GB2457701A

GB2457701A - Inflatable solar heat collector panel

Info

Publication number: GB2457701A
Application number: GB0803222A
Authority: GB
Inventors: Stephen Knowles
Original assignee: IND DESIGN CONSULTANCY Ltd
Current assignee: IND DESIGN CONSULTANCY Ltd
Priority date: 2008-02-22
Filing date: 2008-02-22
Publication date: 2009-08-26
Anticipated expiration: 2028-02-22
Also published as: GB0803222D0; GB2457701B

Abstract

An inflatable solar heat collector panel (1, fig.1) comprises two pairs of sheets 2, 10 of plastic material connected together at their edges and along an array of laterally extending join zones 4 across most of the width of the solar collection panel. The two sheets of a first pair 2 are joined so as to define liquid passageways for heat exchange liquid and comprise first and second plenum chambers 5, 6 along opposite edges of the connected sheets and an array of passageways 7 connecting the first and second plenum chambers. The two sheets (10a, 10b; fig.12) of a second pair 10 are connected together at their edges to define an inflation envelope which completely encloses the first pair of sheets, and are linked to the first pair of sheets by connecting webs (12, fig.1) of plastic sheet material. An inflation nozzle (11,fig.1) is provided for inflating the inflation envelope so that the second pair of sheets is spaced apart from the liquid passageways defined between the first pair of sheets. A fluid entry connector 8 is provided at or near one corner of the solar collection panel and a fluid discharge connector 9 is provided at or near an opposite corner of the solar collection panel.

Description

TITLE

inflatable Solar Heat Collector Panel

DESCRIPTION

Technical Field

The invention provides an inflatable solar heat collector panel that is cheap to produce, lightweight and easy to use. The panel can be stored in a collapsed state and inflated in situ. When inflated, the thermal efficiency of the solar panel is comparable to and can even be better than that of more conventional rigid solar heat collector panels.

Background Art

Inflatable solar heat collector panels are known, but they have never been commercially acceptable because they are expensive to manufacture and difficult to use. Moreover their thermal efficiency often leaves much to be desired. A common theme running through the design of many proposed inflatable solar heat collector panels is that a series of linear welds between two sheets of flexible plastic material defines a heat exchange passage or an array of heat exchange passages which in use can contain a heat exchange fluid such as water. Rigidity and thermal insulation are provided for that heat exchange passage or passages by covering the two interconnected plastic sheets with a third sheet that is transparent to solar energy, and by inflating the space between the two either as single air chamber or as an array of mutually parallel air chambers. GB-A-2408320 discloses one such prior proposal, with the air envelope providing a first array of parallel inflation pockets above and a second array of inflation pockets below the pattern of heat transfer conduits formed between the first-mentioned conjoined sheets.

Each air pocket spans a number of heat exchange conduits, but the construction is such that the plastic material forming the outer envelope necessarily is bonded to the sheets defining the heat exchange conduits along lines that are close to the heat exchange conduits themselves. Good thermal insulation is therefore provided for the heat exchange liquid conduits ( I near the centre of each inflation pocket, but relatively poor heat insulation is provided for the heat exchange conduits near the longitudinal edges of the inflation pockets.

FR-A-2457449 discloses an inflatable solar heat collector which has better heat insulation in the sense that a more constant separation is provided between the passages for heat exchange fluid at the centre of the heat collector panel and the transparent sheets forming the outer inflation envelope. A combination of plastic sheets 2 and connector webs 2b is io provided to create the passages for heat exchange fluid, and a combination of plastic sheets 6 and 7 and connector webs 8 is provided to create the inflation envelope around the heat exchange conduits. The assembly would, however, be extremely difficult to manufacture, and it is not clear whether any manufacturing sequence could be devised, efficiently to weld together the plastic sheets and interconnecting webs in such a manner as efficiently to construct the solar collector panel of FR-A-2457449.

Other inflatable solar heat collector panels have been proposed, for example in GB-A-237701 1, US-A-4 160443 and US-A-4203425. The latter experiences the same problems as those discussed in connection with FR-A-2457449.

