WO2012060801A1 - Photovoltaic and thermal energy system - Google Patents

Photovoltaic and thermal energy system Download PDF

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Publication number
WO2012060801A1
WO2012060801A1 PCT/US2010/002878 US2010002878W WO2012060801A1 WO 2012060801 A1 WO2012060801 A1 WO 2012060801A1 US 2010002878 W US2010002878 W US 2010002878W WO 2012060801 A1 WO2012060801 A1 WO 2012060801A1
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Prior art keywords
solar cell
solar
hot water
sun
solar cells
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PCT/US2010/002878
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French (fr)
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WO2012060801A9 (en
Inventor
Gerald Falbel
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Solarchange, Llc
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Priority to PCT/US2010/002878 priority Critical patent/WO2012060801A1/en
Publication of WO2012060801A1 publication Critical patent/WO2012060801A1/en
Publication of WO2012060801A9 publication Critical patent/WO2012060801A9/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
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/05—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells
    • H01L31/0504—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells specially adapted for series or parallel connection of solar cells in a module
    • H01L31/0508—Electrical interconnection means between PV cells inside the PV module, e.g. series connection of PV cells specially adapted for series or parallel connection of solar cells in a module the interconnection means having a particular shape
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S23/00—Arrangements for concentrating solar-rays for solar heat collectors
    • F24S23/70—Arrangements for concentrating solar-rays for solar heat collectors with reflectors
    • F24S23/74—Arrangements for concentrating solar-rays for solar heat collectors with reflectors with trough-shaped or cylindro-parabolic reflective surfaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
    • F24S30/00—Arrangements for moving or orienting solar heat collector modules
    • F24S30/40—Arrangements for moving or orienting solar heat collector modules for rotary movement
    • F24S30/42—Arrangements for moving or orienting solar heat collector modules for rotary movement with only one rotation axis
    • F24S30/425—Horizontal axis
    • 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
    • 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
    • Y02E10/40—Solar thermal energy, e.g. solar towers
    • Y02E10/47—Mountings or tracking
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/52—PV systems with concentrators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/60—Thermal-PV hybrids
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P80/00—Climate change mitigation technologies for sector-wide applications
    • Y02P80/10—Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P80/00—Climate change mitigation technologies for sector-wide applications
    • Y02P80/20—Climate change mitigation technologies for sector-wide applications using renewable energy

Definitions

  • TITLE PHOTOVOLTAIC AND THERMAL ENERGY SYSTEM
  • Known photovoltaic systems generally employ fixed flat plate solar panels mounted at the latitude angle. These systems are inefficient with regard to a cost per watt for photovoltaic systems.
  • a combined diurnal tracking, concentrator, photovoltaic electricity/solar thermal hot water heating system reduces the cost per watt ratio by reducing the number of solar cells employed in the system by concentrating the sun's insolation on the solar cells. This reduction in the number of solar cells required to provide a given power output is achieved by concentrating sunlight on the cells using refractive or reflective optics, and by employing a simple clock motor to track the sun from sunrise to sunset in the diurnal tracking mode;
  • the combined photovoltaic electricity/solar thermal hot water heating systems in accordance with the present invention are mountable on flat roof industrial and multi-family dwellings, and on pitched roofs such as those generally found on single family residences.
  • the increased heat generated by the concentration of the sun's insolation on the reduced number of solar cells is drawn off by an anti-freeze fluid circulated in an aluminum extrusion to which the solar cells and the concentrator reflective or refractive optics are attached.
  • the circulated fluid is used for the dual purpose of providing domestic hot water or space heating to thereby provide additional cost savings resultant from the combined system, and to maintain solar cells cool to enhance the efficient operation thereof.
  • the optical components of the photovoltaic system employ piano mirrors as reflective side panels and a cylindrical Fresnel lens formed from a combination of two extruded acrylic half lenses cemented together.
  • the diurnal tracking system employs a "checkerboard" mounting pattern on a flat roof, which minimizes shading near noontime.
