WO2007148067A2

WO2007148067A2 - Evacuated solar panel enclosure

Info

Publication number: WO2007148067A2
Application number: PCT/GB2007/002275
Authority: WO
Inventors: John Albinson
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-06-20
Filing date: 2007-06-19
Publication date: 2007-12-27
Anticipated expiration: 2008-12-20
Also published as: GB0612170D0; WO2007148067A3; GB2439340A

Abstract

An evacuated solar panel enclosure has an outwardly- convex and transparent solar radiation window (1) and an inwardly-convex rear membrane (2), has side rail (3) extending between the respective edges of the window (1) and the rear membrane (2) to form a hermetically sealed enclosure. The convex window is so curved that differential air pressure generates a force acting within the convex window tending to urge the edges of the window apart. The convex window is supported at its edges by a side rail (3) which is prevented from displacing laterally by the presence of the enclosing rear membrane and a number of rear struts (8) extending across the rear membrane outside the enclosure. The differential pressure across the inwardly-convex membrane generates a force within the rear membrane tending to urge its edges together. The rear membrane may be of flatter curvature than the convex window.

Description

EVACUATED SOLAR PANEL ENCLOSURE

This invention relates to solar collectors, and particularly concerns an evacuated solar panel enclosure. In particular this invention provides an evacuated enclosure that presents a near flat transparent window to admit solar radiation without the need for intermediate supports to the transparent window within the enclosure.

The design objective for a thermal solar collector panel is to reduce the loss from the collector element arising from re-radiation, conduction and convection. Convection loss may be substantially eliminated by placing the solar adsorption panel within an evacuated enclosure .

When the enclosure solar radiation window is near flat, large forces induced by external air pressure exist to rupture the transparent window. This problem has been overcome in the prior art by constructing the transparent window using convexly-curved glass, to form an arch structure to resist the pressure exerted on the outside of the glass by the atmosphere.

Such a domed structure, however, necessarily increases the thickness and volume of the solar radiation collector and increases its architectural impact and intrusiveness . There therefore exists a need for a solar radiation collector of a reduced thickness, so that the collector may be unobtrusively mounted on buildings .

It is known that support to the solar radiation window of a solar collector can be provided by engaging the internal surface of the window by struts, in the form of thin columns or fins, extending between the transparent window and the back of the collector enclosure. However, these arrangements can provide heat conduction paths to the exterior, reducing the efficiency of the solar collector. The supporting struts may also pose design problems for the solar energy collecting panel enclosed within the evacuated enclosure, by reducing the unobstructed space within the enclosure. Examples of such an arrangement are described in JP57052759, US4289113 and JP2002277064.

It is also known that an evacuated enclosure with a solar radiation window can be made without intermediate supports by providing a window contoured in both its longitudinal and lateral directions, such that in its longitudinal direction the window is composed of a plurality of sinusoidal corrugations whereas in its lateral direction the peaks of such corrugations are contoured in the form of paraboloids so as to provide maximum uniform tensile strength to the window such that it may withstand the forces generated thereon by the atmosphere. Such an arrangement is described in US4184480. The arrangement has the disadvantages that the thickness of the panel is increased as compared to a flat glass panel, and that the glass panel is difficult and expensive to produce.

The present invention seeks to eliminate the need for intermediate support to the solar radiation window forming the evacuated solar panel enclosure, while simultaneously eliminating the need to form the transparent window with corrugations.

According to a first aspect of the present invention there is provided an enclosure for a solar radiation collector, the enclosure comprising an outwardly- convex transparent front panel, and inwardly-convex rear panel, a peripheral sidewall joining the front panel to the rear panel in hermetic sealing engagement, and a sealable evacuation port in fluid connection with the interior of the enclosure.

A second aspect of the present invention provides a solar radiation collector panel comprising an enclosure of the type described above and a heat exchanger mounted within the enclosure for converting incident solar radiation into heat, and heating and energy transfer fluid, inlet and outlet ducts being provided to supply energy transfer fluid to the heat exchanger, and to remove heated fluid from the heat exchanger, respectively.

