WO2005088209A1 - Modular solar radiation collection-distribution system - Google Patents

Modular solar radiation collection-distribution system Download PDF

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Publication number
WO2005088209A1
WO2005088209A1 PCT/US2004/004446 US2004004446W WO2005088209A1 WO 2005088209 A1 WO2005088209 A1 WO 2005088209A1 US 2004004446 W US2004004446 W US 2004004446W WO 2005088209 A1 WO2005088209 A1 WO 2005088209A1
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WO
WIPO (PCT)
Prior art keywords
reflector
solar radiation
distribution system
primary
assembly
Prior art date
Application number
PCT/US2004/004446
Other languages
French (fr)
Inventor
Karl Frederic Roth
Original Assignee
Karl Frederic Roth
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 Karl Frederic Roth filed Critical Karl Frederic Roth
Priority to EP04711258A priority Critical patent/EP1718907A1/en
Priority to PCT/US2004/004446 priority patent/WO2005088209A1/en
Publication of WO2005088209A1 publication Critical patent/WO2005088209A1/en

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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21LIGHTING
    • F21SNON-PORTABLE LIGHTING DEVICES; SYSTEMS THEREOF; VEHICLE LIGHTING DEVICES SPECIALLY ADAPTED FOR VEHICLE EXTERIORS
    • F21S11/00Non-electric lighting devices or systems using daylight
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24SSOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00Arrangements for concentrating solar-rays for solar heat collectors
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24SSOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/70Arrangements for concentrating solar-rays for solar heat collectors with reflectors
    • F24S23/79Arrangements for concentrating solar-rays for solar heat collectors with reflectors with spaced and opposed interacting reflective surfaces
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24HEATING; RANGES; VENTILATING
    • F24SSOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S50/00Arrangements for controlling solar heat collectors
    • F24S50/20Arrangements for controlling solar heat collectors for tracking
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/40Solar thermal energy, e.g. solar towers
    • Y02E10/44Heat exchange systems
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/40Solar thermal energy, e.g. solar towers
    • Y02E10/47Mountings or tracking

Abstract

A solar radiation collection and distribution system includes a solar collection system which includes a primary reflector (10), a secondary reflector (12) and a planar reflector (14). The focal points (1 OP, 12P) of the primary and secondary reflectors (10, 12) are offset by the same number of degrees, and the primary and secondary reflectors (10, 12) are rigidly fixed in an assembly (102) such that their focal points (1 OP, 12P) lie along a common optical axis (15). The assembly (102) is pivotable in elevation and rotatable in azimuth such that the primary reflector (10) continuously tracks the sun. A pivotable planar reflector (14), which reflects downwardly the beam from the secondary reflector (12), pivots at one-half the angular rate at which the assembly (102) pivots. This beam consists essentially of sunlight and is maintained in a substantially constant orientation independent of the elevation and azimuth of assembly (102). A distribution system (120C; 120R) for directing the beam from the planar reflector (14) includes a lateral reflector (110; 78) and a plurality of sunlight 15 distribution reflectors (72, 74; 76A, 76B) which each reflect downwardly a portion of the beam reflected by the lateral reflector (110; 78).

