Hybrid water heater system

Abstract

The system powers a resistive load with switched direct current (DC) power. Rapid switching of the resistive load heats the resistive load with a quasi-DC current. The resistive load can be a water heater element. The water heater can also have another heating element, which allows the quasi-DC signal to preheat the water heater with local solar power, reducing the need for external energy to power the other heating element.

Description

[Technical field]

[0001] (Priority) This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 315,078, filed February 28, 2022.

[0002] FIELD OF THEINVENTION The description relates generally to heating elements, and more specifically to powering direct current (DC) heating elements with a switched DC signal. [Background technology]

[0003] Electric heating elements, particularly the kind used in water heater systems, consist of a resistive element that heats up in response to an electric current passing through the heating element. The need for power to charge the heating element creates an additional load on the power grid.

[0004] In a move to remove loads from the power grid, many consumers are becoming prosumers, producing energy locally using renewable resources. Local energy source systems are typically direct current (DC) sources, such as solar systems. Converting DC power to alternating current (AC) power to heat elements tends to be an inefficient use of energy. The following description includes a description of the figures with figures given as examples of implementations. The drawings should be understood as examples and not as limitations. As used herein, reference to one or more examples should be understood as describing specific features, structures, or characteristics included in at least one implementation of the present invention. Phrases such as "in one example" or "in an alternative example" appearing in this specification provide examples of implementations of the present invention and do not necessarily all refer to the same implementation. However, they are not necessarily mutually exclusive. [Brief description of the drawings]

[0005] [Figure 1]FIG. 1 is a block diagram of an example system for charging a heating element using a switched DC source. [Diagram 2] 13 is a schematic diagram of an example of modifying maximum power point tracking behavior based on impedance changes in the load. [Diagram 3] FIG. 1 is a block diagram of an example hybrid water heating system having a grid electric heating element. [Figure 4] FIG. 1 is a block diagram of an example hybrid water heating system having a gas heating element. [Figure 5A] FIG. 1 is a block diagram of an example controller for a system that charges a heating element with a switched DC source. [Figure 5B] FIG. 1 is a block diagram of an example hybrid water heating system that selects between DC sources. [Figure 6A] 1 is a circuit representation of an example system for switching DC sources. [Figure 6B] 1 is a circuit representation of an example system for switching DC sources. [Figure 7] FIG. 13 is a flow diagram of an example of providing power to a heating element.

[0006] A description of specific details and implementations follows, including a non-limiting description of figures that may show some or all of the examples, as well as other potential implementations. The present invention will now be described in detail with reference to the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] As described herein, the system powers a resistive load with switched direct current (DC) power. Fast switching of the resistive load heats the resistive load with a quasi-DC current. Switching can occur at approximately 10 kHz (kilohertz). Alternatively, the controller can switch the DC power at frequencies greater than 10 kHz, in the range of tens of kilohertz. To the DC system, the fast / high frequency switching appears to be a DC signal, and the system does not react to voltage fluctuations, because voltage drops occur fast enough that they do not significantly change the performance of the load components.

[0008] The resistive load can be a water heater element. The water heater can also have another heating element, which allows a pseudo DC signal to preheat the water heater with local solar power, reducing the need for external energy to power the other heating element. The electric heating element can be powered from a photovoltaic (PV) source or a battery, or from both a PV source and a battery. The additional heating element can be an electric heating element that is charged by grid power. The additional heating element can be a gas heating element.

[0009] In one example, the PV heating element is physically positioned within the water heater vessel such that it is used before additional heating elements. For example, the PV heating element can be positioned near the bottom of the water tank and the other heating elements can be positioned near the top of the tank. Thus, the second heating element can only operate to the extent that the PV heating element does not heat the tank to the desired temperature. In one example, the PV heating element is positioned closer to the thermostat than the other heating elements.

[0010] 1 is a block diagram of an example system for charging a heating element with a switched DC source. System 100 represents an application of a resistive load that changes resistance as temperature changes. The application in system 100 is a water heating element.

[0011] The system 100 includes a water heater 130 with a solar heater 132. In one example, the solar heater 132 represents a resistive element (e.g., an element having a resistance of 1 Ohm (Ω). In one example, the solar heater 132 is constructed from a material that heats up in response to constant fluctuations in electrons rather than direct current. Thus, applying a linear DC signal to the solar heater 132 has little or no heating effect. Conversely, rapidly switching the DC signal can induce constant electronic fluctuations in the material, heating the material. Thus, the solar heater 132 represents a heating element having a material that heats up in response to a high frequency signal rather than a constant voltage signal.

