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WO2009063416A2 - Thin and efficient collecting optics for solar system - Google Patents

Thin and efficient collecting optics for solar system Download PDF

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Publication number
WO2009063416A2
WO2009063416A2 PCT/IB2008/054749 IB2008054749W WO2009063416A2 WO 2009063416 A2 WO2009063416 A2 WO 2009063416A2 IB 2008054749 W IB2008054749 W IB 2008054749W WO 2009063416 A2 WO2009063416 A2 WO 2009063416A2
Authority
WO
WIPO (PCT)
Prior art keywords
guide member
light
light guide
lens
solar energy
Prior art date
Application number
PCT/IB2008/054749
Other languages
French (fr)
Other versions
WO2009063416A3 (en
Inventor
Willem L. Ijzerman
Siebe T. Zwart
Original Assignee
Koninklijke Philips Electronics, N.V.
U.S. Philips Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics, N.V., U.S. Philips Corporation filed Critical Koninklijke Philips Electronics, N.V.
Publication of WO2009063416A2 publication Critical patent/WO2009063416A2/en
Publication of WO2009063416A3 publication Critical patent/WO2009063416A3/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/054—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means
    • H01L31/0543—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means comprising light concentrating means of the refractive type, e.g. lenses
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/10—Prisms
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/12—Light guides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/30—Arrangements for concentrating solar-rays for solar heat collectors with lenses
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/054—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means
    • H01L31/0547—Optical elements directly associated or integrated with the PV cell, e.g. light-reflecting means or light-concentrating means comprising light concentrating means of the reflecting type, e.g. parabolic mirrors, concentrators using total internal reflection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/70—Arrangements for concentrating solar-rays for solar heat collectors with reflectors
    • F24S2023/88—Multi reflective traps
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/40—Solar thermal energy, e.g. solar towers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/52—PV systems with concentrators

Definitions

  • the present invention relates generally to collectors configured to collect electromagnetic radiation and, more particularly, to collectors which have optical elements for collecting and concentrating sun light which is directed to a solar collector.
  • Solar energy collectors have used optical elements to alter the direction of incident sun light. Examples of such solar collectors are disclosed in Russian Pat. No. RU 2,135,909; U.S. Pat. No. 4,344,417 and U.S. Pat. No. 4,505,264.
  • a hollow right angle triangular member of transparent glass or plastic is disclosed to redirect light.
  • Light enters the right angle leg and is directed to a photoelectric module at the base of the triangular member after being reflected from the internal surfaces of the hypotenuse and the right angle leg of the triangular member.
  • U.S. Pat. No. 4.344,417 discloses a structure that is similar to what is disclosed in the Russian patent where solar energy enters a wedge shaped member through the hypotenuse side and is directed to a heating element located on the outside surface of the base of the wedge.
  • U.S. Pat, No. 4,505,264 discloses a thin plate having a succession of two identical prisms of different indexes of refraction which continuously bends the light to direct it to an edge of the thin plate.
  • One way of reducing the cost of a solar system is to reduce the amount of silicon material required to make a solar cell by making the solar cell smaller. This can be done if a system which has a photo-voltaic cell with a reduced area is provided which directs concentrated sun light to the cell.
  • FIG. 1 there is shown a prior art solar system which directs concentrated sun light to a solar cell.
  • a lens 10 having a fixed focal length 12 is oriented to face the sun and a solar cell 14 is located at the focus point of the lens to receive the concentrated sun light. Because the sun moves from east to west, the lens and solar cell assembly must be continuously rotated about its horizontal axis and preferably about both its horizontal axis and vertical axis during the day to capture sunlight throughout the day from dawn to dusk.
  • FIG. 2 there is shown a prior art sun light concentrator system which does not rotate or rotates only about a single axis for capturing sun light from dawn to dusk.
  • Two parabolic reflectors 16 are connected to form a unitary unit where each has a solar cell 18 located at its focal point.
  • the reflectors are coupled to a tracking system, not shown, which rotates the parabolic reflectors and solar cells about its horizontal axis to track the sun.
  • a major disadvantage of this system is that it is relatively bulky and, therefore, care must be exercised when it is installed on a roof to avoid wind force effects.
  • a collector configured to collect and concentrate incident sun light.
  • the embodiment disclosed is thin, flat and can be mounted on a roof with minimum concerns about the effects of wind on the structure.
  • the system tracks and concentrates sun light with small movements of one component of the system.
