CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from South African provisional patent application number 2020/01767 filed on 20 March 2020, which is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to a system and method for driving a load with a renewable energy source. More particularly, but not exclusively, this invention relates to a system and method for driving a resistive load with one or more solar panels.

BACKGROUND TO THE INVENTION

The use of renewable energy has become more prevalent in recent times. Renewable energy is a term which is generally used to refer to an energy source which is naturally replaced over time, and not reliant on other sources, such as fossil fuels which eventually become depleted. Many types of renewable energy sources are available, including sunlight, wind, rain, tides and geothermal heat to name but a few. Renewable energy is often used to generate electricity, and this electricity can then be applied where needed, often as a replacement for conventional electricity that is generated by burning fossil fuels. A disadvantage of renewable energy sources is that they are known to vary over time, and hence they do not provide a constant input for powering equipment.

For example, if photovoltaic (PV) solar panels are used to generate electricity and to drive a load, the available input power from these solar panels is reliant on the amount of sunshine available. When there is more sunshine available, the panel would deliver more power for a given Voltage, and vice versa. Moreover, for a given amount of sunshine, the amount of power that a solar panel is able to produce is also dependent on the voltage draw from the load connected thereto. When a load is directly connected to the solar panel, an operating point of the solar panel will rarely be at peak power, and losses in efficiency are common.

PV panels usually include a number of PV cells arranged in an array. PV cells have a complex relationship between their operating environment and the maximum power they can produce. This relationship is often described by way of a power-voltage curve, and a manufactured solar panel generally has a power-voltage curve or efficiency curve that is indicative of its inherent characteristics. This is usually a relationship which follows a curve similar to an inverse parabola.

A known technique used in an effort to maximise the amount of power extracted from PV panels or wind turbines is called Maximum Power Point Tracking (MPPT). MPPT has been developed to address the problem that the efficiency of power transfer from a PV panel depends on both the amount of sunlight falling on the solar panel and the electrical characteristics of the load being driven.

A problem with known MPPT circuits is that many of these circuits are configured such that in case of a lot of sun being available, the MPPT circuit simply connects the solar panel(s) directly to the load being driven. This results in the operating point of the solar panel(s) not being at an optimum point, or in fact being very far from such an optimum point or efficiency apex of the solar panel. Known MPPT circuits are prone to becoming unstable or inefficient in varying solar conditions, in particular in a country like South Africa where a lot of sunshine is available. Known MPPT circuits are also configured to only work with a predetermined load, and with a predetermined number of solar panels connected thereto. If the load characteristics or the number of panels are changed, large inefficiencies result. The problem is further exacerbated by the fact that most loads have varying characteristics, often defined by a curved relationship between power and voltage. MPPT circuits are inefficient when attempting to track these variable load characteristics.

Many smaller scale or ‘off the grid’ types of water heaters include a low number of solar panels (typically less than three, or two or less) for heating water. A problem occurs if the heating element or other resistive load is driven with a limited number of solar panels, because there is a large mismatch between the maximum power point (MPP) of the solar panels and the power-voltage relationship of the resistive element. This is because the efficiency curve(s) for a low number of solar panels (e.g. only 2) would be located at a lower voltage, relative to the power-voltage relationship or curve of the load. This leads to large losses occurring, because the load is generally driven at a significantly lower power than would theoretically have been possible for a given amount of solar irradiance, and as a result the solar panel(s) are not used efficiently. Smaller heating elements also tend to have a power-voltage relationship or curve which is generally ‘flatter’. In other words, the curve for smaller heating elements has a smaller slope or gradient, and this may cause the MPP of the solar panel to be even further away from the power-voltage relationship of the resistive element. The Applicant considers there to be room for improvement.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present disclosure, there is provided a method of controlling electrical power delivered from a renewable energy source to a load, comprising: receiving electrical power from the renewable energy source; boosting a voltage of the received electrical power by multiplying its voltage by a factor to yield a higher voltage, the higher voltage being greater than a corresponding voltage of a maximum power point defined by a power-voltage relationship of the renewable energy source; inputting the higher voltage into a buck circuit, the buck circuit being configured to reduce an output voltage of the buck circuit, so that the output voltage of the buck circuit is closer to the maximum power point; and delivering the output voltage of the buck circuit to the load.

A further feature may provide for the method to include, by the buck circuit, reducing the output voltage of the buck circuit by implementing maximum power point tracking (MPPT).

A still further feature may provide for the MPPT to be provided by performing pulse width modulation (PWM).

A yet further feature may provide for the buck circuit to function by changing a duty cycle of its output voltage.

A further feature may provide for the duty cycle of the output voltage to be defined by the duty cycle of the PWM.

A still further feature may provide for the method to include monitoring the duty cycle of the buck circuit, and/or changing the factor by which the voltage is boost so as to keep the duty cycle of the buck circuit within a chosen operating range.

Yet further features may provide for the chosen operating range to be between 80% to 100%, or between 90% to 100%, or between 92% to 98%, or between 93% to 98%, or between 93% to 95%, or between 95% to 97%.

A further feature may provide for the buck circuit to include, or be connected to a direct current (DC) to alternating current (AC) converter.

Still further features may provide for the factor to be changed continually, incrementally or increasingly.

A further feature may provide for the factor to be changed dependant on a difference between a current duty cycle of the buck circuit as compared to the chosen operating range. The factor may be dynamically changed or adjusted over time.

Further features may provide for the factor to be a multiplication factor of at least 1.1 , alternatively at least 1 .2, or at least 1 .3, or at least 1 .4, or at least 1 .5, or at least 2.0, or at least 2.5, or at least 3.0.

A still further feature may provide for the load to have a required or optimal power-voltage relationship which can be separated in a boosting region and a bucking region.

A yet further feature may provide for the method to include the step of determining or estimating whether the maximum power point (MPP) of the renewable energy source is located in the boosting region, or in the bucking region. The method may include performing the boosting step if the MPP is determined or estimated to be in the boosting region.

A further feature may provide for the step of determining or estimating whether the maximum power point (MPP) is located in the boosting region to be performed by monitoring the duty cycle of the buck circuit.

A still further feature may provide for the step of boosting the voltage of the received electrical power to include boosting the voltage by the factor such that the higher voltage is located in the bucking region.

A yet further feature may provide for the step of inputting the higher voltage into the buck circuit and reducing the output voltage of the buck circuit to include reducing the output voltage of the buck circuit towards a target point near the required or optimal power-voltage relationship of the load, the target point having a power output that is closer to the maximum power point of the renewable energy source, thereby increasing the quantity of power delivered to the load.

A further feature may provide for the factor to be changed dependant on a difference between the maximum power point of the renewable energy source and the required or optimal power-voltage relationship of the load.

A still further feature may provide for the method to include using a boost circuit to perform the boosting step.

Yet further features may provide for the method to include implementing the boost circuit to be agnostic to the type of renewable energy source connected thereto; and/or implementing the boost circuit to be agnostic to the type of load being driven. The buck circuit may be agnostic to the boost circuit.

A further feature may provide for the method to include the step of bypassing the boost circuit if the maximum power point of the renewable energy source is determined or estimated to be located in the bucking region.

A still further feature may provide for the load to be a resistive load. The resistive load may be a heating element of a water heating apparatus.

Yet further features may provide for the renewable energy source to be provided by an energy converting device which is configured to convert renewable energy into electrical energy, the renewable energy originating from an inherently variable energy source such as sunlight, wind, rain, tidal energy, or geothermal heat.

A further feature may provide for the renewable energy source to be provided by one or more solar energy converting devices, such as photovoltaic solar cells or photovoltaic solar panels.

A still further feature may provide for the method to include implementing the boost circuit to be agnostic to the number of solar panels connected thereto.

Further features may provide for the method to include one or more of the steps of: measuring temperature of water in the water heating apparatus, receiving temperature data, and based on the received temperature data, switching the heating element on or off.

In accordance with another aspect of the present disclosure, there is provided a system for controlling electrical power delivered from a renewable energy source to a load, the system comprising: a boost circuit that is configured to receive electrical power from the renewable energy source and to boost a voltage of the received electrical power by multiplying its voltage by a factor to yield a higher voltage, the higher voltage being greater than a corresponding voltage of a maximum power point defined by a power-voltage relationship of the renewable energy source; and a buck circuit that has an input for receiving the higher voltage and an output for delivering an output voltage of the buck circuit to the load, the buck circuit being configured to reduce the output voltage of the buck circuit, so that the output voltage of the buck circuit is closer to the maximum power point.

A further feature may provide for the system to include a control circuit connected to the boost circuit and the buck circuit. The control circuit may be arranged to control operation of the boost circuit and the buck circuit.

A still further feature may provide for the buck circuit to be arranged to reduce the output voltage of the buck circuit by implementing maximum power point tracking (MPPT).

A yet further feature may provide for the MPPT to be provided by performing pulse width modulation (PWM).

A further feature may provide for the buck circuit to function by changing a duty cycle of its output voltage.

