AU2016222383B2 - Photovoltaic Solar Hot Water System - Google Patents

Photovoltaic Solar Hot Water System Download PDF

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AU2016222383B2
AU2016222383B2 AU2016222383A AU2016222383A AU2016222383B2 AU 2016222383 B2 AU2016222383 B2 AU 2016222383B2 AU 2016222383 A AU2016222383 A AU 2016222383A AU 2016222383 A AU2016222383 A AU 2016222383A AU 2016222383 B2 AU2016222383 B2 AU 2016222383B2
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photovoltaic element
heating elements
electrical power
heating
voltage
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AU2016222383A1 (en
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Rob Taber
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Solar Energy Innovations Pty Ltd
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Solar Energy Innovations Pty Ltd
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    • 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
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • 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
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

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  • Domestic Hot-Water Supply Systems And Details Of Heating Systems (AREA)
  • Photovoltaic Devices (AREA)
  • Heat-Pump Type And Storage Water Heaters (AREA)

Abstract

The invention provides a system for heating water using energy from solar radiation. The system includes a photovoltaic element for generating electrical power in response to incident solar radiation and a water heating device including two or more separate heating elements for heating water using electrical power from the photovoltaic element. At least two of the heating elements having different electrical resistances. A controller selectively electrically connects the photovoltaic element to one of the heating elements having a resistance that when powered by electrical power from the photovoltaic element will maximize the amount of electrical power generated by the photovoltaic element from a prevailing intensity of incident solar radiation. The controller is operable to electrically switch between the heating elements at one or more thresholds of voltage of the electrical power being generated by the photovoltaic element. The invention also provides a control system for controlling a solar powered water heating system and a method for controlling a solar powered water heating system. 111 10 3 3 37 Cold Hot water ( water 330 60 30\ 25k~ c-ontrol lerP Fig.]I

Description

10
33 37 Cold Hot water ( water
330 30\ 60
25k~ c-ontrol lerP
Fig.]I
PHOTOVOLTAIC SOLAR HOT WATER SYSTEM TECHNICAL FIELD
[001] The present invention relates to a photovoltaic powered solar water heating system and a method for-controlling a photovoltaic powered water heating system. In particular, the present invention relates to a solar water heating system that uses electrical power generated by a photovoltaic element in response to incident solar radiation and to a controller and a method for controlling a photovoltaic water heating system.
BACKGROUND
[002] Existing solar water heating systems employ heat exchange systems. Typical existing water heating systems include a solar energy collector, often fastened to a roof or a wall facing the sun, and heat transfer fluid that is either pumped or driven by convection through the collector. The collector is designed to absorb heat energy from incident solar radiation to heat up heat transfer fluid passing through the collector.
[003] The heated heat transfer fluid is delivered to a heat exchanger, such as a coil of tubing, located inside a tank for storing water to be heated. Heat from the heat transfer fluid is exchanged with the water contained in the tank thereby heating the water. The heat transfer fluid is then returned to the collector to be heated-again and the process is repeated continuously.
[004] Existing solar hot water heating systems require that the collector and the tank be located in close proximately to each other to ensure that the length of piping for delivering the heat transfer fluid between the collector and the tank is as short as possible so as to reduce the amount of heat lost during delivery through the piping.
[005] Accordingly, existing solar hot water heating systems usually include a water storage tank directly coupled to the collector or located very close to the collector. Despite the draw backs associated with the use of heat exchangers and heat transfer fluid, all solar hot water systems on the market today use heat exchangers and heat transfer fluid as described above because they have hitherto been the most efficient at converting solar radiation into heated water. As such, solar water heaters using heat exchangers are presently the most cost effective means for heating water using solar radiation.
[006] Photovoltaic arrays are typically used in domestic scenarios to generate electrical power for storage in batteries or for use by domestic electrically powered appliances or for supplying electrical power to the utility grid. Photovoltaic arrays produce DC electrical power whereas typically household appliances, including electrical hot water heaters, use AC electrical power. Furthermore, electrical power from the utility grid is also typically in AC form. Thus, typical photovoltaic arrays employee a converter to convert DC electrical power from the photovoltaic element to AC electrical power. Ln converting DC electrical power to AC electrical power some electrical power, estimated to be about 10 percent, can be lost.
[007] Existing electrically powered hot water systems use heating elements that are optimised to efficiently heat water using AC electrical power from a utility grid. The variability of electrical power that is generated by a photovoltaic element, such as due natural variation in incident solar radiation, renders photovoltaic elements unsuitable for efficiently powering existing electrically powered hot water systems.
[008] The above discussion of background art is included to explain the context of the present invention. it is not to be taken as an admission that any of the documents or other material referred to was published, known or part of the common general knowledge in Australia at the priority date of any one of the claims of this specification.
[009] Any discussion of background art throughout the specification should in no way be considered as an admission that any of the documents or other material referred to was published, known or forms part of the common general knowledge.
SUMMARY OF THE INVENTION
[0010] Accordingly, in a first aspect, the present invention provides a system for heating water using energy from solar radiation, including: a photovoltaic element for generating electrical power in response to incident solar radiation; a water heating device including two or more separate heating elements for heating water using electrical power from the photovoltaic element, at least two of the heating elements having different electrical resistances; and a controller for selectively electrically connecting the photovoltaic element to one of the heating elements having a resistance that when powered by an amount of electrical power from the photovoltaic element will maximize the amount of electrical power generated by the photovoltaic element from a prevailing intensity of incident solar radiation wherein the controller is operable to electrically switch between the heating elements at one or more thresholds of voltage of the electrical power being generated by the photovoltaic element, wherein the controller is operable to electrically connect the photovoltaic element to at least two of the heating elements simultaneously and wherein the voltage threshold at which one of the heating elements is electrically connected to the photovoltaic element is spaced apart from the voltage threshold at which the same one of the heating elements is electrically disconnected from the photovoltaic element to prevent switching between electrical connection and disconnection of the same one of the heating elements to the photovoltaic element with no change, or relatively little change, to the prevailing intensity of incident solar radiation.