[0012] In one example, the water heater 130 represents a hybrid water heater that has a solar heater 132 and may be electrically heated from a grid connection or heated with a gas heater. In one example, rather than switching a DC signal to an AC signal (e.g., nominal 120V or 240V at 50-60Hz), the DC signal may be a low voltage switched DC signal. A low voltage DC signal refers to a signal that is significantly lower than the 120 / 240V of the grid, such as the 48V of a solar panel array. In contrast to the 50-60Hz frequency of a high voltage signal, a low voltage DC signal (which may alternatively be referred to as a pseudo DC signal) may be switched at approximately 10kHz or higher.

[0013] By using a lower voltage, the solar heater 132 is not subject to the limitations and regulations as signals in the grid voltage. Additionally, rather than converting the energy to AC, the energy can be applied in a quasi-DC manner, resulting in more efficient heating.

[0014] The system 100 shows solar cells 110 representing a parallel solar panel that provides the solar energy used to heat the solar heater 132. The system 100 includes a controller 120 that converts the energy from the solar cells 110 into a switched DC signal to charge the solar heater 132. In one example, the controller 120 can use two transistors in parallel on complementary gates to generate two signals that are switched at high frequency. The controller 120 can generate the two signals without the need for a transformer used in traditional switching power supplies. High speed switching to control the solar output can make the energy dispatchable by controlling how the energy is applied to the circuit that receives it. The two complementary signals can be combined by the controller 120 into a single signal output to power the solar heater 132.

[0015] System 100 represents a switched signal 122 and a complementary switched signal 124 in controller 120. The signals shown in controller 120 do not necessarily imply that power flows through the controller, but it should be understood that the controller shapes the power or energy available in the signals shown. System 100 may include other circuit elements, not specifically shown, that shape the energy signal to heat the water heater. Signal 126 represents the switched and shaped signal that is applied to charge solar heater 132.

[0016] In one example, the controller 120 can vary the switching of the signal based on changes in temperature in the water heater 130. Changes in temperature of the water heater 130 can increase the temperature of the material of the solar heater 132 and change the impedance of the solar heater element. In one example, the controller 120 varies the switching by adjusting the frequency of the switching DC signal, which has the effect of changing the impedance match of the input signal.

[0017] FIG. 102 illustrates a switching sequence that the controller 120 may provide to the solar heater 132. The sequence of signals shows a constant DC voltage (VDC) with different frequencies. As shown below the sequence of signals, the period of signal portion 140 is longer than the period of signal portion 150 and shorter than the period of signal portion 160.

[0018] Consider signal portion 140 showing the period of the switched signal during heating by the heating element. Signal portion 140 includes off times 142 and on times 144 of the switched signal. Consider water being heated as the heating element heats up. As it heats up, its rho (ρ) increases. For simplicity, the description refers to an increase in resistance Ω with increasing temperature. As the resistance / impedance changes, energy transfer becomes less efficient due to impedance mismatch. The controller 120 can change the frequency of the switched signal to improve impedance match with the resistive load.

[0019] In one example, the controller 120 includes table information (not specifically shown) for matching measured temperatures with material resistivity information. The table information can indicate switching frequencies to be used when different temperatures are measured to allow impedance matching with the heating element. In one example, diagram 102 represents a switched current signal generated from a DC current from a DC energy source.

[0020] Thus, consider signal portion 150 to represent a response to an increase in temperature, with an increase in frequency resulting in a better impedance match. Signal portion 150 includes an off time 152 and an on time 154 of the switching signal. Further, consider signal portion 160 to represent a response to a decrease in temperature, with a lower frequency improving the impedance match to the heating element. Signal portion 160 includes an off time 162 and an on time 164 of the switching signal.

[0021] Signal portion 140, signal portion 150, and signal portion 160 are not necessarily drawn to scale. The signal portions show only the primary signal without the complementary signal. It will be understood that the different frequencies available may depend on the system's ability to generate different frequencies as well as the accuracy of the temperature measurement. Switching for impedance matching depends on the material / properties of the resistive load connected to receive the switched signal.

