Frequency-controlled heating element

Abstract

A system powers a heating element with switched direct current (DC) power. The high-speed switching of the heating element triggers lattice excitation in the element alloy, heating up the element. The heating element can be used alone or in combination with additional heating elements. The heating element can be used for water heating (e.g., water heaters, spas / hot tubs, swimming pools), oil heating (e.g., enclosed oil-based heaters), space heating, or other heating applications.

Description

FREQUENCY-CONTROLLED HEATING ELEMENTTECHNICAL FIELD

[0001] Descriptions are generally related to heating systems and batteries, and more particular descriptions are related to heating element structure and operation and battery charging.BACKGROUND OF THE INVENTION

[0002] Electrical heating elements traditionally operate on resistive principles, where current is forced through a resistive element to cause heating. Resistive heating, also referred to as joule heating, where electrical energy is converted into thermal energy. The joule heating formula indicates the heat energy generated (Q) is equal to the power ((IA2)R)*t, or the current squared times the resistance and times time. Joule heating requires significant amounts of power and is not very efficient.BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The following description includes discussion of figures having illustrations given by way of example of an implementation. The drawings should be understood by way of example, and not by way of limitation. As used herein, references to one or more examples are to be understood as describing a particular feature, structure, or characteristic included in at least one implementation of the invention. Phrases such as "in one example" or "in an alternative example" appearing herein provide examples of implementations of the invention, and do not necessarily all refer to the same implementation. However, they are also not necessarily mutually exclusive.

[0004] Figure 1 is a block diagram of an example of a system that charges a heating element with a switched DC source.

[0005] Figure 2 is a diagrammatic representation of an example of changing maximum power point tracking behavior based on a change of impedance in the load.

[0006] Figure 3 is a block diagram of an example of a hybrid water heating system with a grid electrical heating element.

[0007] Figure 4 is a block diagram of an example of a hybrid water heating system with a gas heating element.

[0008] Figure 5A is a block diagram of an example of a controller for a system that charges a heating element with a switched DC source.

[0009] Figure 5B is a block diagram of an example of a heating system that selects between DC sources.

[0010] Figures 6A-6B are circuit representations of examples of a system that switches a DC source.

[0011] Figure 7 is a flow diagram of an example of powering a heating element.

[0012] Figures 8A-8B are representations of examples of phonon lattice vibration.

[0013] Figures 9A-9B are line diagrams of an example of a heating element.

[0014] Figure 9C is a line diagram of an example of a frequency-controlled heating element.

[0015] Figure 10 is a representation of an example of a temperature response of a heating element material.

[0016] Figure 11A is a block diagram of an example of a controller for a system that charges a battery with a switched DC source.

[0017] Figure 11B is a block diagram of an example of a battery charging system.

[0018] Figure 12A-12B are block diagrams of an example of battery charging based on impedance detection.

[0019] Figure 13 is a block diagram of an example of a home heating system.

[0020] Descriptions of certain details and implementations follow, including non-limiting descriptions of the figures, which may depict some or all examples, and well as other potential implementations.DETAILED DESCRIPTION OF THE INVENTION

[0021] As described herein, a system provides low-voltage, low-power heating. The heating element is made of an alloy of iron, aluminum, chromium, and nickel. A control circuit charges the heating element with switched DC (direct current) power. The high-speed switching of the heating element triggers lattice excitation in the element alloy, heating up the element. The heating element can be used alone or in combination with additional heating elements. The heating element can be used for water heating (e.g., water heaters, spas / hot tubs, swimming pools), oil heating (e.g., enclosed oil-based heaters), space heating, or other heating applications.

[0022] The high-speed switching can occur at approximately 10 kHz (kilohertz).Alternatively, the controller can switch the DC power at a frequency greater than 10 kHz, in the range of tens of kilohertz. To a DC system, the high-speed / high-frequency switching appears to be a DC signal, seeing that the system does not react to the fluctuations in voltage since they happen fast enough that the drop in voltage does not significantly alter the performance of the load components.

[0023] While applications are specifically directed to use of the high-speed switching for driving a heating element to generate heat, the high-speed switching described herein can be used for other purposes. In one example, The switching is used to charge a battery.

[0024] In one example, the switching is a DC chop of a current waveform. The system can change the duty cycle of the current waveform based on impedance matching, to maximize power transfer from the DC source to the heating element. The application of the switched current to the metal lattice of the heating element provides phonon excitation of the lattice structure. Thus, the heating effect can be referred to as electron excitation or lattice excitation.

[0025] In one example, the DC chopping can be applied in a battery charging system, directly applying a DC source voltage to battery charging. The powering of the heating element and the battery charging system can apply MPPT (maximum power point tracking). Both systems apply impedance matching, adjusting a duty cycle of the switched signal to match impedance between the source and the load.

[0026] FIG. 1 is a block diagram of an example of a system that charges a heating element with a switched DC source. System 100 represents an application of a heating element that generates heat based on lattice excitation. The application in system 100 is a water heating element.

[0027] System 100 includes water heater 130 with solar heater 132. System 100 illustrates solar cells 110, which represent parallel solar panels that provide solar energy used to heat solar heater 132. System 100 includes controller 120 to convert the energy from solar cells 110 to a switched DC signal to charge solar heater 132.

[0028] In one example, solar heater 132 represents a heating element (e.g., an element having a 1 ohm (O) resistance). Solar heater 132 is a low impedance, low power heating element. In one example, solar heater 132 has a maximum of approximately 1.3 ohms of resistance, and can be designed to ideally have 1.0 ohms at a DC control current. In oneexample, the resistance is slightly less than 1.0 ohms, where the resistance increases to 1.0 ohms as the material is heated.

[0029] In one example, solar heater 132 is made up of a material that heats up in response to a constant fluctuation of electrons. It will be understood that a metal will heat up in response to a direct current. However, solar heater 132 does not use joule heating as its primary heating operation.

[0030] With joule heating, also referred to as resistive heating, solar heater 132 would produce heat proportional to the current and the resistance. Instead of simply providing joule heating, solar heater 132 has a structure that responds to high speed switching of the DC input power. More specifically, controller 120 generates a switched current signal, where the voltage can be equal to the voltage of output of solar cells 110.

[0031] In one example, controller 120 can use two transistors in parallel on complementary gates to generate two signals switched at high frequency. Controller 120 can generate the two signals without the need for transformers used in traditional switched power sources. The high speed switching to control the solar output can allow the energy to be dispatchable by controlling how the energy is applied to the circuit that receives it. The two complementary signals can be combined into a single signal output by controller 120 to power solar heater 132.

[0032] In one example, the high speed switching is accomplished with a DC chopper circuit, modulating a DC current signal with a PWM (pulse width modulator) circuit. System 100 represents switched signal 122 and complementary switched signal 124 in controller 120. It will be understood that the signals shown in controller 120 do not necessarily mean that the power flows through the controller, but that the controller shapes the power or energy available in the illustrated signals.