  • concentrated sun light can be directed to the solar cell from dawn to dusk, Because sun light to the photo-voltaic is concentrated the size of the photo-voltaic cell, the solar cell, can be reduced which effectively reduces the cost of the solar cell and the total initial price of the solar system.
  • the solar system comprises three optical components as follows: an array of lenses, a wedge shaped optical member located below the array of lenses, and a light guide member located below and fixed to the wedge shaped member.
  • the light guide member has light reflecting surfaces positioned for received sun light from the array of lenses and directing it to a solar cell located at an exit surface of the light guide member.
  • Each lens in the array of lenses is fixed relative to each other and the array is positioned on top of the wedge shaped member.
  • the array of lenses are moved relative to the wedge shaped member or, in the alternative, the wedge shaped member is moved relative to the array of lenses to direct focused sun light into the light guide member as the sun moves from east to west.
  • the reflecting surfaces located within the light guide member can have an angle of substantially 45 degrees with respect to the vertical axis.
  • the reflecting surfaces are positioned to direct refracted sun light along the light guide member to a collimator such as, for example, a compound parabolic collimator, positioned to direct and further concentrate the light to the solar cell.
  • the solar system comprises four optical components as follows: an array of lenses, a wedge shaped optical member positioned below the array of lenses, a light guide member fixed to the wedge shaped member, and light reflecting surfaces located within the light guide member for directing received sun light to a solar cell located at an exit surface of the light guide member.
  • Each lens of the array of lenses is fixed relative to each other and the array is slideably coupled to the wedge shaped optical member.
  • the lenses can be made of glass, or other transparent substance, having two opposite surfaces, either both curved or one curved and the other plane for changing the direction of the rays of the sun and to refract sun light through the wedge shaped member to the light guide member.
  • One such lens which can be used is known as a plano-convex lens.
  • Tracking structure is provided to move the array of lenses relative to the wedge shaped member or, in the alternative, the wedge shaped member relative to the array of lenses to focus sun light on the reflecting surfaces in the light guide member while tracking the sun.
  • Each reflecting surface located in the light guide member can have an angle of substantially 45 degrees, more or less with respect to the vertical axis.
  • the reflecting surfaces are positioned to direct refracted sun light from the array of lenses to a collimator such as, for example, a compound parabolic collimator positioned to direct and further concentrate the received sun light to the solar cell.
  • the solar system comprises four optical components as follows: an array of lenses, a wedge shaped optical member positioned below the array of lenses, a light guide member fixed to the wedge shaped member, and light reflecting surfaces located within the light guide member for directing sun light through the light guide member to a solar cell located at an exit surface of the light guide member.
  • the array of lenses are fixed to the wedge shaped optical member and are used to refract sun light through the wedge shaped member to the reflecting surfaces in the light guide member.
  • Tracking structure is provided to rotatably and/or linearly move the complete structure to position the array of lenses to receive and focus sun light on the reflecting surfaces in the light guide member.
  • the reflecting surfaces located within the light guide member can have an angle of substantially 45 degrees with respect to the vertical axis and directs the received sun light along the light guide member to a collimator such as, for example, a compound parabolic collimator positioned to further direct and concentrate the sun light to the solar cell.
  • a collimator such as, for example, a compound parabolic collimator positioned to further direct and concentrate the sun light to the solar cell.
  • FIG. 1 is a view of a prior art solar radiation collecting system using a single lens to collect and direct sun light to a solar cell;
  • Fig. 2 is a cross section of a prior art solar radiation collecting system where a solar cell is located at the focal point of a parabolic reflector and the apparatus is rotated around it's axis to maximize the collection of sun light;
  • Fig. 3 is a cross sectional view of an embodiment of optics for a solar radiation collecting system in accordance with the principles of the invention here disclosed.
  • Fig. 4 is a cross sectional view of another embodiment of optics for a solar radiation collecting system in accordance with the principles the invention here disclosed.
  • FIG. 3 there is shown an embodiment of a solar collector system 20 in accordance with the principles of the invention.
  • the embodiment comprises four optical components as follows: an array of lenses 22, a wedge shaped spacer of clear optical material 24, a light guide member 26, and reflecting surfaces 28 arranged in or on the light guide member 26.
  • the array of lenses 22 directs refracted sun light through the wedge shaped spacer 24 and focuses it on the reflecting surfaces 28 in the light guide member 26.
