WO2019226109A1

WO2019226109A1 - Method and device for producing electric energy

Info

Publication number: WO2019226109A1
Application number: PCT/SE2019/050466
Authority: WO
Inventors: Arne Schleimann-Jensen
Original assignee: Arne Jensen Aktiebolag
Priority date: 2018-05-22
Filing date: 2019-05-21
Publication date: 2019-11-28
Also published as: SE1850603A1; WO2019226110A1; SE543610C2

Abstract

Device (100) for providing electricity from an available temperature gradient between a metal pipe (10) through which a warm fluid runs and a cold gas environment (1). The device comprises: a first metal part (110) comprising an abutment surface (111); a second metal part (120) arranged to forma gap (130) between the first (110) and second (120) metal parts; a peltier element (140), connecting the first (110) and second (120) metal parts in said gap (130); a cooling flange (151), connected to the second metal part (120); electric terminals (160); and electric conductors connecting the peltier element (140) and the terminals (160). The invention is characterised in that the device comprises a magnet (114) arranged to be attracted to the metal pipe and to hold the device in place by surface friction on the metal pipe, and in that the abutment surface is constituted by two flat surfaces set at an angle between them, together forming a cylindrical concave shape which is V-shaped in a cross- section taken perpendicularly to the main plane. The invention also relates to a method.

Description

Method and device for producing electric energy

The present invention relates to a method and a device for producing electric energy. In particular, the invention relates to such a method and such a device for producing electric energy from an available temperature gradient present between a pipe and the ambient air. Specifically, the present invention can advantageously be used for producing electric energy at various points in a district heating system.

District heating systems generally comprise numerous system parts, spread out across large areas in order to remotely serve houses and other premises with heat. Such system parts, of course, comprise pipework for lead and return heat carrier, such as water. However, there are typically also operation, service and maintenance installations in the form of spaces that are inspectable by personnel, and even premises accessible for service and maintenance.

Such installations are frequently weather protected, and may therefore be closed from the environment. They may often be located in places where there is no readily available source of electricity, and where it is impractical to otherwise provide for a reliable electric connec tion. However, it is often desirable to arrange various surveillance and remote measure- ment equipment in connection to such installations. Also, closed spaces may for instance have a need for ventilation.

The present invention solves the above described problems. Hence, the invention relates to a device for providing electricity from an available temper ature gradient between a metal pipe through which a warm fluid runs and a cold gas envi ronment, which device has a main plane of extension, wherein the device comprises a first metal part, generally extending in the main plane and comprising an abutment surface ar ranged to be in physical contact with the metal pipe when the device is in an operating position; a second metal part, generally extending in the main plane and arranged at a dis tance from the first metal part, forming a gap between the first and second metal parts, which gap also generally extends in the main plane; a peltier element, connecting the first and second metal parts in said gap, and arranged to produce an electric voltage as a result of a temperature gradient between the first and the second metal parts; a cooling flange, connected to the second metal part on its side facing away from the first metal part; electric terminals; and electric conductors connecting the peltier element and the terminals, and arranged to provide said voltage on said terminals, which device is characterised in that the device further comprises a magnet arranged to be attracted to the metal pipe and to hold the device in place by surface friction between the device and the metal pipe when the device is placed in said operating position, on the surface of the metal pipe and with physical contact between the metal pipe and an abutment surface of the device, and in that the abutment surface is constituted by two flat surfaces set at an angle between them, together forming a cylindrical concave shape which is V-shaped in a cross-section taken perpendicu larly to the main plane. Furthermore, the invention relates to a method for producing electricity from an available temperature gradient between a metal pipe through which a warm fluid runs and a cold gas environment, which method is characterised in that the method comprises the method steps of providing at least one device of the said type; arranging the device in question in an operating position on the metal pipe with the abutment surface abutting the metal pipe, and connecting the terminals of the device to an electricity-consuming apparatus.

