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Stretched membrane solar collector

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Stretched membrane solar collector

An improved solar reflector utilizing a tensioned reflective membrane. The reflector structure includes a membrane attached on the outer surface of a metal strap that is positioned on an end form by means of a curved-face tensioning block.

Inventors: Allen I. Bronstein, Howard Harrenstien
USPTO Applicaton #: #20120320468 - Class: 359847 (USPTO) - 12/20/12 - Class 359 

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The Patent Description & Claims data below is from USPTO Patent Application 20120320468, Stretched membrane solar collector.

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This invention is a continuation-in-part of provisional patent application 61/020,933, which is incorporated by reference herein.


The invention relates to a new method of design and construction of linear tensioned membrane solar reflectors for solar parabolic trough concentrators, solar linear reflectors, and linear heliostats for solar Fresnel reflecting systems, in particular those that utilize thin flexible films for the membrane substrate.

Linear tensioned membrane reflectors have many advantages over more traditional designs incorporating ridged frame structures. They are relatively light and easy to assemble. In part because of the light weight, multiple reflectors can be mounted on a single frame structure which can be balanced on pillow block bearings allowing for tilting adjustments to be made with minimal energy expended.

Trough-shaped linear tensioned membrane reflectors, such as those shown in U.S. Pat. No. 4,293,192, issued Oct. 6, 1981, to Allen I. Bronstein and U.S. Pat. No. 4,510,923, issued Apr. 16, 1985 to Allen I. Bronstein, usually comprises a frame structure with parallel-facing identical end form members, each describing the desired cross-sectional shape of the reflector. A membrane of highly reflecting material, such as metalized reflective plastic film, is wrapped tightly around the edges of the form members and the membrane. The membrane is then placed under 1000 to 7000 pounds per square inch (PSI) of tension in one direction, usually by moving one of the end form members away from the other.

However, linear tensioned membrane reflector technology presents certain problems that do not exist for linear solar reflector technologies constructed with a rigid structural frame structures, especially when the device utilizes certain materials or laminates, such as plastic films, as the membrane\'s substrate. For example, Mylar (Biaxially-oriented polyethylene terephthalate boPET polyester film) is a dimensionally stable material that reacts in undesirable ways when the film is placed under compression. A typical means of mounting the membrane is to adhere it to the underside of a metal strap with a structural adhesive, such as epoxy. The strap is then wrapped around the end form and clamped in place. However, as the strap is bent around the end form the strap\'s inward facing surface and the membrane are placed in compression, wrinkles are produced; they are then crushed and locked in place as the strap is tightened on the end form. These distortions in the film are magnified by the film and transmitted into the membrane as large longitudinal wrinkles and ripples that span across the entire membrane\'s surface, distorting its shape.

It is an objective of this invention to reduce the wrinkles and other shape distortions that may occur when thin films are used as a membrane substrate in tensioned membrane solar reflectors.




The present invention teaches attaching the membrane to the outside of the strap so that when the strap is bent around the end form the membrane is placed under lateral tension rather than lateral compression. A curved attachment block is preferably used to eliminate improper curvatures and edge distortions in the membrane that could be caused by using a flat-faced attachment block. Further, the potential loss of structural integrity caused by not having the membrane sandwiched between the end form and the strap can be ameliorated by wrapping the end of the membrane longitudinally around the strap and attaching the membrane to the inner surface of the strap as well. Slits, notches or other cut-outs along the edge of the membrane that is attached to the inner surface of the strap eliminate bunching and/or wrinkles that could affect the seating of the strap and membrane on the end form.


FIG. 1 shows a perspective view of an embodiment of the invention utilizing the tensioning block.

FIG. 2 shows a cutaway of the center of the strap lying along the end form.

FIG. 3 shows a second cutaway view of the tensioning block attaching the strap to the end form.

FIG. 4 shows an exploded view of the tensioning block and strap.

FIG. 5 shows the attachment of the membrane to the strap.

FIG. 6 shows an exploded view of an alternate tensioning block and strap.



With reference to FIGS. 1, 2 and 3, the trough-like solar reflector 100 shown uses only the metal strap 110 to tension the membrane 120 around the end form 130 peripheral edge 140. In conventional attachment means, the membrane is adhered to the inside of the metal strap using epoxy or similar adhesive. In the embodiment shown, unlike conventional means, the membrane is adhered to the top or outside surface 115 of the metal strap, so that when the membrane and strap are mounted on the end form and held in place, the bending of the strap around the end form puts the strap in tension, thus laterally tensioning the membrane. The strap material and geometry must be such that the strap has sufficient flexibility to bend elastically along its length around the end form but sufficient rigidity so as to not bend significantly along the its width. It will be noted that although a metal strap, for example 1/16 inch aluminum or 1/16 inch steel, has been conventionally used in trough reflectors, other materials, such as carbon composites, might be utilized.

When the membrane is attached to the inside surface of the strap, as in a conventional reflector design, the peripheral edge 140 of the end form 130 can describe ideal cross-sectional profile of the solar reflector 100. In the current invention, however, the cross-sectional profile of the end forms must be adjusted to compensate for the thickness of the metal strap 110, and any cushioning pads 150 that are under it, so that the outside strap surface 115 becomes the correct cross-sectional profile.

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