 100% around the outer tube's periphery.

Table 1 illustrates various examples and possible combinations of materials suitable for use for the inner and outer tube layers for both the weldable and push-on-barb embodiments. It is understood that these examples demonstrate suitable combinations but are not intended to be limiting.

TABLE 1 :

Application Inner Tube material Outer Tube material

1 .weldable acts as a reinforcing layer Weldable Layer

solar collector • moisture curable, silane grafted • PP or rubber modified high density polyethylene XL-HDPE or PP.

• moisture curable, silane grafted

polyolefin elastomer XL-POE, Other options thermoplastic elastomers (TPE),

Other options include thermoplastic Thermoplastic rubbers elastomers (TPE) such as including materials such as Thermoplastic rubbers including thermoplastic vulcanizates materials such as thermoplastic (TPV), styrene block vulcanizates (TPV), styrene block copolymers such as styrene- copolymers such as styrene- ethylbutylene-styrene (SEBS) ethylbutylene-styrene (SEBS) and and polyolefin elastomers polyolefin elastomers (POE). (POE)

Other possible options include Other possible options include thermoplastic materials from the Olefin thermoplastic materials from group including crosslinked or non- the Olefin group including crosslinked polyolefins such as HDPE, PE, and olefin block polypropylene (PP), polyethylene copolymer (OBC).

((PE), including LDPE and HDPE and

their alloys and modifications. The hardness of the outer weldable tube layer will

The hardness will generally be in the generally be in the range of 45 range of 45 Shore A to 90 Shore D and Shore A to 90 Shore D and more specifically within the range of 80 preferably within the range of Shore A to 50 Shore D. However, a 50 Shore A to 50 Shore D, hardness outside of this range may be However, a hardness outside acceptable depending on the particular of this range may be application. acceptable depending on the

particular application.

2.weldable reinforcing layer weldable layer

solar collector • thermoplastic polyvinylchloride • thermoplastic

(PVC) or modified or unmodified polyvinylchloride (PVC) or plasticised PVC such as nitrile modified or modified or unmodified plasticised • unmodified plasticised PVC PVC. such as nitrile modified or unmodified plasticised PVC.

Other options include other materials

from the PVC group of materials. Other options include other materials from the PVC group

The hardness of the inner tube layer of materials. will generally be in the range of 45

Shore A to 90 Shore D and more The hardness of the outer specifically within the range of 80 weldable tube layer will Shore A to 50 Shore D. However, a generally be in the range of 45 hardness outside of this range may be Shore A to 90 Shore D and acceptable depending on the particular more specifically within the application. range of 50 Shore A to 50

Shore D, However, a hardness outside of this range may be acceptable depending on the particular application.

3. Non Softer layer The Reinforcing Layer weldable, for · olefin block copolymer an OBC, • moisture curable, silane use with · moisture curable, silane grafted grafted high density barbed olefin block copolymer (a XL-OBC) polyethylene XL-HDPE manifolds (where additional temperature and +/- • moisture curable, silane pressure resistance is desirable ) grafted polyolefin elastomer

XL-POE,

Other options include:

• thermoplastic elastomers (TPE), Other options include:

• Thermoplastic rubbers include • thermoplastic elastomers materials such as thermoplastic (TPE)

vulcanizates (TPV), • thermoplastic rubbers

• styrene block copolymers such as include materials such as styrene-ethylbutylene-styrene (SEBS) thermoplastic vulcanizates and polyolefin elastomers (POE) (TPV), styrene block

• and other materials from the Olefin copolymers such as styrene- group ethylbutylene-styrene (SEBS) and polyolefin elastomers (POE).