In the following, the invention will be described in detail, with reference to exemplifying embodiments of the invention and to the enclosed drawings, wherein: Figure 1 is a perspective overview of a simplified example of a device according to the pre sent invention;

Figure 2 is a first cross-sectional perspective view of the device illustrated in Figure 1; Figure 3 is a closeup of the first cross-sectional perspective view shown in Figure 2;

Figure 4 is a second cross-sectional perspective view of the device illustrated in Figure 1; Figure 5 is a different perspective overview of the device shown in Figure 1, as seen from a bottom side; Figure 6 is an overview of a device according to the present invention and its environment; and

Figure 7 is a flowchart illustrating a method according to the present invention. All figures share the same reference numerals for the same or corresponding parts.

Hence, Figures 1-5 illustrate, as an example, a device 100 according to the present invention for providing electricity from an available temperature gradient between a metal pipe 10 through which a warm fluid runs and a cold gas environment 1. It is realized that the device 100 is not necessarily drawn to scale, and is simplified in order to illustrate the principles behind the present invention. For instance, certain details are not shown for reasons of clarity.

The device 100 is associated with a main plane P of extension, which plane P extends along a length L and a width W dimension. Perpendicularly to the length L and width W dimen sions, a depth D dimension runs. In general, the depth D dimension is perpendicular to an abutment surface 11 of the pipe 10 to which the device 100 is attached in the below-de scribed operating position. The device 100 comprises at least one, preferably several, magnets 114, arranged to be attracted, using magnetic forces, to the metal pipe 10 and to hold the device 100 in place by surface friction between an abutment surface 111 of the device 100 and a corresponding abutment surface 11 of the metal pipe 10 when the device 100 is placed in an operating position, in which it can produce electricity from the available thermal gradient provided by the pipe 10. This operating position is illustrated in Figures 1-4, and is defined as the position of the device 100 in relation to the pipe 10. In the operating position, the device 100 is arranged on the surface 11 of the metal pipe 10, with physical contact between the metal pipe 10 and the abutment surface 111 of the device 100. The physical contact may be direct of via a thermally conducting attachment paste or similar, as described below. Further, the device 100 comprises a first metal part 110, generally extending in the main plane P and comprising said abutment surface 111. The first metal part 110 may be in the form of one single, connected, metal body. The abutment surface 111 may be a surface of said first metal part 110, hence forming a single, connected surface.

The device 100 also comprises a second metal part 120, also generally extending in the main plane P and at a distance from the first metal part 110 as shown in Figures 1-5. The distance forms a gap 130, such as an open air gap, between the first 110 and second 120 metal parts, which gap 130 also generally extends in the main plane P. The gap 130 may be equidistant, or substantially equidistant, with respect to opposing surfaces of the first 110 and second 120 metal parts, or the distance between parts 110, 120 may vary across the main plane P. However, there is no direct physical contact between the first 110 and second 120 metal parts. Moreover, the device 100 comprises a peltier element 140, physically connecting the first 110 and second 120 metal parts. The peltier element 140 is arranged in said gap 130, and hence physically connects the first 110 and second 120 metal parts in said gap 130.

A peltier element 140 is an electric device which is known as such, and which is arranged to produce, such as using the Seebeck effect, an electrical voltage in the presence of a tem perature gradient between two connected bodies. Hence, the peltier element 140 is ar ranged to produce an electric voltage as a result of a temperature gradient between the first 110 and the second 120 metal parts. Also, the device 100 comprises a cooling flange 151, connected to the second metal part 120 on its side facing away from the first metal part 110.

The device 100 also comprises electric terminals 160, as well as electric conductors electri cally connecting the peltier element 140 to the terminals 160 and being arranged to provide said produced voltage on said terminals 160. The electric conductors may be simple electric cables, and may be comprised in or comprise the below-described circuitry 170. Such a device 100 provides for a very easy achievement of electric power in places without electric supply but with an available temperature gradient between a magnetic metal body and an environment 1. In particular, in district heating systems, inspection rooms and other spaces along the heat fluid pipework provide a lead metal pipe 10 with relatively higher temperature and a return metal pipe 13 with relatively lower temperature, achieving such an available temperature gradient. Hence, by simply placing the device 100 in said operating position magnetically attached to the metal lead pipe 11, a useful electric voltage is imme diately made available on said terminals 160. This is useful in many circumstances, as will be exemplified and described below.

