Solar Collector Panel

1. Field of the Invention

This invention relates to solar energy collector systems, and more particularly to a structure and method for a flat-plat solar energy collector panel which may be used for providing all or some of the energy needs in homes, buildings and other structures.

2. The Prior Art

As is well known, recent increases in the cost of energy for heating have resulted in renewed interest in the collection and utilization of solar energy. In response to this renewed interest, a plethora of solar energy collecting devices have been developed. These devices range from those which are very simple in construction, such as for example the placement of large, flat rows of black plastic tubing on a roof so as to absorb solar energy as water is directed through the tubing, to those devices which are highly complicated, such as solar collectors which are designed to automatically track the sun's position on a daily and/or seasonal basis. See generally the comprehensive review of methods for utilizing solar energy written by Dr. Farrington Daniels in his book Direct Use of the Sun's Energy, published by Ballentine Books, 1977. See also Applied Solar Energy, by Aden B. Meinel and Marjorie P. Meinel, published by Addison-Wesley Publishing Company, 1976.

Despite the wide variety of flat-plate solar collecting devices now available, extensive use of such solar collectors has not yet found its way into either the private housing industry or the area of application for small office buildings and the like. It is believed that several reasons account for this lack of acceptance of solar collectors by the general public. For example, many flat-plate solar collector devices lack the aesthetic appearance which is desired by private homeowners. Other flat-plate collector devices are so complicated in their structure and operation that the cost and time involved in installing and maintaining such devices is prohibitive. Still other flat-plate solar collector devices are not efficient enough in terms of collecting and retaining solar energy to be able to continue providing heat output in the absence of prolonged exposure to the sun's rays. Although this latter problem can be somewhat overcome through the utilization of an appropriate heat storage system, such as an insulated hot water tank or an insulated rock pit, it has nevertheless been found that most such solar collector devices rapidly lose their ability to transfer heat to the heat storage system during periods of cloudiness or in the absence of prolonged exposure to the sun's rays.

Yet another problem is the fact that many flat-plate solar collector devices are not economically feasible because they are not durable enough. For example, solar collectors are typically exposed to severe weather conditions for extended periods, which often adversely affects the solar collectors.

Accordingly, in an attempt to encourage a more widespread use of flat-plate solar collector panels throughout the private housing industry and for small office buildings and the like and to provide an improved solar collector device having an extended lifetime, the solar collector panel of the present invention has been designed to minimize and avoid the aforementioned problems.

The present invention has been designed and constructed from relatively inexpensive materials so that its cost is much more competitive with the cost of conventional building materials currently in use for roof coverings on houses and the like. Furthermore, the solar collector panel of the present invention is simple in design and is very strong and durable. It can be used directly as the covering for the roof of a house or small office building. The rigidity and strength of the solar collector panel of the present invention is derived at least in part from the use of a resignated honeycomb core of Kraft paper which is interposed between two layers of chopped fiberglass mat which are saturated with a catalyzed liquiform resin. Durability is improved by selecting materials which have similar properties of thermal expansion and contraction, thus helping to minimize the adverse affects from exposure to severe weather. A variety of colors can be achieved so as to make the solar collector panel aesthetically acceptable by dyeing the first layer of honeycomb. The novel combination of structure and materials used in the present invention has resulted in a flat-plate collector which has a surprisingly high efficiency in terms of collecting solar energy and transforming it into usable heat energy. For example, it has been found that the solar energy collector of the present invention will continue to transfer heat to the heat storage system even during extended periods of time in which the solar collector panel is only partially or indirectly exposed to the sun's rays.

It is, therefore, a primary object of the present invention to provide an improved solar energy collector panel.

Another object of the present invention is to provide an improved solar energy collector panel that is manufactured from materials having similar thermal expansion properties so as to minimize the adverse affects of temperature variations.

A further object of this invention is to provide an improved solar energy collector panel that is efficient in absorbing solar energy and transferring heat energy to a heat storage medium over relatively longer periods of time, even in the absence of direct exposure of the sun's rays.

It is another object of the present invention to provide a solar collector panel which may be inexpensively fabricated and which is sufficiently strong and durable to permit direct use of the collector as the roof covering for homes and other buildings.

Yet another object of the present invention is to provide an inexpensive and efficient method for fabricating an improved solar collector panel so that its cost is competitive with that of other conventional roof coverings.

An even further object of the present invention is to provide a method of fabrication for a solar collector panel whereby the solar collector panel will have improved rigidity and strength which enable its use as a roof covering.

These and other objects of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawing.

FIG. 1 is a perspective view of a dwelling having a roof constructed from the solar energy panel of the present invention.

FIG. 2 is a perspective view illustrating the underside of one presently preferred embodiment of the solar energy collector panel of the present invention.