  • Figure 1 illustrates a cylindrical pyramid optic concentrator made up of faceted flat sections to spread the sun's irradiance evenly on the solar cells, with solar cells and domestic hot water or space heating, in accordance with the present invention
  • Figure 2 illustrates two types of diurnal tracking systems recessed into a south facing pitched roof, schematically illustrating a diurnal tracking recessed system using either a faceted cylindrical optic, or 1 ⁇ 2 Fresnal lens showing a diurnal clock drive, a connecting strut, and a copper tube for water or space heating;
  • Figure 3 illustrates a 34 solar cell string, arranged in a line and connected in series
  • Figure 4 illustrates sun trajectories at 32° south latitude from a reference
  • Figure 5 illustrates sun elevation angular trajectory within concentrator field at 40° north latitude (derived from the Figure 4 reference);
  • Figure 6 illustrates an extruded acrylic linear Fresnel lens in combination with piano reflective surfaces
  • Figure 7 illustrates a cylindrical faceted concentrator configuration with a 17 cell string
  • Figure 8 illustrates a flat roof mounting of a Fresnal lens concentrator system
  • Figure 8A illustrates the diurnal tracking configuration of the system illustrated by Figure
  • a combined diurnal tracking, concentrator, photovoltaic electrical generation system/domestic hot water or space heating solar thermal system is mountable on flat roof industrial buildings, flat roof multi-unit apartment buildings, and pitched roofs of single family residences.
  • the systems in accordance with the present invention may be exclusively diurnal in which the sun is tracked on a daily basis.
  • the systems in accordance with the present invention achieve a major reduction in the cbst-per-watt for photovoltaic systems as compared to flat plate panels by reducing the number of solar cells required for a given power output by almost 3/1 or 6/1.
  • the increased heat generated by a 3/1 or 6.1 concentration of the sun's insolation on the solar cells is drawn off by an anti-freeze fluid circulated in an aluminum extrusion, to which the solar cells and the pyramidal concentrator reflectors are attached.
  • This coolant is used to provide domestic hot water heating, thus providing additional cost savings for the user as well as making the solar cells more efficient, by keeping them cool.
  • the solar array is moved in elevation to coarsely track the sun from winter to summer solstices in the seasonal tracking mode, or pivoted from sunrise to sunset in the diurnal tracking mode using a simple clock motor to track the position of the sun, thus eliminating a costly closed loop solar tracking system.
  • This provides the additional advantage of achieving ideal near normal incidence of sunlight in one axis on the system throughout the year, as compared to fixed flat plate solar panels mounted at the latitude angle.
  • For the diurnal tracking configuration there is an improvement in energy collected throughout the day by an approximate factor 1.27/1 relative to fixed angle flat plate collectors.
  • the combined electrical energy generation improvement of the solar tracking and the heat removal at the summer solstice equals approximately 40%.
  • the faceted cylindrical pyramid optic concentrator concept consists of a combined photovoltaic/domestic hot water or space heating concentrator-collector unit shown in Figure 1.
  • the insolation incident on the pyramidal concentrator is reflected to commercially available, >17% efficiency solar cells currently available, with a concentration ratio of 3/1.
  • Four cell arrays using standard flat plate panel processes have been fabricated using these cells by SPIRE Inc. In production, 17 cell or 34 cell series strings similar to those currently in production for flat plate panels have been fabricated and will be used.
  • 17 cell modules using the faceted cylindrical concentrator optics are required. As is shown in Figures 1 and 8, these can be arranged in rows, in the north-south direction, on flat roofs or ground installations for industrial applications, thus minimizing wind loads relative to conventional flat plate collectors without domestic water heating. As can be seen in Figure 1, for hot water applications, the 17 cell arrays are mounted to aluminum extrusions into which copper tubes are snapped. These aluminum extrusions/copper tubing provide additional rigidity for large panels and are used as the frame for mounting multiple modules on roofs through a single axis elevation tracking system.