In some embodiments, the first metal part 110 comprises the at least one magnet 114. For instance, the magnets 114 may be located in purpose-made spaces in some or each main plane P corner or main plane P end of the first metal part 110, as is illustrated with four separate magnets 114 in the Figures. Alternatively or additionally, one or several, such as at least two, magnets 114 may be positioned along a central length dimension L line, for instance along the below-described V-shape corner line. This provides for good pipe 20 ad hesion in a simple construction, in particular in case the first metal part 110 is provided with at least two, preferably exactly two, magnets, one in each extreme length dimension L end.

In a preferred embodiment, the terminals 160 are adapted for connecting an additional de vice 200, 300 of the same type as the device 100 in series or in parallel to the device 100 in question, whereby either the voltage or the current available on the terminals 160 in creases, as compared to when using only a single device 100, when the devices 100, 200, 300 in question are in said respective operating position and the said temperature gradient is present. This may be useful in the case where the currently available temperature gradi ent is not enough to produce a required voltage, using only one device 100, to power a particular piece of equipment, or when it is desired to operate equipment requiring a par ticular total current. Preferably, the said adaptation of the terminals 160 are specific for performing such connection between different devices 100, 200, 300, such as providing specifically designed quick-connector terminals for connecting several devices 100, 200, 300 either in series or in parallel, designed to prevent or make impossible erroneous connec tions. For instance, the terminals and/or quick-connectors may be colour-marked or de signed with male/female terminals so as to make possible only one type of connection. In some embodiments, the device 100 comprises circuitry 170 for producing a predeter mined fixed, or at least substantially fixed, voltage on the electric terminals 160 across an allowed temperature gradient interval, such as an interval which is 5-70°C wide. For in stance, absolute working temperatures of the device with respect to the first metal part 110 in the present invention may be around 50-120°C, and for the second metal part 120 around 20-50°C. For instance, an available voltage from the peltier element 140 of 0.4 V may be transformed up, such as by a step-up switch regulator, to a voltage of 5 V for powering a piece of electronic equipment, such as a battery, as described below.

The circuitry 170 and/or the peltier elements 140 may be arranged in a way not protected from moisture, such as without a moisture barrier present and specifically not moisture- protected according to any relevant moisture protection standard. For instance, the peltier elements 140 may be arranged fully exposed in the air of the gap 130, in a way such that water from the environment 1 can readily reach and wet the peltier elements 140. This is possible since the operating temperature of the peltier elements 14 when the device 100 is in said operating position on a lead distric heating pipe 10 in general is such that any such water will quickly evaporate and therefore not damage the peltier elements 140. This way, a simple construction can be achieved.

In some embodiments, the circuitry 170 may also be arranged with a separate encapsula- tion, arranged for being electrically connected to the device 100. In this case, it is preferred that such separately arranged encapsulation is water-protected, such as using a suitable IP classification (for instance IP65) depending on the circumstances.

In some embodiments, at least one, preferably both, of the first 110 and second 120 metal parts are made from a steel or, preferably, aluminium material, such as extruded or cast aluminium. Aluminium is preferred, since this metal has low emissivity while yet high reflectivity. As will be described below, such emissivity and reflectivity are important for maximizing the available temperature gradient. The first part 110 is most preferably made of non-magnetic material, such as aluminium, since this provides more freedom for placing the magnets 114.

Moreover, the first 110 and second 120 metal parts may be joined together using fastening means 180, such as screws. In order to prevent such fastening means 180 to form thermal bridges across the parts 110, 120, a thermally insulating isolating means 181 may be used, for instance a plastic insert, preventing the screw to directly contact one of the metal parts 110, 120. The peltier elements 140 may be held in place by the same fastening means 180, or be fastened by separate fastening means. It is important that good thermal contact is achieved between the peltier element 140 and both metal parts 110, 120, on either side of the peltier element 140. This can, for instance, be assured by the fastening means 180 being arranged to press the metal parts 110, 120 together while press-fitting the peltier elements 140 between them.