Description

MODULAR SOLAR RADIATION COLLECTION-DISTRIBUTION SYSTEM
Technical Field This invention relates to solar radiation collectors, and more particularly to a solar radiation collection and distribution system including a collection system that tracks the sun in elevation and azimuth, and a distribution system that directs a beam of sunlight along a ceiling or rooftop. Background Art There are various arrangements for solar radiation collection, distribution and utilization. Most are of impractical design, suffer numerous surface reflection losses, have insufficient light collection capability, and lack adaptability to diverse end-uses. Where illumination is the intended end-use of the solar energy, a means of effectively distributing the collected visible light must also be provided. One solar illumination concept combines a prime focus primary reflector and a secondary reflector to focus the sunlight collected in a condensed, collimated beam back along the same axis through an aperture in the primary reflector. The beam of condensed light then reflects off a downward-directing planar reflector that directs the light into a building or to an energy receiver. A means of effectively distributing the collected light must also be provided. A prime focus, three-reflector configuration has inherent problems and inefficiencies, particularly at high sun elevations. One problem with such a prime focus configuration is that to transmit most of a collimated beam at high sun elevations (using a practical beam diameter and concentration level), the planar reflector must be of impractical length. With practical lengths, typically half of a beam's cross-section cannot be redirected by the planar reflector when the sun is nearly overhead. Using a smaller beam diameter to increase the percentage of light captured and reflected at high sun elevations generally results in a concentration level so high that system materials are likely to degrade and also increases the risk of fire and other safety hazards. Secondly, since the angle of incidence at the downward-directing planar reflector increases with increasing sun elevation, there are substantial surface reflection losses at high sun elevations when a standard reflecting material such as glass mirror is used for the planar reflector, as well as undesirable spectral absorption characteristics and color shifting, even when a state of the art first surface specular reflecting material such as enhanced reflectivity anodized sheeting is used. Thirdly, at high sun elevations the cross-sections of a planar reflector and its supporting structure begin to occlude the collimated beam from the secondary reflector, significantly reducing system output and efficiency. Disclosure of Invention A solar radiation collection-distribution system according to the present invention: minimizes transmission losses at sun elevation angles above about 75 degrees; maximally and efficiently collects, collimates, spectrally separates and distributes solar radiation at all latitudes and sun elevation angles; and is adaptable to multiple uses including illumination, heating, cooling, water purification, photobioreactors and electric power generation. The invention provides a solar radiation collection system including a primary reflector having an aperture, and a secondary reflector which redirects solar radiation received from the primary reflector in a concentrated beam tlirough the aperture. The primary and secondary reflectors are rigidly disposed in a pivotable assembly. The concentrated beam has an exit angle with respect to the assembly which is different than the angle at which solar radiation is incident on the primary reflector. The solar radiation collection system further includes means for pivoting the assembly in elevation at an angular rate such that the primary reflector continuously tracks the sun, and means for annularly rotating the assembly such that the primary reflector continuously tracks the sun in azimuth. The solar radiation collection system further includes a pivotable planar reflector which receives and reflects downwardly the beam from the secondary reflector, and pivots at one-half the angular rate at which the assembly pivots. The downwardly reflected beam consists essentially of sunlight and is maintained in a substantially constant vertical and horizontal orientation independent of the elevational and azimuthal motion of the assembly. The invention further provides a distribution system including a lateral reflector which reflects the beam reflected from the planar reflector, and a plurality of reflectors which each reflect downwardly a portion of the beam reflected from the lateral reflector. Brief Description of Drawings FIG. 1 is a side elevational view of a two-axis, sun-tracking solar radiation collection system according to the invention, including a primary reflector with an offset focal point and a secondary reflector having a focal point of equal offset so that the two focal points lie along a common optical axis, and a pivotable planar reflector. FIG. 