US20020002972A1

US20020002972A1 - Solar heating reflecting element suitable for molding

Info

Publication number: US20020002972A1
Application number: US09/474,396
Authority: US
Inventors: Lawrence S. Blake; Stephen J. Blake
Original assignee: Individual
Current assignee: SOL Inc Korea
Priority date: 1999-12-29
Filing date: 1999-12-29
Publication date: 2002-01-10

Abstract

A solar energy collecting apparatus for heating a working fluid using the plurality of substantially identical reflective elements arranged in rows is provided. Each reflective element comprises a substantially rectangular element having opposing side walls and opposing end walls which together form a bottom edge for supporting the reflective element on a flat support such as a sheet metal or molded base. Each reflective element further includes a top wall connected with and supported by the side walls and the end walls. The top wall is formed to provide a reflective surface facing away from the bottom edge and is formed in a shape for reflecting solar radiation falling thereon, from a range of incident angles, to a focal axis. The focal axis of each reflective element is substantially parallel with a longitudinal axis of the reflective element and when the reflective elements are arranged in parallel rows, each row includes a focal axis along its longitudinal length. The reflective surface is coated with a reflective layer such as vacuum deposited aluminum, metabolized paint or by other reflective coatings to reflect solar energy to the focal axis. Ideally, the reflective element is formed by molding a material in a mold such that the mold forms the shape of the reflective surface. In the preferred embodiment of the present invention the reflective element is molded in a press mold from a material comprising hydrated silicates of aluminum which is plastic when wet but which becomes a hard ceramic when fired in an oven.

In another aspect of the invention, a solar energy collecting apparatus comprises a working fluid conduit comprising a plurality of fluid carrying members positioned one above each row of reflective elements and substantially coincident with the focal axis of the row. The fluid carrying members are connected together by a plurality of connecting members such that a continuous working fluid conduit passes a working fluid over each row of reflective elements. The working fluid conduit may be movably supported with respect to the base such that each of the plurality of fluid carrying members is movable away from the focal axis when no heating of the working fluid is desired.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to solar collectors and more particularly to solar collectors which include reflective elements for focusing, incident solar radiation onto a working fluid conduit, for heating the working fluid as it passes through the working fluid conduit. The present invention provides an apparatus and method for forming reflective elements and for assembling a solar collector, of simple construction, using a plurality of molded reflective elements assembled together onto a base to form a unitary solar collecting device, of low cost and easy assembly, suitable, e.g., for heating swimming pool water or the like. This invention specifically provides a method for forming the reflective elements from a ceramic or other moldable material and for treating a surface of the molded reflective element so as to provide a highly reflective surface.

2. Description of the Prior Art

Numerous, solar collector devices have been proposed for home use, e.g. for heating a working fluid, of water, which may circulate to a conventional domestic hot water heater for supplementing domestic hot water heating, or, for directly heating swimming pool water, or, for heating a working fluid which circulates to a thermal reservoir or storage tank which then flows to a domestic home heating system or the like to supplement conventional heating systems. Many such devices employ heat absorbing conduits fabricated from highly thermally conductive metals such as aluminum and or copper. A working fluid, which may be water, air or another working fluid is circulated through the metal conduit to receive thermal energy absorbed thereby when the conduit is exposed to solar radiation falling thereon.

Many solar collecting devices also include a chamber for surrounding the heat absorbing conduits, to reduce convective heat loss from the heat absorbing conduits. Such a chamber may enclose individual heat absorbing conduits, as shown in U.S. Pat. No. 4,198,955, or may enclose a plurality of heat absorbing conduits, as shown in U.S. Pat. No. 4,397,305. In either case, a transparent material on a surface facing the sun is typically employed to seal the chamber while allowing solar radiation to pass through the transparent material and onto the heat absorbing conduit.

In other examples, the solar collector may also include reflective lenses or the like to focus or otherwise direct incident solar radiation onto the heat absorbing conduit. In one such device, disclosed in U.S. Pat. No. 4,373,513, by Materna, a solar collector of very simple construction is proposed, employing a single non-tracking reflective element in combination with a plurality of heat absorbing conduits which receive reflected solar energy. The Materna device appears to provide a low cost solar collector, however, details of its construction and fabrication are not provided since the '513 patent teaches other aspects of the invention. U.S. Pat. No. 4,309,984 provides yet another example of a reflective lens type solar collector, however, the details of its construction are complex and the materials of metal and glass require labor intensive manufacturing processes and unit assembly.

Another consideration in the fabrication of a solar collector for general use is that some applications may require more or less heating capacity such that there is an advantage to provide a solar collector which may be easily fabricated in various sizes. It is known to combine multiple solar collector device together in order to increase heating capacity, however, these combinations only allow increases in large steps, e.g. a 100% increase in area by combining two collectors of equal area. Such combinations of individual collector elements may not be practical due to available space and or weight considerations, e.g. on a roof installation. As will be detailed below, the present invention allows incremental increases in heating capacity in small increments without substantially increasing the cost or complexity of the installed solar collector.

A need exists in the art for a very low cost solar heating device, especially for heating water directly. A further need exists for a solar heating device of simple enough construction so as to be shipped in an unassembled condition and assembled on sight by an unskilled and untrained user. Such a low cost and easily to assemble device may be employed e.g. for seasonal heating of swimming pool water or the like and may further allow for disassembly and storage of the device in the off season. A need also exists for a solar collector which is easily variable in collecting area without substantially increasing the cost or complexity of installing the solar collector for a particular application.