  • Each reflecting surface is positioned to receive sun light from at least one lens of the array of lenses.
  • Wedge shaped spacer 24 insures that each lens focus sun light on a reflecting surface by keeping each lens spaced from its receiving reflecting surface in the light guide member at the same distance.
  • the reflecting surfaces in light guiding member 26 can be mirrors that have an angle of substantially 45 degrees, more or less with respect to the vertical axis.
  • Sun light which is refracted by the array of lenses through the wedge shaped spacer and reflected by the mirrors is directed through the light guide member to a collimator 30, such as a compound parabolic collimator, which then further concentrates and directs the sun light to a solar cell 32.
  • the light guide member can be either hollow and filled with either air, or another gas, or evacuated to provide a vacuum.
  • the reflecting surfaces on the bottom and top surfaces can be either on the inside or outside surface where the reflecting surface on the bottom surface is fully reflecting and the reflecting surface of the top surface is partially reflecting.
  • the light guide member can be solid and composed of light conducting material having a desired index of refraction.
  • the reflecting surfaces on the bottom and top surfaces of the guide member are on the outside surfaces.
  • the wedge shaped spacer is fixed to the light guide member with glue 40 having a desired index of refraction.
  • the array of lenses are continuously oriented to focus sun light on the reflecting surfaces at the bottom of the light guide member.
  • this is achieved by moving the lens array 22 horizontally across the wedge shaped spacer as indicated by arrow A-A while keeping the wedge shaped spacer 24 and the light guide member 26 stationary.
  • the wedge shaped spacer 24 and the light guide member 26 are moved horizontally as indicated by arrow B-B while the lens array 22 is kept stationary.
  • the lens array 22 is held stationary and the wedge shaped spacer and the light guide member are moved, only the wedge shaped spacer and the light guide member needs to be encased within a weather resistant enclosure to protected the moving parts from rain, dust, wind, and the like.
  • the complete assemblage should be encased within a weather resistant enclosure to be protected from the elements.
  • one such tracking structure that can be used includes an array of photo diode cells positioned beneath one of the lenses of the lens array 22.
  • the array of photo diode cells is used to locate the position of the focus point of the sun light from that lens.
  • the position of the lens array 22 can be adjusted to maximize the light output. It is understood that other structures for positioning the lens array to track the movement of the sun can be used.
  • a ray of sun light 34 enters a lens 36 of the lens array 22, is refracted by the lens 36, passes through wedge shaped spacer 24 and enters the light guide member 26.
  • the ray of sunlight in the light guide member 26 impinges on and is reflected by reflecting surfaces 28, half silvered reflecting surface 42 at the top of the light guide member, another reflecting surface 28, and finally on compound parabolic collimator 30 which directs and further concentrates the ray of sun light as it moves toward solar cell 32.
  • the angular spread of the light just prior to reaching the collimator 30 is less than 26 degrees.
  • the compound parabolic collimator 30 can increase this angular spread to about 90 degrees more or less.
  • the size of the solar cell can be reduced which, in turn, reduces the initial cost of the system.
  • the wedge shaped spacer is attached to the light guide member with a glue having a low index of refraction. Since the light in the light guide has a limited angular spread, sun light is kept in the light guide member 26 by total internal reflection. If the angular spread in the light guide member is plus or minus 36 degrees, glue having an index of refraction of less than 1.37, where the index of refraction of the light guide is 1.5, was found to give good results. Glue with this low index of refraction can reduce Fresnel losses from about 8% to about 0.2%, more or less. In addition, Fresnel losses at the lens air interfaces can be avoided or substantially reduced by using an antireflection coating.
  • Fig. 4 there is shown an embodiment where the lens array 22, the wedge shaped spacer 24 and the light guide member 26 are coupled together to form a single assemblage with no moving parts.
  • the lens array is fixed to the wedge shaped spacer with glue 44 having a low index of refraction and the wedge shaped spacer is fixed to the light guide member with glue 40 having a low index of refraction.
  • All of the members are securely coupled to each other.
  • the complete assemblage not just a single member, is positioned by a drive structure to continuously face the sun as it moves from east to west.
  • the assemblage can be located within a weather resistant enclosure to protect it from the elements.
