WO2008113837A2 - Heat management system for photovoltaic cell panels and led-based light sources - Google Patents

Heat management system for photovoltaic cell panels and led-based light sources Download PDF

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Publication number
WO2008113837A2
WO2008113837A2 PCT/EP2008/053331 EP2008053331W WO2008113837A2 WO 2008113837 A2 WO2008113837 A2 WO 2008113837A2 EP 2008053331 W EP2008053331 W EP 2008053331W WO 2008113837 A2 WO2008113837 A2 WO 2008113837A2
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WO
WIPO (PCT)
Prior art keywords
management system
heat
heat management
led
sheet
Prior art date
Application number
PCT/EP2008/053331
Other languages
French (fr)
Other versions
WO2008113837A3 (en
Inventor
Johannus Otto Rooymans
Taco Wijnand Neeb
Original Assignee
Lemnis Lighting Patent Holding B.V.
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 Lemnis Lighting Patent Holding B.V. filed Critical Lemnis Lighting Patent Holding B.V.
Publication of WO2008113837A2 publication Critical patent/WO2008113837A2/en
Publication of WO2008113837A3 publication Critical patent/WO2008113837A3/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/024—Arrangements for cooling, heating, ventilating or temperature compensation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/20—Light sources comprising attachment means
    • F21K9/23—Retrofit light sources for lighting devices with a single fitting for each light source, e.g. for substitution of incandescent lamps with bayonet or threaded fittings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/20—Light sources comprising attachment means
    • F21K9/27—Retrofit light sources for lighting devices with two fittings for each light source, e.g. for substitution of fluorescent tubes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
    • F21V29/50—Cooling arrangements
    • F21V29/70—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks
    • F21V29/74—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks with fins or blades
    • F21V29/76—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks with fins or blades with essentially identical parallel planar fins or blades, e.g. with comb-like cross-section
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
    • F21V29/50—Cooling arrangements
    • F21V29/70—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks
    • F21V29/74—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks with fins or blades
    • F21V29/77—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks with fins or blades with essentially identical diverging planar fins or blades, e.g. with fan-like or star-like cross-section
    • F21V29/773—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks with fins or blades with essentially identical diverging planar fins or blades, e.g. with fan-like or star-like cross-section the planes containing the fins or blades having the direction of the light emitting axis
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
    • F21V29/50—Cooling arrangements
    • F21V29/70—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks
    • F21V29/80—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks with pins or wires
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
    • F21V29/50—Cooling arrangements
    • F21V29/70—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks
    • F21V29/83—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks the elements having apertures, ducts or channels, e.g. heat radiation holes
    • 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
    • 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
    • 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
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B10/00—Integration of renewable energy sources in buildings
    • Y02B10/10—Photovoltaic [PV]
    • 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
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B10/00—Integration of renewable energy sources in buildings
    • Y02B10/20—Solar thermal
    • 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
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B10/00—Integration of renewable energy sources in buildings
    • Y02B10/70—Hybrid systems, e.g. uninterruptible or back-up power supplies integrating renewable energies
    • 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
    • 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 heat management systems for use with photovoltaic cell panels and LED-based light sources.
  • Heat sinks are typically made of a metal, in particular metals having a high heat conductivity. Dissipation of heat to the environment, such as a forced air flow, is increased by increasing the surface area of the heat sink, for example by providing fins at the surface of the heat sink.
  • the present invention provides improved heat management systems for use with photovoltaic cell panels and LED-based light sources.
  • the invention relates to a heat management system for use with photovoltaic cell panels or LED-based light sources comprising a body provided with a graphite-containing, thermally anisotropic material.
  • the graphite-containing, thermally anisotropic material is in the form of a flexible sheet.
  • the graphite-containing, thermally anisotropic sheet material may have a lateral heat conductivity on the order of 400 - 500 W/mK, and a transversal heat conductivity on the order of 20 - 50 VWmK.
  • the sheet may be provided with a heat path for permitting heat transport across a thickness of the sheet.
