WO2009030236A2

WO2009030236A2 - Layered structure for generating electrical energy

Info

Publication number: WO2009030236A2
Application number: PCT/DK2008/050217
Authority: WO
Inventors: Lars Nørgaard BJØRN
Original assignee: Inno Power Aps
Priority date: 2007-09-03
Filing date: 2008-09-02
Publication date: 2009-03-12
Also published as: WO2009030236A3

Abstract

A layered structure for generating electrical energy from the tempera- ture differential of a first temperature region and a second temperature regionand comprising a thermoelectric device in communication with said first and second temperature regions so as to generate said electrical energy, which thermoelectric device is connected to an electric circuit to be driven by said electrical energy whereinsaid layered structure comprises a first outer layer of protective material, a second layer of heat conducting material, a third layer comprising a portion of heat insulating material extending over at least a part of said second layer and in that said thermoelectric device is connected to said second layer of heat conducting material over at least another part of said second layer.

Description

Layered structure for generating electrical energy

The present invention relates to a layered structure, such as but not exclusively a slab for generating electrical energy from the tempera- ture differential of a first temperature region and a second temperature region comprising a thermoelectric device in communication with said first and second temperature regions so as to generate said electrical energy, which thermoelectric device is connected to an electric circuit to be driven by said electrical energy. Concrete slabs, tiles and pavestones are well known and widely used building materials used for public pavements, roadways, buildings and squares and in connection with private residences, driveways, and terraces and even for interior building design. The most advanced slabs of today are provided with embossed surfaces such as grooves, dents or bulges to provide a more pleasant appearance or to serve as guidance for pedestrians with impaired vision.

In general more and more intelligence and information processing are being thoroughly integrated into everyday objects and activities, which requires an energy source for powering the electronics for providing this intelligence and information processing. Even with the development of modern battery technology, any device that only is powered with energy based on this technology, is limited of the lifetime of the battery. The use of solar cells as an alternative or in combination with batteries has also been suggested, but the efficiency of solar cells are sensitive to shifting weather patterns, dust and debris deposited on their surface. Moreover, solar cells of today are very fragile and can therefore not be used in a harsh environment. Due to the drawbacks such a durance, maintenance and relatively hight costs associated with these and other energy sources widely used energy sources, there remains a need for reliable and cheap energy sources that can operate over long time periods in remote locations, without the need of maintenance and service.

It is well known to use thermoelectric elements utillizing the thermoelectric effect also known as the Peltier-Seebeck effect for conversion of a thermal differential to a electric voltage. The basic principle is that a voltage is created in the presence of a temperature difference between two metals or semiconductors.

The use of thermoelectric elements is known from JP2003021424, which discloses a utillization of the above-mentioned effect for providing a building element comprising a thermoelectric element connected to a battery and LEDs through a controller unit. By providing thermoelectric elements on the surface of the walls of a house the temperature difference between the inside and the outside of the walls can be utillized for indoor lightning. A indoor application of the a thermoelectric element is known from JP2003193655, which discloses a handrail comprising a thermoelectric element embedded in a peripheal portion of a handrail, which element is conneted to one or more diodes for lightning up the handrail. KR20020030957 discloses a streetlight apparatus having a power supply provided by a thermoelectric element in the ground. The thermoelectric element comprises a first metal side installed on the surface of the ground and a second metal joined with the first metal and being installed in the ground. A battery is connected to the thermoelectric element and the battery is connected to a converter, which provides a AC voltage required by the street light

JP2007103861 discloses the use of thermoelectric elements in roadway constructions and building materials and posible materials for use in the thermoelectric elements at different temperature differences. US 2005/0115600 discloses a thermoelectric device having a first side and a second side wherein the first side is in communication with a means for transmitting ambient thermal energy collected or rejected in a first temperature region and the second side is in communication with a second temperature region thereby producing a temperature gradient across the thermoelectric device and in turn generating an electrical current for driving sensors at remote locations.

