Method of handling energy, and energy handling system

Abstract

A method of handling energy, the method comprising heating (S16) water (18) in a tank (16a) to a temperature (112) of at least 100 °C while keeping a pressure in the tank (16a) amounting at least to a saturation pressure (114) of the water (18) at each temperature (112) of the water (18) to maintain the water (18) in liquid state (20); and conducting (S18) the water (18) in liquid state (20) and with a temperature (112) of at least 100 °C from the tank (16a) to a primary turbine (26) to thereby drive the primary turbine (26). An energy handling system (10a; 10b) is also provided.

Description

[0001] METHOD OF HANDLING ENERGY, AND ENERGY HANDLING SYSTEM

[0002] Technical Field

[0003] The present disclosure generally relates to energy storages using water. In particular, a method of handling energy and an energy handling system are provided.

[0004] Background

[0005] Steam turbines are commonly used to generate electric energy from thermal energy. For a system comprising a steam turbine, the efficiency may be about 30 %. That is, the produced electric energy only amounts to about 30 % of the input thermal energy.

[0006] Summary

[0007] One object of the invention is to provide an improved method of handling energy.

[0008] A further object of the invention is to provide an improved energy handling system.

[0009] These objects are achieved by the method according to appended claim 1 and by the energy handling system according to appended claim 12.

[0010] The invention is based on the realization that by heating water in a tank to a temperature of at least 100 °C while maintaining a sufficient pressure in the tank such that the water is prevented from evaporating, high amounts of energy can be efficiently stored in the tank and a thermal expansion of the water enables higher amounts of energy to be generated by a primary turbine for a given mass of water in comparison with the given mass of water at a temperature below 100 °C. According to a first aspect, there is provided a method of handling energy, the method comprising heating water in a tank to a temperature of at least 100 °C while keeping a pressure in the tank amounting at least to a saturation pressure of the water at each temperature of the water to maintain the water in liquid state; and conducting the water in liquid state and with a temperature of at least 100 °C from the tank to a primary turbine to thereby drive the primary turbine.

[0011] When water is heated under a pressure amounting at least to a saturation pressure at the current temperature of the water, the water can be heated in liquid state to a temperature of approximately 372 °C. At this temperature, the water becomes supercritical at a saturation pressure of at least 220 bar. The water in the tank is heated under pressure, where the pressure increases along with the increase of the temperature of the water, such that the water does not evaporate from liquid to gas. For example, when the water in the tank reaches a temperature of 150 °C, the pressure in the tank amounts at least to the saturation pressure of the water at the temperature of 150 °C (approximately 4.8 bar), when the water in the tank reaches a temperature of 200 °C, the pressure in the tank amounts at least to the saturation pressure of the water at the temperature of 200 °C (approximately 15.6 bar), and when the water in the tank reaches a temperature of 250 °C, the pressure in the tank amounts at least to the saturation pressure of the water at the temperature of 250 °C (approximately 39.7 bar).

[0012] One advantage with maintaining the water in liquid state at temperatures of at least 100 °C is that high amounts of thermal energy can be stored in the water while avoiding energy losses for evaporating the water. The amount of energy savings in this respect may be significant considering that evaporation of one kg of water at a temperature of 100 °C and at atmospheric pressure requires an energy of 2600 kJ. The method enables very high amounts of energy to be stored in the tank. Moreover, the method enables electric energy production to take place at a time when electric energy is actually needed. Furthermore, by maintaining the water in liquid state when heated to a temperature of at least 100 °C, the water will thermally expand, for example in comparison with water at atmospheric pressure and a temperature of io °C. The method advantageously uses this expanded water to drive the primary turbine. For a given mass of water, the primary turbine will be driven more if the water in liquid state has a temperature of at least 100 °C due to the thermal expansion of the water than if driven with water at 10 °C. The method thus makes use of the thermal expansion of the water in liquid states at temperatures of at least 100 °C.

[0013] The method may be said to provide a function corresponding to a large battery, but without using a battery. In contrast to a battery, the method has a substantially smaller environmental footprint. The method provides a superior green solution that enables a transition to using renewable energy sources in large scale and that enables residual energy to be used in an efficient manner.

[0014] The heating of the water in the tank may for example be carried out using renewable energy, such as solar energy or wind energy. Alternatively, or in addition, the water may be heated using waste heat, solar thermal collectors, gas turbines, diesel engines, waste incineration and / or residual heat, e.g., from a process industry. Alternatively, or in addition, the water may be heated by an energy source adjacent to the tank, such as in the tank or below the tank. Examples of such energy sources comprise electric heating elements and heat exchangers. One suitable electric heating element may be a resistive heating element.

[0015] In the method, the heating of the water may take place irregularly. For example, solar energy and wind energy often provide an irregular energy production over several days. By thermally isolating the tank, the water can be held therein with low temperature drops over long time periods, even if the heating of the water is stopped. The heated water may then be conducted to the primary turbine at periods when electric energy is demanded by one or more consumers. This is of great advantage since, for example, solar energy is the highest during day time while electric energy consumption by households may be the lowest during day time. The method thus enables the water to be heated without conducting the water to the primary turbine at a first time period when energy is available, and enables the water to be conducted to drive the primary turbine without heating the water at a second later time period when there is a demand of electric energy. The water for example be heated during day time and the water may be conducted to drive the primary turbine during night time. Alternatively, the water may be heated during the summer season and the water may be conducted to drive the primary turbine during the winter season.

[0016] The tank may thus be thermally isolated to reduce or eliminate a temperature decrease of the water if the heating stops. To this end, the tank may for example be enclosed by a thermal insulation material and / or by vacuum.

[0017] The heating of the water does not necessarily have to be stopped prior to conducting the water to the primary turbine. The heating and the conducting may be performed concurrently. Moreover, both the heating and the conducting may be performed intermittently. The method enables a very efficient utilization of energy from irregular energy sources.

[0018] The heating of the water may comprise adding heat amounting to at least one, such as a plurality of, gigawatt hours (GWh) to liquid water in the tank. In this respect, one kilowatt-hour (kWh) equals 3.6 megajoules (MJ). The ability of the method to store such high amounts of thermal energy and to efficiently produce very high amounts of electric energy therefrom makes the method superior to batteries in terms of energy storage capacity, efficiency and environmental impact. The water may for example be sea water, drinking water and / or fresh water. The principles of the method according to the first aspect are very scalable for handling high amounts of energy.

[0019] The amount of heat added to the water may be determined based on the mass of the water, the specific heat capacity of the water, and the temperature difference of the water, i.e., between an initial temperature of the water and a final temperature of the water to which the water is heated. Thus, the amount of energy that can be stored in the water as thermal energy can be increased by increasing the mass of water, by decreasing an initial temperature of the water, and / or by increasing a final temperature of the water.

[0020] The tank may be configured to contain at least io metric tons of water, such as at least 100 metric tons of water, such as at least 1000 metric tons of water at atmospheric pressure. Alternatively, a volume of the tank may be at least 12 m3, such as at least 120 m3, such as at least 1200 m3.

[0021] The tank may be configured to hold water at a pressure of at least 40 bar. The tank may for example be a pressure vessel, such as a welded steel pressure vessel.

[0022] In order to maintain the pressure in the tank amounting at least to a saturation pressure of the water at each temperature of the water, the tank may be closed during the heating of the water. In this way, the temperature increase of the water will result in a pressure increase in the tank. Alternative ways of maintaining the pressure amounting at least to a saturation pressure of the water at each temperature are however conceivable, including use of a steam pump providing and / or pressurizing water steam within the tank.

