GEOTHERMAL DEVICE AND METHOD

Description

FIELD OF THE INVENTION

[0001] The invention relates to a geothermal probe, an energy converter, a device and a method for generating electrical energy or for extracting heat from geothermal energy. TECHNICAL BACKGROUND

[0002] Geothermal systems are used for energy and / or heat generation. Such systems have an underground section with a geothermal probe. A working fluid circulates within the geothermal probe, which is heated and evaporated by the geothermal energy contained in the soil surrounding the geothermal probe. The evaporated working fluid is fed to an energy converter to generate electrical energy or heat. Existing geothermal probes typically have a circular cross-sectional area, limiting the thermal radiation or heat conduction of the rock or soil surrounding the geothermal probe.

[0003] Existing geothermal energy generation facilities often utilize energy converters with mechanically controlled pistons. Adapting to specific operating conditions to optimize efficiency is therefore not possible without complex modifications, which reduces the number of achievable operating hours per year.

[0004] WO 2015 / 159188 A2 discloses a system for extracting geothermal energy for both heating buildings and generating electrical energy.

[0005] DE 10 2008 029 400 A1 concerns the manufacture and application processes of heat exchangers for geothermal probes, geothermal and building collectors.

[0006] CH 706 507 A1 and DE 10 2008 049 731 A1 each disclose a coaxial geothermal probe and a method for installing such a geothermal probe in the subsurface.

[0007] JP 2002 013828 A relates to an underground heat exchanger and a method for installing the underground heat exchanger.

[0008] JP 2026 095100 A relates to a floor support and a building air conditioning system using the same.

[0009] US 2012 / 175077 A1 relates to a heat exchanger and a heat pump system with such a heat exchanger.

[0010] US 9,121,630 B1 discloses another heat exchanger for thermal energy.

[0011] KR 101 724 286 B1 concerns an underground heat exchange structure with a double pipe system for heat exchange. SUMMARY

[0012] It is an object of the invention to eliminate or at least mitigate the disadvantages of known geothermal probes, known energy converters, and known geothermal devices and methods. This object is achieved according to the invention by the subject matter of the independent patent claims.

[0013] Among other things, a geothermal probe, an energy converter, a device comprising at least one geothermal probe and at least one energy converter, and a method making use of a corresponding device are provided.

[0014] The geothermal probe comprises a coaxial pipe string. A working fluid flows through the coaxial pipe string, at least in part. At least part of the pipe string comprises or is made of a carbon fiber reinforced material. The carbon fiber reinforced material (carbon, carbon fibers, carbon fibers, CFRP) enables the coaxial pipe string to be lighter than conventional materials (e.g., steel). This advantageously reduces the requirements for the lowering mechanism used to lower the pipe string into the borehole.

[0015] Carbon fibers also have a very low thermal conductivity of 17 W / mK. Therefore, heat loss can be advantageously reduced and insulation properties improved.

[0016] The coaxial pipe string can comprise at least one section having a star-shaped cross-sectional area with rounded points and depressions. In particular, an outer contour of the pipe string can have the described shape. The outer contour of the pipe string can also comprise another shape that has an effectively enlarged outer surface compared to a circular shape. The outer contour of this section can essentially correspond to a star shape with at least three points (protrusions), wherein the points and the depressions (indentations) of the star arranged between the points are rounded. The star shape can advantageously also comprise more points and depressions, in particular five points, further in particular seven points, further in particular nine points, further in particular substantially eight points. The heat output absorbed by this section of the pipe string depends proportionally on the outer surface of the section of the pipe string.Since the star shape causes an enlargement of the outer surface of the section of the pipe string, the heat output absorbed by this section of the pipe string can therefore be advantageously increased compared to a conventional shape (e.g. a circular shape).

[0017] The coaxial pipe string comprises at least a first section and a second section. The first section is arranged substantially vertically and comprises the carbon fiber reinforced material. The second section is arranged substantially horizontally. The working fluid is filled into the coaxial pipe string near the earth's surface at a first temperature. The temperature of the working fluid then increases continuously on its way to the end of the pipe string. At the end, the working fluid has a second temperature which is higher than the first temperature. The working fluid should then maintain the second temperature as constant as possible on its way back near the earth's surface. Therefore, a change in the temperature of the working fluid in the first section of the coaxial pipe string, which extends in a substantially vertical direction from the starting point near the earth's surface, is undesirable.Since the first section of the coaxial pipe string comprises the carbon fiber-reinforced material or can be made essentially of it, this section advantageously exhibits particularly good thermal insulation properties. This advantageously prevents or at least reduces a temperature reduction of the returning working fluid compared to other materials. This means that a change in the temperature of the working fluid can be advantageously prevented or at least reduced compared to conventional pipe strings made of other materials.