[0011] In an embodiment, the controller is operable to electrically disconnect the photovoltaic element from one of the heating elements and to electrically connect the photovoltaic element to another one of the heating elements at one of the voltage thresholds.
[0012] In an embodiment, the system further includes a voltage control device for controlling the voltage of the electrical power generated by the photovoltaic element when electrically connected to one of the heating elements so that an optimum amount of electrical power is generated from the prevailing intensity of incident solar radiation.
[0013] In another embodiment, the system further includes a temperature sensor for determining the temperature of water heated by the water heating device and a switch for terminating the electrical power from the photovoltaic element to the heating elements when the water reaches a predetermined temperature.
[0014] Preferably, the predetermined temperature is adjustable.
[0015] In another embodiment, the photovoltaic element includes multiple arrays of photovoltaic cells connected in series.
[0016] In another preferred embodiment, one of the heating elements is a 600 watt heating element and another one of the heating elements is a 1200 watt heating element.
[0017] In an embodiment, the system includes a further heating element that is selectively electrically connectable to a mains electrical power supply for heating water using electrical power from the mains electrical power supply.
[0018] In another aspect, the present invention provides a control system for controlling a solar powered water heating system including a photovoltaic element for generating electrical power in response to incident solar radiation and a water heating device including two or more separate heating elements having different electrical resistances for heating water using electrical power generated by the photovoltaic element, the control system including: a switching device for selectively electrically connecting the photovoltaic element to the heating elements; a voltage sensor for sensing the voltage of electrical power supplied by the photovoltaic element to one of the heating elements electrically connected to the photovoltaic element; and a controller for selecting one of the heating elements having a resistance that when powered by an amount of electrical power from the photovoltaic element will maximize the amount of electrical power generated by the photovoltaic element from a prevailing intensity of incident solar radiation and for controlling the switching device to electrically connect the photovoltaic element to the selected heating element; wherein the control system is operable to electrically switch between the heating elements at one or more thresholds of voltage of the electrical power being generated by the photovoltaic element; and wherein the controller is operable to electrically connect the photovoltaic element to at least two of the heating elements simultaneously; and wherein the voltage threshold at which one of the heating elements is electrically connected to the photovoltaic element is spaced apart from the voltage threshold at which the heating element is electrically disconnected from the photovoltaic element to prevent switching between electrical connection and disconnection of the same one of the heating elements to the photovoltaic element with no change, or relatively little change, to the prevailing intensity of incident solar radiation.
[0019] In an embodiment, the control system is operable to electrically disconnect the photovoltaic element from one of the heating elements and to electrically connect the photovoltaic. element to another one of the heating elements at a predetermined voltage threshold.
[0020] In some embodiments, the controller is operable to electrically connect the photovoltaic element to at least two of the heating elements simultaneously.
[0021] Preferably, the control system further includes a voltage control device. tor controlling the voltage of the electrical power generated by the photovoltaic element when electrically connected to one of the heating elements at an optimum voltage so as to optimise the amount of electrical power generated from the prevailing intensity incident solar radiation.
[0022] In another preferred embodiment, the control system includes a temperature sensor for determining the temperature of water heated by the water heating device and a switch for terminating the supply of electrical power from the photovoltaic element to the heating elements when the water reaches a predetermined temperature.
[0023] Preferably, the control system further includes means tor adjusting the predetermined temperature setting.
[0024] In an embodiment, the system includes a further heating element that uses electrical power from a mains electrical power supply and the controller is operable for selectively connecting the further heating element to the mains electrical power supply.
[0025] In yet another aspect, the present invention provides a method for controlling a solar powered water heating system including a photovoltaic element for generating electrical power in response to incident solar radiation and a water heating device including two or more separate heating elements having different electrical resistances for heating water using electrical power generated by the photovoltaic element, the method including: selecting one of the heating elements having a resistance that when powered by an amount of electrical power from the photovoltaic element will maximize the amount of electrical power generated by the photovoltaic element from a prevailing intensity of incident solar radiation; electrically connecting the photovoltaic element to the selected heating element to cause the photovoltaic element to supply electrical power to the heating element; and electrically switching between the heating elements at one or more thresholds of voltage of the electrical power being generated by the photovoltaic element. One of the heating elements is electrically connected to the photovoltaic element at one voltage threshold and electrically disconnected at another voltage threshold wherein the voltage thresholds are spaced apart to prevent switching between electrical connection and disconnection of the same one of the heating elements to the photovoltaic element with no change, or relatively little change, to the prevailing intensity of incident solar radiation.
[0026] In an embodiment, the method includes electrically disconnecting the photovoltaic element from one of the heating elements and electrically connecting the photovoltaic element to another one of the heating elements at a predetermined voltage threshold.
[0027] In some embodiments, the method includes electrically connecting the photovoltaic element to at least two of the heating elements simultaneously.
[0028] In an embodiment, the method includes controlling the voltage of the electrical power generated by the photovoltaic element when electrically connected to one of the heating elements at an optimum voltage to optimise the amount of electrical power generated by the photovoltaic element from the prevailing intensity of incident solar radiation.
[0029] The method may further include determining the temperature of water heated by the water heating device and terminating the supply of electrical power from the photovoltaic element to the heating elements when the water reaches a predetermined temperature.