The convex window of the enclosure may be so curved that, when the interior of the enclosure is evacuated, compressive force resulting from external air pressure acts substantially within the plane of the convex window and which force is opposed by tension force resulting from the action of external air pressure acting on the rear membrane.

The tension force in the rear membrane may be arranged to be of larger magnitude than the compressive force in the convex window by virtue of the rear membrane being of flatter curvature than the convex window.

A net difference of force between the convex window and the rear membrane may be transferred via a side rail into a network of rear struts positioned outside of the enclosure and adjacent to the rear membrane, the struts further providing a means of mounting the enclosure to a supporting structure.

The inside surface finish to the rear membrane and side components is preferably made reflective to minimise re-radiant loss from the solar radiation adsorption panel.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which:

Figure 1 is an underneath perspective view of a solar panel according to a first embodiment of the invention;

Figure 2 is a perspective view from above of the panel of Figure 1. Figure 3 is a plan view of the panel of Figure 1;

Figure 4 is a sectional view, taken on the line B-B of Figure 3;

Figure 5 is an enlarged partial view of the connection between the parts of the solar panel seen in Figure 4;

Figures 5a and 5b views similar to figure 5, showing alternative arrangements for the connection of the parts;

Figures 6 and 6a are longitudinal sectional views of alternative constructions for the solar panel, taken along the line A-A of Figure 1;

Figure 6b is an enlarged partial sectional view of an alternative arrangement for the end of the solar panel;

Figure 7 is an underneath perspective view of a solar panel according to a second embodiment of the invention;

Figure 8 is a perspective view from above of the panel of Figure 7.

Figure 9 is a plan view of the panel of Figure 7;

Figure 10 is a view of the evacuated panel enclosure viewed from the side;

Figure 11 is a diametral section of the panel of Figure 7, taken on line C-C of Figure 9; and

Figure 12 is a schematic diagram showing the distribution of forces between the curved window, the rear membrane, and supporting struts.

Referring now to the drawings, Figures 1 to 6 illustrate a first embodiment of the invention, in which the convex window and rear membrane are respectively cylindrical in form. This embodiment of the invention thus has a convex window and enclosing rear membrane curved about one axis only. Viewed from one end of the solar panel, the shape of the curvature of the curved window 1 and the rear membrane 2 may be a circular arc, a parabolic or part-elliptical curve, or a catenary curve. While it is preferable for the curved shapes of the convex window and the rear membrane to be similar, so that the spacing between them is substantially constant, it should be understood that the convex window 1 may have a different curving shape from the curvature of the rear membrane 2. The spacing between the convex window and at the rear membrane may be greater at the mid region of the enclosure than adjacent the edges.

In the Figures, the solar panel comprises a front window 1, curved so as to be convex to the outside, and formed as a rectangular part-cylindrical shape having two opposing straight edges and two opposing curved edges. Extending along the straight edges of the front window are two side rails 3, against which the edges of the front window 1 are sealed by means of a sealing element 5 such as an elastomeric sealing strip or a mastic bead.

In the embodiment seen in Figures 1 to 5, a rear membrane 2 is sandwiched between a lower rail 6 and the side rail 3, the lower rail 6 and the side rail 3 being held together by fasteners such as screws 16. Alternatively, the side rail 3 and lower rail 6 may be bonded to the rear membrane 2. The lower rails 6 extending along opposing sides of the rear membrane 2 are fixed together by struts 8 which are joined to the lower rail 6 by respective gussets 7 and bolts 9 at their ends. The rear membrane 2 is designed to be in tensile stress when the enclosure is evacuated, and thus can be of thin sheet material, such as sheet metal. High-strength plastics or composite materials may also be used for the rear membrane 2.