  • the invention further relates to a LED-based light source having such a heat management system.
  • the invention further relates to a photovoltaic cell panel having such a heat management system.
  • Figure 1 shows a LED-based light source designed to fit a fixture for an MR
  • Figure 2 shows a LED-based light source designed to replace a fluorescent tube, provided with a dedicated heat management system.
  • Figure 3 shows an alternate embodiment of the heat management system for the LED-based light source of figure 2.
  • Figure 4 shows a LED-based light source designed to replace a dual CFL, provided with a dedicated heat management system.
  • Figure 5 shows a first embodiment of a heat management system for use with a photovoltaic panel.
  • Figure 6 shows a second embodiment of a heat management system for use with a photovoltaic panel. DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
  • LED- based light sources convert about 10 - 15% of the electric energy to light; the remaining 85 - 90% is lost in the form of heat.
  • LEDs do not require a high temperature for emitting light. To the contrary, LEDs produce light more efficiently at a low temperature. Moreover, high temperatures are harmful to the semi-conducting materials of the LEDs. For these reasons it is essential to provide LED light sources with efficient cooling.
  • LEDs in LED-based iight sources such as used in traffic lights and automobile tail lights, are placed relatively far apart, to aid in heat dissipation.
  • LEDs may be used to produce white light of a pleasant color temperature by combining red, green and blue LEDs together in a close configuration. Due to the close proximity of the individual LEDs to each other, the emitted light becomes blended so that the human eye perceives it as one color. This color is white of the contributing colors are sufficiently balanced. However, the need for placing the LEDs closely together in order to obtain one blended color puts high demands on the cooling system of such an "RGB" LED light source.
  • LED-based iight sources that can be operated on household electric power, e.g. 1 17 V AC or 240 V AC.
  • EP 06124144.4 we disclose a rectifier bridge circuit that allows operation of LEDs on household power.
  • these LED-base light sources must have a galvanic insulation capable of withstanding up to 3,000 Volts. The need for galvanic insulation runs opposite to the need for providing cooling, as electrical insulators tend to be poor heat conductors.
  • Embodiments of the heat management systems of the present invention provide sufficient cooling to a LED-based light source to allow individual LEDs to be placed closely enough together for LEDs that emit light of different colors to be perceived as emitting one, blended, color.
  • the heat management systems of the present invention comprise a body provided with a graphite-containing, thermally anisotropic material, also referred to as anisotropic graphite, preferably in the form of a flexible sheet.
  • a graphite-containing, thermally anisotropic material also referred to as anisotropic graphite, preferably in the form of a flexible sheet.
  • Such materials are commercially available. Particularly suitable is Spreadersh ⁇ eld TM, available from Advanced Energy Technology, Lakewood, OH, USA.
  • These materials have a lateral (that is, in the plane of the sheet) heat conductivity on the order of 400 - 500 W/mK, and a transversal (that is, in a direction perpendicular to the plane of the sheet) of only 20 - 50 W/mK.
  • heat paths may be in the form of metal rivets, preferably copper or aluminum rivets.
  • Materials of this kind are commercially available, for example zSPREADERTM from Advanced Energy Technology, Lakewood, OH, USA.
  • Figure 1 shows a heat management system for a LED-based light assemble designed for replacing an MR-16 halogen bulb.
  • the LED light source contained within assembly 10 preferably is a rectifier circuit as disclosed in our co-pending application EP 06124144.4.
  • Pins 11 and 12 match the pins of a regular MR-16 bulb, and are electrically connected to the AC contacts of the rectifier bridge.
  • the rectifier bridge circuit (not shown) is positioned immediately above connection block 13.
  • connection block Affixed to the connection block is heat sink 14 (shown separately in Figure 1 ), comprising a copper core 15 with sleeves 16. Radiating outwardly from heat sink 14 are fins 17 of graphite foil. Shown in Figure 1 is a heat management system comprising 16 fins, but it will be understood that any suitable number of fins may be selected. Preferably the graphite foil is coated with a high-shine aluminum.