The second metal part 120 may be fastened to the below-described cooling part 150 in any suitable way, such as using screws (not shown in Figures) or thermally conducting glue. It is noted that a good thermal contact is advantageous between the second metal part 120 and the cooling part 150. Therefore, the type of fastening means used between parts 110, 120, preventing direct thermal contact between the connected parts, is not to be used between the second metal part 120 and the cooling part 150.

It is preferred that the abutment surface 111 of the first part 110 is at least 5 cm wide, in a direction L and/or W parallel to the metal pipe 10 abutment surface 11 in the operation position, and that the abutment surface 111 has an area of between 0.005 and 0.05 m².

Furthermore, the first metal part 110 preferably has a thickness of between 0.5 and 3 cm. The gap 130, and in particular an open air gap, is between 0.1 and 1.0 cm wide in a direction D (in the depth dimension) perpendicular to the main plane P. Preferably, the gap 130 is preferably at least 0.1 cm, more preferably at least 0.3 cm, across the entire opposing sur faces of the first 110 and second 120 metal parts.

Regarding the peltier elements 140, in some embodiments at least two discreet, series and/or parallel-connected peltier elements 140 are comprised in the gap 130 of the device 100, together with any cabling, which gap 130 is otherwise filled with air.

Preferably, the cooling flange 151 has at least one black surface 152 on sides not facing the metal pipe 10 abutment surface 11 when the device 100 is in said operating position. Hence, such black surface 152 generally faces away from the said surface 11, in the depth dimen sion D, when the device 100 is in said operating position. Preferably, all or substantially all surfaces 152 of the cooling flange 151, or even of the entire cooling part 150, facing away from the said pipe 10 abutment surface 11 when the device is in the operating position, are black. Such black surfaces 152 may be sooted or in any other suitable way blackened, such as using black paint. The black colour of these surfaces 152 maximizes thermal emission, efficiently cooling the cooling part 150, thereby achieving a stronger thermal gradient be tween the first 110 and second 120 metal parts since the cooling flange 151 and the cooling part 150 are thermally connected the second part 120 and the second part is thermally iso lated from the first part 110 as described above.

Similarly, it is preferred that the abutment surface 111 of the first part 110 is black, in order to maximize thermal absorption of thermal radiation emitted from the pipe 10.

As mentioned above, in certain embodiments such as the exemplifying one illustrated in Figures 1-5, the device 100 may further comprise a cooling part 150, in turn comprising said cooling flange 151.

As is shown in Figures 1-5, the cooling part 150 may extend further than the first 110 and second 120 parts in the main plane P, such as all along the first 110 and second parts 120 or only in one or more of different directions along the main plane P. In this case, it is pre ferred that an exposed surface 153 of the cooling part 150 facing towards the metal pipe 10 abutment surface 11 when the device 100 is in the operating position is a reflective surface. Such a reflective surface 153 may for instance be an exposed metal surface. Preferably, all or substantially all surfaces of the cooling part 150 visible from the pipe 10 when the device 100 is in its operating position on a straight pipe 10 are such reflective surfaces. This will minimize thermal absorption of thermal radiation from the pipe 10, thereby maximizing the thermal gradient or difference between the first 110 and second 120 metal parts.

In a similar manner, a respective side 115 of the first 110 metal part and a respective side 121 of the second metal part 120, which sides 115, 121 face each other in the said gap 130, are both respective reflective surfaces, such as exposed metal surfaces. This will minimize the effect of thermal radiation between the metal parts 110, 120, in turn maximizing the thermal difference or gradient between them.

The terms "low thermal reflectivity" and "high thermal reflectivity", as used herein, relate to a difference in surface properties of different surfaces. Hence, a surface having a "low thermal reflectivity" has a lower thermal reflectivity as compared to a surface having a "high thermal reflectivity". In particular, it is preferred that the high thermal reflectivity surfaces described herein are arranged to reflect at least twice as large a share of a typically consti tuted thermal radiation incident to the surface in question as compared to a low thermal reflectivity surface described herein.