  • Either anti-freeze (or potable water in non-freezing areas) is pumped through the copper tubes, and the waste heat generated by the solar cells with the concentrated insolation is drawn off by the fluid to heat domestic hot water or provide domestic space heating. It is estimated that a 220 electrical watt system will provide enough waste heat to heat water in an 80 gallon tank from 54°F to 120 ° F in one sunny day. This provides a dual function of providing domestic hot water at close to 70% conversion efficiency (achieved by the 6/1 concentrators with mostly optical reflection/transmission losses), while at the same time generating d.c. electricity for use in grid-tied photovoltaic solar systems currently used in residences, or battery-backup co-generation facilities for minimizing peak power usage in industrial applications.
  • FIGS 8 and 8A show a proposed typical mounting of the diurnal tracking configuration on a flat roof.
  • the array is held down to the roof in the presence of wind using "sleepers" made up of wood or galvanized steel angles.
  • the arrays are held down to the roof by the greater than 200 pound combined weight of the optical arrays and the counterweight for each pivoted module. Larger north-south dimensions of the roof repetitions of the basic array shown can proportionally increase its power output. Also, by repeating the array in the east or west direction, the power output can also be increased proportionally.
  • Figure 2 shows the recessed mounting of the diurnal tracking configuration between the roof rafters on a south facing pitched roof with a slope of the local latitude ⁇ 5° for optimum performance, while also improving its aesthetics.
  • the orientation of the pitched roof to due south can vary by as much as ⁇ 15 ° , without significant losses in diurnal energy generation.
  • the diurnal tracking mechanism is composed of a 1600 step/revolution stepper motor driving a 75/1 reduction gearbox and a 5.2/1 chain drive system so that an input pulse rate of one pulse per 150 milliseconds closely tracks the diurnal movement of the sun. After sunset, the motor reverses and returns the orientation of the solar array to the time for beginning of solar collection (approximately 7:20 AM local time).
  • This diurnal tracking configuration designed for flat roofs, is shown in Figure 8.
  • the reflective side panels are piano mirrors and a cylindrical Fresnel lens extruded from acrylic material, focuses the sun in a blurred line image caused by chromatic aberrations behind the 34 cell array.
  • the Fresnel lens has dimensions of 30" x 108". This 108" lens dimension allows the sun to move from winter to summer solstice for the recessed pitched roof configuration shown in Figure 2, while still passing through the Fresnel lens concentrator and reaching the 86 inch long, 34 cell array under full concentration.
  • FIG. 6 illustrates the Fresnel lens employed as the concentrator for the photovoltaic system, illustrating Fresnel facets extruded on the inside surface of the lens.
  • Figure 8 also illustrates the aluminum extrusion on which the solar cells are mounted, and into which the tubing for the fluid coolant is connected. As is shown in Figure 8, preferably, the optical elements are mounted on a flat roof in a "checkerboard" pattern to minimize shading near noon.
  • Figure 2 illustrates a configuration of this system for diurnal tracking for south facing pitched roofs.
  • the pivot axis for these collectors are mounted near the window to capture sun for a maximum time peribd of 7:30 A.M. to 4:30 P.M. with full output and partial output outside this hourly range.
  • the advantage of this approach for the faceted cylindrical reflective configuration is that separate windows on the collectors are not needed.
  • the system uses highly efficiency silicon solar cells currently in production, thus requiring a smaller number of cells for a given power output, thereby reducing solar panel area.
  • the concentrator reduces the number of cells required for a given wattage by a factor of over 2.5/1, or 5/1, thus reducing the highest cost item in a photovoltaic solar panel by at least these ratios.
  • the high elevation angle of the plane of the window or Fresnal lens at the beginning and/or end of the diurnal tracking day allows any snow buildup to slide off, thereby eliminating the zero energy collection applicable to snow covered fixed flat plate solar panels.
  • the waste heat generated by the solar cells is collected by a solar thermal aluminum substrate containing copper tubes, which provides domestic hot water heating at close to 70% efficiency, while removing excess heat from the solar cells to increase the efficiency of operation thereof, thus providing additional economic justification and reducing the overall payback period.