One way of reducing manufacturing and labor costs, as proposed by the present invention, is to provide a solar collector of modular unitary construction. Examples of such solar collectors are given in U.S. Pat. No. 4,718,404, by Sadler, and in U.S. Pat. No. 4,397,305, by Keefe, wherein molded or otherwise formed heat absorbing conduits take advantage of molding techniques to incorporate additional functionality into the molded parts, thereby reducing the total number of parts as compared with non-modular devices and simplifying assembly by providing interlocking and or interconnecting features molded into the individual elements.

Of particular interest with respect to the present invention is the use of ceramic materials for molding heat absorbing conduit elements as disclosed in U.S. Pat. No. 4,383,959 by Sadler. Ceramic materials offer extremely low raw material and manufacturing costs as compared to a solar collector fabricated from metals, especially copper and aluminum, and provide an advantage over heat absorbing conduit elements fabricated from molded or formed plastic or other conventional molding materials since ceramic materials are impervious to the adverse impervious to the adverse effects of the environment, including excessive temperature and ultraviolet radiation due to prolonged expose to the sun. Furthermore, ceramic materials offer substantially rigid mechanical properties providing structural integrity and thermal stability in comparison to plastic molded or other formed elements, and since ceramic elements are molded or formed, they have the further advantage that additional functionality can be molded into the parts, thereby reducing overall part count.

Accordingly, it is a specific object of the present invention to provide a low cost solar collector for heating water or another working fluid. It is further specific object of the present invention to provide a solar collector of modular unitary construction. It is a specific object of the present invention to provide a solar collector formed by assembling a plurality of substantially identical molded elements onto a base such that the solar collector has sufficient area to meet the heating capacity required by a particular application and furthermore that the area and therefore heating capacity of the solar collector be selectable in accordance with the required heating capacity. It is a still further object of the present invention to provide a method for forming a ceramic element for use as a reflective lens or the like for focusing or otherwise directing incident solar radiation onto a heat absorbing conduit. It is a still further object of the present of the present invention to provide a solar collector of such simple construction so as to be able to be shipped to a sight unassembled and assembled at the sight by an unskilled and untrained user. It is a still further object of the present invention to provide a solar collector which is easily assembled for seasonal use and thereafter disassembled for seasonal storage while requiring a minimum of storage space.

SUMMARY OF THE INVENTION

The present invention overcomes the problems cited in the prior by providing a plurality of substantially identical reflective element for reflecting solar energy to a focal axis in a solar collecting apparatus and which can be formed into rows of substantially identical reflective elements. Each reflective element is formed as a substantially rectangular element having opposing side walls and opposing end walls which together form a bottom edge for supporting the reflective element on a flat support such as a sheet metal or mold base. Each reflective element further includes a top wall connected with and supported by the side walls and the end walls. The top wall is formed to provide a reflective surface facing away from the bottom edge and is formed in a shape for reflecting solar radiation falling thereon, from a range of incident angles, to a focal axis. The focal axis of each reflective element is substantially parallel with a longitudinal axis of the reflective element and when the reflective elements are arranged in parallel rows, each row includes a focal axis along its longitudinal length. The reflective surface is coated with a reflective layer such as vacuum deposited aluminum, metalized paint or by other reflective coatings to reflect solar energy to the focal axis. The reflective surface may be formed with a constant radius R with respect to a locus axis, e.g. positioned 4.0 inches above the reflective surface and wherein the focal axis lies equidistant from the reflective surface and the locus axis, e.g., 2.0 inches above the reflective surface. A parabolic reflective surface may also be fabricated to improve the sharpness of the reflective surface focal axis. Ideally, the reflective element is formed by molding a material in a mold such that the mold forms the shape of the reflective surface. In the preferred embodiment of the present invention the reflective element is molded in a press mold from a material comprising hydrated silicates of aluminum which is plastic when wet but which becomes a hard ceramic when fired in an oven.

In another aspect of the present invention a solar energy collecting apparatus for heating a working fluid using the plurality of substantially identical reflective elements arranged in rows is provided. There is provided a working fluid conduit comprising a plurality of fluid carrying members positioned one above each row of reflective elements and substantially coincident with the focal axis of the row. The fluid carrying members are connected together by a plurality of connecting members such that a continuous working fluid conduit passes a working fluid over each row of reflective elements. In another aspect of the present invention the working fluid conduit is movably supported with respect to the base such that each of the plurality of fluid carrying members is movable away from the focal axis when no heating of the working fluid is desired.

There is also provided an adjustable support frame for supporting the solar collecting apparatus in a desired orientation with respect to the sun. The collecting apparatus also includes alignment targets for aligning the shadow of a first target with a second target to optimize the orientation of the solar collector with respect to the sun.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention will best be understood from a detailed description of the invention and a preferred embodiment thereof selected for the purposes of illustration and shown in the accompanying drawing in which: [0015]
FIG. 1 illustrates a plan view of an assembled solar collector, not including an outside enclosure according to the present invention. [0016]
FIG. 2 illustrates a sectional view taken through section A-A, shown in FIG. 1 and including elements of the outside enclosure according to the present invention. [0017]
FIG. 3 illustrates a sectional view taken through B-B of FIG. 1. [0018]
FIG. 4 illustrates a sectional view of a molded reflector element according to the present invention and taken through section C-C shown in FIG. 5. [0019]
FIG. 5 illustrates a plan view of the molded reflector element according to the present invention. [0020]
FIG. 6 illustrates a sectional view of a two piece press mold according to the present invention and taken through section D-D of FIG. 7. [0021]
FIG. 7 illustrates a partially cut away front view of the two piece mold according to the present invention; [0022]
FIG. 8 illustrates a gang press mold according to the present invention and shown in isometric; [0023]
FIG. 9 is an isometric view of a clamp used to secure individual reflector elements to a base; [0024]
FIG. 10 illustrates a hydraulic piston assembly according to the present invention; [0025]
FIG. 11 Illustrates an adjustable stand for supporting a solar collector at an appropriate angle of incidence with respect to the sun, according to the present invention.[0026]

