WO2011003903A2 - Concentrator photovoltaïc device with an improved efficiency - Google Patents

Concentrator photovoltaïc device with an improved efficiency Download PDF

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Publication number
WO2011003903A2
WO2011003903A2 PCT/EP2010/059633 EP2010059633W WO2011003903A2 WO 2011003903 A2 WO2011003903 A2 WO 2011003903A2 EP 2010059633 W EP2010059633 W EP 2010059633W WO 2011003903 A2 WO2011003903 A2 WO 2011003903A2
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WO
WIPO (PCT)
Prior art keywords
photovoltaic device
light
tub
concentrator photovoltaic
chamber
Prior art date
Application number
PCT/EP2010/059633
Other languages
French (fr)
Other versions
WO2011003903A3 (en
Inventor
Olivier Bouesnard
François LECOLLEY
Fabrizio Mazeri
Jean-Baptiste Richir
Tanguy Thibert
Original Assignee
Agc Glass Europe
Arcelor Research Liège
Université de Liège
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 Agc Glass Europe, Arcelor Research Liège, Université de Liège filed Critical Agc Glass Europe
Publication of WO2011003903A2 publication Critical patent/WO2011003903A2/en
Publication of WO2011003903A3 publication Critical patent/WO2011003903A3/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
    • H01L31/04—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
    • H01L31/0547—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

Definitions

  • the invention relates to light-to-electrical conversion devices. More particularly, the invention relates to a concentrator photovoltaic device.
  • a light-to-electrical conversion device takes solar energy and converts it into electricity for use in homes and businesses.
  • Some light-to-electrical conversion devices have efficiencies of at least 30%, and that number is increasing. By tracking the sun, these devices can convert light to electricity during a large portion of the day.
  • photovoltaic cells which are classically made of semiconductors.
  • the most common photovoltaic cells are silicon solar cells, which have efficiencies of about 14 to 20% (in standard conditions, i.e. with an intensity of 1000W/m2, the spectrum AMI .5G, and a temperature of 25°C).
  • Document WO2008/039399 discloses a concentrator photovoltaic device comprising a chamber containing light-to electrical conversion units (such as photovoltaic cells) which is hermetically sealed thanks to a transparent lid and seals. Rods focus light on the photovoltaic cells.
  • light-to electrical conversion units such as photovoltaic cells
  • This document proposes to control the environment of the volume including the photovoltaic cells in order to protect the inside environment from moisture or contaminants of the outside environment and in order to reduce the differential between pressures in the volume containing the cells and pressures in the outside environment.
  • Typical concentrator photovoltaic devices have efficiencies (measured in the precited standard conditions) ranging from 10 to 15% (for an optical concentration factor of 2x to 3x) to 30% (for an optical concentration factor of 50Ox).
  • concentrator photovoltaic device implies the concentration of light on small conversion cells, and thus strong heating is created at the level of these cells and therefore a decrease of the yield to converse light into electricity occurs at the cells level (the cells work less efficiently). As a matter of fact, concentration of light generates hot spots at the cells level which can even become dangerous for the cell integrity. It has been observed that the precited efficiency values decrease with the increase of temperature.
  • One objective of the invention is to solve the previously mentioned issues of the related art.
  • an objective of the invention is to provide a concentrator photovoltaic device which has an good efficiency and more particularly which has a good yield to converse light into electricity.
  • Another objective of the invention according to at least one of its embodiments is to provide such a concentrator photovoltaic device which correspond to an improved compromise efficiency / cost and thus to decrease the price for the production of electricity.
  • Another objective of the invention according to at least one of its embodiments is to provide such a concentrator photovoltaic device which allows a reduction of the overheating which occurs in the concentrator photovoltaic device and more particularly at the light-to-electrical conversion cells level.
  • Another objective of the invention according to at least one of its embodiments is to provide such a concentrator photovoltaic device which allows a reduction or passive control of the pressure in the concentrator photovoltaic device.
  • the invention according to at least one of its embodiments, also aims to provide such a concentrator photovoltaic device which is simple to implement and which is cost effective.
  • the invention is related to a concentrator photovoltaic device according to claim 1.
  • the tub both acts as a container and as a heat dissipating device for the light-to-electrical conversion units.
  • the light-to electrical conversion units being fixed on the surface of the base of the tub, the large surface of the base of the heat conducting tub acts as an efficient radiator which participate to the dissipation of the heat generated by the light focused on the light-to-electrical conversion units.
  • the bottom of the tub is stamped thanks to a machine press.
  • the chamber is hermetically sealed thanks to at least one seal positioned between the top of the tub and the cover sheet.
  • the seal allows to protect the inside environment of the chamber from moisture or contaminants of the outside environment and in order to reduce the differential between pressures in the volume containing the cells and pressures in the outside environment.
  • the seal comprises an elastomer based core spacer surrounded by a butyl coating.
  • the elastomer based core spacer surrounded by a butyl coating is further surrounded by a silicone coating.
  • the seal has a combination of the two following properties :
  • the seal does not comprise any core spacer but only a butyl or a combination of a butyl layer and a silicone layer.
  • the chamber also comprises a capillary tube.