  • the hot water or space heating extrusions "pay their way” by providing housing rigidity normally provided by the extra cost aluminum housings of flat plate panels.
  • This arrangement doubles the voltage per each 84" string, and halves the current, while maintaining the same power output, thereby easing the requirements for reducing the resistance of the conducting ribbons.
  • the total aperture area accepting sunlight of one module is the total aperture area accepting sunlight of one module

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Abstract

A combined diurnal tracking, concentrator, photovoltaic plus domestic hot water solar thermal system is mountable on flat roof industrial buildings or multi-unit apartment buildings for diurnal tracking, and on pitched roofs of single family residences. The systems are configured to reduce the number of solar cells required for given power output, and increased generated heat by a concentration of the sun's insolation on the solar cells. The increased heat is drawn off by anti-freeze fluid circulated in an aluminum extrusion attached to the solar cells and concentrator reflectors for the dual purpose of providing domestic hot water or space heating and maintaining the solar cells cool to enhance their efficiency.

Description

TITLE: PHOTOVOLTAIC AND THERMAL ENERGY SYSTEM
BACKGROUND OF THE INVENTION
Known photovoltaic systems generally employ fixed flat plate solar panels mounted at the latitude angle. These systems are inefficient with regard to a cost per watt for photovoltaic systems.
It is an object of the present invention to decrease the cost per watt for photovoltaic systems, as compared to the flat plate panel systems, by reducing the number of solar cells required for a given power output, while drawing off the heat generated by the concentration of the sun's insolation on the solar cells to maintain the solar cells at a relatively cool temperature to enhance the efficiency thereof, and to provide domestic hot water or space heating.
SUMMARY OF THE INVENTION
A combined diurnal tracking, concentrator, photovoltaic electricity/solar thermal hot water heating system reduces the cost per watt ratio by reducing the number of solar cells employed in the system by concentrating the sun's insolation on the solar cells. This reduction in the number of solar cells required to provide a given power output is achieved by concentrating sunlight on the cells using refractive or reflective optics, and by employing a simple clock motor to track the sun from sunrise to sunset in the diurnal tracking mode; The combined photovoltaic electricity/solar thermal hot water heating systems in accordance with the present invention are mountable on flat roof industrial and multi-family dwellings, and on pitched roofs such as those generally found on single family residences. The increased heat generated by the concentration of the sun's insolation on the reduced number of solar cells is drawn off by an anti-freeze fluid circulated in an aluminum extrusion to which the solar cells and the concentrator reflective or refractive optics are attached. The circulated fluid is used for the dual purpose of providing domestic hot water or space heating to thereby provide additional cost savings resultant from the combined system, and to maintain solar cells cool to enhance the efficient operation thereof. Preferably, the optical components of the photovoltaic system employ piano mirrors as reflective side panels and a cylindrical Fresnel lens formed from a combination of two extruded acrylic half lenses cemented together. Preferably the diurnal tracking system employs a "checkerboard" mounting pattern on a flat roof, which minimizes shading near noontime. BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a cylindrical pyramid optic concentrator made up of faceted flat sections to spread the sun's irradiance evenly on the solar cells, with solar cells and domestic hot water or space heating, in accordance with the present invention;
Figure 2 illustrates two types of diurnal tracking systems recessed into a south facing pitched roof, schematically illustrating a diurnal tracking recessed system using either a faceted cylindrical optic, or ½ Fresnal lens showing a diurnal clock drive, a connecting strut, and a copper tube for water or space heating;
Figure 3 illustrates a 34 solar cell string, arranged in a line and connected in series;
Figure 4 illustrates sun trajectories at 32° south latitude from a reference;
Figure 5 illustrates sun elevation angular trajectory within concentrator field at 40° north latitude (derived from the Figure 4 reference);
Figure 6 illustrates an extruded acrylic linear Fresnel lens in combination with piano reflective surfaces;
Figure 7 illustrates a cylindrical faceted concentrator configuration with a 17 cell string; Figure 8 illustrates a flat roof mounting of a Fresnal lens concentrator system; and
Figure 8A illustrates the diurnal tracking configuration of the system illustrated by Figure
DISCUSSION OF THE BEST MODES FOR CARRYING OUT THE INVENTION
A combined diurnal tracking, concentrator, photovoltaic electrical generation system/domestic hot water or space heating solar thermal system is mountable on flat roof industrial buildings, flat roof multi-unit apartment buildings, and pitched roofs of single family residences. The systems in accordance with the present invention may be exclusively diurnal in which the sun is tracked on a daily basis.