FIG. 3 is a fragmentary perspective view of the solar energy collector panel of FIG. 2 with portions broken away to reveal the construction of the panel.

FIG. 4 is a cross-section of the solar collector panel taken along lines 4--4 of FIG. 2.

FIG. 5 is an exploded perspective view of the solar collector panel of the present invention illustrating the construction of the panel.

FIG. 6 is an exploded perspective view of the solar collector panel of an alternate embodiment of the present invention illustrating the construction of the panel.

FIG. 7 is a top view of one of the fluid channel members of the embodiment of FIG. 6.

FIG. 8 is a perspective view of the assembled fluid channel members of the embodiment of FIG. 6, with portions broken away to reveal the interior construction.

The invention is best understood by reference to the drawing wherein like parts are designated with like numerals throughout.

Referring first to FIG. 1, it will be seen that the solar collector panels generally designated 10 of the present invention are designed to be used as a roof covering for dwelling places and other small buildings. Although each panel 10 may be constructed in any desired size, it has been found in practice that four feet by ten feet (1.22 meters by 3.05 meters) is a convenient size and permits the panels to be easily attached between the trusses on most conventional roofs for dwelling houses and the like. Furthermore, it has been found that a desirable thickness for each panel is approximately 13/8 inches (3.49 centimeters). As will be hereinafter more fully described, each solar collector panel 10 is constructed in a unique manner which enhances the structural rigidity of the panel 10 so that it may be used directly as the roof cover.

As shown best in FIG. 2, each panel 10 is entirely enclosed. The exterior surfaces of panel 10 are made from fiberglass coated with a thin layer of gel coat, described below. The portion of the panel 10 which is utilized for collection of solar energy and transfer of heat to a heat storage medium is contained primarily within the raised bottom portion 12 of panel 10 as will hereinafter be more fully described. A flange 14 extends around the periphery of the panel 10 and is provided with holes 16 through which the panel 10 may be nailed or screwed to the trusses of the roof.

FIGS. 3 and 4 illustrate the internal construction of the solar collector panel 10. As shown in these figures, layers 18 and 20, which form the external surfaces for the panel 10, are made from a material such as a gel coat. Any suitable gel coat could be used for layers 18 and 20, as for example that manufactured by Ram Chemical Company and sold under the name Crystal Clear Gel Coat. Layer 18, which is the surface exposed to the sun's rays, additionally has an ultraviolet inhibitor added to the gel coat which prevents degradation of other polyester resinous materials contained within the solar collector panel 10 described below. The ultraviolet inhibitor is commercially available, and is made by Sherwin Williams Company, Product No. V66-V-Y64. In practice, it has been found desirable to add 2.12 quarts (2.01 liters) of ultraviolet inhibitor solution to each 500 pound (227 Kgm.) drum of clear gel coat. The ultraviolet inhibitor solution should be added just prior to application of the gel coat.

Each of the layers 22 through 25 is made from a layer of chopped fiberglass mat saturated in a mixture of catalyzed resin. Although various weights of fiberglass may be used in order to achieve differing characteristics with respect to strength and rigidity, in practice it has been found desirable to use chopped fiberglass mat which weighs 3/4 ounce per square foot (21.3 gm. per 0.093 square meters). As shown best in FIG. 4, each of the fiberglass layers 22-25 is large enough so that each of the sides of the layers 22-25 may be joined at the peripheral edges 14 of the solar collector panel 10. In this manner, as the catalyzed resin cures, peripheral edges 14 are bonded together, thus forming a completely enclosed collector panel. Furthermore, the plurality of fiberglass layers which are bonded together at the peripheral edges forms a strong surrounding flange 14 (see FIG. 2) which may be utilized in mounting the solar collector panel 10 to the trusses of the roof.

Referring again to FIG. 4, it will be seen that fiberglass layer 24 is draped over a series of tubes 26. For purposes to be hereinafter more fully described, by draping the fiberglass layer 24 over each of the tubes in the manner illustrated, each of the tubes 26 may be individually insulated within an enclosed space formed by the fiberglass layer 24 and layer 32 of black gel coat.

Layers 28 and 30 are formed from an untreated Kraft paper which has a honeycomb structure. The honeycomb structured Kraft paper is available from any of a number of commercial manufacturers. As shown in FIGS. 3 and 4, honeycomb layer 28 is interposed between fiberglass layers 22 and 23. Honeycomb layer 30 is interposed between fiberglass layers 24 and 25. As will be hereinafter more fully described, honeycomb layer 28 is impregnated with resin so as to form a resinated honeycomb core sandwiched between the fiberglass layers 22 and 23. In this manner, resinated honeycomb layer 28 helps to increase the structural strength and rigidity of the solar collector panel 10. Honeycomb layers 30 and 28 are also believed to contribute to the improved efficiency of the solar collector panel, as discussed below. Furthermore, although the illustrated embodiment has been shown with two honeycomb layers, it is presently believed that one layer would also work effectively.