It is an object of the invention to provide a solar heat collector panel that is both efficient and easy to manufacture. It is a further object of the invention to provide a manufacturing sequence which permits the most efficient manufacture of the heat collector panel of the invention.

The Invention The invention provides an inflatable solar heat collector panel having the features of claim 1 herein.

The invention further provides a method for the manufacture of such a heat collector panel, comprising the sequential method steps as set out in claim 12 herein.

In this specification, the sheets and connecting webs of plastic material can be connected together along join lines and join zones by a variety of joining means known per se including sonic welding, heat welding, chemical welding and adhesive. Where this specification refers to a join line, there is intended a single linear join which may, of course, have a significant width along the length of the join, that width either being constant along the length or varying along the length of the join. References to a join zone are intended to be broader in scope, and embrace both single join lines and mutually spaced join lines extending in linear fashion along the length of the join. As a generality, it has been found that a join zone which comprises at its ends a pair of join lines which at their ends curve together to merge with one another to encircle the ends of the join zone, preferably in a substantially semicircular join line, have a significantly greater structural strength than single join lines. That advantage of greater structural strength can be imparted if the join zone is a single join line for most of its length, dividing near the ends of the join zone into two mutually divergent join lines which at their respective ends curve together as defined above to form a substantially semicircular join line. It has been found that if, according to the invention, the connecting webs are joined to the conjoined sheets of the first pair along join lines which overlie the join zones interconnecting the sheets of the first pair, then a considerable increase in the structural integrity of the resulting collector panel can be achieved if the join lines between the webs and the sheets of the first pair terminate substantially at the centre of the above substantially semicircular join lines defining the ends of the join zones.

It is important when defining a structure for a series of overlying conjoined plastic sheet such as those which make up the inflatable solar heat collector panel of the invention, that the structure should be capable of rapid and reliable manufacture. The method of assembly of the invention, referred to above, sets out a sequence for creating the different joins between the first and second pairs of sheets and the connecting webs which can easily be set out and automated and emits the rapid, reliable and therefore inexpensive manufacture of the inflatable heat collector panels of the invention.

In this specification the solar collection panel is described as having a longitudinal dimension and a lateral dimension. Thos terms are used merely to define the length and width of the solar collection panel, and there is no implication that one dimension is longer or shorter than the other. The length can be defined as the direction in which the two plenum chambers lie; and the width is a direction perpendicular to that length. Also in this specification there are references to the centre of a semicircular join line. The intention is to identify the centre of the circle of which the semicircle is one half, and the expression should be interpreted in that way.

Drawings Figure 1 is a plan view of an inflatable solar heat collector panel according to the invention, prior to inflation; Figure 2 is a plan view of the first pair of sheets which in use are positioned between the sheets of the second pair and which define the passageways for the heat exchange liquid; Figure 3 is a plan view similar to that of Figure 1 but showing another heat collector panel according to the invention; Figure 4 is a plan view similar to that of Figure 1 but showing yet another heat collector panel according to the invention; Figure 5 is an enlarged detail of the zone marked C in Figure 3; Figure 6 is an enlarged detail of the zone marked D in Figure 4; Figure 7 is a section taken along the line A-A in Figure 4; Figure 8 is a section taken along the line B-B in Figure 3; and Figures 9 to 12 illustrate the sequence of building up the different layers of the solar energy collector panel of the invention.

Referring first to Figurel, a solar energy collector panel I according to the invention comprises a pair of conjoined first sheets 2 of plastics material connected together at their edges 3 and along an array of laterally extending join zones 4 across most of the width of the panel 1. The sheets 2 are joined at their two laterally spaced respective edges 3 by a weld or line of adhesion.

The edges 3 are shown in broken line in Figure 2 because they are seen through the top sheet of a pair of second sheets 10.