The hardness will generally be in the • other crosslinked or non- range of 10 Shore A to 90 Shore A and crosslinked polyolefins such more specifically within the range of 30 as polypropylene (PP), Shore A to 60 Shore A, with a relative polyethylene ((PE), including hardness that is not more than that of LDPE and HDPE) and their the outer tube layer . The material of alloys and modifications. the inner tube layer preferably • and other materials from possesses the appropriate friction cothe Olefin group efficient for secure barb grip, and has

the appropriate softness for barb The hardness of outer tube locking and sealing. layer will generally be in the range of 45 Shore A to 90 Shore D and more specifically within the range of 80 Shore A to 50 Shore D. However, a hardness outside of this range may be acceptable depending on the particular application. The material of outer tube layer is preferably stiff enough to resist positive and negative internal fluid pressures at elevated temperatures and thus avoid or substantially reduces flex and therefore flex fatigue. 4.Νοη Softer layer The harder Layer

weldable, for • thermoplastic polyvinylchloride • thermoplastic use with (PVC) polyvinylchloride (PVC) barbed • modified or unmodified plasticised • modified or unmodified manifolds PVC such as nitrile modified or plasticised PVC such as nitrile unmodified plasticised PVC. modified or unmodified

plasticised PVC.

Other options include other materials

The hardness of inner tube layer will of materials. generally be in the range of 10 Shore

A to 90 Shore A and more specifically The hardness of outer tube within the range of 30 Shore A to 60 layer will generally be in the Shore A, with a relative hardness that range of 45 Shore A to 90 is not more than that of the outer tube Shore D and more specifically layer . The material of inner tube within the range of 80 Shore A layer preferably possesses the to 50 Shore D. However, a appropriate friction co-efficient for hardness outside of this range secure barb grip, and has the may be acceptable depending appropriate softness for barb locking on the particular application. and sealing. The material of outer tube layer is preferably stiff enough to resist positive and negative internal fluid pressures at elevated temperatures and thus avoid or substantially reduces flex and therefore flex fatigue,

5. Non Softer layer The harder Layer

weldable, for · thermoset elastomers such as • thermoset elastomers such use with EPDM and silicone rubber, as EPDM and silicone rubber. barbed Other options include other materials Other options include other manifolds from the thermoset group of materials. materials from the thermoset group of materials.

The hardness of inner tube layer will

generally be in the range of 10 Shore The hardness of outer tube A to 70 Shore A and more specifically layer will generally be in the within the range of 30 Shore A to 60 range of 45 Shore A to 90 Shore A, with a relative hardness that Shore A and more specifically is not more than that of the outer tube within the range of 70 Shore A layer . The material of inner tube to 90 Shore A. However, a layer preferably possesses the hardness outside of this range appropriate friction co-efficient for may be acceptable depending secure barb grip, and has the on the particular application. appropriate softness for barb locking The material of outer tube and sealing. layer is preferably stiff enough to resist positive and negative internal fluid pressures at elevated temperatures and thus avoid or substantially reduces flex and therefore flex I I fatigue,

It is understood that the above examples are not lim iting and that other combinations of inner and outer polymer tube materials can be co-extruded to form a solar collector tube. However, the above examples show the inner and outer tube materials being from a similar group of polymers to be co-extruded together.

The term "olefin group" described herein refers to materials containing one or more polymer components obtained by the polymerisation of olefinic monomers.

The term "PVC group" described herein refers to materials containing one or more polymer components obtained by the polymerisation of polyvinyl chloride.

The term "thermoset group" group described herein refers to materials containing one or more polymers that are strongly chemically cross-linked.

Installation of the solar collector requires no special skills or equipment by the installer. For the non-weldable version, the number of tubes in the solar collector can be adjusted on site to the required size by simply tearing the web(s) between the tubes. The solar collector is then simply forced onto a barb(s), optionally with the use of a collar.

To overcome the high vacuum pressures associated with fluid draining from known solar collectors back to the pool or spa when the collector turns to the standby/ off mode, it is necessary to provide a dedicated unique vacuum release valve which has been correctly plumbed and positioned within the solar heat collector circuit to provide a 'vacuum break', namely, the vacuum release valve regulates pressure in the tubes in order to avoid a vacuum that could lead to tube collapse, flex fatigue and eventual failure of soft

thermoplastic tubes due to variations in the pressure therein.