DETAILED DESCRIPTION OF THE INVENTION

Referring now specifically to FIG. 1, there is illustrated an assembled solar collector in plan view, referred to generally by [0027] reference numeral 10. The solar collector 10 as illustrated in FIG. 1 does not include an outside enclosure to better show the detail of the elements of the present invention, however, an outside enclosure will be detailed below. The solar collector 10 comprises a base 20, which provides the necessary structural support required for supporting a plurality of rows of reflective elements 60, which are assembled onto the base 20. The base 20 also supports, four hydraulic pistons 320 which are provided near each corner of the base 20 and are used to movably support a working conduit 50 above the rows 70 of reflective elements 60. The working conduit 50 comprises a plurality of hollow tubes 300 connected together by a plurality of connecting tubes 330 for carrying working fluid through the solar collector 10. The base 20 also provides a mounting surface which may be used to mount the solar collector 10 onto a roof or other structure or to support the solar collector on an adjustable support frame 400, shown in FIG. 11. The support frame 400 can be adjusted to incline the collector 10 at various angles to increase expose to the sun.
The Enclosure [0028]
The present invention may be constructed with or without an outside enclosure. The enclosure, referred to generally by [0029] reference numeral 216, is provided to reduce convective heat lose from the working conduit 50 and the working fluid passing therethrough. Fastened to or formed integral with the base 20 are opposing enclosure side members 214, shown in FIG. 2, which extending vertically up from the base to form two sides of a four sided enclosure 216. Similarly, opposing enclosure end members 215, shown in FIG. 3, form the other two sides of the four sided enclosure 216. Each side or end member 214, 215 may be formed from any sheet metal, e.g. from a weather resistant stainless steel or from anodized aluminum or from any otherwise weather resistant material such a weather treated steel. In one embodiment, the side and end members 214, 216 may include a 90 degree bent flange 217 which is fastened to the base 20 by rivets, spot welds or by another suitable means for fastening. In another embodiment, each side or end member may be formed integral with the base by notching the base 20 and bending the side and end members 214, 216 vertically up from the base to form a four sided enclosure. Each side or end member 214, 216 may also include a feature at a top edge thereof for supporting a transparent enclosure top 220. The enclosure top 220 seals the top side of the enclosure while still allowing sun light to enter the enclosure 216. The enclosure top 220 may be formed of PLEXIGLAS, or the like, and should be formed from a material which will not loose transparency after long term exposure to sun light and which will have good weather resistance, e.g. to extreme heat and cold as well as resistance to scratching. One such material is LEXAN ABC manufactured by General Electric Corporation of New York.
In a preferred embodiment, shown in FIGS. 2 and 3, a [0030] bracket 222 is fastened to each side and end member 214, 216 for supporting the enclosure cover 220 which may be bonded or otherwise fastened to the bracket 222. Alternately, the bracket 222 may comprise a four sided frame (not shown) for capturing the enclosure top 220 on four edges thereof. The frame may be fastened to one of the side or end members 214, 216 by a hinge so that the entire transparent top 220 can be opened to provide access to the inside of the enclosure 216, or, the four sided frame and cover 220 may be fastened to the side and end members 214, 215 to seal the enclosure 216. In addition, a moisture seal 225 may also be provided to seal the region between the cover 220 and the enclosure 216.
It is also noted that the base [0031] 20 may be made larger to enclose more area. This is advantageous if it is desired to completely enclose the solar collector as well as the all of the working plumbing associated with pumping the working fluid to and from the collector 10. Such an enclosed unit is shown for illustrative purposes in FIG. 11.
Referring now to FIGS. [0032] 1-5, mounted to the base 20 are a plurality of substantially identical reflector elements 60 arranged in a plurality of rows 70 such that each row 70 includes a longitudinal axis 72. In a preferred embodiment, each reflector element 60 is substantially identically manufactured by a molding, casting or other forming process, or the like, to reduce the manufacturing cost, to take advantage of low cost raw materials and to take advantage of the molding process for, forming the shape of the reflective surface 140. Each parallel row 70 comprises three reflective elements 60 arranged as a first reflector element 62, a second reflector element 64 and a third reflector element 66, such that second reflective element 64 is positioned between the first and third reflective element 62 and 66, in the row 70, although, as few as one, or many more than three reflective elements 60 may be used to form each row 70. Each reflective element 60 includes a longitudinal axis 71 such that when the reflector elements 62, 64, and 66 are positioned end to end to form the row 70, the longitudinal axis 71 of each of the three reflector elements (62, 64, 66) are substantially co-aligned with the row longitudinal axis 72.
Between the [0033] base 20 and the rows 70 there may also be provided an insulating layer 212 which reduces conductive heat loss through the base 20. Such an insulating layer 212 may be formed e.g. from a single STYROFOAM layer or, from a layer of another insulating materials. If the base 20 is a molded or formed element, the insulating layer 212 may also be incorporated into the base 20, e.g. if the base 20 is formed using a fiberglass or plastic material. A molded base 20 has certain advantages over e.g. a sheet metal base since the insulating layer 212 as well as other features such mount elements may also be molded or otherwise incorporated with the base 20. However, the cost of a molding tool is high.
Working Conduit [0034]
Supported above each row of [0035] reflective elements 70 is the working fluid conduit 50 comprised of the plurality of hollow tubes 300 and a plurality connecting tubes 330 for interconnecting the hollow tubes 300. Each hollow tube 300 is preferably formed from a round copper tube, e.g. a 1 inch in diameter tube. Alternately, the hollow tubes 300 may also be formed from a black polycarbonite plastic tubing or other tubing materials suitable for carrying a working fluid therethrough. Each hollow tube 300 is supported above the longitudinal axis 72 of a single row 70 and spans across the entire length of the row 72. The hollow tubes 300 are supported at two ends thereof by two tube support brackets 315. A single tube support bracket 315 is shown partially cut away in FIG. 2 and both support brackets 315 are shown in end view in FIG. 3. Each support bracket 315 includes a plurality of mounting features 325 for receiving and supporting the hollow tube 300 therein. The mounting features 325, which in the present embodiment are shown as a plurality of cut-out V shaped notches in FIG. 2, serve to locate each end of the hollow tubes 300 above the center of one of a row 70. Each tube 300 is fastened to the support brackets 315 by appropriate fastening means such as a clamp or by a snap fit with the mounting feature 325 or by another suitable fastening member.