The edge seams 3 and laterally extending join zones 4 of the sheets of the first pair of the sheets 2 of the first pair divide the space between the first pair of sheets into a fluid flow path comprising a first plenum chamber 5, a second plenum chamber 6, and laterally extending passageways 7 connecting the plenum chambers 5 and 6. A fluid entry connector 8 is provided to pass fluid into the first plenum chamber 5, and a fluid discharge connector is provided to discharge fluid from the second plenum chamber 9.

A second pair of sheets 10 surrounds the sheets of the first pair 2 as an inflation envelope which both supports the sheets of the first pair 2 in a more rigid manner than they could attain on their own and provides thermal insulation for the sheets of the first pair and for the heat exchange fluid contained in the fluid flow path. The sheets of the second pair 10 are shown in Figure 1 as being joined around their edges by an edge join line which overlies the edge join line of the sheets of the first pair 2 laterally across the panel 1 but which is spaced outwardly from the edge join line of the sheets of the first pair down their longitudinal edges, creating an open space 13 laterally outwardly of the sheets of the first pair 2. That open space 13 links the two halves of the inflation envelope above and below the conjoined sheets of the first pair 2 so that it can be inflated through a single inflation nozzle 11.

Figure 2 shows the connected sheets of the first pair 2 without the inflation envelope around them. Figure 3 shows an alternative design in which the sheets of the first pair 2 are the same length and width as the sheets of the second pair 10 so that all four edge join lines overlie one another. This design means that a first inflation nozzle has to be provided for inflation of the sheets of the second pair 10 in an inflation envelope above the sheets of the first pair 2; and a second inflation nozzle has to be provided for inflation of the sheets of the second pair 10 in an inflation envelope below the sheets of the first pair 2. Figure 4 shows an alternative design in which the edge join lines of the sheets of the second pair 10 are all outside the edge join lines of the sheets of the first pair 2.

In addition to the first and second pairs of sheets being connected around their edges in Figures 1 and 3, they are connected by connecting webs 12 of flexible plastic material as shown in Figures 7 and 8. Figure 5 is a detail of the join zone joining the sheets of the first pair and the overlying join line connecting the webs 12 to the conjoined sheets of the first pair 2, being a detail of the area marked C in Figure 3. The sheets of the first pair are joined together by a join zone 16 which is linear for most of the width of the panel but which diverges into a dew-drop shape at the ends of the join zone 16. That dew-drop shape comprises a single join line until near each end of the join zone, when it diverges into two join lines 17 which merge together to encircle the ends of the join zone, creating approximately semicircular ends to the join zone. The join line connecting together the connecting webs 12 and the sheets of the first pair is shown as 17 in Figure 5, and overlies the join zone 16 along most of its length, but lies at the centre of the dew-drop, terminating at approximately the centre of the circle on which the semicircular end of the dew-drop shape 16 lies. This shape creates a very strong join between the sheets of the first pair and between them and the connecting webs, being very resistant to tearing at the join in use.

Figure 4 shows a modified shape of the join zone between the sheets of the first pair 2, and Figure 6 is an enlarged detail of the area marked D in Figure 4. The sheets of the first pair are connected together along a join zone which comprises a pair of mutually spaced parallel laterally extending join lines 16' which at their ends curve together, merging with one another at the ends of the join zone to define, at each end, a substantially semicircular join line. The connecting web is, as in Figure 5, joined to the conjoined sheets of the first pair along a join line 17' which lies generally at the centre of the parallel join lines 16' and terminates at approximately the centre of each semicircular end.

Figures 7 and 8 show the inflation envelope in its inflated condition, which is achieved through the inflation nozzle 11 of Figures 1 to 4. Figures 7 and 8 both show the passages 7 for heat exchange fluid formed between the sheets of the first pair 2, being the laterally extending passageways connecting the plenum chambers at opposite sides of the solar energy collector panel 1. The volume of the passages 7 can be altered by altering the pressure differential between the heat exchange fluid in the passages 7 and the air pressure in the inflation envelope between the sheets of the first and second pairs.

