GB2071305A

GB2071305A - Solar collectors

Info

Publication number: GB2071305A
Application number: GB8032764A
Authority: GB
Original assignee: Enthone Inc; Sunworks Inc
Current assignee: Sunworks Inc; MacDermid Enthone Inc
Priority date: 1977-09-26
Filing date: 1978-09-26
Publication date: 1981-09-16
Also published as: FR2457450A1; GB2005402B; JPS5798758A; JPS5461339A; CA1112528A; AU4010478A; ES473385A1; AU6493680A; DE2838883A1; IT1206551B; IT7851235A0; AU518738B2; JPS5723870B2; GB2071305B; GB2005402A; FR2404184A1

Abstract

A solar energy collection system including a plurality of solar collectors 10 mounted in an array. Each collector includes a solar energy absorber 22 supported within a chamber having front and back transparent covers 12, 13. The front surface of each absorber faces toward the sun to receive direct solar radiation during the day. Mirrors not shown positioned behind the array reflect solar radiation to the back side of the absorbers when solar radiation is not incident on or is incident at a small angle on to the front surface of the absorbers. <IMAGE>

Description

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SPECIFICATION

Improvements in or relating to solar energy collection systems

This invention relates to solar energy collection 5 systems.

The present invention consists in a solar energy collection system comprising a plurality of solar collectors each having a front and a back transparent cover, solar energy absorbers having 10 front and back surfaces disposed in respective collectors, means mounting said collectors in an array so that a front surface of each absorber faces toward the sun to receive direct solar radiation during the day, and reflective means positioned 15 behind said array to reflect solar radiation incident thereon to the back side of said absorbers at times when solar radiation is not incident on or is incident at a small angle with respect to the front surfaces of said absorbers.

20 One embodiment of the invention is formed of evacuated solar energy collectors each having a housing which has two transparent cover members. Each member is formed as a section of a sphere to withstand atmospheric pressure when 25 the collector is evacuated. This section permits the collector to have a large absorber area to collector area ratio in comparison to the more conventional tubular evacuated collectors. It also has a low profile to facilitate the architectural integration of 30 these collectors in close-packed arrays.

Preferably, the housing is formed of two members having surfaces that are sections of a sphere. The members are joined at their rims to form a chamber around an absorber. Means are 35 provided to counteract stresses at the rim of the evacuated housing. Since both members are transparent, the time of effective collection during daylight hours is extended.

The invention will now be described, by way of 40 example, with reference to the accompanying drawings, in which:—

FIG. 1 is a top view of a plurality of solar collectors forming a solar energy collection system according to the invention;

45 FIG. 2 is a view seen in the plane of line 2—2 of Fig. 1;

FIG. 3 is an enlarged view of a portion of Fig. 2;

FIG. 4 is a detail in section of the bottom center of the collector as shown in Fig. 2;

50 FIG. 5 is the top view of a collector shown in Fig. 1 showing one form of absorber therefor;

FIG. 6 is the top view of an alternative form of absorber to that shown in Fig. 5;

FIG. 7 is a yiew seen in the plane of lines 7—7 55 of Fig. 6;

FIG. 8 is a detail in section of a further collector for use in a system according to the invention;

FIG. 9 is a detail in section of another collector for use in a system according to the invention; 60 FIG. 10 is a detail in section of another collector for use in a system according to the invention;

FIG. 11 is a side elevation of an array of collectors embodying the invention;

FIG. 12 is a front elevation of the array of

Fig. 11;

FIG. 13 is a view seen in the plane of lines 13—13 of Fig. 11; and

FIG. 14 is a sectional view seen in the plane of lines 1A—14 of Fig. 12.

Fig. 1 shows a plurality of solar collectors 10 mounted on a support surface 11 in a hexagonal close-packed array. The hexagonal array provides the densest nesting for collectors having circular configurations. Mirrors (not shown) are situated in the interstices between three adjacent collectors to direct energy to transparent lower surfaces of the collectors. A square or other quadilateral array may also be used if dictated by architectural considerations.

As exemplified in Fig. 2, a collector 10 in the system of Fig. 1 comprises a transparent cover member 12 and a preferably transparent lower cover member 13. The cover members are formed as sections of a sphere with a low profile and having peripheral rims 14 and 15, respectively. Members 12 and 13 can be formed by sag molding sheets of glass in a well known technique. The rims 14 and 15 are fitted to a tension ring 16 in seats 17 and 18 provided thereon. Adhesive seals 19 and 20 provide an airtight bond between seats 17 and 18, respectively, and rims 14 and 15, and cushion the rims in the respective seats. A preferred sealing material for all glass to metal seals is a low vapor pressure epoxy marketed by Varian Associates under the trademark TORR-SEAL.