  • FIG. 1 shows the heat management system for a LED-based light source that is designed to replace a fluorescent tube. Different from the fluorescent tube it replaces, the LED-based light source emits light in one direction. The figure shows the non-light emitting side of the light source.
  • Heat management system 20 comprises a semi-cylindrical body 21, provided with ridges 22. Preferably the body and the ridges are made of an anisotropic graphite material, which is optionally coated with a metal foil, such as aluminum. Heat management system 20 may be molded in its entirety from a sheet of anisotropic material. In the alternative body 21 is molded from a sheet, and ridges 22 are manufactured separately. Ridges 22 are attached to body 21 , for example by means of a heat conducting adhesive.
  • Pins 23 and 24 allows for the LED-based light source to be mounted in a conventional TL fixture. At least one of pins 23 and 24 provides an electrical connection to the LEDs (not shown). There is a similar pair of pins (not shown) at the opposite end of the LED-based light source. At least one of this second pair of pins provides an electrical connection to the LEDs.
  • Figure 3 shows an alternate embodiment of the heat management system of figure 2.
  • a string of LEDs 31 is mounted on a strip 32 of heat conducting material.
  • the heat conducting material of strip 32 may be a metal, such as copper or aluminum, or it may be a strip of an anisotropic graphite-containing material. In the latter case the strip may be laminated to a strip of a second material, for strength.
  • LEDs 31 are galvanically insulated from strip 32, for example by a thin block of ceramic material, as disclosed in our co-pending patent application EP06124144.4.
  • the heat management system comprises a body 33 and fins 34. Both body 33 and fins 34 are made of an anisotropic graphite-containing material. Pins 35 and 36 allow for the light source to be mounted in a conventional tube light fixture. At least one of pins 35 and 36 provides an electrical connection for LEDs 31. At the opposite end of the light source is a second pair of pins (not shown), at least one of which provides an electrical connection to LEDs 31.
  • Figure 4 shows a LED-baseci light source designed to replace a dual CFL.
  • Figure 4a shows a conventional dual CFL.
  • Figure 4b shows the rear (non-light emitting) side of the LED replacement.
  • Figure 4c shows a perspective view of the heat management system.
  • the heat management system comprises to U-shaped forms 41 and 42, inner form 41 being mounted symmetrically within form 42. Both forms are made of an anisotropic graphite-containing material. Each U-form can be pressed from unitary sheets of the appropriate size, inner form 42 may be connected to outer form 41 using, for example, a heat conducting adhesive.
  • Outer form 41 is provided with holes 43, 44, and 45, to allow air circulation.
  • Inner form 42 has holes that are located such as to coincide with holes 44 after assembly of the heat management system.
  • Connection block 46 is preferably made of metal, such as copper or aluminum. Fins 47 may be made of metal, or may be made of the anisotropic graphite-containing material. In the latter case these fins may be connected to connection block in the manner described above for connection block 13 of figure 1.
  • PV photovoltaic
  • PV cells that are connected in parallel can use a metal plate as a common electrode.
  • a group of parallel-connected PV cells will be referred to herein as a "galvanic neutral group" of PV cells.
  • Our co-pending application EP07101312.2 discloses PV panels comprising large numbers of PV cells connected in parallel.
  • the common electrode is a plate of a heat conducting metal, such as copper or aluminum.
  • FIG. 5 shows a heat management system 50 for a galvanic neutral group of PV cells.
  • Heat management system 50 comprises a sheet of anisotropic, graphite-containing materia! 51.
  • sheet 51 is of about equal dimensions as the galvanic neutral group of PV cells (not shown).
  • tubes 54 are made of a heat conducting material, such as copper, aluminum, or a graphite- containing material similar or identical to that of sheet 51.
  • a cooling fluid flows through tubes 54.
  • PV panels are mounted at an angle from horizontal, so as to maximize the amount of solar energy received by the panel.
  • the flow of the cooling fluid through tubes 54 may be established by natural convection. It may be desirable to increase the flow of the cooling fluid by providing a circulation pump elsewhere in the cooling fluid circuit. Heat captured by the cooling fluid may be used in any desirable way, for example for heating a water supply or a building.