Hence, instead of "low thermal reflectivity" and "high thermal reflectivity", respectively, the terms "comparatively low thermal reflectivity" and "comparatively high thermal reflectiv ity" can be used, where the "comparatively" term refers to a comparison between two dif- ferent surfaces.

As exemplified above, examples of high thermal reflectivity surfaces include exposed metal surfaces, that may be smooth or polished (reflective for visible light). Examples of low ther mal reflectivity surfaces include sooted or painted surfaces that may have matte or other- wise highly irregular surface textures. It is noted that the sum of thermal radiation reflectivity and the thermal radiation absorp tion for a particular surface is always 1. For high reflectivity surfaces, reflectivity values above 0.9 are preferred. For low reflectivity surfaces, reflectivity values of below 0.1 are preferred.

It is noted that the difference between different such surfaces may also be measured in thermal radiation reflectance, with similar results for the present purposes.

The flange 151 may as such be arranged in any suitable way for providing efficient cooling of the flange 151 in the relatively cooler air environment 1. The flange 151, and preferably the entire cooling part 150, may be manufactured from steel or aluminium. In one preferred embodiment, the cooling part 150 including its cooling flange 151, and possibly also the first 110 and/or second 120 metal parts, are made from extruded aluminium, which extrusion process forms cylindrical aluminium parts that are cut in suitable lengths (in the length di mension L) and fastened one to the other. The second part 120 may even be integrated in the same material body as the cooling part 150, and manufactured as an extruded alumin ium part. This way, a particularly efficient and low-cost production method can be achieved, while still providing a highly efficient device 100.

As illustrated in Figures 1-5, and in particular in Figures 3 and 5, the abutment surface 111 of the first part 110 is constituted by two flat surfaces 112 set at an angle 113 between them. The two flat surfaces 112 together form a cylindrical concave shape which is V-shaped in a cross-section taken perpendicularly to the main plane P, and in particular in a cross- section taken along the width W dimension. Hence, the two flat surfaces 112 may form between them a straight folding line forming the demarcation line between the differently- angled surfaces 112. The surfaces 112 themselves may be flat. Hence, the single, connected surface being on the first metal part 110 then comprises said two flat surfaces 112 as two surface parts.

Hence, the device 100 is then positioned on the pipe 10 abutment surface 11 with the said demarcation line oriented along a main direction of the pipe 10. This provides a way to be able to use one and the same device 100 for different pipes 10 with very varying diameter dimensions. For smaller-diameter pipes, such as the one illustrated in Figures 1-4, the pipe 10 abutment surface 11 will contact the device 100 abutment surface 111 along two contact lines, one such contact line running across each of said differently-angled surfaces 112. As the pipe 10 diameter grows, the contact lines will be more and more separated, until they are arranged on the respective extreme border of the said surfaces 112. As the pipe diam eter grows further from this point, there will still be two distinct contact lines between the abutment surfaces 11, 111, along the outside periphery of the respective surfaces 112. This way, a wide range of pipe diameters can be covered to provide efficient thermal connection between a particular device 100 in the said operating position on the pipe in question.

The present inventors have come to the conclusion that the angle 113 between the said surfaces 112 should be between 3° and 10°, preferably between 5° and 8°. The depth D dimension distance between the said demarcation line and the external periphery of the surfaces 112 (in other words, the depth of the said V-shape) should be between 1 and 10 mm, preferably between 2 and 5 mm. As an example, for a first part 110 width W of about 50 mm, a depth of about 3 mm is suitable.

Figure 7 illustrates a method according to the present invention for producing electricity from an available temperature gradient between the metal pipe 10, through which a warm fluid runs, and the cold gas environment 1, such as air.

In a first step, the method starts.

In a subsequent step, at least one device 100 of the above described type is provided.