The present solar collector eliminates the need for a special type of vacuum release valve with very low break pressure and high unimpeded air flow, special plumbing designs and testing. However, where there is no distinct 'inner' and 'outer' tube layers present, such as the main tube layer embodiment shown in Figures 13 and 14, a special vacuum release valve, special installation equipment and/or skills may still be used if required.

The solar collector of the present invention is extremely hardwearing and efficiently captures, absorbs and transfers heat to the fluid passing there through. It is more resistant to damage during installation where a softer tube material would split or pierce under the weight of a person or force of an object falling on it, such as hailstones. The present solar collector is also resistant to destruction caused by UV or chem ical degradation, or by pests such as rats, cats, possums or birds, which could lead to holes in the tube and leakage of the chemically rich fluids therein onto surrounding structures or environments thus causing damage to them , such as a metal roof or gutter. Furthermore, the solar collector is resistant to chemicals within the fluid and is able to transfer solar radiation absorbed by the harder outer tube layer to the fluid for efficient heating. The materials used for the solar collector may be optimised for both cost and efficiency, and to meet the unique demands of the respective tube layer(s). For instance, the inner tube layer may be optimised to, for example, be chemically resistant to chemicals within the fluid, resistant to splitting and cracking due to flex fatigue, have the appropriate friction co-efficient for secure barb grip, have the appropriate softness for barb locking and sealing and transfer the UV radiation absorbed by the harder outer tube layer to the fluid for efficient heating. The outer tube layer may be optimised to, for example, be resistant to UV weathering, have the appropriate levels of adhesion (Dyne level), stiffness/hardness and tension set in order to maintain a sphincter type compressive force around the barb. The respective tube layer(s) may be optimised to provide a combination of these features, such as in the case of the main tube layer embodiment.

The diameter of the softer inner tube layer is chosen to optimise heat transfer yet allow an efficient and sufficiently rapid fluid flow rate through the solar collector system.

Heat transfer can be further enhanced by incorporation of a spiral within the softer inner tube layer.

The solar collector of the present invention is also attractive, as the outer tube layer may be made in one or more colours to suit a particular look and/or location, without compromising efficiency.

The solar collector of present invention may also be encased in an enclosure or box to create a solar panel and thereby increase the heat generated inside the solar collector. The solar panel may be used on its own or in series. The enclosure or box may be made of any suitable material, and preferably is made of a solar radiation permeable material in order for the solar collector encased therein to absorb solar radiation. Suitable materials include glass, perspex (poly(methyl methacrylate) (PMMA)), polycarbonate Coreflute™ or a combination thereof. The material may be any colour, colourless or combination thereof in order to maximise the amount of solar radiation absorbed. Furthermore, the enclosure or box may include additional means to increase the amount of solar radiation absorbed, such as mirrors, reflectors, corrugations in the material, and the like.

The solar collector, while typically would be mounted on a roof of a structure, could instead be placed directly down onto the earth, or could even be mounted to vertical structures such as buildings and fences.

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

CLAIMS:

I . A polymer tube for use in a solar collector for heating and transferring fluids, the tube having co-extruded concentric inner and outer tube layers, wherein the outer tube layer is composed of a harder polymer than the inner tube layer.

2. A solar collector for heating and transferring fluids, comprising an inlet manifold and an outlet manifold through which fluid is respectively transferred into and out of the solar collector; and

a plurality of polymer tubes each connected between the inlet and outlet manifolds, the polymer tubes having co-extruded concentric inner and outer tube layers, wherein the outer tube layer is composed of a harder polymer than the inner tube layer.

3. A polymer tube as claimed in claim 1 or solar collector as claimed in claim 2, wherein the inner tube layer is the innermost tube layer.

4. A polymer tube as claimed in claim 1 or solar collector as claimed in claim 2, wherein the outer tube layer lies adjacent the inner tube layer.

5. A polymer tube as claimed in claim 1 or solar collector as claimed in claim 2, wherein the inner tube layer has a hardness of between 10 Shore A to 90 Shore D, and the outer tube layer has a hardness of between 45 Shore A to 90 Shore D.