The systems in accordance with the present invention achieve a major reduction in the cbst-per-watt for photovoltaic systems as compared to flat plate panels by reducing the number of solar cells required for a given power output by almost 3/1 or 6/1. The increased heat generated by a 3/1 or 6.1 concentration of the sun's insolation on the solar cells is drawn off by an anti-freeze fluid circulated in an aluminum extrusion, to which the solar cells and the pyramidal concentrator reflectors are attached. This coolant is used to provide domestic hot water heating, thus providing additional cost savings for the user as well as making the solar cells more efficient, by keeping them cool. The solar array is moved in elevation to coarsely track the sun from winter to summer solstices in the seasonal tracking mode, or pivoted from sunrise to sunset in the diurnal tracking mode using a simple clock motor to track the position of the sun, thus eliminating a costly closed loop solar tracking system. This provides the additional advantage of achieving ideal near normal incidence of sunlight in one axis on the system throughout the year, as compared to fixed flat plate solar panels mounted at the latitude angle. For the diurnal tracking configuration, there is an improvement in energy collected throughout the day by an approximate factor 1.27/1 relative to fixed angle flat plate collectors. The combined electrical energy generation improvement of the solar tracking and the heat removal at the summer solstice equals approximately 40%.
The faceted cylindrical pyramid optic concentrator concept consists of a combined photovoltaic/domestic hot water or space heating concentrator-collector unit shown in Figure 1. The insolation incident on the pyramidal concentrator is reflected to commercially available, >17% efficiency solar cells currently available, with a concentration ratio of 3/1. Four cell arrays using standard flat plate panel processes have been fabricated using these cells by SPIRE Inc. In production, 17 cell or 34 cell series strings similar to those currently in production for flat plate panels have been fabricated and will be used.
In order to generate 0.68 Kwatt at local noon, six, 17 cell modules using the faceted cylindrical concentrator optics are required. As is shown in Figures 1 and 8, these can be arranged in rows, in the north-south direction, on flat roofs or ground installations for industrial applications, thus minimizing wind loads relative to conventional flat plate collectors without domestic water heating. As can be seen in Figure 1, for hot water applications, the 17 cell arrays are mounted to aluminum extrusions into which copper tubes are snapped. These aluminum extrusions/copper tubing provide additional rigidity for large panels and are used as the frame for mounting multiple modules on roofs through a single axis elevation tracking system. Either anti-freeze (or potable water in non-freezing areas) is pumped through the copper tubes, and the waste heat generated by the solar cells with the concentrated insolation is drawn off by the fluid to heat domestic hot water or provide domestic space heating. It is estimated that a 220 electrical watt system will provide enough waste heat to heat water in an 80 gallon tank from 54°F to 120°F in one sunny day. This provides a dual function of providing domestic hot water at close to 70% conversion efficiency (achieved by the 6/1 concentrators with mostly optical reflection/transmission losses), while at the same time generating d.c. electricity for use in grid-tied photovoltaic solar systems currently used in residences, or battery-backup co-generation facilities for minimizing peak power usage in industrial applications. In addition to its economic advantages, the removal of heat from the solar cells for hot water heating also advantageously reduces the operating temperature of the solar cells, to improve their efficiency. Typical efficiency losses of silicon cells are 0.5% per °C above 26°C. Therefore, in the summer, by cooling the cells to 25°C, such as in heating a swimming pool, this system will provide a 12.5% improved output as compared to conventional uncooled flat plate panels, which can heat up to 50°C. A photograph of an early prototype of a 17 cell faceted cylindrical concentrator version of the proposed system is shown in Figure 7.