A yet further feature may provide for the duty cycle of the output voltage to be defined by the duty cycle of the PWM.

A further feature may provide for the control circuit to be arranged to monitor the duty cycle of the buck circuit, and responsive thereto, changing the factor by which the voltage is boost so as to keep the duty cycle of the buck circuit within a chosen operating range.

Still further features may provide for the chosen operating range to be between 80% to 100%, or between 90% to 100%, or between 92% to 98%, or between 93% to 98%, or between 93% to 95%, or between 95% to 97%.

Yet further features may provide for the buck circuit to include, or be connected to a direct current (DC) to alternating current (AC) converter.

Further features may provide for the factor to be changed continually, incrementally or increasingly.

A still further feature may provide for the system to include a comparing component arranged to compare a current duty cycle of the buck circuit to the chosen operating range. The factor may be changed dependant on the comparison. The factor may be dynamically changed or adjusted over time.

Yet further features may provide for the factor to be a multiplication factor of at least 1.1 , alternatively at least 1 .2, or at least 1 .3, or at least 1 .4, or at least 1 .5, or at least 2.0, or at least 2.5, or at least 3.0.

A further feature may provide for the load to have a required or optimal power-voltage relationship which may define a boosting region and a bucking region.

A still further feature may provide for the system to include a maximum power point (MPP) estimating component arranged to estimate whether the MPP is located in the boosting region. The control circuit may be arranged to cause the boost circuit to boost the voltage of the received electrical power, if the MPP is estimated to be in the boosting region.

Yet further features may provide for the system to include a buck circuit duty cycle monitoring component arranged to monitor the duty cycle of the buck circuit. The MPP estimating component may be arranged to estimate whether the MPP is located in the boosting region, or in the bucking region, by receiving data from the buck circuit duty cycle monitoring component.

A further feature may provide for the boost circuit to be arranged to boost the voltage of the received electrical power by the factor such that the higher voltage is located in the bucking region.

A still further feature may provide for the buck circuit to be arranged to reduce its output voltage towards a target point near the optimal power-voltage relationship of the load, the target point having a power output that is closer to the maximum power point of the renewable energy source. The reduction of the output voltage of the buck circuit may thereby increase the quantity of power delivered to the load. A yet further feature may provide for the factor to be changed dependant on a difference between the maximum power point of the renewable energy source and the required or optimal power- voltage relationship of the load.

A further feature may provide for the boost circuit to be agnostic to the type of renewable energy source connected thereto. The boost circuit may be agnostic to the type of load being driven. The buck circuit may be agnostic to the boost circuit.

A still further feature may provide for the control circuit to be arranged to bypass the boost circuit if the MPP of the renewable energy source is located in the bucking region, or if the MPP is estimated to be located in the bucking region.

A yet further feature may provide for the load to be a resistive load. The resistive load may be a heating element of a water heating apparatus.

A further feature may provide for the renewable energy source to be provided by an energy converting device which is configured to convert renewable energy into electrical energy, the renewable energy originating from an inherently variable energy source such as sunlight, wind, rain, tidal energy, or geothermal heat.

A still further feature may provide for the renewable energy source to be provided by one or more solar energy converting devices, such as photovoltaic solar cells or photovoltaic solar panels.

A yet further feature may provide for the boost circuit to be agnostic to the number of solar panels connected thereto.

A further feature may provide for the system to include a temperature sensor arranged to measure temperature of water in the water heating apparatus. The system may include a feedback receiving component for receiving feedback data from the load, such as temperature data from the temperature sensor. The feedback may for example be received in real-time or near-real time. The control circuit may be arranged, based on the received temperature data, to switch the heating element on or off.

In accordance with a further aspect of the present disclosure there is provided a water heating apparatus comprising: a container for holding water to be heated; a heating element for heating water in the container; a boost circuit that is configured to receive electrical power from a renewable energy source and to boost a voltage of the received electrical power by multiplying its voltage by a factor to yield a higher voltage, the higher voltage being greater than a corresponding voltage of a maximum power point defined by a power-voltage relationship of the renewable energy source; and a buck circuit that has an input for receiving the higher voltage and an output for delivering an output voltage of the buck circuit to the heating element to heat water in the container, the buck circuit being configured to reduce the output voltage of the buck circuit, so that the output voltage of the buck circuit is closer to the maximum power point.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a high-level block diagram of an exemplary system for controlling electrical power delivered from a renewable energy source to a load;

Figure 2 is another high-level block diagram illustrating an exemplary embodiment of the system where the renewable energy source is provided by solar panels and the load is a heating element of a water heater;

Figure 3 is an example graph illustrating a power-voltage relationship of the renewable energy source, in this case one or more solar panels, showing a number of different maximum power point (MPP) locations, depending on solar irradiance;

Figure 4 is an example graph illustrating power-voltage relationships of a 3kW heating element and a 2kW heating element;

Figure 5 is an example graph illustrating a power-voltage relationship of an exemplary load, illustrating how the power-voltage relationship of the load can be separated in a boosting region and a bucking region;

Figure 6 shows the graphs of Figures 3 and 5 superimposed on top of one another, and diagrammatically illustrates exemplary boosting and bucking operations or modes implemented by the system and method of the present disclosure;

Figures 7-10 are graphs showing various power-voltage relationships of 2kW and 3kW heating elements tested by the applicant during different seasons, having various MPP locations as result of variance in solar irradiation;

Figure 11 is another high-level block diagram similar to the block diagram of Figure 2, showing exemplary components that may form part of control circuitry of the system;

Figure 12 is a block diagram, showing an exemplary boost circuit that may be implemented in the system of Figure 11 ;

Figure 13 is a block diagram, showing an exemplary buck circuit that may be implemented in the system of Figure 11 ;

Figure 14 is a block diagram, showing an exemplary control and buck circuit that may be implemented in the system of Figure 11 ;

Figure 15 is a swim-lane flow-diagram illustrating an exemplary method of controlling electrical power delivered from a renewable energy source to a load;

Figure 16 shows three graphs for water temperature against time over the course of three days, illustrating a variety of possible user interactions with the system of the present disclosure;

Figure 17 shows three further graphs for water temperature against time over the course of three weeks, illustrating a variety of possible user interactions with the system of the present disclosure;

Figure 18 shows a number of different user interfaces that may be displayed to a user of the system of the present disclosure, either by way of a dedicated control panel display, or a display of a mobile device of the user;

Figure 19 is an exemplary circuit diagram of a boost circuit that may be implemented in the system and method of the present disclosure; Figure 20 is an exemplary circuit diagram of a buck circuit that may be implemented in the system and method of the present disclosure;

Figure 21 is another exemplary circuit diagram of a boost circuit that may be implemented in the system and method of the present disclosure;

Figure 22 is another exemplary circuit diagram of a buck circuit that may be implemented in the system and method of the present disclosure;

Figure 23 is an exemplary circuit diagram of a temperature sensor circuit that may be implemented in the system and method of the present disclosure;

Figure 24 is an exemplary driver circuit that may be implemented by the system and method of the present disclosure;

Figure 25 shows further exemplary driver circuits that may be implemented by the system and method of the present disclosure;

Figure 26 is another exemplary circuit diagram of a temperature sensor circuit that may be implemented in the system and method of the present disclosure; and

Figure 27 is an exemplary PWM circuit that may be implemented by the present disclosure.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

There is provided a system and method of controlling power being supplied by a variable energy source or input, such as a renewable energy source, to an appliance or load. The variable energy source may be any energy source which has a power output that varies over time, or that is not constant. Example embodiments of the present disclosure are arranged to use energy supplied by solar panels to drive a water heating appliance. The renewable energy source, in this case one or more solar panels, can be defined by an inherent power-voltage curve, which has an apex at a certain voltage. The apex may also be referred to as the maximum power point (MPP). In an example embodiment, a voltage is received from the solar panel(s) and this voltage is input into a boost converter which steps up the voltage by increasing or multiplying it to a voltage that is greater than that of the MPP of the solar panel (s), and past an optimal power-voltage relationship or curve of a load. This higher voltage may be input into a buck converter which reduces or steps down its output voltage, so that the output voltage of the buck converter can be used to drive the appliance. Embodiments of the present disclosure may be arranged such that the output voltage of the buck converter is closer to the MPP. In particular, the output voltage of the buck converter may cause the appliance to be driven at a higher power point than would have been the case if the solar panel(s) were directly connected to the load or appliance.

When a load is directly connected to a solar panel, an operating point of the solar panel may not be at peak power. The impedance seen by the panel may determine the operating point of the solar panel. A method of moving the operating point towards a peak power point may include varying the impedance seen by the panel(s). Since panels are DC devices, DC-DC converters may be implemented to transform the impedance of one circuit (source) to the other circuit (load). Changing the duty ratio of the DC-DC converter may result in an impedance change as seen by the panel. The l-V or P-V curve of the panel can vary considerably with variation in atmospheric conditions such as solar irradiance and temperature.

