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WO2014089215A1 - Système solaire photovoltaïque de chauffage d'eau - Google Patents

Système solaire photovoltaïque de chauffage d'eau Download PDF

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Publication number
WO2014089215A1
WO2014089215A1 PCT/US2013/073124 US2013073124W WO2014089215A1 WO 2014089215 A1 WO2014089215 A1 WO 2014089215A1 US 2013073124 W US2013073124 W US 2013073124W WO 2014089215 A1 WO2014089215 A1 WO 2014089215A1
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WO
WIPO (PCT)
Prior art keywords
water
resistance
current power
resistance heating
control system
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/US2013/073124
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English (en)
Inventor
Michael Newman
Glen Newman
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SOLAR ENERGY LABS Inc
Original Assignee
SOLAR ENERGY LABS Inc
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Filing date
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Publication of WO2014089215A1 publication Critical patent/WO2014089215A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
    • F24D18/00—Small-scale combined heat and power [CHP] generation systems specially adapted for domestic heating, space heating or domestic hot-water supply
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
    • F24D19/00—Details
    • F24D19/10—Arrangement or mounting of control or safety devices
    • F24D19/1006—Arrangement or mounting of control or safety devices for water heating systems
    • F24D19/1051—Arrangement or mounting of control or safety devices for water heating systems for domestic hot water
    • F24D19/1057—Arrangement or mounting of control or safety devices for water heating systems for domestic hot water the system uses solar energy
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H1/00—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters
    • F24H1/18—Water-storage heaters
    • F24H1/20—Water-storage heaters with immersed heating elements, e.g. electric elements or furnace tubes
    • F24H1/201—Water-storage heaters with immersed heating elements, e.g. electric elements or furnace tubes using electric energy supply
    • F24H1/202—Water-storage heaters with immersed heating elements, e.g. electric elements or furnace tubes using electric energy supply with resistances
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/10—Control of fluid heaters characterised by the purpose of the control
    • F24H15/128—Preventing overheating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/10—Control of fluid heaters characterised by the purpose of the control
    • F24H15/174—Supplying heated water with desired temperature or desired range of temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/20—Control of fluid heaters characterised by control inputs
    • F24H15/212—Temperature of the water
    • F24H15/223—Temperature of the water in the water storage tank
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/20—Control of fluid heaters characterised by control inputs
    • F24H15/242—Pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/30—Control of fluid heaters characterised by control outputs; characterised by the components to be controlled
    • F24H15/305—Control of valves
    • F24H15/315—Control of valves of mixing valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/30—Control of fluid heaters characterised by control outputs; characterised by the components to be controlled
    • F24H15/355—Control of heat-generating means in heaters
    • F24H15/37—Control of heat-generating means in heaters of electric heaters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/40—Control of fluid heaters characterised by the type of controllers
    • F24H15/407—Control of fluid heaters characterised by the type of controllers using electrical switching, e.g. TRIAC
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/40—Control of fluid heaters characterised by the type of controllers
    • F24H15/414—Control of fluid heaters characterised by the type of controllers using electronic processing, e.g. computer-based
    • F24H15/421—Control of fluid heaters characterised by the type of controllers using electronic processing, e.g. computer-based using pre-stored data
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H15/00—Control of fluid heaters
    • F24H15/40—Control of fluid heaters characterised by the type of controllers
    • F24H15/414—Control of fluid heaters characterised by the type of controllers using electronic processing, e.g. computer-based
    • F24H15/45—Control of fluid heaters characterised by the type of controllers using electronic processing, e.g. computer-based remotely accessible
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
    • F24D2101/00—Electric generators of small-scale CHP systems
    • F24D2101/40—Photovoltaic [PV] modules
    • 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

Definitions

  • the invention relates to a direct current (DC), photovoltaic (PV) water heating system.
  • DC direct current
  • PV photovoltaic
  • the invention is a photovoltaic water heating system that controls the electrical energy used to heat the water.
  • a solar water heating system that comprises a series of large diameter pipes connected in series in a wooden box, insulated with sand, and covered with green house glass panes.
  • the pipes contained a volume of water that was directly heated by solar irradiance during the day for use in the evening.
