WO2010041249A1 - High concentration "reverse bulb" solar photovoltaic module - Google Patents

High concentration "reverse bulb" solar photovoltaic module Download PDF

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Publication number
WO2010041249A1
WO2010041249A1 PCT/IL2009/000958 IL2009000958W WO2010041249A1 WO 2010041249 A1 WO2010041249 A1 WO 2010041249A1 IL 2009000958 W IL2009000958 W IL 2009000958W WO 2010041249 A1 WO2010041249 A1 WO 2010041249A1
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WO
WIPO (PCT)
Prior art keywords
reverse
dependent
photovoltaic cell
top face
photovoltaic
Prior art date
Application number
PCT/IL2009/000958
Other languages
French (fr)
Inventor
Yaron Ruziak
Original Assignee
Ziruz Nihul Ltd.
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 Ziruz Nihul Ltd. filed Critical Ziruz Nihul Ltd.
Publication of WO2010041249A1 publication Critical patent/WO2010041249A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/40—Thermal components
    • H02S40/44—Means to utilise heat energy, e.g. hybrid systems producing warm water and electricity at the same time
    • 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
    • H01L31/052—Cooling means directly associated or integrated with the PV cell, e.g. integrated Peltier elements for active cooling or heat sinks directly associated with the PV cells
    • H01L31/0521—Cooling means directly associated or integrated with the PV cell, e.g. integrated Peltier elements for active cooling or heat sinks directly associated with the PV cells using a gaseous or a liquid coolant, e.g. air flow ventilation, water circulation
    • 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
    • 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
    • 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
    • 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
    • Y02E10/60—Thermal-PV hybrids

Definitions

  • the present invention relates to a solar energy converter and, more specifically, a modular, sealed photovoltaic module provided with a very highly concentrating optical system suitable for low cost mass production.
  • the design of the current invention introduces maximal integration of primary and optional secondary optics, photovoltaic receiver, heat sink, connectors and enclosure, allowing for the .lowest possible cost of. High and very high concentrated photovoltaic (HCPV & VHCPV) systems. This is accomplished through highly automated manufacturing processes, as in use in the automotive, construction, and lighting industries. This unique design solves the typical challenges of HCPV & VHCPV modules such as: oxidation, expansion & contraction of internal air, exposure to moisture, and changing optical geometry of the expanding/contracting module elements.
  • photovoltaic conversion stands out due to its direct conversion of sunlight into electricity, and its potential for long service life. Due to the relatively high cost of solar photovoltaic material and modules, as well as their often higher efficiencies at higher levels of incident radiation, a known technique for reducing costs of photovoltaic modules is to concentrate the incident sunlight by use of lenses or mirrors to concentrate a higher flux of light onto a smaller surface area of photovoltaic material.
  • HCPV & VHCPV photovoltaic elements and secondary optics may be appreciably arrested by maintaining these elements in vacuum, controlled atmospheres where oxidation & moisture is prevented, or under protective layers of e.g. epoxy.
  • protective layers involves unavoidable losses as the light enters and leaves a region of differing refractive index.
  • the accurate alignment of the concentrating optics must also be maintained over the lifetime of the device.
  • U.S. Pat. 4045-246 which provides -a solar module with a composite parabolic solar energy concentrator and a solar receiver disposed in an outlet section and cooled by means of a liquid.
  • the module is constructed as follows: the concentrator, having a reflecting surface, is contrived as a discrete assembly, the outlet cross section whereof contains a sealed chamber, with a photoreceiver disposed on the bottom thereof.
  • the liquid circulating inside the sealed chamber operates as a heat-transfer medium.
  • An inlet section of the concentrator is covered with a transparent material
  • the liquid coolant in the space in front of the solar receiver results in high losses of light passing through the layer of liquid and in the reduction of the photoreceiver efficiency.
  • Due to the use of separate pieces and possibly different materials the joints between the concentrator and the sealed chamber wherein the receiver is disposed and the liquid is circulating, and between the concentrator and the transparent material in the inlet section, do not provide for reliable long-term sealing of the concentrator reflecting surface.
  • environmental effects may degrade the unit. These environmental effects will generally include oxidation, and differences in thermal expansion coefficients which eventually lead to separation and/or cracking. The result is that the properties of the concentrator reflecting surface are impaired and the concentrator's efficiency is decreased.
  • the unit must be assembled in its entirety from discrete elements that must be glued, bolted, or otherwise attached in a non-trivial manner which will involve some investment of time and resources.
  • US Patent 4491683 discloses a low concentration solar photovoltaic module comprising a composite parabolic solar energy concentrator having an aperture angle D and contrived in the form of a sealed gas-filled bulb (see Fig. Ia).
  • the side walls of the bulb bend on a predetermined radius to a cylindrical part beside a concentrator radiation outlet surface which is coated with an inside reflecting coating.
  • a photoreceiver having a cooling system is arranged inside the cylindrical portion of the bulb with a gap separating it from the walls.
  • the cooling system disposed inside the concentrator bulb comprises a metal heat sink with air cooling ribs.
  • the invention prolongs the service life of the module, improves its dependability and efficiency, and reduces its cost.
  • Another known problem with concentrating systems is that in general there is a trade-off between the degree of concentration and the required accuracy of alignment (between the focusing system and the sun and between the focusing system and the photovoltaic element). As the concentration factor increases, the required alignment accuracy generally increases as well. Any highly-concentrating system will suffer from this problem unless appropriate measures are taken, such as the addition of secondary optics.
  • An advantage of the sealed photovoltaic element is that the alignment between focusing system and photovoltaic element is fixed within the sealed enclosure and cannot be interfered with or disturbed by the elements, cleaning operations, and the like.
  • US patent 4166917 discloses a sealed glass bulb enclosing a photovoltaic element (see Fig. Ib).
  • This bulb like that of US patent 4491683, has a curved front surface which will prove more dificult to clean than a flat surface of comparable area, and a mirror concentrating incident radiation onto a photovoltaic cell location in the focal plane, with subsequent limited maximum concentration factor.
  • US patent 4491683 refers to US patent 3923881 in connection with the shape of the side wall, which is described in US 3923881 as being '..any substantially smooth non-convex line falling within..' the area contained between a straight line and a parabola (column 3 line 66).
  • the acceptance angle is the range of angles from which inoming light will still hit the photovoltaic element.
  • the range of shapes in US 3923881 is provided to allow as large as possible an acceptance angle such that sun-tracking is unneeded or requires low precision.
  • the provision for high acceptance angle necessarily comes at the cost of lower concentration ratios. For highly concentrating systems, such sidewalls are not suitable.
  • This bulb provides very high concentration factors and, in some embodiments, a flat front face.
  • the preferred embodiment provides a connector at the base, which allows for easy attachment and removal of the bulb, and provides conductors for electrical connection and heat extraction.
  • the connector is adapted for connecting the unit to a substrate, for connecting the photovoltaic cell to an electrical load, and means for conducting heat away from the photovoltaic element.
  • a sealed housing having a top face, said top face being transparent to incident solar rays, and said top face being so formed as to direct incoming radiation onto a focal area within said sealed housing;
  • a connector adapted for reversibly connecting the bottom of said reverse bulb to a substrate mechanically, while also connecting said photovoltaic cell to an electrical load, and connecting said heat collector to a heat sink; wherein the sealed assembly prevents oxidation and corrosion of said photovoltaic cell, and wherein the degree of concentration of solar radiation may reach values of concentration in the range from 10-10000.
  • a sealed housing having a top face, said top face being transparent to incident solar rays, and having reflective side faces disposed to reflect incoming radiation onto a focal area;
  • a second reflecting element of low concentration total internal reflection such as composite parabolic concentrator as part of the sealed housing adapted to lead and homogenize incident radiation onto said photovoltaic cell.