[0022] In one example, a heating system can include a heating element and a controller, which together can be considered a water heating system or a controller / controller system for heating a liquid. The controller 120 is not specifically shown as a power converter circuit that is / includes a switching circuit. Examples are provided below.

[0023] 2 is a schematic diagram of an example of changing maximum power point tracking behavior based on impedance changes in the load. In one example, the controller of the system 100 performs maximum power point tracking (MPPT) to convert energy from the PV source into a switched DC signal.

[0024] Diagram 200 shows two curves, curve 210 and curve 220, plotted as current 202 versus voltage 204. Curve 210 represents a portion of the non-linear voltage-current (VI) characteristic behavior of a solar cell / PV source. A VI characteristic curve may alternatively be referred to as a power characteristic curve or power curve. Curve 220 represents a current x voltage plot of curve 210. It will be understood that diagram 200 is not intended to show the entire VI curve (e.g., the x-axis and y-axis may not start at "0"), but rather, a portion near the "knee" of the power curve where the maximum power point (MPP) is found.

[0025] Diagram 200 shows portions of the curves to highlight the differences described below. It will be understood that diagram 200 is not necessarily to scale and that different PV sources may have different characteristic curves. It will also be understood that the general shape of the curves may be representative of the PV source in general.

[0026] A typical power curve shows the short circuit current (I SC ) to the open circuit voltage (V OC To further illustrate that diagram 200 does not necessarily cover the entirety of curve 210, curve 210 extends from I REF From V REF , which are the respective current and voltage points on the axes shown.

[0027] Diagram 200 shows the V on curve 210 at impedance match 232. PMAX-1 Intersects with I PMAX-1 I PMAX-1 V PMAX-1 2 represents the current of the MPP corresponding to the apex of curve 220. It is observed that the MPP intersects the apex of curve 220. It will be appreciated that the MPP tends to change over time based on changing conditions such as lighting level, panel temperature, panel age, panel cleanliness, and other conditions. As conditions change, the knee of curve 210 changes, causing a corresponding change in curve 220.

[0028] The MPPT algorithm tracks the MPP, which changes as conditions change. However, it will be understood that the MPPT algorithm expects certain conditions to match; that is, the MPPT tracks the MPP assuming a constant impedance is matched. The algorithm tracks the changing conditions of the panel, but if the impedance matched does not match the MPPT algorithm's expectations, the output will not provide the most efficient energy transfer.

[0029] The controller described herein can perform MPPT with adjustments for changes in load impedance. If the resistive load is a heating element, the rho value changes with temperature. In one example, the controller / control circuit described herein provides control over DC signal switching to match the MPP determination with the load impedance. Without adjustments for impedance changes, the MPP is not an MPP. By adjusting the MPPT based on solar characteristics and adjusting distortions to the MPPT curve based on changes to the resistance, the system provides better impedance matching.

[0030] Diagram 200 does not specifically illustrate "distortions" in the MPPT curve. Rather, diagram 200 illustrates impedance match 234, which represents a theoretical location on curve 210 that provides an accurate impedance match with the load. Thus, impedance match 232 may be represented as an ideal impedance match based solely on the conditions and characteristics of the solar panel / solar array, while impedance match 234 represents an ideal impedance match based on the change in the resistance of the load based on the change in temperature of the load.

[0031] Therefore, the I on the curve 210 at the impedance match 234 PMAX-2 and V PMAX-2 The intersection points with are presented to represent the change in MPP based on the load conditions. PMAX-2 V PMAX-2In diagram 200, impedance match 234 does not correspond to the apex of curve 220, but matches the curve adjusted for distortion based on changes in load impedance.

[0032] To view the system as a whole, the impedance matching 234 can be thought of as the MPP of the power curve. The system can include an MPPT unit that tracks the MPP for the power curve adjusted as described above.

[0033] 3 is a block diagram of an example of a hybrid water heating system with a grid electric heating element. System 300 represents a system according to example system 100. System 300 includes a hybrid water heater 320 that can be heated electrically from a grid connection or electrically from solar energy. The solar energy can be low voltage (e.g., 48V or the voltage of a solar panel).