  • the capillary tube allows hot air to get out the chamber and fresh air to get in the chamber which then improves the overall heat dissipation in the concentrator photovoltaic device.
  • the capillary tube is in thermal contact with the tub.
  • the capillary tube and the air flowing into it participate to heat dissipation and then the overall heat dissipation of the concentrator photovoltaic device is further improved.
  • the chamber also comprises a cartridge of a desiccant material.
  • This desiccant allow for a further reduction of the humidity in the chamber.
  • the volume of the chamber is superior than 0.01 m 3 and more preferentially superior than 0.1 m 3 .
  • the means to focus light on the at least one light-to electrical conversion unit comprise at least one reflecting panel.
  • At least one of the reflecting panels is covered at least partially by a diffusing coating.
  • such a diffusing coating can allow to reduce the hot point effect and then allow to protect the cells from over heating.
  • the means to focus light on the at least one light-to electrical conversion unit comprise at least one converging lens.
  • the tub is made of at least one metal.
  • the at least one metal allows both good heat dissipation and rigidity.
  • the light-to electrical conversion unit(s) is(are) glued to the tub thanks to thermal conductive but electrically insulating glue or adhesive tape.
  • the glue or adhesive tape is thermally conductive which improves heat conduction from each light-to-electrical conversion unit to the tub in order to optimize the radiator function of the tub, thus the glue or adhesive tape reinforce the overall heat dissipation in the concentrator photovoltaic device.
  • the glue is electrically insulating to prevent electrical current leakages from the light-to electrical conversion units to the tub that would reduce the efficiency of the concentrator photovoltaic device.
  • the transparent cover sheet is made of low iron glass.
  • the transparent cover sheet is provided with at least one anti reflective coating.
  • Fig. 1 is a side cross-sectional view of a concentrator photovoltaic device in accordance with a first embodiment of the present invention
  • Figure 1 is a side cross-sectional view of a concentrator photovoltaic device 1000 in accordance with a first embodiment of the present invention.
  • FIG. 1 is a top view of the concentrator photovoltaic device 1000 of figure 1.
  • the concentrator photovoltaic device 1000 comprises a chamber 100 including :
  • a concentrator photovoltaic device can comprise an unspecified number of such units
  • - means 103 to focus transmitted light on the light-to electrical conversion units 104, and more particularly, on a receiving area of the light-to electrical conversion units 104.
  • the means to focus light 103 comprise, for each light-to electrical conversion unit 104, a reflecting structure comprising two reflecting panels 1031, 1032 which are fixed together and oriented in order to concentrate or focus precited transmitted light on the receiving area of the light-to electrical conversion unit 104.
  • a reflecting structure comprising two reflecting panels 1031, 1032 which are fixed together and oriented in order to concentrate or focus precited transmitted light on the receiving area of the light-to electrical conversion unit 104.
  • transmitted light in the normal direction toward the receiving area is received by the receiving area and transmitted light coming from other directions than normal direction (within the acceptance angle formed by the reflecting panels) are reflected by each reflecting panel toward the receiving area of the light-to electrical conversion unit 104, thus increasing collection efficiency.
  • each reflecting panel 1031 , 1032 is folded in order to form a predetermined number (e.g. 3) of segments.
  • a diffusing coating can be provided on the reflecting panels 1031, 1032 in order to diffuse the light reflected by the reflecting panels 1031, 1032 and to avoid hot spot on the light-to electrical conversion units 104.
  • Such a diffusing coating can comprise one or a mixture of the following organic materials :
  • the means to focus light 103 comprise, for each light-to electrical conversion unit 104, a converging lens that is disposed above the conversion unit 104 at a determined distance (which can be easily obtained by classical calculations well known by the man skilled in the art once the lens is chosen) that allows the concentration or focusing of precited transmitted light on the receiving area of the light-to electrical conversion unit 104. All type of lens can be used in the context of the invention.
  • the means to focus light 103 can be realized with any other optical devices such as plan and/or concave and/or convex mirrors, provided that it allows the precited transmitted light to be focused on the receiving area of the light-to electrical conversion units 104.
  • the transparent cover sheet 102 is for example a 5mm width low iron glass sheet such as CLEAR VISION sold by AGC Flat Glass Europe in order that the cover sheet has a high transmittance of about 92%. It can also be made of any other material that is transparent or at least translucent, provided that the more transparent the cover sheet, the more important the transmitted light focused on the light-to electrical conversion units, and the more efficient the concentrator photovoltaic device.
  • a first anti-reflective coating is provided on the top side 1021 of the cover sheet 102 and/or a second anti- reflective coating is provided at the bottom side 1022 of the cover sheet 103 in order to further limit the reflection losses at the interfaces exterior environment / cover sheet and/or cover sheet / interior environment.
  • the anti-reflective coating(s) can be a single quarter wave layer of MgF 2 or any other single layer or multi-layer anti-reflective coating. As a matter of fact, the less reflections at these interfaces, the more important the transmitted light focused on the light-to electrical conversion units, and the more efficient the concentrator photovoltaic device.
  • the tub 101 is made of a heat conducting material.
  • the tub both acts as a container and as a heat dissipating device for the light-to-electrical conversion units.