The prior art described above generally focuses on the use of thermoelectric elements in specific applications or on the materials to be used for manifacturing the thermoelectric elements. However, it is still difficult to utillize the relatively small distance and corresponding temperature differential across thermoelectric devices in practical use.

With this background it is the object of the present invention to provide an intelligent and sturdy building element such as a slab, which is self-powered.

This is achieved by a layered structure according to the opening paragraph comprising a first outer layer of protective material, a second layer of heat conducting material, a third layer comprising a portion of heat insulating material extending over at least a part of said second layer and in that said thermoelectric device is connected to said second layer of heat conducting material over at least another part of said second layer.

The outer protecting layer provides an encapsulation of the following layers, which protects them from the environment in which the structure is to be installed. Besides being protective, the first outer layer is also heat conducting and therefore conducts heat to the second layer of heat conducting material, which ensures that the heat is guided to the thermoelectric element, which can generate electric energy from a temperature difference across the layered structure. Moreover, the heat in- sulating portion of said third layer, provides a relative light construction, which makes the structure easy to handle and install.

In a further development of the invention said third layer is sandwiched between said second layer of heat conducting material and a fourth layer of a heat conducting material, which fourth layer also is connected to said thermoelectric device.

The fourth layer provides an even better guidance of heat through the thermoelectric element and makes operation under lower temperature differences possible.

In another embodiment of the invention said first outer layer of protective material encloses said second layer and said third layer.

This provides an even better protection of the second and third layers from the surrounding environment, which makes sure that the relatively sensitive layers and parts thereof can function properly under even very harsh conditions. In another embodiment said first outer layer of protective material encloses said second layer, said third layer and said fourth layer.

This provides a completely encapsulated layered structure with two sides having the same appearance and which therefore are unaf- fected of their direction of installation.

In another embodiment said electric circuit is disposed in said third layer, preferably in said portion of heat insulating material.

By placing the electric circuit close to the thermoelectric elements it is easier to connect the two and furthermore the electric circuit can be embedded in the heat insulating material and thereby being even better protected from moist and water penetrating into the layered structure.

In order to obtain a better heat transport across the layered structure an embodiment according to the invention provided with heat pipes in said third layer for providing an improved heat transport between said first and second temperature regions.

The better heat transport the lower temperature difference across the layered structure is required to make operation of the electric circuit possible. In a preferred embodiment the layered structure comprises at least one signalling means to be driven by said electric circuit, which makes it possible to provide information or guidance at remote places where the layered structure is installed.

In another embodiment at least one of said heat-conducting layers comprises means for extending the surface area to improve the heat transport across the layered structure.

In a particular embodiment of the invention the outer protective layer is concrete comprising silica in order to provide an outer protective layer with the desired strength and properties to seal and encapsulate the other layers and furthermore to obtain good heat conducting properties.

An other aspect of the invention comprises a device of a first layer of heat conducting material, a second layer comprising a portion of heat insulating material extending over at least a part of said first layer of heat conducting material and in that said thermoelectric device is connected to said first layer of heat conducting material over at least another part of said first layer.

Hereby is achieved a device or assembly which easily can be cast into a outer protective shell in a mass production or in situ where it is desirable with a self-powered and intelligent building element.

In another embodiment of the device said second layer is sandwiched between said first layer of heat conducting material and a third layer of a heat conducting material, which third layer also is connected to said thermoelectric device.

In another embodiment of the device said electric circuit is disposed in said second layer, preferably in said portion of heat insulating material.

In another embodiment of the device said second layer com- prise heat pipes for providing an improved heat transport between said first and second temperature regions.

In another embodiment of the device said device comprises at least one signalling means to be driven by said electric circuit.

In another embodiment of the device at least one of said heat conducting layers comprises means for extending the surface area.