[0034] The hybrid water heater 320 includes a tank with a solar heater 322 that can be placed near the base on the tank or near a thermostat 324. The solar heater 322 represents a resistive load that changes impedance with changes in temperature according to any example herein. The thermostat 324 represents a mechanical or digital thermostat in the tank. A digital thermostat can have improved accuracy and can provide better feedback to the controller to allow for improved impedance matching with the solar heater 322. The temperature of the heating element can be inferred or calculated based on the temperature in the tank.

[0035] Grid heater 326 represents an electric heating element powered by grid power from a grid connection to grid 302. In one example, grid heater 326 is physically located near the top of the hot water tank, such as in the top half, while solar heater 322 can be in the bottom half. In one example, rather than a particular half of the tank, solar heater 322 can be physically located closer to thermostat 324 than grid heater 326.

[0036] System 300 includes controller 310, which may represent a gateway controller that is a controller that manages the input of solar energy from multiple solar cells connected in parallel. Solar 330 represents a solar array that may include multiple solar panels connected in parallel. Controller 310 may include or control a converter circuit that generates switched pseudo-DC power (e.g., low voltage power) to provide to solar heater 322. This power enables solar heater 322 to heat a liquid in hybrid water heater 320. Controller 310 may provide MPPT as described above.

[0037] In one example, the controller 310 can alternatively provide energy from solar 330 to an energy storage device (e.g., a battery). Energy storage device 350, along with local solar 330, represents a local energy storage device at the consumer's facility. For example, when the hybrid hot water heater 320 is at a desired temperature, the solar heater 322 does not require additional solar energy, which the controller 310 can then provide to the energy storage device 350. Later, if the solar 330 does not provide enough energy to charge the solar heater 322, the controller 310 can select the energy storage device 350 as the energy source for charging the heating element.

[0038] In one example, the gateway controller allows the operation of the solar power to be dispatchable or controllable from a remote management. The controller 310 can communicate with a mobile application (app) 370 that can remotely control the operation of the heater, such as controlling the temperature of the hybrid water heater 320. The controller 310 can communicate with a network 360, such as the Internet. The network communication can allow the controller 310 to receive command signals from a management source, such as a grid controller.

[0039] In one example, hybrid water heater 320 is typically an electric water heater that can provide heating from a grid connection, such as a 220V connection, via grid heater 326 based on power from grid 302. Solar heater 322 represents a heating element / heater that generates heat from solar 330 and / or energy storage device 350 and operates at a lower voltage than grid heater 326.

[0040] Thermostat 324 represents a control element within the water heater and provides feedback that the target temperature has been reached and no additional heating is needed. In one example, hybrid water heater 320 first applies energy from solar 330 via solar heater 322 to heat the water heater and turns on grid heater 326 only if the target temperature has not been reached. However, less grid energy is needed to heat the water because the water can be heated by solar energy first. If solar heater 322 does not need to operate while solar 330 is generating solar energy, controller 310 can direct excess solar energy to charge energy storage device 350.

[0041] In one example, the chilled water input line 342 and the hot water output line 344 can be connected to one or more heat pumps to provide additional energy recovery. Heat pump 340 represents such a heat pump on the hot water output line 344. A similar heat pump can be provided on the chilled water input line 342.

[0042] 4 is a block diagram of an example of a hybrid water heating system with a gas heating element. System 400 represents a system according to the example of system 100. System 400 includes a hybrid water heater 420 that can be heated electrically by a gas connection or from solar energy. The solar energy can be low voltage (e.g., 48V or the voltage of a solar panel).

[0043] The hybrid water heater 420 includes a tank with a solar heater 422 that can be placed near the base on the tank or near a thermostat 424. The solar heater 422 represents a resistive load that changes impedance with changes in temperature according to any example herein. The thermostat 424 represents a mechanical or digital thermostat within the tank. A digital thermostat can have improved accuracy and can provide better feedback to the controller to allow for improved impedance matching with the solar heater 422.

[0044] Gas heater 426 represents a gas heating element powered by a gas connection to gas line 402. In one example, gas heater 426 is physically located near the top of the hot water tank, such as in the top half, while solar heater 422 can be in the bottom half. In one example, rather than a particular half of the tank, solar heater 422 can be physically located closer to thermostat 424 than gas heater 426.