2 is a rear 45-degree view of the FIG. 1 collection system. FIG. 3 is a front isometric view of the FIG. 1 collection system. FIG. 4 illustrates a conventional prime focus optical configuration. FIG. 4a illustrates an offset focal point configuration according to the invention. FIG. 5 shows an elevational view of the FIG. 1 primary, secondary and planar reflectors when the sun is at zenith, and a ceiling-mounted distribution system for distributing sunlight. FIG. 6 is an elevational view of a turntable shown in FIGs. 1, 2 and 3, including a base and drive assembly. FIG. 7 schematically shows the configuration of the primary, secondary and planar reflectors and resultant beam divergence when a non-collimating secondary reflector is used, according to a second mode of the collection system. FIG. 8 schematically shows a rooftop distribution system for distributing sunlight collected by the FIG. 5 or FIG. 7 collection system. Modes for Carrying Out the Invention As defined herein: the term "solar radiation" means radiation over the sun's total spectrum reaching the Earth, including infrared (IR), visible, and ultraviolet (UN) components; the term "concentration level" means the amount of solar radiation per unit area; the terms "light beam" and "beam" are synonymous and mean a beam of solar radiation characterized by proportions of visible, IR and UN radiation, depending on the particular segment of the total optical path traversed; the term "condensed beam" means a beam having a greater flux density than incident solar radiation; and the term "sunlight", where applied to a beam used for daylighting applications, means that IR and UN have been substantially spectrally separated from the beam. A. Solar radiation collection system Referring to FIGs. 1, 2 and 3, a solar radiation collection and distribution system according to the invention includes a collection system 100 having a concave primary reflector 10 incorporating a downwardly offset focal point (i.e., a focal point offset from the prime focus geometry optical axis), a secondary reflector 12, of lesser diameter and preferably having a complementary offset focal point on the same optical axis as the focal point of primary reflector 10, which maximally collimates light reflected from reflector 10, and a planar reflector 14 that reflects the collimated light beam from reflector 12 in a downward direction. Preferably, primary reflector 10 is concavely parabolic. Preferably, reflector 12 is convexly hyperbolic. As best shown in FIG. 1, primary and secondary reflectors 10 and 12 are rigidly attached by a support structure 13, thereby determining a primary/secondary reflector assembly 102 in which they preferably share a common offset focal point optical axis 15 (see FIG. 4a). Secondary reflector 12 directs the non-diffuse light collected by primary reflector 10 through aperture 16 in primary reflector 10. Aperture 16 is of slightly greater dimension than the entering light beam to allow for transmission of scattered light rays. As shown in FIGs. 1 and 5, center-line 21 of counterweighted support arms 20 and 22 is preferably oriented to be coplanar with optical axis 15 of the collimated light beam reflected from reflector 12 through aperture 16. Such coplanar orientation is not required, but preferred because of compatibility with optional mechanical actuation means. Although reflectors 10 and 12 are conically shaped, alternative reflector surface shapes providing similar or improved performance in given situations are feasible, including combinations of substantially spherical and conical shapes, multi-focal point shapes, and/or shapes providing prime and offset focal points. FIGs. 4 and 4a show, respectively, a conventional prime focus optical configuration, and the offset focal point configuration of the present invention. In FIG. 4, prime focus primary and secondary reflectors 10', 12', respectively, are oriented perpendicular to central axis 11'. In FIG. 4a, focal points 10P, 12P, respectively, of primary reflector 10 and secondary reflector 12 are offset from central axis 11 along axis 15 by a predetermined number of degrees within a range of about 5° to about 45°, and preferably about 15° for a 30- centimeter (cm) diameter beam. As shown in FIG. 5, such offset of the focal points provides an exit angle 103E from assembly 102 different than the solar radiation incidence angle 1031 for a prime focus configuration. Specifically, the focal point offsets ensure that the exit angle of the collimated beam sent to the planar reflector 14 is always less than 90° above the horizon when the sun elevation is 90° (i.e., directly overhead), so that a substantial portion of the beam cross-section can be redirected by planar reflector 14. The necessary amount of offset of the focal points is determined by the desired diameter of the collimated beam where the beam intersects planar reflector 14, the desired length of planar reflector 14, and the losses acceptable in the concentration level of the beam cross-section reflected from reflector 12 at the highest sun elevations. For example, with the sun at maximum elevation and a 23-cm diameter collimated beam, nearly 100% of the beam will intersect the surface of a planar reflector of practical size, e.g., of 1.7-meters (m) length in a 15° offset focal point system.- For a 30-cm diameter beam with the same offset and a planar reflector 1.7-m in length, there is approximately a 15% loss in the reflected beam when the sun is at zenith. A conventional