The enclosure is completed by provision of end cheeks 11 to join the respective curved edges of the convex window 1 and rear membrane 2. As can be seen from figure 6, the curved edge of the convex window 1 is received in a rebate extending along one edge of the end cheek, and a sealing element such as a resilient sealing strip or a bead of mastic 15 is provided between the convex window 1 and the end cheek 11. This resilient or deformable sealing element will allow an amount of relative longitudinal movement between the enclosure components while preventing ingress of air to the evacuated chamber defined between the convex window 1, the rear membrane 2 and the side rail 3 and end cheeks 11. The rear membrane 2 is attached along the opposite edge of the end cheek 11, again in sealing fashion to prevent ingress of air. The rear membrane 2 is clamped to the end cheeks 11 by respective capping strips 18 extending along the outside surface of the rear membrane, and secured to the end cheeks 11 by means of screws 17 which pass through the capping strips and the rear membrane to engage the end cheeks 11. Tubular connections 12 are provided to extend through bushes 14 set in the end cheek 11 at appropriate locations to connect with the passageway of an absorption member 4, to enable a heat transfer fluid to be circulated through the passageway of the absorption member 4. The bushes 14 may be provided with '0' rings or other movable seals to allow for relative longitudinal movement of the absorption panel 4 and the enclosure components resulting from thermal stress, while providing a seal against external air pressure. The enclosure is provided with at least one air evacuation pipe 13 fixed into the end cheek 11, to allow air to be evacuated from within the enclosure, after the parts are assembled and sealed together. The evacuation pipe 13 may be provided with a non-return valve, or may be simply crimped or otherwise sealed once evacuation has been completed. The seal between the end cheek 11 and the convex window 1 is effected using a mastic bead seal 15. The seal between the side rail 3 and the end cheek 11 may similarly effected using a mastic bead seal 15 between the inside face of the end cheek 11 and an end of the side rail 3. As well as promoting a seal between the rear membrane2 and the end cheek 11, the capping strip 18 acts to resist bending force within the end cheeks 11 induced by the action of air pressure on the rear membrane 2. A sealing material or component may be interposed between the rear membrane 2 and the end cheek 11.

A solar radiation adsorption panel 4 is supported within the enclosure. In the illustrated embodiment, heat resisting and insulating brackets 10 set at intervals into the side rails 3 engage the edges of the absorption panel to support the panel. Preferably, an amount of play exists between the panel 4 and the brackets 10 to prevent the transmission of force between the side rails 3 and the panel 4. Alternatively, as shown in the embodiment of Figure 5b, the panel 4 may be slightly bowed, and may be resiliently deformed so as to exert an outward force through the brackets 10 to hold a sealing strip 22 against the side rail 3, the brackets 10 being mounted to a bar 20 extending along the sealing strip 22 to distribute the force from the brackets 10 along the length of the strip 22.

The absorption panel 4 comprises a conductive heat- collecting sheet to which a tubular fluid passageway is secured. Solar energy incident on the panel 4 heats the conductive sheet, and this heat is conducted into a fluid passing through the passageway. In alternative embodiments, the absorptive panel may be formed from two pieces of pressed metal sheet which, when placed together and bonded, define a fluid passageway between them. Figure 3 shows a solar panel having two separate serpentine passageways. Heat- transfer fluid is supplied to one end of each of the serpentine passageways, and after passing through the passageway heated fluid is collected from the other end. Alternative arrangements of the fluid passageway foreseen, in which fluid enters the solar panel and exits the solar panel through tubular connections 12 in the same end cheek 11.

As may be seen in Figures 1 and 4, a number (in this case four) of struts 8 extend across the solar panel between the lower rails 6 and behind the rear membrane 2. The struts 8 can be used to provide a network of fixing points for convenient attachment to an external supporting structure (not shown) . The struts 8 are connected to the lower rails 6 in the embodiments shown in Figures 1 to 5. In the arrangements shown in Figure 5a each strut 8 is attached to the lower rail 6 by means of a mounting block 21 fixed to the lower rail 6 by a screw or bolt 9, and in the alternative arrangement shown in Figure 5b the strut 8 abuts and is fixed, for example by bonding, brazing or welding, to the lower rail 6. In each case, the struts exert an outward force on the lower rail 6 to counteract an inward force exerted by the tension generated in the rear membrane 2 when the enclosure is evacuated. The connection between each strut 8 and the lower rail 6 transfers any residual bending moment arising from the unbalanced forces applied to the side and lower rails 3 and 6 by the window 1 and membrane 2.