The invention will be explained in detail in the following by means of examples of embodiments with reference to the schematic drawing, in which

Fig. 1 is a side view of a layered structure according to the in- vention,

Fig. 2 is an enlarged cross sectional view of the layered structure of Fig. 1,

Fig. 3 is cross sectional view of another embodiment according to the invention, Fig. 4 is a side view of a particular embodiment according to the invention,

Fig. 5 is a side view of yet another embodiment according to the invention,

Fig. 6 is cross sectional view showing more details of a layered structure according to the invention,

Fig. 7 is another sectional view showing the details of another embodiment of a layered structure according to the invention,

Fig. 8 is a cross sectional view of a layered structure according to the invention showing a layer comprising heat pipes, and

Fig. 9 is a schematic illustration of an electric circuit in a layered structure according to the invention.

Fig. 1 illustrates a side view of slab 1 having a layered structure comprising an outer protective layer 2 and a heat-conducting layer 3. The outer protective layer 2 is preferably a concrete cast comprising a mixture of sand, cement, calcinated flint and silica. In a preferred embodiment the mixture comprises 13-14 % silica. The silica additive gives the concrete extra strength and furthermore increases the slab's conductivity and furthermore provides the slab with a pleasant appearance. It is obvious that a mixture of concrete can be achieved with many different mixing ratios using the above-mentioned materials and still achieving the desired properties and that the mixture can be added or substituted other materials. However, other materials having similar heat conducting and protective properties can be used in combination with or instead of concrete.

Fig. 2 shows a layer 4 of heat insulating material sandwiched between a protective layer 2 and a heat-conducting layer 3. As will become apparent from the following description, the heat insulating material serves to guide the heat transport through the desired areas of the layered structure. Furthermore, the heat insulating material 4 helps to provide a substantially light building material compared to for instance traditional slabs, since the density of heat insulating materials normally is relatively small compared to the one of the other protective layer 2. In a preferred embodiment the heat-insulating layer 4 is of polyethylene (PE) or a material having similar heat insulating properties. In general the heat-insulating material should have poor heat conducting properties compared to the heat-conducting layer 3.

Even at a small distance into the ground the temperature is relatively constant and independent of the temperature above the ground. This relation can be utilized by providing a relatively high slap, which extends deeper into the ground to achieve a more constant temperature difference across the slap and still keeping the total weight relatively low due to the use of a relatively light insulating material. The actual construction and the ability to transfer heat through the layered structure can be adapted depending on the conditions under which the slap is to be used in order to achieve an optimal heat flow. For instance when the layered structure is used indoor as a tile on a heated floor a slim construction can be achieved. In Fig. 3 the outer protective layer comprises a top side 5a and side walls 6a, 6b which encapsulates the inner layers 4 in order to achieve a traditional square appearance. Evidently, said outer layer could extend into a part of one or more of the layers and hence achieve different surface areas of the individual layers. Figs. 4 and 5 illustrate embodiments where the heat conducting elements 3 are provided with means 7 for extending the surface area and thereby improving the heat transport from e.g. the ground into the layered structure. The heat conducting layers 3 are conceivable with protrusions or depressions such as spikes, ribs or grooves for extending the outer surface in order to achieve an improved heat transport.

If the slab is to be placed directly on the ground it is desirable to penetrate as deeply into the soil as possible and to have a large surface towards the ground. This can be achieved by providing the heat conducting layers 3 with protrusions 7 which poke intro the ground and which furthermore provide a better installation.

Fig. 6 illustrates the principle of a layered structure for generating electrical energy from the temperature differential of a first temperature region and a second temperature region. If there is a temperature differential between the surface 24 of the outer protective structure 2 and the outer surface 26 of the heat conducting layer 3 there exists a heat transport through the layered structure as illustrated by the arrows 22a and 22b. The layered structure is suitable used for many building elements such as slabs, tiles, flagstones and bricks, which can be provided with a protective layer having good heat conducting capabilities. The heat-conducting layer 3 will typically be an aluminium panel, which conduct heat to the thermoelectric elements or of a material having similar or even better heat conducting properties. The purpose of the heat insulating layer is to ensure that the heat mainly passes through the thermoelectric elements 9a, 9b.