  • this assemblage can be coupled to a drive positioning structure which slides, arrow B, pivots, arrow C, and/or rotates, arrow D, the complete assemblage for tracking sunlight from the sun. While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that various omissions and substitutions and changes of the form and details of the apparatus illustrated and in the operation may be done by those skilled in the art, without departing from the spirit of the invention.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Electromagnetism (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Sustainable Energy (AREA)
  • Thermal Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Photovoltaic Devices (AREA)
  • Optical Elements Other Than Lenses (AREA)

Abstract

A solar system (20) uses optics (22, 26) to transmit concentrated sun light (34) to at least one solar cell (32) of reduced size. By directing concentrated sun light (34) to a solar cell (32), the size of the solar cell (32) can be reduced to provide a solar system (20) which is initially less expensive to produce.

Description

THIN AND EFFICIENT COLLECTING OPTICS FOR SOLAR
SYSTEM
This patent application claims the benefit of U.S. Provisional Application No. 60/987,435, filed on November 13, 2007.
The present invention relates generally to collectors configured to collect electromagnetic radiation and, more particularly, to collectors which have optical elements for collecting and concentrating sun light which is directed to a solar collector.
Solar energy collectors have used optical elements to alter the direction of incident sun light. Examples of such solar collectors are disclosed in Russian Pat. No. RU 2,135,909; U.S. Pat. No. 4,344,417 and U.S. Pat. No. 4,505,264.
In the Russian patent, a hollow right angle triangular member of transparent glass or plastic is disclosed to redirect light. Light enters the right angle leg and is directed to a photoelectric module at the base of the triangular member after being reflected from the internal surfaces of the hypotenuse and the right angle leg of the triangular member.
U.S. Pat. No. 4.344,417 discloses a structure that is similar to what is disclosed in the Russian patent where solar energy enters a wedge shaped member through the hypotenuse side and is directed to a heating element located on the outside surface of the base of the wedge.
U.S. Pat, No. 4,505,264 discloses a thin plate having a succession of two identical prisms of different indexes of refraction which continuously bends the light to direct it to an edge of the thin plate.
Currently, a primary concern about photo voltaic systems based on solar energy is that the total initial investment is relatively high compared to the monetary value of the electric power obtained. In some countries such as, for example, Germany, Italy and United States, this initial cost is offset with subsidies which help to make the systems more cost effective. One factor which contributes to the relatively high initial coast is that solar cells are currently made of poly- or mono-crystalline silicon material, and the price of these materials is a dominant factor in determining the price of solar cells. As a result, solar cells have not experienced the scaling factor predicated by "Moore's law" for the semiconductor industry and the corresponding price erosion.
One way of reducing the cost of a solar system is to reduce the amount of silicon material required to make a solar cell by making the solar cell smaller. This can be done if a system which has a photo-voltaic cell with a reduced area is provided which directs concentrated sun light to the cell.
Referring to Fig. 1 , there is shown a prior art solar system which directs concentrated sun light to a solar cell. A lens 10 having a fixed focal length 12 is oriented to face the sun and a solar cell 14 is located at the focus point of the lens to receive the concentrated sun light. Because the sun moves from east to west, the lens and solar cell assembly must be continuously rotated about its horizontal axis and preferably about both its horizontal axis and vertical axis during the day to capture sunlight throughout the day from dawn to dusk.
Referring to Fig. 2, there is shown a prior art sun light concentrator system which does not rotate or rotates only about a single axis for capturing sun light from dawn to dusk. Two parabolic reflectors 16 are connected to form a unitary unit where each has a solar cell 18 located at its focal point. The reflectors are coupled to a tracking system, not shown, which rotates the parabolic reflectors and solar cells about its horizontal axis to track the sun. A major disadvantage of this system is that it is relatively bulky and, therefore, care must be exercised when it is installed on a roof to avoid wind force effects.
In practice, it has been determined that fixed systems concentrate sun light with a factor of 3 to 4. Systems that rotate about a single axis can achieve a concentration factor of 30.
In an exemplary embodiment of the present invention, a collector configured to collect and concentrate incident sun light is disclosed. The embodiment disclosed is thin, flat and can be mounted on a roof with minimum concerns about the effects of wind on the structure. With the use of optics the system tracks and concentrates sun light with small movements of one component of the system. By having the ability to track the sun, concentrated sun light can be directed to the solar cell from dawn to dusk, Because sun light to the photo-voltaic is concentrated the size of the photo-voltaic cell, the solar cell, can be reduced which effectively reduces the cost of the solar cell and the total initial price of the solar system.