Figure 1 shows a high-level block diagram of a system for controlling electrical power delivered from a renewable energy source to a load. Figure 2 shows another block diagram where the renewable energy source is provided by a number of solar panels and where the load is a water heater, (also referred to as a geyser in South Africa). Figures 3 to 10 show power-voltage graphs which will be described in more detail below. Figure 11 is another high-level block diagram, similar to Figure 1 , and illustrates exemplary parts of control circuitry as blocks, each of which are shown in more detail in Figures 12 to 14. An exemplary method is shown in the swim-lane flow-diagram of Figure 15. Figures 16 to 18 are example graphs and diagrams of an exemplary system according to the present disclosure. Figures 19 to 27 show various circuit diagrams that may be implemented by the system and method of the present disclosure.

Referring now to Figure 1 , there is shown a system (10) for controlling electrical power delivered from a renewable energy source (12) to a load (14). The renewable energy source may be any type of energy source able to provide electricity. This includes energy sources such as those provided by solar energy, hydro-electric power, wind turbines, gas turbines, geothermal energy converting devices, etc. In the embodiments of the present disclosure, use of one or more solar panels (16) as the renewable energy source will be described. However, those skilled in the art will appreciate that many other types of energy sources that are inherently variable may be used. The renewable energy source (12) may be provided by one or more solar energy converting devices, such as photovoltaic solar cells of the photovoltaic solar panels (16). In an embodiment, the system (10) includes control circuitry (18) which has a number of different components forming part thereof. The control circuitry may include a memory (20) and one or more processor(s) (22) for executing the functions of components described below, which may be provided by hardware or by software units executing as part of, or on behalf of, the control circuitry (20). The software units may be stored in the memory (20) and instructions may be provided to the processor (22) to carry out the functionality of the described components. In some cases, for example in a cloud computing implementation, software units arranged to manage and/or process data on behalf of the control circuitry (18) may be provided remotely, for example by a remote server (24) which may be connected to a remote database (26). The remote server (24) may be in data communication with the control circuitry (18), for example by way of the Internet, or another communications path. However, some or all of the components (including the remote server (24)) may be provided locally. Some or all of the components may be provided by a software application (app) downloadable onto and executable on the control circuitry (18), for example as firmware or the like. Some of the functionalities of the system may be provided by the server (24) and database (26).

A user (28) may also be enabled to interact with the system (10), and may have an associated user device (30) which may be in data communication with the control circuitry (18) and/or with the remote server (24). Some or all of the components may be provided by a software application (app) downloadable onto and executable on the user device (30). The system (10) may further include a renewable energy input component (32) for receiving electrical energy from the renewable energy source (12). A user interface component (34) may be provided to facilitate a user interface to be provided, either on a display of a dedicated control panel (136) (shown in Figure 2) that is connected to the control circuitry, or via the user device (30). A boost circuit (38) and a buck circuit (40) may form part of the control circuitry (18), or may be connected thereto. The boost and buck circuits (38, 40) are described in more detail below.

The control circuitry (18) may further include, or be connected to a buck circuit duty cycle monitoring component (42), which may be arranged to monitor a duty cycle of the buck circuit (40). An MPP estimating component (44) may be arranged to estimate an MPP of the renewable energy source. A comparing component (46) may, in turn, be arranged to compare a current duty cycle of the buck circuit (40) with a chosen operating range. The control circuitry (18) may also include a transmitting component (48) and a receiving component (50). A power output component (52) may be arranged to output power to the load (14) being driven. The system may also include a feedback receiving component (54) that may be operable to receive feedback data from the load (14). Turning now to Figure 2, an embodiment of the system (100) is shown where the renewable energy source (112) is provided by one or more solar panels (116), each solar panel including a number of photovoltaic (PV) cells, arranged in an array. Similar reference numerals may be used throughout the Figures, to indicate similar components. One or more miniature circuit breakers (MCB’s) (156) may be arranged between the renewable energy source (112) and the control circuitry (118), as well as between the control circuitry and an alternating current (AC) input (119). The MCB’s may also be arranged to protect parts of the system, for example by including fuses or the like. Solar reverse polarity protection may for example be implemented by Boost FET base Diode(s). Grid feedback safety or protection may also be provided, for example with relay-based power path management. In Figure 2, Direct Current (DC) electricity is indicated by the reference numeral (158), and AC electricity (which may form example also be provided by a pulse-width modulated (PWM’d) square wave) by the reference numeral (160). The user (128) may be enabled to interact with the system (100) via a dedicated control panel (136), or via the user device (130) such as a mobile device associated with the user (128). A mobile application (app) may be downloadable and executable on the user device (130) to enable the user (128) to interact with the system (100). User interactions are diagrammatically indicated by the reference numeral (162). The flow of information or data is generally indicated by “comms” (also in Figure 11 described below) and by the reference numeral (164) in Figure 2. The control circuitry (118) may include the boost circuit (138), the buck circuit (140) and a control circuit (141 ) (which may also be referred to as a control and buck circuit). The buck circuit (140) may utilise pulse-width modulation (PWM) as will be described in more detail below. One or more microcontrollers (168.1 , 168.2, 168.3) may be implemented in each of the boost circuit (138), the buck circuit (168) and the control circuit (141 ). The control circuit may further include a real-time clock (RTC) (170). The control circuitry (118) and/or the control circuit (141) may be Bluetooth ™ or WiFi™ compatible, and able to be in wireless data communications with the user device (130), the control panel (136) and the remote server (24) (shown in Figure 1). Wired communication may also be possible. The power output component (152) is also shown in Figure 2, and it may also be referred to as an interface between the control circuit (118) and the load, which is in the present embodiment a water heater (115).

The control circuit (141) may be connected to the boost circuit (138) and to the buck circuit (140), and arranged to control operation of the boost circuit and the buck circuit. A switching circuit (174) may also be provided by the control circuit (141) and it may be operable to switch between the AC input (e.g. from AC mains electricity) and solar power provided by the renewable energy source (112). The buck circuit (140) may include a current sensor (176), and optionally the buck circuit (140) may include an H-bridge and MOSFET drivers (178) bounded by broken lines in Figure 2. The H-bridge may for example be used to convert DC (from the solar panels, or from the boost circuit) into AC. As an alternative to the H-bridge and MOSFET drivers (178), the buck circuit (140) may include a chopper circuit, or a DC chopper circuit, which may for example implement PWM to convert the DC to AC. An exemplary PWM circuit (7016) which may be implemented is shown in Figure 27. The feedback receiving component (54) (shown in Figure 1) may be provided by the microcontroller(s) (168) associated with the control circuit (141 ), and it may be arranged to receive feedback data from a temperature sensor (180) that may be provided in the water heater (115) to measure a current temperature of the water inside a container (111) or tank of the water heater (115). The feedback receiving component may also receive feedback from other feedback generating devices or sensors. The load in the present embodiment is a water heating element (114) of the water heater (115). There is thus provided a water heating apparatus (115) which includes the container (111) for holding water to be heated and the heating element (114) for heating water in the container (111) under control of the control circuitry (118), which may include the boost circuit (138) and the buck circuit (140).

It will be appreciated that each of the boost circuit (138), the buck circuit (140) and the control circuit (141) may operate in isolation, or they may operate together. The boost circuit may also be bypassed in certain circumstances. Control of the various components may be performed by the control circuit (141), but it may also be performed by any one or more of the components forming part of the control circuitry (118), or even remotely. Timing data from the RTC (170) may be provided to any one or more of the microcontrollers (168) for facilitating switching.

The temperature sensor (180) may be arranged to measure temperature of the water in the water heating apparatus or water heater (115). The feedback receiving component (54) of the system (10, 100) may be arranged to receive feedback data from the load, such as temperature data from the temperature sensor (180). The feedback data from the load may be received in near real time. The control circuit (141 ) may be arranged, based on the received temperature data, to switch the heating element (114) on or off. This may facilitate more accurate control of the water temperature in the water heater (115).

Turning to Figure 3, the power-voltage relationship of a renewable energy source, in this case a solar panel (116) is diagrammatically illustrated. The efficiency of the solar panel is defined by the efficiency of its solar cells, in other words the portion of energy in the form of sunlight that can be converted via photovoltaics into electricity. As seen in the various efficiency curves in Figure 3, depending on solar irradiance on a particular day, the MPP of the solar panel is located at a particular voltage. Various MPP’s (172.1 , 172.2, 172.3, 172.4, 172.5, 172.6) are diagrammatically illustrated as curves (174.1 , 174.2, 174.3, 174.4, 174.5, 174.6) for their received irradiance values of 200 W/m ² 400 W/m ² 600 W/m ² 800 W/m ² 1000 W/m ² and 1200 W/m ² respectively. These efficiency curves are typically an inherent characteristic of the solar panel(s) (116). It will be understood that if an operating point of the solar panel(s) is located at a voltage that is not at the MPP, then the solar panel is not being used as efficiently as it could have been, and the power delivered to a load would be less than optimal. These efficiency curves may be referred to as the power-voltage relationship(s) of the renewable energy source. They are shown as curves for the solar panels, but it will be appreciated that power-voltage relationships for other types of renewable energy sources may have different curves or graphs that represent them. However, it is envisaged that most if not all types of renewable energy sources have one or more MPP’s. It is also noteworthy that if solar panels are arranged in series, the efficiency curves (174.1 , 174.2, 174.3, 174.4, 174.5, 174.6) tend to move towards the right in Figure 3 (i.e. voltage would increase and power would remain more or less constant), whereas if the solar panels are arranged in parallel, the curves tend to move upwards in Figure 3 (i.e. power would increase and voltage would remain more or less constant). For practical considerations, solar panels may typically be arranged in series.