[0033] System 100 can include other circuit elements not specifically illustrated, which will shape the energy signals to heat the water heater. Signal 126 represents the switched and shaped signal applied to charge solar heater 132. In one example, signal 126 is a single ended switched signal as opposed to the complementary signal illustrated.

[0034] In one example, controller 120 can change the duty cycle of the switching of the current signal based on monitoring and detecting a change in impedance matching between solar cells 110 and solar heater 132. In one example, system 100 also includes temperaturecontrols, and can turn off the heating element in response to an over temperature condition of the water, a temperature condition of controller 120, or a combination.

[0035] In one example, water heater 130 represents a hybrid water heater that has solar heater 132 and can also be heated either electrically from a grid connection or heated with a gas heater. In one example, rather than switching the DC signal into an AC signal (e.g., nominally 120 V or 240 V at 50-60 Hz), the DC signal can be a low-voltage switched DC signal. The low-voltage DC signal refers to a signal that is significantly lower than the 120 / 240 V of the grid, such as the 48 V of a solar panel array. In contrast to the 50-60 Hz frequency of the high-voltage signal, the low-voltage DC signal (which could alternatively be referred to as a pseudo-DC signal) can be switched at approximately 10 kHz or higher.

[0036] In one example, controller 120 generates output signal 126 in a range of 30-48 V. It will be understood that the current of signal 126 will be relatively high, potentially dozens of amps, as solar cells 110 can generate hundreds of watts of power. By using a lower voltage, solar heater 132 would not be subject to the restrictions and regulations as the signals at grid voltage. Additionally, rather than converting the energy into AC, the energy can be applied in a pseudo-DC manner, resulting in higher efficiency heating.

[0037] Diagram 102 represents a sequence of switching that controller 120 can provide to solar heater 132. Diagram 102 illustrates operation 142, which is heating up solar heater 132 when there is a mid-level solar irradiance on solar cells 110. The sequence of signals illustrates a DC current signal that is chopped at a selected duty cycle for impedance matching, resulting in a chopped DC current signal. As illustrated under the sequence of signals, the period of operation 142 illustrates a signal portion that represents the switching frequency (e.g., 10 kHz) at a 50% duty cycle, for a mid-level solar irradiance condition.

[0038] Instead of using table-based MPPT (maximum power point tracking) for maximum power transfer, system 100 can monitor the impedance matching through feedback. By monitoring current and voltage, if there is a change in voltage of signal 126, controller 120 can adjust the duty cycle to adjust the impedance matching. More specifically, to match the impedance of solar heater 132, controller can operate to maintain desired ratio of voltage and current. Thus, a drop in voltage can indicate that controller should adjust the duty cycle lower to reduce the amount of current.

[0039] It will be understood that maximum power is transferred when all power available from solar cells 110 is transferred to the heating element. If the power transfercircuitry does not regulate the input voltage, the maximum power can be transferred at the input voltage. The output current can be adjusted based on adjusting the duty cycle of the current signal. Thus, the current perceived at the output, and received at solar heater 132, will be the weighted average of the switched current signal. By controlling the current signal, system 100 operates in current mode rather than in voltage mode.

[0040] Diagram 102 illustrates operation 144, which is heating up solar heater 132 when there is a high-level solar irradiance on solar cells 110. The high-level solar irradiance can approach the highest output of the solar cells, for example, in the range of 1300 W / mA2, or whatever is supported by the solar cells. As illustrated underthe sequence of signals, the period of operation 144 illustrates a signal portion that represents the switching frequency at an 87.5% duty cycle, for a high-level solar irradiance condition. In one example, the duty cycle can be as high as 98% for maximum solar irradiance.

[0041] Diagram 102 illustrates operation 146, which is heating up solar heater 132 when there is a low-level solar irradiance on solar cells 110. The low-level solar irradiance can approach the lowest output of the solar cells, for example, in the range of 200 W / mA2, or whatever is supported by the solar cells. As illustrated underthe sequence of signals, the period of operation 146 illustrates a signal portion that represents the switching frequency at a 12.5% duty cycle, for a low-level solar irradiance condition. In one example, the duty cycle can be as low as 2% for minimum solar irradiance.

[0042] In one example, heating system can include the heating element and the controller, which can together be considered a water heating system or a controller / controller system to heat liquid. Controller 120 does not specifically illustrate the power converter circuit that is / includes the switching circuit. Examples are provided below.

[0043] As indicated in diagram 102, the output of controller can be a high frequency chopped current signal or chopped DC signal with varying duty cycle. The controller can vary the duty cycle in response to detected conditions, such as the detected impedance change of the load. Thus, in one example, the output signal has a controllable duty cycle based on monitoring impedance, based on detection of a change in impedance. In one example, solar heater 132 is 1 ohm, providing very low resistance. The voltage output of the solar panels can be on the order of 35 V or 40 V. With low voltage and 1 ohm impedance, it will be understood that the current input to the heating element will be relatively high.

[0044] Consider a system having solar cells 110 that generate an output at 36 VDC, and up to 1200 W. With 1.0 ohms of resistance, the current will necessarily flow at over 30 amps, since P=VI, where V=IR, and thus, P=(IA2)*R, meaning the current is l=sqrt(P / R)=sqrt(P) when R=l. In one example, system 100 operates in a range of approximately 36 A at 36 V at full solar irradiance.

[0045] In diagram 102, VDC can represent a peak DC output voltage. The output voltage should be fairly consistent from one period to the next. However, the voltage can drift in response to varying energy output of the solar cells. The voltage can also shift in response to varying impedance of the heating element, for example, as the heating element changes temperature.

[0046] It will be understood that the current described can refer to an average current over time, averaging many periods of output. Thus, changing the duty cycle will change the output current by changing the average output current. The current is highest at the highest duty cycle and lowest at the lowest duty cycle. In one example, impedance matching to the heating element refers to maintaining a desired ratio between the peak output voltage and the average current. Maintaining the desired ratio can refer to maintaining a constant ratio or adjusting the operation to substantially maintain the constant ratio.

[0047] FIG. 2 is a diagrammatic representation of an example of changing maximum power point tracking behavior based on a change of impedance in the load. In one example, the controller of system 100 performs MPPT (maximum power point tracking) to convert the energy from the PV source to the switched DC signal.

[0048] Diagram 200 illustrates 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 (V- I) characteristic behavior of a solar cell / PV source. The V-l characteristic curve can alternatively be referred to as the power characteristic curve or power curve. Curve 220 represents a plot of the current times the voltage of curve 210. It will be understood that diagram 200 is not intended to show the entire V-l 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 MPP (maximum power point) is found.

[0049] Diagram 200 illustrates a portion of the curves to highlight the differences discussed below. It will be understood that diagram 200 is not necessarily to scale, and different PV sources can have different characteristic curves. It will also be understood thatthe general shape of the curves can be generally representative of PV (photovoltaic) sources.