[0045] System 400 includes controller 410, which may represent a gateway controller that is a controller that manages the input of solar energy from multiple solar cells connected in parallel. Solar 430 represents a solar array that may include multiple solar panels connected in parallel. Controller 410 may include or control a converter circuit that generates switched pseudo-DC power (e.g., low voltage power) to provide to solar heater 422. This power enables solar heater 422 to heat a liquid in hybrid water heater 420. Controller 410 may provide MPPT as described above.

[0046] In one example, the controller 410 can alternatively provide energy from solar 430 to an energy storage device (e.g., a battery). The energy storage device 450, along with the local solar 430, represents a local energy storage device at the consumer's facility. For example, when the hybrid hot water heater 420 is at a desired temperature, the solar heater 422 does not require additional solar energy, which the controller 410 can then provide to the energy storage device 450. Later, if the solar 430 does not provide enough energy to charge the solar heater 422, the controller 410 can select the energy storage device 450 as the energy source for charging the heating element.

[0047] In one example, the gateway controller allows the operation of the solar power to be dispatchable or controllable from a remote management. The controller 410 can communicate with a mobile application (app) 470 that can remotely control the operation of the heater, such as controlling the temperature of the hybrid water heater 420. The controller 410 can communicate with a network 460, such as the Internet. The network communication can allow the controller 410 to receive command signals from a management source, such as a grid controller.

[0048] In one example, hybrid water heater 420 is a gas water heater, typically heated from a gas source such as natural gas through gas line 402. Gas heater 426 represents a heater that generates heat from a gas source. Solar heater 422 represents a heating element / heater that generates heat from solar 430 and / or energy storage device 450 and operates on low voltage.

[0049] Thermostat 424 represents a control element within the water heater and provides feedback that the target temperature has been reached and no additional heating is needed. In one example, hybrid water heater 420 first applies energy from solar 430 via solar heater 422 to heat the water heater, and turns on gas heater 426 only if the target temperature has not been reached. However, less gas heating is needed to heat the water because the water can be heated by solar energy first. If solar heater 422 does not need to operate while solar 430 is generating solar energy, controller 410 can direct excess solar energy to charge energy storage device 450.

[0050] In one example, the chilled water input line 442 and the hot water output line 444 can be connected to one or more heat pumps to provide additional energy recovery. Heat pump 440 represents such a heat pump on the hot water output line 444. A similar heat pump can be provided on the chilled water input line 442.

[0051] 5A is a block diagram of an example controller for a system that charges a heating element with a switched DC source. Controller 510 represents a controller according to example system 100, example system 300, or example system 400. Controller 510 may include a microcontroller, a logic array, a control board, a processor, or other components.

[0052] The controller 510 includes or controls a power converter circuit that generates and transfers energy from a DC energy source to a resistive load that changes impedance in response to changes in temperature. Converter 520 represents the power converter circuit. Converter 520 includes switching circuitry 522 for switching DC power from the DC energy source to the resistive load. In one example, switching circuitry 522 is controlled by control signals provided by the controller 510. In one example, signals controlling switching circuitry 522 can be considered to be provided by a control circuit separate from the controller 510 and can be part of the converter 520.

[0053] The MPPT 512 represents a maximum power point tracking unit of the controller 510. The operation of the MPPT 512 enables the controller 510 to track the maximum power point based on the state of the PV source as well as based on changes in the impedance of the load due to temperature changes.

[0054] Feedback 514 represents control logic within controller 510 that enables the controller to receive feedback information to monitor changing conditions within the system. For example, and specifically for purposes of what is described herein, feedback 514 can enable controller 510 to receive and respond to temperature changes in a resistive load. In one example, controller 510 receives feedback 514 at least in part by monitoring a thermostat in a water heater. Based on the change in temperature, controller 510 can adjust the switching of switching circuitry 522 to provide a better impedance match between the power generated from the energy source and the resistive load.

[0055] Source selection 516 represents the ability of controller 510 to manage how power is directed within the system. In one example, source selection 516 allows controller 510 to select a solar energy source as the source for powering a resistive heating element or charging an energy storage device. In one example, source selection 516 allows controller 510 to select between a solar energy source and an energy storage source for generating and providing switched DC power to a resistive load.