In a subsequent step, the device 100 in question is arranged in the said operating position on the metal pipe 10 in question, with the abutment surface 111 of the first part 110 of the device 100 in question abutting the abutment surface 11 of the metal pipe 10, and the ter minals 160 of the device 100 are connected to an electricity-consuming apparatus 20. In preferred embodiments, the metal pipe 10 is a district heating pipe in a district heating system, while the said warm fluid is district heating heat medium, such as hot water. The pipe 10 is preferably a lead pipe, as opposed to a return pipe 13. The cold gas environment 1 may preferably be the air within a closed installation 2 which is a part of the district heat ing system. That the environment 1 is "cold" means that it is colder than the available tem perature from the pipe 10.

The return pipe 13 which may be present together with the lead pipe 10 in one and the same closed installation 2. That the installation 2 is "closed" is intended to mean that it is weather-protected to such an extent so that it can maintain a temperature of the environ ment 1 which may be different from an external temperature due to the presence of the pipes 10, 13 and the fluids transported therethrough.

The said air in the said environment 1 may of course be cooled by the fluid in the return pipe 13, which in general is cooler than the warm fluid in the lead pipe 10. However, the said air may also over time be cooled by an externally environmental air and/or ground in relation to the installation 2 in question. What is important is that the air in the said envi ronment 1 in the installation 2 is maintained at a cooler temperature than the pipe 10 on which the device 100 is used in the operating position.

In some embodiments, the electricity-consuming apparatus 20 may comprise a fan 22 for ventilating a closed space within said closed installation 2, such as an installation or inspec tion space in a district heating system. The closed space may be or comprise the environ ment 1 discussed above.

The electricity-consuming apparatus 20 may further comprise a battery 21, in which case the method may comprise feeding electricity from the device 100 to the battery 21 until the battery 21 is charged to a predetermined level, such as a fully charged level, and to operate the fan 22 using electricity from the device 100 only when the battery 21 is fully charged. This way, the fan 22 can be used as an energy sink when the battery 21 cannot receive more electric charge. The fan 22 may not need to be operated while the battery 21 is charging, in order to provide sufficient ventilation of the said space.

In additional embodiments, the electricity-consuming apparatus 20 may comprise a meas- urement equipment 23, such as a piece of equipment arranged to monitor the pipes 10, 13 and check for damages, stops or similar. In this and in other cases, the electricity-consuming apparatus 20 is completely powered using electrical energy provided by the device 100.

The electricity-consuming apparatus 20 may furthermore comprise a mobile telephone communication means 24, for delivering measurement data wirelessly to a remote server 30 for collection, storing and/or processing. In this case, the electricity-consuming appa ratus 20 may be electrically powered by the device 100 to perform measurements and to deliver corresponding measurement data to the remote server 30 using said mobile tele phone communication means 24. This way, a stationary or temporary pipework monitoring system may be easily installed and operated even in spaces where there is no grid-provided electricity available.

As discussed above, the method may further comprise providing at least two devices 100, 200, 300 of the above discussed type; arranging each of said devices 100, 200, 300 on the metal pipe 10 in question, or even on different available lead pipes 10 in said environment 1, one device 100, 200, 300 after the other along a main longitudinal direction of the metal pipe 10 in question, with the respective abutment surface 111 of each device abutting the metal pipe 10 in question as described above. Then, the devices 100, 200, 300 in question are connected to each other in parallel or series, depending on the required voltage and current, using their respective terminals 160, and then the terminals 150 of at least one of the devices 100, 200, 300 are connected to the electricity-consuming apparatus 20 in ques tion.