  • an improved solar water heating system comprised a separate solar collector and a storage tank.
  • the solar collector used the decrease in the density of the water when heated to move water into the tank. This arrangement created a thermo- siphonic flow.
  • Solar water heating systems have been evolving along those same technological lines ever since. Essentially, there is a tank, a collector, and a means to move heat energy from the collector to the tank.
  • the solar water heating system discloses a solar water heating system that uses solar generated electricity from photovoltaic panels to power specialized electric resistance heating elements that are fully immersed in the water heater tank.
  • the resistance heating elements are connected in various parallel combinations, directly to the DC output of the photovoltaic solar panels.
  • a computer control system selects the configuration of resistance elements to match the electric power output characteristics of the photovoltaic panels.
  • the computer control system measures the power characteristics of the photovoltaic panels and operates electrical/mechanical relays that provide the direct connection of the DC power from the photovoltaic array to the resistance heating element combinations.
  • the heating element combinations are determined to extract the optimum amount of power from the photovoltaic array.
  • the solar water heating system of the Fanney et al. patent is, however, limited to a maximum of 7 combinations of resistance and those combinations are not mathematically optimized to achieve even step changes in power delivery from the PV panel array.
  • Ashkenazy United States Patent Application Publication No. 20120187106 entitled “Photovoltaic Heater”, filed on March 29, 2012, discloses a photovoltaic heating system that relies on an inverter device for the conversion of direct current from a photovoltaic solar array to alternating current (AC) to power a conventional resistance heating element.
  • DC to AC inverters have been used in PV systems for homes for many years to provide AC power for the various loads and appliances including resistance water heaters.
  • the Ashkenazy Application further discloses a switching circuit that disconnects the inverter's AC power from the resistance heating elements and connects the AC power from the electrical grid to the resistance heating elements. Consequently, the resistance heating elements are switched between one AC power source of a variable level (solar) to another AC power source of a known and constant level (electrical grid).
  • the solar photovoltaic water heating system of the present invention comprises a solar PV array consisting of PV panels, a water storage tank for storing heated water, resistance heating elements in the water tank for heating the water, and a programmable control system for delivering DC power from the PV panels to the resistance heating elements.
  • the solar photovoltaic water heating system of the present invention assures safety for the users of the hot water and assures safety in connection with the use of direct electric current.
  • the solar photovoltaic water heating system is an advancement over other DC power powered direct PV heating systems in that the present invention employs formulae and methods for more accurately determining power output from the PV panels of the PV array in order to optimize energy deliver over a wider range of operating conditions.
  • a feature of the present invention is the programmable control system that switches or redirects power available from the PV panels of the PV array when the hot water load demand has been met.
  • a further feature of the present invention is a method implemented by the control system that causes the photovoltaic water heating system to store higher temperature water in the storage tank but then safely delivers water at a lower temperature to the users of the hot water, thus allowing more energy to be stored in the tank during periods of high solar irradiance.
  • the programmable control system which includes a high temperature limit switch to insure water temperatures do not exceed the practical operating limit of the particular storage tank being used, thereby prolonging the life of the storage tank and reducing warranty claims and issues.
  • An additional feature of the present invention is a method implemented by the control system for determining the best resistance values for multiple resistance heating elements that are used in varied connection arrangements to maximize electrical energy delivery from the PV array.
  • the method includes formulae to determine resistance values for the resistance heating elements that create more even steps in the power point tracking of the energy delivered from the PV array to the resistance heating elements.
  • a further feature of the present invention is a method of accumulating and storing data related to the energy delivered by the PV array to the resistance heating elements and to report that data to a remote data acquisition system.
  • Another feature of the present invention is a multiple resistance heating element having four individual and discrete heating elements in a single assembly.
  • the four prong resistance heating element is adaptable for use with either AC or DC electrical power.
  • An additional feature of the present invention is a structure for the four pronged resistance heating element that can be used for either AC or DC electrical power.
  • FIG. 1 is a schematic diagram of a solar photovoltaic water heating system in accordance with the present invention.
  • FIG. 2 is a perspective view of a storage tank in accordance with the present invention.
  • FIG. 3 is a top plan view of the storage tank in accordance with the present invention.