  • Figs. IA-B is prior art showing sealed photovoltaic collectors disclosed in US patent 4166917 and US patent 4491683, respectively;
  • Figs. 2A-B illustrates the geometrical properties of a parabola
  • Fig. 3 is a schematic view of the confocal concentrating optical system
  • Fig. 4 is an isometric view of the reverse bulb
  • Fig. 5 is an exploded view of the reverse bulb
  • Fig. 6 is prior art depicting a tracking system
  • Fig. 7 is a schematic view of the mass producible sealed reverse bulb.
  • Fig. 8 is a schematic view of the reverse bulb with a secondary Newtonian reflector.
  • Fig. 9 is a schematic view of the reverse bulb with reflecting sides and the PV cell and diffusing optic at the top.
  • Fig. 10 is a schematic view of the reverse bulb with a reflecting parabolic sides and diffusing optic at the focal plane.
  • Fig. 11 is a schematic view of the reverse bulb with a spherical collecting surface.
  • Fig. 12 is a schematic view of the reverse bulb with a Fresnel mirror and the PV collector at the top.
  • Fig. 13 is a schematic view of the reverse bulb with a planar collector that directs light to the PV collector at one side.
  • Fig. 14 is a schematic view of a plurality of reverse bulbs installed at the focus of a parabolic trough.
  • the term 'concentrated' refers to ⁇ 10X concentration.
  • 'highly-concentrated' refers to ⁇ 1OOX concentration.
  • the term 'very-highly concentrated' refers to -1000X concentration.
  • the term 'Newtonian optics' refers to the light-collecting configuration of Newton's telescope wherein light is reflected from a parabolic mirror onto a secondary mirror, and from there to a receiving surface such as a detector,an eye, or a photovoltaic converter.
  • 'PV refers to a photovoltaic cell, this being an element adapted for conversion of incident radiation into electrical current.
  • the core of the present invention is to disclose and provide a photovoltaic system with the following properties:
  • a sealed enclosure has several advantages: a. Prevents exposure of the photovoltaic cell to various possibly damaging factors such as oxidation, collection of dust, rain/moisture. b. Maintains precise optical alignment between concentrating optics and photovoltaic element, which is critical in high concentration-coefficient systems. c.
  • the sealed enclosure may be filled with a working liquid such as water, which has high heat capacity. This allows the entire photovoltaic element to be surrounded by the working liquid, which allows for faster heat dissipation [mainly through convection and conduction] than would be possible otherwise [mainly through conduction/radiation].
  • the device can improve upon the sealed enclosures known (c.f. US patent 4166917 and US patent 4491683) since there will be only one interface of refractive mismatch, namely the first air-glass interface.
  • the glass-fliud interface if properly index-matched, will not cause such a loss since the amount of loss is proportional to the index mismatch:
  • the photovoltaic element will preferably extend out to this radius, since if it does not, the sunlight incoming past the edge of the photovoltaic element is lost, (see Fig. 2b). If some maximum height H is stipulated for the unit, due to practical constraints, then the radius 204 of the parabola at this height is found using Eqs. 1,2
  • the concentration factor is the ratio of the light input area to the light output area, which will in this case be
  • Fig. 3 presenting an embodiment of a sealed confocal concentrating optical system of the current invention 100, comprising a front Fresnel lens 10, a focal point 20, and a second optical element 40.
  • Sun rays pass through the lens 10, incident in a direction parallel to the optical axis 15.
  • the front lens can be a Fresnel lens as mentioned or in general a diffraction optical element providing conversion of the parallel sunlight beam into a converging beam that converges at the focal point 20.
  • a second optical element 40 is disposed confocally relative to the first optical element 10 so that the diverging light beam propagating after the focal point 20 is converted into a parallel beam.
  • the proposed photovoltaic module combines high coefficient of concentration and compactness of the device, and the second optical element allows the incoming light to be spread evenly over the receiving photovoltaic element 30. It should be noted that the use of a second optical element 40 is not strictly necessary to spread the incoming light from a point to an evenly-spread spot, for several reasons. Firstly, the top lens 10 may be constructed in such fashion that the incoming light converges to a spot instead of a point.
  • the photovoltaic element may be placed above or below the focal point, where the incoming rays will form a spot instead of a point.
  • the angular size of the sun itself will inevitably serve to spread out the focal point into a spot of a size determined by the focal length.
  • the aforesaid installation includes a base member 401 which holds a plurality of reverse bulbs 402.
  • the base member has internal channels [not seen] that contain wires to conduct electrical current, as well as means for extraction of heat from the reverse bulbs.
  • This heat extraction means may take one of several forms: either additional channels for active, forced conduction of a flowing heat-extracting medium such as oil or water, or means for passively dissipating heat directly from the base member, such as heat-sink fins or the like.
  • Heat sink fins may for example be disposed on the underside of the base member.
  • the reverse bulbs are maintained under vacuum for extending the operation life by preventing the atmosphere from acting on photovoltaic cell e.g. through oxidation.
  • the standard epoxy coating on the PV elements themselves can therefore be dispensed with, eliminating the front and back interfaces. It is within the scope of the invention to fill the reverse bulbs with any suitable gases or liquids as well, including hydrogen, noble gases, and heat-conducting liquids such as water, oil, and alcohol.
  • the parabolic, near-parabolic, spherical or aspherical surface 501 is mirrored on its inner surface, allowing light to be conducted to the diffusive element 502 which spreads the incoming light evenly upon the photovoltaic element 503.
  • the base member 505 holds the entire unit in place, as it can be locked securely into a substrate by suitable means such as holes 504 through which the unit is screwed down onto the substrate.
  • Conductors 506 are provided to conduct electricity, and in some embodiments heat as well is conducted by these or additional members.
  • independent conductors are used for electricity and heat, for example two conductors for electricity and a third and fourth for heat.
  • This third and fourth conductor could comprise hollow tubes for conducting liquid and thus transferring heat by convection, or solid rods of e.g. metal for transfer of heat by conduction.
  • the tracking system comprises a support 603, the collecting surface 601, and tracking means 602 for changing the orientation of the collecting surface with respect to the support.
  • the tracking means 602 orients the collecting surface to be normal to the Sun as the latter traverses on celestial sphere, to provide parallelism of the sunrays and optical axis of the optical system of the reverse bulbs of the system.
  • the reverse bulbs of the system for instance on a substrate as in Fig. 4, are preferably attached to a tracking system such as shown in Fig. 6.
  • the reverse bulb body 701 is made similarly to the body of a conventional light bulb.
  • the top of the reverse bulb is provided with a focusing element 705, for example a Fresnel lens impressed into the bulb glass at the time of manufacture. Formation of the Fresnel lens can be performed while the glass of the bulb is in a molten or otherwise malleable state, and eliminates a need for attachment of a separate lens.
  • the interior of the bulb is either filled with a noble gas, another suitable gas, a working liquid, or maintained in a partial vacuum.
  • the interior of the bulb is optionally provided with a diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, increasing the angular acceptance of the system and decreasing the requisite tracking accuracy.
  • the system is preferably provided with a modular connecting system such as a base 703 provided with holes 706 for easy and reversible attachment to a substrate member.
  • the base 703 of the system will be preferably provided with conductors made a highly heat-conductive material to allow for dissipation of waste heat from the system.
  • a sealed system has the further benefit that the fine alignment between optical elements and photovoltaic module is now preserved and isolated from any disturbance. It may be found that use of a light-transmissive fluid of high heat capacity or conductivity such as hydrogen or water may increase the rate of heat conduction away from the photovoltaic module, which is a key concern in highly concentrating systems due to the high amount of power incoming to the system. This fluid can be sealed within the unit or may be forced in and out of the unit through channels communicating with the outside of the otherwise-sealed unit.
  • Modern high-efficiency PV cells of e.g. 30% efficiency leave 70% of the incoming radiation to heat the PV module, which must be cooled by some means to prevent extreme heating.
  • the efficiency of such PV cells generally decreases with temperature making it doubly important to keep the PV unit as cool as possible.
