US20080236569A1

US20080236569A1 - System and Method for Concentrating Sunlight

Info

Publication number: US20080236569A1
Application number: US12/053,617
Authority: US
Inventors: Rocco Joseph Tuccio
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-03-26
Filing date: 2008-03-23
Publication date: 2008-10-02

Abstract

A system for concentrating solar energy is provided. The solar concentrating system uses a membrane formed of a flexible material to form either a reflective or refractive surface of a predefined shape. A quantity of fluid disposed on the membrane deforms the membrane into the predefined shape. In one embodiment the fluid is a liquid and the deformation of the membrane is determined by the mass of fluid and the effect of gravity. In another embodiment, the fluid is a gas and the deformation of the membrane is determined by the pressure of the gas contained in a cavity formed by the membrane on the bottom and a transparent layer forming the top surface of the cavity.

Description

I. FIELD OF THE INVENTION

The present invention relates generally to the field of energy production; and more specifically to a system and method for concentrating sunlight for electrical energy generation.

II. BACKGROUND OF THE DISCLOSURE

Concentrated solar power systems use mirrors and/or lenses to concentrate sunlight so that it may be harnessed to generate electricity. Dish-stirling systems generate electricity using a reflective parabolic dish that tracks the sun to focus sunlight onto a stirling engine. Other systems use fresnel lenses or concave mirrors to concentrate sunlight onto a solar cell for electricity generation. Fewer solar cells are needed to utilize a given area of insulation because the optics concentrate the sunlight from the given area onto a smaller area of fewer solar cells. These systems have economic advantages over un-concentrated solar cell systems due to the relative high cost of solar cells compared to the lower cost of the concentrating optics.
An object of the present invention is to concentrate sunlight using an optical system that is less expensive than conventional optics.

III. SUMMARY OF THE DISCLOSURE

An embodiment of the present invention is a system for concentrating solar energy for the purpose of harnessing solar energy and/or converting the solar energy into electrical or thermal energy. Optical elements, such as lenses and reflectors, are used to concentrate sunlight. These optical elements consist of a transparent fluid, which acts as a refractive material, contained in a flexible sheet impermeable to the fluid, such as mylar. The fluid can be a liquid such as water.
The sheet is suspended between two parallel support structures so that the sheet's shape is formed by the force of gravity. The sheet forms the bottom wall of a fluid-holding container. The two vertically scaling walls of the container may be an extension of the transparent sheet material or another material impermeable to the contained fluid that is bonded to the sheet. The uppermost wall is a material such as mylar sheet or acrylic.
Because the liquid filled lens cannot move to track the sun and still maintain its shape, a system of mirrors tracks the sun during the day to create an image of the sun at zenith so that the sun's rays incident to the lens are parallel to the lens's optical axis. One mirror tracks the sun to reflect the sunlight to another mirror positioned above the lenses which then reflects the sunlight downward.
An alternative embodiment of the present invention uses a gaseous fluid, such as air, disposed at a predefined pressure within a sealed optical element structure. The element structure has a top surface constructed of a transparent material that maybe either flexible or rigid, and a bottom surface constructed of a flexible material. The bottom surface can be reflective, thus forming a reflective optical element.
Another embodiment of the present invention is a system for concentrating solar energy. The system includes a membrane surface constructed of a thin flexible material; a quantity of fluid having a predefined index of refraction. The quantity of fluid is disposed on a top surface of the membrane surface and deforms the membrane surface into a surface having a predefined cross-section. Also a support structure is provided for supporting the membrane surface and the quantity of fluid. The support structure allows the membrane surface to deform under the influence of the quantity of fluid and gravity.
Another embodiment of the present invention is a system for concentrating solar energy onto a heat pipe. The system includes an optically transparent top layer; an optically reflective bottom layer, the bottom layer being a flexible material; and a frame bonded to the top layer and the bottom layer forming an air-tight cavity therebetween. The cavity is filled with a gas at a predetermined pressure for deforming the bottom layer into an arc cross-section.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings wherein:

FIG. 1 illustrates a system for concentrating sunlight, in accordance with the present invention;

FIG. 2 illustrates a perspective view of one embodiment that produces nine areas of concentrated solar energy, in accordance with the present invention;

FIG. 3 illustrates two orthogonal views of a single lens, in accordance with the present invention; and

FIG. 4 illustrates two orthogonal views of a two-lens system, in accordance with the present invention;

FIG. 5 illustrates a reflective embodiment of the present invention;

FIG. 6 illustrates another embodiment of the present invention; and

FIG. 7 illustrates orthogonal views of the embodiments shown in FIG. 5 and FIG. 6.

V. DETAILED DESCRIPTION OF DISCLOSURE

Referring to FIGS. 1, 2, and 3 the solar energy concentration system 100 consists of the transparent sheet 103, containing a fluid having an index of refraction greater than air and constrained to the curvature of the transparent sheet 103. The transparent sheet 103 is suspended between two parallel support structures 202. These parallel support structures 202, fluid, and lens side walls 303 comprise a lens that converges light in one dimension. The fluid is sealed between the transparent sheet 103, lens side walls 303, and an upper transparent wall 302. Two lens frames 104 support the lenses so that they may be suspended above the ground in a manner allowing adjustment of the angle of the lens frame 104 with respect to the ground. Support pillars 101 support the lens frame 104. A stationary mirror 106 is supported by a mirror frame 203 and the mirror support structure 105. The stationary mirror 106 is angled such that the incident rays, being parallel to the earth's axis of rotation, are reflected downward producing an image of the sun at zenith 120. The sun's rays 108 incident to the stationary mirror 106 are reflected off of the tracking mirror 107, which tracks the sun 121 throughout the day to provide stationary mirror 106 with incident rays that are parallel to the earth's axis of rotation. Tracking of the sun is accomplished by a motorized equatorial mount 109, which allows motion in right ascension R.A. and declination. The concentrated sunlight is directed towards the solar cells 110 where it is converted into electricity. Alternatively, the sunlight can be directed to heat engines or any other suitable energy conversion device instead of the solar cells 110.
FIG. 3 shows two orthogonal views of a single lens. The lens is shown to focus light rays 307 one-dimensionally to a line of highest concentration 310. This line of concentrated solar energy may be used in other embodiments of the invention not specifically illustrated if, for example, the energy is to be focused onto a fluid containing pipe or a linear array of solar cells.
FIG. 4 shows the effect of adding a second lens with parallel support structures 405 running perpendicular to the first. This focuses sunlight two-dimensionally to create a spot of concentrated sunlight incident on solar cells 110 instead of a line 310 as in FIG. 3.
Alternatively, in place of a refractive lens system, an embodiment shown in FIG. 5 uses a reflective surface 501. In the present embodiment, the reflective surface made of a thin, light flexible material is shaped into a surface having a cross-section formed due to the weight of fluid 503 held in the cavity 505 formed by the curvature of the reflective surface 501.
The reflective surface 501 is mounted on a rotating support assembly 507 that allows the reflective surface 501 to rotate in synchrony with the motion of the sun throughout a full day. The rotating support assembly 507 includes support legs 519 terminating in wheels 521. A set of guide rails 523 form a circular course over which the wheels 521 travel. The rotation of the reflective surface 501 is performed in order to maximize the amount of sunlight impacting a thermally conductive pipe 509 (i.e., heat pipe).
The thermally conductive pipe 509 is suspended above the reflective surface 501 running parallel to a horizontal axis. The pipe 509 is positioned at or near a focal point in order to absorb energy from sunlight incident to the pipe 509. The pipe 509 is disposed with water or other fluid having a high thermal conductivity. The fluid circulates through the pipe 509, entering at one end in a cooled state, and exiting from the top in the form of heated fluid or gas, which is transported to a steam turbine by a collector pipe 511. Other energy conversion systems may be used in place of a steam turbine. Such alternative energy conversion systems include stirling engines, thermal-electric devices, etc. The fluid returns from the steam turbine, or other energy conversion system, by a feeder pipe 513 once the fluid has cooled.
The pipe 509 is joined to the feeder pipe 513 and collector pipe 511 with a rotating coupling assembly at each end. The rotating coupling assembly allows the pipe 509 to rotate along with the reflective surface assembly 515. Additionally, support members 515 provide support to the pipe 509 and attach the pipe 509 to the rotating support assembly 507. Vertical dashed line 517 indicates the center of rotation of the rotating support assembly 507.