In a preferred embodiment shown in Fig. 7 the layered structure of a slab 1 comprises a first outer protective layer 2 of a concrete mixture comprising silica, which layer encloses a second layer 3a of heat conducting material, a third layer comprising a thermoelectric element 9 sandwiched between and connected to the first heat conducting layer 3a and the forth layer of heat conducting material. The third layer also comprises a heat-insulating portion surrounding the thermoelectric element 9. A thermoelectric element can be understood as a group of elements connected in series as illustrated in Fig. 6 or a stack as illustrated in Fig. 7.

Fig. 7 also illustrates the purpose of the outer protective layer 2, which surrounds or encapsulates the heat conducting layer 3a adjacent to and in connection with a layer comprising heat insulating material 4 and thermoelectric elements 9. Hereby, the outer layer provides a sealed massive shell, which protects the intelligence provided on the printed circuit board 8. The second heat conducting layer 3b is partly integrated in the walls 6a, 6b of the outer, which naturally provides a lower part of the slab 1 to be mounted in the ground, whereas the top side 5a naturally forms a upper side of the slab with an appearance preferably corre- sponding to traditional slabs without intelligence. Hence, the high of a building element such as a slab according to the invention is to be understood as the distance between the lower surface to be placed facing towards the ground and the outer surface, which is visible when the slab is installed. The thermoelectric element 9 generally determines the thickness of the third layer. The thermoelectric element 9 is preferably positioned in the middle of the layered structure and thereby being surrounded by the heat insulating material. This configuration ensures that the heat transport is guided through the thermoelectric element, which thereby is able to generate electrical energy from even small temperature differences. In a preferred embodiment the third layer also comprises an electric circuit on a printed circuit board 8, which typically is embedded in the heat insulating material 4. The electric circuit of the printed circuit board 8 is connected to the thermoelectric element 9 in order to control and utilize the electrical energy generated by the thermoelectric element 9. Evidently, the third layer can comprise several thermoelectric elements 9a, 9b connected in series as illustrated in Fig. 6. In Fig. 8 is shown an embodiment where a first heat conducting layer 3a is connected to a second heat conducting layer 3b by means of heat pipes 11a, lib. A heat pipe is a heat transfer mechanism that can transport large quantities of heat based on very small difference in temperature between a relatively hot and a relatively cold temperature re- gion. Inside a heat pipe, at the hot interface a fluid turns to vapour and the gas naturally flows and condenses on the cold interface. The liquid falls or is moved by capillary action back to the hot interface to evaporate again and repeat the cycle.

Fig. 9 is a schematic illustration of an electric circuit in a slab 1 according to a preferred embodiment of the invention. It is important to notice that the parts 12, 14, 16, 18 and 20 of the electric circuit and the thermoelectric element 9 illustrated in fig. 9 are all fully integrated and encapsulated by a protective layer, which protects from the surrounding environment in order to make it work under even very harsh conditions. The term interface 20 should be understood as a means for communicating with the surroundings and not necessarily an interface at the surface of the slab 1. It is conceivable that at least a part of such an interface for instance a LED is positioned at the surface of the slab in order to emit light. However, the slab and the electric circuit and thermoelectric ele- ments providing it with intelligence are still fully integrated and protected from the surrounding environment. The thermoelectric element 9 is made from heavily doped Bismuth Telluride, which allows a great number of elements per square centimetre, which result in a higher output voltage per degree of temperature difference. Experiments has shown that at temperature differences above 3-4 degrees celcius the elements can produce an output voltage of approximately 2 V. However, by operating the thermoelectric elements 9 with a load resulting in an output voltage of approximately 0.8-0.9 V the efficiency of the elements is im- proved. The loading of the thermoelectric elements 9 to obtain the most efficient output voltage is controlled by a microprocessor 18. In a preferred embodiment it is desired to achieve a supply voltage of approximately 4.2 V, which is achieved by a DC-DC converter 14. In order to ensure that the DC-DC converter 14 always is supplied with a voltage of the same polarity irrespective of which direction the energy is flowing through the layered structure, a diode bridge 12 is inserted between the thermoelectric element 9 and the DC-DC converter 14. In a preferred embodiment the diode bridge 9 is constructed with Schottky diodes with a voltage drop of 0.2 V to ensure the most efficient use of energy. A ca- pacitor (not shown) is connected to the output of the diode bridge 12 to ensure a constant load on the thermoelectric elements and low impedance towards the DC-DC converter 14.