  • FIG. 8 illustrating another embodiment of the reverse bulb, with optional diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, and base 703 for easy and reversible attachment to a base member.
  • This embodiment is provided with a reflective coating on the inside of the glass 701 and secondary Newtonian-type reflector 707.
  • the reflective coating serves as a parabolic or non-parabolic mirror which reflects light onto the secondary Newtonian reflector 707, from which the light is again reflected onto the optional diffusive optic 702 and from there onto the photovoltaic converter 704.
  • This embodiment uses mirrored surfaces instead of a lens. Visible also are the heat and/or electrical conductors 708 as well as the holes 706 for connecting the device to a substrate.
  • Fig. 9 illustrating another embodiment of the reverse bulb, with optional diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, and base 703 with holes 706 for easy and reversible attachment to a substrate member.
  • This embodiment is also provided with a reflective coating on the inside of the sealed enclosure 701. This reflective coating serves as a parabolic or non-parabolic mirror which reflects light onto the optional diffusive optic 702.
  • the diffusive optic 702 and photovoltaic element 704 are located at the top surface of the bulb, eliminating the need for a second Newtonian reflecting surface.
  • This embodiment also uses a mirrored surface instead of a lens. In this case the electrical and heat conductors 708 traverse the entire length of the bulb to reach the photovoltaic element 704 at the top of the bulb.
  • Fig. 10 illustrating another embodiment of the reverse bulb 701, with optional diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, and base 703 provided with holes 706 for easy and reversible attachment to a base member.
  • This embodiment also uses a mirrored surface instead of a lens, and places the diffusive optic at the focal plane.
  • the size of the photovoltaic element is not as large as the full parabola width at the focal plane, but may be significantly smaller, thus avoiding the limitation described in Eq. 6 on the concentration ratio.
  • all the other embodiments listed above avoid this limitation as well, since the photovoltaic element is not located at the focal plane or is significantly smaller than the full parabolic width at the focal plane.
  • Fig. 11 illustrating another embodiment of the reverse bulb 701, with optional diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, and base 703 for easy and reversible attachment to a substrate member.
  • This embodiment uses a lens- or sphere-shaped top surface, and places the diffusive optic at the focal plane.
  • all the other embodiments have smooth or nearly-smooth top surfaces; this embodiment is the only one without a smooth top surface.
  • the electrical/thermal connectors 708 conduct electricity and/or heat from the photovoltaic element.
  • Fig. 12 showing en embodiment wherein a series of concentric circular mirrors 709 reflect incoming light onto the photovoltaic receiver 704.
  • the material of the cylindrical body 710 may be for instance epoxy or glass, as long as it is largely transparent to incoming solar radiation. This material is preferable endowed with high heat conductivity. Conductors abstract heat and electricity from the PV cell as in the other embodiments.
  • Fig. 13 is an embodiment wherein a flat light-absorbing plate 710 is utilized to conduct light to the PV cell 704, which as before is connected through base member 703 to a substrate, and connects electrically and thermally by means of connectors 708.
  • the slab is constructed in a manner similar to that of an LCD BLU (backlight unit), and is adapted to collect light from the entire surface of the plate 710 and conduct it to the photovoltaic elements 704.
  • This backlight unit is covered with a one way coating that allows the light in but serves as a total internal reflector to enhance light absorption by the PV cell.
  • Such a one-way mechanism can be accomplished after the fashion of a Faraday isolator, volume diffractive element, phase diffractive element, or the like as will be obvious to one skilled in the art.
  • the reverse bulb of the present invention can be used as a 'plug-in' photovoltaic collector placed at the focus of a larger system.
  • a parabolic trough provided with a series of reverse bulbs in a line at the focus of the parabolic trough.
  • Such a system is shown conceptually in Fig. 14 where one can see a series of reverse bulbs 1401 of the current invention, which are located at the focus of the parabolic trough 1402.
  • the bulbs are held in place by the bulb-holding substrate 1403 which conducts heat and electrical energy away from the reverse bulbs.
  • the focus of larger system can also be rather diffuse as light only needs to reach the relatively large surfaces of the reverse bulbs.
  • the primary and secondary optical elements are chosen from a group consisting of a refractive optical element, a reflective optical element, a Fresnel lens, a relief diffractive optical element, an absorptive diffractive optical element, a volume phase diffractive optical element, and any combination thereof.
  • a top refractive unifying optical element is provided in the form of a Fresnel lens of circular symmetry.
  • a reflective unifying optical element is provided that is parabolic in profile.
  • a side reflective unifying optical element is provided that is near-parabolic in profile.
  • a side reflective unifying optical element is provided that is parabolic or near-parabolic in profile, and a top second reflective optical element in Newtonian configuration is provided.
  • the photovoltaic element is located at the top face of the unit.
  • the front face of the unit is provided in the shape of a converging lens.
  • a diffusive optical element is provided that directs incoming radiation onto the area of the photovoltaic element.
  • the unifying element is disposed confocally to the focusing element.
  • the housing is maintained under vacuum of less than 10 mbar.
  • the housing is filled with gas.
  • the filled gas is selected from the group consisting of: helium, neon, argon, krypton, xenon, radon, and any combination thereof.
  • the housing is filled with fluid.
  • the reverse bulbs are provided with the connectors adapted to releasably connect to a substantially plane base structure which accomodates a plurality of said reverse bulbs.
  • the connector is adapted for heat abstraction from the photovoltaic cell to an active/passive heat sink.
  • the connector is adapted for electrical connection to the substrate holding said connector.
  • the connector is adapted to releasably connect to a bulb holder of a predetermined form.
  • the base structure is adapted for tracking the sun's position and optimally orienting a plurality of the reverse bulbs.
  • an external light-collecting member is used to concentrate light onto one or more reverse bulbs, increasing the concentration factor of the overall system.
  • a dust-repellent coating be used to coat the outer surfaces of the reverse bulbs of the present invention, such that the accumulation of dust on these outer surfaces is impeded.
  • a water-repellent coating be used to coat the outer surfaces of the reverse bulbs of the present invention, such that the accumulation of water on these outer surfaces is impeded.
  • an anti-reflection coating be used to coat the surfaces of the reverse bulbs of the present invention.

Abstract

The invention provides bulb like solar module that collects light, instead of emitting light in normal bulb. The module is used in a concentrating photovoltaic (CPV) system that is protected from the elements and associated aging effects, and that is easily installed and removed. The bulb includes: (a) a sealed housing in the form of a bulb whose face is transparent to incident solar radiation;(b) concentrating means in the form of a system of lenses and/or mirrors disposed so as to concentrate the incident solar radiation onto a small area within the housing;(c) a photovoltaic cell accommodated within the housing at the focus of the lens or mirror; (d) a connector adapted for mating and transferring electrical/thermal energy from the PV unit to the supporting frame.

Description

HIGH CONCENTRATION "REVERSE BULB" SOLAR PHOTOVOLTAIC
MODULE
FIELD OF THE INVENTION
The present invention relates to a solar energy converter and, more specifically, a modular, sealed photovoltaic module provided with a very highly concentrating optical system suitable for low cost mass production. The design of the current invention introduces maximal integration of primary and optional secondary optics, photovoltaic receiver, heat sink, connectors and enclosure, allowing for the .lowest possible cost of. High and very high concentrated photovoltaic (HCPV & VHCPV) systems. This is accomplished through highly automated manufacturing processes, as in use in the automotive, construction, and lighting industries. This unique design solves the typical challenges of HCPV & VHCPV modules such as: oxidation, expansion & contraction of internal air, exposure to moisture, and changing optical geometry of the expanding/contracting module elements.
BACKGROUND OF THE INVENTION
Amongst the various methods known for utilization of the sun's -energy, photovoltaic conversion stands out due to its direct conversion of sunlight into electricity, and its potential for long service life. Due to the relatively high cost of solar photovoltaic material and modules, as well as their often higher efficiencies at higher levels of incident radiation, a known technique for reducing costs of photovoltaic modules is to concentrate the incident sunlight by use of lenses or mirrors to concentrate a higher flux of light onto a smaller surface area of photovoltaic material.