Referring to FIG. 6, an embodiment of the present invention is shown in which the fluid is a gas. The optical element 600 is constructed of a frame 602 supporting a top layer 604 of transparent, gas impermeable material and a bottom layer 606 of either a reflective or transparent gas impermeable material. The frame 602 forms the perimeter of the optical element 600. A filler plug 608 is disposed on a side of the frame 602. The filler plug 608 allows the optical element 600 to be filled with a gas, such as air.
The top layer 604 and the bottom layer 606 are bonded to the frame 602 forming an air-tight cavity. Additionally, support members 610 are disposed at opposite sides of the frame 602. The support members 610 are used for rotating and supporting the optical element 600 when in installed into the energy producing system, such as the system shown in FIG. 7.
When a gas such as air is pumped into the optical element 600 through the filler plug 608, the top layer material 604 and the bottom layer 606 material expand and stretch to take on a circular cross-sectional shape, or a portion of a circular cross-section, based on the pressure of the gas inside the optical element 600. Thus, by controlling the pressure, the curvature of the optical element can be controlled as well.
Alternatively, the top layer 604 can be made of a rigid material such as glass or acrylic plastic. In this alternative construction only the bottom layer 606 of the optical element 600 will expand and stretch when pressurized gas is introduced into the optical element 600.
A benefit of using a gas-filled optical element as shown in FIG. 6 and described above, is that the shape of such an optical element is not appreciably affected by gravity. Consequently, unlike a liquid-filled embodiment, the gas-filled optical element can be used with a dual-axis tacking system in which one axis is the altitude and the other is the azimuth (i.e., alt-az tracking). A dual axis tracking system allows for the light rays incident to the heat pipe to be perpendicular to the surface of the heat pipe surface, which in turn allow for better efficiency.
FIG. 7 illustrates orthogonal views of a reflective optical element, such as the embodiments shown in FIG. 5 or FIG. 6, using a single axis tracking system 700 a and 700 b. Additionally, for comparison, orthogonal views of a reflective optical element, such as the embodiments shown in FIG. 6, using a dual axis tracking alt- az system 700 c and 700 d is shown.
Referring to view 700 a, the incident light rays 702 pass through the transparent top surface 706, and impact the reflective surface 708. Support members 710 is bonded to the edge of the reflective surface 708 and the transparent surface 706, such that the cavity formed therebetween is either air or water tight depending on the particular embodiment. As can be seen, in view 700 a the reflected light rays 704 appear to intersect at a relatively small spot.
Turning to view 700 b, a view of the optical element of view 700 a is shown from a 90° offset. As is evident from view 700 b with only a single tracking axis, the incident light rays 702 from the sun will at times throughout the day impact the reflective surface 708 at non-perpendicular angles relative to the optical axis. The resultant reflected light rays 704 will similarly shift by an equal angle from the perpendicular.
Consequently, using a single axis tracking system necessitates having a heat pipe (not shown) that extends beyond the length of the optical element so that the angled reflected light rays 704 will still impact the heat pipe. In addition, at sever incident angles, such as times approaching sunrise and sunset, the reflected light rays 704 at the extremes of the optical element will be internally reflected as a result of the critical angle of the transparent surface 706. Moreover, reflected light rays 704 at these extreme angles will not efficiently impart all the reflected energy to the heat pipe, as some portion of the reflected light rays 704 may be reflected rather than absorbed by the heat pipe.
However, when a dual axis tracking system is used as in the optical element shown in view 700 c and corresponding orthogonal view 700 d, the incident light rays 702 are made to impact the reflective surface 708 at an angle parallel to the optical axis. Consequently, while the incident light rays 702 and reflected light rays 704 appear identical, or nearly so in views 700 a and 700 c, the reflected light rays 704, as seen from the perspective of view 700 d, impact the heat pipe at a perpendicular angle.
The result is a more efficient transfer of energy from the incident light rays 702 to the heat pipe. Little to no internal reflection occurs when the incident light rays 702 and the reflected light rays 704 are parallel to the optical axis of the transparent surface 706 and the reflective surface 708. Moreover, because the reflected light rays 704 arrive at the same point along the heat pipe throughout the entire day, the heat pipe can be dimensioned to have the same length as the optical element.
Alternatively, the heat pipe described in the embodiments above can be replaced with photovoltaic elements (solar cells) or other direct-to-electricity conversion devices.
The direct embodiments of the present invention are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present invention. Various modifications and variations can be made without departing from the spirit or scope of the invention.