[0050] Typical power curves extend from the short circuit current (Isc) on the y-axis to the open circuit voltage (Voc) on the x-axis. To further illustrate that diagram 200 illustrates does not necessarily cover the entirety of curve 210, curve 210 extends from IREF to V EF, which are respective current and voltage points at the axes illustrated.

[0051] Diagram 200 illustrates IRMAX-I, which intersects with VR AX-I on curve 210 at impedance match 232. IRMAX-I represents a current for the MPP, which corresponds to VR AX- i. It will be observed that MPP intersects the apex of curve 220. It will be understood that the MPP tends to change over time based on changing conditions, such as illumination level, panel temperature, panel age, cleanliness of the panel, and other conditions. As the conditions change, the knee of curve 210 will change, and the corresponding curve 220 will change.

[0052] MPPT algorithms track the MPP as it changes with changing conditions. However, it will be understood that MPPT algorithms expect to match a particular condition. Namely, MPPT tracks the MPP assuming a constant impedance to be matched. While the algorithms track for changes in the conditions of the panels, the output will not result in the highest efficiency energy transfer when the impedance to be matched does not match the expectations of the MPPT algorithm. Furthermore, MPPT algorithms traditionally operate on "tables" of information due to the assumptions being made, and finding a measured value and setting a value from the table based on it.

[0053] The controllers described herein can perform MPPT with adjustment for a change to the impedance matching, whetherthe solar cells output different power amounts or the impedance of the heating element changes in different conditions.

[0054] Diagram 200 illustrates impedance match 234, which represents a theoretical place on curve 210 that provides accurate impedance matching with the load. Thus, while impedance match 232 can represent impedance match 232 as an ideal impedance match based solely on the conditions and characteristics of the solar panel / solar array, impedance match 234 represents the ideal impedance match based on a change to resistance of the load based on changes in system operation.

[0055] Thus, the intersection of IRMAX-2 with VRMAX-2 on curve 210 at impedance match 234 is presented to represent a change to the MPP based on the load conditions. I RMAX-2represents a current for the preferred impedance match point, which corresponds to VRMAX- 2. In diagram 200, impedance match 234 would not correspond with the apex of curve 220, but would match up with a curve that is adjusted for the distortion based on the change in load impedance.

[0056] For purposes of a total system view, impedance match 234 can be considered the MPP for the power curve. The system can include an MPPT unit that tracks the MPP for the adjusted power curve as described above.

[0057] FIG. 3 is a block diagram of an example of a hybrid water heating system with a grid electrical heating element. System 300 represents a system in accordance with an example of system 100. System 300 includes 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., 48 V or the voltage of solar panels).

[0058] Hybrid water heater 320 includes a tank with solar heater 322 that can be located near a base on the tank or near thermostat 324. Solar heater 322 represents a heating element that operates on lattice excitation in accordance with any example herein. Thermostat 324 represents a thermostat, whether mechanical or digital, within the tank. A digital thermostat can have improved accuracy and provide better feedback to the controller to enable improved impedance matching with solar heater 322. Based on the temperature inside the tank, the temperature of the heating element can be inferred or calculated.

[0059] Grid heater 326 represents an electrical heating element to be powered by grid power, from a grid connection to grid 302. In one example, grid heater 326 is physically located near a top of the water heater tank, such as in the top half, where solar heater 322 can be in the bottom half. In one example, rather than specific halves of the tank, solar heater 322 can be located physically closer to thermostat 324 than grid heater 326.

[0060] System 300 includes controller 310, which can represent a gateway controller, which is a controller that manages the input of solar energy from multiple solar cells connected in parallel. Solar 330 represents a solar array, which can include multiple solar panels connected in parallel. Controller 310 can include or can control a converter circuit that generates switched pseudo-DC power (e.g., low voltage power) to provide to solar heater 322. With the power, solar heater 322 can heat up the liquid in hybrid water heater 320. Controller 310 can provide MPPT as described above.

[0061] In one example, controller 310 can alternatively provide the energy from solar 330 to an energy storage device (e.g., a battery). Energy storage 350 represents local energy storage at a consumer premises along with the local solar 330. For example, when hybrid water heater 320 is at a desired temperature, solar heater 322 would not need additional solar energy, which controller 310 can then provide to energy storage 350. At a later time, when solar 330 does not provide sufficient energy to charge solar heater 322, controller 310 can select energy storage 350 as the energy source to charge the heating element.

[0062] In one example, the gateway controller enables the operation of the solar power to be dispatchable or controllable from a remote management. Controller 310 can be in communication with mobile application (app) 370, which can control the operation of the heater remotely, such as controlling the temperature of hybrid water heater 320. Controller 310 can be in communication with network 360, such as the Internet. Network communication can enable controller 310 to receive command signals from a management source, such as a grid controller.

[0063] In one example, hybrid water heater 320 is an electric water heater, which can normally be heated from a grid connection, such as a 220 V connection through grid heater 326 based on power from grid 302. Solar heater 322 represents a heating element / heater that generates heating from solar 330 and / or energy storage 350, and operates at a lower voltage than grid heater 326.

[0064] Thermostat 324 represents a control element in the water heater, which provides feedback that additional heating is not required because a target temperature has been reached. In one example, hybrid water heater 320 first applies energy from solar 330, through solar heater 322 to heat the water heater, and only turns on grid heater 326 if a target temperature has not been reached. However, since the water can first be heated by the solar energy, less grid energy is needed to heat the water. If solar heater 322 does not need to operate while solar 330 is generating solar energy, controller 310 can direct the excess solar energy to charge energy storage 350.

[0065] In one example, cold water input line 342 and 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 hot water output line 344. A similar heat pump can be provided on cold water input line 342.

[0066] FIG. 4 is a block diagram of an example of a hybrid water heating system with a gas heating element. System 400 represents a system in accordance with an example of system 100. System 400 includes hybrid water heater 420 that can be heated by a gas connection or electrically from solar energy. The solar energy can be low voltage (e.g., 48 V or the voltage of solar panels).

[0067] Hybrid water heater 420 includes a tank with solar heater 422 that can be located near a base on the tank or near thermostat 424. Solar heater 422 represents a heating element that operates on lattice excitation in accordance with any example herein. Thermostat 424 represents a thermostat, whether mechanical or digital, within the tank. A digital thermostat can have improved accuracy and provide better feedback to the controller to enable improved impedance matching with solar heater 422.

[0068] Gas heater 426 represents a gas heating element to be powered by a gas connection to gas line 402. In one example, gas heater 426 is physically located near a top of the water heater tank, such as in the top half, where solar heater 422 can be in the bottom half. In one example, rather than specific halves of the tank, solar heater 422 can be located physically closer to thermostat 424 than gas heater 426.