Keeping the photovoltaic element in operating order for as long as possible is important in light of the fact that the cost of a solar module often is amortized over a time scale of 20-25 years. The degradation processes of HCPV & VHCPV photovoltaic elements and secondary optics (if used) may be appreciably arrested by maintaining these elements in vacuum, controlled atmospheres where oxidation & moisture is prevented, or under protective layers of e.g. epoxy. The use of protective layers, however, involves unavoidable losses as the light enters and leaves a region of differing refractive index. Also, in the case of Very Highly Concentrating systems, the accurate alignment of the concentrating optics must also be maintained over the lifetime of the device.
For an example of a concentrating photovoltaic system in the prior art we turn to U.S. Pat. 4045-246, which provides -a solar module with a composite parabolic solar energy concentrator and a solar receiver disposed in an outlet section and cooled by means of a liquid. The module is constructed as follows: the concentrator, having a reflecting surface, is contrived as a discrete assembly, the outlet cross section whereof contains a sealed chamber, with a photoreceiver disposed on the bottom thereof. The liquid circulating inside the sealed chamber operates as a heat-transfer medium. An inlet section of the concentrator is covered with a transparent material The liquid coolant in the space in front of the solar receiver results in high losses of light passing through the layer of liquid and in the reduction of the photoreceiver efficiency. Due to the use of separate pieces and possibly different materials, the joints between the concentrator and the sealed chamber wherein the receiver is disposed and the liquid is circulating, and between the concentrator and the transparent material in the inlet section, do not provide for reliable long-term sealing of the concentrator reflecting surface. Thus environmental effects may degrade the unit. These environmental effects will generally include oxidation, and differences in thermal expansion coefficients which eventually lead to separation and/or cracking. The result is that the properties of the concentrator reflecting surface are impaired and the concentrator's efficiency is decreased. Furthermore the unit must be assembled in its entirety from discrete elements that must be glued, bolted, or otherwise attached in a non-trivial manner which will involve some investment of time and resources.
US Patent 4491683 ('683) discloses a low concentration solar photovoltaic module comprising a composite parabolic solar energy concentrator having an aperture angle D and contrived in the form of a sealed gas-filled bulb (see Fig. Ia). The side walls of the bulb bend on a predetermined radius to a cylindrical part beside a concentrator radiation outlet surface which is coated with an inside reflecting coating. In accordance with '683, a photoreceiver having a cooling system is arranged inside the cylindrical portion of the bulb with a gap separating it from the walls. The cooling system disposed inside the concentrator bulb comprises a metal heat sink with air cooling ribs. The invention prolongs the service life of the module, improves its dependability and efficiency, and reduces its cost. From the standpoint of heat dissipation and electrical connection it is often desirable to put the photovoltaic element at the base of the unit, such that the heat and electric conductors do not block the incoming sunlight. Thus what has been done e.g. in US patent 4491683 is to truncate the bottom of the parabola at the focal plane, and place the photovoltaic module at the focal plane (see Fig. Ia). The photovoltaic receiver 4 occupies the full area of the focal plane, less the small gaps Δ. It will be shown in the detailed description that such an arrangement limits the possible concentration factor. For example, for a parabolic collector with a height H of 20cm, and a photovoltaic sidelength of 10cm, the maximum concentration factor possible is 4. This figure could be increased by using a smaller PV module, at the expense of wasting that sunlight incident past the edge of the PV module. It will be seen in the description of the sealed photovoltaic element of the instant invention that this problem of limited possible concentration factor is eliminated by changing the optical configuration in several possible ways- Furthermore the use of a cylindrical neck in this device to spread the light more evenly is a cause for extra reflections, which will tend to reduce the efficiency of the device since each reflection involves an unavoidable loss.
Another known problem with concentrating systems is that in general there is a trade-off between the degree of concentration and the required accuracy of alignment (between the focusing system and the sun and between the focusing system and the photovoltaic element). As the concentration factor increases, the required alignment accuracy generally increases as well. Any highly-concentrating system will suffer from this problem unless appropriate measures are taken, such as the addition of secondary optics. An advantage of the sealed photovoltaic element is that the alignment between focusing system and photovoltaic element is fixed within the sealed enclosure and cannot be interfered with or disturbed by the elements, cleaning operations, and the like.
Finally, it will be noticed that the aforementioned cleaning operation will be greatly facilitated by a flat collector geometry. Cleaning the curved surface of e.g. US patent '683 will generally require complicated mechanism or human attention to each unit , whereas a flat,uniform surface may be dealt with robotically or at least more quickly than otherwise.
Similarly, US patent 4166917 discloses a sealed glass bulb enclosing a photovoltaic element (see Fig. Ib). This bulb, like that of US patent 4491683, has a curved front surface which will prove more dificult to clean than a flat surface of comparable area, and a mirror concentrating incident radiation onto a photovoltaic cell location in the focal plane, with subsequent limited maximum concentration factor. It should be pointed out that US patent 4491683 refers to US patent 3923881 in connection with the shape of the side wall, which is described in US 3923881 as being '..any substantially smooth non-convex line falling within..' the area contained between a straight line and a parabola (column 3 line 66). The acceptance angle is the range of angles from which inoming light will still hit the photovoltaic element. The range of shapes in US 3923881 is provided to allow as large as possible an acceptance angle such that sun-tracking is unneeded or requires low precision. However as noted above, the provision for high acceptance angle necessarily comes at the cost of lower concentration ratios. For highly concentrating systems, such sidewalls are not suitable.
As can be seen above, the prior art concerning photovoltaic systems in sealed enclosures do not provide high concentration factors due to inevitable compromises in their design. Providing a sealed compact solar photovoltaic module with improved optics for high concentration factors is an unmet and long-felt need.
SUMMARY OF THE INVENTION
It is hence one object of the invention to disclose a sealed photovoltaic module or 'reverse bulb' (so-called due to its similarity to a light-bulb that receives instead of emitting light). This bulb provides very high concentration factors and, in some embodiments, a flat front face. The preferred embodiment provides a connector at the base, which allows for easy attachment and removal of the bulb, and provides conductors for electrical connection and heat extraction. The connector is adapted for connecting the unit to a substrate, for connecting the photovoltaic cell to an electrical load, and means for conducting heat away from the photovoltaic element.
It is an object of the present invention to provide a reverse bulb comprising:
(a) a sealed housing having a top face, said top face being transparent to incident solar rays, and said top face being so formed as to direct incoming radiation onto a focal area within said sealed housing;
(b) a photovoltaic cell accommodated within said housing, said photovoltaic cell being located at or near said focal area;
(c) a heat collector in thermal contact with said photovoltaic cell;
(d) a connector adapted for reversibly connecting the bottom of said reverse bulb to a substrate mechanically, while also connecting said photovoltaic cell to an electrical load, and connecting said heat collector to a heat sink; wherein the sealed assembly prevents oxidation and corrosion of said photovoltaic cell, and wherein the degree of concentration of solar radiation may reach values of concentration in the range from 10-10000.
It is a further object of the invention to provide the reverse bulb of described above further provided with secondary optics attached to said photovoltaic cell, to allow incoming radiation to be evenly spread over ihe photovoltaic surface. It is a further object of the present invention to provide the reverse bulb described above where said top face is flat.
It is a further object of the present invention to provide the reverse bulb described above or any of its dependent claims, where the form of said top face is that of a Fresnel lens of profile selected from a group consisting of circular, square, octangular, symmetric, and asymmetric, and wherein the top face is largely planar allowing for easy cleaning or curved to suit the optical requirements.
It is a further object of the present invention to provide the reverse bulb described above, where the form of said top face is selected from a group consisting of: a converging lens, a spherical lens, an aspherical lens.