[0018] The first section of the pipe string has a length of more than 3000 m, more particularly more than 5000 m. The second section of the pipe string can be arranged at a depth of at least 1000 m, more particularly more than 3000 m, more particularly more than 5000 m, more particularly substantially 6000 m or more. The second section has a length of more than 2000 m, more particularly substantially 3000 m or more.

[0019] The first section and the second section of the coaxial pipe string are connected by a third section of the coaxial pipe string arranged therebetween, which has a bend. The radius of the curvature of the third section is at least 50 m, in particular 100 m, more particularly 200 m, more particularly 400 m, more particularly at least 600 m or more. The curved third section of the pipe string advantageously enables a continuous connection of the first section to the second section, although a longitudinal axis of the first (vertical) section can enclose an angle of more than 20°, in particular more than 40°, more particularly more than 60°, more particularly more than 80°, more particularly substantially 90°, with a longitudinal axis of the second (horizontal) section.

[0020] The coaxial pipe string comprises at least one central riser and a coaxially arranged downpipe. The downpipe can surround the riser. An annular gap is arranged between the riser and the downpipe. The distance between the riser and the downpipe is ensured by spacers. The downpipe is fluidly connected to the coaxially arranged riser at the lower end of the pipe string through several overflow openings. The opening cross-section of the overflow openings is smaller than the cross-sectional area of ​​the riser. This ensures that the evaporated working medium always spreads in the direction of flow and does not re-enter the downpipe. The overflow openings are arranged circumferentially on the riser. The overflow openings can be rounded to reduce flow resistance. The downpipe can be at least partially filled with the working medium, which can be in liquid form in at least part of the downpipe.The working fluid can then be continuously heated on its way to the end section of the pipe string by the geothermal energy of the earth surrounding the pipe string. In particular, the working fluid can be heated to such an extreme that it evaporates. The working fluid can be present as a gas in at least part of the riser pipe. The coaxial arrangement of the riser pipe and downpipe enables a compact design of the pipe string, advantageously requiring only a single borehole.

[0021] The pipe string can comprise the star-shaped cross-sectional area with rounded points and depressions in the second section, i.e., particularly in the horizontally arranged section of the pipe string. The coaxially arranged downpipe can comprise an outer contour corresponding to the star shape and a circular inner contour. The riser pipe arranged centrally in the coaxial pipe string can comprise a circular outer contour, with the diameter of the riser pipe being reduced compared to the inner diameter of the downpipe, thus creating an annular gap between the two.

[0022] The downpipe and / or the riser pipe each comprise at least two interconnected pipe sections. The pipe sections can have a length of substantially 12 m. The transitions between the downpipe pipe sections can be offset from the transitions between the riser pipe sections. This advantageously simplifies assembly. The pipe sections can be connected to each other in a gas- and / or liquid-tight manner.

[0023] At least a portion of the pipe string and / or the downpipe and / or the riser pipe may have a coating. The coating may comprise at least one of a corrosion protection layer, a thermal insulation layer, a mirror coating, and a DLC ("diamond-like carbon") layer. This may improve thermal insulation and / or anti-corrosion resistance and / or resistance during assembly (when the inner pipe is inserted into the outer pipe) and / or resistance to the working fluid circulating in the pipe string.

[0024] The working medium can contain at least one compound suitable as a refrigerant or consist of one or more such compounds. In particular, the working medium can comprise water and additives. The additives can include corrosion inhibitors. The additives can be configured to advantageously increase the heat capacity of the working medium. The additives can give the working medium a higher boiling point than water, preventing it from evaporating prematurely in the downpipe. The working medium and the pipe string can be configured to create different hydrostatic pressures in the downpipe and the riser. This pressure difference can advantageously cause the working medium to circulate independently in the pipe string. Optionally, the circulation of the working medium can be assisted by a pump or compressor.