[0030] In an embodiment, the method includes selectively electrically connecting a further heating element to a mains electrical power supply
BRIEF DESCRIPTION OF THE FIGURES
[0031] The invention will now be described in more detail with reference to embodiments of the invention illustrated in the accompanying drawings, wherein:
[0032] Figure 1 is a schematic illustration of a system in accordance with an embodiment of the invention including a photovoltaic element, a controller and a water heating device including a water storage tank and a plurality of separate heating elements;
[0033] Figure 2 is a schematic illustration of an embodiment of the system of Figure 1 that shows components of the controller;
[0034] Figure.3 is a schematic illustration of another embodiment of the system of Figurel wherein the controller including a voltage control device; and
[0035] Figure 4 is a graph illustrating current versus voltage curves for the photovoltaic element of an embodiment of the system of Figure 1 in response to incident solar radiation.
DETAILED DESCRIPTION
[0036] Figure 1 is a schematic illustration of a system in accordance with an embodiment of the invention including a photovoltaic element 20, a controller and a water heating device 30 including a water storage tank 35 and a plurality of separate heating elements 32, 34, 36. Solar radiation 10 from the sun 15 is incident on a photovoltaic element 20 which is made up of a plurality of photovoltaic cells. Two of the heating elements 32, 34 are selectively electrically connected to the photovoltaic element 20 by the controller 60 to enable electrical power generated by the photovoltaic element 20 in response to the incident solar radiation 10 to be supplied to one or more of the heating elements 32, 34 to thereby heat water contained in the water storage tank 35.
[0037] A further one of the heating elements 36 is a boost element that is selectively electrically connectable to a mains electrical power supply 25 for heating water using electrical power from the mains electrical power supply 25.
[0038] The efficiency with which electrical power is generated by the photovoltaic element 20 is determined by the voltage at which the photovoltaic element 20 operates. The voltage at which the photovoltaic element operates is determined by variables including the prevailing intensity of incident solar radiation 10 and the resistance of a load applied to the photovoltaic element 20. At least two of the heating elements 32, 34 have different electrical resistances and are selectively electrically connectable to the photovoltaic element 20 by the controller 60 to vary the resistance of the load applied to the photovoltaic element 20. Thus, the controller 60 can selectively electrically connect one or more of the heating elements 32, 34 having a resistance that when powered by the photovoltaic element 20 will maximize the amount of electrical power generated by the photovoltaic element 20 from a prevailing intensity of incident solar radiation. As will be described in more detail below, the controller 60 is operable to electrically switch between the heating elements 32, 34 at one or more voltage thresholds. Thus, the controller 60 may thereby determine and select which one of the photovoltaic powered heating elements 32, 34 should be connected to enable the photovoltaic element 20 to operate at a voltage that maximises the amount of electrical power being generated by the photovoltaic element 20 from the prevailing intensity of incident solar radiation 10.
[0039] The photovoltaic element 20 may be comprised of a plurality of individual panels of photovoltaic cells that are electrically connected to each other in any suitable manner, such as in series, so as to enable the photovoltaic element 20 to generate electrical power at voltages anywhere from 0 volts to around 300 volts or more.
[0040] The heating elements 32, 34, 36 are located separately within the water storage tank 35. Two of the heating elements 32, 34 that are selectively electrically connectable to the photovoltaic element 20 are each located separately within the tank 35 and each have a different electrical resistance. The boost heating element 36 that is selectively electrically connectable to the mains power supply 25 is located separately from the other heating elements 32, 34. The water storage tank 35 includes a cold water inlet 33 and a hot water outlet 37. The water storage tank 35 is operable to receive and store a volume of water for heating by the heating elements 32, 34, 36. The individual heating elements 32, 34, 36 each have a predetermined resistance. With respect to heating elements used to heat water it is generally the case that a heating element with a higher wattage or heating capacity will have a lower resistance and a heating element with a lower wattage or heating capacity will have a higher resistance. In the embodiment illustrated in the Figures, the resistance of the first heating element 32 is less than the resistance of second heating element 34. The resistance of the first heating element 32 may be such that the heating element has a maximum heating capacity of about 1200 watts (or alternatively about 900 watts). The resistance of the second heating element 34 may be such that the heating element 34 has maximum heating capacity of about 600 watts. It is to be appreciated that heating elements of a variety of resistances may be employed as long as the resistance of the first heating element 32 is less than the resistance of the second heating element 34. The boost heating element 36 has a resistance such that it has a maximum heating capacity of about 2400 watts or preferably about 3600 watts.
[0041] The heating elements 32, 34, 36 are located separately within the tank with a first one of the heating elements 32 located near a base of the tank 35. A second one of the heating elements 34 is spaced from and above the first heating element 32. The boost heating element 36 may be positioned anywhere, but preferably at the top of the tank 35, spaced apart from the first and second heating elements 32, 34. The boost heating element 36 is provided to "top-up" heating of water contained in the tank 35 or to heat water in the tank when the amount of solar radiation 10 incident on the photovoltaic element has been insufficient to heat water in the tank 35 to a desired temperature. The first and second heating elements 32, 34 are provided for "bulk-heating" of water in the tank 35 when the amount of solar radiation 10 incident on the photovoltaic element 20 has been sufficient to provide a substantial amount of heating of water in the tank 35.
[0042] Figure 2 illustrates an embodiment of the system of. Figure 1 and, in particular, an embodiment of the controller 60. The controller 60 is electrically connected to the photovoltaic element 20 and to each of the photovoltaic powered heating elements 32, 34. The controller 60 includes a switching device 62 that includes photovoltaic powered heating element switches 32A, 34A electrically connected between the photovoltaic element 20 and a respective one of the photovoltaic powered heating elements, 32, 34. The switches 32A, 34A are operable to selectively electrically connect a respective one of the photovoltaic powered heating elements 32, 34 to the photovoltaic element 20. The heating element switches 32A, 34A may be solid state switches or mechanical relays controlled by switching signals from a processing unit 70 of the controller 60.