The method may furthermore comprise blackening the part ofthe pipe 10 abutment surface 11 that will abut the device 100 in question in its operating position, before the device 100 is positioned in said operating position on the pipe 10. This blackening may take place in any suitable manner, such as using black paint, and serves the purpose of maximizing ther mal radiation from the pipe 10 to the device 100, in turn maximizing the thermal gradient between the device 100 parts 110, 120 as discussed above. In yet another embodiment, the method may comprise providing the abutment surface 11 of the pipe 10 with a thermally conducting paste or other adhesive formulation, providing both good thermal connection between the pipe 10 and the device 100 and also adhesion between pipe 10 and the device 100. However, in other embodiments, no such adhesive formulation is required, since the magnets 114 provide sufficient adhesion, due to the com- bination of magnetically attractive force and surface friction between surfaces 11, 111, for the device 100 not to move after being positioned in the operating position on the pipe 10. For instance, the device 100 may be placed vertically on top of a horizontally running pipe 10. If such an adhesive formulation is used, it is preferred that it is arranged along the two direct contact lines forming between the differently-angled surfaces 112 and the pipe 10 abutment surface 11 as described above. Hence, the device 100 may contact the pipe 10 directly or indirectly, via the thermally conducting adhesive formulation.

Suitable adhesive formulations to use include, for instance, any conventional, commercially available thermal paste with high thermal conductivity. Such thermal pastes do not nor- mally dry or harden, but stay in paste/liquid form achieving a very thin, filling, thermal cou pling between the pipe 10 and the device 100.

In a subsequent step, the method ends. Above, preferred embodiments have been described. However, it is apparent to the skilled person that many modifications can be made to the disclosed embodiments without de parting from the basic idea of the invention.

For instance, the device 100 may include other features, in addition to the ones described above. I n general, all that has been said in connection to the method is equally applicable to the described device, and vice versa.

Furthermore, the cooling flange 151 can have any sha pe and form, as long as it acts as a n efficient heat sink, cooling the second metal part 120.

Hence, the invention is not limited to the described embodiments, but can be varied within the scope of the enclosed claims.

Claims

C L A I M S

1. Device (100) for providing electricity from an available temperature gradient between a metal pipe (10) through which a warm fluid runs and a cold gas environment (1), which device (100) has a main plane (P) of extension, wherein the device (100) comprises

a first metal part (110), generally extending in the main plane (P) and compris ing an abutment surface (111) arranged to be in physical contact with the metal pipe (10) when the device (100) is in an operating position;

a second metal part (120), generally extending in the main plane (P) and ar- ranged at a distance from the first metal part (110), forming a gap (130) between the first (110) and second (120) metal parts, which gap (130) also generally extends in the main plane (P);

a peltier element (140), connecting the first (110) and second (120) metal parts in said gap (130), and arranged to produce an electric voltage as a result of a temper- ature gradient between the first (110) and the second (120) metal parts;

a cooling flange (151), connected to the second metal part (120) on its side facing away from the first metal part (110);

electric terminals (160); and

electric conductors connecting the peltier element (140) and the terminals (160), and arranged to provide said voltage on said terminals (160),

c h a r a c t e r i s e d i n that the device (100) further comprises a magnet (114) arranged to be attracted to the metal pipe (10) and to hold the device (100) in place by surface friction between the device (100) and the metal pipe (10) when the device (100) is placed in said operating position, on the surface (11) of the metal pipe (10) and with physical contact between the metal pipe (10) and an abutment surface (111) of the device (100), and in that the abutment surface (111) is constituted by two flat surfaces (112) set at an angle (113) between them, together forming a cylindrical concave shape which is V-shaped in a cross-section taken perpendicularly to the main plane (P).

2. Device (100) according to claim 1, c h a r a c t e r i s e d i n that the first metal part (110) comprises the magnet (114).

3. Device (100) according to claim 1 or 2, c h a r a c t e r i s e d i n that the abutment surface (111) is a single, connected surface of the first metal part (110) compris ing said two flat surfaces (112) as two surface parts.

4. Device (100) according to any one of the preceding claims, c h a r a c t e r - i s e d i n that at least one, preferably both, of the first (110) and second (120) metal parts are made from a steel or aluminium material.

5. Device (100) according to any one of the preceding claims, c h a r a c t e r - i s e d i n that the abutment surface (111) is at least 5 cm wide, along a dimension (L) parallel to the metal pipe (10) abutment surface (111) in the operation position, and has an area of between 0.005 and 0.05 m².