[0023] The water may be driven from the tank to the primary turbine by the pressure of the water in the tank. Thus, no pump may be needed for supplying the water to the primary turbine.

[0024] The water may be conducted from the tank to the primary turbine through an outlet line interconnecting the tank and the primary turbine, such as a pipe. Except for respective connections to the tank and the primary turbine, the outlet line may be closed, in particular closed to atmosphere. The conduction of the water from the tank to the primary turbine may be controlled by controlling an outlet valve, e.g., arranged on the outlet line. During conduction of the water from the tank to the primary turbine, the outlet line may provide the only outlet of water from the tank. A primary electric generator may be coupled to the primary turbine to generate electric energy from the rotation of the primary turbine. The electric energy may be transmitted to one or more consumers. The electric load on the primary electric generator provides a braking function of the primary turbine. Thus, the conduction of the water from the tank to the primary turbine may also be controlled by controlling an electric load on the primary electric generator.

[0025] The water in the tank may be heated to a temperature of at least 150 °C, such as to a temperature of at least 200 °C, such as to a temperature of at least 220 °C, such as to a temperature of 250 °C. For all temperatures between 100 °C and 300 °C of water at a corresponding saturation pressure, the specific volume of the water will increase with a temperature increase of the water.

[0026] The method may further comprise controlling a flow of the water through the primary turbine. The flow of the water through the primary turbine may for example be controlled by controlling the outlet valve, e.g., arranged on the outlet line, and / or by controlling the electric load on the primary electric generator.

[0027] The method may further comprise conducting the water in liquid state and with a temperature of at least 100 °C through a primary side, downstream of the primary turbine, of a primary heat exchanger comprising the primary side and a secondary side. By passing the water through the primary side of the primary heat exchanger, very high amounts of energy can be efficiently extracted from the heated water. Firstly, since the primary turbine is driven by the water at a higher specific volume than at atmospheric pressure, the energy production by the primary turbine is increased. Secondly, since the water is maintained in liquid state, energy released by the water in terms of a temperature decrease at the primary heat exchanger is efficiently taken up by the secondary side without energy losses associated with state transitions of the water. Thirdly, the expansion of the water in liquid state at temperatures of at least 100 °C also increases the efficiency of the primary heat exchanger. For a given mass of water in liquid state, a larger volume will be heat exchanged at the primary heat exchanger for water with a temperature of at least IOO °C than for water with a temperature below 100 °C due to the thermal expansion of the water.

[0028] The water may be conducted from the primary turbine to the primary side through an intermediate line interconnecting the primary turbine and the primary side, such as a pipe. Except for respective connections to the primary turbine and to the primary side, the intermediate line may be closed, in particular closed to atmosphere.

[0029] The flow of the water through the primary turbine may be controlled based on a temperature on the secondary side. When the temperature on the secondary side decreases, the flow of the water through the primary turbine may be controlled to increase, and vice versa.

[0030] The method may further comprise circulating a secondary fluid in a heat engine system through the secondary side. The heat engine system may be used to extract electric energy. For example, the secondary fluid may drive a secondary turbine which in turn drives a secondary electric generator to generate electric energy. Also this electric energy may be transmitted to one or more consumers. In many implementations, the electric energy generated by the secondary electric generator is higher than the electric energy generated by the primary electric generator.

[0031] Throughout the present disclosure, the heat engine system and the operation thereof may for example be constituted by any of the heat engine systems and the operations thereof, respectively, as described in international patent application WO 2012049259 Al, the content of which is incorporated by reference in its entirety.

[0032] The method may further comprise controlling the heat engine system to execute a thermodynamic cycle involving a supercritical state of the secondary fluid.

[0033] The secondary fluid may comprise carbon dioxide. The method may further comprise heating the water in the tank to a temperature of 100 °C at atmospheric pressure; evacuating air from a top of the tank after the heating at atmospheric pressure; and closing the tank after the evacuation of air. In these cases, the heating of the water in the tank to a temperature of at least 100 °C may be performed after closing the tank. The tank may be closed after all air has been evacuated from the tank such that the tank only contains water in gas and liquid states.

[0034] Prior to heating the water in the tank at atmospheric pressure, the tank may be filled to a level taking a specific volume of the water into account for a given target temperature. For example, if a target temperature of 250 °C is selected, the specific volume of the water at the target temperature will be 1251 liters per metric ton. Thus, in this case, the tank may be filled with water of, e.g., 10 °C, to 80 % of a total volume of the tank to take the thermal expansion of the water in liquid state at the target temperature of 250 °C into account.

[0035] The tank may be a first tank. In these cases, the method may further comprise conducting the water downstream of the primary turbine into a second tank; and heating the water in the second tank to a temperature of at least 100 °C while keeping a pressure in the second tank amounting at least to a saturation pressure of the water at each temperature of the water to maintain the water in liquid state. At each instant, one of the tanks may be in a unique one of a filling state, a heating state and a ready state. By using at least two tanks, these two tanks may simultaneously adopt different states among the three states, e.g., reducing a time of interrupted generation of electric energy. By using at least three tanks, i.e., also an additional third tank, these three tanks may simultaneously adopt unique states among the three states. In this way, the primary turbine can be driven continuously.

[0036] In the filling state of a tank, the tank may be filled with water from the primary turbine, e.g., through a closed line, such as an intermediate line or an inlet line as described herein. In the heating state, water in the tank may be heated to a temperature of at least 100 °C while keeping a pressure in the tank amounting at least to a saturation pressure of the water at each temperature of the water to maintain the water in liquid state. In the ready state of a tank, water may be conducted in liquid state and with a temperature of at least 100 °C from the tank to the primary turbine.

[0037] At a first time period, the first tank may be in the filling state, the second tank may be in the heating state, and the third tank may be in the ready state. At a second time period, different from the first time period, the third tank may be in the filling state, the first tank may be in the heating state, and the second tank may be in the ready state. At a third time period, different from each of the first and second time periods, the second tank may be in the filling state, the third tank may be in the heating state, and the first tank may be in the ready state.

[0038] Each tank may be of the same design, have the same associated components, and / or function in the same way as described in connection with the first tank.

[0039] The method may further comprise heat exchanging between the water in the first tank and the water in the second tank when a volume of the water in liquid state in the first tank has decreased below a threshold value. The threshold value may for example be less than 40 %, such as less than 20 %, such as 10 %, of a total volume of the respective tank. Alternatively, or in addition, the threshold value may for example be at least 5 %, such as 20 %, of the total volume of the respective tank. To this end, each tank may comprise a tank heat exchanger associated with one or more of the other tanks. For example, the first tank may comprise a first tank heat exchanger and the second tank may comprise a second tank heat exchanger. A heat exchanging line may then circulate a heat exchanging medium between the primary and second tank heat exchangers to heat exchange with the water in the primary and second tanks, respectively. Other types of heat exchanging between water in the primary and second tanks are conceivable. According to a second aspect, there is provided an energy handling system comprising a tank configured to contain water and to withstand an internal pressure of at least 15 bar; an energy source configured to heat water in the tank to a temperature of at least 100 °C; a primary turbine; and an outlet valve configured to control a flow of water out from the tank and to the primary turbine. The energy handling system according to the second aspect may be of any type as described in connection with the first aspect. Alternatively, or in addition, the method according to the first aspect may be carried out using an energy handling system as described in connection with the second aspect.