Figures 8 and 8A show a proposed typical mounting of the diurnal tracking configuration on a flat roof. As can be seen, there are no roof penetrations for mounting the solar array, thus eliminating possible leaks caused by the mounting of the solar array. The array is held down to the roof in the presence of wind using "sleepers" made up of wood or galvanized steel angles. The arrays are held down to the roof by the greater than 200 pound combined weight of the optical arrays and the counterweight for each pivoted module. Larger north-south dimensions of the roof repetitions of the basic array shown can proportionally increase its power output. Also, by repeating the array in the east or west direction, the power output can also be increased proportionally.
Figure 2 shows the recessed mounting of the diurnal tracking configuration between the roof rafters on a south facing pitched roof with a slope of the local latitude ±5° for optimum performance, while also improving its aesthetics. In addition, the orientation of the pitched roof to due south can vary by as much as ±15°, without significant losses in diurnal energy generation.
The diurnal tracking mechanism is composed of a 1600 step/revolution stepper motor driving a 75/1 reduction gearbox and a 5.2/1 chain drive system so that an input pulse rate of one pulse per 150 milliseconds closely tracks the diurnal movement of the sun. After sunset, the motor reverses and returns the orientation of the solar array to the time for beginning of solar collection (approximately 7:20 AM local time).
This diurnal tracking configuration, designed for flat roofs, is shown in Figure 8. In this configuration, the reflective side panels are piano mirrors and a cylindrical Fresnel lens extruded from acrylic material, focuses the sun in a blurred line image caused by chromatic aberrations behind the 34 cell array. As also shown in Figure 6, the Fresnel lens has dimensions of 30" x 108". This 108" lens dimension allows the sun to move from winter to summer solstice for the recessed pitched roof configuration shown in Figure 2, while still passing through the Fresnel lens concentrator and reaching the 86 inch long, 34 cell array under full concentration. 6 illustrates the Fresnel lens employed as the concentrator for the photovoltaic system, illustrating Fresnel facets extruded on the inside surface of the lens. Figure 8 also illustrates the aluminum extrusion on which the solar cells are mounted, and into which the tubing for the fluid coolant is connected. As is shown in Figure 8, preferably, the optical elements are mounted on a flat roof in a "checkerboard" pattern to minimize shading near noon.
Figure 2 illustrates a configuration of this system for diurnal tracking for south facing pitched roofs. The pivot axis for these collectors are mounted near the window to capture sun for a maximum time peribd of 7:30 A.M. to 4:30 P.M. with full output and partial output outside this hourly range. The advantage of this approach for the faceted cylindrical reflective configuration is that separate windows on the collectors are not needed.
In summary, the following advantages are applicable to the systems of the present invention:
1. The system uses highly efficiency silicon solar cells currently in production, thus requiring a smaller number of cells for a given power output, thereby reducing solar panel area.
2. The concentrator reduces the number of cells required for a given wattage by a factor of over 2.5/1, or 5/1, thus reducing the highest cost item in a photovoltaic solar panel by at least these ratios.
3. By mounting the encapsulated cells directly to the aluminum extrusion using thermally conducting paste or thermal conducting interface sheets, and not permanently bonding them to the cover glass as is prevalent in flat plate collectors, solar systems can be economically upgraded with more efficient solar cells as they become available, an advantage which is impossible with flat plate solar panels.
The high elevation angle of the plane of the window or Fresnal lens at the beginning and/or end of the diurnal tracking day allows any snow buildup to slide off, thereby eliminating the zero energy collection applicable to snow covered fixed flat plate solar panels.