In an embodiment of the invention the solar system comprises three optical components as follows: an array of lenses, a wedge shaped optical member located below the array of lenses, and a light guide member located below and fixed to the wedge shaped member. The light guide member has light reflecting surfaces positioned for received sun light from the array of lenses and directing it to a solar cell located at an exit surface of the light guide member. Each lens in the array of lenses is fixed relative to each other and the array is positioned on top of the wedge shaped member. When tracking the sun, the array of lenses are moved relative to the wedge shaped member or, in the alternative, the wedge shaped member is moved relative to the array of lenses to direct focused sun light into the light guide member as the sun moves from east to west. The reflecting surfaces located within the light guide member can have an angle of substantially 45 degrees with respect to the vertical axis. The reflecting surfaces are positioned to direct refracted sun light along the light guide member to a collimator such as, for example, a compound parabolic collimator, positioned to direct and further concentrate the light to the solar cell.
In another embodiment, the solar system comprises four optical components as follows: an array of lenses, a wedge shaped optical member positioned below the array of lenses, a light guide member fixed to the wedge shaped member, and light reflecting surfaces located within the light guide member for directing received sun light to a solar cell located at an exit surface of the light guide member. Each lens of the array of lenses is fixed relative to each other and the array is slideably coupled to the wedge shaped optical member. The lenses can be made of glass, or other transparent substance, having two opposite surfaces, either both curved or one curved and the other plane for changing the direction of the rays of the sun and to refract sun light through the wedge shaped member to the light guide member. One such lens which can be used is known as a plano-convex lens. Another type of lens which can be used is known as a Fresnel type of lens. Tracking structure is provided to move the array of lenses relative to the wedge shaped member or, in the alternative, the wedge shaped member relative to the array of lenses to focus sun light on the reflecting surfaces in the light guide member while tracking the sun. Each reflecting surface located in the light guide member can have an angle of substantially 45 degrees, more or less with respect to the vertical axis. The reflecting surfaces are positioned to direct refracted sun light from the array of lenses to a collimator such as, for example, a compound parabolic collimator positioned to direct and further concentrate the received sun light to the solar cell.
In still another embodiment, the solar system comprises four optical components as follows: an array of lenses, a wedge shaped optical member positioned below the array of lenses, a light guide member fixed to the wedge shaped member, and light reflecting surfaces located within the light guide member for directing sun light through the light guide member to a solar cell located at an exit surface of the light guide member. In this embodiment the array of lenses are fixed to the wedge shaped optical member and are used to refract sun light through the wedge shaped member to the reflecting surfaces in the light guide member. Tracking structure is provided to rotatably and/or linearly move the complete structure to position the array of lenses to receive and focus sun light on the reflecting surfaces in the light guide member. The reflecting surfaces located within the light guide member can have an angle of substantially 45 degrees with respect to the vertical axis and directs the received sun light along the light guide member to a collimator such as, for example, a compound parabolic collimator positioned to further direct and concentrate the sun light to the solar cell.
The foregoing has outlined, rather broadly, the preferred feature of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention and that such other structures do not depart from the spirit and scope of the invention in its broadest form.
Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claim, and the accompanying drawings in which similar elements are given similar reference numerals. Fig. 1 is a view of a prior art solar radiation collecting system using a single lens to collect and direct sun light to a solar cell;
Fig. 2 is a cross section of a prior art solar radiation collecting system where a solar cell is located at the focal point of a parabolic reflector and the apparatus is rotated around it's axis to maximize the collection of sun light;
Fig. 3 is a cross sectional view of an embodiment of optics for a solar radiation collecting system in accordance with the principles of the invention here disclosed; and
Fig. 4 is a cross sectional view of another embodiment of optics for a solar radiation collecting system in accordance with the principles the invention here disclosed.
Referring to Fig. 3, there is shown an embodiment of a solar collector system 20 in accordance with the principles of the invention. The embodiment comprises four optical components as follows: an array of lenses 22, a wedge shaped spacer of clear optical material 24, a light guide member 26, and reflecting surfaces 28 arranged in or on the light guide member 26. The array of lenses 22 directs refracted sun light through the wedge shaped spacer 24 and focuses it on the reflecting surfaces 28 in the light guide member 26. Each reflecting surface is positioned to receive sun light from at least one lens of the array of lenses. Wedge shaped spacer 24 insures that each lens focus sun light on a reflecting surface by keeping each lens spaced from its receiving reflecting surface in the light guide member at the same distance. The reflecting surfaces in light guiding member 26 can be mirrors that have an angle of substantially 45 degrees, more or less with respect to the vertical axis. Sun light which is refracted by the array of lenses through the wedge shaped spacer and reflected by the mirrors is directed through the light guide member to a collimator 30, such as a compound parabolic collimator, which then further concentrates and directs the sun light to a solar cell 32.