[0040] The energy handling system may further comprise an electronic control system including at least one data processing device and at least one memory having at least one computer program stored thereon, the at least one computer program comprising program code which, when executed by the at least one data processing device, causes the at least one data processing device to perform, or command performance of, various steps as described herein. The control system may be configured to control the energy source to heat the water in the tank to a temperature of at least 100 °C. The control system may further be configured to control the outlet valve, e.g., by controlling an opening area thereof, to conduct the water in liquid state and with a temperature of at least 100 °C from the tank to the primary turbine. The control system may further be configured to control the primary turbine.

[0041] According to one variant, the control system is configured to control the flow of water through the primary turbine. In such variants, the control system may for example control the outlet valve and / or an electric load on a primary electric generator driven by the primary turbine.

[0042] The energy handling system may further comprise a primary heat exchanger arranged downstream of the primary turbine, the primary heat exchanger including a primary side and a secondary side. The energy handling system may further comprise a secondary temperature sensor configured to measure a temperature of a secondary fluid at the secondary side. In these cases, the at least one computer program may comprise program code which, when executed by the at least one data processing device, causes the at least one data processing device to control the flow of water through the primary turbine based on a temperature as measured by the secondary temperature sensor.

[0043] The energy handling system may further comprise a heat engine system containing the secondary fluid. In these cases, the heat engine system may be configured to execute a thermodynamic cycle involving a supercritical state of the secondary fluid. The heat engine system may be controlled by the control system.

[0044] The secondary fluid may comprise carbon dioxide.

[0045] The energy handling system may further comprise an exhaust valve at a top of the tank for evacuating air from the tank. The exhaust valve may be controlled by the control system.

[0046] The tank may be a first tank. In these cases, the energy handling system may further comprise a second tank configured to contain water and to withstand an internal pressure of at least 15 bar; an energy source configured to heat water in the second tank to a temperature of at least 100 °C; and a second outlet valve configured to control a flow of water out from the second tank and to the primary turbine. The energy handling system may further comprise a third tank configured to contain water and to withstand an internal pressure of at least 15 bar; an energy source configured to heat water in the third tank to a temperature of at least 100 °C; and a tertiary outlet valve configured to control a flow of water out from the third tank and to the primary turbine. Each of the secondary and tertiary outlet valves may be controlled by the control system.

[0047] The energy handling system may further comprise a tank heat exchanger arranged to heat exchange between water in the first tank and water in the second tank. The energy handling system may further comprise a tank heat exchanger arranged to heat exchange between water in first tank and water in the third tank, and a tank heat exchanger arranged to heat exchange between water in second tank and water in the third tank.

[0048] Brief Description of the Drawings

[0049] Further details, advantages and aspects of the present disclosure will become apparent from the following description taken in conjunction with the drawings, wherein:

[0050] Fig. 1: schematically represents one example of an energy handling system and exemplifying components of a primary section thereof;

[0051] Fig. 2: schematically represents the energy handling system in Fig. 1 and exemplifying components of a secondary section thereof;

[0052] Fig. 3: is a diagram showing specific volumes and saturation pressures of water at different temperatures;

[0053] Fig. 4: schematically represents a first state of the energy handling system;

[0054] Fig. 5: schematically represents a second state of the energy handling system;

[0055] Fig. 6: schematically represents a third state of the energy handling system;

[0056] Fig. 7: schematically represents an energy handling system according to a further example; and

[0057] Fig. 8: is a flowchart outlining general steps of a method.

[0058] Detailed Description

[0059] In the following, a method of handling energy and an energy handling system will be described. The same or similar reference numerals will be used to denote the same or similar structural features.

[0060] Fig. 1 schematically represents one example of an energy handling system 10a. The energy handling system 10a of this example comprises a primary section 12 and an optional secondary section, here embodied as a heat engine system 14. In Fig. 1, one exemplifying implementation of the primary section 12 is shown. One exemplifying implementation of the heat engine system 14 is shown in Fig. 2.

[0061] Referring again to Fig. 1, the primary section 12 of this example comprises a first tank 16a, a second tank 16b and a third tank 16c. In this example, each tank i6a-i6c has the same dimensions, design and associated components. All tanks i6a-i6c function in the same manner. When description is given for one tank i6a-i6c, this description may also apply to the other tanks i6a-i6c, at least in some state of operation of the energy handling system 10a.

[0062] Each tank i6a-i6c is in this example configured to withstand an internal pressure of at least 40 bar. To this end, the tanks i6a-i6c may for example be welded steel pressure vessels. In this specific and non-limiting example, each tank i6a-i6c has a generally cylindrical shape with spherical ends (Fig. 7). Each tank i6a-i6c may for example have a diameter of 40 m, a height of 10.5 m and a volume of approximately 3500 m3. Each tank i6a-i6c contains water 18, in Fig. 1 both in liquid state 20 and in gas state 22. Fig. 1 also indicates an atmosphere 24 outside of the tanks i6a-i6c.

[0063] The primary section 12 further comprises a primary turbine 26. The primary turbine 26 may for example be a volumetric turbine or a centrifugal turbine.

[0064] The primary section 12 of this example further comprises a first outlet line 28a connected to the first tank 16a, a second outlet line 28b connected to the second tank 16b, and a third outlet line 28c connected to the third tank 16c. Each of the outlet lines 28a-28c is connected to a geodetically low or lowest portion of the respective tank i6a-i6c. Moreover, each of the outlet lines 28a- 28c is connected at an outlet junction 30. The primary section 12 of this example further comprises an outlet central line 32 interconnecting the outlet junction 30 and the primary turbine 26. Each of the outlet lines 28a-28c and the outlet central line 32 is closed to the atmosphere 24. The energy handling system 10a of this example comprises an electronic control system 34. The control system 34 of this example comprises a data processing device 36 and a memory 38. The memory 38 has a computer program stored thereon which, when executed by the data processing device 36, causes the data processing device 36 to perform, or command performance of, various steps as described herein.

[0065] The primary section 12 of this example further comprises a first heating element 40a for heating the water 18 in the first tank 16a, a second heating element 40b for heating the water 18 in the second tank 16b, and a third heating element 40c for heating the water 18 in the third tank 16c. In this example, each heating element 4oa-4oc is here positioned inside of a respectively associated tank i6a-i6c. The heating elements 4oa-4oc are here exemplified as electric resistive heating elements. Thus, when an electric current is passed through the heating elements 4oa-4oc, the heating elements 4oa-4oc generate heat. The heating elements 4oa-4oc thus represent one of many examples of types of energy sources according to the present disclosure. The heating elements 4oa-4oc are controlled by the control system 34.

[0066] The primary section 12 of this example further comprises a first outlet valve 42a arranged at the first outlet line 28a, a second outlet valve 42b arranged at the second outlet line 28b, and a third outlet valve 42c arranged at the third outlet line 28c. When the first outlet valve 42a is open and each of the second outlet valve 42b and the third outlet valve 42c is closed, the first outlet line 28a and the outlet central line 32 form a common outlet line interconnecting the first tank 16a and the primary turbine 26. As such, each outlet valve 42a- 42c is configured to control a flow 44 of water 18 from a respectively associated tanks i6a-i6c to the primary turbine 26.

[0067] Each outlet valve 423-420 is controlled by the control system 34. The control system 34 may for example command any of the outlet valves 423-420 to adopt a fully closed position, a first open position to provide a first opening area, and a second position to provide a second opening area, larger than the first opening area. The outlet valves 423-420 may for example be knife valves.