(i.e., non-offset) prime focus collector of similar three-reflector design would have significantly greater losses at solar elevations close to or at the zenith. After the collecting area of primary reflector 10, focal length, and degree of downward offset are selected, along with the desired diameter for the collimated beam, the values are input to a standard optical engineering program which calculates and optimizes the aspheric coordinates of the primary and secondary reflectors for maximum performance. As shown in FIG. 3, reflector 10 includes a plurality of hydroformed aluminum . reflector panels 18 fastened to an underlying supporting framework (not shown). As shown in FIG. 2, the proximal ends 20E, 22E, respectively, of counterweighted support arms 20, 22 are attached to the back of the primary reflector 10, and pivot on a shaft 24 which is symmetric about center-line 21 and supported by two vertical side supports 26 and 28. Thus, center-line 21 is the pivoting axis of assembly 102. Referring to FIG. 2, an elevation linear actuator 29, attached between side support 28 and support arm 22, actuates the primary/secondary reflector assembly 102 to track the sun in elevation, or any other non-terrestrial sunlight source. Many commercially available linear actuators are suitable, including the 0.46-m Maxi 8500 with a 36-volt dc motor, available from Venture Manufacturing Co. of Dayton, Ohio. Referring again to FIGs. 1, 2 and 3, planar reflector 14 pivots about an axis 14A parallel to and centered over aperture 40 of turntable 42 which rotates primary/secondary assembly 102 in azimuth. Planar reflector 14 is rigidly attached to a support structure 80 which is rigidly attached to and rotates with shaft 24. Front reflecting surface 14S of reflector 14 intersects and is in the same plane as pivoting axis 14A, which coincides with the pivoting axis 21 of support arms 20 and 22. Thus, the pivoting axis 14A of planar reflector 14 is centered on and intersects the optical axis 15 of the beam reflected by secondary reflector 12. As arms 20 and 22 pivotally rotate at an angular rate which enables primary reflector 10 to elevationally track the sun, planar reflector 14, attached to shaft 24, is driven by a planar reflector gear motor 36 to pivotally rotate at one-half that angular rate. Because the collimated beam of light from secondary reflector 12 is centered between and parallel to arms
20 and 22, the beam is synchronously maintained in substantially vertical alignment through the center of turntable aperture 40 as the arms rotate. Such beam orientation is not mandatory, but is compatible with preferred means for planar reflector actuation. Planar reflector 14 is thus continually adjusted to redirect the beam reflected from secondary reflector 12 in a substantially constant orientation through aperture 40, independent of the elevation of assembly 102. Referring to FIGs. 2 and 6, bottom ends 26E, 28E, respectively, of side supports 26 and 28 attach to turntable 42 which rests on four equally spaced roller bearings, of which two, 44, 46, are shown in FIG. 6. Ends 26E, 28E are held in alignment by four equally spaced lateral bearings fixed to turntable base 52, of which two, 48, 50, are shown in FIG. 6. Turntable drive sprocket 54 is attached to turntable 42 with four stand-offs, of which two, 56, 58, are shown in FIG. 6, and extends through turntable base 52. Turntable 42, base 52 and aperture 40 are each sufficiently large in diameter to allow transmittance of ambient light into a sky window 60 (see FIG. 5) during periods of reduced direct solar radiation. Referring to FIGs. 1 and 6, a turntable azimuth drive-gear motor 62 is operatively connected to a sun-tracking device 32. Many commercially available motors are suitable for motor 62, including Model 5NG28 available from Grainger Co. of Long Beach, CA. Sprocket 54 is driven by a chain 55 which is operatively linked to motor 62 so that turntable 42 is annularly rotatable, and the collimated beam is directed in a substantially constant orientation in the horizontal plane, independent of the sun's changing azimuth. There are a number of commercially available devices suitable for tracking the sun and controlling solar collector alignment. Such devices may be classified either as predictive or active. A predictive device uses a microprocessor to store and/or compute azimuth and elevation coordinates for the primary reflector. An active device utilizes sensors which in real time detect changes in the sun's position by continually measuring the radiation incidence angle at the primary reflector. A predictive device may be preferred in