Technical field

This invention relates to harnessing thermal energy and to the conversion of thermal energy into electricity.

Background

The inventor believes that energy savings can be achieved by improving thermal energy harvesting and associated energy storage systems.

Thermal energy is available in abundance, with some sunny areas exposed to approximately 1 kilowatt hour per square meter.

In addition to solar energy there are also many other unharvested sources of thermal energy, such as cars, power plants, factories and other industries, which all dissipate large amounts of thermal energy into the environment.

Photo voltaic solar electricity generators are not capable of capturing all of the energy contained in sunlight, with some sources stating that only about 20 percent is absorbed, and this 20 percent is only converted into electricity at an efficiency of around 10-15 percent.

The Seebeck effect entails that when there is a difference in temperature between two dissimilar electrical conductor or semiconductor substances, there will be a resulting electric potential difference (or Voltage difference) between the two substances.

When the Seebeck effect is applied in reverse - in other words, when heat or cold is produced by applying an electrical current through two dissimilar electrical conductor or semiconductor substances - it is referred to as the Peltier effect.

The inventor having considered the above proposes the invention hereinbelow. Summary of invention

According to a first aspect of the invention, there is provided a thermal energy to electrical energy extraction system which includes: a thermoelectric converter, for converting thermal energy into electrical energy and generating an electrical energy output, the thermoelectric convertor being connectable to a thermal energy source; an electric conditioner connectable to the thermoelectric converter for conditioning the electrical energy output and generating a conditioned electrical output; a measuring means for measuring the electric energy within the system; and a controller for controlling the thermoelectric converter in order to vary the conditioned electrical output based on the measurements obtained from the measuring means.

The thermoelectric converter may be configured to convert thermal energy into electrical energy with a coinciding generated voltage and current.

The thermoelectric convertor may take the form of a Seebeck generator.

The thermoelectric convertor may take the form of a Peltier cell.

The thermoelectric convertor may take the form of a thermopile which includes: a mounting base with apertures extending therethrough; a first conductor mounted on a first surface of the mounting base; a second conductor mounted on a second surface of the mounting base; and protrusions extending from at least one of the conductors through the apertures for interconnecting the first and second conductors. The mounting base may take the form of a printed circuit board.

The first and second conductors may be composed from different conductive materials.

The thermopile may further include semiconductor connectors located within the apertures for interconnecting the first and second conductors.

It is to be appreciated that when thermal energy flows from one conductor to the other a net voltage and current flow will be created.

The thermal energy source may include a thermal collector, the thermal collector being configured to convert solar energy into thermal energy. The thermal energy source may include a fuel powered engine generating thermal energy as a by - product, a power plant for generating electricity, a factory, incinerator, a hot water reservoir functioning as a thermal storage tank, or any other object or source containing thermal energy.

The thermal energy source may be a black coloured body for absorbing solar energy. The electric conditioner may take the form of a direct current to direct current converter (DC to DC converter) for conditioning a voltage of an electrical source to a desired output voltage.

The electric conditioner may be configured to condition the generated voltage and current of the thermoelectric converter to required levels. By controlling the electric conditioner, the desired output voltage and current can thus be regulated.

Designing the DC to DC converter may include selection of respective inductor and capacitors by taking into account the load or an applicable energy storage device.

The DC to DC convertor may take the form of a conventional Boost convertor for stepping up voltage while stepping down current from its input to its output / supply.

The thermal energy to electrical energy extraction system may include multiple electric conditioners. The multiple electric conditioners may be connected in parallel to the electric supply generated by the thermoelectric converter in order to further condition the electric output so as to generate an optimised sine wave triangular load current.

The multiple electric conditioners may be connected in parallel to the thermal to electricity converter, with each conditioner operating at a different phase time relative to a reference signal / phase character, so as to prevent overlapping of the off or dead time of the multiple conditioners with a resultant generally continuous flow of electricity from the converter to the load.