[0025] The pipe string can be sealed from the borehole and / or the soil surrounding the borehole. At least part of the pipe string and / or the downpipe and / or the riser pipe can be designed as a double-walled pipe.

[0026] The annular gap can comprise a thermal insulation material in at least one section. The annular gap can comprise a vacuum in at least one section to insulate the riser pipe from the downpipe. The downpipe can be designed as a thermally insulating pipe in at least one section, particularly a section close to the surface, to advantageously prevent or reduce cooling of the recirculated working medium.

[0027] The pipe string and the working medium can be configured such that the working medium at the lower end (end piece, base piece), in the region of the fluidic connection between the downpipe and the riser pipe, has a temperature of more than 100°C, in particular more than 120°C, in particular more than 140°C, in particular more than 160°C, in particular substantially 170°C or higher. The pipe string can also be configured such that, in particular through the various thermal insulation measures, the working medium at the upper end (starting piece, head piece) of the riser pipe near the earth's surface has a temperature of more than 60°C, in particular more than 80°C, in particular more than 100°C, in particular more than 120°C, in particular substantially 130°C or higher.

[0028] The geothermal probe or pipe string can have a constant outer diameter. The pipe string can be configured such that the riser pipe and / or the downpipe each have a constant diameter.

[0029] The geothermal probe can be arranged floatingly within the borehole. A substance, such as water, can be contained within the borehole. This substance can enable the pipe string lowered into the borehole to exert buoyancy forces as it penetrates the substance. This can advantageously reduce the weight to be supported during the lowering process of the pipe string. The substance in the borehole can also contribute to the stability of the borehole, as it can exert a counterforce to the forces acting on the borehole (e.g., from the surrounding soil).

[0030] The geothermal probe can comprise a headpiece having multiple inlets and / or outlets. The inlets and / or outlets can be arranged circumferentially on the headpiece. The inlets and / or outlets, or the transitions to the coaxially arranged downpipe and / or the central riser pipe, can be designed to optimize flow. The transitions can be rounded. The total opening area of ​​the outlets can be larger than the cross-sectional area of ​​the riser pipe.

[0031] The energy converter can comprise a heat exchanger. The energy converter can also comprise an expansion machine (piston machine). The energy converter can also consist essentially of an expansion machine. The heat exchanger can comprise a first and a second working medium that exchange heat. The working medium, which is arranged in a geothermal probe of the type described above, can be the first working medium of the heat exchanger. The second working medium can have a low boiling point, in particular a lower boiling point than water, so that a high vapor pressure can be achieved at relatively low temperatures. The second working medium of the heat exchanger can comprise carbon dioxide and, if appropriate, additives. The expansion machine can comprise at least one cylinder with a movably mounted piston. The piston can be movable by the second working medium.The moving piston can advantageously drive a generator to generate electrical energy. Optionally, the generator or the mechanical connection between the piston and generator can include a gearbox.

[0032] This means that the first working medium is poured into the downpipe of the pipe string in cold liquid form. The first working medium can then be continuously heated on its way to the lower end of the pipe string. If the boiling point is exceeded, the first working medium evaporates. At the lowest end of the pipe string, the first working medium is discharged through the riser pipe towards the heat exchanger. In the heat exchanger, the first working medium transfers its heat to the second working medium, which is also in the heat exchanger, and is thereby cooled. The temperature of the first working medium can thereby drop by approximately 30°C. Several such heat exchangers can be arranged in parallel and / or in cascade (series). Each of the heat exchangers can cause the temperature of the first working medium to drop by approximately 30°C.In particular, so many heat exchangers can be provided that the temperature of the first heat exchanger drops to substantially 0°C or below. The first working medium is then filled into the downpipe of the pipe string. The second working medium is heated by the first working medium in the heat exchanger, in particular to a temperature of substantially 30°C. The second working medium can be heated in the heat exchanger such that it evaporates. This can create a pressure of more than 20 bar, in particular more than 40 bar, furthermore in particular more than 50 bar, furthermore in particular more than 60 bar, furthermore in particular substantially 70 bar. The evaporated second working medium can then be fed to the expansion machine and admitted into a cylinder chamber through an electronic inlet. Due to the pressure, the second working medium can then move a piston located in the cylinder.The movement of the piston can increase the volume occupied by the second working medium. This expansion can cause the temperature and pressure of the second working medium to decrease. The second working medium can be removed from the cylinder chamber by means of an electronic outlet, wherein it can have a residual pressure of more than 5 bar, in particular more than 10 bar, furthermore in particular more than 20 bar, furthermore in particular more than 30 bar, furthermore in particular substantially 34 bar. The temperature of the second working medium can have decreased to substantially 0°C. The second working medium can also be expanded in the expansion machine to such an extent that it has a temperature of less than 0°C. The second working medium can then be fed back into the heat exchanger.