The task of the DC-DC converter is to increase the output of the thermoelectric element to a supply voltage of 4.2 V, which is suitable to charge a battery 16, preferably a Lithium-ion battery. In periods with excess of electrical energy the battery can be charged. In a preferred embodiment is used a DC-DC converter being able to start itself at an input of 0.85 V, which means that the system is self-powered at temperature differences of just 1-2 degrees Celsius. The input voltage at the DC-DC converter 14 is measured by the microprocessor 18 in order to control the system load and increase the efficiency of the thermoelectric element.

A microprocessor 18 controls the battery charging, energy flow and use of energy as well as communication with an interface 20. The microprocessor 18 measures the voltage at the output of the thermoelectric element 9 and controls the load on the element to achieve the optimum operating voltage and efficiency of the thermoelectric element 9. The load is managed by controlling the charging current to the battery. The microprocessor preferably has two internal speeds, so that in peri- ods with low energy supply, the energy consumption can be lowered to approximately 30 μA. In periods with no energy supply from the thermoelectric element 9, the systems can turn it self off and wait until a useable supply once again in available. This function will be used in peri- ods when the slab is being stored in a warehouse or transported. Furthermore, this makes the slab very easy to install because it does not require any extraordinary skills.

The system controlled by the microprocessor 18 allows communication via an interface by means of light, sound and RF- communication. The slab also provides a number of possibilities for building in sensors. It is furthermore possible to provide the system with a sensor embedded in the layered structure to provide the system with further intelligence.

In a preferred embodiment the layered structure 1 is a wet cast- ing of concrete comprising silica, which enables a proper and solid integration of components into the slab 1. The slabs are cast in silicone moulds and are vibrated while hardening. During production the silicone moulds are filled with concrete. The components to be placed in the slab are lowered into the concrete mass after the mould has been filled in and the components are kept in the correct position by the silicone mould. In this connection components can be understood as an assembly comprising at least one heat conducting layer, a layer comprising a thermoelectric element, a heat insulating material and a electric circuit. The concrete and the components contained in the silicone mould are then vi- brated in order to remove air bubbles from the concrete. Finally, the concrete undergoes a hardening process, which binds and encapsulates the components. This approach has shown to be optimal for integration of electric components and after hardening the electric components and the thermoelectric elements are fully encapsulated, which makes it diffi- cult for moist and water to penetrate to them. Furthermore, the components are thereby encapsulated in a perfectly sealed and massive construction, which protects them from deformation, vibrations and penetration of water and moist from the surrounding environment. This provides a self-containing integrated building element, which is suitable to be installed in environments with very hard conditions. In order to protect the electric circuit 8 from moist and water during the casting it is normally protected in a sealing bag.

In this way sophisticated electronics and software can be built into the building materials to allow them to communicate directly with their surroundings and still being self-contained units. This for instance provides an intelligent slab in the sense of comprises means for communicating information to the surroundings, receive information to be transmitted to the surroundings, operating according to the surrounding environment to achieve the a reliable performance. It is desirable to obtain these properties at remote places where wiring of cables is expensive and difficult. Furthermore, it is desirable to obtain a building element with easily fits into existing infrastructure and which can be installed and last under even very rough conditions. Hence, it is relatively easy to replace an existing slab with a slab according to the invention in order to provide information access or signalling at remote places without the need of cables for supplying the cable with energy or to provide it with information.