  • the light-to electrical conversion units being fixed on the surface of the base of the tub, the large surface of the base of the heat conducting tub acts as an efficient radiator which participate to the dissipation of the heat generated in the concentrator photovoltaic device 1000 by the light focused on the light-to-electrical conversion units 104.
  • the tub 101 is made of a metal.
  • the metal chosen to be resistant to corrosion, to be able to withstand the overpressure inside the chamber, and to be able to easily fix a tracking system (described hereafter) on the tub.
  • the tub is made of 0,5mm to 1,5mm (for instance lmm) width steel and is coated with an Aluzinc coating sold by Arcelor-Mittal. As a matter of fact, this coating prevents corrosion of the tub's steel and allows external applications of the tub 101.
  • the tub 101 can also be made of any other metal such as alumina, copper, ... or alloy of metals or any other non metal heat conducting material.
  • the tub 101 is preferably manufactured thanks to a stamping processing step and is for example a parallelepiped of 820 mm wide x 970mm long x 140mm high.
  • stamping process is done thanks to machine press that can be a stamping press or a punching machine press.
  • machine press can be a stamping press or a punching machine press.
  • a classical punching machine press can be used.
  • the stamping process comprises three steps : stamping the tub, stamping the edge of the tub and stamping the bottom of the tub.
  • stamping process can comprise only one of the previously mentioned three steps, for instance the stamping of the bottom of the tub.
  • the geometry of the stamped bottom of the tub is non developable.
  • the depth of the tub is a function of the thickness of the tub, of the matrix radius and of the radius of the punch.
  • the depth of the tub can be increased.
  • the steel used for the tub is DX56, and more particularly AZ (that has a particular good resistance to corrosion), which are steels (extra- stamping) that are well suited for the stamping process (Re is low, r is high and n is high). If the tub thickness is increased, the risk is to lower r and n.
  • the steel used can also be enamelled.
  • the chamber 100 is hermetically sealed thanks to a seal 105, for example a double barrier seal made with a butyl coating (e.g GDI 15 from K ⁇ mmerling) surrounding a silicone (e.g. DC895 from Dow Corning) based core spacer and positioned between the tub 101 and the cover sheet 102 in order to protect the inside environment from moisture or contaminants of the outside environment.
  • a seal 105 for example a double barrier seal made with a butyl coating (e.g GDI 15 from K ⁇ mmerling) surrounding a silicone (e.g. DC895 from Dow Corning) based core spacer and positioned between the tub 101 and the cover sheet 102 in order to protect the inside environment from moisture or contaminants of the outside environment.
  • a seal 105 for example a double barrier seal made with a butyl coating (e.g GDI 15 from K ⁇ mmerling) surrounding a silicone (e.g. DC895 from Dow Corning) based core spacer and positioned between the tub 101 and the cover
  • the seal can comprises an elastomer (e.g. natural rubber, butyl rubber, Nitrile rubber, silicone rubber, polyisoprene, Polybutadiene, Styrene-butadiene, Chloroprene, EPDM, EVA, ”) based core spacer surrounded by a butyl coating (e.g. the "Vitroband" product sold by Bayer Vitrotechnic).
  • the elastomer based core spacer surrounded by a butyl coating can be further surrounded by a silicone coating, e.g. DC895 from Dow Corning.
  • the volume of the chamber is delimited by the tub 101 and its cover sheet 102 and is chosen to be superior to 0.01 m3, for example to be 0.1 m3. In this volume, depending on the tub and transparent cover widths, internal thermal convection can occur that would allow to cool the light-to electrical conversion units 104 and then reinforces the overall heat dissipation in the concentrator photovoltaic device.
  • the light-to-electrical conversion units 104 are crystalline silicon based "solar cells” or “photovoltaic cells”.
  • the light-to-electrical conversion units are triple-junction conversion cells, such as one containing a gallium- indium phosphide diode, for converting light in the visible portion of the light spectrum, a gallium arsenide diode, for converting light in the red and near infrared portion of the light spectrum, and a germanium diode, for converting light further in the infrared portion of the light spectrum.
  • triple-junction conversion cells such as one containing a gallium- indium phosphide diode, for converting light in the visible portion of the light spectrum, a gallium arsenide diode, for converting light in the red and near infrared portion of the light spectrum, and a germanium diode, for converting light further in the infrared portion of the light spectrum.
  • incident light 10 follows an optical path :
  • each the light-to-electrical unit 104 converts the light into electrical energy, which is then transmitted to an electrical load, such as a motor, electronic device, or even a battery for storing the energy for later use.
  • an electrical load such as a motor, electronic device, or even a battery for storing the energy for later use.
  • Figure 1 does not show the chamber 100 coupled to an electrical load or battery.
  • each light-to electrical conversion unit 104 is glued on the surface of the base of the tub 101 thanks to a thermal conductive but electrically insulating glue 106.
  • a thermal conductive but electrically insulating conductive tape can be used to glue the light-to electrical conversion unit 104.
  • the glue is thermally conductive which improves heat conduction from each light-to electrical conversion unit 104 to the tub 101 in order to optimize the radiator function of the tub 101, thus the glue reinforce the overall heat dissipation in the concentrator photovoltaic device 1000.