The solar panel may be assembled by a first attaching the struts 8 to the lower rails 6, then placing the rear membrane 2 over the assembled lower rails and attaching the side rails 3 to the rear membrane and lower rails. End cheeks 11 are then attached to the lower membrane and sealed against the ends of the side rails 3, to form a rectangular framework extending upwardly from the rear membrane 2. These solar absorption panel 4 is then mounted between the side rails 3, and the necessary connections between the fluid passageway of the panel 4 and the tubular connectors 12 are made. Finally, the convex window 1 is placed on to the side rails 3 and end cheeks 11, sealing elements having previously been placed in position to receive the edges of the convex window. The enclosure may then be evacuated by connecting the pipe 13 to a vacuum source.

Atmospheric pressure will then press the convex window firmly onto its sealing components. The pressure difference across the convex window may tend to flatten the convex window, urging its straight edges apart. This will in turn urge the side rails 3 apart. This effect is resisted by the tendency of the rear membrane 2 to pull the side rails 3 together, the force exerted by the rear membrane being increased as the pressure differential across it increases. These forces generate a clockwise turning moment A in the side rail 3, as is schematically illustrated in Figure 12. The tension in the rear membrane 2, together with the compressive force in the struts 8, generate an anticlockwise turning moment B in the side rail 3 (shown schematically in Figure 12) to counteract the moment A generated between the tension in the rear membrane 2 and the compression in the convex window 1. The side rails 3 are thus held in their correct position relative to the convex window 1 and the rear membrane 2 by the struts 8, and are urged into close contact with their respective sealing components, by the differential pressures acting across the convex window 1 and the rear membrane 2.

A second embodiment of the invention is illustrated in Figures 7 to 11. In this embodiment, these solar panel is generally circular and the convex window 1 and enclosing rear membrane 2 are substantially axisymmetrically curved to form shallow domes. As in the previous embodiment, the convex window is convex- toward the outside of the enclosure, and the rear membrane 2 is convex towards the inside of the enclosure. The form of the curvature of the convex window 1 and the rear membrane 2, i.e. the shape of a diametral section of the convex window 1 and the rear membrane 2, may be a circular arc, a parabolic or part-elliptical curve, or a catenary curve.

In this arrangement, the perimeter of the convex window 1 is supported in a receiving rebate formed in a circular side rail 3. As before, the rebate is lined with a resilient sealing material or a sealing strip 5. The rear membrane 2 is sandwiched between a circular lower rail 6 and the side rail 3, these elements being held together by screws 16 passing through the rear membrane 2. To facilitate manufacture, the side rail 3 and/or the lower rail 6 may be assembled from two or more part-circular sections .

The lower rail 6 is attached to a number of diametral struts 8 connecting to the lower rail 6 by gussets 7 and bolts 9, the struts extending across the concave face of the rear membrane 2 with a spacing between the struts and the rear membrane. The struts serve to maintain the shape of the circular lower rail, and provide a means by which the solar panel may be amounted to a supporting structure.

A circular solar radiation adsorption panel 4 is supported by means of insulating and heat resisting brackets 10 set at intervals into the side rail 3.

The absorption panel 4 is similar to that described in relation to the earlier embodiment, but in this case the fluid passageway is terminated at each of its ends in a spigot which extends substantially perpendicularly to the plane of the panel 4. The rear membrane 2 is provided with bushes 14 to accept the solar radiation adsorption panel 4 feed pipes 12 at appropriate locations to connect with the spigots, so that a heat transfer fluid can be supplied to the panel 4 and heated fluid can be collected therefrom. The bushes may be provided with ¹O¹ rings to allow relative movement of the panel feed pipes in the rear membrane 2 while maintaining an airtight seal.