The light guide member can be either hollow and filled with either air, or another gas, or evacuated to provide a vacuum. When the light guide member is hollow, the reflecting surfaces on the bottom and top surfaces can be either on the inside or outside surface where the reflecting surface on the bottom surface is fully reflecting and the reflecting surface of the top surface is partially reflecting. In another embodiment, the light guide member can be solid and composed of light conducting material having a desired index of refraction. In this embodiment the reflecting surfaces on the bottom and top surfaces of the guide member are on the outside surfaces. The wedge shaped spacer is fixed to the light guide member with glue 40 having a desired index of refraction.
As the sun moves from east to west, the array of lenses are continuously oriented to focus sun light on the reflecting surfaces at the bottom of the light guide member. In one embodiment as shown in Fig. 3, this is achieved by moving the lens array 22 horizontally across the wedge shaped spacer as indicated by arrow A-A while keeping the wedge shaped spacer 24 and the light guide member 26 stationary. In another embodiment the wedge shaped spacer 24 and the light guide member 26 are moved horizontally as indicated by arrow B-B while the lens array 22 is kept stationary. In the embodiment where the lens array 22 is held stationary and the wedge shaped spacer and the light guide member are moved, only the wedge shaped spacer and the light guide member needs to be encased within a weather resistant enclosure to protected the moving parts from rain, dust, wind, and the like. In the embodiment where only the lens array is moved, the complete assemblage should be encased within a weather resistant enclosure to be protected from the elements.
Operating a solar collector system to track the sun as it moves from east to west can be performed in different ways known to those with ordinary skill in the art. For example, one such tracking structure that can be used includes an array of photo diode cells positioned beneath one of the lenses of the lens array 22. The array of photo diode cells is used to locate the position of the focus point of the sun light from that lens. By means of an electronic circuit coupled to a drive mechanism, the position of the lens array 22 can be adjusted to maximize the light output. It is understood that other structures for positioning the lens array to track the movement of the sun can be used.
Returning to Fig. 3, during operation, a ray of sun light 34 enters a lens 36 of the lens array 22, is refracted by the lens 36, passes through wedge shaped spacer 24 and enters the light guide member 26. The ray of sunlight in the light guide member 26 impinges on and is reflected by reflecting surfaces 28, half silvered reflecting surface 42 at the top of the light guide member, another reflecting surface 28, and finally on compound parabolic collimator 30 which directs and further concentrates the ray of sun light as it moves toward solar cell 32.
Due to the sun tracking structure, in air the angular spread of the light just prior to reaching the collimator 30 is less than 26 degrees. The compound parabolic collimator 30 can increase this angular spread to about 90 degrees more or less. Thus, by using a collimator the size of the solar cell can be reduced which, in turn, reduces the initial cost of the system.
To avoid Fresnel losses at the interface between the wedge shaped spacer 24 and the light guide member 26, the wedge shaped spacer is attached to the light guide member with a glue having a low index of refraction. Since the light in the light guide has a limited angular spread, sun light is kept in the light guide member 26 by total internal reflection. If the angular spread in the light guide member is plus or minus 36 degrees, glue having an index of refraction of less than 1.37, where the index of refraction of the light guide is 1.5, was found to give good results. Glue with this low index of refraction can reduce Fresnel losses from about 8% to about 0.2%, more or less. In addition, Fresnel losses at the lens air interfaces can be avoided or substantially reduced by using an antireflection coating.
Referring to Fig. 4, there is shown an embodiment where the lens array 22, the wedge shaped spacer 24 and the light guide member 26 are coupled together to form a single assemblage with no moving parts. The lens array is fixed to the wedge shaped spacer with glue 44 having a low index of refraction and the wedge shaped spacer is fixed to the light guide member with glue 40 having a low index of refraction. All of the members are securely coupled to each other. In operation, the complete assemblage, not just a single member, is positioned by a drive structure to continuously face the sun as it moves from east to west. In this embodiment where all the members are fixed to each other, the assemblage can be located within a weather resistant enclosure to protect it from the elements. It is also here noted that, depending on the type of installation, this assemblage can be coupled to a drive positioning structure which slides, arrow B, pivots, arrow C, and/or rotates, arrow D, the complete assemblage for tracking sunlight from the sun. While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that various omissions and substitutions and changes of the form and details of the apparatus illustrated and in the operation may be done by those skilled in the art, without departing from the spirit of the invention.