  • the glue 106 is electrically insulating to prevent electrical current leakages from the light-to electrical conversion units 104 to the tub 101 that would reduce the efficiency of the concentrator photovoltaic device 1000.
  • bus bars 107 are disposed on the light-to electrical conversion unit 104 in order to collect electricity generated by the light-to electrical conversion units 104.
  • the glue is preferably a silicone or acrylic based adhesive to resist the shear stress induced by the different movement of the light-to electrical conversion units 104 and of the tub 101 during heating and cooling of these components in function of the evolution in the day of the solar illumination.
  • the length of the light-to electrical conversion units 104 is also optimized to reduce the shear stress on the glue.
  • glue 106 is the tape reference number 8820 sold by 3M.
  • Figure 3 is a side cross-sectional view of a concentrator photovoltaic device 3000 in accordance with a second embodiment of the present invention.
  • the concentrator photovoltaic device 3000 is the same as the concentrator photovoltaic device 1000 of figure 1 and 2 except that the chamber 300 of the concentrator photovoltaic device 3000 comprises a capillary tube 308 that is inserted in an orifice previously realized in the tub 301.
  • the capillary tube 308 inner diameter and length should limit water diffusion when internal and external temperatures are equal, but also permits the air to flow through the channel when external and internal temperatures are different.
  • the inner diameter is greater than 0.5mm, and more preferably greater than lmm.
  • the length of the tube is greater than 5 cm, and preferably greater than 15 cm.
  • a cartridge 309 comprising a desiccant agent can be placed in the chamber 301.
  • the desiccant agent is preferably a molecular sieve "phonosorb®" sold by GRACE- DA VISON in order to keep a high adsorption capacity even at high temperature or in very dry environment (below 10% relative humidity).
  • the capillary tube and the air flowing into it participate to heat dissipation and then the overall heat dissipation of the concentrator photovoltaic device is further improved.
  • the capillary tub 308 of figure 3 is replaced by a global capillary tube which comprises a dessicant cartridge.
  • the global capillary tube comprises :
  • a first capillary tub which makes the channel from the inside of the chamber 300 to the desiccant cartridge
  • a second capillary tube which makes the channel from the desiccant cartridge to the external environment.
  • the first capillary tube and the dessicant cartridge are placed inside the chamber, the second capillary tube being inserted in a hole created on a side wall of the tub such that a first part of the second capillary tub is positioned inside the chamber and a second part of the second capillary tub is positioned outside the chamber.
  • an adhesive or mechanical means is provided to hermetically seal the remaining hole.
  • the first capillary tube can be in thermal contact with the tub in order to dissipate more heat.
  • the heat of the tub is used to heat the desiccant agent of the dessicant cartridge and makes it release some water when air is flowing outside the chamber.
  • An additional external mesh can be provided to prevent dust coming into second capillary tube.
  • the concentrator photovoltaic device according to the invention can be used with a sun tracking system (system which orients the concentrator photovoltaic device such that it has the best orientation toward the sun along the day), to maximize the collected energy.
  • a sun tracking system system which orients the concentrator photovoltaic device such that it has the best orientation toward the sun along the day
  • the tracking system shall be preferentially a single axis tracking system, to minimize the system complexity.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Photovoltaic Devices (AREA)

Abstract

The invention relates to a concentrator photovoltaic device (1000) comprising a chamber (100) including : - a tub (101) defining a volume for containing at least one light-to electrical conversion unit which are fixed to the surface of the base of the tub; - a transparent cover sheet (102) positioned at the top of the tub and transmitting the incident light from the exterior to the interior of the chamber; - means to focus (103) transmitted light on the at least one light-to electrical conversion unit. According to the invention, the tub is made of a heat conducting material.

Description

Concentrator photovoltaic device with an improved efficiency.
1. Field of the invention
The invention relates to light-to-electrical conversion devices. More particularly, the invention relates to a concentrator photovoltaic device.
2. Description of the related art
As their efficiency increases, light-to-electrical conversion devices are becoming more cost effective and attractive green sources of energy. A light-to- electrical conversion device takes solar energy and converts it into electricity for use in homes and businesses. Some light-to-electrical conversion devices have efficiencies of at least 30%, and that number is increasing. By tracking the sun, these devices can convert light to electricity during a large portion of the day.
Among such light-to-electrical conversion devices are the photovoltaic cells which are classically made of semiconductors.
The most common photovoltaic cells are silicon solar cells, which have efficiencies of about 14 to 20% (in standard conditions, i.e. with an intensity of 1000W/m2, the spectrum AMI .5G, and a temperature of 25°C).
In order to improve the overall cost efficiency of the solar module made of such photovoltaic cells, it has been proposed to concentrate or focus the solar energy incident on the cells.
Document WO2008/039399 discloses a concentrator photovoltaic device comprising a chamber containing light-to electrical conversion units (such as photovoltaic cells) which is hermetically sealed thanks to a transparent lid and seals. Rods focus light on the photovoltaic cells.