  • FIG. 4 is a side elevation view of the storage tank in accordance with the present invention.
  • FIG. 5 is a perspective view of a four pronged electrical resistance heating element in accordance with the present invention.
  • Fig. 6 is a schematic diagram of a resistance value switching circuit in accordance with the present invention.
  • Fig. 7 is a schematic diagram of another resistance value switching circuit in accordance with the present invention.
  • Fig. 8 is a data table showing irradiance performance of a typical photovoltaic panel.
  • Fig. 9 is a flowchart of the control logic that is used in the photovoltaic water heating system to control energy delivery from a solar panel array to the four pronged electrical resistance heating element.
  • Fig. 10 is a graph illustrating of a theoretical ideal power curve for an infinitely variable resistance load for a variable direct current power source and illustrating the power curve for the four pronged resistance heating element, connected in various combinations to provide a variable resistance load.
  • Figs. 11 a and l ib are graphs illustrating two power point matching curves that illustrate step changes in power (wattage) as a function of changes in solar irradiance.
  • Fig. 12a and 12b are data tables used in developing resistance values for optimum operation of the photovoltaic water heating system in accordance with the present invention.
  • Fig. 13a-13c are data tables used in developing system resistance values for optimum operation of the photovoltaic water heating system in accordance with the present invention.
  • the solar photovoltaic water heating system 1 includes a photovoltaic panel array 31 consisting of individual solar photovoltaic panels 18, a water storage tank 10 with resistance heating elements 15, a programmable control system 16, and an alternating current power source 32.
  • the control system 16 is connected between the storage tank 10 and the photovoltaic panel array 31 and the alternating current power source 32 in order to control the delivery of power from either the photovoltaic panel array 31 or the alternating current power source 32 to the resistance heating elements 15.
  • One of the heating elements 15 may be a standard alternating current resistance heating element that is only connected to the alternating current power source 32.
  • both heating elements 15 may be alternating current and direct current compatible, resistance heating elements such as the resistance heating element 15 shown in Fig. 5 and described below.
  • the photovoltaic panels 18 are conventional and produce direct current power when exposed to irradiance 19 from the Sun 20.
  • the amount of direct current power produced by each photovoltaic panel 18 depends on the level of irradiance 19 impinging on the photovoltaic panels 18. Consequently, because the level of irradiance 19 varies based on the time of day and atmospheric conditions, the level of direct current power produced by each photovoltaic panel 18 varies accordingly.
  • Figs. 13a- 13c arc graphs that show the typical energy available from the photovoltaic array 31 for different voltages, power levels, and averages.
  • the water storage tank 10 is generally conventional and is shown in Figs. 2-4.
  • the water storage tank 10 includes a cold water inlet 22 extending to near the bottom of the storage tank 10 for the introduction of cold water 12 into the storage tank 10.
  • the storage tank 10 further includes a hot water outlet 21 extending into the upper part of the storage tank 10.
  • a mixing valve 17 is connected to the hot water outlet 21 and to a cold water shunt 33 in order to provide a mixture of hot and cold water to the hot water outlet 11 , which in turn is connected to a consumer water system (not shown).
  • the mixing valve 17 is thermostatically controlled to ensure that the hot water 11 is not too hot for a consumer water system such as residential hot water system.
  • the operation of the mixing valve 17 allows the water in the storage tank 10 to be raised substantially higher than a normal residential consumer water system thereby allowing the solar photovoltaic water heating system 1 to store more energy in the storage tank 10.
  • the water storage tank 10 further includes a cover 25 for housing and protecting the control systems 16 and associated wiring.
  • a pressure relief safety valve 23 is also connected to and in communication with the interior of the water storage tank 10. If the pressure inside the water storage tank 10 exceeds a preselected level for the relief safety valve 23, the relief safety valve 23 opens so that the pressure inside the water storage tank 10 can be relieved.
  • the resistance heating elements 15 are located in the water storage tank 10 at one or more levels to ensure consistency of the water temperature in the water storage tank 10. As shown in Fig. 5, the resistance heating element 15 comprises, for example, four individual resistance heating rods 29 connected through a stainless steel fitting 26.
  • the resistance heating rods 29 may be formed of stainless steel, inconel, carbon steel, or copper.