At least the upper sheet of the second pair 10 is transparent to solar radiation, so that heat from the sun can pass through directly to heat the heat exchange fluid in the passages 7. Similarly at least the upper sheet of the first pair 2 is made from a material with a high absorption of solar radiation. The connecting webs are also preferably made from a material transparent to solar radiation, so as to allow the maximum possible passage of heat to the fluid in the channels 7. The pocketed construction of the resulting inflation envelope provides excellent heat insulation, because an air chamber of significant width is formed over the entire footprint of the plenum chambers 5 and 6 and the connecting channels 7, with no low areas along the edges of the connecting channels; and because internal air circulation due to potential convection currents is reduced by the connecting webs which divide the envelope into a series of confined air zones 18a, 18b, etc as shown in Figures 7 and 8.

Figures 9 to 12 illustrate the method of manufacture of a solar heat collector panel according to the invention. The sequence of making the various welds, seams or adhesive joins to create the join zones and join lines connecting together the various components of the panel is very important, and the sequence set out below should be followed.

If the method of joining the two sheets of the first pair 2 is heat welding or sonic welding, then the first step may be to connect together the two sheets of the first pair 2 around their outer periphery. It will be understood that one of the joins may in fact be a fold, where a single sheet is folded in half in order to create the two sheets of the first pair 2. Next, the laterally extending join zones 4 of Figure 2 or Figure 4 are created. Alternatively the laterally extending join zones 4 may be created first, followed by the join around the outer periphery.

If the method of joining the two sheets of the first pair 2 is chemical welding or adhesive, then the chemical solvent or adhesive is preferably applied to the bottom sheet in a pattern that traces the whole of the edge connection and the laterally extending join zones 4 before the top sheet is placed over the bottom sheet and the two sheets pressed together until the join has formed.

In a next step, the connecting webs 12 are secured in place, either by heat or sonic welding or by chemical welding or adhesive. The lines of the joins should be centrally of the join zones 4. The resulting assembly is illustrated in Figure 9. Although not illustrated in Figure 9, during this assembly process the fluid entry and discharge connectors 8 and 9 are inserted into the plenum chambers formed along the opposite longitudinal edges of the conjoined sheets. For example, they may be inserted between the edges of the overlaid sheets, and the joined sheets may be lapped around them with a sonic, heat or chemical weld seal or an adhesive seal creating a fluid-tight join.

Alternatively the connectors 8 or 9 may pass through an aperture formed in one sheet of the first pair, and sealed in fluid-tight manner using a sonic, heat or chemical weld seal or an adhesive seal.

Next, the sheets of the second pair 10 are secured in place, preferably one at a time. Figures 10 to 12 show those two sheets of the second pair 10 marked as sheets lOa and lOb respectively. A sheet lOa is folded concertina-fashion as shown in Figure 10 so that the join line can be held over and around the folded sheet, and then the join line between one folded over edge portion of the first connecting web 12 is created, again by any suitable means such as sonic or heat welding, chemical welding or adhesive. The folded portion of the sheet lOa is then partially unfolded to allow a similar join to be created for the next connecting web 12 of the array, as shown in Figure 11, and so on until all of the connecting webs 12 on the top (or the bottom) of the final solar panelare connected to the sheet iDa. Finally the sequence of joins illustrated in Figures 10 and 11 is repeated for the other sheet lOb of the second pair, and finally the edges of the sheets of the second pair are joined together to create the final assembly as illustrated in Figure 12. During the joning together of the outer edges, the join may pass around the connectors 8 and 9 and around the inflation nozzle 11 while creating a good seal; or the connectors and inflation nozzle may pass though apertures in the sheet lOa or lOb with the junction well sealed by a sonic, thermal, chemical or adhesive seal.

The creation of a join zone 16 between the connecting webs and the sheets of the first pair, with rounded ends to each join zone 16, creates a very strong and tear-resistant array of joins. The positioning of the join lines 17 centrally of those join zones 16, terminating at the centre of the rounded ends of the join zones, also adds considerably to the tear resistant strength. Preferably the joins between the connecting webs 12 and the sheets lOa and lOb are also join zones with rounded ends to each join zone exactly as described above with reference to the join zones 16.