Claims

What is claimed is:
1. A solar energy collector comprising: at least one lens 36 for receiving sun light 34; a light guide member 26 having a top surface 42, a bottom surface 28 and an end surface, said light guide member 26 positioned to receive sun light through said top surface from said at least one lens 36; and at least one reflecting surface 28 on said bottom surface of said light guide member 26 for directing sun light 34 from said top surface of said light guide member 26 toward said end surface of said light guide member 26.
2. The solar energy collector of claim 1 wherein said light guide member 26 is a solid member of light conducting material.
3. The solar energy collector of claim 1 wherein said light guide member 26 is hollow.
4. The solar energy collector of claim 3 wherein said hollow light guide member 26 is filled with air.
5. The solar energy collector of claim 3 wherein said hollow light guide member 26 is filled with a gas other than air or contains a vacuum.
6. The solar energy collector of claim 1 further comprising: a spacer 24 located between said at least one lens 36 and said light guide member 26 to position said at least one reflecting surface 28 at said bottom surface of said light guide member 26 at a focus point of said at least one lens 36.
7. The solar energy collector of claim 6 wherein said at least one lens 36 is slidably coupled to said spacer 24, and said spacer is fixed 44 to said light guide member 26.
8. The solar energy collector of claim 7 wherein said at least one lens 36 comprises an array of lenses 22 aligned with said top surface of said light guide member 26 and positioned to direct sunlight into said light guide member 26.
9. The solar energy collector of claim 8 wherein each lens 36 of said array of lenses 22 is a plano-convex lens.
10. The solar energy collector of claim 9 wherein said spacer 24 is composed of light transmitting material and is wedge shaped wherein an apex of said wedge shaped spacer is located at said end surface of said light guide member 26.
11. The solar energy collector of claim 1 further comprising: a collimator 30 located within said light guide member immediate prior to said end surface of said light guide member 26 to direct sun light 34 from said reflecting surface 28 to said end surface of said light guide member.
12. The solar energy collector of claim 11 wherein said collimator 30 is a compound parabolic collimator.
13. The solar energy collector of claim 12 further comprising: at least one solar cell 32 located at said end surface of said light guide member 26 to receive sun light 34 from said compound parabolic collimator 30.
14. The solar energy collector of claim 1 further comprising: drive structure coupled to move said at least one lens 36 relative to said light guide member 26, or to move said light guide member 26 relative to said at least one lens 36 for tracking sun light 34.
15. The solar energy collector of claim 1 wherein said at least one lens 36 is fixed to said light guide member 26 and further comprising: drive structure coupled to simultaneously move both said light guide member and said at least one lens for tracking sun light.
16. A method for directing concentrated sun light to a solar cell 32 comprising: providing at least one lens 36 for receiving sun light 34; positioning said at least one lens 36 to focus sun light on a reflecting surface 28 at a bottom surface of a light guiding member 26; and orienting said reflecting surface 28 to direct sun light 34 from said at least one lens 36 along said light guiding member 26 toward a solar cell 32 at an end surface of said light guiding member.
17. The method of claim 16 further comprising: moving said at least one lens 36 relative to said reflecting surface 28 at said bottom surface of said light guiding member 26 for tracking said sun light.
18. The method of claim 17 further comprising: providing a compound parabolic collimator 30 in front of said solar cell 32.
19. The method of claim 18 wherein said at least one lens 36 comprises at least two lenses positioned above said light guiding member 26; and wherein each lens 36 is positioned to focus sun light 34 onto a separate reflecting surface 28 at said bottom of said light guiding member 26; and further comprising: positioning a wedge shape spacer 24 between said light guiding member 26 and said at least two lenses to keep said lenses focused on said reflecting surfaces as said lenses are moved along a top surface of said wedge shape spacer 24.
20. The method of claim 19 further comprising: locating an assemblage of said lenses 22, said wedge shape spacer 24 and said light guiding member 26 in a weather resistant enclosure.
PCT/IB2008/054749 2007-11-13 2008-11-12 Thin and efficient collecting optics for solar system WO2009063416A2 (en)

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