This document proposes to control the environment of the volume including the photovoltaic cells in order to protect the inside environment from moisture or contaminants of the outside environment and in order to reduce the differential between pressures in the volume containing the cells and pressures in the outside environment. Typical concentrator photovoltaic devices have efficiencies (measured in the precited standard conditions) ranging from 10 to 15% (for an optical concentration factor of 2x to 3x) to 30% (for an optical concentration factor of 50Ox).
However, concentrator photovoltaic device implies the concentration of light on small conversion cells, and thus strong heating is created at the level of these cells and therefore a decrease of the yield to converse light into electricity occurs at the cells level (the cells work less efficiently). As a matter of fact, concentration of light generates hot spots at the cells level which can even become dangerous for the cell integrity. It has been observed that the precited efficiency values decrease with the increase of temperature.
3. Objectives of the invention
One objective of the invention is to solve the previously mentioned issues of the related art.
More particularly, an objective of the invention according to at least one of its embodiments is to provide a concentrator photovoltaic device which has an good efficiency and more particularly which has a good yield to converse light into electricity.
Another objective of the invention according to at least one of its embodiments is to provide such a concentrator photovoltaic device which correspond to an improved compromise efficiency / cost and thus to decrease the price for the production of electricity.
Another objective of the invention according to at least one of its embodiments is to provide such a concentrator photovoltaic device which allows a reduction of the overheating which occurs in the concentrator photovoltaic device and more particularly at the light-to-electrical conversion cells level.
Another objective of the invention according to at least one of its embodiments is to provide such a concentrator photovoltaic device which allows a reduction or passive control of the pressure in the concentrator photovoltaic device. The invention, according to at least one of its embodiments, also aims to provide such a concentrator photovoltaic device which is simple to implement and which is cost effective.
4. Summary of the invention
According to a particular embodiment, the invention is related to a concentrator photovoltaic device according to claim 1.
Thus, the tub both acts as a container and as a heat dissipating device for the light-to-electrical conversion units. As a matter of fact, the light-to electrical conversion units being fixed on the surface of the base of the tub, the large surface of the base of the heat conducting tub acts as an efficient radiator which participate to the dissipation of the heat generated by the light focused on the light-to-electrical conversion units.
Preferentially, the bottom of the tub is stamped thanks to a machine press.
Then, such an stamping process allows that bottom to be stiffened.
Preferentially, the chamber is hermetically sealed thanks to at least one seal positioned between the top of the tub and the cover sheet.
The seal allows to protect the inside environment of the chamber from moisture or contaminants of the outside environment and in order to reduce the differential between pressures in the volume containing the cells and pressures in the outside environment.
Preferentially, the seal comprises an elastomer based core spacer surrounded by a butyl coating.
Preferentially, the elastomer based core spacer surrounded by a butyl coating is further surrounded by a silicone coating.
Thus, the seal has a combination of the two following properties :
low permeability and low mechanical resistance thanks to the butyl coating and, if any, the silicone coating;
relative mechanical resistance thanks to the elastomer based core spacer. Obviously, according to another embodiment of the invention, the seal does not comprise any core spacer but only a butyl or a combination of a butyl layer and a silicone layer.
Preferentially, the chamber also comprises a capillary tube.
Thus the capillary tube allows hot air to get out the chamber and fresh air to get in the chamber which then improves the overall heat dissipation in the concentrator photovoltaic device.
Preferentially, the capillary tube is in thermal contact with the tub.
Thus the capillary tube and the air flowing into it participate to heat dissipation and then the overall heat dissipation of the concentrator photovoltaic device is further improved.
Preferentially, the chamber also comprises a cartridge of a desiccant material. This desiccant allow for a further reduction of the humidity in the chamber.
Preferentially, the volume of the chamber is superior than 0.01 m3 and more preferentially superior than 0.1 m3.
In this volume, depending on the tub and transparent cover widths, internal thermal convection can occur that would allow to cool the light-to electrical conversion units and then reinforces the overall heat dissipation in the concentrator photovoltaic device.
According to a first embodiment of the present invention, the means to focus light on the at least one light-to electrical conversion unit comprise at least one reflecting panel.
Preferentially, at least one of the reflecting panels is covered at least partially by a diffusing coating.
Thus, such a diffusing coating can allow to reduce the hot point effect and then allow to protect the cells from over heating.
According to a first embodiment of the present invention, the means to focus light on the at least one light-to electrical conversion unit comprise at least one converging lens. Preferentially, the tub is made of at least one metal.
Thus the at least one metal allows both good heat dissipation and rigidity.
In a preferred embodiment, the light-to electrical conversion unit(s) is(are) glued to the tub thanks to thermal conductive but electrically insulating glue or adhesive tape.
Thus the glue or adhesive tape is thermally conductive which improves heat conduction from each light-to-electrical conversion unit to the tub in order to optimize the radiator function of the tub, thus the glue or adhesive tape reinforce the overall heat dissipation in the concentrator photovoltaic device. But the glue is electrically insulating to prevent electrical current leakages from the light-to electrical conversion units to the tub that would reduce the efficiency of the concentrator photovoltaic device.
According to an embodiment of the invention, the transparent cover sheet is made of low iron glass.
Preferentially, the transparent cover sheet is provided with at least one anti reflective coating.
