This application claims the benefit of priority of U.S. patent application Ser. No. 11/983,971, filed Nov. 13, 2007, the content of which is incorporated herein by reference in its entirety.
The present disclosure relates generally to solar concentrators. More specifically, to moldable reflective solar concentrators.
Solar radiation is a diffuse energy resource. Average solar radiation intensity on earth is around 800 W/m2, varying with location, weather and season. Normally, an apparatus for a solar energy application needs a large area to collect solar radiation. Therefore, to make solar power the main stream energy supply, a breakthrough has to be made in creating an extremely low cost solar collector.
A solar concentrator is widely used for condensing solar radiation and is proved as a promising means for realizing extremely low cost solar collection. Generally there are two types of solar concentrator: one is a Fresnel Lens (FS) based on refraction of light, and the other is a parabolic reflector based on reflection of light. Due to the decisive factor of cost, in most of the large scale solar energy application systems, reflective solar concentrators are adopted to collect and condense solar radiation.
Most reflective solar concentrators are designed into a concave reflector structure which is generally in either a parabola form or a parabolic trough form. Most, and probably near all, of these reflectors have been built of relatively rigid materials such as metals. Usually, rigid reflective components are molded and assembled into a predetermined geometric shape and retained by suitable fastening means. Since this type of apparatus is an open system, to protect against wind and load, the rigid reflective components and fastening parts must be made of materials with certain stiffness, thickness and mass. Conventional solar concentrators for large scale solar systems appear bulky, heavy and expensive. The manufacturing processes for forming precision geometric shapes for rigid parts are proved complicated, slow and expensive. In addition, in the open systems, the reflective surface of the reflector structure is directly exposed to the outdoor condition and lacks protection from dust and other contaminations.
Most solar concentrators are effective only with directly incident solar radiation, so most solar concentrators are driven by a power system and a control system to track the sun and maintain direct solar incidence. When the solar concentrator is heavy, it adds significant loads to the tracking system and makes it complicated and expensive.
Several types of solar concentrators using non-rigid, lightweight and cheap materials were proposed to reduce the weight and to lower the cost. Among them, the most typical is the inflatable reflector structure. This structure employs an inflatable balloon which, when inflated, provides the structural frame to hold the concentrator portion of the apparatus in the parabola or parabolic trough shape in the desired position. In some of this type of structure, the reflector surface which forms the concentrator consists of a metallic coating on the inner surface of the balloon and in some other structures the concentrator portion is formed by a diaphragm type structure which is located within the balloon and has its perimeter attached to the inside surface of the balloon so that when the balloon is inflated the diaphragm is pulled into its desired operating shape.
U.S. Pat. No. 2,977,596 to Justice et al. disclosed such a structure using a diaphragm means to form an operating shape. In this disclosure, an air source is employed to maintain the inner pressure of the balloon. U.S. Pat. No. 4,672,389 to Ulry disclosed an inflatable reflector structure in which the concave reflector surface is constructed of a non-rigid flexible material, which is maintained in position and form by means other than the strength of the material itself. Ulry employs an inflation means in communication with the interior of an envelope, which is essentially a balloon, to provide and maintain fluid at super ambient pressure within the interior of the envelope. In GB 2 104 644, Leroy disclosed an inflatable solar collector structure with an element shaped into a parabolic trough reflector and maintained by inflation means. The inflation means is used to generate an internal pressure of the element that is greater than atmosphere. In U.S. Pat. No. 4,328,792, Shores disclosed a solar heat collector with an element which is a closed structure. However this element is composed of two parts: a parabolic trough reflector and a transparent cover. These parts are conventional components made of rigid materials such as metals.
There are certain difficulties connected with these inflatable structures. One of the more obvious ones is the tendency of the balloon to become distorted due to wind and other factors. This distortion, of course, results in some distortion of the reflecting surface of the concentrator which is an undesirable characteristic. The inflatable structure erected by an internal pressure above the external pressure of the structure needs a support system to stand up, and therefore extra fastening means such as rims are necessary. An inflation means in communication with the interior of the structure must be provided to maintain the internal fluid at super ambient pressure within the interior of the structure. Almost all of inflatable systems are used for short term and temporary purposes. Inflatable systems are mainly used in remote areas as a portable and collapsible apparatus.
For large scale and permanent solar applications, solar collectors made of light-weight and low cost materials with a simple structure, a strong resistance to outdoor conditions, and the capability of being easily manufactured are long expected. Obviously, inflatable systems are not the candidates that can fulfill the mission.