[0068] The primary section 12 of this example further comprises a primary electric generator 46. The primary electric generator 46 is coupled to the primary turbine 26 and generates electric energy from rotation of the primary turbine 26. The primary electric generator 46 is in signal communication with the control system 34. For example, an electric load of the primary electric generator 46 may be controlled by the control system 34.

[0069] The primary section 12 of this example further comprises a primary heat exchanger 48. The primary heat exchanger 48 comprises a primary side 50 and a secondary side 52.

[0070] The primary section 12 of this example further comprises a first inlet line 54a connected to the first tank 16a, a second inlet line 54b connected to the second tank 16b, and a third inlet line 54c connected to the third tank 16c. Each of the inlet lines 543-540 is connected to a geodetically high or highest portion of the respective tank i6a-i6c. Moreover, each of the inlet lines 54a- 54c is connected at an inlet junction 56. The prefixes outlet and inlet of the outlet junction 30 and the inlet junction 56 are thus here selected with respect to the tanks i6a-i6c.

[0071] The primary section 12 of this example further comprises an intermediate line 58. The intermediate line 58 interconnects the primary turbine 26 and the primary side 50. The primary section 12 of this example further comprises an inlet central line 60 interconnecting the primary side 50 and the inlet junction 56. Each of the intermediate line 58, the inlet central line 60 and the inlet lines 543-540 are closed to the atmosphere 24. The outlet lines 28a-28c, the outlet central line 32, the intermediate line 58, the primary side 50, the inlet central line 60 and the inlet lines 543-540 form one example of a primary circuit 62.

[0072] The primary section 12 of this example further comprises a first inlet valve 64a arranged at the first inlet line 54a, a second inlet valve 64b arranged at the second inlet line 54b, and a third inlet valve 64c arranged at the third inlet line 54c. When the first inlet valve 64a is open and each of the second inlet valve 64b and the third inlet valve 64c is closed, the inlet central line 60 and the first inlet line 54a form a common inlet line interconnecting the primary side 50 and the first tank 16a.

[0073] Each inlet valve 643-640 is controlled by the control system 34. The control system 34 may for example command any of the inlet valves 643-640 to adopt a fully closed position, a first open position to provide a first opening area, and a second position to provide a second opening area, larger than the first opening area. The inlet valves 643-640 may for example be knife valves.

[0074] The primary section 12 of this example further comprises a first exhaust valve 66a arranged at a geodetically highest portion of the first tank 16a, a second exhaust valve 66b arranged at a geodetically highest portion of the second tank 16b, and a third exhaust valve 66c arranged at a geodetically highest portion of the third tank 16c. Each exhaust valve 66a-66c is controlled by the control system 34. The control system 34 may for example command any of the exhaust valves 66a-66c to adopt a closed position and an open position.

[0075] The primary section 12 of this example further comprises a first safety valve 68a connected to the first tank 16a, a second safety valve 68b connected to the second tank 16b, and a third safety valve 68c connected to the third tank 16c. Each safety valve 68a-68c is here exemplified as a mechanical safety valve configured to open to the respectively associated tank i6a-i6c when a pressure within the respectively associated tank i6a-i6c decreases below the atmospheric pressure prevailing in the atmosphere 24.

[0076] In this example, the first tank 16a comprises a first primary temperature sensor 70a, the second tank 16b comprises a second primary temperature sensor 70b, and the third tank 16c comprises a third primary temperature sensor 70c. Each primary temperature sensor 703-700 is configured to measure a temperature of the water 18 in the respectively associated tank i6a-i6c. Each primary temperature sensor 703-700 is in signal communication with the control system 34.

[0077] In this example, the first tank 16a comprises a first pressure sensor 72a, the second tank 16b comprises a second pressure sensor 72b, and the third tank 16c comprises a third pressure sensor 72c. Each pressure sensor 723-720 is configured to measure a pressure of the water 18 in the respectively associated tank i6a-i6c. Each pressure sensor 723-720 is in signal communication with the control system 34. The pressure sensors 723-720 are entirely optional.

[0078] In this example, the first tank 16a comprises a first level sensor 74a, the second tank 16b comprises a second level sensor 74b, and the third tank 16c comprises a third level sensor 74c. Each level sensor 743-740 is configured to measure a level of the water 18 in liquid state 20 in the respectively associated tank i6a-i6c. Each level sensor 743-740 is in signal communication with the control system 34.

[0079] In this example, the first tank 16a comprises a tank heat exchanger y6ab, and the second tank 16b comprises a tank heat exchanger y6ba. The primary section 12 of this example further comprises an intermediate heat exchanging circuit y8ab interconnecting the tank heat exchanger 763b and the tank heat exchanger 6ba, and an intermediate pump 8oab arranged to circulate a heat exchanging medium in the intermediate heat exchanging circuit 78ab.

[0080] Furthermore, in this example, the first tank 16a comprises a tank heat exchanger 6ac, and the third tank 16c comprises a tank heat exchanger 760a. The primary section 12 of this example further comprises an intermediate heat exchanging circuit 783c interconnecting the tank heat exchanger 6ac and the tank heat exchanger 760a, and an intermediate pump 8oac arranged to circulate a heat exchanging medium in the intermediate heat exchanging circuit 783c.

[0081] Furthermore, in this example, the second tank 16b comprises a tank heat exchanger 6bc, and the third tank 16c comprises a tank heat exchanger 760b. The primary section 12 of this example further comprises an intermediate heat exchanging circuit y8bc interconnecting the tank heat exchanger y6bc and the tank heat exchanger y6cb, and an intermediate pump 8obc arranged to circulate a heat exchanging medium in the intermediate heat exchanging circuit y8bc.

[0082] The heat engine system 14 of this example contains a secondary fluid 82, here exemplified as carbon dioxide. The heat engine system 14 here also comprises a secondary temperature sensor 84 configured to measure a temperature of the secondary fluid 82 in the heat engine system 14. The secondary temperature sensor 84 is in signal communication with the control system 34-

[0083] Fig. 2 schematically represents one specific exemplifying implementation of the heat engine system 14. The heat engine system 14 of this example comprises a secondary circuit 86 through which the secondary fluid 82 circulates in a closed-loop and fluid-tight manner, and undergoes a transcritical thermodynamic cycle.

[0084] The heat engine system 14 of this example comprises a secondary fluid reservoir 88, a compressor 90, a secondary turbine 92 and a secondary electric generator 94. The compressor 90 and the secondary electric generator 94 are in signal communication with the control system 34. For example, the control system 34 may control a driving of the compressor 90 and may control an electric load of the secondary electric generator 94. The secondary electric generator 94 is arranged to be driven by rotation of the secondary turbine 92 to generate electric energy. Arrow 96 indicates a flow direction of the secondary fluid 82 in the secondary circuit 86. When the compressor 90 is driven, the secondary fluid 82 circulates in the secondary circuit 86.

[0085] Fig. 2 further denotes a high-pressure side 98 of the secondary circuit 86 upstream of the secondary turbine 92, and a low-pressure side 100 of the secondary circuit 86 downstream of the secondary turbine 92. The secondary side 52 of the primary heat exchanger 48 is here provided at the high- pressure side 98.