Claims

1. A system for concentrating solar energy, said system comprising:

a membrane surface constructed of a thin flexible material;

a quantity of fluid having a predefined index of refraction, said quantity of fluid being disposed on a top surface of said membrane surface for deforming said membrane surface into a surface having a predefined cross-section;

a support structure for supporting said membrane surface and said quantity of fluid, said support structure allowing said membrane surface to deform under the influence of said quantity of fluid and gravity.

2. The system as in claim 1, further comprising:

a solar collecting apparatus for collecting solar energy and converting said solar energy to a second form of energy.

3. The system as in claim 2, wherein said solar collecting apparatus is formed of at least one photovoltaic cell adapted for receiving concentrated solar energy.

4. The system as in claim 2, wherein said solar collecting apparatus is a heat pipe.

5. The system as in claim 1, further comprising:

a rotating base supporting said support structure; and

a tracking unit for controlling the azimuth of said rotating base to track a movement of a sun across a sky and orient said membrane surface to maximize incidence of said solar energy onto said membrane surface.

6. The system as in claim 5, further comprising an altitude tracking system for adjusting said angle of said membrane surface to maximize incident solar energy.

7. The system as in claim 1, further comprising:

at least one flat reflective surface positioned remotely of said membrane surface; and

a tracking unit for controlling said position of said at least one flat reflective surface to track a movement of said sun across said sky and orient said flat reflective surface to maximize incidence of said solar energy onto said membrane surface.

8. The system as in claim 1, wherein said membrane surface is reflective of at least a portion of wavelengths of said solar energy.

9. The system as in claim 1, wherein said membrane surface is transparent of at least a portion of wavelengths of said solar energy.

10. The system as in claim 1, further comprising:

a second membrane surface, transparent to at least a portion of wavelengths of said solar energy, said second membrane surface being disposed above said membrane surface and deformed by a second quantity of fluid; and

a second support structure for supporting said second membrane surface.

11. The system as in claim 1, wherein said fluid is a liquid.

12. The system as in claim 1, further comprising a covering surface formed of transparent material for sealingly holding said quantity of fluid between said membrane surface and said covering surface.

13. The system as in claim 12, wherein said fluid is a gas.

14. A system for concentrating solar energy onto a heat pipe, comprising:

an optically transparent top layer;

an optically reflective bottom layer, said bottom layer being a flexible material; and

a frame bonded to said top layer and said bottom layer forming an air-tight cavity therebetween, said cavity being filled with a gas at a predetermined pressure for deforming said bottom layer into an substantial circular arc cross-section.

15. The system as in claim 14, further comprising a dual-axis tracking system for tracking the position of a sun's motion throughout a day.

16. The system as in claim 14, wherein said top layer is a rigid material.

17. The system as in claim 14, wherein said top layer is a flexible material deformable by said gas filling said cavity.

18. The system as in claim 14, further comprising a heat pipe of thermally conductive material and configured for transporting a thermal fluid across said system at a focal position of light reflected by said bottom layer.