  • the temperature of the cooling fluid at entry points 55 may be kept as low as possible by extracting heat from the cooling fluid by means of a heat pump.
  • a heat pump Such an arrangement maximizes the efficiency of the PV cells, by keeping them at as low an operating temperature as possible.
  • the decision as to whether to include a heat pump in the system requires an energy balance calculation and a cost calculation, both of which are well within the general skill of the average heat management engineer.
  • FIG. 6 shows an alternate embodiment of the heat management system for a panel of PV cells.
  • Heat management system 60 comprises two sheets 61 and 62 of anisotropic, graphite-containing material. Each sheet 61 and 62 consist of a flat sheet 63, and a corrugated sheet 64. Corrugated sheets 64 can be easily formed from a flat sheet by pressing, making use of the flexibility of the material.
  • Corrugated sheets 64 comprise ridges 65 and trenches 66.
  • the two sheets 64 are assembled, for example with a heat-conducting adhesive, at mating ridges 65. After assembly the combined trenches 66 form channels through which a cooling fluid can flow.
  • Each sheet 61 and 62 comprises a U-profiJe 67, with holes 68 corresponding to trenches 66. After assembly two U-profiles 67 form a main channel for the cooling fluid, in fluid connection with the channels formed by trenches 66. It will be understood that the sheets may have similar or identical U-profiles at their opposite ends as well, so that the finished heat management system comprises two main channels, one for supply of cooling fluid, and one for removal of heated cooling fluid.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Optics & Photonics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Power Engineering (AREA)
  • Arrangement Of Elements, Cooling, Sealing, Or The Like Of Lighting Devices (AREA)

Abstract

A heat management system is disclosed for LED-based light sources and photovoltaic cell panels. The heat management system is made at least in part of an anisotropic, graphite-containing material. The heat management system is particularly suitable for RGB light sources, and for light sources designed to be connected to household electrical power.

Description

HEAT MANAGEMENT SYSTEM FOR PHOTOVOLTAIC CELL PANELS AND LED-BASED LIGHT SOURCES
BACKGROUND OF THE INVENTION
1. Field of the Invention
[oooi] The present invention relates to heat management systems for use with photovoltaic cell panels and LED-based light sources.
2. Description of the Related Art
[0002] Many electronic devices generate heat when in operation, and therefore require cooling. In many cases cooling is provided by a heat sink, often in conjunction with a forced air flow, propelled by a fan.
[0003] Heat sinks are typically made of a metal, in particular metals having a high heat conductivity. Dissipation of heat to the environment, such as a forced air flow, is increased by increasing the surface area of the heat sink, for example by providing fins at the surface of the heat sink.
[0004] It has been proposed to use sheets of anisotropic heat conducting materials to provide cooling to electronic devices such as cellular phones and lap top computers. These materials have a high heat conductivity in the plane of the sheet, and a much lower heat conductivity in a direction perpendicular to the plane of the sheet. Accordingly, sheets of these materials act to rapidly transport heat away from a heat source.
[0005] There is an ongoing need for providing improved heat management systems for electronic systems. There is also a need for providing heat management systems that allow recovery of the dissipated heat so it may be used for energy- saving purposes.
[0006] The present invention provides improved heat management systems for use with photovoltaic cell panels and LED-based light sources. SUMMARY OF THE INVENTION
[0007] The invention relates to a heat management system for use with photovoltaic cell panels or LED-based light sources comprising a body provided with a graphite-containing, thermally anisotropic material.
[0008] Preferably, the graphite-containing, thermally anisotropic material is in the form of a flexible sheet. The graphite-containing, thermally anisotropic sheet material may have a lateral heat conductivity on the order of 400 - 500 W/mK, and a transversal heat conductivity on the order of 20 - 50 VWmK. The sheet may be provided with a heat path for permitting heat transport across a thickness of the sheet.
[0009] The invention further relates to a LED-based light source having such a heat management system.