It is a further object of the present invention to provide a reverse bulb comprising:
(a) a sealed housing having a top face, said top face being transparent to incident solar rays, and having reflective side faces disposed to reflect incoming radiation onto a focal area;
(b) a photovoltaic cell accommodated within said housing at or near said focal area;
(c) a heat collector in thermal contact with said photovoltaic cell;
(d) a connector adapted for connecting the bottom of said reverse bulb to a substrate mechanically, while also connecting said photovoltaic cell to an electrical load and connecting said heat collector to a heat sink; wherein the sealed assembly prevents oxidation and corrosion of said photovoltaic cell, and wherein the degree of concentration of solar radiation may reach very high values of concentration,
It is a further object of the present invention to provide the reverse bulb described above wherein said top face is planar, allowing for easy cleaning of the light-receiving surface.
It is a further object of the present invention to provide the reverse bulb described above, where said reflective side faces are provided with a shape selected from a group consisting of: parabola, near-parabolic, spherical, and aspherical.
It is a further object of the present invention to provide the reverse bulb described above, where said photovoltaic element is located at or below the focal plane of said side faces. It is a further object of the present invention to provide the reverse bulb described above, where said photovoltiac element is located at or above or below the focal plane of said side faces.
It is a further object of the present invention to provide the reverse bulb described above, further provided with a second reflecting element in Newtonian configuration adapted to reflect incident radiation onto said photovoltaic cell.
It is a further object of the present invention to provide the reverse bulb described above, further provided with a second reflecting element of low concentration total internal reflection such as composite parabolic concentrator as part of the sealed housing adapted to lead and homogenize incident radiation onto said photovoltaic cell.
It is a further object of the present invention to provide the reverse bulb described above wherein said sealed housing is evacuated to a pressure of less than 10 mbar.
It is a further object of the present invention to provide the reverse bulb described above wherein said housing is filled with gas.
It is a further object of the present invention to provide the reverse bulb described above, wherein said gas is selected from the group consisting of: hydrogen, nitrogen, -helium, neon, argon, krypton, xenon, radon, and any combination thereof.
It is a further object of the present invention to provide the reverse bulb described above additionally provided with an external light collector adapted to direct or concentrate additional light onto said top face.
It is a further object of the present invention to provide the reverse bulb described above additionally provided with a heat engine in thermal communication with said connector adapted for providing energy from the waste heat of said reverse bulb.
It is a further object- of the present invention to provide the reverse bulb described above, additionally comprising a substantially planar substrate element adapted to reversibly connect to a plurality of said reverse bulbs by means of said connectors, said base structure being adapted for rotation along two axis to track the sun's position and thereby optimally orient said reverse bulbs.
It is a further object of the present invention to provide a method for highly or very highly- concentrated photovoltaic conversion of solar radiation comprising:
(a) providing a sealed housing having a top face, said top face being transparent .to incident solar rays, said top face being so formed as to concentrate radiation onto a focal area within said sealed housing; (b) providing a photovoltaic cell accommodated within said housing, said photovoltaic cell being located at or near said focal area;
(c) providing a heat collector in thermal contact with said photovoltaic cell;
(d) providing a connector adapted for connecting the bottom of said reverse bulb to a substrate mechanically, while also connecting said photovoltaic cell to an electrical load and connecting said heat collector to a heat sink;
(e) connecting said connector to said electrical load and said heat sink; wherein the sealed assembly prevents oxidation and corrosion of said photovoltaic cell and optical and mechanical elements, and wherein the degree of concentration of solar radiation may reach very high values in the range 10-10,000.
It is a further object of the present invention to provide the method described above where the form of said top face is that of a Fresnel lens, and wherein the top face is largely planar allowing for easy cleaning & optimizing light collection area.
It is a further object of the present invention to provide the method described above where the form of said top face is selected from a group consisting of: a converging lens, a spherical lens, an aspherical lens.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to understand the invention and to see how it may be implemented in practice, a plurality of embodiments is adapted to now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which
Figs. IA-B is prior art showing sealed photovoltaic collectors disclosed in US patent 4166917 and US patent 4491683, respectively;
Figs. 2A-B illustrates the geometrical properties of a parabola; Fig. 3 is a schematic view of the confocal concentrating optical system;
Fig. 4 is an isometric view of the reverse bulb;
Fig. 5 is an exploded view of the reverse bulb;
Fig. 6 is prior art depicting a tracking system;
Fig. 7 is a schematic view of the mass producible sealed reverse bulb.
Fig. 8 is a schematic view of the reverse bulb with a secondary Newtonian reflector.
Fig. 9 is a schematic view of the reverse bulb with reflecting sides and the PV cell and diffusing optic at the top.
Fig. 10 is a schematic view of the reverse bulb with a reflecting parabolic sides and diffusing optic at the focal plane.
Fig. 11 is a schematic view of the reverse bulb with a spherical collecting surface.
Fig. 12 is a schematic view of the reverse bulb with a Fresnel mirror and the PV collector at the top.
Fig. 13 is a schematic view of the reverse bulb with a planar collector that directs light to the PV collector at one side.
Fig. 14 is a schematic view of a plurality of reverse bulbs installed at the focus of a parabolic trough.
DETAILED DESCRIPTION OF THE INVENTION
The following description is provided, alongside all chapters of the present invention, so as to enable any person skilled in the art to make use of said invention and sets forth the best modes contemplated by the inventor of carrying out this invention. Various modifications, however, are adapted to remain apparent to those skilled in the art, since the generic principles of the present invention have been defined specifically to provide a sealed very highly concentrating solar photovoltaic module and a method of using the same.
The term 'concentrated' refers to ~10X concentration.
The term 'highly-concentrated' refers to ~1OOX concentration.
The term 'very-highly concentrated' refers to -1000X concentration. The term 'Newtonian optics' refers to the light-collecting configuration of Newton's telescope wherein light is reflected from a parabolic mirror onto a secondary mirror, and from there to a receiving surface such as a detector,an eye, or a photovoltaic converter.
The term 'PV refers to a photovoltaic cell, this being an element adapted for conversion of incident radiation into electrical current.
The core of the present invention is to disclose and provide a photovoltaic system with the following properties:
1. sealed enclosure
2. highly concentrating optics
3. flat front face in most embodiments
The use of a sealed enclosure has several advantages: a. Prevents exposure of the photovoltaic cell to various possibly damaging factors such as oxidation, collection of dust, rain/moisture. b. Maintains precise optical alignment between concentrating optics and photovoltaic element, which is critical in high concentration-coefficient systems. c. Optionally the sealed enclosure may be filled with a working liquid such as water, which has high heat capacity. This allows the entire photovoltaic element to be surrounded by the working liquid, which allows for faster heat dissipation [mainly through convection and conduction] than would be possible otherwise [mainly through conduction/radiation]. By using a working fluid with an index of refraction matched to the glass of the outer enclosure, the device can improve upon the sealed enclosures known (c.f. US patent 4166917 and US patent 4491683) since there will be only one interface of refractive mismatch, namely the first air-glass interface. The glass-fliud interface, if properly index-matched, will not cause such a loss since the amount of loss is proportional to the index mismatch:
2π,
R = ni + n2
Systems with sealed enclosures are known (c.f. US patent 4166917 and US patent 4491683) which use truncated parabolic or near-parabolic concentrating elements with the photovoltaic element located at the focal plane of the parabola. We now show below that, for the inventions of patents '917 and '683 and their ilk, the concentration factor possible using a PV collector at the focal place of a truncated parabola ( Fig. 2a,b) is limited to the ratio of the height of the sealed enclosure to the radius of the photovoltaic element.