An object of the present invention is to provide a reflector structure through which moldable, light-weight and low-cost materials, including glass, are used to manufacture a solar concentrator without loss of the quality and performance of conventional solar concentrators made of high quality rigid materials such as metals. Another object of the present invention is to provide a non-inflatable reflector structure to eliminate the extra fastening means and inflation means of the inflatable structures so as to simplify the concentrator system, but still retain the integrity and performance that is usually associated with flexible inflated structures.
A further object of the present invention is to provide a non-inflatable reflector structure to avoid the distortion of the reflector surface caused by wind and other factors when in use, and to guarantee the accuracy of the geometric shape of the reflector surface formed in the manufacture process.
Furthermore, an object of the present invention is to provide an enclosed, non-inflatable reflector structure that is a single body of thin walled material that is constructed without any other elements so that it can be easily manufactured and utilized.
Another object of the present invention is to provide a non-inflatable reflector structure that is a closed structure, but which has an opening to connect the interior of the structure to the atmosphere so that the pressure within the interior of the structure is equal to the atmospheric pressure. Consequently the reflector structure is formed by the material strength itself rather than the internal pressure of the structure being above atmospheric pressure.
Furthermore, an object of the present invention is to provide a non-inflatable reflector structure that facilitates the metallic coating process for forming the reflector.
The final object of the present invention is to provide a method for manufacturing the novel solar concentrator in an easy and fast way.
In summary, an enclosed, hollow core structure enables moldable, light-weight and cheap materials, including glass, to be used to construct a strong mechanical structure to protect against wind and other factors. The structure also allows for the formation of an accurate concave geometric surface to hold a metallic reflective layer to concentrate sunlight.
In one embodiment, a solar concentrator comprises an upper transparent surface and a lower transparent surface. A reflective layer is on the lower transparent surface. The lower transparent surface is shaped such that the reflective layer reflects and concentrates incident light.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.
FIG. 1 is an example of a reflector structure.
FIG. 2 is an example of the reflector structure of FIG. 1 along line X-X.
FIG. 3 is an alternative example of a reflector structure.
FIG. 3B is another alternative example of a reflector structure.
Reference will now be made in detail to the present exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Referring to FIG. 1, the solar concentrator body is a bottle of moldable, lightweight and cheap material, such as glass or plastic. In this embodiment, the bottle is blow molded with a transparent material to form a unitary body with a thin wall and a bottle neck 11 connecting the interior of the structure to atmosphere. The structure may comprise a metallic reflective layer covering a certain geometric area of the body.
The enclosed body of thin walled transparent material is substantially a bottle with a bottle neck as an opening to communicate with the external atmosphere of the closed body. The bottle itself is a strong mechanical structure to support itself to collect and concentrate sunlight without any other supporting systems. The thin wall of the bottle body has to have a certain thickness and stiffness to have enough material strength to form the predetermined geometric shape and to retain it without any inflating system. The bottle neck 11 is made rigid so that it can be used as a connection for integration into systems.
An upper half portion 12 of the thin wall of the enclosed body is transparent to allow light to enter the enclosed structure. A lower half portion 13 is formed into a concave parabola or parabolic trough shape so that the sunlight incident on it can be reflected and concentrated to a predetermined point or line.
A metallic reflective layer 14, shown in FIG. 2, is coated on the surface of the parabola or parabolic trough at the outside surface of the bottle. And an alternative method is to cover the outer surface of the parabola or parabolic trough with mirror films. A third alternative is to coat a certain geometric portion of the inner surface of the body with a metal or mirror film.
Referring to FIG. 2, the bottom portion 13 of the bottle is formed into a parabolic trough shape in the blow molding process. Thereafter, the bottom portion 13 of the bottle is coated with at least one metallic reflective material 14 on the outside surface. Upper portion 12 is kept clear and transparent to radiation 10. An alternative process for coating the outside surface of the parabolic trough is to cover the surface with mirror films.
The incident sunlight 10 penetrates through the upper portion 12 of the bottle and reaches the lower surface 13 with the reflective layer 14 and is reflected back. The reflected sunlight penetrates through the top portion of the bottle again and is concentrated on a focal line located outside of body system.
FIG. 3A shows an embodiment of the solar concentrator having a parabolic upper half 22 and a parabolic lower half 23 that meet in a median area 24. The reflective material is not shown. Lower half 23 has a bottle neck 21. Depending upon formation method used, upper half 22, median area 24, and lower half 23 with bottle neck 21 may be seamlessly formed from one preform, or each part may be separately formed and fused together. The solar concentrator may also be made through a process where bottle neck 21 may be integrally formed with lower half 23 and the remaining pieces are fused together through a method such as thermosetting.