The measuring means may take the form of voltage and / or current sensors. The controller may take the form of a programmable micro controller.

The controller may be configured to provide an output control signal to a switching device included within the thermoelectric converter for manipulating the required conditioned output.

The thermal energy extraction system may be connectable to an energy storage device. The energy storage device may take the form of one or more batteries.

The thermal energy to electrical energy extraction system may further include a closed loop pumping and circulation system to allow flow of thermal conducting fluid from the thermal collector towards the thermal storage tank in the presence of thermal energy supply, and flow of thermal conducting fluid from the thermal storage tank towards the thermal collector in the absence of thermal energy supply.

A such, the system may be configured to allow flow of thermal conducting fluid from the thermal collector towards the thermal storage tank in the presence of solar energy supply, and flow of thermal conducting fluid from the thermal storage tank towards the thermal collector in the absence of solar energy supply, respectively, thereby causing the thermoelectric converter to generate electrical energy in the presence as well in the absence of solar energy supply. Brief description of the drawings

The invention will now be described by means of a non-limiting example with reference to the accompanying drawings.

In the drawings: Figures 1 and 2 depict the electric conditioner in the form of a DC to DC convertor illustrating the concept of covering the voltage and current levels of a specific input source and the coinciding time cycles related thereto;

Figure 3 shows a schematic representation of the complete DC to DC electronic extractor system for optimizing the electricity extraction from the thermal to electricity conversion cell, utilising microprocessor control in order to optimise time sequencing;

Figure 4 is a graph illustrating the extraction current versus time for the inductor charge cycle of the DC to DC energy convertor, being the first cycle of the DC to DC energy extraction as depicted in Figure 3;

Figure 5 is a graph illustrating the transfer of charge current to the capacitor or battery, being the second cycle of the DC to DC extractor as depicted in Figure 3;

Figure 6 is a graph illustrating the effective final DC charge / current extracted

© from the system shown in Figures 1 and 2;

Figure 7 is a schematic representation of a large scale low cost thermal energy to electricity converter, with multiple DC to DC converters sequentially separated from each other for ensuring an overlap of extraction cycles;

Figure 8 is a graph of the thermal energy versus time heat transfer and electricity output curves as obtained for the system shown in Figure 7, illustrating an almost continuous extraction of current over time;

Figure 9 is a graph of the observed power versus temperature difference performance for the complete thermal energy extraction unit; Figures 10 and 1 1 show possible microelectronic structures for generating a microelectronic thermo-pile using different metal depositions on both sides of a printed circuit, in accordance with the second aspect of the invention; and

Figure 12 is a schematic illustration of a preferred embodiment larger scale low cost thermal energy to electricity converter that can be used for generating electricity for households using a multi cycle thermal transfer process, in the presence as well as in the absence of solar energy supply.

Detailed description of the invention Reference numeral 10 generally depicts a thermal energy extractor system 10, in accordance with the invention;

Turning now to Figures 1 and 2, the electric conditioner, in the form of a conventional DC to DC converter is typically controlled by varying the on - and - off timing (duty cycle) of a switching device included within the converter circuit. Designing a DC to DC converter it is important to select the respective inductor and capacitors taking into account the load or an applicable energy storage device.