[0056] 5B is a block diagram of an example hybrid water heating system that selects between DC sources. System 502 represents a system according to example system 100, or example system 300, or example system 400. Alternatively, system 502 represents the control within the system as control circuit 550. Alternatively, control circuit 550 can be referred to as "electronics," which refers to the electronic control components that manage the operation of the system. Control circuit 550 can include a microcontroller, logic array, control board, processor, or other components. In one example, control circuit 550 represents an example of controller 510.

[0057] Solar 530 represents a solar panel or multiple panels in parallel to provide PV energy to system 502. Energy storage device 540 represents an energy storage device that can be charged from energy from solar 530. In one example, control circuitry 550 can include a multiplexer (mux) 552 to select between solar 530 and energy storage device 540.

[0058] Converter 554 represents converter hardware that allows control circuit 550 to convert energy from a selected source to generate a switched DC signal. Converter 554 provides switched DC power to heating element 562 of water heater 560 according to any example herein.

[0059] 6A is a circuit representation of an example system for switching DC sources using a switching device. System 602 represents converter hardware according to any example herein.

[0060] System 602 includes a node receiving an input voltage VIN 612. VIN 612 may be filtered or conditioned with filter 622, which represents a circuit that may filter and shape an input signal. Inductor 632 represents a magnetic energy storage device that controls the input impedance of the signal. Capacitor 642 represents an output energy storage device for charging and holding the output voltage to form a switching output.

[0061] The switch 660 represents any type of switching circuitry that performs high speed switching of DC signals. High speed switching produces high frequency signals having frequencies at least an order of magnitude higher than typical grid AC power signals. In one example, the system 602 provides a switched DC current.

[0062] The controller 652 represents control logic such as provided by a controller device to control the switching of the switch 660. In one example, the controller 652 controls the switching of the switch 660 via a pulse width modulator (PWM) signal. The system 602 provides a switched output signal to a load 672, which may be a resistive load according to any example herein.

[0063] 6A is a circuit representation of an example system for switching DC sources using a switching device. System 604 represents converter hardware according to any example herein.

[0064] System 604 includes a node receiving an input voltage VIN 614. VIN 614 may be filtered or conditioned with filter 624, which represents a circuit that may filter and shape an input signal. Inductor 634 represents a magnetic energy storage device that controls the input impedance of the signal. Capacitor 644 represents an output energy storage device for charging and holding the output voltage to form a switching output.

[0065] Transistor 670 represents any type of transistor or transistor-based driver circuit for performing high speed switching of DC signals. In one example, transistor 670 is a high speed metal oxide semiconductor field effect transistor (MOSFET). In one example, system 604 includes multiple power MOSFETs in parallel to provide higher current capability to system 604. The high speed switching by the transistors produces a high frequency signal having a frequency at least an order of magnitude higher than a typical grid AC power signal. In one example, system 604 provides a switching DC current.

[0066] Controller 654 represents control logic such as provided by a controller device to control the switching of transistor 670. In one example, controller 654 controls the switching of transistor 670 via a pulse width modulator (PWM) signal. PWM 656 represents a PWM generator within controller 654. System 604 provides the switched output signal to a load 674, which may be a resistive load according to any example herein.

[0067] 7 is a flow diagram of an example of powering a heating element. Process 700 represents a process of providing energy to a heating element according to any of the systems described. In one example, the system controller selects 702 a photovoltaic (PV) power source as the energy source for charging the heating element.

[0068] In one example, the controller performs MPPT on the power curve (e.g., VI curve) of the PV power source at 704. In one example, the MPPT tracks the maximum impedance match point of the system even when a resistive load changes impedance with temperature changes. With a frequency selected based on the MPP found by the MPPT, the system can charge the heating element at 706 by switching power from the PV power source at a high frequency.

[0069] The controller may monitor the temperature of the heating element at 708. If no temperature change is detected at the "no" branch of 710, the controller may continue to monitor the temperature at 708. In one example, the temperature change refers to a change detectable by the system. For example, the temperature change may be detected as a threshold step of temperature change.

[0070] If the controller detects a temperature change in the "Yes" branch of 710, in one example, the controller adjusts the switching frequency based on the temperature change to match the impedance to the heating element at 712. The controller can then cause the converter hardware to charge the heating element at the newly selected frequency of the switched DC power at 706. Thus, the controller can change the frequency of the switched DC power based on the detection of a change in the operating environment or operating conditions of the heating element.