[0069] System 400 includes controller 410, which can represent a gateway controller, which is a controller that manages the input of solar energy from multiple solar cells connected in parallel. Solar 430 represents a solar array, which can include multiple solar panels connected in parallel. Controller 410 can include or can control a converter circuit that generates switched pseudo-DC power (e.g., low voltage power) to provide to solar heater 422. With the power, solar heater 422 can heat up the liquid in hybrid water heater 420. Controller 410 can provide MPPT as described above.

[0070] In one example, controller 410 can alternatively provide the energy from solar 430 to an energy storage device (e.g., a battery). Energy storage 450 represents local energy storage at a consumer premises along with the local solar 430. For example, when hybrid water heater 420 is at a desired temperature, solar heater 422 would not need additional solar energy, which controller 410 can then provide to energy storage 450. At a later time, when solar 430 does not provide sufficient energy to charge solar heater 422, controller 410 can select energy storage 450 as the energy source to charge the heating element.

[0071] In one example, the gateway controller enables the operation of the solar power to be dispatchable or controllable from a remote management. Controller410 can be incommunication with mobile application (app) 470, which can control the operation of the heater remotely, such as controlling the temperature of hybrid water heater 420. Controller 410 can be in communication with network 460, such as the Internet. Network communication can enable controller 410 to receive command signals from a management source, such as a grid controller.

[0072] In one example, hybrid water heater 420 is a gas water heater, which can normally be heated from a gas source, such as natural gas through gas line 402. Gas heater 426 represents a heater that generates heating from a gas source. Solar heater 422 represents a heating element / heater that generates heating from solar 430 and / or energy storage 450, and operates at a low voltage.

[0073] Thermostat 424 represents a control element in the water heater, which provides feedback that additional heating is not required because a target temperature has been reached. In one example, hybrid water heater 420 first applies energy from solar 430, through solar heater 422 to heat the water heater, and only turns on gas heater 426 if a target temperature has not been reached. However, since the water can first be heated by the solar energy, less gas heating is needed to heat the water. If solar heater 422 does not need to operate while solar 430 is generating solar energy, controller 410 can direct the excess solar energy to charge energy storage 450.

[0074] In one example, cold water input line 442 and 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 hot water output line 444. A similar heat pump can be provided on cold water input line 442.

[0075] FIG. 5A is a block diagram of an example of a controller for a system that charges a heating element with a switched DC source. Controller 510 represents a controller apparatus in accordance with a controller of an example of system 100, or an example of system 300, or an example of system 400. Controller 510 can include a microcontroller, logic array, a control board, processor, or other component.

[0076] Controller 510 either includes or controls a power converter circuit that generates and transfers the energy from a DC energy source to a heating element in accordance with any example herein. Converter 520 represents the power converter circuit. Converter 520 includes switching circuit 522 to switch DC power (more specifically, the current signal of the power) from the DC energy source to the heating element. In oneexample, switching circuit 522 is controlled by control signals provided by controller 510. In one example, the signals that control switching circuit 522 can be considered to be provided by control circuitry separate from controller 510, and can be part of converter 520.

[0077] MPPT 512 represents a maximum power point tracking unit of controller 510. The operation of MPPT 512 enables controller 510 to track the maximum power point based on conditions of the PV source as well as based on changing impedance of the load due to temperature changes.

[0078] Feedback 514 represents control logic in controller 510 to enable the controller to receive feedback information to monitor changing conditions in the system. For example, and specifically for purposes of what is described herein, feedback 514 can enable controller 510 to receive and respond to changes in power received at the heating element, which changes the impedance matching. In response to changes in conditions that affect impedance matching, controller 510 can adjust the switching of switching circuit 522 to change the duty cycle, providing better impedance matching between the power generated from the energy source and the heating element.

[0079] Source selection 516 represents an ability for controller 510 to manage how power is directed in the system. In one example, source selection 516 enables controller 510 to select a solar energy source as the source to power either a heating element or to charge an energy storage device. In one example, source selection 516 enables controller 510 to select between a solar energy source and an energy storage source to produce switched DC power to provide to the heating element.

[0080] It will be understood that controller 510 does not include an inverter, nor does the controller operate with an inverter. Rather, the system can simply provide high speed switching of the current to heat up the heating element, while maintaining a low voltage. In one example, the solar heating element and the controller are not connected to the power grid. Rather, the system simply includes solar cells that are connected to the heating element, without connecting the heating element to the grid, or passing through any circuitry that connects power from the solar cells to the grid.

[0081] In one example, the solar heating element and the controller are connected to the power grid. By being connected to the grid, the operation of the solar heating unit can be dispatchable, responding to control signals sent out by the utility that operates the power grid. Having a dispatchable operation enables system to have visibility into gridconditions, allowing controller 510 to adjust operation of the solar heater based on grid conditions.

[0082] FIG. 5B is a block diagram of an example of a hybrid water heating system that selects between DC sources. System 502 represents a system in accordance with an example of system 100, or an example of system 300, or an example of system 400. System 502 alternatively represents the control in the system as control circuit 550. Alternatively, control circuit 550 can be referred to as "the electronics," referring to the electronic control components that manage the operation of the system. Control circuit 550 can include a microcontroller, logic array, a control board, processor, or other component. In one example, control circuit 550 represents an example of controller 510.

[0083] Solar 530 represents a solar panel or multiple panels in parallel to provide PV energy for system 502. Energy storage 540 represents an energy storage device that can be charged up from energy from solar 530. In one example, control circuit 550 can include multiplexer (mux) 552 to select between solar 530 and energy storage 540.

[0084] Converter 554 represents converter hardware that enables control circuit 550 to convert energy from the selected source to generate a switch DC signal. Converter 554 provides the switched DC power to heating element 562 of heating system 560 in accordance with any example herein.

[0085] Heating system 560 represents any type of heating system that utilizes heating elements in accordance with any example herein. In one example, heating element 562 represents a single heating element for a single device, such as a single heating element with a single water heater tank. In one example, multiple heating elements can be deployed per device, such as multiple heating elements 562 per water heater tank.

[0086] FIG. 6A is a circuit representation of an example of a system that switches a DC source. System 602 can represent converter hardware to power a heating element in accordance with any example herein. System 602 can represent converter hardware to charge a battery in accordance with any example herein.

[0087] System 602 includes a node to receive input voltage, VIN 612. VIN 612 can be filtered or conditioned with filter 622, which represents circuitry that can filter and shape the input signal. Inductor 632 represents a magnetic energy storage device that controls the input impedance of the signal. Capacitor 642 represents output energy storage to charge and hold the output voltage to form the switched output.

[0088] Switch 660 represents any type of switching circuitry to perform high-speed switching of the DC signal. The high-speed switching generates a high frequency signal with a frequency at least an order of magnitude higher than a typical grid AC power signal. In one example, system 602 provides a switched DC current.

[0089] Controller 652 represents control logic, such as provided by a controller device, to control the switching of switch 660. In one example, controller 652 controls the switching of switch 660 through a pulse width modulator signal. System 602 provides the switched output signal to load 672, which can be a heating element or battery in accordance with any example herein.