Disposed within chamber 21 defined by cover members 12 and 13 is an absorber 22. As shown in Fig. 5, absorber 22 is in the form of a closely-wound parallel double spiral. Inlet and outlet lines 23 and 24, respectively, are provided and expansion elbows 25 and 26 may be provided in the inlet and outlet lines respectively.

The inlet and outlet lines 23 and 24 extend through a closure member 27 which closes a bottom opening 28 in lower member 13.

Absorber 22 is supported within chamber 21 by means of a plurality of support members 29 which may be of a ceramic or other highly heat resistant material. As exemplified in Fig. 5, absorber 22 may include a plurality of radial stiffening members 30. The absorber has a selective coating on its top and also on its bottom if member 13 is transparent. The spiral is close wound to present maximum absorber area and adjacent turns may be in contact with each other. Where the convolutes of the spiral are not in contact, as shown in Fig. 5, the interior surface of back member 13 is coated to be reflective to reflect solar radiation to the underside of the absorber. The absorber tubing and lines 23 and 24 may be glass or metal.

Member 27 is a metallic member having passageways 30 and 31 for inlet and outlet lines 23 and 24 respectively. The inlet and outlet lines are braised to the plug to provide an airtight seal. Plug 27 is bonded to the edge defining opening 28 by means of an adhesive 32. A check valve 33 is fitted into a third passage 34 in plug 27 to

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permit collector 10 to be evacuated.

Member 27 and opening 28 are preferably circular and centrally located on member 13 to prevent thermal and pressure stress 5 concentrations from developing due to high temperatures along lines 23 and 24.

Collector 10 is supported by a plurality of legs 35 having supporting feet 36. Legs 35 may be fastened to ring 16 by means of a bolt 37. 10 Generally, three legs 35 will be sufficient.

A heat exchange medium such as ethyl glycol may be circulated through absorber 22, entering through inlet line 23 and exiting to a storage medium or energy utilization device through outlet 15 24. Inlet and outlet lines 23 and 24 will be suitably insulated to prevent the collected heat from being lost to the ambient atmosphere. Inlet and outlet lines 23 and 24 may be connected to suitable manifolds or headers to serve all the 20 collectors 10 shown in Fig. 1.

When the collector is evacuated, compressive atmospheric forces will tend to force the surfaces 12 and 13 towards a planar shape. This will create radial compressional forces and tangential 25 tensional forces in the members. The tangential forces will increase in magnifde from the center toward the edges. The compressive forces are counteracted by tension ring 16 which also counteracts the tangential forces tending to 30 diametrically enlarge rims 14 and 15.

The tension ring is shown as being formed in one piece. However, it is to be understood that it may be formed of two butt welded bands which are joined together, the inner band being narrower 35 than the outer band to provide seats 17.

Figs. 6 and 7 exemplify an alternate absorber

40 which may be used in the collector shown in Figs. 1 through 5. Absorber 40 includes a panel

41 having a heat exchange grid in intimate heat 40 exchange relationship therewith. The grid comprises headers 42 and 43 and a plurality of conduits 44 extending therebetween. Inlet and outlet lines 45 and 46 are taken from headers 41 and 42 respectively.

45 Fig. 8 examplifies an alternate sealing member 47 for opening 28. A formed glass sealing member 47 is attached to lower member 13 by glass solder indicated at 48. Tubes 23 and 24 extend through member 47 and plugs 49 and 50 50 provide a vacuum seal therefor. A vacuum closure pull 51 is provided to be sealed after the collector 10 is evacuated. Plugs 49 and 50 can be any suitable glass-to-metal sealing material. An example of such a material is an alloy sold under 55 the trademark KOVAR by Carpenter Technology Corporation of Reading, Pennsylvania.

A second collector 52 for use in a system according to the invention, shown in Fig. 9, is formed of memoers 53 and 54 which are 60 generally sections of a sphere. Members 53 and 54 are provided with rims 5b and 66, respectively, which are short cylindrical sections. Memoers 53 and 54, including rims 55 and 56, may each be die cast in a manner similar to the way the screen 65 portions of cathode ray tubes and television picture tubes are made. Rims 55 and 56 are joined together at their ends by a glass solder 57. An annular tension ring 58 is attached to the outer surfaces of rings 55 and 56 through an adhesive seal 59. The seal also acts as a cushion between the metal and the glass.