  • the stainless steel fitting 26 is threaded into the side of the water storage tank 10 to form a water and pressure tight seal.
  • Each individual resistance heating rod 29 has a pair of connecting wires 27 that allow each resistance heating rod 29 to be individually connected to either the photovoltaic array 31 or the direct current power source 32 through a switching circuit, such as one of switching circuits 34 (Fig. 6) and 35 (Fig. 7).
  • the switching circuits 34 and 35 are controlled by the control system 16 in order to select the optimum load resistance, such as direct current load resistance RloadDC 37 or RloadDC 39 for the direct current power source 31 (photovoltaic array 31 ) or alternating current load resistance RloadAC 36 or RloadAC 38 for the alternating current power source 32 (public power grid).
  • the switching circuit 34 illustrates a first configuration and is configured to provide seven resistance values for the direct current load resistance RloadDC 37 and one resistance value for the alternating current load resistance RloadAC 36.
  • the switching circuit 34 comprises a DC switch 41 , an AC switch 42, and a resistance array including fixed value resistors R4, R6, R7, and R9 with their associated switches.
  • the resistors R4, R6, R7, and R9 represent each of the four individual heating rods 29 in the resistance heating element 15.
  • the control system 16 opens and closes the DC switch 41, the AC switch 42, and the switches associated with each of the resistors R4, R6, R7, and R9 in order to select the optimum direct current load resistance RloadDC 37 for the direct current power source 31 or the optimum alternating current load resistance RloadAC 36 for the alternating current power source 32. Selection of the optimum load resistance RloadDC 37 or RloadAC 36 maximizes the energy delivered to the water in the water storage tank 10 by either the direct current power source 31 or the alternating current power source 32.
  • the switching circuit 35 illustrates a second configuration and is configured to provide 14 resistance values for the direct current load resistance RloadDC 39 and one resistance value for the alternating current load resistance RloadAC 38.
  • the switching circuit 35 comprises a DC switch 43, an AC switch 44, and a resistance array including fixed value resistors Rl l , R12, R13, and R14 with their associated switches.
  • the resistors Rl l , R12, R13, and R14 represent each of the four individual heating rods 29 in the resistance heating element 15.
  • the control system 16 opens and closes the DC switch 43, the AC switch 44, and the switches associated with each of the resistors Rl l , R12, R13, and R14 in order to select the optimum direct current load resistance RloadDC 39 for the direct current power source 31 or the optimum alternating current load resistance RloadAC 38 for the alternating current power source 32. Selection of the optimum load resistance RloadDC 39 or RloadAC 38 maximizes the energy delivered to the water in the water storage tank 10 by either the direct current power source 31 or the alternating current power source 32.
  • the formula set forth below establishes the values for the fixed resistors R4, R6, R7, and R9 (the resistance heating rods 29 of the resistance heating element 15).
  • the control system 16 runs an algorithm to open and close the switches in the switching circuit 34 to produce the optimum load resistance for the power source that is available.
  • the formula first solves for the single resistor R4 (one of the four heating rods 29 of the heating element 15).
  • the value for the resistor R4 is then used in a ratio determination method, described in greater detail below, to determine the three other fixed resistance values for resistors R6, R7, and R9 (the other three of the four heating rods 29 of the heating element 15).
  • the fixed resistance values of resistors R4, R6, R7, and R9 are used by the control system 16 in various single and parallel connection arrangements to create up to seven different direct current load resistance values Rl , R2, R3, R4, R5, R6, and R7, and one alternating current load resistance value R8 (see table, Fig. 12a).
  • the resistance values R1 -R7 are used in connection with the direct current power source 31
  • the resistance value R8 is used in connection with the alternating current power source 32.
  • the resistance value R8 is the optimum value for the alternating current power source 32, and the resistance value R8 is the lowest available resistance and results from the parallel connection of all four fixed resistors R4, R6, R7, and R9 (resistance heating rods 29 of the resistance heating element 15).