From the equation of a parabola 201 y = ax2 Eq. 1
and the distance 202 between the focal point and the bottom of the parabola:
F = - Eq. 2
Aa
it can be seen that the radius xi0Wer 205 of the parabola at the focal plane (y=F), where the photovoltaic element is placed, is
W = 2F Eq. 3
The photovoltaic element will preferably extend out to this radius, since if it does not, the sunlight incoming past the edge of the photovoltaic element is lost, (see Fig. 2b). If some maximum height H is stipulated for the unit, due to practical constraints, then the radius 204 of the parabola at this height is found using Eqs. 1,2
χ∞r = 2VHF Eq. 4
The concentration factor is the ratio of the light input area to the light output area, which will in this case be
c =pw/| = H Eq 5
V X lower ) r
Since the photovoltaic module has some minimum size xmm , it is clear that the concentration factor must be limited, to n H 2H
C = — = Eq. 6
F *m,n Recapitulating the example used in the background, for a parabolic collector with an already unwieldy height H of 20cm, and a photovoltaic half-sidelength xmm of 10cm, the maximum concentration possible in such a system is 4. For much higher concentrations such as about 1000, one would need to use a photovoltaic module of very small non standard size or to increase the height of the unit to large dimensions which in turn would increase the weight and fragility of the units (especially when considering that the unit is preferably constructed from glass which has a low thermal expansion coefficient).
The following embodiments of the invention are directed towards providing and disclosing means and methods of concentrating solar radiation at concentration factors of at least about 1000. Reference is now made to Fig. 3, presenting an embodiment of a sealed confocal concentrating optical system of the current invention 100, comprising a front Fresnel lens 10, a focal point 20, and a second optical element 40. Sun rays pass through the lens 10, incident in a direction parallel to the optical axis 15. The front lens can be a Fresnel lens as mentioned or in general a diffraction optical element providing conversion of the parallel sunlight beam into a converging beam that converges at the focal point 20. In accordance with one embodiment of the current invention, a second optical element 40 is disposed confocally relative to the first optical element 10 so that the diverging light beam propagating after the focal point 20 is converted into a parallel beam. The proposed photovoltaic module combines high coefficient of concentration and compactness of the device, and the second optical element allows the incoming light to be spread evenly over the receiving photovoltaic element 30. It should be noted that the use of a second optical element 40 is not strictly necessary to spread the incoming light from a point to an evenly-spread spot, for several reasons. Firstly, the top lens 10 may be constructed in such fashion that the incoming light converges to a spot instead of a point. Second, the photovoltaic element may be placed above or below the focal point, where the incoming rays will form a spot instead of a point. Third, the angular size of the sun itself will inevitably serve to spread out the focal point into a spot of a size determined by the focal length. By use of one or more of these effects, the use of a secondary spreading optic can be avoided. This point holds for all the embodiments mentioned below.
Reference is now made to Fig. 4, showing an exemplary embodiment of a solar photovoltaic installation 400. The aforesaid installation includes a base member 401 which holds a plurality of reverse bulbs 402. The base member has internal channels [not seen] that contain wires to conduct electrical current, as well as means for extraction of heat from the reverse bulbs. This heat extraction means may take one of several forms: either additional channels for active, forced conduction of a flowing heat-extracting medium such as oil or water, or means for passively dissipating heat directly from the base member, such as heat-sink fins or the like. Heat sink fins may for example be disposed on the underside of the base member.
According to one embodiment the reverse bulbs are maintained under vacuum for extending the operation life by preventing the atmosphere from acting on photovoltaic cell e.g. through oxidation. The standard epoxy coating on the PV elements themselves can therefore be dispensed with, eliminating the front and back interfaces. It is within the scope of the invention to fill the reverse bulbs with any suitable gases or liquids as well, including hydrogen, noble gases, and heat-conducting liquids such as water, oil, and alcohol.
Reference is now made to another possible embodiment of the instant invention, shown in Fig. 5 in an exploded view. The parabolic, near-parabolic, spherical or aspherical surface 501 is mirrored on its inner surface, allowing light to be conducted to the diffusive element 502 which spreads the incoming light evenly upon the photovoltaic element 503. The base member 505 holds the entire unit in place, as it can be locked securely into a substrate by suitable means such as holes 504 through which the unit is screwed down onto the substrate. Conductors 506 are provided to conduct electricity, and in some embodiments heat as well is conducted by these or additional members. In some embodiments independent conductors are used for electricity and heat, for example two conductors for electricity and a third and fourth for heat. This third and fourth conductor could comprise hollow tubes for conducting liquid and thus transferring heat by convection, or solid rods of e.g. metal for transfer of heat by conduction.
Reference is now made to the prior art Fig. 6, showing a standard tracking system adapted to provide an optimal angle of incidence of the sunrays on the collecting surface 601. The tracking system comprises a support 603, the collecting surface 601, and tracking means 602 for changing the orientation of the collecting surface with respect to the support. The tracking means 602 orients the collecting surface to be normal to the Sun as the latter traverses on celestial sphere, to provide parallelism of the sunrays and optical axis of the optical system of the reverse bulbs of the system. By means of the tracking system, the requirement for a large acceptance angle from which incoming light is focused onto the photovoltaic element, is removed. The reverse bulbs of the system, for instance on a substrate as in Fig. 4, are preferably attached to a tracking system such as shown in Fig. 6.
Reference is now made to Fig. 7, illustrating ; the reverse bulb 700 adapted for mass production at existing means of production, such as light-bulb production lines (with certain obvious modifications to the line as will be obvous to one skilled in the art). The reverse bulb body 701 is made similarly to the body of a conventional light bulb. In accordance with one embodiment of the current invention, the top of the reverse bulb is provided with a focusing element 705, for example a Fresnel lens impressed into the bulb glass at the time of manufacture. Formation of the Fresnel lens can be performed while the glass of the bulb is in a molten or otherwise malleable state, and eliminates a need for attachment of a separate lens. The interior of the bulb is either filled with a noble gas, another suitable gas, a working liquid, or maintained in a partial vacuum. The interior of the bulb is optionally provided with a diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, increasing the angular acceptance of the system and decreasing the requisite tracking accuracy. The system is preferably provided with a modular connecting system such as a base 703 provided with holes 706 for easy and reversible attachment to a substrate member. The base 703 of the system will be preferably provided with conductors made a highly heat-conductive material to allow for dissipation of waste heat from the system.
As in a light bulb, the use of a noble gas or vacuum will be found to have beneficial effects for the photovoltaic elements, chiefly that oxidation can be reduced or eliminated. Thus the lifetime of the system can be greatly enhanced. The use of a sealed system has the further benefit that the fine alignment between optical elements and photovoltaic module is now preserved and isolated from any disturbance. It may be found that use of a light-transmissive fluid of high heat capacity or conductivity such as hydrogen or water may increase the rate of heat conduction away from the photovoltaic module, which is a key concern in highly concentrating systems due to the high amount of power incoming to the system. This fluid can be sealed within the unit or may be forced in and out of the unit through channels communicating with the outside of the otherwise-sealed unit. Modern high-efficiency PV cells of e.g. 30% efficiency leave 70% of the incoming radiation to heat the PV module, which must be cooled by some means to prevent extreme heating. The efficiency of such PV cells generally decreases with temperature making it doubly important to keep the PV unit as cool as possible.
Reference is now made to Fig. 8, illustrating another embodiment of the reverse bulb, with optional diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, and base 703 for easy and reversible attachment to a base member. This embodiment is provided with a reflective coating on the inside of the glass 701 and secondary Newtonian-type reflector 707. The reflective coating serves as a parabolic or non-parabolic mirror which reflects light onto the secondary Newtonian reflector 707, from which the light is again reflected onto the optional diffusive optic 702 and from there onto the photovoltaic converter 704. This embodiment uses mirrored surfaces instead of a lens. Visible also are the heat and/or electrical conductors 708 as well as the holes 706 for connecting the device to a substrate.