5. Brief description of the drawings
Other features and advantages of the invention will appear more clearly in the non- limiting embodiments of the invention which are described hereafter with reference to the accompanying drawings of which:
Fig. 1 is a side cross-sectional view of a concentrator photovoltaic device in accordance with a first embodiment of the present invention;
Fig. 2 is a top view of the concentrator photovoltaic device of figure 1; Fig. 3 is a side cross-sectional view of a concentrator photovoltaic device in accordance with a second embodiment of the present invention.
6. Description of at least one embodiment of the invention
Figure 1 is a side cross-sectional view of a concentrator photovoltaic device 1000 in accordance with a first embodiment of the present invention.
Figure 2 is a top view of the concentrator photovoltaic device 1000 of figure 1. The concentrator photovoltaic device 1000 comprises a chamber 100 including :
- a tub 101 defining a volume for containing light-to electrical conversion units 104 (on figure 1 only three light-to electrical conversion units are represented, nevertheless, a concentrator photovoltaic device according to the invention can comprise an unspecified number of such units) ;
- a transparent cover sheet 102 positioned at the top of the tub 101 which transmit incident light from the exterior to the interior of the chamber 100;
- means 103 to focus transmitted light on the light-to electrical conversion units 104, and more particularly, on a receiving area of the light-to electrical conversion units 104.
According to a first embodiment of the invention, the means to focus light 103 comprise, for each light-to electrical conversion unit 104, a reflecting structure comprising two reflecting panels 1031, 1032 which are fixed together and oriented in order to concentrate or focus precited transmitted light on the receiving area of the light-to electrical conversion unit 104. As a matter of fact, transmitted light in the normal direction toward the receiving area is received by the receiving area and transmitted light coming from other directions than normal direction (within the acceptance angle formed by the reflecting panels) are reflected by each reflecting panel toward the receiving area of the light-to electrical conversion unit 104, thus increasing collection efficiency. Preferably, each reflecting panel 1031 , 1032 is folded in order to form a predetermined number (e.g. 3) of segments.
According to an embodiment of the invention, a diffusing coating can be provided on the reflecting panels 1031, 1032 in order to diffuse the light reflected by the reflecting panels 1031, 1032 and to avoid hot spot on the light-to electrical conversion units 104.
Such a diffusing coating can comprise one or a mixture of the following organic materials :
• Polyethylene, • Polyethylene terephthalate,
• Poly(methyl methacrylate)
• Epoxy
• Polyurethane
• Polyvinyl chloride,
and can be deposited thanks to rollcoating, spraycoating, spinning or printing techniques.
According to a second embodiment of the present invention, the means to focus light 103 comprise, for each light-to electrical conversion unit 104, a converging lens that is disposed above the conversion unit 104 at a determined distance (which can be easily obtained by classical calculations well known by the man skilled in the art once the lens is chosen) that allows the concentration or focusing of precited transmitted light on the receiving area of the light-to electrical conversion unit 104. All type of lens can be used in the context of the invention.
Obviously, the means to focus light 103 can be realized with any other optical devices such as plan and/or concave and/or convex mirrors, provided that it allows the precited transmitted light to be focused on the receiving area of the light-to electrical conversion units 104.
The transparent cover sheet 102 is for example a 5mm width low iron glass sheet such as CLEAR VISION sold by AGC Flat Glass Europe in order that the cover sheet has a high transmittance of about 92%. It can also be made of any other material that is transparent or at least translucent, provided that the more transparent the cover sheet, the more important the transmitted light focused on the light-to electrical conversion units, and the more efficient the concentrator photovoltaic device.
Preferably a first anti-reflective coating is provided on the top side 1021 of the cover sheet 102 and/or a second anti- reflective coating is provided at the bottom side 1022 of the cover sheet 103 in order to further limit the reflection losses at the interfaces exterior environment / cover sheet and/or cover sheet / interior environment. The anti-reflective coating(s) (not illustrated on figures 1 and 2) can be a single quarter wave layer of MgF2 or any other single layer or multi-layer anti-reflective coating. As a matter of fact, the less reflections at these interfaces, the more important the transmitted light focused on the light-to electrical conversion units, and the more efficient the concentrator photovoltaic device.
The tub 101 is made of a heat conducting material. Thus, the tub both acts as a container and as a heat dissipating device for the light-to-electrical conversion units. As a matter of fact, the light-to electrical conversion units being fixed on the surface of the base of the tub, the large surface of the base of the heat conducting tub acts as an efficient radiator which participate to the dissipation of the heat generated in the concentrator photovoltaic device 1000 by the light focused on the light-to-electrical conversion units 104.
Preferentially, the tub 101 is made of a metal. Advantageously, the metal chosen to be resistant to corrosion, to be able to withstand the overpressure inside the chamber, and to be able to easily fix a tracking system (described hereafter) on the tub.
For example, the tub is made of 0,5mm to 1,5mm (for instance lmm) width steel and is coated with an Aluzinc coating sold by Arcelor-Mittal. As a matter of fact, this coating prevents corrosion of the tub's steel and allows external applications of the tub 101. The tub 101 can also be made of any other metal such as alumina, copper, ... or alloy of metals or any other non metal heat conducting material.