Referring to Figure 4, there are shown power-voltage relationships (or optimal efficiency curves) of two types of heating elements (114.1 , 114.2), rated 2kW and 3kW respectively, and that may for example be used in the water heater (115) of Figure 2. The power absorption of each of the 2kW and 3kW elements is illustrated by each of the curves (182.1 , 182.2). Naturally, other types of heating elements may also be used if needed.

In Figure 5 is shown an example power-voltage curve (188) for a load (such as the heating element (114) of Figure 2. As will become apparent from what follows, and as shown diagrammatically in Figure 5, the curve for the heating element (114) or load may define a boosting region (184) and a bucking region (186) (also shown in Figure 6). It should be understood that the position or values of the curves and graphs shown in Figures 3-6 are for explanatory purposes, and actual values may vary in practice. The load may thus have a required or optimal power-voltage relationship or curve (188) which may define the boosting region (184) and the bucking region (186).

Figure 6 shows the graphs of Figures 3 and 5 superimposed on top of one another. As can be seen in Figure 6, depending on the amount of received solar irradiance, the MPP of the one or more solar panels (116) may be located either above the curve (188) in the boosting region (184) or below it in the bucking region (186). On a fairly sunny day, the received irradiance may be 1000 W/m ² , and the MPP of the panel(s) (116) may be located as indicated by reference numeral (172.5). If the solar panel(s) are directly connected to the load (114), the power absorption of the load may be in the region of the intersection designated (190) at a power of Pi and a voltage of Vi. This means that the actual power being output to the load would only be at about Pi, while theoretically the solar panel(s) could have provided power at P _mpp which corresponds to the MPP of the panel(s). Hence, a significant decrease in power delivered to the load would result. In order to address this, the present disclosure may enable the boost circuit (138) to receive electrical power from the renewable energy source (112) and to boost a voltage of the received electrical power by multiplying its voltage by a factor (192) (also referred to as a boost factor) to yield a higher voltage (V _B ) at the higher voltage point (199) in the graph of Figure 6. In other words, the boost circuit (138) may be arranged to boost its input voltage from the boosting region (184) into the bucking region (186). The factor (192) by which the voltage is boost is diagrammatically indicated by the dashed arrow in Figure 6, however it will be appreciated that the factor (192) may for example be a multiplication factor that is dynamically determined by the system (100) in real time, or near-real time, and a magnitude of the factor (192) may also be dependant on how far the relevant MPP is located in the boosting region (184) for a given load and for a given amount of received solar irradiance.

As is evident from Figure 6, the higher voltage (V _B ) is greater than a corresponding voltage (V _mpp ) of the maximum power point (MPP) (172.5) defined by the power-voltage relationship of the renewable energy source (12) (in this instance provided by the one or more solar panels (116)). Referring to Figures 2 and 6, the buck circuit (140) has an input (194) for receiving the higher voltage (V _B ) and an output (196, 152) for delivering an output voltage of the buck circuit (140) to the load (114). The buck circuit (140) may be arranged to reduce or step-down the output voltage of the buck circuit (140), so that an output voltage (V ₂ ) of the buck circuit is located near a target point (198) in Figure 6 which is near the power-voltage relationship of the load (114) (in this case the heating element). In other words, the output voltage (V ₂ ) of the buck circuit (140) may be operable to drive the load by a power (P ₂ ) which is closer to the MPP (172.5) of the renewable energy source (12, 112, 116). Stated differently, the output voltage (V ₂ ) of the buck circuit (140) may also be closer to the equivalent voltage (V _mpp ) of the MPP (172.5) than the higher voltage (V _B ). The higher voltage (V _B ) may also be referred to as the boost voltage. The system (10, 100) may also be arranged such that the boost factor (192) may be reduced if the higher voltage point (199) for V _B is significantly higher than the voltage V ₂ of the target point (198), or to increase the boost factor (192) if the higher voltage point (199) for V _B is located closer to the voltage V ₂ of the target point (198).

The boost circuit may be associated with power losses (202), and the buck circuit may also be associated with power losses (204), however the overall power losses (202, 204) of the system (100) may be less than would have been the case if the load was directly connected to the solar panel(s) (116). This is also evident from Figure 6, as the output voltage (V ₂ ) of the buck circuit (140) may result in the load (114) being driven at a higher power level P _å as compared to Pi. It will be appreciated that in practice P _å may be significantly greater than Pi. Thus, more solar energy may be converted to thermal energy for storage in the water (in the case of the load being the heating element).

In Figure 7 is shown a power-voltage graph illustrating test data for an example of summer conditions. MPP’s (206, 208, 210, 212, 216, 218) are shown for a corresponding number of solar panels arranged in series, for respectively one, two, three, four, five, and six solar panels arranged in series. The power-voltage curves for a 3kW element (203) and for a 2kW element (201 ) are also shown in Figure 7. The power-voltage efficiency curves (or power-voltage relationships such as those shown in Figure 3) of the solar panels are omitted from Figure 7 for the sake of clarity, and only the MPP’s are shown. In the example of one solar panel, the MPP (206) is located in the boost region for both the 3kW element and the 2kW element. Conversely, for the case of six solar panels, the MPP (218) is located in the bucking region (the bucking region may also be designated by “PWM” (pulse width modulation) in Figures 7-10) for the 3kW element. It will be understood that for two solar panels, the corresponding MPP (208) is located in the boost region for both 3kW and 2kW elements, and thus the boost circuit will be used as described above. However, for the scenarios where five or six solar panels are used, their MPP’s (214, 218) may be located in the buck region for the 3kW element and the boost circuit may be bypassed. The control circuit (141) may be arranged to bypass the boost circuit in such a scenario. If a larger number of solar panels is used, then the boost circuit may be bypassed, or a pass-through may be provided for the boost circuit. In a region such as South Africa, where solar irradiance is especially high (due to the lensing effect or due to other factors), the MPP’s may be even higher than depicted. This means that the system may provide even better efficiency, because the MPP would be further in the boosting region if the received irradiance is more (and losses would have been greater if the panels were directly connected to the load and if the present system is not implemented). Figures 8-10 are similar to Figure 7, but show graphs for Winter (Figure 8), Autumn or Spring (Figure 9), and 9AM on a typical Summer morning (Figure 10).

The Power-Voltage graphs in Figures 8-10 show test data gathered using 72 cell, 300-330 Watt solar panels. The type of solar panel used for these tests is a Canadian solar MAXPOWER CS6U- 325. For this particular solar panel, the relevant electrical data is as follows: Voltage at Max Power (Vmp) = 37.2 V and Current at Max Power (Imp) = 8.88 A. Tests were conducted in Cape Town, South Africa, and the actual maximum power that was extracted during summer was higher than expected, as Cape Town often has above average solar radiation during summer. Voltage may be scaled by adding solar panels in series. Two heating elements (2kW and 3kW rated elements) were used to indicate the possible power absorption with varying voltages. This data may be used as a reference to ascertain which mode the control circuit (141) may be operating in (for example a boosting mode, or a bucking mode). 2 kW and 3 kW elements are the most common sizes installed in South African households, but other types may also be used. For the graphs in Figures 7 to 10, the three variables being compared on each graph are: the 2 KW element power absorption (201 ), the 3 KW element power absorption (203), and the maximum power available (211) from the solar panel array under given conditions.

The boost mode and the bucking (or PWM) mode are also indicated in the graphs. The boost mode and bucking mode may also be referred to as the operating modes of the control circuit (141) (and/or of the control circuitry (118)). The overall system (10, 100) architecture may be arranged to accommodate for these varying conditions. The system (10, 100) may operate in the boosting mode (step-up), or in the bucking mode (PWM or step-down), or the system may use AC mains electricity or grid electricity as a back-up means to drive the load (or battery power may be used in some circumstances). An available solar power line (211) may shift depending on the environmental conditions, specifically by solar irradiance received. The operating modes of the system (10, 100) are designated as follows: 3kW Boost (Step Up) and PWM Buck (Step Down) (217); 2kW Boost (Step Up) and PWM Buck (Step Down) (219); 2kW PWM Buck (Step Down) (227); and 3kW PWM Buck (Step Down) (229). Referring to Figure 7, it will be appreciated that in practice, the solar irradiance received may be greater than expected. For example, for a test rig of four (212) solar panels, an estimated maximum power output of the solar panels would be about 1250 Watts. However, it may happen that as a result of more solar irradiance being received (or as result of the lensing effect of clouds or the like), the actual MPP may be at about 1600 Watts as indicated by the point (231) in the graph. This may result in the system operating in the boost mode, to boost the voltage into the bucking region, and then to buck the voltage back towards the required or optimal power-voltage curve of the load (i.e. towards the target point (198) as described above). Having less than three, or two or less solar panels may be advantageous, especially if smaller households are to be serviced. Smaller heating elements also have curves that are generally “flatter” and thus the likelihood of operating in the boost mode may be higher. It may also be the case that the system may operate in boost mode for a part of a day, and in buck mode for another part of the day.