The DC to DC convertor used will typically be a conventional Boost convertor for stepping up voltage while stepping down current from its input to its output / supply. The basic functioning of a Boost converter is firstly, in the on state the switch S is closed, resulting in a gradual rise in the current through the inductor. In the off state, with switch S in the open position, the current through the inductor flows through the diode D, the capacitor C and the Load R. The result is that energy accumulated within the inductor during the on state, is transferred into the capacitor. This energy can then be used to power the load R during the off stage. Figure 3 shows a schematic representation of a DC to DC convertor 16 electronic extractor system 10 for optimizing the electricity extraction from the thermoelectric convertor 12, utilising controller / microprocessor 18 in order to optimise time sequencing. Energy storage battery 48 is included to store electrical energy not supplied to the load. One limiting factor of a DC to DC converter is that the current through the inductor decays to zero, see Figures 4, 5 and 6. In such an event there may be serious implications to the efficacy of the DC to DC converter and to the energy harvesting capabilities of the entire system. Figure 4 illustrates the extraction current versus time for the inductor charge cycle of the DC to DC convertor being the first cycle of the DC to DC extractor as depicted in Figure 3, reference numeral 20 showing an initial increase in energy stored in the coil, followed by a time-period of no energy storage 22, in which period potential energy is no longer stored and wasted. Figure 5 illustrates the transfer of charge current to the capacitor or battery, being the second cycle of the DC to DC extractor as depicted in Figure 3, reference numeral 24 showing a decrease in energy stored in the capacitor/battery over time, followed by a resultant period of no energy storage, 26.

Factors considered when designing the converter 12 is the applicable load, the size and inductance of the inductor as well as the size and capacitance of the capacitor. All the factors will also have an impact on the duty cycle of the switch and impact on the method in which the duty cycle is controlled by means of the controller 18.

Thus, according to a first aspect of the invention, more clearly shown in Figure 7, there is provided a thermal energy to electrical energy extraction system 10 which includes a thermoelectric converter 12, connectable to a thermal energy source, an electric conditioner in the form of a DC to DC convertor 16, connectable to the thermoelectric converter 12 for conditioning the electric energy output of the thermoelectric converter 12, generating a conditioned electrical output and optimizing the conversion efficiency of thermal energy to electrical energy, a measuring means typically in the form of voltage and current sensors (not shown) for measuring the electric energy within the system 10 and a controller 18 for controlling the converter 12 in order to vary the conditioned electrical output based on the measurements obtained from the voltage and current sensors. Battery 48 is provided for storage of surplus electrical energy.

The thermoelectric converter 12 will typically be in the form of a Seebeck generator. Alternatively, the thermoelectric convertor 12 can also be the form of a Peltier cell. In use, the thermoelectric converter 12 is connected a thermal energy source which can be a hot water reservoir or a solar energy absorber/collector for converting thermal energy into electrical energy with a coinciding generated voltage and current.

Electric conditioner 16 will preferably be in the form of a direct current to direct current converter (DC to DC converter) and will condition the generated voltage and current of the thermoelectric converter 12 to required levels.

By controlling the thermoelectric converter 12 the desired output voltage and current can thus be regulated.

In order to condition the electric output to, for instance, to generate an optimised sine wave triangular load current, Figure 7 further illustrates a plurality of electric conditioners 16 which are connected in parallel to the thermal to electricity convertor 12, with each conditioner 16 operating at a different phase time, relative to a reference signal ,and such that the off or dead time of each conditioner 16 does not coincide or occurs at the same time. By optimizing the conditioner transfer times in terms of the reference signal (phase character), an almost continuous flow of electricity from the convertor to the load can be realized, see Figure 8 where reference numeral 50 indicates an optimized optimised sine wave triangular load current.

This novel configuration, technique and system, increases and optimizes the flow of electricity from the thermal to electricity converter to the load and increases the conversion efficiency of the system.

Figure 9 is a graphic representation showing the increase in electrical energy extraction when using a DC - DC convertor, reference numeral 52, compared to a reduced efficiency, reference numeral 54, when incorporating a direct load. The controller 18 will be a programmable micro controller and the electronic conditioners 16 are typically controlled by analyzing the various electrical inputs and outputs measured by means of the voltage and current sensors. The controller will typically provide an output control signal to a switching device included within the converter circuit in order to manipulate the required conditioned output.

Figure 12 depicts a preferred embodiment, when in use, of the thermal energy extractor system 10, in accordance with the invention.