The waste heat generated by the solar cells is collected by a solar thermal aluminum substrate containing copper tubes, which provides domestic hot water heating at close to 70% efficiency, while removing excess heat from the solar cells to increase the efficiency of operation thereof, thus providing additional economic justification and reducing the overall payback period.
The hot water or space heating extrusions "pay their way" by providing housing rigidity normally provided by the extra cost aluminum housings of flat plate panels.
Experimentation has identified a potential limitation in obtaining the required current output from conventional solar cells as a result of limitations in the conductivity of the ribbon wire used to route the current generated in the cells out to the collector terminals. Modifications to the construction of standard cells used for non-concentrating cells in flat plate collectors can mitigate the limitations. More specifically, use of thicker and wider ribbons and more "fingers" in the solar cell will reduce the combined cell and ribbon resistance by a factor of approximately 10/1. A preferred method of solving this high current problem is to use standard 125mm. x 125mm. solar cells cut in half to 62.5mm x 125. mm, arranged in strings as shown in Figure 1. This arrangement doubles the voltage per each 84" string, and halves the current, while maintaining the same power output, thereby easing the requirements for reducing the resistance of the conducting ribbons. There are additional considerations in making the ribbon wider since for wider ribbon, some sunlight is prevented from reaching the cell, thereby reducing the quantity of electrical energy generated by the solar cell. Accordingly, a tradeoff is necessary in which optimum combination of ribbon with number of ribbons per cell, ribbon thickness, and "finger spacing" maximize the output power of the cell string. This tradeoff is eased by using www.1366tech.com "corrugated" reflective ribbon, manufactured by Ulbrich, Inc., which directs the reflected solar irradiance back onto the solar cell, thereby compensating for the shadow effect and allowing the use of a wider ribbon to reduce electrical resistance and increase electrical conductivity. PERFORMANCE AND COST/WATT
The expected solar power collected by each 17 cells module shown in Figure 8A using 17% efficiency cells is calculated in Table I. The manufacturing cost of the modules is summarized in Table II. Calculations of diurnal tracking as exposed to flat plate collectors are indicated in Table III.
TABLE I: SOLAR POWER COLLECTION (6/1 FRESNEL LENS SYSTEM)
The total aperture area accepting sunlight of one module
The total area of the 17 cells
The light transrnittance, of the acrylic Fresnel Lens
Net concentration ratio considering transrnittance
The net output of the cells without concentration: (manuf. rating/cell x I 7 =
The net output of the cells from the pyramid reflections 45 x 4.93 =
TOTAL OUTPUT OF ONE 17 CELL MODULE
TABLE II
MATERIAL COST PER 17 CELL MODULE USING CHINESE SOLAR CELLS
Prototype quantity quote for sealed 34 cell strings;
Cost of extruded acrylic Fresnel lens -(500 quantity)
Cost of aluminized polyester reflective side reflectors
Cost of aluminum extrusion and copper tube
Cement and thermal conduction -compound
.'TOTAL MATERIAL COST
Assembly labor
TOTAL COST PER 240 WATT 17 CELL MODULE
TOTAL COST IN $/WATT = $468/221.9 $2.11 /WAIT+ FREE HOT WATER
TABLE III
For flat photovoltaic panels (and solar thermal panels) the solar power absorbed by the panel degrades proportional to the cosine of the angle between the perpendicular to the panel and the angle to the sun. For a diurnal tracking system the solar collector is always perpendicular ΓΝ ONE AXIS to the sun Ime, in the elevation plane, so the cosine multiplier is always 1.0. The intergrated energy for fixed flat plate collectors and a diurnal tracking system in watt-hours is given as follows showing that A diurnal tracking system WHOSE PIVOT AXIS IS MOUNTED AT AN ELEVATION ANGLE OF THE LOCAL LATITUDE, provides 27% more Kilowatt-hours per sunny day as compared to fixed panels:
FIXED FLAT PLATE COLLECTOR: DIURNAL TRACKING SYSTEM:
TIME IRRADIANCE ABSORBED TIME IRRADIANCE ABSORBED
(AT EQUINOX) (AT EQUINOX)
12: NOON 1,000 WATTS/m2 12: NOON 1,000 WATTS/m2
1:00, 11:00 966 WATTS/m' 1:00, 11:00 1,000 WATTS/m'
2:00, 10:00 866 WATTS/m2 2:00m 10:00 1, 000 WATTS/m2
3:00, 9:00 707 WATTS/m' 3:00, 9:00 1,000 WATTS/m'
4:00, 8:00 500 WATTS/m2 4:00, 8:00 1,000 WATTS/m2
TOTAL: 7.1 KILOWATT-HOURS/m2 TOTAL: 9.0 KILOWATT-HOURS/m2

Claims

Claim 1. Photovoltaic electrical generator system including at least one solar cell, and means for moving said at least one solar cell for diurnal tracking of the sun.