  • MPP Maximum Power Point (MPP-the optimum transfer of energy from the power source to the resistance load)
  • W/m Watts per square meter of solar irradiance
  • V Photovoltaic array operating MPP voltage (volts) @ 1000 W/m 2
  • Vw Photovoltaic array MPP voltage at a stated level of solar irradiance (w)
  • Iw Photovoltaic array MPP current at a stated level of solar irradiance (w)
  • R 4 is used to determine R 6 , and R 7 wherein
  • R 6 is a multiple of two (2) times the value of R 4
  • R is a multiple of four (4) times the value of the value of R4.
  • Rg is determined by inserting the derived value for optimal AC operation as follows:
  • W A c desired power output for alternating current power source
  • VAC voltage for the alternating current power source
  • VAC 240 volts
  • R 5 1 / ((1/ R 7 ) + (1/R 6 ))
  • R 4 Value of resistance to be determined using proprietary formula*
  • the direct current load resistance RloadDC 37 and the alternating current load resistance RloadAC 36 for the switching circuit 34 are selected by the switch configurations defined by the binary bits, in the column "Switch RS.”
  • Each of the binary bits indicates the status of the associated switches for the fixed resistors R4, R6, R7 and R9.
  • the control system 16 based on the output from direct current power source 31 , closes the DC switch 41 , opens the AC switch 42, and sets the binary code to 1 1 10.
  • the associated switches for fixed resistors R4, R6, and R7 are closed, and the direct current load resistance RloadDC 37 equals the parallel combination of fixed resistors R4, R6, and R7, equals resistance Rl , and equals 23.82 ohms (Fig. 12a, line Rl).
  • the control system 16 closes the AC switch 42, opens the DC switch 41 , and sets the binary code to 1 1 1 1.
  • the formula set forth below establishes the values for fixed resistors Rl 1 , R12, R13, and R14 (the four resistance heating rods 29 of the resistance heating element 15).
  • the control system 16 runs an algorithm to open and close the switches in the switching circuit 35 to produce the optimum load resistance for power source that is available.
  • the formula first solves for the single resistor Rl 1 (one of the four heating rods 29 of the heating element 15).
  • the value for the resistor Rl l is then used in a ratio determination method, described in greater detail below, to determine the three other fixed resistance values for resistors R12, R13, and R14 (the other three of the four heating rods 29 of the heating element 15).
  • the fixed resistance values of resistors Rl 1 , R12, R13, and R14 are used by the control system 16 in various single and parallel connection arrangements to create up to 14 different direct current load resistance values Rl , R2, R3, R4, R5, R6, R7, R8, R9, R10, Rl l , R12, R13, and R14 and one alternating current load resistance value R15 (see table, Fig. 12b).
  • the resistance values R1 -R14 are used in connection with the direct current power source 31
  • the resistance value R15 is used in connection with the alternating current power source 32
  • the resistance value R15 is the optimum value for the alternating current power source 32
  • the resistance value R15 is the lowest value and results from the parallel connection of all four fixed resistors Rl 1 , R12, R13, and R14 (resistance heating rods 29 of the resistance heating element 15).
  • MPP Maximum Power Point (MPP-the optimum transfer of energy from source to the resistance load)
  • W/m 2 Watts per square meter of solar irradiance
  • V Photovoltaic array operating MPP voltage (volts) @ 1000 W/m 2
  • I K Photovoltaic array operating MPP current (amps) @ 1000 W/m 2
  • Vw Photovoltaic array MPP voltage at a stated level of solar irradiance (w)
  • Iw Photovoltaic array MPP current at a stated level of solar irradiance (w)
  • R] 2 is a 1.20 ratio of Rn - R 13 is a 1.50 ratio of Rn .
  • Ri4 is a 2.00 ratio of Rn .
  • R2 1 / ((1/R11)+(1/R12)+(1/R14))
  • R3 1 / ((1/R11)+(1/R13)+(1/R14))
  • R4 1 / ((1/R12)+(1/R13)+(1/R14))
  • Rl 1 Fixed resistance value derived using proprietary Formula of Claim 1.*
  • R12 Fixed resistance value equal to 1.20 x Rl 1 *
  • R13 Fixed resistance value equal to 1.50 x Rl 1 *
  • R14 Fixed resistance value equal to 2.00 x Rl 1 *
  • the direct current load resistance RloadDC 39 and the alternating current load resistance RloadAC 38 for the switching circuit 35 are selected by the switch configurations, defined by the binary bits, in the column "Switch RS.”