[0043] The controller 60 also includes a voltage sensor V, such as a voltmeter, that determines the voltage of the electrical power supplied by the photovoltaic element 20 when electrically connected to any one of the photovoltaic powered heating elements 32, 34. The voltage sensor V continuously monitors the voltage and sends a signal to the processing unit 70 indicative of the voltage of the electrical-energy being generated by the photovoltaic element 20. The voltage of the electrical power generated by the photovoltaic element 20 is dependent on the intensity of solar radiation 10 incident on the photovoltaic element 20 and on the resistance of the load applied to the photovoltaic element 20. The resistance of the load is dependent on which one or more of the photovoltaic powered heating elements 32, 34 is electrically connected to the photovoltaic element 20 by the controller 60 at any given time.
[0044] The processing unit 70 of the controller 60 uses voltage information from the voltage sensor V and information regarding the load applied to the photovoltaic element 20 to determine which one, or both, of the photovoltaic powered heating elements 32, 34 should be connected to enable the photovoltaic element 20 to operate at a voltage that maximises the amount of electrical power being generated by the photovoltaic element 20 from the prevailing intensity of incident solar radiation 10. The load that is being applied to the photovoltaic element 20 is the known electrical resistance of the one of the photovoltaic powered heating elements 32, 34 electrically connected to the photovoltaic element 20 when the voltage reading is taken.
[0045] In another embodiment of the system, the processing unit 70 of the controller 60 executes an algorithm to determine which one, or both, of the photovoltaic powered heating elements 32, 34 should be connected to enable the photovoltaic element 20 to operate at a voltage that maximises the amount of electrical power being generated by the photovoltaic element 20 from the prevailing intensity of incident solar radiation 10. The algorithm may use information such as voltage information from the voltage sensor V or the power output of the photovoltaic element 20 or other information to determine which one of the photovoltaic powered heating elements 32, 34 should be connected to enable the photovoltaic element 20 to operate at a voltage that maximises the amount of electrical power being generated by the photovoltaic element 20 from the prevailing intensity of incident solar radiation 10.
[0046] The processing unit 70 is operable to send a control signal to the switching device 62 to close one, or both, of the photovoltaic powered heating element switches 32A, 34A and to open one or the other of the heating element switches 32A, 34A so as to connect one or the other or both of the photovoltaic powered heating elements 32, 34 to the photovoltaic element 20 that the processing unit has determined will enable the photovoltaic element 20 to operate at a voltage that maximises the power output from the prevailing intensity of incident solar radiation 10. Accordingly, the processing unit 70 is operable to load the photovoltaic element 20 with a selected one or both of the available photovoltaic powered heating elements 32, 34 that enables the photovoltaic element 20 to operate at a voltage at which the photovoltaic element 20 generates the maximum amount of electrical power and/or that results in generating the most heat in water contained in the tank 35.
[0047] The controller 70 is operable to electrically disconnect the photovoltaic element 20 from one of the photovoltaic powered heating elements 32, 34 and to electrically connect the photovoltaic element 20 to the other one of the photovoltaic powered heating elements 32, 34 at a predetermined voltage threshold. For example, when a first one of the heating element switches 32A is closed a first one of the heating elements 32, which has the lowest resistance and the highest wattage, is electrically connected to the photovoltaic element 20. In this scenario, when the voltage sensor V detects a voltage of electrical power generated by the photovoltaic element 20 of greater than a threshold voltage of about 180 or about 200 volts, or any increment therebetween, then the processing unit 70 sends a signal to control the switching device 62 to maintain the first switch 32A closed to maintain the electrical connection between the photovoltaic element 20 and the first heating element 32.
[0048] If the voltage sensor V detects a voltage drop below the threshold of about 180 or about 200 volts, or any increment therebetween, perhaps due to a fall in intensity of solar radiation 10 incident on the photovoltaic element 20, then the processing unit 70 sends a signal to open the first heating element switch 32A and to close the second heating element switch 34Athereby disconnecting the first one of the photovoltaic powered heating elements 32 and connecting the second one of the photovoltaic powered heating elements 34, which has the highest resistance and the lowest wattage, is electrically connected to the photovoltaic element 20. Because the second heating element 34 has a higher resistance than the first heating element 32 the resistive load on the photovoltaic element 20 is increased resulting in the voltage of electrical power generated by the photovoltaic element 20 increasing for the same lower level of intensity of solar radiation 10 incident on the photovoltaic element 20. By operating at a higher voltage the photovoltaic element 20 will generate more electrical power for the same lower level of intensity of solar radiation 10 incident on the photovoltaic element 20 thereby increasing the efficiency of the photovoltaic element 20.If the voltage sensor V detects a voltage increase above the threshold of about 180 or about 200 volts, or any increment therebetween, perhaps due to an increase in intensity of solar radiation 10 incident on the photovoltaic element 20, then the processing unit 70 sends a signal to open the second heating element switch 34A and to close the first heating element switch 32Athereby disconnecting the second one of the photovoltaic powered heating elements 34 and connecting the first one of the photovoltaic powered heating elements 32 to the photovoltaic element 20. Because the first heating element 32 has a lower resistance and a higher wattage than the second heating element 34 the resistive load on the photovoltaic element 20 is decreased resulting in the voltage of electrical power generated by the photovoltaic element 20 decreasing for the same higher level of intensity of solar radiation 10 incident on the photovoltaic element 20. However, even though the voltage at which the photovoltaic element 20 operates is decreased, at least initially, more electrical power may be generated and/or more heating of water contained in the tank 35 will occur for the same higher level of intensity of solar radiation 10 incident on the photovoltaic element than would be generated if the controller 60 did not switch from the second heating element 34 to the first heating element 32. This is because the performance of the photovoltaic element 20, in terms of the power that it generates, diminishes dramatically if the voltage at which it operates exceeds a certain threshold.