[ooio] Finally, the invention further relates to a photovoltaic cell panel having such a heat management system.
BRiEF DESCRIPTION OF THE DRAWINGS
[OOii] Figure 1 shows a LED-based light source designed to fit a fixture for an MR
16 halogen lamp, provided with a dedicated heat management system.
[0012] Figure 2 shows a LED-based light source designed to replace a fluorescent tube, provided with a dedicated heat management system.
[0013] Figure 3 shows an alternate embodiment of the heat management system for the LED-based light source of figure 2.
[0014] Figure 4 shows a LED-based light source designed to replace a dual CFL, provided with a dedicated heat management system.
[0015] Figure 5 shows a first embodiment of a heat management system for use with a photovoltaic panel.
[0016] Figure 6 shows a second embodiment of a heat management system for use with a photovoltaic panel. DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0017] The following is a description of certain embodiments of the invention, given by way of example only.
[0018] Although much more energy efficient than incandescent tight bulbs, LED- based light sources convert about 10 - 15% of the electric energy to light; the remaining 85 - 90% is lost in the form of heat. Unlike conventional light sources, LEDs do not require a high temperature for emitting light. To the contrary, LEDs produce light more efficiently at a low temperature. Moreover, high temperatures are harmful to the semi-conducting materials of the LEDs. For these reasons it is essential to provide LED light sources with efficient cooling.
[0019] The LEDs in LED-based iight sources, such as used in traffic lights and automobile tail lights, are placed relatively far apart, to aid in heat dissipation.
[0020] It has been found that LEDs may be used to produce white light of a pleasant color temperature by combining red, green and blue LEDs together in a close configuration. Due to the close proximity of the individual LEDs to each other, the emitted light becomes blended so that the human eye perceives it as one color. This color is white of the contributing colors are sufficiently balanced. However, the need for placing the LEDs closely together in order to obtain one blended color puts high demands on the cooling system of such an "RGB" LED light source.
[0021] It is also desirable to provide LED-based iight sources that can be operated on household electric power, e.g. 1 17 V AC or 240 V AC. In our co-pending patent application EP 06124144.4 we disclose a rectifier bridge circuit that allows operation of LEDs on household power. For safety reasons these LED-base light sources must have a galvanic insulation capable of withstanding up to 3,000 Volts. The need for galvanic insulation runs opposite to the need for providing cooling, as electrical insulators tend to be poor heat conductors.
[0022] Embodiments of the heat management systems of the present invention provide sufficient cooling to a LED-based light source to allow individual LEDs to be placed closely enough together for LEDs that emit light of different colors to be perceived as emitting one, blended, color. [0023] The heat management systems of the present invention comprise a body provided with a graphite-containing, thermally anisotropic material, also referred to as anisotropic graphite, preferably in the form of a flexible sheet. Such materials are commercially available. Particularly suitable is Spreadershϊeld ™, available from Advanced Energy Technology, Lakewood, OH, USA. These materials have a lateral (that is, in the plane of the sheet) heat conductivity on the order of 400 - 500 W/mK, and a transversal (that is, in a direction perpendicular to the plane of the sheet) of only 20 - 50 W/mK.
[0024] This highiy anisotropic character of the heat conductivity of these materials makes them particularly suitable for rapid transport of heat away from the source. These materials are therefore particularly suitable as passive heat spreaders, and in heat shields.
[0025] For active source cooling it is desirable to provide localized heat paths within the sheet material, permitting rapid heat transport across the thickness of the sheet. These heat paths may be in the form of metal rivets, preferably copper or aluminum rivets. Materials of this kind are commercially available, for example zSPREADER™ from Advanced Energy Technology, Lakewood, OH, USA.
[0026] Figure 1 shows a heat management system for a LED-based light assemble designed for replacing an MR-16 halogen bulb. The LED light source contained within assembly 10 preferably is a rectifier circuit as disclosed in our co-pending application EP 06124144.4. Pins 11 and 12 match the pins of a regular MR-16 bulb, and are electrically connected to the AC contacts of the rectifier bridge. The rectifier bridge circuit (not shown) is positioned immediately above connection block 13.