Each [0036] bracket 315 comprises an L-bracket of sufficient thickness so as to provide the appropriate stiffness to support each of the hollow tubes 300 while being supported only at opposing distal ends by two hydraulic pistons 320. Two brackets 315, positioned one at each end of the rows 70, are each supported by a pair of hydraulic pistons 320. The four hydraulic pistons 320 movably support the two support brackets 315 such that the brackets 315 and the hollow tubes 300, supported by the brackets 315, are movable to adjust the distance between the hollow tubes 300 and the reflector elements 60. As will be detailed below, the four hydraulic piston 320 move in unison to raise and lower the entire working fluid conduit with respect to the reflector element rows 70.
In order to provide a continuous fluid conduit, the connecting [0037] tubes 330 are fitted onto the ends of adjacent hollow tubes 300 to allow the fluid to flow from one hollow tube 300 to an adjacent tube 300 through the connecting tube 330 which connects the adjacent tubes together. The connecting tubes 310 are sized to snugly fit over each hollow tube 300 to prevent the working fluid from leaking. Alternately, hose clamps may be used to further prevent leaking. As shown in FIG. 1, an inlet hose or line 450 is provided between a cold working fluid flow inlet 30 and a first hollow tube 460 to pump a cold working fluid from the pump high pressure line 510 through the solar heater 10. The cold working fluid is heated by sun light which is reflected onto each hollow tube 300 by each of the reflector elements 60 as the working fluid passes through each hollow tube 300 suspended across each row 70. An outlet hose 470 exits from a last hollow tube 480 to transport the, now heated, working fluid from the solar collector back to a working fluid reservoir which in the preferred embodiment is a swimming pool. A check valve 350 is provided at the inlet 30 to prevent the working fluid from reversing direction and a pressure relief valve 360 is provided at the outlet hose 40 to allow the working fluid pressure to be relieved, e.g., if the working fluid pressure should exceed about 160 to 180 pounds per square inch. This precaution prevents damage to the solar collector should the pressure of the working fluid exceed safe limits. Additional gate valves or the like may also be provided in the flow inlet 30 or the flow outlet 40 as required.
In the preferred embodiment, the [0038] pump 340 may be a swimming pool filter pump which removes water from the swimming pool at a low pressure line 500 and pumps the water through a filter element 520, the solar collector 10 and then through the outlet line 40 to return the water to the swimming pool. Alternately, a direct return line may also be provided at the filter so that a portion of the water entering the pool filter is returned to the pool directly while the remaining portion of the water leaving the pool filter passes through the solar collector 10. The portions may be adjusted according to the heating capacity of the solar collector or according to the need for heating.
Hydraulic Pistons [0039]
Also provided are two hydraulic piston flow circuits for providing high pressure water to each of the [0040] hydraulic pistons 320. Two inlet lines 370 and 371 connect between the flow inlet 30 and the two hydraulic pistons 320 located at a back side 550 of the solar collector 10, as shown in FIG. 1. Piston connecting lines 372 and 373 connect the two pistons 320 at the backside 550, to the two piston 320 at a front side 555 of the solar collector 10. A return line 370 connects from the two pistons 320 at the front side 555 to the flow outlet line 40. The pump 340 therefore forces high pressure working fluid through the hydraulic piston flow circuit and into each of the four hydraulic pistons 320. Each piston 320 is therefore maintained at the pressure of the high pressure pump line 510 as long as the pump 340 is operating. Working fluid at the pressure of the high pressure pump line 510 within each piston 320 raises each piston to its full height thereby raising the entire working conduit to a focal axis of the reflector elements 60, as will be detailed below, thereby providing the maximum heating effect. Should the pump be turned off, or fail, each piston 320 will lower to a low pressure position thereby lowering the working conduit out of the focal axis of the reflective elements 60 to reduce the amount of solar energy reflected onto the hollow tubes 300.
A [0041] hydraulic piston 320 is shown in cross-section in FIG. 10. Each hydraulic piston 320 comprises a movable piston 375 contained within a cylinder housing 380. The cylinder housing 380 includes a conduit section 385 for receiving working fluid from the piston conduit 385 and a chamber 390 for receiving high pressure working fluid from the conduit section 385. A flexible bladder 395 is supported within the chamber 390 and seals the chamber 390 from the conduit section 385 such that as the working fluid pressure within the conduit section 385 increases, the working fluid forces the bladder into the chamber thereby forcing a lower end of the piston 375 upward. Each piston 375 is connected at an upper end thereof to one of the support points 310 for supporting the support brackets 315. A compression spring 400 surrounds the piston 375 and is captured between a flange 410 formed on the piston, and a flange 415 formed on the cylinder housing 380. The compression spring 400 forces the piston downward when the fluid pressure in the chamber is below a set pressure. A bottom side 396 of each hydraulic piston 320 is attached to the base 20. Of course a simple support system such fixedly attaching each of the support brackets 315 to the base 20 such that the working conduit 50 is fixedly supported at the focal axis each reflective element 60 may also be used without deviating from the present invention. Alternatively, electronic solenoids may also be used in place of the hydraulic pistons 320 to electro-magnetically support each of the hollow tube 300 and to lower the hollow tubes 300 when the pump is not operating by using an electronic controller.
In order to improve the thermal absorption properties of the fluid conduit, the surface of the [0042] hollow tubes 300 is coated with a black paint or another coating having good thermal absorption properties, e.g. a dendrite coating or other black roughened coating may be used. Likewise, the connecting hoses 330 and the hoses 450 and 470 may also be provided in a black polycarbonite or other black plastic tubing to improve thermal absorption of the working fluid conduit 50. To further improve performance, each hollow tube 300 is formed from a 1 inch diameter copper tubing having a wall thickness of e.g. 0.06 inches and each copper tube is partially formed to an elliptical shape over the portion of the tube length which is suspended above the row 70. This leaves a short round portion 560 at each end of the hollow tube 300 to allow mounting of the connecting tubes 330 and to provide a round mounting area for easy mounting with the support bracket 315. The long axis of the ellipse is supported substantially parallel with the base 20 as is shown in FIG. 4. This feature of the invention serves to place most of the fluid carrying conduit in the plane of the focal axis where the reflected sun light is more highly concentrated. In order to form each tube 300 into an elliptical shape, the tubes may be rolled between formed rollers. Each tube 300 may also be filed with sand during the rolling process to prevent cracking during the rolling.
Reflective Element [0043]
Referring now to FIGS. 4 and 5 there are illustrated a side view of a single [0044] reflective element 60, in FIG. 5, and a sectional view of the reflective element 60 taken through section C-C of FIG. 5, shown in FIG. 4. The reflector element 60 includes a hollow cavity 90 on a bottom side thereof, referred to generally by reference numeral 95. The hollow cavity 90 is open at the bottom side 95 and enclosed by two side walls 100 and two end walls 110 which together form an edge 92 adjacent to the bottom side 95, for supporting the reflector element on the base 20 or other layer. The hollow cavity 90 is further bounded by a top wall 120. Top wall 120 is opposed to the bottom side 95 and is formed to provide a reflective surface 140 facing away from the hollow cavity 90. The top wall 120 is supported by each side wall 100 and by each end wall 110 such that the longitudinal axis 72 of the reflective element 60 is substantially parallel with the side walls 100 which are longer than the end walls 110.