Moreover, even if more solar panels are provided in series, the solar panels may nevertheless cause the MPP to “break through” the power-voltage relationship or optimal curve of the load, if there is a lot of sunlight. The present disclosure may at least partially alleviate this problem. Even though the buck circuit may be fairly efficient on its own, there may be significant losses if the MPP is located above the curve of the load. Hence, the present disclosure may implement boosting by the factor (192) past the curve of the load, and then bucking to bring the operating point closer to the MPP (i.e. towards the target point (198)). Even though the boost circuit (38, 138) may have heat losses, these heat losses may be insignificant in comparison to the power losses that would result if the renewable energy source (12) were simply connected to the load (14) directly. The system (10, 100) may be arranged to track the curve (188) of the load dynamically, to bring the operating point as close as possible to the load’s optimal power-voltage relationship.

For the boosting mode, installations and conditions where the available solar power is above the heating element's ability to absorb energy due to its resistance (which may be a fixed resistance), may require the system (10, 100) to boost the voltage. This may allow the Step Down Buck (PWM) portion of the control circuitry (18, 118) (i.e. the Buck circuit (40, 140)) to match the max power point of the heating element's (14, 114) power absorption capability. In other words, the system (10, 100) may be arranged to perform boosting and bucking in order to track the required or optimal power-voltage relationship of the load. One or two solar panels may cause the system to boost under most conditions, as the cumulative DC voltage is quite low. This may change as the number of solar panels increases and the system voltage becomes higher.

For the bucking mode, the PWM or Buck (Step Down) circuit (140) of the system may run constantly as this circuit may also convert the incoming DC from the solar panel to a high frequency (900 Hz) AC. The duty cycle of this AC wave may vary depending on the input voltage and MPP of the solar panel array. This may be provided by active control which may match the element's power absorption and the MPP of the solar panel (s).

The buck circuit (140) may further be arranged to reduce its output voltage by implementing maximum power point tracking (MPPT). To implement the MPPT, the buck circuit may perform pulse width modulation (PWM). The buck circuit (140) may function by changing a duty cycle of its output voltage. The duty cycle of the buck circuit’s (140) output voltage may be defined by the duty cycle of the PWM performed. The output of the buck circuit (40, 140) may be a pulse-width modulated square wave which may be used to drive the load (14, 114).

An exemplary embodiment of the system (100) is shown in Figures 11 to 14. To facilitate explanation, the system (100) is shown at a high level in Figure 11 , with the boost circuit (138), buck circuit (140) and control circuit (141) illustrated by blocks. It will be appreciated that control and bucking may be provided by either or both of the buck circuit (140) and the control circuit (141). The boost circuit (138), buck circuit (140) and control circuit (141) may collectively be referred to as control circuitry (118). An input (139) of the boost circuit (138) may be provided by a PV supply connector or input. The buck circuit may also be referred to as a PV to PWM circuit. Referring to Figure 12, Direct Current DC is received by the PV supply connector or input (139) from the solar panel(s) and this DC is fed to the boost circuit (138). A heatsink (220) may be provided for the boost circuit (138). The boost circuit may include a DC input (222) and a DC output (224). One or more field-effect transistor (FET) drivers (226.1 , 226.2) may also be provided and these FET drivers may be under control of the microcontroller (168.1 ) of the boost circuit (138). The boost circuit (138) may also include a bypass N-FET (n-channel FET) (228), which, under control of the microcontroller (or microcontroller unit MCU) (168.1 ) may be operable to bypass the boost circuit in certain circumstances. For example, if it is determined by the control circuit (141 ) that the current MPP of the solar panel(s) (116) is in the bucking region, then the boost circuit (138) may be bypassed under control of the MCU (168.1 ). The heatsink (220) may facilitate excess heat to be dissipated from one or more of the components of the boost circuit (138), for example from the Switching N-FET(s) (232), inductor(s)(234), Shottky Diode(s) (236), FET driver(s) (226.2) or any of the other components of the boost circuit (138). The boost circuit and/or the microcontroller (168.1 ) of the boost circuit may include or may provide the buck circuit duty cycle monitoring component (42) (referred to above with reference to Figure 1 ) arranged to monitor the duty cycle of the buck circuit (140).

It will be appreciated that the MCU (168.1) may, in turn, be controlled by the control circuit (141). Data communications (as well as PV input or other voltage supply (e.g. a 12V supply)) between the various components forming part of the control circuitry (118) may be provided via printed- circuit-board-to-printed-circuit-board (PCB-PCB) connector(s) (230) (also shown in Figures 13 and 14) and designated as “Comms”. The boost circuit (138) may further include one or more switching N-FET’s (232), one or more inductor(s) (234) and one or more Shottky diode(s) (236). The output voltage of the boost circuit (138) may be provided to the buck circuit (140) by way of a boost power PCB-PCB connector (238.1). The DC input (222) may include or be connected to a voltage sensor or voltage divider. The DC output (224) may include or be connected to a voltage sensor or voltage divider. The boost circuit (138) may further include a low-dropout (LDO) (240) or LDO regulator. Arrows that may represent relatively lower voltage DC (e.g. about 12 Volts) are designated (242) in Figure 12. Relatively thicker arrows that may represent relatively higher voltages are designated (244) in Figure 12. For example, the voltage that is output by the boost circuit may be between 0-300V in the present example embodiment, whereas the DC that is input into the boost circuit may be between 60V to 171V (or below about 200V), or the input voltage may be between 60V-230V (or below about 250V).

Turning now to Figure 13, there is shown an example of a PV to PWM buck circuit (140) according to an embodiment. The buck circuit (140) may also include a heatsink (221) even though it is envisaged that its heat (power) losses may be less than that of the boost circuit (138) (as is diagrammatically shown in Figure 6). The output voltage of the boost circuit (138) may be received by the buck circuit (140) by way of a boost power PCB-PCB connector (238.2) or mounting pad which may for example be connectable to the PCB-PCB connector (238.1) of the boost circuit in Figure 12. A current sensor (246) may be implemented by the buck circuit (140), as well as an LDO (248). Components of the buck circuit (140) may be controlled locally by an MCU (168.2) associated with the buck circuit (140) as illustrated in Figure 2, or control may be performed by an MCU (168.3) of the control circuit (141). In Figure 13, control of the buck circuit is provided by the MCU (168.3) of the control circuit (141) by way of an input-output (I/O) connector (250) (also shown in Figure 14). The buck circuit may include a DC input (252) and a PWM output (254). The DC input (252) may include or be connected to a voltage sensor or voltage divider. The PWM output (254) may also include or be connected to a voltage sensor or voltage divider. The buck circuit (140) may include a PV input connector (256) to receive power from the solar panel(s) (for example when the boost circuit is bypassed). As before, arrows that may represent relatively lower voltage DC (e.g. about 12 Volts) are designated (242) in Figure 13. Relatively thicker arrows that may represent relatively higher voltages are designated (244) in Figure 13.

For example, the voltage that is received by the buck circuit (140) may be between 0-300V in the present example embodiment, whereas the voltage that is output to the control circuit (141) (and/or to the load (114)) may be between 0-300V PWM (pulse-width modulated) at about 900Hz. In order to perform the PWM, the buck circuit may use one or more switching N-FET’s (260) driven by one or more FET driver(s) (262) under control of the MCU of the control circuit (141 ). The heatsink (221) may facilitate excess heat to be dissipated from these Switching N-FET’s (260), or from other components of the buck circuit (140). A temperature sensor (such as a negative temperature coefficient (NTC) temperature sensor) or thermistor (264) may be provided to measure temperature in the heatsink (221) and to feedback this data to the control circuit via the I/O connector. A similar temperature sensor (not shown) may also be provided for the boost circuit (138) (or for the boost circuit’s heatsink (220)). The temperature data from the temperature sensor (264) may be used by the control circuit (138) to prevent or to detect overheating (for example by cutting out voltage or reducing voltage to inhibit damage to components or circuitry). An example safety shutdown may be performed if a temperature of about 120 °C is sensed in any one of the heatsinks. The buck circuit (140) may further include a PWM PV signal PCB-PCB connector (266) for outputting about 0-300V PWM at 900Hz to the control circuit (141) and/or to the load (114).