[0033] Within the heat exchanger, the circuits of the first and second working medium are separated from each other in such a way that the working media do not contaminate each other (hermetic separation).

[0034] The energy converter can comprise a fully electronic engine control system. The fully electronic engine control system can be configured to control an electronic intake and an electronic exhaust of the cylinder. The fully electronic engine control system can also be configured to be able to determine a travel distance of the piston. The engine control system can be configured to provide control signals (e.g., switching times) based on which valves release the electronic intake and / or the electronic exhaust of the cylinder. The fully electronic engine control system makes it possible to improve the precision of the control of the valves at the electronic intake and / or the electronic exhaust. For example, shorter switching times can advantageously be realized. Furthermore, a mechanical connection (e.g., by means of a camshaft) can be avoided.Since the working medium is under very high pressure, precise control of the electronic inlet and / or the electronic outlet is particularly advantageous in order to achieve high efficiency.

[0035] The cylinder and / or piston may be coated to improve sliding properties. For example, they may include a DLC ("diamond-like carbon") coating to reduce friction between the moving surfaces.

[0036] The energy converter can be configured to use magnetism to prevent the piston from coming to a standstill as a result of a critical operating condition of the piston. The piston can come to a standstill if there is only an insufficient pressure difference between the electronic inlet and the cylinder chamber or between the cylinder chamber and the electronic outlet. In general, the pressure difference between the electronic inlet and the electronic outlet of the expansion machine can be ensured by an expansion valve. In addition, to prevent a critical operating condition, the energy converter can comprise at least one pair of cooperating corresponding magnets. For example, the piston can be mechanically connected to a crankshaft. The crankshaft can comprise a flywheel on which a first magnet is arranged. A second magnet can be arranged on a housing part of the energy converter or the expansion machine.The magnets can interact in such a way that the movement of the crankshaft and / or the piston is supported, thus advantageously preventing an unintentional stoppage of the piston. The fully electronic engine control system can be configured to support this safety mechanism, e.g., by variable valve switching times.

[0037] The second working medium can be heated within the heat exchanger and cooled in the expansion machine by performing work on the piston, and a travel distance of the piston can be configured such that an average piston pressure is at least 30 bar, in particular wherein the average piston pressure is at least 40 bar, further in particular wherein the average piston pressure is at least 50 bar, further in particular wherein the average piston pressure is substantially 52 bar. The high average piston pressure can be determined in particular by the choice of working medium and the achievable vapor pressure. As a result, the useful power, the torque, and the achievable efficiency of the energy converter configured in this way can be advantageously increased compared to a conventional internal combustion engine.

[0038] The piston can have at least one closed piston ring. The piston can also have a plurality of closed piston rings. The piston can also have exclusively closed piston rings. Alternatively, the piston, in particular an outer running surface of the piston, can be adapted to the cylinder, in particular an inner running surface of the cylinder corresponding to the running surface of the piston, in such a way that the piston does not require a piston ring. Both measures advantageously make it possible to reduce the losses that would be caused by the escape of at least a portion of the second working medium. Both measures support the realization of the effectively very high pressures of the second working medium, or the average piston pressure, in the cylinder chamber. Therefore, the efficiency of the expansion machine can be advantageously improved.

[0039] The energy converter can comprise multiple heat exchangers. The expansion machine can comprise multiple cylinders and pistons movably arranged therein. The expansion machine can also be a multiple expansion machine with multiple cylinders.

[0040] The device for generating electrical energy or for extracting heat from geothermal energy can comprise at least one geothermal probe and at least one energy converter. The device can comprise a plurality of geothermal probes of the type described, in particular more than 3, furthermore in particular more than 5, furthermore in particular more than 7, furthermore in particular more than 10, furthermore in particular more than 15, furthermore in particular more than 20. The device can also comprise a plurality of energy converters.