[0027] Affixed to the connection block is heat sink 14 (shown separately in Figure 1 ), comprising a copper core 15 with sleeves 16. Radiating outwardly from heat sink 14 are fins 17 of graphite foil. Shown in Figure 1 is a heat management system comprising 16 fins, but it will be understood that any suitable number of fins may be selected. Preferably the graphite foil is coated with a high-shine aluminum.
[0028] Plate 18 is also made of graphite foil. Holes 19 allow air circulation alongside fins 17 and through plate 18. [0029] Figure 2 shows the heat management system for a LED-based light source that is designed to replace a fluorescent tube. Different from the fluorescent tube it replaces, the LED-based light source emits light in one direction. The figure shows the non-light emitting side of the light source. Heat management system 20 comprises a semi-cylindrical body 21, provided with ridges 22. Preferably the body and the ridges are made of an anisotropic graphite material, which is optionally coated with a metal foil, such as aluminum. Heat management system 20 may be molded in its entirety from a sheet of anisotropic material. In the alternative body 21 is molded from a sheet, and ridges 22 are manufactured separately. Ridges 22 are attached to body 21 , for example by means of a heat conducting adhesive.
[0030] Pins 23 and 24 allows for the LED-based light source to be mounted in a conventional TL fixture. At least one of pins 23 and 24 provides an electrical connection to the LEDs (not shown). There is a similar pair of pins (not shown) at the opposite end of the LED-based light source. At least one of this second pair of pins provides an electrical connection to the LEDs.
[0031] Figure 3 shows an alternate embodiment of the heat management system of figure 2. A string of LEDs 31 is mounted on a strip 32 of heat conducting material. The heat conducting material of strip 32 may be a metal, such as copper or aluminum, or it may be a strip of an anisotropic graphite-containing material. In the latter case the strip may be laminated to a strip of a second material, for strength.
[0032] LEDs 31 are galvanically insulated from strip 32, for example by a thin block of ceramic material, as disclosed in our co-pending patent application EP06124144.4.
[0033] The heat management system comprises a body 33 and fins 34. Both body 33 and fins 34 are made of an anisotropic graphite-containing material. Pins 35 and 36 allow for the light source to be mounted in a conventional tube light fixture. At least one of pins 35 and 36 provides an electrical connection for LEDs 31. At the opposite end of the light source is a second pair of pins (not shown), at least one of which provides an electrical connection to LEDs 31. [0034] Figure 4 shows a LED-baseci light source designed to replace a dual CFL. Figure 4a shows a conventional dual CFL. Figure 4b shows the rear (non-light emitting) side of the LED replacement. Figure 4c shows a perspective view of the heat management system.
[0035] As can be seen from figure 4c, the heat management system comprises to U-shaped forms 41 and 42, inner form 41 being mounted symmetrically within form 42. Both forms are made of an anisotropic graphite-containing material. Each U-form can be pressed from unitary sheets of the appropriate size, inner form 42 may be connected to outer form 41 using, for example, a heat conducting adhesive.
[0036] Outer form 41 is provided with holes 43, 44, and 45, to allow air circulation. Inner form 42 has holes that are located such as to coincide with holes 44 after assembly of the heat management system.
[0037] Connection block 46 is preferably made of metal, such as copper or aluminum. Fins 47 may be made of metal, or may be made of the anisotropic graphite-containing material. In the latter case these fins may be connected to connection block in the manner described above for connection block 13 of figure 1.
[0038] Panels of photovoltaic ("PV") cells produce a significant amount of heat. In most applications this heat is just dissipated to the environment. The amount of heat generated by a PV pane! is up to 750 W/m2. It is important to cool PV panels in order to keep them operating at optimum efficiency. It is desirable to cool PV panels in a manner that allows for the heat energy to be used, rather than simply dissipated.
[0039] PV cells that are connected in parallel can use a metal plate as a common electrode. A group of parallel-connected PV cells will be referred to herein as a "galvanic neutral group" of PV cells. Our co-pending application EP07101312.2 discloses PV panels comprising large numbers of PV cells connected in parallel. The common electrode is a plate of a heat conducting metal, such as copper or aluminum.