The enclosure is provided with an evacuation pipe 13, for evacuating air from within the enclosure. In the illustrated embodiment, the pipe 13 is fixed into the rear membrane 2. It is however foreseen that the evacuation pipe 13, may be provided in the circular side rail 3.

In both the described embodiments, the evacuation of air from the solar radiation panel enclosure results in air pressure exerting a force on the convex window 1 which results in the edges of the convex window being urged outwardly. This outward force is resisted by an inward force produced by the tension acting in the rear membrane 2, the balance of force being taken by the supporting struts 8. The greater force acting in the rear membrane 2 is guaranteed by arranging the curvature of the rear membrane 2 to be flatter than the curvature of the convex window 1. The difference of force is taken by the struts 8 which are kept under compression to ensure mechanical stability of the evacuated enclosure. The convex window 1 may be formed from suitable glass or transparent plastics material. The remaining components may be formed from metal sections, from reinforced plastics or other composite materials, or from natural materials such as wood.

Claims

CLAIMS :

1. An evacuatable enclosure for a solar radiation adsorption panel, comprising: a convex transparent window, adapted to admit solar radiation into the enclosure; a concave rear membrane substantially corresponding in shape and dimensions to the convex window; and a side frame sealingly joining the perimeter of the rear membrane to the perimeter of the transparent curved window.

2. An enclosure as claimed in Claim 1 wherein the convex window is rectangular in shape and cylindrical in form, having two opposing straight edges and two opposing curved edges.

3. An enclosure as claimed in any claim 2, wherein curved end sealing plates extend between respective curved edges of the convex window and the rear membrane, and straight side sealing plates extended between respective straight edges of the convex window and the rear membrane.

4. An evacuated enclosure as claimed in claim 1, wherein the convex window and rear membrane are circular and domed, and a circular side sealing plate extends between the respective edges of the convex window and the rear membrane.

5. An enclosure as claimed in any preceding claim, wherein the convex window is so curved that when the enclosure is evacuated, the convex window exerts an outwardly-directed force on the side sealing plate or plates, and the rear membrane exerts an inwardly- directed force on the side sealing plate or plates.

6. An enclosure as claimed in any preceding claim, wherein the rear membrane is of flatter curvature than the convex window.

7. An enclosure as claimed in any preceding claim, wherein a number of rear struts are provided to extend across the concave face of the rear membrane outside the enclosure.

8. An enclosure for a solar radiation collector, the enclosure comprising an outwardly-convex transparent front panel, and inwardly-convex rear panel, a peripheral sidewall joining the front panel to the rear panel in hermetic sealing engagement, and a sealable evacuation port in fluid connection with the interior of the enclosure.

9. An enclosure according to claim 8, wherein the convex window is so curved that, when the interior of the enclosure is evacuated, force on the convex window resulting from differential pressures acts to urge opposing edges of the convex window apart, and force resulting from the differential air pressure acting on the rear membrane acts to urge opposing edges of the rear membrane towards each other.

10. A solar radiation collector panel comprising an enclosure according to claim 8 or claim 9, and a heat exchanger mounted within the enclosure for converting incident solar radiation into heat and heating and energy transfer fluid, the collector panel further comprising inlet and outlet ducts provided to supply an energy transfer fluid to the heat exchanger and to remove fluid from the heat exchanger, respectively.

11. A solar radiation collector panel according to claim 10, wherein the convex window is rectangular in outline and part-cylindrical in form, and comprises two substantially parallel straight edges, and two curved edges extending substantially perpendicularly to the straight edges.

12. A solar radiation collector panel according to claim 10, wherein the convex window is circular in outline, and axisymmetrically domed.

13. A solar radiation collector panel according to any of claims 10 to 12, wherein a number of rear struts are provided to extend across the concave face of the rear membrane outside the enclosure.