A thin layer 32 of black gel coat is applied to the upper surface of fiberglass layer 23. A plurality of tubes 26 are then bonded to this layer of gel coat in heat transfer relation. As described below, the black pigment in gel coat layer 32 serves to increase absorption of solar energy while the solid bond which is formed between tubes 26 and gel coat layer 32 serves to increase the rate of transfer of heat to fluids flowing through the tubes 26. Tubes 26 may be made of any suitable material, although it is generally preferred that the material for tubes 26 have a coefficient of thermal expansion approximately the same as that of gel coat layeer 32 so that the solar collector panel will not experience cracking or splitting of the various layers due to expansion and contraction caused by temperature variations. Thus, variations in temperature will not compromise the solid bond formed between gel coat layer 32 and tubes 26, thereby improving the heat transfer between tubes 26 and heat absorptive layer 32.

As shown in FIG. 3, an inlet manifold tube 31 is connected to each of the tubes 26 so that fluid may be communicated to the tubes 26 through the manifold tube 31. A corresponding outlet manifold tube 33 (FIG. 5) is provided at the opposite end of tubes 26. Each of the manifold tubes 31 and 33 is provided with vertical fittings 34 and 35, respectively, (see also FIG. 2) which may be coupled to a source of water supply. In this manner, water or other suitable heat transfer fluid is circulated through the tubes 26 and serves as the heat storage medium in an insulated water storage tank (not shown).

Reference is now made to FIG. 5 in connection with a description of the method for manufacturing the solar collector panel 10. A flat mold (not shown) is initially coated with a thin layer 18 of gel coat. As previously described, layer 18 of gel coat is mixed with a predetermined amount of ultraviolet inhibitor solution so as to prevent penetration of ultraviolet rays which would subsequently degrade the polyester resinous materials in the fiberglass layers 22-25. Layer 18 is allowed to cure and then a layer of chopped fiberglass mat saturated with catalyzed resin is rolled out over layer 18 to render it bubble free. Chopped fiberglass layer 22 is then oversprayed with catalyzed resin. The raw paper honeycomb layer 28 is next placed directly into the wet laminate formed by layer 22. The honeycomb layer 28 is then covered with a good grade of wax-type paper and is weighted with sandbags to approximately 10 pounds per square foot (49 kilograms per square meter). This presses the honeycomb layer 28 into place. As the catalyzed resin cures, heat and styrene gas are given off and are entrapped by the waxpaper. This entrapped heat and liberation of gas partially reduces the viscosity of the catalyzed resin and permits it to climb the cell walls of the first honeycomb layer 28. After a sufficient period of time to permit the resin to partially cure, the sandbags and waxpaper are removed and excess styrene fumes are blown out of the individual cells of honeycomb layer 28. Honeycomb layer 28 is then given a light overspray of catalyzed resin to give a tacky surface for placement of layer 23. Honeycomb layer 28 may be tinted with any of a variety of colors for purposes of achieving an aesthetically desirable color for the panel.

A second layer 23 of fiberglass mat which is saturated with a catalyzed resin in then carefully rolled into place over the upper surface of honeycomb layer 28. The second layer 23 of fiberglass mat is allowed to partially cure and is then coated with a layer 32 of black gel coat. While the layer 32 of gel coat is still wet, tubes 26 and intake manifold 31 and outtake manifold 33 are pressed onto the black gel coat layer 32, thus being bonded in heat transfer relation thereto.

A third layer 24 of fiberglass mat saturated with catalyzed resin is then draped over tubes 26 as shown best in FIG. 4. Between each of the tubes 26, the saturated fiberglass layer 24 comes into contact with the black gel coat layer 32 and is bonded thereto, thus individually enclosing each tube 26 within a small space formed between the fiberglass layer 24 and black gel coat layer 32. As hereinafter described, it is believed that this helps to insulate the tubes 26, thereby decreasing any heat loss through tubes 26.

A second unimpregnated layer of Kraft honeycomb paper 30 is next placed on top of the fiberglass layer 24. Layer 25 of fiberglass is then rolled out over the top of honeycomb layer 30 and is given an overspray of catalyzed resin in the same manner as described previously. Layer 25 is allowed to partially cure and is then covered with a thin layer 20 of colored gel coat.

Significantly, by using the first honeycomb layer 28 as a wick to pull resin into the cell structure of the layer 28, surprising strength and rigidity is imparted to the solar collector panel 10. This strength and rigidity permits the collector panel 10 to be used directly as the covering for a roof without any auxiliary structure. Furthermore, the materials used in collector panel 10 are relatively inexpensive and therefore the solar collector panel 10 can be made and sold at a cost which is much more competitive than most other flat-plate collectors with the cost of conventional roof coverings.