applications where high accuracy sun-tracking is important, such as the present invention where used for long distance distribution. Preferably, device 32 separately tracks the sun in elevation and azimuth. As shown in FIG. 1, device 32 is attached to support structure 13 proximate to secondary reflector 12. Referring to FIGs. 1 and 2, device 32 is powered by a battery 34 which is charged by a photovoltaic panel 38 attached to primary reflector 10. Device 32 includes integral motor drivers which drive linear actuator 29 and azimuth drive motor 62 to adjust the orientation of elevation arms 20, 22, thereby maintaining alignment of primary reflector 10 with the sun. When utilizing a predictive device, linear actuator and azimuth drive motors integrate the position sensors. B. Beam-expanding secondary reflector FIG. 7 schematically shows a second mode of a solar collection system 104 according to the invention, including a primary reflector 106, a planar reflector 66, and a non- collimating secondary reflector 64 which causes a concentrated beam to first condense and then expand for more efficient distribution in non-collimated beam applications such as illumination of a building with a high ceiling, e.g., an aircraft hangar, where the full output of the collection system is diffused through a single skylight without further distribution. Parallel lines 65A, 65B, 65C, 65D, 65E indicate the relative spacing between each successive optical component, the figure showing significant beam expansion over a relatively short distance. Although secondary reflector 64 can be configured to perform with primary reflector
10, an alternative primary reflector 106 is indicated to signify that a different optical shape would be needed to get an expanding beam. Beam expansion can also be obtained by using a collimating secondary reflector and modifying the shape of the primary reflector. The focal length of secondary reflectors 64, 106 can be selected to minimize the beam diameter at any point in the distribution system, such as where the beam enters a building, allowing the benefit of smaller roof penetrations; or where it intersects planar reflector 66, allowing for complete reflection by planar reflector 66 at all but the highest sun elevations. Planar reflector 66 is identical in construction to planar reflector 14, except for additional width to accommodate more of the expanded beam. The resulting divergence or expansion of the beam can be largely corrected, if desired, by a concave lateral reflector 110 (see FIG. 5) which further collimates or focuses the beam, or by a condensing lens. A beam-expanding secondary reflector can also improve the performance of a prime focus collector. C. Reflective surfaces Various reflecting surfaces including glass mirror and enhanced reflectivity aluminum sheeting may be used for solar collectors, but none is without deficiencies. The innovative assembly, geometry and combination of complementary materials and coatings used in the invention provide higher output and greater durability than has heretofore been achieved. A significant advantage of the invention is provided by use of a multi-layer polymeric, dielectric reflecting material for surface 14S and the reflecting surfaces of reflectors 10 and 12, such as the preferred RADIANT LIGHT FILM™ developed and distributed by the
Specialty Film Division of Minnesota, Mining and Manufacturing Company (3M) of St. Paul, MN. The material eliminates the large surface reflection losses at high incidence angles typical of second surface reflector materials such as mirror glass. Use of a dielectric reflecting material also allows substantial removal of the undesirable infrared component of solar radiation when building illumination is the end-use of the collected light. This is because of the material's high infrared transmittance at off-axis incidence angles. In water heating and other applications where maximum energy transmission is desired, a full spectrum metallic reflective material is preferred for the reflecting surfaces.
D. Spectral separation considerations The multi-layer dielectric material reflects the visible light spectrum of 400-700nm at all incidence angles. At normal incidence the reflectance of the infrared spectrum extends to just beyond lOOOnm. An observed, but unadvertised, property of this material is its more efficient transmittance of the infrared spectrum at non-normal incidence angles, where the film reflects only up to about 800nm at approximately 45-60° incidence, although solar infrared radiation extends beyond 1200nm. Due to the resulting improved infrared transmittance at non-normal incidence angles, the material acts as a very effective cold mirror (i.e., a visible light-reflecting, heat-passing mirror) when used for planar reflector 14. Use of a dielectric reflecting material thus allows planar reflector 14 to perform two functions: redirecting the beam from secondary reflector 12; and spectrally separating the undesirable infrared radiation without requiring additional transmission-reducing filtering elements.