[0041] The method for generating electrical energy or for extracting heat from geothermal energy can comprise a device and / or a geothermal probe and / or an energy converter of the type described above. According to the method, a first working medium can be heated and evaporated using geothermal energy with the aid of a geothermal probe. The first working medium can transfer the energy thus obtained to a second working medium, different from the first working medium, by means of a heat exchanger, and heat this second working medium. The second working medium can be used to perform work on the piston of an expansion machine, whereby electrical energy can be generated due to the piston movement. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Fig. 1 shows a simplified schematic representation of a geothermal probe, Fig. 2shows a simplified schematic cross-sectional view of the end piece (foot piece) of the pipe string, Fig. 3 shows a simplified schematic cross-sectional view of a section of the pipe string, Fig. 4 shows a simplified schematic representation of a device according to the invention, Fig. 5 shows a simplified schematic representation of a device according to the invention, Fig. 6 shows a simplified schematic representation of the head piece of the geothermal probe. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] Figure 1 shows a simplified schematic representation of a geothermal probe 10. The head piece (starting piece) 14 of the geothermal probe 10 is attached to the earth's surface 12. Starting from the earth's surface 12, a first section A1 of the geothermal probe 10 extends in a substantially vertical direction over a length L1.

[0044] Adjacent to the first section A1, the geothermal probe 10 comprises a second section A2. The second section A2 has a curve. The radius of the curve of the second section A2 is at least 600 m. Due to the curve, the second section A2 has a length L2 along the vertical direction. The sum of the lengths L1 and L2 can be at least 100 m, in particular more than 500 m, furthermore in particular more than 2000 m, furthermore in particular more than 4000 m, furthermore in particular between 5000 m and 6000 m or more. The enlarged illustration in section 16 shows the flow directions of the working medium within the pipe string in the first and second sections A1, A2. The pipe string comprises a central riser pipe 20 and a coaxially arranged downpipe 22.

[0045] In particular, the first section A1 and / or the second section A2 of the pipe string can comprise or be made of a carbon fiber reinforced material. In the first and second sections A1, A2, the average temperatures of the working medium in the riser pipe 20 are significantly different from the average temperatures of the working medium in the downpipe 22. Therefore, particularly good thermal insulation is advantageous in the first and second sections A1, A2. Carbon fiber reinforced material has significantly improved thermal insulation properties (e.g., compared to steel). This can prevent or at least reduce heat loss from the recirculated working medium, thus increasing the efficiency of the process. Furthermore, the weight of these sections can be reduced using the carbon fiber reinforced material.

[0046] The geothermal probe 10 comprises a third section A3 adjoining the second section A2. The third section A3 is arranged essentially horizontally. The third section A3 has a horizontal length L4. The pipe string extends relative to the head piece 14 of the geothermal probe 10 in the horizontal direction over a length L3. Since the second section A2 has a curve, the length L3 is greater than the length L4. The length L3 can be at least 100 m, in particular more than 500 m, furthermore in particular more than 1000 m, furthermore in particular more than 2000 m, furthermore in particular essentially 3000 m or more. The horizontal extension of the pipe string is particularly advantageous since the temperature of the surrounding ground increases with increasing distance from the earth's surface 12.The horizontal arrangement of the third section A3 of the pipe string ensures sufficient heat input from the surrounding soil into the pipe string to sufficiently heat the working fluid so that it evaporates and reaches the desired temperature. The evaporated working fluid is then returned through the riser pipe 20.

[0047] The enlarged view in section 18 shows the end piece (foot piece) 40 of the pipe string. The downpipe 22, arranged coaxially around the riser pipe 20, is fluidically connected to the riser pipe 20. As a result, the flow direction is reversed in the region of the end piece 40 of the pipe string as soon as the working medium enters the riser pipe 20 from the downpipe 22.