Claim 2. The system as claimed in claim 1, further including an optical element for concentrating sunlight onto said at least one solar cell.
Claim 3. The system as claimed in claim 2, wherein said optical element comprises a Fresnel lens.
Claim 4. The system as claimed in claim 3, wherein said optical element includes at least one piano reflective surface.
Claim 5. The system as claimed in claim 4, further including a plurality of said solar cells and optical elements arranged in a checkerboard pattern.
Claim 6. The system as claimed in claim 1, including means for coupling a pipe to said at least one solar cell for removing heat therefrom by fluid flow through said pipe.
Claim 7. The system as claimed in claim 6, including means for supplying heat removed from said at least one solar cell to a water heating system for heating water within a water storage tank or for providing space heating.
Claim 8. The system as claimed in claim 1, wherein said means for moving said at least one solar cell for diurnal tracking of the sun includes a clock motor.
Claim 9. A combined photovoltaic electrical generator and thermal hot water or space heating system, said system comprising: at least one solar cell, and means for moving said at least one solar cell for diurnal tracking of the sun; a pipe having a first end coupled to said at least one solar cell, and a second and coupled to a hot water or space heating system; wherein fluid flow through said pipe removes heat from said at least one solar cell and supplies said heat to said hot water or space heating system.
Claim 10. The system as claimed in claim 9, wherein said means moving said at least one solar cell includes a clock motor for pivoting said at least one solar cell for diurnal tracking of the sun.
Claim 11. The system as claimed in claim 9, further including an optical element for concentrating sunlight onto said at least one solar cell.
Claim 12. The system as claimed in claim 11, wherein said optical element includes a Fresnel lens and at least one piano reflective surface.
Claim 13. The system as claimed in claim 1, wherein a plurality of said solar cells form a string, the ratio of width to length along said string being at least 2/1.
Claim 14. A method for generating photovoltaic electrical energy, said method including the steps of: mounting at least one solar cell to a roof structure; and moving said at least one solar cell for diurnal tracking of the sun.
Claim 15. The method as claimed in claim 14, wherein the step of moving said at least one solar cell includes pivoting said at least one solar cell by a clock motor.
Claim 16. The method as claimed in claim 14, including the step of providing an optical element for concentrating sunlight onto said at least one solar cell.
Claim 17. The method as claimed in claim 16, further including the steps of providing a plurality of said solar cells and optical elements, and arranging said plurality of said solar cells and said optical elements in a checkerboard pattern.
Claim 18. The method as claimed in claim 14, further including the step of causing fluid flow proximate to said at least one solar cell for removing heat from said at least one said solar cell for improving the efficiency thereof.
Claim 19. The method as claimed in claim 18, further including the step of providing said heat removed from said at least one solar cell to a thermal hot water or space heating system.
Claim 20. The method as claimed in claim 19, wherein the step of providing heat removed from said at least one solar cell to a thermal hot water or space heating system includes providing a pipe having a first end in fluid communication with said at least one solar cell and a second end in fluid communication with the hot water or space heating system.
PCT/US2010/002878 2010-11-01 2010-11-01 Photovoltaic and thermal energy system WO2012060801A1 (en)

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