Referring to FIG. 3B, another embodiment of the solar concentrator is shown as a bottle of transparent materials with the bottom portion 32 formed into a parabola shape in a blow molding process. The inside surface of the parabola is coated with a metallic reflective layer or is covered with at least one mirror film. The solar concentrator of FIG. 3B may alternatively have the outside surface of the parabola 32 coated with a metallic reflective layer or covered with at least one mirror film.
The top portion 35 is kept transparent and sunlight 30 can penetrate through the top portion 35 to reach the reflective layer on the bottom portion 32 of the bottle. The light 30 reflects back and penetrates the top portion 35 of the bottle again and converges at a focal point outside the bottle. As shown in FIG. 3B, the bottle neck 31 is formed in the blow molding process to connect the interior of the bottle to atmosphere.
The bottle necks 11, 21, and 31 may be configured to equilibrate with atmospheric conditions, or may be gated to maintain specific internal conditions.
Comparing FIG. 3A and 3B, the solar concentrator of FIG. 3A has substantially mirror-image shaped upper and lower halves 22 and 23. In contrast, in FIG. 3B, top portion 35 is not the same shape as bottom portion 32. The shape of transparent top portion 35 can vary in shape and be different from bottom portion 32. The upper portion may even have a flat shape. Other shape considerations may also be implemented when selecting of the upper half, such as selecting a cylindrical shape for upper half portion 12. In addition, a spherical shape for either or both of the upper and lower half may be advantageous. Changes in the shape of bottom portion 32 results in a change in focal point or focal line for the solar concentrator, so the shape of bottom portion 32 may be adjusted to provide a specific area of concentrated light incidence.
A first method for manufacturing the solar concentrator includes the following steps: (a) injection molding a pre-form of the bottle to also have a bottle neck; (b) blow molding the pre-form into a bottle with at least one half portion formed into either a parabolic trough shape or a parabola shape; (c) coating the outside surface of the parabolic trough or parabola with reflective materials such as silver or aluminum or covering the surface with at least one mirror film.
An alternate method comprises: (d) moulding each half of the solar concentrator using a method such as thermoforming plastic sheets against molds; (e) coating an interior or exterior side of at least one half with reflective materials such as silver or aluminum or covering the side with at least one mirror film; and (f) sealing the halves together.
In both formation methods, a material may be selected that is non-rigid during the molding process and that becomes rigid when the molding process is complete. Exemplary materials include such transparent materials as glass, PET (polyethyleneterephthalate), PETE, etc. Using a material that is rigid as a final product reduces the amount of infrastructure needed for supporting or positioning the collector.
An alternative material selection can result in use of a material that is non-rigid after the molding process. The bottle neck would need to be closed, through a mechanism such as a gas gate, after the solar concentrator is filled with a gas or other liquid. The gas or other liquid is capable of creating sufficient internal pressure to support the parabolic shape or parabolic trough shape of the reflector. A concentrator made according to the first blow molding formation method would benefit from having no seams or openings other than the bottle neck or gas gate through which the internal contents could escape. This avoids the need to refill the collector due to leakage along seams, avoids weak points along the seams, and avoids the complexity of joining parts along seams.
From the description above, a number of advantages of the solar concentrator and the methods for its production become evident. The reflector structure can be an enclosed hollow core body structure that enables non-rigid, lightweight and cheap materials such as plastic and glass to be used. The materials may be selected to build a thin walled body structure that is a strong mechanical object which supports itself without any supporting or inflating systems. The enclosed body structure can be a strong mechanical structure that effectively prevents the distortion of the geometric surface of the concentrator when in the manufacture process and when in use. The enclosed body structure provides a natural protection to the reflective surface from dust and any other contamination and makes maintenance much easier. The solar concentrator significantly simplifies the coating process for the reflective layer. The solar concentrator can be easily incorporated into systems and need less power to be driven to track the sun. The method to manufacture this novel solar concentrator is cheap, easy and fast.
Accordingly, the bottle solar concentrator and its production method provides an approach to realize an ultra-light and exclusively cheap solar concentrator and its highly efficient manufacturing. This approach realizes the self-protection of the reflective surface from dust and other contaminations. This approach also makes a system based on the solar concentrator ultra-light and robust and where the solar concentrator can be driven to track the sun with less power and with a relatively simple control system.
In the preceding specification, various preferred embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various other modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.