[0049] In another embodiment, if while the first one of the photovoltaic powered heating elements 32 is connected to the photovoltaic element 20 and the voltage sensor V detects a voltage increase above a threshold of about 280 volts or about 300 volts, or any increment therebetween, perhaps due to an increase in intensity of solar radiation 10 incident on the photovoltaic element
, then the processing unit 70 sends a signal to close the second heating element switch 34A and to maintain closed the first heating element switch 32A. As a result, both the first and the second the photovoltaic powered heating elements 32, 34 are thereby connected to the photovoltaic element 20. The resistive load applied to the photovoltaic element 20 is thereby decreased resulting in the voltage of electrical power generated by the photovoltaic element 20 decreasing for the same higher level of intensity of solar radiation incident on the photovoltaic element 20. However, even though the voltage at which the photovoltaic element 20 operates is decreased, at least initially, more electrical power may be generated and/or more heating of water in the tank 35 will occur for the same higher level of intensity of solar radiation 10 incident on the photovoltaic element 20 than might be generated if the controller did not connect both the first and the second heating elements 32, 34 to the photovoltaic element 20. This is because the performance of the photovoltaic element 20, in terms of the power that it generates, diminishes dramatically if the voltage at which it operates exceeds a certain threshold. Accordingly, in some embodiments, the processing unit 70 of the controller 60 is operable to electrically connect the photovoltaic element to at least two of the heating elements 32, 34 simultaneously.
[0050] The performance of the photovoltaic element 20, in terms of the power that it generates at different voltages, and the diminishing power output beyond a certain voltage threshold is illustrated in Figure 4. Figure 4 is a graph illustrating current versus voltage curves for the photovoltaic element 20 in response to incident solar radiation 10 and is typical of the current versus voltage curves for photovoltaic elements generally. Curve A represents a relatively higher intensity of incident solar radiation 10 and curve B represents a relatively lower intensity of incident solar radiation 10. For each of the curves A and B there is a respective optimal voltage Y and Z at which the photovoltaic element 20 is capable of generating optimal electrical power. It can be seen from curves A and B that the performance of the photovoltaic element 20, in terms of the power that it generates, diminishes dramatically if the voltage at which it operates exceeds a certain threshold. As such, embodiments of the invention in which the controller 60 is operable to switch from the second heating element 34 to the first heating element 32 when the voltage exceeds a threshold allows the photovoltaic element 20 to operate at a voltage that is below the threshold at which its performance in terms of its power generation might otherwise decrease dramatically.
[0051] In another embodiment-of the system, the processing unit 70 of the controller 60 executes an algorithm to electrically disconnect the photovoltaic element 20 from one of the photovoltaic powered heating elements 32, 34 and to electrically connect the photovoltaic element 20 to the other one of the photovoltaic powered heating elements 32, 34 based on changes in voltage, perhaps due to a fall in intensity of solar radiation 10 incident on the photovoltaic element 20. Accordingly, the algorithm may use information regarding changes in voltage of the power generated by the photovoltaic element 20 to determine when it is appropriate to switch between the photovoltaic powered heating elements 32, 34 so as to maximize the power output of the photovoltaic element 20.
[0052] Another advantage of the above described embodiments of the invention is that in comparison to the first photovoltaic powered heating element 32, which has a lower resistance and a higher wattage or heating capacity, the second photovoltaic powered heating element 34, which has a higher resistance and a lower wattage or heating capacity, will more efficiently convert a lower level of electrical power capable of being generated by the photovoltaic element 20, due to a fall in intensity of incident solar radiation 10, into heat in the water contained in the water storage tank 35. In other words, where the electrical power capable of being generated by the photovoltaic element 20 is below a certain threshold the provision of this electrical energy to the higher resistance and lower heating capacity or wattage heating element 34 results in more heating of the water contained in the water storage tank 35 than if the lower resistance and higher heating capacity or wattage heating element 32 were to be electrically connected to the photovoltaic element.
[0053] Accordingly, the above system is advantageous in that it provides a plurality of heating elements 32, 34 each having a different electrical resistance and heating capacity or wattage that can be selectively electrically connected to the photovoltaic element 20 under different prevailing intensities of incident solar radiation 10 to cause the photovoltaic element 20 to maximise the electrical power generated by the photovoltaic heating element 20. The above system is also advantageous in that it more efficiently converts the available electrical power generated by the photovoltaic element 20 which varies according to the prevailing intensity of incident solar radiation 10 into heat in the water contained in the water storage tank 35.
[0054] In other embodiments, the controller 60 is operable to determine when there has been a substantial rise or fall in voltage that warrants switching between the heating elements 32, 34. In one embodiment, the voltage threshold at which one of the heating elements 32, 34 is electrically connected to the photovoltaic element 20 is spaced apart from the voltage threshold at which the same one of the heating elements 32, 34 is electrically disconnected from the photovoltaic element 20. The spacing of the voltage thresholds at which one of the heating elements 32, 34 is electrically connected and disconnected to the photovoltaic element 20 may be 10 volts or 20 volts or 30 volts or 40 volts or 50 volts or 60 volts or more.
[0055] For example, when the first heating element 32 is electrically connected to the photovoltaic element 20 and the voltage sensor V detects a voltage of electrical power generated by the photovoltaic element 20 of greater than a threshold voltage, such as 180 or 200 volts, or any increment therebetween, then the processing unit 70 controls the switching device 62 to maintain the first switch 32A closed to maintain the electrical connection between the photovoltaic element 20 and the first heating element 32. If the voltage sensor V detects a voltage drop below 180 or 200 volts, or any increment therebetween, perhaps due to a fall in intensity of solar radiation 10 incident on the photovoltaic element 20, then the processing unit 70 sends a signal to open the first heating element switch 32A and to close the second heating element switch 34A. Because the resistance of the second heating element 34 is lower than the first heating element 32 the voltage of electrical power generated by the photovoltaic element will increase to, say 200 volts.