[0048] Figure 2shows a simplified schematic cross-sectional representation of the end piece 40 of the pipe string. The end piece 40 of the pipe string has circular symmetry, which is indicated by the dash-dot line 42. The end piece 40 also has a chamfered base plate 44. The base plate 44 facilitates the insertion of the pipe string into the borehole. The end piece 40 has a plurality of overflow openings 24 near the base plate 44, through which the downpipe 22 is fluidly connected to the riser pipe 20. The overflow openings 24 are arranged circumferentially on the riser pipe 20 in a flow-optimized manner. The overflow openings 24 can be rounded to reduce flow resistance. A total opening area of ​​the overflow openings 24 can be smaller than a cross-sectional area of ​​the riser pipe 20. This allows the working medium to enter the downpipe 22 into the riser pipe 20. The pipe string has an annular gap 26 between the riser pipe 20 and the downpipe 22.Within the annular gap 26, the tubing string can provide spacers to ensure the coaxial arrangement of the downpipe 22 around the riser pipe 20. On the outside, the downpipe 22 has a double wall 28. The double wall 28 can be designed to prevent leakage of the working medium from the tubing string into the borehole. The annular gap 26 ensures the thermal insulation of the riser pipe 20 from the downpipe 22. To further improve the thermal insulation, the annular gap 26 can have additional thermal insulation materials and / or corresponding coatings. In particular, the surfaces of the annular gap 26, the riser pipe 20, the downpipe 22, and the double wall 28 can be coated and / or mirrored.

[0049] Figure 3shows a simplified schematic cross-sectional view of the pipe string in the third section A3. The riser pipe 20 has a circular outer cross-sectional contour 20a. The downpipe 22 is arranged coaxially to the riser pipe 20 and has a corresponding circular inner cross-sectional contour 22a. The annular gap 26 extends between the inner cross-sectional contour 22a of the downpipe 22 and the outer cross-sectional contour 20a of the riser pipe 20. The outer cross-sectional contour 22b of the downpipe 22 corresponds to a star shape with rounded points (protrusions) 66 and depressions (indentations) 68. The outer wall, corresponding to the outer cross-sectional contour 22b of the downpipe 22, forms the inner wall 62 of the double wall 28. The double wall 28 also comprises an outer wall 64 whose shape corresponds to the inner wall 62, so that the inner wall 62 and the outer wall 64 are at a constant distance from one another. Due to the special shape of the double wall 28 orThe outer cross-sectional contour 22b of the downpipe 22 effectively increases the outer surface of the pipe string in this section enormously. Since heat conduction between two bodies having different temperatures depends on the effective surface through which the heat flow takes place, heat conduction from the soil surrounding the pipe string into the pipe string can be increased. Therefore, the shape of the outer cross-sectional contour 22b of the downpipe 22 improves the heating of the working fluid using the geothermal energy provided by the soil. On the other hand, it is desirable that heat conduction between the downpipe 22 and the riser 20 be as low as possible so that the working fluid, once heated, maintains its temperature as constant as possible until it is used at the earth's surface 12. Therefore, changing the shape of the inner cross-sectional contour 22a of the downpipe 22 would be counterproductive.The outer cross-sectional contour 22b can of course also have other shapes with effectively enlarged outer surfaces (compared to circular outer contours).

[0050] Figure 4shows a simplified schematic representation of a device 100 for generating electrical energy from geothermal energy. It shows the geothermal probe 10 with the borehole 19 and the pipe string comprising the riser pipe 20 and the downpipe 22. The working fluid heated in the geothermal probe 10 is fed to a circulation pump 105 via the supply line 102. The first working fluid is then fed to the (first) heat exchanger 110. In the heat exchanger 110, the heat of the working fluid of the geothermal probe 10 is used to heat a second working fluid that is used in the energy converter 106. The heat exchanger 110 can be configured to extract heat from the first working fluid in such a way that the temperature of the first working fluid is reduced by substantially approximately 30°C. The device 100 can also comprise a plurality of heat exchangers 110, which can be designed correspondingly.The multiple heat exchangers can be arranged in parallel or cascaded (one after the other). The number of heat exchangers can be such that the first working medium has a temperature of substantially 0°C or below after passing through all heat exchangers.

[0051] The first working fluid of the geothermal probe 10 can then be temporarily stored in a reservoir 124. The reservoir 124 can be used to control the amount of working fluid in the geothermal probe 10. From the reservoir 124, the first working fluid is then fed back to the geothermal probe 10 via the supply line 104.