Referring now to Figure 14, an example of a control circuit (141) (also referred to as a control and buck circuit) according to the present disclosure is illustrated. An AC mains input (268) may be provided via an AC input connector terminal block (270). AC power may be represented by dashed arrows (272) in Figure 14. As before, arrows that may represent relatively lower voltage DC (e.g. about 12 Volts) are designated (242) in Figure 14. Relatively thicker arrows that may represent relatively higher voltages are designated (244) in Figure 14. The PCB-PCB connector (230) or bus and/or the I/O connector (250) may provide communications with the other components of Figures 12 and 13. A relatively lower voltage supply may be provided, for example a 12V supply (274) (which may also provide 12 V to the boost and buck circuits (138, 140)). A 12V supply flyback (276) at about 9 Watts may be provided, as well as an LDO (278), for example a 3.3V LDO. The MCU (168.3) may control one or more (or all) of the components of the control circuit (141) (or one or more of the components of the boost and buck circuits (138, 140) that may form part of the control circuitry (118)). The control circuit (141) may further include an onboard battery (280) and a real-time clock (282). The MCU (168.3) of the control circuit may be connected to a relay driver (284) for driving an AC/P V relay power select circuit (286), which may be operable to switch between AC mains power, and PV power received from the boost and/or buck circuits (138, 140) (and/or from the solar panels (116). The control circuit (141) may further include a PWM PV signal PCB-PCB connector (266) or mounting pad for inputting about 0-300V PWM at about 900Hz into the control circuit (141) and/or via the AC/P V relay power select circuit (286) to the load (114). A water heater element output connector (terminal block) (288) may be provided for this purpose.

The water heater element output connector (288) may also be operable to output AC mains power to the water heater’s heating element (114), if needed. A screen connector or interface (290) may be provided as an interface between the MCU of the control circuit and the control panel (136) (shown in Figure 2). The user interface component (34) (shown in Figure 1 ) may thus be provided by the screen connector (290), or by way of a WiFi™ or Bluetooth™ connection, or by way of GSM or Long-Term Evolution (LTE) wireless module or modem. A GSM or LTE module (292) may be provided by the control circuit (141 ) and the control circuit (141 ) may also include a WiFi™ or Bluetooth™ or Bluetooth™ Low Energy (BLE) or Universal Asynchronous Receiver/Transmitter (UART) module (294) for data communications with one or more of the other components of the system (100). A light-emitting diode (LED) connector (296) may be connected to one or more LED’s (298) associated with the system (100). The control circuit may further include a 3.9V buck component (300) and a 5V buck component (302) connected to the 12V supply.

Referring to Figures 1 to 14, the system (10, 100) and the control circuit (141) may be arranged to monitor the duty cycle of the buck circuit (140), and responsive thereto, the control circuit (141) may change the factor (192) by which the voltage (from the renewable energy source (12, 112)) is boost so as to keep the duty cycle of the buck circuit within a chosen operating range. The chosen operating range may be selected to be between 80% to 100%, or between 90% to 100%, or between 92% to 98%, or between 93% to 98%, or between 93% to 95%, or between 95% to 97%. However, it will be appreciated that other values for the operating range may be used. An operating range of the duty cycle of the buck circuit (140) of between 95% to 97% may be preferable, depending on practical considerations, and it may also be preferable to keep the duty cycle of the buck circuit below 100%. As an example, and referring again to Figure 6, V _mpp may be about 72 Volts, P _mpp may be about 720 Watts, P1 may be about 620 Watts, and P2 may be about 700 Watts (or even more if the operating range is properly maintained) for an example case of two 360 Watt solar panels being implemented. The present disclosure may enable an increase in the amount of power delivered from a solar panel by about 55 Watts per panel (for an exemplary solar panel rated at 300-330 Watt). These values may however vary in practice, depending on the amount of solar irradiance, the type of solar panel, and the magnitude of the load driven. It may be advantageous to use this increase in output power to heat water, and to store this energy in the water container or tank (111 ) as thermal heat. In other words, the system may be arranged to “dump” or store excess solar energy and convert it into thermal energy. The system may also be arranged to implement only renewable energy, without the need for AC mains electricity. One or more batteries may be provided for storing energy from the renewable energy source, and for powering the various components of the control circuitry.

The buck circuit (40, 140) may further include, or be connected to a direct current (DC) to alternating current (AC) converter, and it may be operable to convert DC received from the boost circuit (or from the solar panel(s) into AC, or to simulate AC by performing PWM and switching the received DC. This may for example be implemented instead of using the H-bridge (178) shown in Figure 2. An example of such a PWM circuit (7016) is shown in Figure 27. The factor (192) (see Figure 6) may be changed continually, incrementally, increasingly or dynamically over time. The control circuit (141) (and/or the control circuitry (118)) may be operable to change the factor (192).

As described above, the system (100) may include a comparing component (46). The comparing component (46) may for example be provided by one or more of the MCU’s (168.1 , 168.2, 168.3), or by hardware or software operating on the control circuitry (118). The comparing component (46) may be arranged to compare a current duty cycle of the buck circuit (140) to the chosen operating range, and the factor (192) may be changed dependant on this comparison. The factor (192) may also be dynamically changed or adjusted over time. In an embodiment of the system, the factor may be a multiplication factor of at least 1 .1 , alternatively at least 1 .2, or at least 1 .3, or at least 1.4, or at least 1.5, or at least 2.0, or at least 2.5, or at least 3.0. Other multiplication factors may also be used. This may provide a functionality similar to a “leverage ratio” or a “gear- ratio” whereby the input voltage from the renewable energy source is boost into the bucking region. This ratio may be adjusted if the control circuitry determines that the MPP of the renewable energy source is deep into the boost region, relative to the power-voltage relationship of the load. The system may be arranged to boost more when there is more solar irradiance, and to boost less (or not at all) when there is less solar irradiance.

It will be appreciated that the system (10, 100) may include the maximum power point (MPP) estimating component (44) arranged to estimate whether the MPP is located in the boosting region (184) (or if it is located in the bucking region (186)). The control circuit (141 ) may be arranged to cause the boost circuit (138) to boost the voltage of the received electrical power, if the MPP is estimated by the MPP estimating component (44) to be in the boosting region (184). The system may also include the buck circuit duty cycle monitoring component (42) arranged to monitor the duty cycle of the buck circuit (140). It may also be possible to provide a component for monitoring the duty cycle of other parts of the system (10, 100). The MPP estimating component (44) may be arranged to estimate whether the MPP is located in the boosting region, or in the bucking region, by receiving data from the buck circuit duty cycle monitoring component (42). The duty cycle of the buck circuit (140) may be indicative of the location of the MPP of the renewable energy source (12, 112) (such as the solar panel(s) (16, 116)), and this information may be used by the control circuit (141) to decide whether or not to perform boosting or bucking. If it is estimated that the MPP is in the bucking region (186), then the boost circuit (138) may be bypassed and bucking may be performed by the buck circuit (140), (e.g. in order to perform MPPT). On the other hand, if it is estimated that the MPP is located in the boosting region (184), then a process similar to the process described above with reference to Figure 6 is performed in order to provide a voltage to the load which is preferably close to the output voltage or target voltage (V2). Similar procedures may also be performed for the other locations of the MPP’s (172.1 to 172.6), depending on received solar irradiance, weather factors, operational circumstances, etc. Boosting may be performed until the duty cycle of the buck circuit approaches 100%, or until it is above 90%, or until it is within the operating range as described above. In an example embodiment, the boost circuit may be bypassed when a number of solar panels used is less than a predetermined threshold. For example, if less than four solar panels are used, the boost circuit may be bypassed. Alternatively, if four or more solar panels are used, the boost circuit may be connected. Alternatively, the boost circuit may be bypassed, depending on a quantity of received solar energy which may be determined by the system. Embodiments are also possible wherein the boost circuit may be omitted.

The boost circuit (38, 138) may be arranged to boost the voltage of the received electrical power by the factor (192) such that the higher voltage (V _B ) is located in the bucking region (186). The buck circuit may, in turn, be arranged to reduce its output voltage towards the target point (198) (an example of which is shown in Figure 6) near the optimal or required power-voltage relationship (188) of the load. This target point (198) may have a power output that is closer to the MPP (172.5, for the case of 1000W/m ² ) of the renewable energy source (12, 112). This may result in an increase in the quantity of power delivered to the load (14, 114) being driven by the system (10, 100). The factor (192) may be changed dependant on a difference between the MPP (172.5) of the renewable energy source and the required or optimal power-voltage relationship (188) of the load. In other words, if the MPP is located further into the boost region (184), then the factor may be increased, or if the MPP is closer to the required or optimal power-voltage relationship (188) (or curve) of the load, then the factor (192) may be reduced. This may provide advantages over known systems, because the factor or multiplication factor may be leveraged to provide a “leverage ratio” or a “gear-ratio” as mentioned above. The boost circuit (38, 138) (and the system (10, 100) in general) may be arranged to be agnostic to the type of renewable energy source (12) connected thereto. The boost circuit (38, 138) (and the system (10, 100) in general) may also be arranged to be agnostic to the type of load (14) being driven. This may provide versatility of the present disclosure, seeing as it can be implemented in a variety of applications. The buck circuit may be arranged to perform variable or dynamic bucking, and the boost circuit may perform more, or less boosting (or the multiplication factor may be varied) in order to keep the buck circuit within the operating range as described above.