As exemplified in Fig. 10, a further collector 60 for a system according to the invention has an upper member 61 and lower member 62. Both have surfaces defined on sections of a sphere. Member 61 includes a relatively thick rim 63 and member 62 includes a rim 64. Rim 64 is dimensioned to telescope into rim 63. A glass solder seal 65 provides an airtight seal between concentric rims 63 and 64. A ledge 66 may be provided projecting from rim 63 to provide a uniform stop to abut the end of rim 64. The increased thickness of rim 63 obviates the metallic tension ring.

A ring 67 having a lower flange or support ears 68 is provided around rim 63 to provide support for collector 60. Ring 67 merely acts as a support means for the collector. Ring 67 is attached to rim 63 through an epoxy seal 69.

Members 61 and 62, including rims 63 and 64 respectively, can each be die formed and then assembled in a manner similar to the way some television picture tubes are made.

The collector housings shown in Figs. 9 and 10 may be formed in an elliptical or rectangular configuration as seen from the top. In such case, the absorber shape would follow that of the housing and could take the form of Fig. 5 or 6 or any other suitable form.

The collectors described above may be mounted to the structure they serve or may be mounted to a free standing support as exemplified in Figs. 11—14, which show a collection system according to the invention. The system of Figs. 11—13 exemplifies a support structure 70 which comprises a plurality of parallel support members 71—75 of generally l-cross-section defining channels 76 to receive the edges of collectors 80. The members 71—75 are disposed at an angle to the vertical dependent on the latitude of installation.

The collectors 80 are shown as having a generally rectangular configuration, and are of the structure shown in Fig. 9. The structure of Fig. 10 may also be used for the rectangular collector.

The collectors 80 have a tension or support band 81, previously exemplified, which are received in channels 76 of the members 71—75. Bottom members 82—85 retain the columns of collectors. If desired, cross members such as 82—85 may be provided for each collector. A top cross member 86 is provided to rigidize support member 70. A mirror assembly 87 is disposed on the north side of collectors 80. Mirror assembly 87 comprises two mirror surfaces 88 ana 89 at an angle A dependent on the latitude of installation. A support exemplified by a strut 90 is provided for the mirror assembly.

in Fig. 13, the east is to tne riqnt. Mirror surface 89 will reflect the morning sun rays to the

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back side of the collectors and to the absorbers therein. As the sun continues to rise, mirror surface 89 will reflect less light and in the afternoon mirror surface 88 will reflect sunlight to 5 the rear of collectors 80. At midday the mirror surfaces will be shadowed by the collectors, except for the light that may pass therebetween.

This arrangement substantially extends the time of effective heat collection by the absorbers, 10 and provides a sun tracking effect to stationary collectors.

The collectors described above have a high ratio of absorber to collector area and volume. The configuration and construction of the housing will 1 5 withstand the atmosphere pressure when evacuated, and will eliminate losses due to convection currents. With the elimination of convection currents, the collector may operate at very high temperatures, resulting in reduction in 20 size of associates equipment in an overall solar heating system. Moreover, the disclosed collector structure provides greater collecting efficiency with respect to time in a day through the ability to accept reflected solar energy through the rear 25 cover member at low angles of azimuth of the sun.

While the cover members are preferably formed as sections of a sphere convex to the outside, any convex shape such as paraboloid capable of withstanding atmospheric pressure may be 30 utilized.

While preferred embodiments of the invention have been set forth for purposes of disclosure, modification to the disclosed embodiments of the invention as well as other embodiments thereof 35 may occur to those skilled in the art. Accordingly,

the appended claims are intended to cover all embodiments of the invention and modifications to the disclosed embodiments which do not depart from the scope of the invention.

Claims

40 CLAIMS

1. A solar energy collection system comprising a plurality of solar collectors each having a front and a back transparent cover, solar energy absorbers having front and back surfaces disposed

45 in respective collectors, means mounting said collectors in an array so that a front surface of each absorber faces toward the sun to receive direct solar radiation during the day, and reflective means positioned behind said array to reflect solar

50 radiation incident thereon to the back side of said absorbers at times when solar radiation is not incident on or is incident at a small angle with respect to the front surfaces of said absorbers.

2. A system as claimed in claim 1, wherein

55 each of said covers is formed of glass.

3. A system as claimed in claim 1 or 2, wherein each of said collectors is evacuated.

4. A system as claimed in any one of the preceding claims, wherein said reflecting means

60 comprises two surfaces, a first surface positioned to reflect early morning solar radiation and the second surface positioned to reflect late afternoon solar radiation.

5. A solar energy collection system

65 constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.