Reference is now made to Fig. 9, illustrating another embodiment of the reverse bulb, with optional diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, and base 703 with holes 706 for easy and reversible attachment to a substrate member. This embodiment is also provided with a reflective coating on the inside of the sealed enclosure 701. This reflective coating serves as a parabolic or non-parabolic mirror which reflects light onto the optional diffusive optic 702. However in this embodiment the diffusive optic 702 and photovoltaic element 704 are located at the top surface of the bulb, eliminating the need for a second Newtonian reflecting surface. This embodiment also uses a mirrored surface instead of a lens. In this case the electrical and heat conductors 708 traverse the entire length of the bulb to reach the photovoltaic element 704 at the top of the bulb.
Reference is now made to Fig. 10, illustrating another embodiment of the reverse bulb 701, with optional diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, and base 703 provided with holes 706 for easy and reversible attachment to a base member. This embodiment also uses a mirrored surface instead of a lens, and places the diffusive optic at the focal plane. Note that the size of the photovoltaic element is not as large as the full parabola width at the focal plane, but may be significantly smaller, thus avoiding the limitation described in Eq. 6 on the concentration ratio. Obviously all the other embodiments listed above avoid this limitation as well, since the photovoltaic element is not located at the focal plane or is significantly smaller than the full parabolic width at the focal plane.
Reference is now made to Fig. 11, illustrating another embodiment of the reverse bulb 701, with optional diffusive optic 702 that diffuses the incident radiation onto the full area of the photovoltaic element 704 from a range of incident angles, and base 703 for easy and reversible attachment to a substrate member. This embodiment uses a lens- or sphere-shaped top surface, and places the diffusive optic at the focal plane. We note that all the other embodiments have smooth or nearly-smooth top surfaces; this embodiment is the only one without a smooth top surface. As before the electrical/thermal connectors 708 conduct electricity and/or heat from the photovoltaic element.
Reference is now made to Fig. 12 showing en embodiment wherein a series of concentric circular mirrors 709 reflect incoming light onto the photovoltaic receiver 704. The material of the cylindrical body 710 may be for instance epoxy or glass, as long as it is largely transparent to incoming solar radiation. This material is preferable endowed with high heat conductivity. Conductors abstract heat and electricity from the PV cell as in the other embodiments.
Reference is now made to Fig. 13 which is an embodiment wherein a flat light-absorbing plate 710 is utilized to conduct light to the PV cell 704, which as before is connected through base member 703 to a substrate, and connects electrically and thermally by means of connectors 708. The slab is constructed in a manner similar to that of an LCD BLU (backlight unit), and is adapted to collect light from the entire surface of the plate 710 and conduct it to the photovoltaic elements 704. This backlight unit is covered with a one way coating that allows the light in but serves as a total internal reflector to enhance light absorption by the PV cell. Such a one-way mechanism can be accomplished after the fashion of a Faraday isolator, volume diffractive element, phase diffractive element, or the like as will be obvious to one skilled in the art.
The reader should appreciate that due to the modular and easily-implemented nature of the reverse bulb of the present invention, it can be used as a 'plug-in' photovoltaic collector placed at the focus of a larger system. For example, one may imagine a parabolic trough provided with a series of reverse bulbs in a line at the focus of the parabolic trough. Such a system is shown conceptually in Fig. 14 where one can see a series of reverse bulbs 1401 of the current invention, which are located at the focus of the parabolic trough 1402. The bulbs are held in place by the bulb-holding substrate 1403 which conducts heat and electrical energy away from the reverse bulbs. It will be appreciated that such a compound system can reach extremely high concentration factors due to the multiplication of the individual concentration factors of the two systems comprising the compound system. The focus of larger system can also be rather diffuse as light only needs to reach the relatively large surfaces of the reverse bulbs.
In it is within provision of the invention to provide a sealed enclosure containing a photovoltaic element and converging optics so disposed as to concentrate incident radiation by a large concentration factor of between 10 and 10,000.
It is within the scope of the invention to provide a heat engine adapted to utilize the waste heat conducted out of a plurality of reverse bulbs and produce electrical or mechanical energy thereby.
In accordance with a further embodiment of the current invention, the primary and secondary optical elements are chosen from a group consisting of a refractive optical element, a reflective optical element, a Fresnel lens, a relief diffractive optical element, an absorptive diffractive optical element, a volume phase diffractive optical element, and any combination thereof.
In accordance with one embodiment of the current invention, a top refractive unifying optical element is provided in the form of a Fresnel lens of circular symmetry.
In accordance with a further embodiment of the current invention, a reflective unifying optical element is provided that is parabolic in profile.
In accordance with a further embodiment of the current invention, a side reflective unifying optical element is provided that is near-parabolic in profile.
In accordance with a further embodiment of the current invention, a side reflective unifying optical element is provided that is parabolic or near-parabolic in profile, and a top second reflective optical element in Newtonian configuration is provided.
In accordance with a further embodiment of the current invention, the photovoltaic element is located at the top face of the unit.
In accordance with a further embodiment of the current invention, the front face of the unit is provided in the shape of a converging lens.
In accordance with a further embodiment of the current invention, a diffusive optical element is provided that directs incoming radiation onto the area of the photovoltaic element.
In accordance with a further embodiment of the current invention, the unifying element is disposed confocally to the focusing element.
In accordance with a further embodiment of the current invention, the housing is maintained under vacuum of less than 10 mbar.
In accordance with a further embodiment of the current invention, the housing is filled with gas.
In accordance with a further embodiment of the current invention, the filled gas is selected from the group consisting of: helium, neon, argon, krypton, xenon, radon, and any combination thereof.
In accordance with a further embodiment of the current invention, the housing is filled with fluid.
In accordance with a further embodiment of the current invention, the reverse bulbs are provided with the connectors adapted to releasably connect to a substantially plane base structure which accomodates a plurality of said reverse bulbs. In accordance with a further embodiment of the current invention, the connector is adapted for heat abstraction from the photovoltaic cell to an active/passive heat sink.
In accordance with a further embodiment of the current invention, the connector is adapted for electrical connection to the substrate holding said connector.
In accordance with a further embodiment of the current invention, the connector is adapted to releasably connect to a bulb holder of a predetermined form.
In accordance with a further embodiment of the current invention, the base structure is adapted for tracking the sun's position and optimally orienting a plurality of the reverse bulbs.
In accordance with a further embodiment of the current invention, an external light-collecting member is used to concentrate light onto one or more reverse bulbs, increasing the concentration factor of the overall system.
It is within the scope of the invention to utilize the heat energy extracted from the reverse bulbs described to operate a heat engine of any variety, to further utilize the incoming solar energy that is not utilized by the photovoltaic converter.
It is within provision of the invention that a dust-repellent coating be used to coat the outer surfaces of the reverse bulbs of the present invention, such that the accumulation of dust on these outer surfaces is impeded.
It is within provision of the invention that a water-repellent coating be used to coat the outer surfaces of the reverse bulbs of the present invention, such that the accumulation of water on these outer surfaces is impeded.
It is within provision of the invention that an anti-reflection coating be used to coat the surfaces of the reverse bulbs of the present invention.

Claims

CLAIMS:
1. A reverse bulb comprising:
(a) a sealed housing having a top face, said top face being transparent to incident solar rays, and said top face being so formed as to direct incoming radiation onto a focal area within said sealed housing;
(b) a photovoltaic cell accommodated within said housing, said photovoltaic cell being located at or near said focal area;
(c) a heat collector in thermal contact with said photovoltaic cell;
(d) a connector adapted for reversibly connecting the bottom of said reverse bulb to a substrate mechanically, while also connecting said photovoltaic cell to an electrical load, and connecting said heat collector to a heat sink; wherein the sealed assembly prevents oxidation and corrosion of said photovoltaic cell, and wherein the degree of concentration of solar radiation may reach values of concentration in the range from 10-10000.
2. The reverse bulb according to claim 1 or any of its dependent claims, where the form of said top face is that of a Fresnel lens of profile selected from a group consisting of circular, square, octangular, symmetric, and asymmetric, and wherein the top face is largely planar allowing for easy cleaning & to maximize light collection area or curved to suit the optical requirements.