[0071] Generally, with reference to the description herein, in one aspect, a controller device includes a resistive load that changes resistance based on temperature and a converter circuit for powering the resistive load from a direct current (DC) source, the converter circuit including a switching circuit for using high speed switching of current from the DC source to generate a pseudo DC current for powering the resistive load.

[0072] According to an example of the controller device, the resistive load includes a material that heats in response to a high frequency signal rather than a constant voltage signal. According to any of the above examples of the controller device, the resistive load includes a water heater element. According to any of the above examples of the controller device, in one example, the converter circuit generates a low voltage pseudo DC signal. According to any of the above examples of the controller device, in one example, the controller device includes a maximum power point tracking (MPPT) system that detects a maximum power point of a voltage-current characteristic curve of a photovoltaic (PV) source, and the converter circuit powers the resistive load with power from the PV source. According to any of the above examples of the controller device, in one example, the converter circuit changes switching based on detection of a temperature change in the resistive load to change an impedance match to the resistive load. According to any of the above examples of the controller device, in one example, the change in switching includes a change in frequency of the switching circuit.

[0073] Generally, with reference to the description herein, in one aspect, a hot water heater system includes a hot water tank, a photovoltaic (PV) source, an electric heating element that changes resistance based on temperature, a maximum power point tracking (MPPT) unit that detects the maximum power point of the PV source, and a control circuit including a switching circuit that uses fast switching of current from a DC power source to generate a pseudo DC current for powering a resistive load.

[0074] According to the example water heater system, the control circuit changes the switching based on detection of a temperature change in the resistive load to change the impedance match to the resistive load. According to any of the above examples of the water heater system, in one example, the change in switching includes a change in frequency of the switching circuit. According to any of the above examples of the water heater system, in one example, the electric heating element comprises a solar heating element and further comprises a second heating element. According to any of the above examples of the water heater system, in one example, the solar heating element is located near a bottom of the water heater tank and the second heating element is located near a top of the water heater tank. According to any of the above examples of the water heater system, in one example, the second heating element comprises an electric grid heating element heated by power from a grid system. According to any of the above examples of the water heater system, in one example, the second heating element comprises a gas heating element. According to any of the above examples of the water heater system, in one example, the water heater system includes a thermostat that monitors the temperature of the water in the water heater tank and provides detection of the temperature change to the control circuit. According to any of the above examples of the water heater system, in one example, the water heater system includes an energy storage device for storing energy from the PV source and a control circuit for alternatively charging the electric heating element from the energy from the energy storage device. According to any of the above examples of the water heater system, in one example, the pseudo DC signal includes a low voltage pseudo DC signal. According to any of the above examples of the water heater system, in one example, the control circuit further includes a maximum power point tracking (MPPT) system for detecting a maximum power point of a voltage-current characteristic curve of the PV source.

[0075] Generally, with reference to the description herein, in one aspect, a method includes charging an electric heating element with power from a photovoltaic (PV) source, including detecting a maximum power point of a voltage-current characteristic curve of a PV source, detecting a temperature change in an operating environment of an electric heating element that changes resistance based on temperature, and adjusting switching of a switching circuit based on the detection of the temperature change to change an impedance match to the electric heating element. According to an example of the method, adjusting the switching includes changing a frequency of the switching circuit.

[0076] The flow diagrams shown herein provide examples of sequences of various process operations. The flow diagrams may depict operations performed by software or firmware routines as well as physical operations. The flow diagrams may depict examples of implementations of states of a finite state machine (FSM) that may be implemented in hardware and / or software. Although shown in a particular sequence or order, unless otherwise specified, the order of operations may be modified. Thus, the illustrated diagrams should be understood as examples only, and processes may be performed in different orders and some operations may be performed in parallel. Furthermore, one or more operations may be omitted. Thus, not all implementations perform all operations.

[0077] To the extent that various operations or functions are described herein, they may be described or defined as software code, instructions, configuration, and / or data. The content may be directly executable (in "object" or "executable" format), source code, or difference code (in "delta" or "patch" code). The software content of what is described herein may be provided via a product on which the content is stored, or via a method of operating a communication interface to transmit data through the communication interface. A machine-readable storage medium may cause a machine to perform the described functions or operations, and includes any mechanism for storing information in a form accessible by a machine (e.g., computing device, electronic system, etc.), such as recordable / non-recordable media (e.g., read-only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.). A communication interface includes any mechanism for interfacing with any of the hardwired, wireless, optical, etc. media to communicate with another device, such as a memory bus interface, a processor bus interface, an Internet connection, a disk controller, etc. The communications interface may be configured by providing configuration parameters and / or sending signals to prepare the communications interface to provide data signals describing the software content. The communications interface may be accessed via one or more commands or signals sent to the communications interface.