[0040] Figure 5 shows a heat management system 50 for a galvanic neutral group of PV cells. Heat management system 50 comprises a sheet of anisotropic, graphite-containing materia! 51. In general sheet 51 is of about equal dimensions as the galvanic neutral group of PV cells (not shown). At side 52, opposite from the contact side with the PV cells, sheet 51 has tubes 54 pressed into it. Tubes 54 are made of a heat conducting material, such as copper, aluminum, or a graphite- containing material similar or identical to that of sheet 51.
[0041] In use a cooling fluid flows through tubes 54. Generally, PV panels are mounted at an angle from horizontal, so as to maximize the amount of solar energy received by the panel. The flow of the cooling fluid through tubes 54 may be established by natural convection. It may be desirable to increase the flow of the cooling fluid by providing a circulation pump elsewhere in the cooling fluid circuit. Heat captured by the cooling fluid may be used in any desirable way, for example for heating a water supply or a building.
[0042] The temperature of the cooling fluid at entry points 55 may be kept as low as possible by extracting heat from the cooling fluid by means of a heat pump. Such an arrangement maximizes the efficiency of the PV cells, by keeping them at as low an operating temperature as possible. However, such an arrangement carries a cost penalty in the form of the energy demand of the heat pump. In practice the decision as to whether to include a heat pump in the system requires an energy balance calculation and a cost calculation, both of which are well within the general skill of the average heat management engineer.
[0043] Figure 6 shows an alternate embodiment of the heat management system for a panel of PV cells. Heat management system 60 comprises two sheets 61 and 62 of anisotropic, graphite-containing material. Each sheet 61 and 62 consist of a flat sheet 63, and a corrugated sheet 64. Corrugated sheets 64 can be easily formed from a flat sheet by pressing, making use of the flexibility of the material.
[0044] Corrugated sheets 64 comprise ridges 65 and trenches 66. The two sheets 64 are assembled, for example with a heat-conducting adhesive, at mating ridges 65. After assembly the combined trenches 66 form channels through which a cooling fluid can flow.
[0045] Each sheet 61 and 62 comprises a U-profiJe 67, with holes 68 corresponding to trenches 66. After assembly two U-profiles 67 form a main channel for the cooling fluid, in fluid connection with the channels formed by trenches 66. It will be understood that the sheets may have similar or identical U-profiles at their opposite ends as well, so that the finished heat management system comprises two main channels, one for supply of cooling fluid, and one for removal of heated cooling fluid.
[0046] Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

Claims

WHAT IS CLAIMED IS:
1. Heat management system for use with photovoltaic ceil panels or LED-based light sources comprising a body provided with a graphite-containing, thermally anisotropic material.
2. Heat management system according to claim 1 , wherein the graphite- containing, thermally anisotropic material is in the form of a flexible sheet.
3. Heat management system according to claim 2, wherein the graphite- containing, thermally anisotropic sheet material has a lateral heat conductivity on the order of 400 - 500 W/rnK, and a transversal heat conductivity on the order of 20 - 50 W/mK.
4. Heat management system according to claim 2 or 3, wherein the graphite- containing, thermally anisotropic sheet material is provided with a heat path for permitting heat transport across a thickness of the sheet.
5. Heat management system according to claim 4, wherein the heat path takes the form of a rivet.
6. Heat management system according to any one of claims 1 - 5, wherein the body comprises a number of fins.
7. Heat management system according to any one of claims 1 - 5, wherein the body comprises a sheet.
8. Heat management system according to claim 7, wherein the sheet has a tube pressed into it.
9. A LED-based light source having a heat management system according to any one of the preceding claims.
10. A photovoltaic cell panel having a heat management system according to any one of claims 1 - 8.
PCT/EP2008/053331 2007-03-20 2008-03-19 Heat management system for photovoltaic cell panels and led-based light sources WO2008113837A2 (en)

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