[0090] FIG. 6B is a circuit representation of an example of a system that switches a DC source. System 604 can represent converter hardware to power a heating element in accordance with any example herein. System 604 can represent converter hardware to charge a battery in accordance with any example herein.

[0091] System 604 includes a node to receive input voltage, VIN 614. VIN 614 can be filtered or conditioned with filter 624, which represents circuitry that can filter and shape the input signal. Inductor 634 represents a magnetic energy storage device that controls the input impedance of the signal. Capacitor 644 represents output energy storage to charge and hold the output voltage to form the switched output.

[0092] Transistor 670 represents any type of transistor or transistor-based driver circuitry to perform high-speed switching of the DC signal. In one example, transistor 670 is a high power MOSFET (metal-oxide-semiconductor field effect transistor). In one example, system 604 includes multiple power MOSFETs in parallel to provide higher current capability to system 604. The high-speed switching with the transistors generates a high frequency signal with a frequency at least an order of magnitude higher than a typical grid AC power signal. In one example, system 604 provides a switched DC current.

[0093] 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 through a pulse width modulator signal. PWM 656 represents a PWM generator in controller 654. In one example, controller 654 includes circuitry to control the PWM generator to drive the switch circuit. System 604 provides the switched output signal to load 674, which can be a heating element or battery in accordance with any example herein.

[0094] FIG. 7 is a flow diagram of an example of powering a heating element. Process 700 represents a process to provide energy to a heating element in accordance with any system described. In one example, the system controller selects a PV power source as the source for energy to charge the heating element, at 702.

[0095] In one example, the controller performs MPPT to determine the maximum power for the PV power source, at 704. By knowing the maximum power, the system can monitor and adjust the impedance matching through switching the output current. In one example, the MPPT tracks the maximum impedance matching point of the system, even when the resistive load changes forthe heating element, and even in changing light conditions for the PV power source. With a frequency selected based on the MPP found by MPPT, the system can charge the heating element by switching power from the PV power source at a high frequency, at 706.

[0096] The controller can monitor the impedance matching between the PV power source and the heating element with a feedback loop, at 708. If the impedance match is good, at 710 YES branch, the controller can continue to monitor the impedance matching, at 708.

[0097] If the controller detects a degradation of the impedance matching, at 710 NO branch, in one example, the controller adjusts a duty cycle of the output current to match impedance between the solar source and the heating element, at 712. The controller can then cause the converter hardware to charge the heating element with the newly selected duty cycle, at 706.

[0098] FIG. 8A is a representation of an example of phonon lattice vibration in two dimensions. Lattice 802 represents a metallic lattice for a heating element in accordance with any example herein. The different atoms are not specifically identified in the lattice structure, but the metal alloy is an Fe-Cr-AI-Ni alloy (an alloy of iron, chromium, aluminum, and nickel). Thus, a heating element can be a metal coil composed of an alloy of iron, chromium, aluminum, and nickel.

[0099] It will be understood that a metal alloy has atoms of different metal types held in a structure with metallic bonds. Such a solid consists of closely packed atoms. In metals, the electrons of the outermost electron shell of the metal atoms do not stay local to their originating atom. Rather, the electrons of the outermost shell are nonlocalized, overlapping with neighboring atoms, allowing the electrons to move freely throughout the metal crystal.

[0100] The circles represent positions of the alloy atoms. The lighter color circles represent lattice positions 812, which are the lattice positions of the atoms when the metal is at rest, in a non-excited state. The darker circles represent displaced positions 814, which are the lattice positions at an instant in time when a phonon has excited the lattice structure.

[0101] It will be observed that the phonon excites the atoms as a wavefunction propagating through the lattice structure, displacing atoms in accordance with the wave energy of the phonon. Thus, at any given instant, some atoms will be displaced farther than others. Displacement overlap 824 illustrates an atom in lattice 802 that in a moment in the phonon wave will occupy the same position it would be in if the lattice were undisturbed. Phonon displacement 822 illustrates the distance between a position a different atom would occupy in the undisturbed lattice compared to the position it occupies in the moment of phonon propagation through lattice 802 that is illustrated. A short time difference (At) later, the displacement of the atoms will have changed as the phonon propagates through the lattice.

[0102] In lattice 802, the distance 810 can represent the wavelength (X) of the phonon. It will be understood that different atomic structures will respond differently to different phonon wavelengths. The lattice of the alloy described can have a different resonant frequency compared to other metallic structures. Application of a phonon in a band of frequencies close to the lattice resonant frequency can improve the transfer of energy through phonon excitation.

[0103] The structure of the alloy enables the conversion of solar energy into heat energy through phonon excitation of the lattice structure. Instead of joule heating, the control circuit powers the heating element with a high frequency signal to cause the lattice structure to "ring". Experimentation with the alloy described and the controller described has demonstrated to the inventors that the structure resonates with phonon excitation when powered from the PV source.

[0104] Experimentation has also demonstrated to the inventors that the heating of the water occurs with increases in efficiency as compared to joule heating under similar conditions. Applying the switched power to a 1 ohm heating element (made of Fe-Cr-AI) in a baseline the same configuration described yielded a baseline energy transfer to water heating. However, applying the switched power to a 1 ohm heating element in accordancewith what is described herein, with an Fe-Cr-AI-Ni alloy structure, yielded energy transfer up to 30% more efficiently than the use of traditional joule heating, higher than the baseline energy transfer with the other material.

[0105] The inventors have concluded that heating through phonon excitation of the lattice can provide more efficient heating than joule heating. The inventors have observed that the efficiency of the phonon excitation appears to be at its peak when the solar irradiance on the solar panels is low. It is suspected that the heating capacity of the element does not increase with the increased current from the solar panels because the increase in the current injects more energy into the lattice. The increase in energy may create a hot- phonon bottleneck, where the lattice is not able to fully relax to its default structure between phonon wave maxima. Thus, the increase in current may dampen the oscillation of the lattice structure, limiting the ability to convert additional energy to heat.

[0106] At the same time, it is believed based on experimentation that the structure of the alloy with the introduction of the nickel improves the alloy's ability to convert solar energy into heat energy. Analysis of the outermost electron shells of the component metals reveals the following:

[0107] Fe has a structure of [Ar] 4s2 3d6, with a full 4s orbital, and one more electron in the 3d orbital than the relatively stable 3d5 state (all five d orbitals have a single electron), which is one electron more than the nearest stable state;

[0108] Cr has a structure of [Ar] 4sl 3d5, with a single electron in the 4s orbital, in favor of the relatively stable 3d5 state, which is one electron more than the nearest stable state; however, such a structure has the effect of reducing the conductivity of the 4s electron due to interference from the 3d orbitals;

[0109] Al has a structure of [Ne] 3s2 3pl, with a full 3s orbital, and one electron in the outer 3p orbital, which is one electron shy of the nearest stable state.