The [0045] reflective surface 140 is formed to reflect sunlight incident onto the reflective surface 140 to a focal axis 132, which is substantially parallel with the longitudinal axis 72 of the reflective element 60. As shown in FIG. 4, the reflective surface 140 has a constant radius R about a locus point 130. In the case where R is constant the reflective surface 140 is cylindrical with a focal axis 132 which is equidistant between the locus axis 130 and the reflective surface 140 such that if the radius R=4.0 inches, the focal axis 132 lies 2.0 inches above the vertex of reflective surface 140. If a width of the reflective element 60 is approximately 4.0 inches and the radius R is also 4.0 inches, the subtended angle of the reflective surface 140 is approximately 53 degrees. It is noted that by using a cylindrical reflective surface 140 the focal axis of a cylindrical surface will be slightly blurred which can result in less effective heating.
In a preferred embodiment, a parabolic shaped [0046] reflective surface 140 is provided. Although a parabolic reflective surface is only slightly altered from a cylindrical surface having the same focal axis, the parabolic surface provides a finer focal axis 132 thereby concentrating more energy onto the hollow tube 300. Since it is more difficult to fabricate a parabolic surface than a cylindrical surface the cylindrical surface is often used as a close approximation. However, in the present invention each reflective element 60 is molded and the problem of fabricating a parabolic surface need only be addressed once when forming the mold surface. Once the mold is formed to the parabolic shape, each reflective element may then be replicated in the form of a parabolic cylinder.
The points of a parabolic curve in an X-Y coordinate system are given as the set of points M(X, Y) where[0047]
Y ²=2pX (1)
For a parabolic surface P, a focal axis F is positioned at the point F=(p/2, 0). Thus by setting p=4 inches, a focal axis of the parabolic surface P is positioned at F=(2, 0) or 2.0 inches above the vertex of the parabola just as was given for the cylindrical surface shown in FIG [0048] 6.
Holddown Clamp [0049]
The [0050] reflective surface 140 is coated to reflect solar energy received thereon to the focal axis 132, which in the present examples is 2.0 inches above the vertex of the reflective surface. With a width of approximately 4.0 inches each, row of reflective elements 60, 61, 62 is placed on the base 20 with its side walls 100 parallel to the side walls of an adjacent row so that the rows 70 are spaced slightly more than 4.0 inch centers. Between adjacent rows 70 are mounted sheet metal clamps 200, shown in the sectioned side view of FIG. 3 and shown in isometric view in FIG. 9. Each clamp 200 is attached to the base 20 by three mounting features 208 which in the present example interlock with the base 20 by a snap fit by applying a downward force to force the locking features 208 into slots provided in the base 20. The clamp 200 has a length 202 which is substantially equal to the length of a row 70. The clamp 200 include a plurality of bendable tabs 204 which when the clamp 200 is mounted to the base 20 protrude above the reflective element reflective surfaces 140. The tabs 204 are then bent over the tops of each reflective element 60, 61, 62 to hold the elements against the base 20 or the insulating layer 212, if present. In the case where an insulating layer 212 is provided, each clamp 200 is passed through slots provided in the insulating layer 212. The clamp 200 provides a total of 12 bendable tabs 204 for holding one edge of six reflective elements, three in a first row 70 and three in an adjacent row 70. Adjacent tabs 204 are bent in opposite directions to secure one row the first row of reflective elements by the tabs 204 bent in one direction and the second row of reflective elements by the tabs bent in the opposite direction. Each reflective element 60, 61, 62 is therefore clamped by four bendable tabs 204 which are positioned at each corner of the element. One clamp 200 is also positioned at end of the outer most rows 70 such that the end clamps hold only one row of reflective elements in place. To assemble the rows 70, the clamps 200 are secured to the base 20 and three reflective elements 60 are positioned onto the insulating layer in a row between opposing clamps 200 and the clamp tabs 204 are bent over to secure each reflective element in place. It is also noted that the reflective elements are easily replaceable if required.
In another embodiment, the [0051] clamps 200 may be formed from the base 20 by notching the base 20 to notch out a clamp 200 such as the one shown in FIG. 9 and then bending the clamp 200 by 90 degrees from the base 20 to extend the clamp 200 upward from the base 20. The reflector elements 60 may then be installed between rows of clamps and secured by bending the tabs 204 over the reflective surfaces 140 as described above. In this case it may be advantageous to apply sections of an insulating layer 212 between the rows of bent up clamps 200 instead of a sheet of insulating layer.
Adjustable Frame [0052]
The [0053] solar collector 10 may also be mounted onto an adjustable frame 600 shown in FIG. 11. The frame 600 can be used to orient the solar collector 10 to face the sun and set at an angle with respect to the sun which provides maximum heating capacity, e.g. by setting the optimal angle at high noon or optimized at another angle for another condition, e.g. for receiving early morning sun. The frame 600 includes a supporting base 610 having two support members 620, mounted on pivoting feet 615, and a plurality of cross members 630 for stiffening the support base 610 and for securing to and supporting the base 20. A pair of adjustable support legs 635 are pivotally mounted to the support base 610 and also mounted on pivoting feet 615. At least one cross brace 640 is attached to each of the adjustable support legs 635 near the lower end thereof such that the support legs 635, the cross brace 640 and the support base 610 form a four sided frame for supporting the solar collector 10. Each adjustable support leg 635 includes a slot 645 passing therethrough. Two pivot pins 650 each mount to the support base 610 and pass through each slot 645 in the adjustable legs 635. A locking device 655 attaches to each pivot pin 650 to lock the pivot pin 650 at any desired position along the slot 645 such that the solar collector 10 may be supported at a plurality of inclination angles. One type of locking device 655 may include providing a threaded portion on the ends of the pivot pins 650 and providing a locking nut threaded onto the pivot pin 650 such that when the nut is tightened the adjustable support legs 635 are clamped against the base support 610 to secure the base support 610 at a desired inclination angle. Of course other locking mechanisms and adjustable frame assemblies may be provided without deviating from the present invention.
To assist in selecting an inclination angle, a target [0054] 660 is provided on the transparent top 220 and a matching target is provided directly below the target 660 on the base 20. To set the desired inclination angle of the adjustable frame 600 the shadow of the target 660 is observed on the base 20. At the appropriate time of day the inclination angle and direction of facing the solar collector 10 is set by adjusting the position of the collector until the shadow of the target 660 provided on the transparent top 220 is positioned directly over the matching target provided on the base 20.
Fabrication of the Reflector Elements [0055]