As described above, the control circuit (141) or the control circuitry (18) may be arranged to bypass the boost circuit (38, 138) if the MPP of the renewable energy source is located in the bucking region (186), or if the MPP is estimated to be located in the bucking region (186). Stated differently, the boost circuit (38, 138) may be bypassed if the MPP is estimated not to be located in the boosting region (184). In such a scenario, the control circuit may connect the buck circuit to the input power from the renewable energy source and it may then buck the voltage towards the target point (198). The MPP of the renewable energy source may also be referred to as the apex of the power-voltage relationship of the renewable energy source. In the embodiment described with reference to Figures 2 and 11 , the load is shown to be a resistive load, in this case provided by the heating element (114) of the water heating apparatus or water heater (115). However, it should be appreciated that other types of loads may also be driven using the present disclosure, for example inductive loads, constant voltage loads, or constant current loads. The renewable energy source (12) may be provided by any energy converting device which is configured to convert renewable energy into electrical energy. The renewable energy may originate from an inherently variable energy source such as sunlight, wind (for example using wind turbines), rain, tidal energy, or geothermal heat. The boost circuit (38, 138) may also be agnostic to the number of solar panels connected thereto, and the buck circuit (40, 140) may be agnostic to the boost circuit (38, 138). Stated differently, the boost circuit may be “transparent” to the buck circuit. When a relatively small number of solar panels (116) are used (for example only two), the MPP of the two panels may be significantly into the boost region (184) in Figure 6, especially on a sunny day. The present disclosure may thus enable efficient use of a small number of solar panels (for example four or less, three or less, or two or less). Many types of solar panels may be used, but relatively small types of solar panels (with a typical power output of about 200 to 400 Watts each, or less than 400 Watts each, or less than 300 Watts each) may be used. However, embodiments that use larger solar panels are also possible.

Referring to Figure 15, The system (10, 100) may implement a method for controlling electrical power delivered from a renewable energy source (12, 120) to a load (14, 114). An exemplary method (1000) for controlling electrical power delivered from a renewable energy source to a load is illustrated in the swim-lane flow diagram of Figure 15 (in which respective swim-lanes delineate steps, operations or procedures performed by respective entities or devices). At the control circuit (141) (or at the control circuitry (118)), electrical power is received (1010) from the renewable energy source (12, 112). The MPP estimating component (44) may estimate whether the MPP (172.1 to 172.6) is in the boosting region (184) or if it is in the bucking region (186). The MPP estimating component may for example do this by monitoring the duty cycle of buck circuit (40, 140). If (1012) it is determined that the MPP is located in the boosting region (184) (see Figure 6), then the electrical power from the renewable energy source may be delivered (1014) to the boost circuit (138) where the electrical power may be received (1020). If the MPP is estimated not to be in the boosting region (184) (in other words it is estimated that the MPP is in the bucking region (186)), then the control circuit (141) may bypass (1016) the boost circuit (138), and electrical power from the renewable energy source may be received (1018) by the buck circuit (140).

In the case of the MPP being estimated to be in the boosting region (184), the boost circuit (38, 138) may boost the voltage of the received electrical power by multiplying (1022) its voltage by the factor (192) to yield the higher voltage (V _B ), the higher voltage (V _B ) being greater than a corresponding voltage of the maximum power point (172.5, in the example case of 1000W/m ² ) defined by the power-voltage relationship (174.5 in this case, see Figure 3) of the renewable energy source (12). The higher voltage (V _B ) may be provided (1024) as an input to the buck circuit (140) where the higher voltage (V _B ) may be received (1026). The buck circuit (140) may be arranged to reduce (1028) an output voltage of the buck circuit (140), so that the output voltage of the buck circuit is closer to the MPP (172.5 in this case). This step (1028) may be performed irrespective of whether the boost circuit (138) is bypassed or not. The output voltage of the buck circuit may be delivered (1030) to the load (14, 114). The system (10, 100) may further be arranged to monitor or sense an output voltage or an output current of the renewable energy source, and to control the boost and/or buck circuits based on the sensed output voltage or output current of the renewable energy source (12, 112).

It will further be understood that the system (10, 100) may be arranged to implement the buck circuit duty cycle monitoring component (42) to monitor the duty cycle of the buck circuit (40, 140) irrespective of the load characteristics. In other words, the system (10, 100) may automatically determine if the MPP is located in the boosting or bucking regions (184, 186), without actually having access to data relating to the resistive curve (188) of the load being driven, or without having access to the efficiency curves (174.1 to 174.6) of the solar panels (16, 116). Instead, the system (10, 100) may be arranged to estimate that if the buck circuit duty cycle approaches 100% (or if it is higher than about 95%), then the operating point is likely in the bucking region (186) and bucking may be performed to buck the voltage back towards the target point (198). If the duty cycle of the buck circuit (40, 140) is higher than 97%, then the factor (192) of boosting may be increased (for example from a multiplication factor of 1.5 to a multiplication factor of 2.0). Conversely, if the duty cycle of the buck circuit is below 95%, then the factor of boosting may be reduced (for example, from a multiplication factor of 2.0 to a multiplication factor of 1.5, or from 3.0 to 2.0).

The step (1028) of reducing the output voltage of the buck circuit (40, 140) may include reducing it towards the target point (198) near the optimal power-voltage relationship (188) of the load (14, 114). Referring again to Figure 6, the target point (198) may have a power output (P2) that is closer to a theoretical maximum power output (P _mpp ) that could be provided at the MPP (172.5) for the renewable energy source (12). Thereby, the quantity of power delivered to the load may be increased, as an operating point for the load would otherwise have been in a region of the intersection designated (190) at a power of Pi and a voltage of Vi.

In Figure 16 is shown three graphs (2010, 2012, 2014) for water temperature against time over the course of three days, illustrating a variety of possible user interactions with the system and method of the present disclosure. An example family of two people may use the system and they may be enabled to optimise the use of warm water and to maximise cost savings. It will be appreciated that the system (10, 100) may be retro-fitted to an existing water heater, and to an existing array of solar panels (or an existing facility with one or more solar panels), which may also provide versatility and cost savings. The user interface component (34) may provide a variety of options to a user. The system (10, 100) may provide a user interface via the dedicated display (136) (shown in Figure 2) or the user interface may be provided on the user device (130) via WiFi or via the Internet. Different features may be available depending on a subscription package offered to the user(s).

In the first part and last parts (2016, 2018) of the graphs, power may be provided to the heating element (114) by way of AC mains power. Solar power may be provided (2019) to the heating element during the day. The water heater (115) may have a maximum and minimum temperature selected for it, where the maximum may be a temperature selected to prevent damage to the water heater due to overheating. A first maximum temperature (2021) or setpoint of about 90°C or below 100°C may be selected for solar heating, and a second maximum temperature (2023) or setpoint may be selected for AC mains heating (for example about 60°C for Day 1 in Figure 16). The user(s) may use warm water as indicated by the first and second usage events (2020, 2022). Water may be heated using solar heating and the temperature may increase over time as indicated by the reference numeral (2024). As shown in Figure 16, the temperature drops off as the usage events (2020, 2022) occur, as the users use hot water for example by showering or the like. For Day 2 and Day3, the user(s) (28) may adapt their hot water usage events (2020, 2022) and may save energy, because more solar energy may be used to heat the water, instead of AC mains electricity. Day 1 shows an example where the user(s) ignores the user interface (34) of the system (10, 100) and simply showers or uses hot water as and when they like. For Day 2, the users adjust the times of their hot water usage events (2020, 2022). For ideal or near-ideal solar supply on Day 2, the maximum set temperature may be reached during the day and the users may use the warm water heated by solar energy. A similar scenario is depicted for Day 3, where the time of each of the usage events (2020, 2022) is reduced. The system (10, 100) may be arranged to provide guidance to users (28) in order to schedule their hot water usage events more efficiently, maximising solar energy usage and minimising AC mains electricity usage. The system (10, 100) may for example suggest times for the users to take showers, baths or other warm water usage events. The flat parts (2026) of the graphs indicates where the water temperature is maintained at the maximum temperature for Day 1 and Day 2, or at an example setpoint of 55°C for Day 3. For Day 1 , it may be necessary for the system to rely on AC mains power early in the morning to heat water in time for the expected usage event in the morning, whereas for Days 2 and 3, it may not be necessary for the system to rely on AC mains at all. This may provide benefits to the user, both in terms of cost savings and reducing overall electricity usage, making their homes more “green” or energy efficient. The system may also be arranged to predict the usage events and to control components based on the predicted or expected usage events, and to provide suggestions to the user(s) to change their usage events to save electricity.

For Day 2 and Day 3 the user (28, 128) may select the first maximum temperature (2021) or setpoint for solar heating (e.g. about 90°C), but the setpoint of the water heater for using AC mains may be reduced to the minimum temperature (2025). This may reduce the overall AC mains electricity usage while still enabling the user to use hot water when needed.