E. Spectral separation and reflective film substrates Building codes and energy efficiency goals increasingly emphasize demand for lower solar heat gain from windows, skylights and other daylighting fixtures. Reflective films are typically laminated to an aluminum sheet substrate which can then be formed into various shapes for lighting assemblies such as luminaire reflectors and tubular skylights. Aluminum and other metals which have very high reflectance of the infrared solar spectrum, when used as the supporting substrate for an infrared transmitting/visible light reflecting material reflect heat initially passed through the film, back through the film and into the collection system/building airspace, causing increased loads on air conditioning equipment. This undesirable heat reflection and transmission is remedied in the invention by a transparent infrared-passing supporting substrate underlying the reflective film, such as glass for secondary reflector 12, and heat absorbing materials or coatings (e.g., black-painted, impregnated or anodized) for primary reflector 10 and planar reflector 14. Preferably, the substrate for planar reflector 14 is black-painted, tempered float glass. Preferably, the substrate for primary reflector 10 is black anodized aluminum. A heat absorbing substrate removes substantial portions of the infrared spectrum in sunlight collection applications, allowing the heat to be sinked, insulated, or radiated away from the collection system and building workspace. Use of transparent and heat absorbing substrates is also effective for spectrally separating heat in daylighting applications using tubular skylights, light pipes and/or angled light wells. E. Concentrator photovoltaic applications
Although a non-transparent (e.g., black-painted) heat absorbing substrate for secondary reflector 12 will work well in many daylighting applications, the substrate used for secondary reflector 12 preferably is heat resistant, transparent, anti-reflection coated, slump-formed glass. Infrared-sensitive concentrator photovoltaic cells or similar devices converting thermal energy into electrical energy can then make effective use of the infrared portion of the solar radiation spectrum. In such collector configurations a full spectrum reflective material is used for primary reflector 10. F. Reflective surface durability Many years of government and commercial research have failed to produce a cost- effective and durable highly specular reflecting material for solar energy applications. Outdoor weatherability and cleaning of the material without damage also continue to be unsolved problems. RADIANT LIGHT FILM™, if utilized unmodified in the invention, has UN degradation problems, static dust attraction, poor weatherability, and ineffective abrasion resistance resulting in damage during cleaning. For these reasons, this material is not approved or marketed by 3M for outdoor use in solar concentrator applications. The most effective current method to protect reflecting surfaces in solar collectors from weathering is enclosing the reflectors in a plastic cover. The disadvantage of this method is additional surface reflection losses caused by the difference in refractive index between air and the plastic material used for the enclosure. This problem is solved in the invention by applying an aliphatic polyurethane clear coating to the reflective film, making a plastic enclosure unnecessary. When formulated with UN absorbers, such coatings are commonly used as a gloss clear coat for vehicle paints. Polyurethanes have a refractive index that is close enough to that of plastics used in dielectric and other reflective films, that they impart significantly less surface reflection losses than other protective coatings or enclosures. When applied to the reflective film, a polyurethane coating provides the additional necessary properties of durable UN resistance, weatherability, chemical resistance, minimal electrostatic dust attraction, and ease of cleaning without damage to the reflective surface. G. Distribution and utilization considerations Referring to FIG. 5, after passing through turntable aperture 40 the condensed beam transits roof sky window 60, before being distributed and utilized inside a building. Windowpane 68 of sky window 60 includes a first layer of anti-reflection coated glass (preferably LUXAR™, available from Abrisa Glass and Coatings of Santa Paula, CA) having a hot mirror coating on its bottom side that absorbs residual portions of the infrared spectrum, thus preventing this heat from entering the building. A seasonally removable metal frame having an anti-reflection coated, heat reflecting plastic film 70 is suspended under sky window 60, enclosing air space providing additional insulating properties with minimal reduction of visible light transmission. Obvious means of distributing such a condensed