Accordingly, the processing unit 70 is configured to only disconnect the second heating element 34 and reconnect the first heating element 32 if the voltage sensor detects a substantial rise in voltage above the threshold at which the processing unit is configured to disconnect the first heating element 32 and connect the second heating element 34.
[0056] The substantial rise in voltage above the threshold required to reconnect to first heating element 32 may be 10 volts or 20 volts or 30 volts or volts or 50 volts or 60 volts or more. For example, if the threshold at which the first heating element 32 is disconnected is 180 volts then the predetermined voltage at which the first heating element 32 is reconnected may be 220 volts, or 240 volts or 260 volts. If the second heating element 34 is electrically connected to the photovoltaic element 20 and the voltage sensor V detects a substantial voltage increase to a level above one of the abovementioned thresholds of 220, 240 or 260 volts or any other predetermined threshold, perhaps due to an increase in intensity of solar radiation 10 incident on the photovoltaic element 20, then the processing unit 70 sends a signal to open the second heating element switch 34A and to close the first heating element switch 32A to thereby connect the first heating element 32.
[0057] The aforementioned embodiments are advantageous as they prevent the processing unit 70 from constantly switching between the heating elements 32, 34 with no change, or relatively little change, to the intensity of incident solar radiation 10. Although the above described embodiments envisage predetermined thresholds it is to be appreciated that the thresholds may be dynamically determined. Also, the spacing of the voltage thresholds at which one of the heating elements 32, 34 are electrically connected and disconnected to the photovoltaic element 20 may be dynamically determined.
[0058] The processing unit 70 is also configured so that when the second heating element 34 is electrically connected to the photovoltaic element 20 and the voltage sensor V detects an increase in voltage of electrical power generated by the photovoltaic element 20 to a level greater than a threshold voltage, such as 180 volts, but below an even higher threshold, say 220 volts, perhaps as a result of an increase in to the intensity of incident solar radiation , then the processing unit 70 controls the switching device 62 to maintain the second switch 34A closed to maintain the electrical connection between the photovoltaic element 20 and the second heating element 34. The aforementioned embodiment is advantageous as it prevents the processing unit from constantly switching between the heating elements 32, 34 with no change, or relatively little change, to the intensity of incident solar radiation 10.
[0059] The processor 70 may also be configured to smooth the voltage signal received from the voltage sensor V so as to prevent switching between heating elements 32, 34 as a result of small fluctuations in voltage or due to artefacts in the voltage signal. The processor 70 may also be configured to switch between heating elements 32, 34 when a voltage threshold has been exceeded for a predetermined amount of time so as to reduce the effect on switching resulting from small fluctuations in voltage or artefacts in the voltage signal. The processor 70 may include other means for preventing switching between heating elements 32, 34 as a result of small fluctuations in voltage or artefacts in the voltage signal.
[0060] In another embodiment of the system, the processing unit 70 of the controller 60 determines, perhaps by execution of an algorithm, when there has been a substantial rise or fall in voltage that is sufficient to warrant switching between heating elements 32, 34. Thus, the algorithm is operable to detect and process information based on changes in voltage to electrically disconnect the photovoltaic element 20 from one of the photovoltaic powered heating elements 32, 34 and to electrically connect the photovoltaic element 20 to the other one of the photovoltaic powered heating elements 32, 34 based on sufficient changes in voltage, perhaps due to an increase or fall in intensity of solar radiation 10 incident on the photovoltaic element 20.
[0061] The processing unit 70 of the controller 60 may also determine, perhaps by execution of an algorithm, when there has been a rise or fall in voltage that is so brief as to be insufficient to warrant switching between heating elements 32, 34. Thus, the algorithm is operable to detect and process information based on genuine and sustained changes in voltage to electrically disconnect the photovoltaic element 20 from one of the photovoltaic powered heating elements 32, 34 and to electrically connect the photovoltaic element 20 to the other one of the photovoltaic powered heating elements 32, 34 perhaps due to a sustained increase or fall in intensity of solar radiation 10 incident on the photovoltaic element 20.
[0062] As illustrated in Figures 1 to 3, the illustrated embodiments of the system further include a boost heating element 36. The boost heating element 36 is electrically connected via a boost element switch 36A of the controller 60 to a mains power supply 25, which may be an AC power supply of, say, 240 volts. The processing unit 70 of the controller 60 determines whether the operation of the photovoltaic powered heating elements 32, 34 is insufficient to heat the water in the tank 35 to a required temperature and may send a signal to the boost heating element switch 36A to electrically connect the boost heating element 36 to the mains power supply 25; The resistance of the boost heating element 36 may be such that the boost heating element has a maximum heating capacity of 2400 watts or 3400 watts or higher. The controller 60 may switch on the boost heating element 36 when the level of electrical power generated by the photovoltaic element 20 is insufficient to heat the water in the tank 35 to a predetermined temperature which may be set manually or in circumstances where there is higher than normal demand for heated water from the system.