Although not illustrated, the solar panel may advantageously also comprise eyelets around the outer periphery of the connected sheets iDa and lOb of the second pair, so that the inflated panel may be anchored in use to the ground or to some structure over which it is laid. Alternatively or in addition, anchorage pockets may be formed around the edge of the lower panel lOb, enabling those pockets to be filled in use with ballast or other anchorage material such as sand.

The inlet nozzle 8 may be connected to a water supply or a supply of other heat exchange fluid. That may be a mains supply (preferably passing first through a suitable pressure regulator) or a header tank. Warm or even hot water (or other heat exchange fluid) may be removed through the fluid discharge connector 9 after the contents of the laterally connecting passageways 7 have been heated by sotar radiation.

Claims

CLAIMS: 1. An inflatable solar heat collector panel comprising: a first pair of sheets of plastic material connected together at their edges and along an array of laterally extending join zones across most of the width of the solar collection panel, so as to define, between the connected sheets, liquid passageways for heat exchange liquid comprising longitudinally extending first and second plenum chambers along opposite edges of the connected sheets, and an array of laterally extending passageways connecting the first and second plenum chambers, at least an upper one of the first pair of sheets of plastic material being made from a material with a high absorption of solar radiation; a second pair of sheets of plastic material connected together at their edges to define an inflation envelope which completely encloses the first pair of sheets and is linked to the first pair of sheets by an array of laterally extending connecting webs of plastic sheet material, each connecting web being joined along one edge to a respective one of the second pair of sheets along a join line or a join zone extending laterally across most of the width of the respective one of the second pair of sheets and being joined along an opposite edge to the first pair of interconnected sheets along a join line with overlies a join zone which interconnects those first pair of sheets; an inflation nozzle being provided in an upper or a lower one of the second pair of sheets for inflating the inflation envelope so that when thus inflated each of the upper and lower ones of the second pair of sheets is held spaced from the liquid passageways defined between the first pair of sheets by a balance between air pressure within the envelope and tension in the connecting webs, at least the upper one of the second pair of sheets being made of a material substantially transparent to solar radiation; and a fluid entry connector being provided at or near one corner of the solar heat collection panel for introducing heat transfer fluid through the air chamber defined between the second pair of sheets and into the first plenum chamber, and a fluid discharge connector being provided at or near an opposite corner of the solar heat collection panel for discharging heat transfer -12-fluid from the second plenum chamber and through the air chamber defined between the second pair of sheets.
2. An inflatable solar heat collector panel according to claim 1, wherein both of the sheets of the first pair are made from a material with a high absorption of solar radiation.
3. An inflatable solar heat collector panel according to claim 1 or claim 2, wherein both of the sheets of the second pair are made from a material that is substantially transparent to solar radiation.
4. An inflatable solar heat collector panel according to any preceding claim, where each of the connecting webs between the upper sheet of the first pair and the upper sheet of the second pair is made from a material that is substantially transparent to solar radiation.
5. An inflatable solar heat collector panel according to claim 4, wherein each of the connecting webs between the lower sheet of the first pair and the lower sheet of the second pair is made from a material that is substantially transparent to solar radiation.
6. An inflatable solar heat collector panel according to any preceding claim, wherein each lateral join zone joining together the sheets of the first pair comprises, at least at its ends, a pair of laterally extending join lines which merge together to encircle the ends of the join zone.
7. An inflatable solar heat collector panel according to claim 6, wherein each lateral join zone comprises a pair of mutually spaced parallel laterally extending join lines which at their ends curve together, merging with one another at the ends of the join zone to define, at each end, a substantially semicircular join line. -13-
8. An inflatable solar heat collector panel according to claim 6, wherein each lateral join zone comprises a single join line for most of its width, dividing near the ends of the join zone into two mutually divergent join lines which at their ends curve together, merging with one another at the ends of the join zone to define, at each end, a substantially semicircular join line.
9. An inflatable solar heat collector panel according to claim 7 or claim 8, wherein each connecting web is connected to the first pair of interconnected sheets along a join line which terminates at approximately the centre of the semicircular join line of the join zone which it overlies.