In order to fabricate each of the [0056] reflective elements 60, there is provided a press mold 74, shown in FIGS. 6 and 7, having a bottom section 76 and a top section 78. Each press mold section, 76 and 78 may be formed from a soft material such as plaster of Paris, or the like, of from a harder material such as wood or metal. The bottom section 76 includes a protruding male portion 80 which has the same shape and form of the hollow cavity 90 and which is used to shape the reflector element 60 at the bottom side 95, thereof. The side walls 82, of the male portion 80, are used to form the side walls 100 of the reflector element 60 and are formed with a draft angle 84 which allows the formed reflector element 60 to be easily removed from the press mold 74. The end walls 86 of the male portion 80 may also be formed with a draft angle and are provided to form the end walls 110 of the reflective element 60. The press mold top, or female section 78 is used in cooperation with the bottom section 76 and includes a parabolic surface 88 which forms the parabolic reflective surface 140 of the reflective element 60. The mold parabolic surface 88 may be polished so as to provide a smooth uniformly parabolic surface to the reflective element reflective surface 140, thereby improving the reflective properties thereof. The top section 78 also includes end surface 89 which cooperates with the end walls 86 of the bottom section 76 to form the end walls 110 of the reflective element 60.
In order to fabricate a single [0057] reflective element 60, a layer of substantially uniformly thick clay, such as pottery clay or the like, is applied over the bottom section 76. Such a clay is usually comprised substantially of hydrated silicates of aluminum which is plastic when wet but which becomes a hard ceramic when heated or fired in an oven. To form a clay layer, a clay brick may be rolled into a uniformly thick sheet prior to applying it to the press mold 74. Once applied over the bottom section 76, the top section 78 is pressed onto the clay layer with sufficient force to form the clay layer into the shape of the reflective element 60. The top section 78 is then removed and the formed clay is removed from the bottom section. The press mold 74 may be coated with a mold release layer such as mold soap or the like.
Alternately, a plurality of [0058] reflective elements 60 may be formed in a gang mold 89 which includes a bottom section 81 and a top section 83. The top and bottom sections 81, 83 each include a plurality of mold portions 85 having substantially identical characteristics as the single press mold 74, described above and shown in FIG. 6 and 7. In this case, a substantially uniform layer of clay may be applied over the entire bottom section 81 of the gang mold 89 with the top section 83 being pressed onto the bottom section 81 thereby forming a plurality of reflective elements simultaneously.
Similarly, one or a plurality of [0059] reflective elements 60 may be formed by a slip casting method which is well known. In this case, two mold section having substantially similar characteristics for forming a reflective element 60 as are described for press mold 74, above, are clamped together and configured with a series of gates through which a liquid clay or slip is poured or pumped into the slip mold such that the liquid clay completely fills each mold cavity thereby forming one or more reflective elements 60 from the liquid clay contained between the mold sections. The liquid clay is then allowed to dry either by air drying or by heating or baking the mold sections in an oven. Once dry, the reflective elements 60 are removed from the mold and may be cleaned of excess clay in the gate areas and separated into individual clay reflective elements 60.
Once formed, whether by press molding or slip casting, each clay [0060] reflective element 60 is heated of fired in a ceramic furnace or oven by techniques which are well known. One example of a firing cycle includes heating the clay reflective elements to a temperature of 1350 degrees Fahrenheit and then slow cooling the elements over a 12 hour period. This cycle may be repeated several time to complete the firing.
In addition to firing, the clay reflective elements are also glazed by applying a liquid clay over the surface of each clay element by spaying, dipping or brushing the liquid clay onto the surfaces of each clay [0061] reflective element 60. The glazing is used to fill any surface voids in the formed elements and to decrease the porosity of each of the element surfaces. The glazing may also be used for coloring. After application of the glaze, the element is again heated or fired in order harden the liquid clay applied on the surfaces.
By firing and glazing the clay elements, each element is transformed into a [0062] ceramic reflector element 60. The ceramic element has excellent properties for use in a solar collector. Such properties include a low coefficient of thermal expansion a low coefficient of thermal conductivity, good resistance to moisture and ultraviolet radiation, excellent mechanical stiffness and little or no maintenance required over the product life. In addition, the raw material, clay, is readily abundant and low in cost. Of course other methods of forming ceramic reflective elements from clay or of forming reflective elements from other plastic materials such as plastics, fiberglass or the like may also be used without deviating from the present invention. However, a clay reflector element 60 is impervious to moisture and will not crack, warp or significantly change its dimensions or shape over temperature extremes caused by prolonged exposure to the sun or by snow and ice. Furthermore, the elements may be easily replaced if damaged.
Once the ceramic [0063] reflective elements 60 have been formed, the parabolic reflector surface 140 is then coated with a reflective layer which may comprise a paint which is brushed or sprayed onto the surface 140. In a preferred embodiment, a metalized layer may be deposited onto the surface 140 such as by electro-plating, vacuum deposition or by other well know metal deposition techniques. In another embodiment, a reflective MYLAR layer may also be bonded onto the surface 140. Such a MYLAR layer is available in sheets with a highly reflective layer on one surface and an adhesive backing on an opposite surface from 3M Corporation of Minnesota. Ideally, the reflective layer deposited onto the surface 140 will have very high reflectivity and low absorption throughout the full range of infrared wavelengths. In addition the reflective layer should maintain its reflective properties throughout the product life without being significantly affected by environmental elements. In addition, the reflective layer should be scratch and chip resistant. In the preferred embodiment, a layer of metal aluminum is applied onto the reflective surface 140 using a vacuum deposition technique. In this case, one or more reflective elements 60 are placed in a vacuum chamber with each element 60 having a high electrical charge, e.g. a negative charge applied thereto. At the same time, aluminum vapor having a highly opposite charge, e.g. positive, is introduced to the vacuum chamber. In this way a uniform layer of aluminum is applied onto the reflective surface 60 while the other surfaces of the reflective element are masked or otherwise blocked from receiving the aluminum coating.
It will also be recognized by those skilled in the art that, while the invention has been described above in terms of preferred embodiments, it is not limited thereto. Various features and aspects of the above described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment, and for particular applications, e.g. an infrared sensor assembly and an infrared video camera system, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially utilized in any number of environments and implementations. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the invention as disclosed herein. [0064]