  • Each of the binary bits indicates the status of the associated switches for the fixed resistors Rl l , R12, R13, and R14.
  • the control system 16 based on the output from direct current power source 31, closes the DC switch 43, opens the AC switch 44, and sets the binary code to 1010.
  • the associated switches for fixed resistors Rl l and R13 are closed, and the direct current load resistance RloadDC 39 equals the parallel combination of fixed resistors Rl 1 and R13, equals resistance R6, and equals 35.72 ohms (Fig. 12a, line R6).
  • the control system 16 closes the AC switch 44, opens the DC switch 43, and sets the binary code to 1 1 1 1.
  • the control system 16 is programmed to implement the control method 50 that controls the selection of the optimized resistance for either the direct current power source 18 or the alternating power source 32.
  • the control method 50 has a Main Command Logic Routine 52, a Sampler Logic Subroutine 54 and a Read Power Subroutine 56.
  • the control method 50 begins at loop step 58 of the Main Command Logic Routine 52.
  • the internal processor of control system 16 steps through the logic sequence continually while the system has power applied and is in operation.
  • each resistance value corresponds to a "Mode" of operation of the solar photovoltaic water heating system 10.
  • step 60 the routine 52 sets the resistance to Mode 14 (R14 of configuration 2, Fig. 12b), the highest value for the resistance of the resistance heating element 15.
  • step 62 the routine 52 moves to step 62, where routine 52 imposes a two second delay.
  • step 64 the routine 52 moves to step 64, and branches to step 104 of the Read Power Subroutine 56.
  • step 106 the subroutine 56 uses the highest resistance value R14 to read power available from the photovoltaic array 31.
  • the routine 52 detemiines that Mode is greater than 15 or the subroutine 54 is sampling to higher resistances, the routine 52 follows the no branch to step 70.
  • the term "Mdiff" means the difference by which the Mode changes when determining the next power reading by means of subroutine 56.
  • the routine 52 decreases the resistance by reconfiguring the fixed resistors Rl l , R12, R13, and R14 to create a lower value of total resistance. Lowering the resistance is accomplished by turning on the next resistance value in parallel with the previous Mode resistance value, i.e changing from R14 to R13 in Fig, 12b (0001 to 0010).
  • step 76 that branches to step 80 of subroutine 54.
  • step 84 the subroutine 54 sets the resistors associated with the Mode (Mode + Mdiff).
  • the fixed resistors Rl l , R12, R13, and R14 are selected in accordance with the switch configurations shown in Fig. 12b.
  • step 86 the subroutine 54 proceeds to step 86 that imposes a 0.1 second delay.
  • step 86 the subroutine 54 proceeds to step 88, and then branches to step 104 of subroutine 56.
  • the Read Power Logic Subroutine 56 again determines the power value for the photovoltaic array 31 as previously described. Once the subroutine 56, has completed its operation, control is transferred from step 108 back to step 88 any of the subroutine 54.
  • step 98 the subroutine 54 proceeds to step 100, where the sampling direction for the resistance is again switched. From step 100, the subroutine 54 proceeds to step 102, which returns to step 76 of the routine 52. From step 76, the routine 52 proceeds to step 78, and then returns to the beginning at step 58.
  • step 90 Pcurrent is less than Pprevious, the subroutine 54 follows the no branch to step 98.
  • step 100 the sampling direction for the resistance is again switched.
  • step 102 the subroutine for proceeds to step 102, which returns to step 76 of the routine 52.
  • step 76 the routine 52 proceeds to step 78, and then returns to the beginning at step 58. Consequently, method 50 continues sampling the power from the photovoltaic array 31 until a change is detected against the power trend.
  • the control determination and switching process continues by constantly sampling values at varying time intervals as determined by the change rate of solar irradiance.
  • the programmable control system 16 of the present invention also monitors the water temperature and the water pressure in the storage tank 10.
  • the storage tank 10 includes a temperature sensor 28 and a pressure sensor 14.
  • the temperature sensor 28 and the pressure sensor 14 are connected to the control system 16.
  • the control system 16 connects either the direct current power source 18 or the alternating current power source 32 to the resistance heating elements 15.