[0086] The heat engine system 14 of this example further comprises a first secondary heat exchanger 102. The first secondary heat exchanger 102 is arranged to heat exchange between the high-pressure side 98 and the low-pressure side 100 of the secondary circuit 86. For example, heat may be transferred from the secondary fluid 82 at the low-pressure side 100 to the secondary fluid 82 at the high-pressure side 98 via the first secondary heat exchanger 102.

[0087] The heat engine system 14 of this example further comprises a second secondary heat exchanger 104. The second secondary heat exchanger 104 is arranged to heat exchange between the secondary fluid 82, here at the low- pressure side 100 downstream of the first secondary heat exchanger 102 and upstream of the secondary fluid reservoir 88, and a tertiary fluid 106 in an energy sink 108. For example, heat may be transferred from the secondary fluid 82 in the secondary circuit 86 between the first secondary heat exchanger 102 and the secondary fluid reservoir 88 to the tertiary fluid 106 in the energy sink 108 by the second secondary heat exchanger 104. The tertiary fluid 106 may for example comprise groundwater, seawater or fresh water.

[0088] Fig. 3 is a diagram showing specific volumes 110 (with circles) of the water 18 in liquid state 20 and saturation pressures 114 (with squares) of the water 18 at different temperatures 112. The unit of the specific volume 110 is liters per metric ton. The unit of the saturation pressure 114 is bar, where one bar equals 100000 Pa. For example, at a temperature 112 of 100 °C, the saturation pressure 114 is 1.014 bar, at a temperature 112 of 150 °C, the saturation pressure 114 is 4.758 bar, at a temperature 112 of 200 °C, the saturation pressure 114 is 15.55 bar, at a temperature 112 of 250 °C, the saturation pressure 114 is 39.73 bar, and at a temperature 112 of 300 °C, the saturation pressure 114 is 85.88 bar. As shown in Fig. 3, the saturation pressure 114 increases drastically when the temperature 112 increases above 250 °C. If the tanks i6a-i6c are designed to handle at least 40 bar pressure, the water 18 may be heated up to a temperature 112 of 250 °C in liquid state 20.

[0089] With collective reference to Figs. 1 to 3, exemplifying methods of operation of the energy handling system 10a will be described.

[0090] The first outlet line 28a is initially be filled with water 18 between the first tank 16a and the primary turbine 26 via the first tank 16a. During this filling, the first exhaust valve 66a is controlled to be open such that the first tank 16a is at atmospheric pressure and the first outlet valve 42a is controlled to be open such that water 18 can pass from the first tank 16a to the primary turbine 26. The filling may for example take place through the first safety valve 68a or through a dedicated closable filling line (not shown) connected to the first tank 16a, such as to a geodetic top portion thereof. Once the water 18 reaches the primary turbine 26, the first outlet valve 42a is controlled to close.

[0091] The first tank 16a is then filled with water 18 in liquid state 20 under atmospheric pressure, e.g., by controlling the first exhaust valve 66a to open. The water 18 may for example be sea water, drinking water or fresh water. The water 18 may for example have a temperature 112 of below 100 °C, such as 10 °C. The temperature 112 of the water 18 when filling the first tank 16a may depend on the temperature 112 of the used sea water, drinking water or fresh water. During this filling, the first outlet valve 42a may be controlled to be closed. The degree of filling of the first tank 16a takes the thermal expansion of the water 18 in liquid state 20 at temperatures 112 above 100 °C into consideration. For example, since the water 18 in liquid state 20 has a specific volume 110 of 1251 liters per metric ton at a temperature 112 of 250 °C, the water 18 may be filled to 80 % or less of the total volume of the first tank 16a if the target temperature 112 is 250 °C. In the example where the first tank 16a has a volume of 3500 m3, the first tank 16a may thus be filled with a volume of 2800 m3 of water 18 in liquid state 20, e.g., at a temperature 112 of 10 °C. The second outlet line 28b and the second tank 16b are then filled with water 18 in a corresponding way. That is, the second outlet line 28b is filled with water 18 between the second tank 16b and the primary turbine 26 via the second tank 16b, for example through the second safety valve 68b or through a dedicated closable filling line (not shown) connected to the second tank 16b, such as to a geodetic top portion thereof. During this filling, the second exhaust valve 66b and the second outlet valve 42b are controlled to be open.

[0092] The second tank 16b is then filled with water 18 in liquid state 20 under atmospheric pressure, e.g., by controlling the second exhaust valve 66b to open. The water 18 may for example have a temperature 112 of below 100 °C, such as 10 °C. During this filling, the second outlet valve 42b may be controlled to be closed. Also the degree of filling of the second tank 16b takes the thermal expansion of the water 18 in liquid state 20 at temperature 112 above 100 °C into consideration. Thus, for a target temperature 112 of 250 °C, the second tank 16b may be filled with water 18 under atmospheric pressure to approximately 80 % of its total volume.

[0093] The third outlet line 28c is then filled with water 18 in a corresponding way. That is, the third outlet line 28c is filled with water 18 between the third tank 16c and the primary turbine 26 via the third tank 16c, for example through the third safety valve 68c or through a dedicated closable filling line (not shown) connected to the third tank 16c, such as to a geodetic top portion thereof. During this filling, the third exhaust valve 66c and the third outlet valve 42c are controlled to be open. The third outlet valve 42c is then controlled to close and the third exhaust valve 66c is controlled to be kept open such that the third tank 16c can receive the water 18 at atmospheric pressure a first time from the first tank 16a via the inlet central line 60.

[0094] The first heating element 40a then starts to heat the water 18 at atmospheric pressure, i.e., while keeping the first exhaust valve 66a open. For example, the first heating element 40a may be controlled by the control system 34 to be in a state where the first heating element 40a can receive electric energy from an external source, such as residual electric energy, while the second heating element 40b and the third heating element 40c may be controlled by the control system 34 to be in a state where the second heating element 40b and the third heating element 40c do not receive the electric energy.

[0095] Once the temperature 112 of the water 18 reaches 100 °C, the water 18 will start boiling and some of the water 18 in liquid state 20 will evaporate to gas state 22. Since any air inside of the first tank 16a is lighter than the water 18 in gas state 22, i.e., has lower density, air will evacuate through the first exhaust valve 66a before the water 18 in gas state 22. Once some water 18 in gas state 22 starts to evacuate through the first exhaust valve 66a, the first exhaust valve 66a is closed. To this end, a human user may for example instruct the control system 34 to close the first exhaust valve 66a upon observing evacuation of the water 18 in gas state 22 through the first exhaust valve 66a. Alternatively, this closing of the first exhaust valve 66a may be automized. For example, the first exhaust valve 66a may for example be controlled by the control system 34 to close at a certain time limit after the water 18 reaches a temperature 112 of 100 °C. Such time limit may for example be set taking an initial filling volume of the water 18 in the first tank 16a into consideration. When the first exhaust valve 66a is closed, the first tank 16a contains only, or substantially only, water 18 in liquid state 20 and gas state 22. Should the temperature 112 of the water 18 in the first tank 16a decrease below a temperature 112 of 100 °C, air from the atmosphere 24 will again enter the first tank 16a through the first safety valve 68a and the first tank 16a can thereby be prevented from collapsing.