6. A polymer tube or solar collector as claimed in claim 5, wherein the inner tube layer has a hardness of between 80 Shore A to 50 Shore D or 30 Shore A to 60 Shore A, and the outer tube layer has a hardness of between 80 Shore A and 50 Shore D or between 70 Shore A and 90 Shore A.

7. A polymer tube as claimed in claim 1 or solar collector as claimed in claim 2, wherein the polymer tube(s) is composed of a thermoplastic material or of a thermoset material.

8. A polymer tube or a solar collector as claimed in claim 7, wherein when the polymer tube is composed of a thermoplastic material from either the Olefin group or the

Polyvinylchloride (PVC) group.

9. A polymer tube or solar collector as claimed in claim 7, wherein the polymer tube is composed of a thermoplastic elastomer, a thermoplastic rubber or a thermoplastic alloy. 10. A polymer tube or solar collector as claimed in claim 9, wherein the thermoplastic elastomer, thermoplastic rubbers or thermoplastic alloys include olefin based polymers comprising an olefin block copolymer or cross linked or non-cross linked polyolefins.

I I . A polymer tube or solar collector as claimed in claim 8, wherein where the polymer tube is composed of a material from the PVC group, the material comprises a PVC, a modified plasticised PVC or unmodified plasticised PVC.

12. A polymer tube or solar collector as claimed in claim 7, wherein where the polymer tube is composed of a thermoset material, the material comprises a thermoset elastomer.

13. A solar collector as claimed in claim 2, wherein the polymer tubes are laterally connected via a co-extruded web.

14. A solar collector as claimed in claim 13, wherein the web is made of a hard, rigid material or a soft, flexible material.

15. A solar collector as claimed in claim 13, wherein the web is co-extruded using the same material as that of the inner tube layer, the outer tube layer or using another material. 16. A solar collector as claimed in claim 13, 14 or 15, wherein the web is plasticised with elastic properties to give flexibility and allow for variable spacing between the polymer tubes.

17. A polymer tube as claimed in claim 1 or a solar collector as claimed in claim 2, wherein the tube, or tubes, has a strip co-extruded thereon that covers less than 100% of an outer surface of the tube.

18. A polymer tube as claimed in claim 1 or a solar collector as claimed in claim 2, wherein the polymer tube comprises an outermost tube layer co-extruded with the inner and outer tube layers.

19. A polymer tube or a solar collector as claimed in claim 18, wherein the outermost tube layer covers less than 100% of the outer tube layer.

20. A polymer tube or a solar collector as claimed in claim 17, wherein the strip covers approximately 25% to 75% of the outer tube layer.

21 . A polymer tube for use in a solar collector for heating and transferring fluids, the tube having at least one tube layer and a co-extruded strip thereon, wherein the strip covers less than 100% of an outer surface of the tube layer.

22. A polymer tube as claimed in claim 21 , including an inner tube layer co-extruded inside of the at least one tube layer, and wherein the strip covers approximately 25% to 75% of the at least one tube layer.

23. A polymer tube for use in a solar collector for heating and transferring fluids, the tube having co-extruded concentric inner and outer tube layers, wherein the outer tube layer is weldable.

24. A polymer tube as claimed in claim 23, wherein the inner tube layer is made of a cross linked polymer.

25. A polymer tube as claimed in claim 24, wherein the inner tube layer is comprised of a moisture curable, silane grafted cross-linked high density polyethylene or a moisture curable, silane grafted cross-linked polyolefin elastomer.

26. A polymer tube as claimed in claim 23, wherein the outer layer is comprised of one of the following: a polypropylene, a polyethylene (LDPE or HDPE), an olefin block copolymer, a thermoplastic elastomer or a thermoplastic rubber.

27. A polymer tube as claimed in any one of claims 23 to 26, wherein the polymer tube has a strip co-extruded thereon that covers less than 100% of an outer surface of the tube.

28. A solar collector for heating and transferring fluids, comprising an inlet manifold and an outlet manifold through which fluid is respectively transferred into and out of the solar collector; and

a plurality of polymer tubes as claimed in any one of claims 23 to 27, each polymer tube being weldable to either the inlet manifold or outlet manifold, or to both.