Three similar graphs are shown in Figure 17, for an version of the system (10, 100) (which may include advanced user features), where the user may be able to interact with the system via their user device (130). In the present embodiment (or in the other embodiments described herein) a mobile application (app) may be downloadable and executable onto the user device (130) to enable the user to interact with the system (10, 100). The three further graphs (2028, 2030, 2032) in Figure 17 shows water temperature against time over the course of three weeks, illustrating a variety of possible user interactions with the system of the present disclosure. The system may provide a report to the user via the user device (130), the report showing water usage and energy usage over a time period, for example during Week 1. The user (128) may react and adjust hot water usage events (2020) accordingly, as shown for Week 2 and Week 3. The user (128) may for example adjust the setpoint of the water heater using the app on their user device (130). For Week 1 , the setpoint of the water heater may be 55°C. It will be appreciated that even though the setpoint for the water heater may be set, the system (10, 100) may enable the water heater to heat water to higher temperatures using solar energy, towards the maximum temperature for the water heater (115). The maximum temperature may for example be configured upon installation of the system (10, 100).

For Week 2, the user may adjust the setpoint to 45°C in order to use less AC mains electricity. The hot water usage events of the user may also be reduced by the user and the user may utilise feedback, guidance or suggestions from the user interface provided by the system to adjust the times of their water usage events to use more solar heated water, instead of water heated by AC mains. It will be appreciated that the graphs in Figures 16 and 17 are examples and actual water usage and temperatures may be different. The graphs may be representative of average water usage over the course of a period of time. The user may also be enabled to use the app on their user device (130) to adjust the setpoint for the water heater’s heating element (114) to be 45°C during the night, and 70°C during the day. The user may select a minimum temperature of 45°C, and the system may be arranged to only use AC mains electricity to heat water if the minimum water temperature of 45°C is reached.

For the example embodiment of the system illustrated in Figure 17, the first maximum temperature (2021 ) or setpoint of about 90°C or below 100°C for the water heater (115) may be selected by the user (28, 128) for solar heating. The second maximum temperature (2023) or setpoint may be selected for AC mains heating (for example about 55°C for Week 1 , about 45°C for Week 2 and about 40°C for Week 3 in Figure 17). The user (28, 128) may also be enabled to adjust the minimum temperature (2025). Overall AC mains power usage may be reduced, and the use of solar power may be more efficiently implemented by the present disclosure.

Figure 18 shows examples of a number of different user interfaces that may be displayed to a user of the system of the present disclosure, either by way of the dedicated control panel display (136), or by way of the display of the user device (130) or mobile device of the user (e.g. via the app). Examples of information that may be provided to user(s) (28, 128) are described below.

A home screen or page (2050):

• A total amount of renewable energy harvested during a day;

• A report showing hot water usage events or the like;

• The type of renewable energy source connected to the system;

• Current heat action - e.g. a bar graph that fills up as water is heated;

• Current water temperature;

• Heat control settings - for example to enable or disable boost settings;

• Error messages, for example if the system detects that the water heater is overheating, or if there is a fault elsewhere in the system (for example a leak is detected in the water tank (111)); and

• Time and Date.

A settings screen or page (2052):

• AC heating maximum temperature setpoint;

• Solar heating maximum temperature setpoint;

• Water heater minimum temperature;

• AC mains supply time window or timer (a time period adjusted by the user to select when the system is allowed to use AC mains power);

• Heat allowance settings;

• Boost cycle (or boost mode) settings start or stop;

• Cost per kWh, to provide estimates and cost saving calculations or projections;

• Critical time settings, for example to specify when the user needs hot water to be available;

• Water heater capacity, for example the volume of the container (111); and

• Legionnaires Cycle, (Bacterial cleansing cycle) which may be used to periodically heat the water in the container past about 55°C or 60°C to get rid of bacteria. The user may be enabled to adjust the frequency or repetition rate and/or the temperature of such a cleansing or sterilising cycle.

A report screen or page (2054):

• Solar harvesting kWh, for example illustrating the amount of solar energy harvested over a time period;

• Average water heater temperature losses or heat losses, or the magnitude of temperature decrease after each hot water usage event, or the amount of standing heat losses (for example due to bad insulation around the container (111);

• Average heating time for AC mains (or for solar heating);

• Average time on idle (maintaining heat);

• Total DC kWh, daily, weekly, monthly or lifetime; and

• Amount of money saved (e.g. as result of use of the system, and/or by adjusting usage events by using guidance from the system).

A user interface page, screen or infographic (2056):

• Heating power supply in use for AC power (2056.1 ) and for solar power (2056.2), this may for example be graphically presented to the user in a pie-chart or the like;

• Temperature status for water in the container (111), for example currently heating (2056.3), maintaining temperature or idle (2056.4), or temperature dropping (2056.5). These status indicators may be colour-coded, for example red for heating, blue for temperature dropping and yellow or orange for maintaining temperature; and

• Control input (2056.6) may also be provided, to enable the user to adjust setpoints, adjust settings, or make other adjustments to the system.

The firmware implemented on the control circuitry (118) may be arranged to provide one or more of the following features by way of hardware and/or software:

• MPPT (Boost and/or H-bridge and/or PWM); Source control (AC or DC); Time and date (RTC external);

• EEPROM (External); Safety limits; Scheduling (2 x Peak usage - User set-able);

• Limits logging: o Maximum voltage; Maximum temperature; Maximum current; and Maximum heating efficiency;

• Fault logging: o Reverse Polarity; Temperature probe errors; Over threshold temp water heater counts; and Over threshold temp device counts;

• Cumulative Logging o Total PV Power produced; Relay activation counts;

• Status LEDs; Element measurement; Default configured for operation; and Firmware Over-The-Air (FOTA) (Bluetooth Low Energy (BLE)/WIFI/GSM or equivalent technology).

Software that may be implemented by the control circuitry or by the server in communication with the control circuitry may include the following setup or configurable features:

• Geyser Volume; Set Time and date; Set Element Power; Set WiFi Password; PV Installation specifications; Live data; Limits logging; Temperature Set-point (User configurable); and Anti-bacterial cycle (User configurable).

Figures 19 to 27 show exemplary circuit diagrams of components that may be implemented in the system (10, 100) and method (1000) of the present disclosure. Figure 19 is an exemplary circuit diagram of a boost circuit (3138) that may be used. Figure 20 is an exemplary circuit diagram of a buck circuit (3140). An alternative exemplary boost circuit (5138) is shown in Figure 21 , and an alternative exemplary buck circuit (5140) is shown in Figure 22, which may for example be a 5V buck converter circuit.

Figure 23 is an exemplary circuit diagram of a temperature sensor circuit (3004) (that may for example be used to sense temperature of water in the system (10, 100)). The temperature sensor (3004) may for example be arranged to sense temperatures of between -55 °C to 125 °C. Figure 24 is an exemplary circuit diagram of a 12V flyback MOSFET driver (7000) that may be implemented by the system (10, 100) and method of the present disclosure. Figure 25 shows exemplary driver circuits that may be implemented by the present disclosure. The drivers shown in Figure 25 may include a high-side gate driver (7010), as well as a low-side gate driver (7012). These drivers (7000, 7010, 7012) may for example be implemented by the boost circuit (138) and/or by the buck circuit (140) and/or by the control and buck circuit (141). Figure 26 shows an exemplary k-type probe temperature sensor (7014) that may be implemented by the system and method of the present disclosure, for example in the exemplary system (100) shown in Figures 2 and 11-14. It will be appreciated that other types of temperature sensors may be used. The k- type probe temperature sensor (7014) may for example be arranged to co-exist with an existing thermostat in a water heater. In other words, the k-type probe temperature sensor may be inserted into an existing pocket or aperture wherein the thermostat of an existing water heater is located. The existing thermostat may act as a safety backstop. The k-type probe temperature sensor (7014) may be used in addition to, or as an alternative to the temperature sensor (3004) shown in Figure 23. In Figure 27 is shown an exemplary PWM circuit (7016) that may for example be implemented by the boost circuit (140) (instead of the H-bridge (178)). The system (10, 100) may further include one or more of snubber circuits to inhibit voltage spikes or a sudden rise in voltage in components of the system. The one or more snubber circuits may be arranged to protect components of the system from damage and may provide safety against overheating, fire or other damage. In certain circumstances, and in addition to the heatsink(s), an electrical fan or other cooling device may also be provided to cool components of the system (10, 100), in particular to cool the control circuitry (18, 118). Flowchart illustrations and block diagrams of methods, systems, and/or computer program products according to embodiments are used herein. Each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, may provide functions which may be implemented by computer readable program instructions. In some alternative implementations, the functions identified by the blocks may take place in a different order to that shown in the flowchart illustrations. Some portions of this description describe the embodiments of the invention in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations, such as accompanying flow diagrams, are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. The described operations may be embodied in software, firmware, hardware, or any combinations thereof.

The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Finally, throughout the specification and accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.