Claims

What I claim and desire to secure by Letters of Patent of the United States are the following:

1. A solar energy collecting apparatus for heating a working fluid comprising:

a plurality of substantially identical reflective elements arranged in rows each reflective element including a reflective surface formed in a shape and coated with a reflective layer to reflect solar energy incident thereon to a focal axis;

a working fluid conduit comprising a plurality of fluid carrying members positioned one above each row of reflective elements and substantially coincident with the focal axis, each fluid carrying member being connected with another fluid carrying member by a connecting member such that a continuous working fluid conduit passes a working fluid over each row of reflective elements; and,

a base member for fixedly supporting the reflective elements in rows and for supporting the fluid carrying members of the working fluid conduit.

2. The solar energy collecting apparatus according to claim 1 wherein the working fluid conduit is movably supported with respect to the base and the plurality of substantially identical reflective elements arranged in rows such that each of the plurality of fluid carrying members is movable away from the focal axis.

3. The solar energy collecting apparatus according to claim 1 wherein each of the reflective elements is formed by molding a material in a mold and wherein the mold forms the shape of the reflective surface.

4. The solar energy collecting apparatus according to claim 3 wherein the mold is a press mold.

5. The solar energy collecting apparatus according to claim 3 wherein the material comprises hydrated silicates of aluminum which is plastic when wet but which becomes a hard ceramic when fired in an oven.

6. The solar energy collecting apparatus according to claim 1 wherein the reflective layer is selected from the group consisting of, a reflective paint, a metalized layer and an adhesive backed reflective coating.

7. The solar energy collecting apparatus according to claim 5 wherein the reflective layer comprises a metalized layer deposited by electro-plating.

8. The solar energy collecting apparatus according to claim 5 wherein the reflective layer comprises a layer of metal aluminum applied by vacuum deposition.

9. The solar energy collecting apparatus according to claim 1 further comprising a pump for pumping the working fluid through the continuous working conduit.