[0096] The water 18 in the first tank 16a is then heated further by the first heating element 40a while keeping the first tank 16a closed, here by keeping the first exhaust valve 66a and the first outlet valve 42a closed. Since the first tank 16a is closed, the increasing temperature 112 of the water 18 will cause the pressure in the first tank 16a to increase. This increase of the pressure will in turn prevent some or all of the water 18 in liquid state 20 from evaporating. That is, the increasing temperature 112 will cause the pressure of the water 18 to be equal to or above the saturation pressure 114 at each temperature 112. Since the pressure in the first tank 16a increases and the water 18 is thereby maintained in liquid state 20, no energy, or substantially no energy, is used to evaporate the water 18.

[0097] Once the temperature 112 of the water 18 in the first tank 16a reaches the target temperature 112, here 250 °C, e.g., as determined by the first primary temperature sensor 70a, the pressure in the first tank 16a will be at least 39.73 bar which corresponds to the saturation pressure 114 of the water 18 at the temperature 112 of 250 °C. Moreover, at a temperature 112 of the water 18 in the first tank 16a of 250 °C, the specific volume 110 of the water 18 will be 1251 liters per metric ton. Thus, the water 18 in liquid state 20 will occupy almost the entire volume of the first tank 16a and the water 18 in gas state 22 will be compressed above the water 18 in liquid state 20. At this temperature 112 of the water 18, the first outlet valve 42a is controlled by the control system 34 to open. The water 18 is thereby conducted in liquid state 20 and with a temperature 112 of 250 °C from the first tank 16a to the primary turbine 26 to thereby drive the primary turbine 26. Electric energy is thereby generated by the primary electric generator 46.

[0098] The water 18 is here driven from the first tank 16a to the primary turbine 26 by the pressure of the water 18 inside of the first tank 16a. When the water 18 in liquid state 20 leaves the first tank 16a, the water 18 in gas state 22 will expand.

[0099] Due to the primary turbine 26 being driven by the volume of the water 18, and not by the mass thereof, the thermal expansion of the water 18 may be said to provide a bonus function since the primary turbine 26 is driven more by water 18 with a relatively large expansion in comparison with water 18 with a relatively small expansion, or no expansion, for a given mass of water 18. For example, by conducting a given mass of water 18 in liquid state 20, with a temperature 112 of 250 °C and hence a specific volume 110 of 1251 liters per metric ton to the primary turbine 26, the primary turbine 26 will generate 20 % more power in comparison with conducting the given mass of water 18 in liquid state 20, with a temperature 112 of 99 °C and hence a specific volume 110 of 1043 liters per metric ton to the primary turbine 26. The flow 44 of the water 18 through the primary turbine 26 can for example be controlled by controlling the opening area of the first outlet valve 42a, by controlling the electric load of the primary electric generator 46, and / or by controlling the opening area of the third inlet valve 64c.

[0100] The flow 44 is here controlled based on the temperature of the secondary fluid 82. A target temperature of the secondary fluid 82 may for example be set to 120 °C. Thus, when the temperature of the secondary fluid 82 lies below the target temperature, the flow 44 is increased, and when the temperature of the secondary fluid 82 lies above the target temperature, the flow 44 is decreased.

[0101] The water 18 is then led from the primary turbine 26 to the primary side 50 through the closed intermediate line 58. The primary heat exchanger 48 performs heat exchanging between the water 18 in the primary section 12 and the secondary fluid 82 in the heat engine system 14.

[0102] The secondary fluid 82 in the secondary fluid reservoir 88 may for example have a temperature of 15 °C, a pressure of 85 bar, a density of 874.33 kg / m3 and a specific energy of 232.07 kJ / kg (kilojoule per kilogram). The compressor 90 may increase the pressure of the secondary fluid 82 from 85 bar to 125 bar, which in turn causes a temperature increase to 17 °C and a decrease of density to 232.07 kg / m3. If the secondary fluid 82 is then heated from 17 °C to 120 °C at the primary heat exchanger 48, the density will decrease to 221.57 kg / m3 and the specific energy will increase to 513.25 kJ / kg. The secondary fluid 82 has now expanded 4.064 times.

[0103] In the heat engine system 14, the pressure of the secondary fluid 82 on the low-pressure side 100 of the secondary turbine 92 is always high enough such that the secondary fluid 82 does not evaporate. For carbon dioxide, this pressure amounts at least to 72 bar. The pressure on the high-pressure side 98 may for example be 125 bar and the pressure on the low-pressure side 100 may for example be 85 bar. This gives a pressure difference of 40 bar for driving the secondary turbine 92. By avoiding that the secondary fluid 82 in the low-pressure side 100 evaporates, energy in the secondary fluid 82 on the low-pressure side 100 can more efficiently be heat exchanged with the secondary fluid 82 on the high-pressure side 98. The pressures on the high- pressure side 98 and on the low-pressure side 100 may be controlled by controlling the secondary turbine 92 and / or the compressor 90, e.g., by the control system 34. By heat exchanging the secondary fluid 82 at the low- pressure side 100 with the secondary fluid 82 at the high-pressure side 98 by the first secondary heat exchanger 102, a large temperature difference and a small area of the first secondary heat exchanger 102 are enabled. When the secondary fluid 82 at the secondary side 52 is heated by the water 18 at the primary side 50, the secondary fluid 82 may transition into the supercritical state. The heat engine system 14 is thus controlled to execute a thermodynamic cycle of the secondary fluid 82 involving the supercritical state of the secondary fluid 82.

[0104] Electric energy is thus also generated by the secondary electric generator 94, in addition to by the primary electric generator 46. For example, by heating the water 18 in the first tank 16a to a temperature 112 of 250 °C and heat exchanging the water 18 at the primary heat exchanger 48 such that the temperature 112 of the water 18 decreases to 120 °C, approximately 576.9 kJ / kg of water 18 can be transferred to the secondary side 52. In this example, one kWh (kilowatt-hour) or 3.6 MJ (megajoules) of stored energy will correspond to 6.24 kg of water 18.

[0105] The power output by the primary electric generator 46 and the secondary electric generator 94 can for example be controlled by the circulation of the water 18 in the primary circuit 62. The circulation of the water 18 in the primary circuit 62 can in turn for example be controlled by controlling the degree of opening of the outlet valves 423-420, by controlling an electric load on the primary electric generator 46, and / or by controlling the degree of opening of the inlet valve 643-640.

[0106] The pressure of the water 18 is reduced at the primary heat exchanger 48.

[0107] The degree of pressure drop depends inter alia on the temperature 112 of the secondary fluid 82. For example, downstream of the primary heat exchanger 48, the temperature 112 of the water 18 may be 120 °C and the pressure may be 2-3 bar. By heating the water 18 in the first tank 16a to 250 °C, and utilizing a temperature 112 decrease of the water 18 at the primary heat exchanger 48 from 250 °C to 120 °C, a thermal energy of approximately 160 kWh per 1000 kg water 18 can be transferred to the heat engine system 14.

[0108] The water 18 is then led from the primary heat exchanger 48 to a receiving tank among the tanks i6a-i6c, here by the inlet central line 60 and the third inlet line 54c to the third tank 16c, e.g., by controlling the third inlet valve 64c to be open and the first inlet valve 64a and the second inlet valve 64b to be closed. The third tank 16c is filled a first time under atmospheric pressure and evacuated from air in the same manner as described in connection with the first and second tanks 16a and 16b. Once all tanks i6a-i6c have been filled with water 18 a first time and evacuated from air, all exhaust valve 66a-66c are controlled to be kept closed. In this way, the tanks i6a-i6c and the primary circuit 62 contains only, or substantially only, water 18 in liquid state 20 and gas state 22. With substantially only water 18 in the tanks i6a-i6c and in the primary circuit 62 may be meant that each of the tank i6a-i6c and the primary circuit 62 contains at least 99 % by mass of water 18. Since the primary circuit 62 is closed between the tanks i6a-i6c and the primary turbine 26, between the primary turbine 26 and the primary heat exchanger 48, and between the primary heat exchanger 48 and the tanks i6a-i6c, no evaporation, or substantially no evaporation, of the water 18 will occur in the primary circuit 62.