[0078] Various components described herein may be means for performing the described operations or functions. Each component described herein includes software, hardware, or a combination thereof. A component may be implemented as a software module, a hardware module, dedicated hardware (e.g., application specific hardware, application specific integrated circuits (ASICs), digital signal processors (DSPs), etc.), an embedded controller, hardwired circuitry, etc.

[0079] In addition to those described herein, various modifications can be made to the disclosed and implementations of the invention without departing from the scope of the invention. Thus, the examples and embodiments herein should be construed in an illustrative and not a limiting sense. The scope of the invention should be determined solely by reference to the claims that follow.

Claims

1. A controller device, a resistive load that changes resistance based on temperature; and a converter circuit for powering the resistive load from a direct current (DC) source, the converter circuit including a switching circuit for using high speed switching of current from the DC source to generate a pseudo DC current for powering the resistive load.

2. The controller device of claim 1 , wherein the resistive load comprises a material that heats up in response to a high frequency signal rather than a constant voltage signal.

3. The controller device of claim 1 , wherein the resistive load comprises a water heater element.

4. The controller device of claim 3 , wherein the converter circuit generates a low voltage pseudo DC signal.

5. a maximum power point tracking (MPPT) system for detecting a maximum power point of a voltage-current characteristic curve of the photovoltaic (PV) source; The controller device of claim 1 , wherein the converter circuit powers the resistive load with power from the PV source.

6. The controller device of claim 1 , wherein the converter circuitry alters switching based on detection of a temperature change in the resistive load to alter an impedance match to the resistive load.

7. The controller apparatus of claim 6 , wherein the change in the switching comprises a change in frequency of the switching circuitry.

8. 1. A water heater system comprising: A water heater tank, a photovoltaic (PV) source; an electric heating element that changes resistance based on temperature; and a control circuit including a maximum power point tracking (MPPT) unit that detects a maximum power point of the PV source, and a switching circuit that uses fast switching of current from the PV source to generate a pseudo DC current for powering the resistive load.

9. 9. The hot water heater system of claim 8, wherein the control circuitry varies switching based on detection of a temperature change in the resistive load to vary an impedance match to the resistive load.

10. The hot water heater system of claim 9 , wherein the change in the switching comprises a change in frequency of the switching circuit.

11. The hot water system of claim 8 , wherein the electric heating element comprises a solar heating element and further comprises a second heating element.

12. 12. The hot water heater system of claim 11, wherein the solar heating element is located near a bottom of the hot water tank and the second heating element is located near a top of the hot water tank.

13. The hot water heater system of claim 11 , wherein the second heating element comprises an electric grid heating element heated by electrical power from a grid system.

14. The water heater system of claim 11 , wherein the second heating element comprises a gas heating element.

15. 9. The hot water heater system of claim 8, further comprising a thermostat that monitors a temperature of water in said hot water tank and provides said detection of said temperature change to said control circuitry.

16. The hot water system of claim 8 , further comprising an energy storage device that stores energy from the PV source, and wherein the control circuit alternatively charges the electric heating element from energy from the energy storage device.

17. The water heater system of claim 8 , wherein the pseudo DC signal comprises a low voltage pseudo DC signal.

18. The control circuit includes: The hot water heater system of claim 8, further comprising a maximum power point tracking (MPPT) system for detecting a maximum power point of a voltage-current characteristic curve of the PV source.

19. 1. A method for heating water, comprising the steps of: Detecting a maximum power point of a voltage-current characteristic curve of a photovoltaic (PV) source; Detecting a change in temperature in an operating environment of an electric heating element that changes resistance based on temperature; charging the electric heating element with power from the PV source, comprising adjusting switching of a switching circuit based on detection of the temperature change to change an impedance match to the electric heating element.

20. 20. The method of claim 19, wherein adjusting the switching comprises changing a frequency of the switching circuit.

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