The tub 101 is preferably manufactured thanks to a stamping processing step and is for example a parallelepiped of 820 mm wide x 970mm long x 140mm high. Such stamping process is done thanks to machine press that can be a stamping press or a punching machine press. For instance, a classical punching machine press can be used.
Preferentially, the stamping process comprises three steps : stamping the tub, stamping the edge of the tub and stamping the bottom of the tub. Obviously the stamping process can comprise only one of the previously mentioned three steps, for instance the stamping of the bottom of the tub.
Then, such a stamping process allows that the bottom of the tub is stiffened.
For instance, the geometry of the stamped bottom of the tub is non developable.
The depth of the tub is a function of the thickness of the tub, of the matrix radius and of the radius of the punch.
If the thickness of the tub or if the radius of the punch is increased, then the depth of the tub can be increased.
For instance the steel used for the tub is DX56, and more particularly AZ (that has a particular good resistance to corrosion), which are steels (extra- stamping) that are well suited for the stamping process (Re is low, r is high and n is high). If the tub thickness is increased, the risk is to lower r and n.
The steel used can also be enamelled.
Preferentially, the chamber 100 is hermetically sealed thanks to a seal 105, for example a double barrier seal made with a butyl coating (e.g GDI 15 from Kόmmerling) surrounding a silicone (e.g. DC895 from Dow Corning) based core spacer and positioned between the tub 101 and the cover sheet 102 in order to protect the inside environment from moisture or contaminants of the outside environment.
More generally, the seal can comprises an elastomer (e.g. natural rubber, butyl rubber, Nitrile rubber, silicone rubber, polyisoprene, Polybutadiene, Styrene-butadiene, Chloroprene, EPDM, EVA, ...) based core spacer surrounded by a butyl coating (e.g. the "Vitroband" product sold by Bayer Vitrotechnic). Furthermore, the elastomer based core spacer surrounded by a butyl coating can be further surrounded by a silicone coating, e.g. DC895 from Dow Corning.
The volume of the chamber is delimited by the tub 101 and its cover sheet 102 and is chosen to be superior to 0.01 m3, for example to be 0.1 m3. In this volume, depending on the tub and transparent cover widths, internal thermal convection can occur that would allow to cool the light-to electrical conversion units 104 and then reinforces the overall heat dissipation in the concentrator photovoltaic device.
According to a first embodiment of the invention, the light-to-electrical conversion units 104 are crystalline silicon based "solar cells" or "photovoltaic cells".
According to a second embodiment of the invention, the light-to-electrical conversion units are triple-junction conversion cells, such as one containing a gallium- indium phosphide diode, for converting light in the visible portion of the light spectrum, a gallium arsenide diode, for converting light in the red and near infrared portion of the light spectrum, and a germanium diode, for converting light further in the infrared portion of the light spectrum. It will be appreciated, however, that other types of conversion cells are able to be used in accordance with the present invention.
In operation, incident light 10 follows an optical path :
from the sun 1 ,
through the transparent cover sheet 102,
through the means 103 which focus transmitted light
- onto a receiving area of the light-to electrical conversion units 104.
Then, each the light-to-electrical unit 104 converts the light into electrical energy, which is then transmitted to an electrical load, such as a motor, electronic device, or even a battery for storing the energy for later use. To simplify the illustration, Figure 1 does not show the chamber 100 coupled to an electrical load or battery.
Preferentially, each light-to electrical conversion unit 104 is glued on the surface of the base of the tub 101 thanks to a thermal conductive but electrically insulating glue 106. Obviously, according to the invention, instead of the thermal conductive but electrically insulating glue, a thermal conductive but electrically insulating conductive tape can be used to glue the light-to electrical conversion unit 104.
Thus the glue is thermally conductive which improves heat conduction from each light-to electrical conversion unit 104 to the tub 101 in order to optimize the radiator function of the tub 101, thus the glue reinforce the overall heat dissipation in the concentrator photovoltaic device 1000. But the glue 106 is electrically insulating to prevent electrical current leakages from the light-to electrical conversion units 104 to the tub 101 that would reduce the efficiency of the concentrator photovoltaic device 1000. As a matter of fact, bus bars 107 are disposed on the light-to electrical conversion unit 104 in order to collect electricity generated by the light-to electrical conversion units 104.
Moreover, the glue is preferably a silicone or acrylic based adhesive to resist the shear stress induced by the different movement of the light-to electrical conversion units 104 and of the tub 101 during heating and cooling of these components in function of the evolution in the day of the solar illumination. The length of the light-to electrical conversion units 104 is also optimized to reduce the shear stress on the glue.
An example of such glue 106 is the tape reference number 8820 sold by 3M.
Figure 3 is a side cross-sectional view of a concentrator photovoltaic device 3000 in accordance with a second embodiment of the present invention.
The concentrator photovoltaic device 3000 is the same as the concentrator photovoltaic device 1000 of figure 1 and 2 except that the chamber 300 of the concentrator photovoltaic device 3000 comprises a capillary tube 308 that is inserted in an orifice previously realized in the tub 301.