[0109] Fig. 4 schematically represents a first state of the energy handling system 10a according to one specific example. In the first state, the first tank 16a is in a ready state 116, the second tank 16b is in a heating state 118 and the third tank 16c is in a filling state 120. In each of the ready state 116, the heating state 118 and the filling state 120, the exhaust valves 66a-66c are closed. In the ready state 116 of the first tank 16a, the first inlet valve 64a is controlled to be closed and the first heating element 40a may be controlled to not heat the water 18, or may be controlled to heat the water 18 to maintain a target temperature 112, e.g., as determined based on the first primary temperature sensor 70a. Moreover, in the ready state 116 of the first tank 16a, the first outlet valve 42a can be controlled to open to conduct the water 18 to the primary turbine 26.

[0110] When the level of the water 18 in liquid state 20 in the first tank 16a has decreased below a threshold value by conduction to the primary turbine 26, e.g., below 10 % of a total volume of the first tank 16a and as determined by the first level sensor 74a, the intermediate pump 8oab is controlled to circulate the heat exchanging medium in the intermediate heat exchanging circuit 78ab such that heat is transferred from the water 18 in the first tank 16a to the heat exchanging medium in the intermediate heat exchanging circuit 78ab by the tank heat exchanger y6ab, and such that heat is transferred from the heat exchanging medium in the intermediate heat exchanging circuit y8ab to the water 18 in the second tank 16b by the tank heat exchanger y6ba.

[0111] In the heating state 118 of the second tank 16b, the second inlet valve 64b and the second outlet valve 42b are controlled to be closed and the second heating element 40b is controlled to heat the water 18. In the filling state 120 of the third tank 16c, the third inlet valve 64c is controlled to be open and the third outlet valve 42c is controlled to be closed. The third tank 16c thereby receives the water 18 from the first tank 16a. Moreover, in the filling state 120 of the third tank 16c, the third heating element 40c is controlled to not heat the water 18.

[0112] Fig. 5 schematically represents a second state of the energy handling system 10a according to one specific example. In the second state, the first tank 16a is in the filling state 120, the second tank 16b is in the ready state 116 and the third tank 16c is in the heating state 118. In the ready state 116 of the second tank 16b, the second inlet valve 64b is controlled to be closed and the second heating element 40b may be controlled to not heat the water 18, or may be controlled to heat the water 18 to maintain a target temperature 112, e.g., as determined based on the second primary temperature sensor 70b. Moreover, in the ready state 116 of the second tank 16b, the second outlet valve 42b can be controlled to open to conduct the water 18 to the primary turbine 26.

[0113] When the level of the water 18 in liquid state 20 in the second tank 16b has decreased below a threshold value by conduction to the primary turbine 26, e.g., below 10 % of a total volume of the second tank 16b and as determined by the second level sensor 74b, the intermediate pump 8obc is controlled to circulate the heat exchanging medium in the intermediate heat exchanging circuit y8bc such that heat is transferred from the water 18 in the second tank 16b to the heat exchanging medium in the intermediate heat exchanging circuit 78bc by the tank heat exchanger y6bc, and such that heat is transferred from the heat exchanging medium in the intermediate heat exchanging circuit y8bc to the water 18 in the third tank 16c by the tank heat exchanger 760b.

[0114] In the heating state 118 of the third tank 16c, the third inlet valve 64c and the third outlet valve 42c are controlled to be closed and the third heating element 40c is controlled to heat the water 18. In the filling state 120 of the first tank 16a, the first inlet valve 64a is controlled to be open and the first outlet valve 42a is controlled to be closed. The first tank 16a thereby receives the water 18 from the second tank 16b. Moreover, in the filling state 120 of the first tank 16a, the first heating element 40a is controlled to not heat the water 18.

[0115] Fig. 6 schematically represents a third state of the energy handling system 10a according to one specific example. In the third state, the first tank 16a is in the heating state 118, the second tank 16b is in the filling state 120 and the third tank 16c is in the ready state 116. In the ready state 116 of the third tank 16c, the third inlet valve 64c is controlled to be closed and the third heating element 40c may be controlled to not heat the water 18, or may be controlled to heat the water 18 to maintain a target temperature 112, e.g., as determined based on the third primary temperature sensor 70c. Moreover, in the ready state 116 of the third tank 16c, the third outlet valve 42c can be controlled to open to conduct the water 18 to the primary turbine 26. When the level of the water 18 in liquid state 20 in the third tank 16c has decreased below a threshold value by conduction to the primary turbine 26, e.g., below 10 % of a total volume of the third tank 16c and as determined by the third level sensor 74c, the intermediate pump 8oac is controlled to circulate the heat exchanging medium in the intermediate heat exchanging circuit y8ac such that heat is transferred from the water 18 in the third tank 16c to the heat exchanging medium in the intermediate heat exchanging circuit 78ac by the tank heat exchanger 760a, and such that heat is transferred from the heat exchanging medium in the intermediate heat exchanging circuit y8ac to the water 18 in the first tank 16a by the tank heat exchanger y6ac.

[0116] In the heating state 118 of the first tank 16a, the first inlet valve 64a and the first outlet valve 42a are controlled to be closed and the first heating element 40a is controlled to heat the water 18. In the filling state 120 of the second tank 16b, the second inlet valve 64b is controlled to be open and the second outlet valve 42b is controlled to be closed. The second tank 16b thereby receives the water 18 from the third tank 16c. Moreover, in the filling state 120 of the second tank 16b, the second heating element 40b is controlled to not heat the water 18. By controlling the energy handling system 10a to operate in accordance with Figs. 4 to 6, electric energy can be generated by the primary electric generator 46 and the secondary electric generator 94 without interruption.

[0117] According to an alternative variant, the energy handling system 10a comprises only two tanks i6a-i6c, such as the first tank 16a and the second tank 16b. In these cases, the first tank 16a may be in the ready state 116 simultaneously with the second tank 16b being in the filling state 120 and vice versa. When any of the tanks 16a and 16b is in the heating state 118, the other of the tanks 16a and 16b may remain in an empty state. In such variant, there may be interruptions in the generation of electric energy.

[0118] In a further alternative variant, the energy handling system 10a comprises more than three tanks i6a-i6c. In such variant, two or more of the tanks 16a- 16c may simultaneously adopt one of the ready state 116, the heating state 118 and the filling state 120.

[0119] Fig. 7 schematically represents an energy handling system 10b according to a further example. The energy handling system 10b comprises a tank i6d including a spherical top portion and a spherical bottom portion. The tank i6d comprises a thermal insulation material 122. The thermal insulation material 122 may for example comprise an all-metallic reflective material, a fibrous material and / or a powdered material. Each tank i6a-i6c may comprise a spherical top portion and a spherical bottom portion similar to the tank i6d. Alternatively, or in addition, each tank i6a-i6c may comprise the thermal insulation material 122 similar to the tank i6d. The tank i6d further comprises the first primary temperature sensor 70a, the first pressure sensor 72a and the first level sensor 74a.