beam are light pipes or fiber optics. These distribution means however are not ideal because of component expense, absorption by transmissive materials, and losses due to multiple surface reflections. A distribution system according to the invention allows eliminating light pipes or fiber optics for distributing sunlight, as well as the associated losses of these elements. H. Distribution system The sun, subtending an average of 0.53 degrees of arc, is not a point source of light. Because of this, and irregularities of the reflecting surfaces, there will be significant inherent divergence or de-collimation of the condensed beam of sunlight. True collimation is not possible given such parameters. Referring to FIG. 5, undesirable divergence in a ceiling- mounted distribution system 120C is minimized by a concave lateral reflector 110 which condenses the beam by providing additional collimation or focusing, as desired, and directs the beam, which is generally parallel to ceiling 122, to convex reflectors 74 and 72. Progressive cross-sections are reflected downwardly by reflectors 74 and 72. Beam- condensing lateral reflector 110 is computer designed using standard optical engineering software to match the beam divergence at the desired point of lateral reflection. Reflector 110 performs two functions: condensing and redirecting the beam along a ceiling or roof; and limiting surface reflection lossses because only one additional optical element has been added. FIG. 8 shows a rooftop distribution system 120R wherein a planar lateral reflector 78 directs a beam toward convex reflectors 76A and 76B. A rooftop distribution system allows higher beam concentration levels to be distributed outside a building where fire and other potential hazards can be minimized. A planar lateral reflector can be used in both building- interior and building-exterior configurations where total distribution distances are relatively short, so that further collimation or focusing of the beam is unnecessary. Thus, a solar radiation collection and distribution system according to the invention further includes a distribution system including a lateral reflector and a plurality of downwardly reflecting reflectors. For multi-story applications where the beam travels extended vertical distances, one or more condensing lenses may be added to the optical path at any point beyond the planar reflector, to keep the beam divergence within the desired range. This invention is not to be limited by the modes shown in the drawings and described herein which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims. Industrial Applicability A solar radiation collection system according to the invention is adaptable to daylight illumination of buildings, water heating, cooling and purification, materials processing, photobioreactors, and electric power generation, and is particularly advantageous when the sun's elevation angle is above 75 degrees. A distribution system according to the invention is adaptable to roof- and ceiling-mounted daylighting configurations, and allows elimination of costly and inefficient light pipes or fiber optics now used, or designated for use, with other proposed sunlight distribution systems.

Claims

-3/6
CT ATMS
WHAT IS CLAIMED IS: 1. A solar radiation collection and distribution system comprising a collection system comprising (a) a primary reflector having an aperture therethrough; (b) a secondary reflector for redirecting, in a concentrated beam, radiation received from the primary reflector along an optical axis through the aperture; (c) the primary and secondary reflectors rigidly disposed in a pivotable assembly; (d) means for pivoting the assembly in elevation at an angular rate such that the primary reflector continuously tracks the sun; (e) means for annularly rotating the assembly such that the primary reflector continuously tracks the sun azimuthally; and (f) a pivotable planar reflector for receiving and reflecting downwardly the beam received from the secondary reflector; characterized by: (g) the beam having an exit angle (103E) with respect to the assembly (102) different than the incidence angle (1031) of solar radiation incident on the primary reflector (10); and (h) the planar reflector (14) pivoting about a pivoting axis (14 A) at one-half said angular rate, the downwardly reflected beam consisting essentially of sunlight and maintained in a substantially constant vertical and horizontal orientation independent of the elevation and azimuth of the assembly (102).
2. A solar radiation collection and distribution system according to claim 1 wherein the primary reflector (10) is concave and the secondary reflector (12) is convex.
3. A solar radiation collection and distribution system according to claim 1 wherein the optical axis (15) of said concentrated beam intersects the pivoting axis (14A) of the planar reflector (14).