3. The reverse bulb according to claim 1 or any of its dependent claims, where the form of said top face is selected from a group consisting of: a converging lens, a spherical lens, an aspherical lens.
4. The reverse bulb according to claim 1 or any of its dependent claims further provided with reflective secondary optics in the form of a parabolic mirror deposited on the interior of said housing adapted to reflect incident radiation homogenously onto said photovoltaic cell.
5. A reverse bulb comprising:
(a) a sealed housing having a top face, said top face being transparent to incident solar rays, and having reflective side faces disposed to reflect incoming radiation onto a focal area;
(b) a photovoltaic cell accommodated within said housing at or near said focal area; (c) a heat collector in thermal contact with said photovoltaic cell;
(d) a connector adapted for connecting the bottom of said reverse bulb to a substrate mechanically, while also connecting said photovoltaic cell to an
. electrical load and connecting said heat collector to a heat sink; wherein the sealed assembly prevents oxidation and corrosion of said photovoltaic cell, and wherein the degree of concentration of solar radiation may reach very high values of concentration,
6. The reverse bulb of claim 5 wherein said top face is planar, allowing for easy cleaning of the light-receiving surface.
7. The reverse bulb according to claim 5 or any of its dependent claims, where said reflective side faces are provided with a shape selected from a group consisting of : parabola , near-parabolic, spherical, and aspherical.
8. The reverse bulb according to claim 5 or any of its dependent claims, where said photovoltaic element is located at or below the focal plane of said side faces.
9. The reverse bulb according to claim 5 or any of its dependent claims, where said photovoltaic element is located at or above the focal plane of said side faces.
10. The reverse bulb according to claim 5 or any of its dependent claims, further provided with a second reflecting element in Newtonian configuration adapted to reflect incident radiation onto said photovoltaic cell.
11. The reverse bulb according to claim 1, claim 5, or any one of their dependent claims, further provided with secondary optics attached to said photovoltaic cell, adapted to allow incoming radiation to be evenly spread over the photovoltaic surface.
12. The reverse bulb according to claim 1, claim 5, or any one of their dependent claims, where said top face is flat.
13. The reverse bulb according to claim 1, claim 5, or any one of their dependent claims, wherein said sealed housing is evacuated to a pressure of less than 10 mbar.
14. The reverse bulb according to claim 1, claim 5, or any one of their dependent claims, wherein said housing is filled with gas.
15. The reverse bulb according to claim 14, wherein said gas is selected from the group consisting of: hydrogen, nitrogen, helium, neon, argon, krypton, xenon, radon, and any combination thereof.
16. The reverse bulb according to claim 1, claim 5, or any one of their dependent claims, aditionally provided with an external light collector adapted to direct additional light onto said top face.
17. The reverse bulb according to claim 1, claim 5, or any one of their dependent claims, aditionally provided with a heat engine in thermal comunication with said connector adapted for providing energy from the waste heat of said reverse bulb.
18. The reverse bulb according to claim 1, claim 5, or any of their dependent claims, additionally comprising a substantially planar substrate element adapted to reversibly connect to a plurality of said reverse bulbs by means of said connectors, said base structure being adapted for rotation along two axis to track the sun's position and thereby optimally orient said reverse bulbs.
19. A method for highly-concentrated photovoltaic conversion of solar radiation comprising:
(a) providing a sealed housing having a top face, said top face being transparent to incident solar rays, said top face being so formed as to concentrate radiation onto a focal area within said sealed housing;
(b) providing a photovoltaic cell accommodated within said housing, said photovoltaic cell being located at or near said focal area;
(c) providing a heat collector in thermal contact with said photovoltaic cell;
(d) providing a connector adapted for connecting the bottom of said reverse bulb to a substrate mechanically, while also connecting said photovoltaic cell to an electrical load and connecting said heat collector to a heat sink;
(e) connecting said connector to said electrical load and said heat sink; wherein the sealed assembly prevents oxidation and corrosion of said photovoltaic cell and optical and mechanical elements, and wherein the degree of concentration of solar radiation may reach very high values in the range 10-10,000.
20. The method according to claim 19, where the form of said top face is selected from a group consisting of: a converging lens, a spherical lens, an aspherical lens.
21. The method according to claim 19 or any of its dependent claims further provided with reflective secondary optics in the form of a parabolic mirror deposited on the interior of said housing adapted to reflect incident radiation homogeηously onto said photovoltaic cell.
22. A method for photovoltaic conversion of solar radiation comprising:
(a) providing a sealed housing having a top face, said top face being transparent to incident solar rays, and having reflective side faces disposed to reflect incoming radiation onto a focal area;
(b) providing a photovoltaic cell accommodated within said housing at or near said focal area;
(c) providing a heat collector in thermal contact with said photovoltaic cell;
(d) providing a connector adapted for connecting the bottom of said reverse bulb to a substrate mechanically, while also connecting said photovoltaic cell to an electrical load;
(e) connecting said connector to an electrical load; wherein the sealed assembly prevents oxidation and corrosion of said photovoltaic cell, and wherein the degree of concentration of solar radiation may reach very high values, and wherein said top face could be largely planar allowing easy cleaning.
23. The method according to claim 22 where said reflective side faces are provided with a shape selected from a group consisting of: a parabola, near-parabolic shape, spherical, aspherical.
24. The method according to claim 22 or any of its dependent claims, where said photovoltiac element is located at or below the focal plane of said side faces.
25. The method according to claim 22 or any of its dependent claims, further provided with a second reflecting element in Newtonian configuration.
26. The reverse bulb according to claim 19, claim 22 or any of their dependent claims, further provided with secondary optics of low or negative concentration factor attached to said photovoltaic cell, adapted to allow incoming radiation to be evenly spread over the photovoltaic surface.
27. The method according to claim 19, claim 22 or any of their dependent claims, wherein said sealed housing is evacuated to a pressure of less than 10 mbarl
28. The method according to claim 19, claim 22, or any of their dependent claims, wherein said sealed housing, is filled with gas.
29. The method according to claim 28- wherein said gas is selected from the group consisting of: hydrogen, nitrogen, helium, neon, argon, krypton, xenon, radon, and any combination thereof.
30. The method according to claim 19, claim 22, or any one of their dependent claims, wherein said connector is adapted for heat abstraction from said photovoltaic cell to a heat sink adapted for removal of heat from said heat collector.
31. The method according to claim 19, claim 22, or any one of their dependent claims, additionally comprising a substantially planar base element adapted to reversibly connect to a plurality of said reverse bulbs by means of said connectors, said base structure adapted to be rotated in two dimensions to track the sun's position and optimally orient said reverse bulbs.
32. The method according to claim 19, claim 22, or any one of their dependent claims, aditionally provided with an external light collector to direct additional light onto said top face.
33. The reverse bulb according to claim 19, claim 22 or any one of their dependent claims, aditionally provided with a heat engine in thermal comunication with said connector adapted for utilizing energy from the waste heat of said reverse bulb.
34. The reverse bulb according to claim 19, claim 22 or any one of their dependent claims , where the form of said top face is that of a Fresnel lens of profile selected from a group consisting of circular, square, octangular, symmetric, and asymmetric, and wherein the top face is largely planar allowing for easy cleaning & to maximize light collection area or curved to suit the optical requirements combined with secondary optics of total internal reflection that is part of the sealed housing adapted to reflect & homogenize incident radiation onto said photovoltaic cell.
35. A planar back light unit adapted to collect light from the entire surface of said planar back light unit and conduct said light to a photovoltaic element disposed at one corner of said back light unit, said planar back light unit being adapted to utilize total internal reflection of the light therein so as to minimize loss of absorbed light.
36. The planar back light unit of claim 35 using an optical system selected from the group consisting of: a volume diffractive element, a phase diffractive element, a Faraday isolator.
PCT/IL2009/000958 2008-10-07 2009-10-11 High concentration "reverse bulb" solar photovoltaic module WO2010041249A1 (en)

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US61/103,286 2008-10-07

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