10. An inflatable solar heat collector panel according to any preceding claim, wherein the sheets of the second pair are connected together at their edges along two opposite edges leaving a space between those joins and the respective mutually joined edges of the first pair of sheets; and along another two opposite edges by being joined to the mutually joined edges of the first pair of sheets.
II. An inflatable solar heat collector panel according to any of claims 1 to 9, wherein the sheets of the second pair are connected together around their whole perimeter, leaving a space between that join and the mutually joined edges of the first pair of sheets.
12. A method for the manufacture of an inflatable solar heat collector panel according to any preceding claim, comprising the following sequential steps: (a) placing the plastic sheets of the first pair one over the other, and joining them together at their edges and along lateral join zones across most of the width of the solar collector panel, with the fluid entry connector passing in fluid-tight manner between the joined edges of the first pair of sheets at or near one corner thereof or through an aperture created in the upper or lower sheet of the first pair of sheets at or near the said corner; and the fluid discharge connector passes in fluid-tight -14 -manner between the sealed edges of the first and second sheets near an opposite corner thereof or passes through an aperture in the upper or lower one of the first pair of interconnected sheets at or near the said opposite corner; and (b) sequentially securing the connecting webs above and below each of the lateral join zones interconnecting the sheets of the first pair, each join line which connects together a connecting web and the interconnected sheets of the first pair overlying its respective join zone interconnecting the first pair of sheets; (c) connecting together the free edge of each connecting web and an upper or lower sheet of the second pair, the connecting webs being joined to the said upper or lower sheet of the first pair in sequence, working from one longitudinal end of the solar heat collector panel to the other, along join lines or zones which are parallel to one another from one connecting web to the next; (d) connecting together the sheets of the second pair around their outer periphery, with the fluid entry and discharge connectors passing in fluid-tight manner between the joined edges of the second pair of sheets at or near one corner thereof or through apertures created in the upper of lower sheet of the second pair of sheets at or near one corner thereof; and creating a running seal around an inflation nozzle which extends in use from the outside of the solar heat collector panel to the inside, for inflation of the inflation envelope of the solar heat collector panel prior to use.Amendments to the claims have been filed as follows CLAIMS: 1. An inflatable solar heat collector panel comprising: a first pair of sheets of plastic material connected together by being joined together one to the other at their edges and by being joined together one to the other along an array of laterally extending join zones across most of the width of the solar collection panel, so as to define, between the connected sheets, liquid passageways for heat exchange liquid comprising longitudinally extending first and second plenum chambers along opposite edges of the connected sheets, and an array of laterally extending passageways connecting the first and second plenum chambers, at least an upper one of the first pair of sheets of plastic material being made from a material with a high absorption of solar radiation; a second pair of sheets of plastic material connected together by being joined together one to the other at their edges to define an inflation envelope which completely encloses the first pair of sheets and is linked to the first pair of sheets by an array of laterally extending connecting webs of plastic sheet material, each connecting web being joined along one edge to a respective one of the second pair of sheets along a join line or a join zone extending laterally across most of the width of the respective one of the second pair of * S. sheets and being joined along an opposite edge to the first pair of 0.S* interconnected sheets along a join line which overlies a join zone which S...: interconnects those first pair of sheets; an inflation nozzle being provided in an upper or a lower one of the second pair of sheets for inflating the inflation envelope so that when thus inflated each of the upper and lower ones of the second pair of sheets is held * spaced from the liquid passageways defined between the first pair of sheets by a balance between air pressure within the envelope and tension in the connecting webs, at least the upper one of the second pair of sheets being made of a material substantially transparent to solar radiation; and a fluid entry connector being provided at or near one corner of the solar heat collection panel for introducing heat transfer fluid through the air chamber defined between the second pair of sheets and into the first plenum chamber and a fluid discharge connector being provided at or near an opposite corner of the solar heat collection panel for discharging heat transfer fluid from the second plenum chamber and through the air chamber defined between the second pair of sheets.2. An inflatable solar heat collector panel according to claim 1, wherein both of the sheets of the first pair are made from a material with a high absorption of solar radiation.3. An inflatable solar heat collector panel according to claim 1 or claim 2, wherein both of the sheets of the second pair are made from a material that is substantially transparent to solar radiation.4. An inflatable solar heat collector panel according to any preceding claim, where each of the connecting webs between the upper sheet of the first pair and the upper sheet of the second pair is made from a material that is substantially transparent to solar radiation.