The system 10 includes a low cost black body thermal energy collector, or thermal energy source 14, consisting of an arrangement of black metal plates and pipes for converting solar energy into thermal energy. A suitable thermal conductive fluid, in this case water, is pumped and circulated within a thermal conductor which includes a closed loop pumping and circulation system 27 to a thermal energy transfer area where thermal energy is transferred to a thermal energy storage tank 28.

Thermal energy is harvested by the thermoelectric generator/convertor 12 which is a number of thermopiles 34 arranged in series, converting the thermal energy into electrical energy as the thermal energy conducting fluid passes therethrough. The thermal energy is also transferred inside the thermal storage tank 28 by means of a thermal exchanger system 36, which in for this embodiment consists of a copper coil circulating the thermal energy conducting fluid. The closed loop pumping and circulation system 27 is closed cycle and the pressure in the thermal exchanger system 36 is thus not influenced by external water pressure as supplied from the supply line 25.

A secondary thermal storage tank 38, with a conventional electrical element heater 40 can be coupled to the first tank 28, in order to supply high temperature water to a household, should it be required.

A smart electronic controller 18 is coupled to a series of sensors and controls for ensuring that electricity is supplied by the thermal energy harvesting system at maximum efficiency.

During day time, thermal energy is collected by the thermal collector 14 and thermal energy is transferred through the pumping and closed loop liquid system 27 towards the thermal storage tank 28, the fluid passing through the thermoelectric generator 12. !t is estimated that about 30% of the transferred thermal energy through the thermoelectric generator 12 is converted to electric energy, and the electrical energy is fed to an external load/grid electricity supply 30 that is coupled to the system 10. The remaining thermal energy that flows through the thermoelectric convertor 12 is subsequently stored in thermal storage tank 28. This is referred to as the first cycle of conversion.

An ordinary hot water geyser system found in many household is used for this purpose. Hot water can be drawn for various household purposes as occurs with a normal geyser system and fresh water can be supplied to the geyser from an external water line.

During night time, no solar energy is incident on the thermal collector 14 and if thermal conducting fluid (hot water) is circulated from the thermal storage tank 30 through the system 27, towards thermal collector 14, the surface of thermal collector 14 subsequently acts as a radiator transferring thermal energy to the cool night air environment. The temperature of the thermal collector 14 will hence be lower during night.

A temperature gradient is thus again available between thermal storage tank 28 and the thermal collector 14. When fluid is subsequently circulated towards the thermal collector 14 passing through the thermoelectric generator 12, again about 30 % of the thermal energy is converted into into electricity. This is referred to the second cycle of conversion.

A continuous supply of electricity is therefore supplied from the system 10 both during day and night. Energy is effectively stored during day time as hot water in the reservoir 28. No expensive battery systems are required for storing energy. The total conversion efficiency of the system has been found to be as high as 60%. The cost outlay of the system is extremely low. The closed loop pumping and circulation system will typically include electronic control units consisting of a range of sensors, electronic micro-processor, electronic driving circuitry and actuators (valves) control the flow of fluids continuously and ensures that the thermal energy to electricity conversion process always occurs optimally. The thermal energy extraction system 10 can alternatively include an energy storage device in the form of one or more batteries for storing excess electricity.

Figures 10 and 1 1 show possible microelectronic structures for generating the microelectronic thermo-pile 34 using different metal depositions 42 and 44, respectively, on both sides of a printed circuit 46. Metal conductors 42 and 44 are made of different conductive materials.

It is to be appreciated that when thermal energy flows from one conductor to the other a net voltage and current flow will be created.

A major goal of these structures is to ensure that a maximum thermal gradient is maintained between the two sides of the structure, while a high thermal conduction occurs between the two sides, and a high electric conduction of charge carriers occurs between the two sides. Hence some elongation of the middle thermal conduction blocks is required.

The applicant considers the invention advantageous in that a thermoelectric system is described which includes sequential extraction techniques to promote efficient conversion of thermal into electrical energy and also a substantial constant level of electrical energy output.