Due to the sealed and massive structure of a slab according to the invention it does not require any further maintenance compared to traditional slabs, because the intelligence encapsulated in the outer concrete layer is duly encapsulated to resist very tough conditions.

A preferred application of the invention is as information and warning point at public places such as train stations, where installations of existing traditional slabs at selected points are replaced with slabs according to the invention, which are provided with a wireless communication interface such as Bluetooth in order to serve as a guidance for vision impaired persons provided with a Bluetooth enabled device. Furthermore, it can facilitate access to information about timetables or changes to departures and arrivals of trains for travellers in general. Experiments has shown that a standard GSM mobile phone can powered by means of the thermoelectric element 9 and be fully integrated and sealed in a slab and still function in order to provide information to and from the slab. Hence, in general a slab according to the invention can serve as an in- formation and access point at remote locations, where traditional communication equipment is difficult or impossible to install, maintain and operate.

The invention should not be regarded as limited to the embodi- ments shown and described in the above, but several modifications and combinations may be carried out without departing from the scope of the appended claims.

Claims

P A T E N T C L A I M S

1. A layered structure for generating electrical energy from the temperature differential of a first temperature region and a second temperature region and comprising a thermoelectric device in communica- tion with said first and second temperature regions so as to generate said electrical energy, which thermoelectric device is connected to an electric circuit to be driven by said electrical energy c h a r a c t e r i z e d in that, said layered structure comprises a first outer layer of protective material, a second layer of heat conducting material, a third layer comprising a portion of heat insulating material extending over at least a part of said second layer and in that said thermoelectric device is connected to said second layer of heat conducting material over at least another part of said second layer.

2. A layered structure according to claim 1, wherein said third layer is sandwiched between said second layer of heat conducting material and a fourth layer of a heat conducting material, which fourth layer also is connected to said thermoelectric device.

3. A layered structure according to claim 1 or 2, wherein said first outer layer of protective material encloses said second layer and said third layer.

4. A layered structure according to claim 1 or 2, wherein said first outer layer of protective material encloses said second layer, said third layer and said fourth layer.

5. A layered structure according to any of the previous claims, wherein said electric circuit is disposed in said third layer, preferably in said portion of heat insulating material.

6. A layered structure according to any of the previous claims, wherein said third layer comprises heat pipes for providing an improved heat transport between said first and second temperature regions.

7. A layered structure according to any of the previous claims, wherein said layered structure comprises at least one signalling means to be driven by said electric circuit.

8. A layered structure according to any of the previous claims, wherein at least one of said heat conducting layers comprises means for extending the surface area.

9. A layered structure according to any of the previous claims, wherein said outer protective layer is concrete comprising silica.

10. A device for generating electrical energy from the temperature differential of a first temperature region and a second temperature region and comprising a thermoelectric device in communication with said first and second temperature regions so as to generate said electrical energy, which thermoelectric device is connected to an electric circuit to be driven by said electrical energy c h a r a c t e r i z e d in that, said device comprises a first layer of heat conducting material, a second layer comprising a portion of heat insulating material extending over at least a part of said first layer of heat conducting mate- rial and in that said thermoelectric device is connected to said first layer of heat conducting material over at least another part of said first layer.

11. A device for generating electrical energy according to claim 10, wherein said second layer is sandwiched between said first layer of heat conducting material and a third layer of a heat conducting material, which third layer also is connected to said thermoelectric device.

12. A device for generating electrical energy according to claim 10 or 11, wherein said electric circuit is disposed in said second layer, preferably in said portion of heat insulating material.

13. A device for generating electrical energy according to any of the previous claims, wherein said second layer comprises heat pipes for providing an improved heat transport between said first and second temperature regions.

14. A device for generating electrical energy according to any of the previous claims, wherein said device comprises at least one signal- ling means to be driven by said electric circuit.

15. A device for generating electrical energy according to any of the previous claims, wherein at least one of said heat conducting layers comprises means for extending the surface area.

16. Use of a device for generating electrical energy according to claim 10-15 for embedding in a protective material such as a concrete comprising silica.