[0110] It is thus assumed that Fe-Cr-AI (known as KANTHAL) has Fe with +1, Cr with +1, and Al with -1, for an alloy that generally has a +1 electron carrier outer shell.

[0111] Ni has a structure of [Ar] 4s2 3d8, with a full 4s orbital, and two electrons missing from a stable 3d orbital (all five d orbitals having two electrons), which is two electrons low from the nearest stable state. Thus, it is assumed that Ni has a -2 electron carrier outer shell. The inventors thus believe that adding nickel to the alloy to make Fe-Cr-AI-Ni results in a metal which is hole dominant, with one electron shy in the outer shell, thus being a -1electron carrier outer shell. For this reason, the inventors suspect that structure receives electrons well while still being very susceptible to phonon vibration propagation through the structure.

[0112] It will be understood that if the inventors' analysis is incorrect, the alloy composition driven by the switched frequency current signal still performs as has been observed and indicated herein. More specifically, experimentation has shown that the heating element described is capable of melting table salt from the energy provided by a solar panel. The heating element can melt the table salt even without full-irradiance conditions, although it will take longer than when there is full sunlight on the solar panels.

[0113] FIG. 8B is a representation of an example of phonon lattice vibration in three dimensions. Lattice 804 represents an example of a lattice in accordance with lattice 802. Distance 830 represents a phonon wavelength in accordance with distance 810 of lattice 802. In addition to the two-dimensional displacement identified for lattice 802, it will be understood that the phonon wave can propagate through the alloy between layers of atoms, as illustrated by phonon displacement 832.

[0114] FIG. 9A is a line diagram of an example of a heating element. Heating element 902 illustrates a heating element in accordance with any example herein. The view illustrated is a "packaged" view of the heating element. Heating element 902 is a frequency- controlled heating element.

[0115] In one example, heating element 902 has interface 910 with threading 920, which can allow the heating element to be screwed into a heating element socket of a water heater. For applications outside of a water heater, interface 910 can be designed to interface with the specific application.

[0116] Heating element 902 includes rod 930, which represents an outer cover for the heating element, with the Fe-Cr-AI-Ni material encased inside rod 930. In one example, rod 930 is a simple steel casing. Other materials can be used that have good heat transfer properties. Any number of materials can work for rod 930, but steel has sufficient properties while being relatively inexpensive.

[0117] Lead 1 and Lead 2 carry the power and ground connections through the control circuit board and to the solar power source. The leads connect between the heating element in rod 930.

[0118] FIG. 9B is a circuit representation of an example of the heating element of FIG. 9A. Heating element 904 is illustrated as a cutaway view, seeing inside interface 910 and inside rod 930. In the cutaway view, the coiled wire is represented by the coil shapes making up element 932.

[0119] Element 932 can be referred to as the excitation element, being the Fe-Cr-AI-Ni alloy material. The gauge and length of element 932 can be controlled to make the length of wire from Lead 1 to Lead 2 to be as close as possible to 1.0 ohms. The resistivity of the material is controlled, and does not change significantly for the range of temperatures of the intended use of the element.

[0120] Since the heating element is designed to be as close as possible to 1.0 ohms over the operating temperature of the device, changes in current will not significantly change the resistivity. Thus, heating element 904 is controlled by frequency rather than current.Similarly, changes in voltage will not significantly change the resistivity. Thus, heating element 904 is controlled by frequency rather than voltage. The heating element can be controlled by the switching frequency rather than current or voltage.

[0121] In one example, element 932 is made of solid 6 gauge, 8 gauge, 10 gauge, or 12 gauge wire wound into the classic heating element coil shape. In one example, the coil of element 932 is relatively loose, as a tighter coil would increase the inductance of the heating element, which can increase the impedance of the high frequency current delivered through the leads.

[0122] In one example, rod 930 is filled with a ceramic powder. Thus, rod 930 can surround element 932 with the inside of the rod filled with potting material. In one example, in place of a ceramic powder, another potting material can be used. The ceramic can be selected to be non-conductive and a good conductor of heat. Thus, element 932 heats up, which heats up ceramic 934 and in turn, heats up rod 930. Depending on the application for heating element 904, rod can be steel, nichrome, cupronickel, or some other material.

[0123] In one example, rod 930 has a length represented by length 944 and a width (diameter) represented by diameter 942. The length can be selected based on the gauge of the wire and the coiling of element 932. The width can similarly be affected by the gauge of the wire and how it is coiled.

[0124] In one example, ceramic 934 operates as a heat-storage component for heating element 904. The heat conductivity of the ceramic can allow for some heat retention by the ceramic, maintaining a fairly constant heat environment for element 932. In one example, the resistivity of element 932 is slightly less than 1.0 ohms, and when the element begins to heat up, ceramic 934 can provide heat retention to raise the resistivity to approximately exactly 1.0 ohms.

[0125] Lead 1 and Lead 2 carry the power in a circuit loop from the PV panel, through element 932, and back to PV ground. In one example, element 932 is specifically designed to connect to the leads with some gap into rod 930. Since element 932 heats up, having the leads extend some distance into rod 930 before connecting to the element can reduce the transfer of heat to interface 910. In one example, interface 910 is potted with insulator 912 to reduce the transfer of heat up into interface. The control circuit (not specifically shown) accelerates the electrons from the panel by creating the high frequency current signal to drive the material.

[0126] FIG. 9C is a I ine diagram of an example of a frequency-controlled heating element. Heating element 906 provides an example of a heating element in accordance with heating element 902, where heating element 906 is specifically shown shorter and wider than what is illustrated for heating element 902. Heating element 906 is illustrated as a cutaway view, seeing inside interface 950 and inside rod 960.

[0127] Element 962 can be referred to as the excitation element, being the Fe-Cr-AI-Ni alloy material. The gauge and length of element 962 can be controlled to make the length be as close as possible to 1.0 ohms. In one example, element 962 is made of solid wire (6 gauge, 8 gauge, 10 gauge, or 12 gauge) wound into the classic heating element coil shape. In one example, the coils of element 962 are closer together than the coils of element 932, but with larger loops. Controlling the coil for inductance can reduce the change in impedance in response to high frequency current delivered through the leads.

[0128] In one example, rod 960 is filled with a ceramic powder. Potting 964 represents the ceramic powder or other potting material that is selected to be non-conductive and a good conductor of heat. Thus, element 962 heats up, which heats up potting 964 and in turn, heats up rod 960. Depending on the application for heating element 906, rod can be steel, nichrome, cupronickel, or some other material.

[0129] In one example, rod 960 has a length represented by length 974 and a width (diameter) represented by diameter 972. The length can be selected based on the gauge of the wire and the coiling of element 962. The width can similarly be affected by the gauge of the wire and how it is coiled. Rod 960 of heating element 906 is shown with a shorter length and a wider diameter than rod 930 of heating element 904, illustrating that there can be variations in width and length of the heating element.