[0063] The embodiment illustrated in Figure 3 is identical to the embodiment illustrated in Figure 2 except for the inclusion of a voltage control device 80. Accordingly, the same reference numerals are used for identical components in Figure 3 as for Figure 2. In one embodiment, the voltage control device 80 controls the voltage of the photovoltaic element 20 to achieve an optimum (maximised) amount of electrical power generated from the prevailing intensity of incident solar radiation 10. The voltage control device 80 independently controls the voltage of the electrical power generated by the photovoltaic element 20 when one or the other of the photovoltaic powered heating elements 32, 34 is electrically connected to the photovoltaic element 20. This typically involves increasing the voltage of the electrical power, generated by the photovoltaic element 20 to a higher level than would be the case if one of the photovoltaic heating elements 32, 34 were directly electrically connected to the photovoltaic element 20 absent the voltage control device 80. The optimal (maximized) power output associated with higher voltages is due to the characteristic of photovoltaic elements in that they typically generate more electrical power at higher voltages for the same intensity of incident solar radiation 10. Thus, the voltage control device 80 is operable to further increase the efficiency of the photovoltaic element 20 to ensure that the optimum amount of electrical power is produced from the prevailing intensity of incident solar radiation 10. The voltage control device 80 is electrically connected between the photovoltaic element 20 and the switches 32A, 34A. As such, the voltage control device 80 is operable to apply further control to the voltage of the photovoltaic element 20 in addition to the control upon voltage exhibited by the selective connection of the photovoltaic element 20 to the photovoltaic powered heating elements 32, 34.
[0064] The voltage control device 80 is operable for continuously determining the voltages at which the photovoltaic element 20 is able to produce the maximum amount of electrical power for a given intensity of solar radiation 10 incident on the photovoltaic element 20. For example, the photovoltaic element may comprise an array of photovoltaic cells that are connected in series whereby the voltage at which the photovoltaic element 20 generates an optimum amount of electrical energy may vary depending on the intensity of solar radiation 10 incident on the photovoltaic element 20.
[0065] Referring to the current versus voltage curves of Figure 4, for each of the curves A and B there is a respective optimal voltage Y and Z at which the photovoltaic element 20 is capable of generating optimal electrical power. The voltage control device 80 is operable to continuously control the voltage at which the photovoltaic element 20 produces electrical power as close as possible to the optimal voltage Y or Z for a given intensity of solar radiation 10 incident on the photovoltaic element 20. Thus, the voltage control device 80 is operable to optimise the electrical power generated by the photovoltaic element thereby further maximising efficiency.
[0066] In the embodiments illustrated in Figures 1 to 3, the system further includes a water temperature sensor 90 that is mounted to the water storage tank 35 so as to be operable for sensing the temperature of water contained in the tank 35. The temperature sensor 90 is connected to the processing unit 70 and sends a signal to the processing unit 70 as to the current temperature of water in the tank 70. The processing unit 70 receives the signal from the temperature sensor 90 and determines whether the temperature of the water in the tank 35 is above or below a predetermined temperature. When the processing unit 70 determines the temperature to be below the predetermined temperature the processing unit 70 sends a signal to a switch 95 to permit the supply of electrical power from the photovoltaic element 20 to the one or more photovoltaic powered heating elements 32, 34 so as to continue heating the water. As mentioned above, the controller 60 may also switch on the boost heating element 36 when the level of electrical power generated by the photovoltaic element 20 is insufficient to heat the water in the tank 35 to the predetermined temperature. When the processing unit 70 determines the temperature to be above the predetermined temperature the processing unit 70 sends a signal to a switch 95 to terminate the supply of electrical power from the photovoltaic element 20 to the one or more photovoltaic powered heating elements 32, 34 so as to discontinue heating the water. The controller 60 may further include a user adjustable temperature setting device (not shown) that enables adjustment of the predetermined temperature at which the processing unit 70 sends a signal to the switch 95 to either permit or terminate the supply of electrical power from the photovoltaic element 20 to the one or more photovoltaic powered heating elements 32, 34. In another embodiment, the boost heating element 36 may be switched on or off by a separate thermostat (not shown) in the tank 35 that is operable to determine the temperature of the water in the tank 35 and to determine when to switch the boost heating element 36 on or off. In embodiments where the boost heating element 36 is switched by a separate thermostat the system provides for automatic boost heating of water in the tank 35.
[0067] Embodiments of the present invention are advantageous in that the photovoltaic element 10 delivers electrical power via an electrical cable that is not subject to substantial losses of power if the photovoltaic element 10 is located distally from the photovoltaic powered heating elements 32, 34 and the tank 35 of the water heating device 30. Thus, embodiments of the present invention provide greater flexibility in strategically locating the photovoltaic element 10, or multiple photovoltaic elements 10, where maximum sun light is available or where the photovoltaic elements 10 are not as visible or unsightly.
[0068] While various embodiments of the invention have been set forth above, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Thus, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

Claims (16)

  1. Claims: 1. A system for heating water using energy from solar radiation, including:
    a photovoltaic element for generating electrical power in response to incident solar radiation;
    a water heating device including two or more separate heating elements for heating water using electrical power from the photovoltaic element, at least two of the heating elements having different electrical resistances; and
    a controller for selectively electrically connecting the photovoltaic element to one of the heating elements having a resistance that when powered by an amount of electrical power from the photovoltaic element will maximize the amount of electrical power generated by the photovoltaic element from a prevailing intensity of incident solar radiation;
    wherein the controller is operable to electrically switch between the heating elements at one or more thresholds of voltage of the electrical power being generated by the photovoltaic element; and
    wherein the controller is operable to electrically connect the photovoltaic element to at least two of the heating elements simultaneously; and
    wherein the voltage threshold at which one of the heating elements is electrically connected to the photovoltaic element is spaced apart from the voltage threshold at which the same one of the heating elements is electrically disconnected from the photovoltaic element to prevent switching between electrical connection and disconnection of the same one of the heating elements to the photovoltaic element with no change, or relatively little change, to the prevailing intensity of incident solar radiation.