[0052] The second working medium heated in the first heat exchanger 110 can be fed to a dryer 112 to remove any residual moisture still contained in the second working medium. The second working medium can then be fed to a speed controller (throttle) 114. The speed controller 114 can influence the flow rate of the second working medium. The second working medium is then fed to the expansion valve 115. The expansion valve 115 comprises a high-pressure side 115a and a low-pressure side 115b. Starting from the high-pressure side 115a of the expansion valve 115, the second working medium is then fed to the expansion machine 116 (piston machine). The expansion machine 116 comprises an electronic inlet 116a and an electronic outlet 116b. The energy converter 106 also comprises a fully electronic motor control 118.The fully electronic engine control unit 118 provides control signals for the electronic inlet 116a and the electronic outlet 116b. The fully electronic engine control unit 118 can also be configured to provide control signals such that a working travel of the piston can be varied. The electronic inlet 116a and the electronic outlet 116b each comprise a valve by means of which the second working medium can be supplied to at least one cylinder in the expansion machine 116 or by means of which the second working medium can be removed from the cylinder. The second working medium is supplied to at least one cylinder of the expansion machine 116 at an initially relatively high pressure.Within the cylinder, the second working fluid performs work on a piston, increasing the volume occupied by this portion of the second working fluid, causing the pressure of this portion of the second working fluid to drop and cool. The "used portion" of the second working fluid is then discharged through the electronic outlet 116b of the expansion machine 116. From the electronic outlet 116b, the second working fluid is fed to the low-pressure side 115b of the expansion valve 115. The second working fluid can then be temporarily stored in a reservoir 117. From the reservoir 117, it is fed back to the first heat exchanger 110 for reheating.

[0053] If the pressure at the electronic inlet 116a and the electronic outlet 116b is equal, the piston can come to a standstill within a cylinder of the expansion engine 116. The expansion valve 115 ensures a pressure difference between the electronic inlet 116a and the electronic outlet 116b of the expansion engine 116. Additionally, the crankshaft, to which the piston of the expansion engine 116 is coupled, can provide a flywheel that, using corresponding magnets, can support the movement of the piston beyond such a critical point. The magnets can be neodymium magnets.

[0054] The expansion machine 116 is coupled to a generator 120 via a corresponding coupling. The generator 120 is configured to generate electrical energy based on the coupling, which is mechanically driven by the cylinder movement of the expansion machine 116. The electrical energy can be supplied to a transformer 122 and subsequently used in a conventional power grid (high-voltage grid). The generator 120 and / or the transformer 122 can be components of the energy converter 106. The fully electronic engine control 118 can also be configured to receive control signals from the dryer 112, the speed controller 114, the expansion valve 115, the generator 120, and / or the accumulator 117 and to adapt the control signals output accordingly.In particular, the fully electronic engine control 118 can be configured to ensure the pressure difference between the electronic inlet 116a and the electronic outlet 116b based on the control signals.

[0055] The dryer 112, the speed controller 114, the expansion valve 115, the accumulator 117, the fully electronic engine control 118, the generator 120, the accumulator 124 and the second heat exchanger 126 are optional components of the device 100.

[0056] According to the invention, the working medium of the geothermal probe 10 is water, to which additives may be added. According to the invention, the second working medium used in the energy converter 106 is carbon dioxide, to which additives may be added.

[0057] Figure 5shows a simplified schematic representation of a device 100 for generating heat from geothermal energy. The device 100 essentially corresponds to the device shown in Fig. 4 shown embodiment. However, instead of an energy converter 106 or an expansion machine 116, the device 100 comprises a (second) possibly differently designed heat exchanger 126. The first working medium of the geothermal probe 10 is fed from the circulation pump 105 to the heat exchanger 126. There, the heat of the working medium can be used to heat a suitable energy carrier, which is fed from the heat exchanger 126 to the district heating network 128. Thus, the device 100 enables the generation of both electrical and thermal energy.

[0058] Figure 6shows a simplified schematic representation of the headpiece (starting piece) 14 of the geothermal probe 10. The headpiece 14 comprises a plurality of outlets 15 through which the heated working medium can escape from the central riser pipe 20 of the geothermal probe 10. The plurality of outlets 15 are arranged circumferentially on the headpiece 14 and thus enable flow-optimized escape of the working medium. The transitions from the riser pipe 20 to the outlets 15 can be rounded to reduce flow resistance. A total cross-sectional area of ​​the outlets 15 can be larger than a cross-sectional area of ​​the riser pipe 20. The outlets 15 are coupled to the supply line 102. The head piece 14 can comprise at least two outlets 15, in particular also three outlets 15, further in particular four outlets 15, further in particular six outlets 15 or more.