[0130] In one example, potting 964 operates as a heat-storage component for heating element 906. The heat conductivity of the ceramic can allow for some heat retention by the ceramic, maintaining a fairly constant heat environment for element 962. In one example, the resistivity of element 962 is slightly less than 1.0 ohms, and when the element begins to heat up, potting 964 can provide heat retention to raise the resistivity to approximately exactly 1.0 ohms.

[0131] Lead 1 and Lead 2 carry the power in a circuit loop from the PV panel, through element 962, and back to PV ground. In one example, element 962 is specifically designed to connect to the leads with some gap into rod 960. Since element 962 heats up, having the leads extend some distance into rod 960 before connecting to the element can reduce the transfer of heat to interface 950. In one example, interface 950 is potted with insulator 952 to reduce the transfer of heat up into interface. The control circuit (not specifically shown) accelerates the electrons from the panel by creating the high frequency current signal to drive the material.

[0132] FIG. 10 is a representation of an example of a temperature response of a heating element material. Diagram 1000 illustrates a temperature response of a heating element metal. In one example, the resistivity does not change significantly with increases in temperature.

[0133] Curve 1012 illustrates the temperature response. In one example, curve 1012 has bump 1014, where at a certain temperature the response is not linear. In much of the rest of the curve, the response can be fairly linear. Not all materials will have such a non-linear bump, but the response can be fairly linear with increases in temperature.

[0134] While the resistivity may not change significantly with temperature change, there can be some change. With the change in resistivity, the heating element coil can be designed to have a resistivity of slightly less than 1.0 ohms when there is no current throughthe element. When current goes through and the element heats up, the change in resistivity can raise the impedance of the heating element to be approximately 1.0 ohms.

[0135] FIG. 11A is a block diagram of an example of a controller for a system that charges a battery with a switched DC source. Controller 1110 represents a controller in accordance with an example of system 100, or an example of system 300, or an example of system 400. Controller 1110 can include a microcontroller, logic array, a control board, processor, or other component.

[0136] Controller 1110 either includes or controls a power converter circuit that generates and transfers the energy from a DC energy source to a battery. Converter 1120 represents the power converter circuit. Converter 1120 includes switching circuit 1122 to switch DC power (more specifically, the current signal of the power) from the DC energy source to the battery. In one example, switching circuit 1122 is controlled by control signals provided by controller 1110. In one example, the signals that control switching circuit 1122 can be considered to be provided by control circuitry separate from controller 1110, and can be part of converter 1120.

[0137] MPPT 1112 represents a maximum power point tracking unit of controller 1110. The operation of MPPT 1112 enables controller 1110 to track the maximum power point based on conditions of the PV source as well as based on changing impedance of the load due to temperature changes or battery saturation.

[0138] I mpedance matching 1114 represents control logic in controller 1110 to enable the controller to monitor changing conditions in the system and adjust for impedance matching. For example, impedance matching 1114 can enable controller 1110 to monitor conditions related to the charging of a battery, such as voltage levels, current levels, temperature, or other conditions. In response to changes in conditions that affect impedance matching, controller 1110 can adjust the switching of switching circuit 1122 to change the duty cycle, providing better impedance matching between the power generated from the energy source and the heating element.

[0139] It will be understood that controller 1110 does not include an inverter, nor does the controller operate with an inverter. Rather, the system can simply provide high speed switching of the current to charge a battery, while maintaining a low voltage.

[0140] FIG. 11B is a block diagram of an example of a battery charging system. System 1102 represents a system in accordance with an example of system 100, or an example ofsystem 300, or an example of system 400. System 1102 alternatively represents the control in the system as control circuit 1140. Alternatively, control circuit 1140 can be referred to as "the electronics," referring to the electronic control components that manage the operation of the system. Control circuit 1140 can include a microcontroller, logic array, a control board, processor, or other component. In one example, control circuit 1140 represents an example of controller 1110.

[0141] Solar 1130 represents a solar panel or multiple panels in parallel to provide PV energy for system 1102. Battery 1150 represents an energy storage device that can be charged from energy from solar 1130.

[0142] Converter 1142 represents converter hardware that enables control circuit 1140 to convert energy from the selected source to generate a switched DC signal. Converter 1142 provides the switched DC power to charge battery 1150 in accordance with any example herein.

[0143] FIG. 12A-12B are block diagrams of an example of battery charging based on impedance detection. System 1202 illustrates a battery charging system in accordance with an example of system 1102. System 1204 illustrates an example of system 1202 under different impedance conditions. System 1202 and system 1204 can be referred to as a battery charger. The battery charger can have converter circuitry to pass high speed switched signals to charge the battery.

[0144] Solar cells 1210 represent one or more solar cells that generate energy when exposed to light. Control circuit 1220 represents a control circuit in accordance with any example described. Control circuit 1220 is a controller to manage the high-speed switching of energy from solar cells 1210, at a low voltage. The low voltage refers to a voltage in the range of dozens of volts, much lower than a typical grid AC voltage.

[0145] Converter 1222 represents circuitry of control circuit 1220 that performs the high-speed switching and generates a pseudo-DC signal. With frequencies around 10 kHz or higher, the signal can appear to some electronics to be approximately a DC signal when the response time of the electronics is much less than the frequency of the switched signal. Switched signal 1232 represents the output power generated by converter 1222 to charge battery 1230. For illustration, one of the switching periods is illustrated with crosshatch shading for the "on" portion of the duty cycle and dot shading for the "off" portion of the duty cycle.

[0146] System 1202 illustrates a condition where battery 1230 has relatively low charge, resulting in a relatively low perceived impedance. Impedance detector 1224 enables control circuit 1220 to monitor the input impedance to battery 1230 and adjust the operation of converter 1222 to adjust the duty cycle of switched signal 1232. Thus, switched signal 1232 has a relatively high duty cycle, where the signal is on for more time than it is off.

[0147] System 1204 illustrates a changed condition of battery 1230, where it has a relatively higher charge (more than 50% charged). In one example, battery 1230 provides charge level and charge target information to control circuit 1220. As battery 1230 increases in charge, its perceived impedance increases.

[0148] Impedance detector 1224 can detect the increased impedance of battery 1230 and trigger converter 1222 to reduce the duty cycle of the output signal. Thus, in system 1204, switched signal 1234 has a relatively low duty cycle, where the signal is off for more time than it is on.

[0149] FIG. 13 is a block diagram of an example of a home heating system. System 1300 illustrates a heating system in accordance with an example of system 100 or system 502. In one example, system 1300 applies heating elements in accordance with any example herein for space heating, to provide heating for a residence, a business, or a place of education.

[0150] Solar cell 1310 represents one or more solar cells that generate energy when exposed to light. Control circuit 1320 represents a control circuit in accordance with any example described. Control circuit 1320 is a controller to manage the high-speed switching of energy from solar cell 1310, at a low voltage. The low voltage refers to a voltage in the range of dozens of volts, much lower than a typical grid AC voltage.