  • the control system 16 disconnects either the direct current power source 18 or the alternating from the resistance heating elements 15.
  • the direct current power source 18 can be diverted to a direct current power takeoff 30 that can be used to charge batteries, to power an inverter, or to drive a second resistance heating load such as a hot water space heating system.
  • the control system 16 further monitors the data from the pressure sensor 14 so that the pressure in the storage tank 10 remains in a preselected safe pressure range. If the pressure in the water storage tank 10 rises above the preselected pressure range, the control system 16 disconnects either the direct current power source 18 or the alternating current power source 32 from the resistance heating elements 15. If the pressure continues to rise in the water storage tank 10, the pressure relief safety valve 23 will open relieving the pressure in the storage tank 10. Further, if the pressure drops below the preselected pressure range, the control system 16 disconnects either the direct current power source 18 or the alternating current power source 32 from the resistance heating elements 15 so that the water in the storage tank 10 does not begin to boil at a low- pressure.
  • the control system 16 is programmable, either through a direct interface or remotely through a remote interface, and can be programmed to collect operating data including, but not limited to, the temperature and pressure data over time, the power delivered to the resistance heating elements 15, the amount of energy delivered to the resistance heating elements 15 by the direct current power source 18 over time, and the amount of energy delivered to the resistance heating elements 15 by the alternating current power source 32 over time.
  • Such data can be stored locally by the control system 16 or it can be transmitted to a remote data acquisition system (not shown) either over a wired network or a wireless network. Further, with advanced internal programming, the control system 16 is capable of learning to optimize energy delivery.
  • control system 16 can monitor the time of day, the solar irradiance 19, and the temperature of the storage tank 10 and thereby determine the optimal time to switch from the direct current power source 18 to the alternating current power source 32 by means of the switching circuit 34, switches 41 and 42 or by means of the switching circuit 35, switches 43 and 44.
  • the time of the day from around 2-3pm to 5-6pm depending on geographic location, offers the greatest chance that the solar array 31 will provide sufficient energy to bring the storage tank 10 to its maximum temperature in which case the alternating current power source 32 will not be used thereby increasing the efficiency of the solar photovoltaic water heating system 1.
  • the time periods above are also the less likely time periods in which a high consumption of hot water will be used while the sun is still out.
  • the graph shows an idealized power curve (power from the direct current photovoltaic power source 31 versus load resistance) that defines the maximum power point, i.e., the point of optimum transfer of energy from the power source to the resistance load where the load resistance is infinitely variable.
  • the graph in Fig. 10 compares the idealized power curve to the operating curve for the solar photovoltaic water heating system 1 of the present invention.
  • the graph in Fig. 10 shows that by matching the resistance using the switching circuits 34 and 35, the performance of the solar photovoltaic water heating system 1 of the present invention closely tracks the idealized power curve.
  • Figs. 1 1a and 1 lb show plots of the step changes in the load resistance that occur when using the formula and method of the present invention.
  • the steps in the changes of the load resistance must be in as equal incremented values as possible. Resistance values that have changes that create anything other than a smooth curve will vary the load resistance above or below the maximum power point matching for a given level of solar irradiance. Resistance values that cause points to deviate from a smooth curve plotting will cause losses of energy delivery to the medium being heated.
  • Figs. 13a-c are examples of data tables derived from measured and published performance information regarding photovoltaic panels. The data then is used to determine the various photovoltaic water heating system operating parameters, which in turn is used to determine the resistance values of the heating rods 29.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Control Of Electrical Variables (AREA)

Abstract

L'invention concerne un système solaire photovoltaïque de chauffage d'eau comportant un réseau de panneaux solaires photovoltaïques, une cuve de stockage contenant de l'eau à chauffer, un élément de chauffe par résistance dans l'eau à chauffer. Le système de chauffe d'eau fait correspondre la résistance de charge de l'élément de chauffe par résistance avec la puissance produite par le réseau de panneaux solaires photovoltaïques afin de rendre maximiser la quantité d'énergie transférée à l'eau dans la cuve de stockage.
PCT/US2013/073124 2012-12-05 2013-12-04 Système solaire photovoltaïque de chauffage d'eau Ceased WO2014089215A1 (fr)

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