  2. 2. The system of claim 1, wherein the controller is operable to disconnect the photovoltaic element from one of the heating elements and to electrically connect the photovoltaic element to another one of the heating elements at one of the voltage thresholds.
  3. 3. The system of any one of claims 1 to 2, further including a voltage control device for controlling the voltage of the electrical power generated by the photovoltaic element when electrically connected to one of the heating elements so that an optimum amount of electrical power is generated from the prevailing intensity of incident solar radiation.
  4. 4. The system of claim 3, wherein the voltage control device is operable to maximize the voltage of the electrical power generated by the photovoltaic element.
  5. 5. The system of any one of the preceding claims, further including a temperature sensor for determining the temperature of water heated by the water heating device and a switch for terminating the electrical power from the photovoltaic element to the heating elements when the water reaches a predetermined temperature.
  6. 6. The system of any one of the preceding claims, wherein the photovoltaic element includes multiple arrays of photovoltaic cells connected in series.
  7. 7. The system of any one of the preceding claims, wherein one of the heating elements is a 600 watt heating element and another one of the heating elements is a 1200 watt heating element.
  8. 8. The system of any one of the preceding claims, further including a further heating element that is selectively electrically connectable to a mains electrical power supply for heating water using electrical power from the mains electrical power supply.
  9. 9. A control system for controlling a solar powered water heating system including a photovoltaic element for generating electrical power in response to incident solar radiation and a water heating device including two or more separate heating elements saving different electrical resistances for heating water using electrical power generated by the photovoltaic element, the control system including: a switching device for selectively electrically connecting the photovoltaic element to the heating elements; a voltage sensor for sensing the voltage of electrical power supplied by the photovoltaic element to one of the heating elements electrically connected to the photovoltaic element; and a controller for selecting one of the heating elements having a resistance that when powered by an amount of electrical power from the photovoltaic element will maximize the amount of electrical power generated by the photovoltaic element from a prevailing intensity of incident solar radiation and for controlling the switching device to electrically connect the photovoltaic element to the selected heating element; wherein the control system is operable to electrically switch between the heating elements at one or more thresholds of voltage of the electrical power being generated by the photovoltaic element; and wherein the controller is operable to electrically connect the photovoltaic element to at least two of the heating elements simultaneously; and wherein the voltage threshold at which one of the heating elements is electrically connected to the photovoltaic element is spaced apart from the voltage threshold at which the same one of the heating elements is electrically disconnected from the photovoltaic element to prevent switching between electrical connection and disconnection of the same one of the heating elements to the photovoltaic element with no change, or relatively little change, to the prevailing intensity of incident solar radiation.
  10. 10. The system of claim 9, wherein the control system is operable to disconnect the photovoltaic element from one of the heating elements and to electrically connect the photovoltaic element to another one of the heating elements at one of the voltage thresholds.
  11. 11. The system of any one of claims 9 to 10, further including a voltage control device for controlling the voltage of the electrical power generated by the photovoltaic element when electrically connected to one of the heating elements at an optimum voltage to optimise the amount of electrical power generated from the prevailing intensity of incident solar radiation.
  12. 12. The system of claim 11, wherein the voltage control device is operable to maximize the voltage of the electrical power generated by the photovoltaic element.
  13. 13. A method for controlling a solar powered water heating system including a photovoltaic element for generating electrical power in response to incident solar radiation and a water heating device including two or more separate heating elements having different electrical resistances for heating water using electrical power generated by the photovoltaic element, the method including:
    selecting one of the heating elements having a resistance that when powered by an amount of electrical power from the photovoltaic element will maximize the amount of electrical power generated by the photovoltaic element from a prevailing intensity of incident solar radiation; and
    electrically connecting the photovoltaic element to the selected heating element to cause the photovoltaic element to supply electrical power to the heating element; and
    electrically switching between the heating elements at one or more thresholds of voltage of the electrical power being generated by the photovoltaic element; wherein one of the heating elements is electrically connected to the photovoltaic element at one voltage threshold and electrically disconnected at another voltage threshold wherein the voltage thresholds are spaced apart to prevent switching between electrical connection and disconnection of the same one of the heating elements to the photovoltaic element with no change, or relatively little change, to the prevailing intensity of incident solar radiation.
  14. 14. The method of claim 13, including electrically disconnecting the photovoltaic element from one of the heating elements and electrically connecting the photovoltaic element to another one of the heating elements at one of the voltage thresholds.
  15. 15. The method of any one of claims 13 to 14, including controlling the voltage of the electrical power generated by the photovoltaic element when electrically connected to one of the heating elements so that an amount of electrical power is generated by the photovoltaic element from the prevailing intensity of incident solar radiation.
  16. 16. The method of any one of claim 15, including maximizing the voltage of the electrical power generated by the photovoltaic element.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5293447A (en) * 1992-06-02 1994-03-08 The United States Of America As Represented By The Secretary Of Commerce Photovoltaic solar water heating system
US20130263843A1 (en) * 2012-04-09 2013-10-10 David Kreutzman Pv water heating system
US20130266300A1 (en) * 2012-04-09 2013-10-10 David Kreutzman Renewable Energy Hot Water Heating Elements
US20140348493A1 (en) * 2013-03-14 2014-11-27 David Kreutzman Micro-grid pv system hybrid hot water heater

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5293447A (en) * 1992-06-02 1994-03-08 The United States Of America As Represented By The Secretary Of Commerce Photovoltaic solar water heating system
US20130263843A1 (en) * 2012-04-09 2013-10-10 David Kreutzman Pv water heating system
US20130266300A1 (en) * 2012-04-09 2013-10-10 David Kreutzman Renewable Energy Hot Water Heating Elements
US20140348493A1 (en) * 2013-03-14 2014-11-27 David Kreutzman Micro-grid pv system hybrid hot water heater

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