The solar collector panel 10 is operated by being first mounted at an optimal angle of incidence to the sun's rays. This angle may vary depending on different geographic regions of the country. The fittings 34 and 35 are connected in series to a source of water supply or to other collector panels. Light is then admitted through layers 18 and 22, with ultraviolet light being at least partially screened out by the ultraviolet inhibitor mixed into layer 18. The sunlight is reflected through the individual cells of honeycomb layer 28 and is then absorbed in layers 23 and 32. The black pigment in layer 32 helps to increase the absorption. As the solar energy is absorbed by layers 23 and 32 the temperature of layers 23 and 32 increases to the point where heat energy is transferred to the liquid (not shown) passing through tubes 26.

In the embodiment of FIG. 6, a pair of molded fiberglass channel members 40 and 42 are used in place of tubes 26, manifolds 31 and 33, and gel coat layer 32 (see FIG. 5). As shown best in FIGS. 7 and 8, channel members 40 and 42 are molded so that they each have a plurality of raised ribs 44 that are spaced apart and may be bonded together to form a plurality of fluid channels 46 therebetween. The number of ribs 44 and the spacing therebetween is selected so as to decrease the water pressure to a suitable level by dividing the water into a number of small streams, thus helping to prevent the risk of bursting the bond that holds channel members 40 and 42 together.

A rib 48 also extends about the entire periphery of each channel member 40 and 42. The spaces 47 and 49 formed at the ends of each channel member 40 and 42 form inlet and outlet manifold channels for disbursing the water through the individual channels 46. As shown best in FIG. 7, the manifold channels 47 and 49 vary in width (i.e., are tapered at their ends). Tapering the manifold channels at the ends thereof has been found to result in a more uniform distribution of the fluid through the channels 46.

Ribs 44 and 48 of channel members 40 and 42 may be bonded together by any conventional method such as, for example, resin bonding or electromagnetic microwave welding. One or both channel members 40 and 42 may be sprayed black to increase the absorption of solar energy.

As further illustrated in FIGS. 7 and 8, each channel member 40 and 42 is provided with a hole 50 which communicates with one of the manifold channels, as for example channel 47. By placing the holes 50 of each channel member 40 and 42 at opposite ends, each manifold channel 47 and 49 will communicate with one of the holes 50 of either channel member 40 or channel member 42.

A threaded female coupling 52 (see FIG. 8) is filament wound from fiberglass and is resin bonded to each channel member 40 and 42 in alignment with the hole 50 formed therein. Thus, water may enter through one female coupling 52 (not shown) that is located on the opposite side of the collector panel, fill manifold channel 47 and fluid channels 46, then exit through manifold channel 49 and female coupling 52.

The use of channel members 40 and 42 is particularly advantageous because it has been found that they are extremely efficient in transferring heat to fluids flowing therethrough. Moreover, channel members 40 and 42 are easily molded from fiberglass, which has a thermal expansion property essentially the same as that of fiberglass layers 22-25. This helps to minimize the adverse wear and tear caused by temperature variations as described above. Moreover, since the channel members 40 annd 42 are identically constructed, they may be made from the same mold.

Except for the use of channel members 40 and 42 in place of tubes 26, manifolds 31 and 33, and gel coat layer 32, the embodiment of FIG. 6 is otherwise manufactured and used in essentially the same way as the embodiment of FIG. 5, as previously described.

In addition to the strength and durability of the solar collector panel of the present invention, actual tests of the solar collector panel have indicated a surprisingly high degree of efficiency in terms of collecting solar energy and transferring it in the form of heat energy to a heat storage medium such as water or other circulating liquid. Although it is not known for certain why the solar collector panel of the present invention has demonstrated such a surprisingly high efficiency, it is presently believed that both the structure and the particular types of materials used in constructing the solar panel may be contributing factors to the surprisingly effective operation of the solar collector panel of the present invention.

For example, it is presently believed that during periods of cloudiness or intermittent exposure to the sun's rays, transfer of heat energy to the heat storage medium continues for relatively long periods of time because of the ability of the solar collector to more efficiently retain the collected solar energy. It is believed that the double honeycomb layers 28 and 30 help to suppress thermal infrared radiation losses by absorbing thermal infrared radiation in the walls of the individual cell structures. It is also believed that the honeycomb layers 28 and 30 further help to reduce loss of thermal energy by inhibiting convective losses, since the numerous individual cells prevent large air current movement.

In addition to the foregoing, it is also presently believed that the use of saturated fiberglass may have thermal properties which contribute at least in part to the surprising efficiency of the solar collector panel. Similarly, resin coated honeycomb layer 28, as well as honeycomb layer 30 may have thermal properties contributing to the collector's surprising efficiency.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.