6. Device (100) according to any one of the preceding claims, c h a r a c t e r - i s e d i n that the first part (110) has a thickness, in a depth dimension (D), of be tween 0.5 and 3 cm.

7. Device (100) according to any one of the preceding claims, c h a r a c t e r - i s e d i n that the abutment surface (111) comprises a straight folding line forming the demarcation line between the differently-angled surfaces (112).

8. Device (100) according to any one of the preceding claims, c h a r a c t e r - i s e d i n that the angle (113) is between 3° and 10°.

9. Device (100) according to claim 8, c h a r a c t e r i s e d i n that the angle (113) is between 5° and 8°.

10. Device (100) according to any one of the preceding claims, c h a r a c t e r - i s e d i n that a depth, perpendicularly to said main plane (P) of extension, of said V-shape is between 1 and 10 mm.

11. Device (100) according to claim 10, c h a r a c t e r i s e d i n that a depth, perpendicularly to said main plane (P) of extension, of said V-shape is between 2 and 5 mm.

12. Device (100) according to any one of the preceding claims, c h a r a c t e r - i s e d i n that the first metal part (110) has a cylindrical shape.

13. Method for producing electricity from an available temperature gradient between a metal pipe (10) through which a warm fluid runs and a cold gas environment (1), c h a r - a c t e r i s e d i n that the method comprises the method steps of

providing at least one device (100,200,300) according to any one of the pre ceding claims;

arranging the device (100,200,300) in question in an operating position on the metal pipe (10) with the abutment surface (111) abutting the metal pipe (10), and connect ing the terminals (160) of the device (100,200,300) to an electricity-consuming apparatus (20).

14. Method according to claim 13, c h a r a c t e r i s e d i n that the metal pipe (10) is a district heating pipe (10) in a district heating system, in that the warm fluid is district heating heat medium, in that the cold gas environment (1) is the air within a closed installation (2) which is a part of the district heating system, which air is cooled by an exter nally environmental air and/or ground in relation to the installation (2).

15. Method according to claim 14, c h a r a c t e r i s e d i n that the electric ity-consuming apparatus (20) comprises a fan (22) for ventilating a space within said closed installation (2).

16. Method according to claim 15, c h a r a c t e r i s e d i n that the electric ity-consuming apparatus (20) further comprises a battery (21), and in that the method com prises feeding electricity from the device (100,200,300) to the battery (21) until the battery (21) is charged to a predetermined level, and to operate the fan (22) using electricity from the device (100,200,300) once the battery (21) is fully charged.

17. Method according to any one of claims 13-16, c h a r a c t e r i s e d i n that the metal pipe (10) is a lead line in said district heating system.

18. Method according to any one of claims 13-17, c h a r a c t e r i s e d i n that the electricity-consuming apparatus (20) comprises a piece of measurement equip ment (23).

19. Method according to claim 18, c h a r a c t e r i s e d i n that the electric ity-consuming apparatus (20) comprises a mobile telephone communication means (24) for delivering measurement data to a remote server (30), in that the electricity-consuming ap paratus (20) is electrically powered by the device (100,200,300) to perform measurements and to deliver corresponding measurement data to the remote server (30) using said mobile telephone communication means (24).

20. Method according to any one of claims 13-19, c h a r a c t e r i s e d i n that the method comprises providing at least two devices (100,200,300) according to any one of claims 1-15, arranging each of said devices (100,200,300) on the metal pipe (10), one after the other along a main longitudinal direction of the metal pipe (10), with the respec tive abutment surface (111) abutting the metal pipe (10), connecting the devices (100,200,300) in question to each other in parallel or series using their respective terminals (160), and connecting the terminals (160) of the device (100,200,300) to the electricity-con suming apparatus (20).

21. Method according to any one of claims 13-20, c h a r a c t e r i s e d i n that the method further comprises blackening the part of the pipe (10) surface (11) that will abut the device (100,200,300) in question before the device (100,200,300) is positioned in said operating position.