[0059] The headpiece 14 also includes a plurality of inlets 17 through which the (cold or cooled) working medium can enter the coaxially arranged downpipe 22 of the geothermal probe 10. The plurality of inlets 17 are arranged circumferentially on the headpiece 14 and thus enable flow-optimized introduction of the working medium. The transitions from the inlets 17 to the coaxially arranged downpipe 22 can be rounded to reduce flow resistance. The inlets 17 are coupled to the supply line 104. The headpiece 14 can include at least two inlets 17, in particular three inlets 17, further in particular four inlets 17, further in particular six inlets 17 or more.

Claims

1. Geothermal probe (10) comprising a coaxial pipe string, wherein the coaxial pipe string is at least partially flowed through by a working medium, and wherein at least part of the pipe string comprises a carbon fibre reinforced material, wherein the coaxial pipe string comprises at least a first section (A1) and a second section (A3), wherein the first section (A1) is arranged substantially vertically and comprises the carbon fibre reinforced material, and wherein the second section (A3) is arranged substantially horizontally, wherein the first section (A1) of the pipe string comprises a length of more than 3000 metres and the second section (A3) comprises a length of more than 2000 metres, wherein the first section (A1) and the second section (A3) of the coaxial pipe string are connected by a third section (A2) of the coaxial pipe string arranged therebetween and comprising a bend, wherein the bend has a radius of at least 50 metres, wherein the coaxial pipe string comprises a central rising pipe (20) and a coaxially arranged downpipe (22), wherein an annular gap (26) is arranged between the rising pipe (20) and the downpipe (22), which annular gap comprises, at least in one section, a thermal insulation material or a vacuum which insulates the rising pipe (20) from the downpipe (22), wherein spacers are provided within the annular gap (26) to maintain the coaxial arrangement of the downpipe (22) around the rising pipe (20), wherein the downpipe (22) and the rising pipe (20) are fluidically connected at a bottom end of the pipe string by a plurality of overflow openings (24), wherein the overflow openings (24) are arranged circumferentially on the rising pipe (20) and comprise a total opening area which is smaller than a cross-sectional area of the rising pipe (20).

2. Geothermal probe (10) according to claim 1, wherein the coaxial pipe string comprises at least one section comprising a star-shaped cross-sectional area with rounded prongs (66) and sinks (68).

3. Geothermal probe (10) according to any one of the preceding claims, further comprising a head piece (14) comprising a plurality of outlets (15) arranged circumferentially on the head piece (15) and having a total opening area larger than a cross-sectional area of the rising pipe (22).

4. Geothermal probe (10) according to any one of the preceding claims, wherein the geothermal probe (10) is arranged in a borehole (19) and is suspended therein.

5. Device (100) for generating electrical energy or for obtaining heat from geothermal energy, comprising at least one geothermal probe (10) according to any one of claims 1 to 4 and an energy converter (106).

6. Device (100) according to claim 5, wherein the energy converter (106) comprises at least one heat exchanger (110) and at least one expansion machine (116), wherein the heat exchanger (110) is flowed through by a first and a second working medium, wherein the expansion machine (116) comprises at least one cylinder with a movably mounted piston, wherein the piston is moved by the second working medium.

7. Device (100) according to claim 6, wherein the energy converter (106) comprises a fully electronic motor control (118), wherein the fully electronic motor control (118) is at least configured to control an electronic inlet (116a) and an electronic outlet (116b) of the cylinder.

8. Device (100) according to any one of claims 6 to 7, wherein the energy converter (106) is configured to prevent the piston from coming to a standstill as a result of a critical operating state of the piston by means of magnetism.

9. Device (100) according to any one of claims 6 to 8, wherein the second working medium is heated within the heat exchanger (110) and cooled in the expansion machine (116) by performing work on the piston, and a travel distance of the piston is configured such that a mean piston pressure is at least 30 bar.

10. Device (100) according to any one of claims 6 to 9, wherein the piston comprises at least one closed piston ring or wherein the piston is adapted to the cylinder such that the piston does not comprise a piston ring.

11. Device (100) according to any one of claims 6 to 10, wherein the second working medium comprises carbon dioxide.

12. Method for generating electrical energy or for obtaining heat from geothermal energy using a device (100) according to any one of claims 5 to 11.