Thus the chamber 300 is connected to outside environment thanks to the capillary tube 308 to allow hot air to get out of the chamber 300 and fresh air to get in of the chamber 300 which then improve the overall heat dissipation in the concentrator photovoltaic device. The capillary tube 308 inner diameter and length should limit water diffusion when internal and external temperatures are equal, but also permits the air to flow through the channel when external and internal temperatures are different. The inner diameter is greater than 0.5mm, and more preferably greater than lmm. The length of the tube is greater than 5 cm, and preferably greater than 15 cm.
Moreover, in order to further reduce the humidity in the chamber, a cartridge 309 comprising a desiccant agent can be placed in the chamber 301. The desiccant agent is preferably a molecular sieve "phonosorb®" sold by GRACE- DA VISON in order to keep a high adsorption capacity even at high temperature or in very dry environment (below 10% relative humidity).
According to an embodiment of the present invention, the capillary tube
308 can be in thermal contact with the tub 301.
Thus the capillary tube and the air flowing into it participate to heat dissipation and then the overall heat dissipation of the concentrator photovoltaic device is further improved.
According to another embodiment (non illustrated) of the invention, the capillary tub 308 of figure 3 is replaced by a global capillary tube which comprises a dessicant cartridge.
For instance, the global capillary tube comprises :
a first capillary tub which makes the channel from the inside of the chamber 300 to the desiccant cartridge and
a second capillary tube which makes the channel from the desiccant cartridge to the external environment.
For instance, the first capillary tube and the dessicant cartridge are placed inside the chamber, the second capillary tube being inserted in a hole created on a side wall of the tub such that a first part of the second capillary tub is positioned inside the chamber and a second part of the second capillary tub is positioned outside the chamber. Preferentially, an adhesive or mechanical means is provided to hermetically seal the remaining hole.
The first capillary tube can be in thermal contact with the tub in order to dissipate more heat. The heat of the tub is used to heat the desiccant agent of the dessicant cartridge and makes it release some water when air is flowing outside the chamber. An additional external mesh can be provided to prevent dust coming into second capillary tube.
The concentrator photovoltaic device according to the invention can be used with a sun tracking system (system which orients the concentrator photovoltaic device such that it has the best orientation toward the sun along the day), to maximize the collected energy.
The tracking system shall be preferentially a single axis tracking system, to minimize the system complexity.
Obviously, the invention is not limited the above described embodiments.

Claims

1. Concentrator photovoltaic device (1000; 3000) comprising a chamber (100; 300) including :
- a tub (101; 301) defining a volume for containing at least one light-to electrical conversion unit (104) which are fixed to the surface of the base of the tub ;
- a transparent cover (102) sheet positioned at the top of the tub and transmitting the incident light from the exterior to the interior of the chamber ;
- means (103) to focus transmitted light on the at least one light-to electrical conversion unit ;
characterized in that the tub is made of a heat conducting material.
2. Concentrator photovoltaic device according to claim 1 , characterized in that the bottom of the tub is stamped thanks to machine press.
3. Concentrator photovoltaic device according to claim 2, characterized in that the chamber (100; 300) is hermetically sealed thanks to at least one seal (105) positioned between the top of the tub and the cover sheet.
4. Concentrator photovoltaic device according to claim 3, characterized in that the seal comprises an elastomer based core spacer surrounded by a butyl coating.
5. Concentrator photovoltaic device according to claim 4, characterized in that the elastomer based core spacer surrounded by a butyl coating is further surrounded by a silicone coating.
6. Concentrator photovoltaic device according to anyone of claim 1 to 5, characterized in that the chamber (100; 300) also comprises a capillary tube (308).
7. Concentrator photovoltaic device according to anyone of claims 1 to 6, characterized in that the chamber (100; 300) also comprises a cartridge of a desiccant material (309).
8. Concentrator photovoltaic device according to anyone of claims 1 to 7, characterized in that volume of the chamber (100; 300) is superior than 0.01 m3 and more preferentially superior than 0.1 m3.
9. Concentrator photovoltaic device according to anyone of claims 1 to 8, characterized in that the means to focus light on the at least one light-to electrical conversion unit comprise at least one reflecting panel.
10. Concentrator photovoltaic device according to claim 9, characterized in that at least one of the reflecting panels is covered at least partially by a diffusing coating.
11. Concentrator photovoltaic device according to anyone of claims 1 to 10, characterized in that the means to focus light on the at least one light-to electrical conversion unit comprise at least one converging lens.
12. Concentrator photovoltaic device according to anyone of claims 1 to 1 1, characterized in that the tub (101; 301) is made of at least one metal.
13. Concentrator photovoltaic device according to anyone of claims 1 to 12, characterized in that the light-to electrical conversion unit(s) is(are) glued to the tub thanks to thermal conductive but electrically insulating glue or adhesive tape (106).
14. Concentrator photovoltaic device according to anyone of claims 1 to 13, characterized in that the transparent cover sheet (102) is made of low iron glass.
15. Concentrator photovoltaic device according to anyone of claims 1 to 14, characterized in that the transparent cover sheet (102) is provided with at least one anti reflective coating.
PCT/EP2010/059633 2009-07-08 2010-07-06 Concentrator photovoltaïc device with an improved efficiency WO2011003903A2 (en)

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