10. The solar energy collecting apparatus according to claim 2 further comprising:

four hydraulic pistons attached to the base such that one piston is positioned substantially at each corner of the solar collector and wherein a hydraulic flow circuit passes a fluid at a high pressure to each of the four hydraulic pistons;

two support brackets each supported at distal ends thereof by one of the four hydraulic pistons hydraulic piston, and wherein each of the support brackets supports one end of each of each of the fluid carrying members such that when the fluid is at the high pressure each of the support bracket is raised by the hydraulic pistons thereby raising each of the fluid carrying members to a position which is substantially coincident with the focal axis and further wherein when the fluid is at a low pressure each of the support brackets is lowered to move each of the fluid carrying members away from the focal axis.

11. The solar energy collecting apparatus acoording to claim 10 wherin the fluid is the working fluid.

12. The solar energy collecting apparatus according to claim 11 further comprising a pump for pumping the working fluid through the continuous working conduit and the hydraulic flow circuit.

13. The solar energy collecting apparatus according to claim 10 further comprising:

a fours sided enclosure comprising two opposing side member and two opposing end members each fastened to the base for enclosing the rows of reflective elements, the four hydraulic pistons and the working fluid conduit; and

an enclosure cover comprising a transparent top for allowing sunlight to enter the enclosure and fall onto the reflective elements, the cover being fastened to the four sided enclosure by a bracket such that the cover and the four sided enclosure and the base form an chamber enclosing the reflective elements and the working fluid conduit and wherein the chamber is substantially sealed form outside air to reduce convective heat lose from the working fluid conduit as the working fluid passes through the solar collector.

14. The solar energy collecting apparatus according to claim 1 wherein each of the rows comprises a plurality of reflective elements assembled together.

15. The solar energy collecting apparatus according to claim 1 wherein each of the fluid carrying members comprises a hollow tube having an elliptical shape and wherein the long axis of the ellipse is substantially parallel to the base.

16. A reflective element for reflecting solar energy to a focal axis in a solar collecting apparatus comprising:

a substantially rectangular element having opposing side walls and opposing end walls which together form a bottom edge for supporting the reflective element on a flat support member and further comprising a top wall connected with and supported by the side walls and the end walls, and wherein the top wall further includes;

a reflective surface facing away from the bottom edge and formed in a shape for reflecting solar radiation falling thereon from a range of incident angle to a focal axis said focal axis being substantially parallel with a longitudinal axis of the reflective element; and,

wherein the reflective surface is coated with a reflective layer for reflecting solar energy.

17. The reflective element according to claim 16 wherein the reflective surface has a constant radius R with respect to a locus axis positioned above the reflective surface and wherein the focal axis lies equidistant from the reflective surface and the locus axis.

18. The reflective element according to claim 16 wherein the reflective surface has a surface conforming to a shape defined by the set of points M (X, Y) wherein a vertex of the shape lies at the point V=(0, 0) and wherein Y²=2pX and further wherein the focal axis of the surface is positioned at the point F=(p/2, 0).

19. The reflective element according to claim 18 wherein p falls in the range of 0.5 to 3 inches.

20. The reflective element according to claim 17 wherein R falls in the range of 2 to 6 inches.

21. The solar energy collecting apparatus according to claim 16 wherein the reflective element is formed by molding a material in a mold and wherein the mold forms the shape of the reflective surface.

22. The reflective element according to claim 21 wherein the mold is a press mold.

23. The reflective element according to claim 21 wherein the molding material comprises hydrated silicates of aluminum which is plastic when wet but which becomes a hard ceramic when fired in an oven.

24. A method for heating a working fluid with solar radiation comprising the steps of:

attaching a plurality of substantially identical reflective elements each having a focal axis to a base arranged in a plurality of rows such that each row includes a focal axis which is substantially parallel with a longitudinal axis the row;

supporting a working fluid conduit on the base comprising a plurality of fluid carrying members positioned one above each row of reflective elements in a position which is substantially coincident with the focal axis; and,

interconnecting each fluid carrying member with another fluid carrying member by a connecting member such that a continuous working fluid conduit passes a working fluid over each row of reflective elements; and,

pumping a working fluid through the working fluid conduit while the reflective elements are exposed to sun light.

25. The method according to claim 24 further comprising the step of moving the working fluid conduit with respect to the base and the plurality of rows such that each of the plurality of fluid carrying members is movable away from the focal axis.

26. The method according to claim 24 further comprising the step of forming each of the reflective elements by molding a material in a mold and wherein the mold forms the shape of the reflective surface.

27. The method according to claim 24 further comprising the step of supporting the solar collecting apparatus by an adjustable support frame for supporting the solar collecting apparatus in a desired orientation with respect to the sun.

28. A method for making a reflective element for reflecting solar energy to a focal axis in a comprising the steps of:

forming an element having opposing side walls and opposing end walls which together form a bottom edge for supporting the reflective element on a flat support member and further comprising a top wall connected with and supported by the side walls and the end walls;

forming a reflective surface facing away from the bottom edge in a shape for reflecting solar radiation falling thereon from a range of incident angle to a focal axis, said focal axis being substantially parallel with a longitudinal axis of the reflective element; and,

coating the reflective surface with a reflective layer for reflecting solar energy to the focal axis.

28. The method according to claim 27 further comprising the step of forming the reflective surface with a constant radius R with respect to a locus axis positioned above the reflective surface and wherein the focal axis lies equidistant from the reflective surface and the locus axis.

29. The method according to claim 27 further comprising the step of forming the reflective surface to conform to a shape defined by the set of points M (X, Y) wherein a vertex of the shape lies at V=(0, 0) and wherein Y²=2pX and further wherein the focal axis of the surface is positioned at the point F=(p/2, 0).