[0151] In one example, system 1300 has a one-to-one relationship of controller circuits to heating elements. In one example, a single controller can provide power to multiple heating elements. Converter 1330[l] represents a first controller circuit to generate signal 1332[1] to control the heating of element 1342[1], Converter 1330[N] represents an Nth controller circuit to generate signal 1332 [N] to control the heating of element 1342 [N] . N can be any integer.

[0152] Heat exchanger 1340 represents a heat exchange unit to transfer heat from element 1342[1:N], collectively, elements 1342. Elements 1342 represent heating elements in accordance with any example herein. Heat exchanger 1340 provides one or more mechanisms to transfer the heat to a target for space heating. Target 1350 represents theheating target. In one example, heat exchanger 1340 includes a fluid heated by elements 1342 and a radiator and blower for convective heating. In one example, in place of fluid, heat exchanger 1340 can include a salt compound.

[0153] Flow diagrams as illustrated herein provide examples of sequences of various process actions. The flow diagrams can indicate operations to be executed by a software or firmware routine, as well as physical operations. A flow diagram can illustrate an example of the implementation of states of a finite state machine (FSM), which can be implemented in hardware and / or software. Although shown in a particular sequence or order, unless otherwise specified, the order of the actions can be modified. Thus, the illustrated diagrams should be understood only as examples, and the process can be performed in a different order, and some actions can be performed in parallel. Additionally, one or more actions can be omitted; thus, not all implementations will perform all actions.

[0154] To the extent various operations or functions are described herein, they can be described or defined as software code, instructions, configuration, and / or data. The content can be directly executable ("object" or "executable" form), source code, or difference code ("delta" or "patch" code). The software content of what is described herein can be provided via an article of manufacture with the content stored thereon, or via a method of operating a communication interface to send data via the communication interface. A machine readable storage medium can cause a machine to perform the functions or operations described, and includes any mechanism that stores 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 that interfaces to any of a hardwired, wireless, optical, etc., medium to communicate to another device, such as a memory bus interface, a processor bus interface, an Internet connection, a disk controller, etc. The communication interface can be configured by providing configuration parameters and / or sending signals to prepare the communication interface to provide a data signal describing the software content. The communication interface can be accessed via one or more commands or signals sent to the communication interface.

[0155] Various components described herein can be a means for performing the operations or functions described. Each component described herein includes software,hardware, or a combination of these. The components can be implemented as software modules, hardware modules, special-purpose hardware (e.g., application specific hardware, application specific integrated circuits (ASICs), digital signal processors (DSPs), etc.), embedded controllers, hardwired circuitry, etc.

[0156] Besides what is described herein, various modifications can be made to what is disclosed and implementations of the invention without departing from their scope.Therefore, the illustrations and examples herein should be construed in an illustrative, and not a restrictive sense. The scope of the invention should be measured solely by reference to the claims that follow.

Claims

CLAIMSWhat is claimed is:

1. A heating element comprising a metal coil composed of an alloy of iron, chromium, aluminum, and nickel, the metal coil having a resistance of less than 1.3 ohms.

2. The heating element of claim 1, wherein the resistance is 1.0 ohms.

3. The heating element of claim 1, wherein the metal coil comprises a coiled wire having a gauge and length to control the resistance to approximately 1.0 ohms.

4. The heating element of any of claims 1 to 3, further comprising: a rod surrounding the metal coil.

5. The heating element of claim 4, wherein the rod comprises a steel rod.

6. The heating element of claim 4, wherein the rod is filled with potting material to fill an inside of the rod surrounding a coiled wire.

7. The heating element of claim 6, wherein the potting material comprises a ceramic powder.

8. The heating element of claim 6, wherein the coiled wire has a resistivity below 1.0 ohms when no current passes through it, and when it is heated up, has a resistivity of 1.0 ohms.

9. The heating element of claim 6, wherein the potting material comprises a material to store heat to regulate the resistance of the coiled wire.

10. A controller apparatus comprising: switching circuitry to generate a switched signal from energy from a DC (direct current) source and provide the switched signal to a heating element, the switched signalbeing a high frequency signal in current mode, the heating element being a metal coil composed of iron, chromium, aluminum, and nickel, and having a resistance of less than 1.3 ohms; and circuitry to monitor impedance of the heating element.

11. The controller apparatus of claim 10, wherein the high frequency signal comprises a chopped DC current signal.

12. The controller apparatus of claim 11, wherein the chopped DC current signal comprises a chopped DC signal with a controllable duty cycle.

13. The controller apparatus of claim 12, wherein the switching circuitry comprises a switch circuit driven by a pulse width modulator to create the chopped DC signal with the controllable duty cycle.

14. The controller apparatus of claim 12, wherein the switching circuitry is to change a duty cycle of the switched signal in response to detection of a change in impedance of the heating element.

15. The controller apparatus of claim 14, wherein the switching circuitry is to change the duty cycle to maintain a substantially constant ratio between a peak output voltage and an average output current.

16. The controller apparatus of claim 10, further comprising: a maximum power point tracking (MPPT) system to detect a maximum power point for energy transfer between a photovoltaic (PV) source and the heating element; wherein the switching circuitry is to power the heating element with power from the PV source.

17. The controller apparatus of claim 16, wherein the switching circuitry is to vary a duty cycle of the high frequency signal based on detection of a change in impedance matching between the PV source and the heating element.

18. A water heater system having at least one heating element in accordance with any of claims 1 to 9.

19. A home heating system having at least one heating element in accordance with any of claims 1 to 9.

20. A hybrid water heater system having at least one heating element in accordance with any of claims 1 to 9, and further comprising: a second heating element powered from grid power.

21. A battery charger comprising: switching circuitry to generate a switched signal from energy from a DC (direct current) source and provide the switched signal to a battery, the switched signal being a high frequency signal in current mode; and circuitry to monitor impedance of the battery.

22. The battery charger of claim 21, wherein the high frequency signal comprises a chopped DC current signal.

23. The battery charger of claim 21, wherein the switched signal comprises a chopped DC signal with a controllable duty cycle.

24. The battery charger of claim 23, wherein the switching circuitry comprises a switch circuit driven by a pulse width modulator to create the chopped DC signal with the controllable duty cycle.

25. The battery charger of claim 23, wherein the switching circuitry is to change a duty cycle of the switched signal in response to detection of a change in perceived impedance of the battery.-SO-26. The battery charger of claim 25, wherein the switching circuitry is to change the duty cycle to maintain a substantially constant ratio between a peak output voltage and an average output current.

27. The battery charger of claim 21, further comprising: a maximum power point tracking (MPPT) system to detect a maximum power point for energy transfer between a photovoltaic (PV) source and the battery; wherein the switching circuitry is to charge the battery with power from the PV source.

28. The battery charger of claim 27, wherein the switching circuitry is to vary a duty cycle of the high frequency signal based on detection of a change in impedance matching between the PV source and the battery.

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