4. A solar radiation collection and distribution system according to claim 1 wherein the primary reflector (10) has a focal point (10P) offset from a central prime focus, first optical axis (11) by a predetermined number of degrees, and the secondary reflector (12) has a focal point (12P) offset from axis (11) by said number of degrees, the focal points (10P, 12P) disposed along a second optical axis (15).
-2/6 5. A solar radiation collection and distribution system according to claim 1 wherein the assembly (102) and the planar reflector (14) pivot independently about a common axis (14A-21).
6. A solar radiation collection and distribution system according to claim 1 wherein said concentrated beam redirected by the secondary reflector (12) is substantially collimated.
7. A solar radiation collection and distribution system according to claim 1 further comprising a distribution system (120C; 120R) comprising a lateral reflector (110; 78) which reflects the beam reflected from the planar reflector (14).
8. A solar radiation collection and distribution system according to claim 7 wherein the lateral reflector (110) is concave and further collimates said beam.
9. A solar radiation collection and distribution system according to claim 7 wherein the distribution system (120C; 120R) further comprises a plurality of reflectors (72, 74; 76A, 76B), each reflecting downwardly a portion of the beam reflected from the lateral reflector (110; 78).
10. A solar radiation collection and distribution system according to claim 1 wherein: said means for pivoting the assembly (102) in elevation at said angular rate comprises a sun-tracking device (32) operatively connected to and driving a linear actuator (29) attached between a side support (28) of the solar collection system and a support arm (22) attached to the primary reflector (10); and said means for annularly rotating the assembly (102) comprises the sun-tracking device (32) operatively connected to and driving an azimuth drive-gear motor (62) operatively linked to a turntable (42) on which the assembly (102) is mounted.
11. A solar radiation collection and distribution system according to claim 1 wherein the secondary reflector (64) causes the concentrated beam reflected therefrom to first condense and then expand. -1/6
12. A solar radiation collection and distribution system according to claim 1, further comprising: means for reducing surface reflection losses at high solar radiation incidence angles at the primary reflector (10), secondary reflector (12) and planar reflector (14); means for reducing weathering of and damage from ultraviolet radiation to the primary reflector (10), secondary reflector (12) and planar reflector (14); and means for separating a portion of the infrared solar radiation from the visible component at the primary reflector (10), secondary reflector (12) and planar reflector (14).
13. A solar radiation collection and distribution system according to claim 12 wherein: said means at the planar reflector (14) for reducing surface reflection losses comprises a reflecting surface (14S) comprising a multi-layer polymeric, dielectric material; said means, at each reflector (10, 12, 14), for reducing weathering and ultraviolet radiation damage comprises a polyurethane clear coating over said reflecting surface; said means for separating a portion of the infrared solar radiation at the primary reflector (10) comprises a first infrared-absorbing substrate underlying said dielectric material; said means for separating a portion of the infrared solar radiation at the secondary reflector (12) comprises a transparent infrared-passing substrate underlying said dielectric material; and said means for separating a portion of the infrared solar radiation at the planar reflector (14) comprises a second infrared-absorbing substrate underlying said dielectric material.
14. A solar radiation collection and distribution system according to claim 13 wherein: said first infrared-absorbing substrate is black anodized aluminum; and said second infrared-absorbing substrate is black-painted, tempered float glass.
15. A solar radiation collection and distribution system according to claim 7 wherein the distribution system (120C) further comprises at least one sky window (60) comprising a first layer of anti-reflection coated glass. 0/6
16. A solar radiation collection and distribution system according to claim 15 wherein a layer (70) of plastic film is suspended under each sky window (60) and encloses an air space below said coated glass layer.
17. A solar radiation collection and distribution system according to claim 16 wherein the layer (70) of plastic film is disposed within a removable frame.
PCT/US2004/004446 2004-02-13 2004-02-13 Modular solar radiation collection-distribution system WO2005088209A1 (en)

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