* ** 5. An inflatable solar heat collector panel according to claim 4, wherein each of the connecting webs between the lower sheet of the first pair and the lower sheet of the second pair is made from a material that is substantially . transparent to solar radiation. ***I6. An inflatable solar heat collector panel according to any preceding claim, wherein each lateral join zone joining together the sheets of the first pair * ** comprises, at least at its ends, a pair of laterally extending join lines which merge together to encircle the ends of the join zone.7. An inflatable solar heat collector panel according to claim 6, wherein each lateral join zone comprises a pair of mutually spaced parallel laterally extending join lines which at their ends curve together, merging with one another at the ends of the join zone to define, at each end, a substantially semicircular join line.8. An inflatable solar heat collector panel according to claim 6, wherein each lateral join zone comprises a single join line for most of its width, dividing near the ends of the join zone into two mutually divergent join lines which at their ends curve together, merging with one another at the ends of the join zone to define, at each end, a substantially semicircular join line.9. An inflatable solar heat collector panel according to claim 7 or claim 8, wherein each connecting web is connected to the first pair of interconnected sheets along a join line which terminates at approximately the centre of the semicircular join line of the join zone which it overlies.10. An inflatable solar heat collector panel according to any preceding claim, wherein the sheets of the second pair are connected together at their edges along two opposite edges leaving a space between those joins and the respective mutually joined edges of the first pair of sheets; and along another two opposite edges by being joined to the mutually joined edges of the first :.:: 20 pairof sheets.11. An inflatable solar heat collector panel according to any of claims ito 9, wherein the sheets of the second pair are connected together around their whole perimeter, leaving a space between that join and the mutually joined edges of the first pair of sheets.12. A method for the manufacture of an inflatable solar heat collector panel according to any preceding claim, comprising the following sequential steps: (a) placing the plastic sheets of the first pair one over the other, and connecting them together by joining them together one to the other at their edges and by joining them together one to the other along lateral join zones across most of the width of the solar collector panel, with the fluid entry connector passing in fluid-tight manner between the joined edges of the first pair of sheets at or near one corner thereof or through an aperture created in the upper or lower sheet of the first pair of sheets at or near the said corner; and the fluid discharge connector passes in fluid-tight manner between the sealed edges of the first and second sheets near an opposite corner thereof or passes through an aperture in the upper or lower one of the first pair of interconnected sheets at or near the said opposite corner; and (b) sequentially securing the connecting webs above and below each of the lateral join zones interconnecting the sheets of the first pair, each join line which connects together a connecting web and the interconnected sheets of the first pair overlying its respective join zone interconnecting the first pair of sheets; (c) connecting together the free edge of each connecting web and an upper or lower sheet of the second pair, the connecting webs being joined to the said upper or lower sheet of the first pair in sequence, * ** working from one longitudinal end of the solar heat collector panel to the other, along join lines or zones which are parallel to one another from one connecting web to the next; * * * S. S (d) connecting together the sheets of the second pair by joining them together one to the other around their outer periphery, with the fluid entry *. .: 25 and discharge connectors passing in fluid-tight manner between the joined edges of the second pair of sheets at or near one corner thereof or through apertures created in the upper of lower sheet of the second pair of sheets at or near one corner thereof; and creating a running seal around an inflation nozzle which extends in use from the outside of the solar heat collector panel to the inside, for inflation of the inflation envelope of the solar heat collector panel prior to use.