[0120] The energy handling system 10b further comprises a heating element 40d for heating the water 18 in the tank i6d. The heating element 4od is here positioned inside of the tank i6d. The heating element 4od of this example is a heat exchanger for heat exchanging between a heat exchanging medium heated by an external energy source and the water 18 in the tank i6d. The heating element 40d is a further example of an energy source according to the present disclosure.

[0121] The energy handling system 10b of this example further comprises a pump 124. The pump 124 is controlled by the control system 34. By driving the pump 124, the circulation of the heat exchanging medium through the heating element 4od, and hence the heating of the water 18 in the tank i6d, can be controlled.

[0122] The energy handling system 10b further comprises the first safety valve 68a and the first exhaust valve 66a connected to the top portion of the tank i6d. The energy handling system 10b further comprises the first outlet line 28a connected to the tank i6d, the first outlet valve 42a arranged at the first outlet line 28a, the primary turbine 26, the primary electric generator 46 and an outlet line 126 downstream of the primary turbine 26. The first outlet line 28a here interconnects the tank i6d and the primary turbine 26.

[0123] Using the energy handling system 10b, the water 18 in the tank i6d can be heated to a temperature 112 of at least 100 °C, such as to a temperature 112 of 250 °C, while keeping a pressure in the tank i6d amounting at least to the saturation pressure 114 of the water 18 at each temperature 112 of the water 18 to maintain the water 18 in liquid state 20, and the water 18 can be conducted in liquid state 20 and with a temperature 112 of at least 100 °C from the tank i6d of the primary turbine 26 to thereby drive the primary turbine 26. The energy handling system 10b may not comprise the primary heat exchanger 48 and the energy handling system 10b may for example be used for district heating where the water 18 in the outlet line 126 is conducted to a remote region.

[0124] Fig. 8 is a flowchart outlining general steps of a method of handling energy. The method may comprise heating S10 the water 18 in the tank i6a-i6d to a temperature 112 of 100 °C at atmospheric pressure. The method may further comprise evacuating S12 air from a top of the tank i6a-i6d after the heating of the water 18 to a temperature 112 of 100 °C at atmospheric pressure. The method may further comprise closing S14 the tank i6a-i6d after the evacuation of air.

[0125] The method comprises heating S16 the water 18 in the tank i6a-i6d to a temperature 112 of at least 100 °C while keeping a pressure in the tank 16a- i6d amounting at least to the saturation pressure 114 of the water 18 at each temperature 112 of the water 18 to maintain the water 18 in liquid state 20. The method further comprises conducting S18 the water 18 in liquid state 20 and with a temperature 112 of at least 100 °C from the tank i6a-i6d to the primary turbine 26 to thereby drive the primary turbine 26.

[0126] The method may further comprise controlling S20 the flow 44 of the water 18 through the primary turbine 26. The tank i6a-i6d may be a first tank 16a. In this case, the method may further comprise conducting S22 the water 18 downstream of the primary turbine 26 into a second tank 16b, 16c. The method may further comprise heating S24 the water 18 in the second tank 16b, 16c to a temperature 112 of at least 100 °C while keeping a pressure in the second tank 16b, 16c amounting at least to a saturation pressure 114 of the water 18 at each temperature 112 of the water 18 to maintain the water 18 in liquid state 20. The method may further comprise heat exchanging S26 between water 18 in the first tank 16a and water 18 in the second tank 16b, 16c when a volume of the water 18 in liquid state 20 in the first tank 16a has decreased below a threshold value.

[0127] The method may further comprise conducting S28 the water 18 in liquid state 20 and with a temperature 112 of at least 100 °C through the primary side 50. The method may further comprise controlling S30 the flow 44 of the water 18 through the primary turbine 26 based on the temperature on the secondary side 52.

[0128] The method may further comprise circulating S32 a secondary fluid 82 in a heat engine system 14 through the secondary side 52. The method may further comprise controlling S34 the secondary fluid 82 in the heat engine system 14 to execute a thermodynamic cycle involving a supercritical state of the secondary fluid 82.

[0129] While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed. Accordingly, it is intended that the present invention may be limited only by the scope of the claims appended hereto.

Claims

CLAIMS1. A method of handling energy, the method comprising:- heating (S16) water (18) in a tank (i6a-i6d) to a temperature (112) of at least 100 °C while keeping a pressure in the tank (i6a-i6d) amounting at least to a saturation pressure (114) of the water (18) at each temperature (112) of the water (18) to maintain the water (18) in liquid state (20); and- conducting (S18) the water (18) in liquid state (20) and with a temperature (112) of at least 100 °C from the tank (i6a-i6d) to a primary turbine (26) to thereby drive the primary turbine (26).

2. The method according to claim 1, wherein the water (18) in the tank (i6a-i6d) is heated to a temperature (112) of at least 150 °C.

3. The method according to any of the preceding claims, further comprising controlling (S20) a flow (44) of the water (18) through the primary turbine (26).

4. The method according to any of the preceding claims, wherein the method further comprises conducting (S28) the water (18) in liquid state (20) and with a temperature (112) of at least 100 °C through a primary side (50), downstream of the primary turbine (26), of a primary heat exchanger (48) comprising the primary side (50) and a secondary side (52).

5. The method according to claims 3 and 4, wherein the flow (44) of the water (18) through the primary turbine (26) is controlled (S30) based on a temperature on the secondary side (52).

6. The method according to claim 4 or 5, further comprising circulating (S32) a secondary fluid (82) in a heat engine system (14) through the secondary side (52).

7. The method according to claim 6, further comprising controlling (S34) the heat engine system (14) to execute a thermodynamic cycle involving a supercritical state of the secondary fluid (82).

8. The method according to claim 6 or 7, wherein the secondary fluid (82) comprises carbon dioxide.

9. The method according to any of the preceding claims, further comprising:- heating (S10) the water (18) in the tank (i6a-i6d) to a temperature (112) of 100 °C at atmospheric pressure;- evacuating (S12) air from a top of the tank (i6a-i6d) after the heating at atmospheric pressure;- closing (S14) the tank (i6a-i6d) after the evacuation of air; wherein the heating of the water (18) in a tank (i6a-i6d) to a temperature (112) of at least 100 °C is performed after closing the tank (i6a-i6d).

10. The method according to any of the preceding claims, wherein the tank (i6a-i6d) is a first tank (16a), and wherein the method further comprises:- conducting (S22) the water (18) downstream of the primary turbine (26) into a second tank (16b, 16c); and- heating (S24) the water (18) in the second tank (16b, 16c) to a temperature (112) of at least 100 °C while keeping a pressure in the second tank (16b, 16c) amounting at least to a saturation pressure (114) of the water (18) at each temperature (112) of the water (18) to maintain the water (18) in liquid state (20).

11. The method according to claim 10, further comprising heat exchanging (S26) between the water (18) in the first tank (16a) and the water (18) in the second tank (16b, 16c) when a volume of the water (18) in liquid state (20) in the first tank (16a) has decreased below a threshold value.

12. An energy handling system (10a; lob) comprising:- a tank (i6a-i6d) configured to contain water (18) and to withstand an internal pressure of at least 15 bar;- an energy source (4oa-4od) configured to heat water (18) in the tank (i6a-i6d) to a temperature (112) of at least 100 °C;- a primary turbine (26); and- an outlet valve (423-420) configured to control a flow (44) of water (18) out from the tank (i6a-i6d) and to the primary turbine (26).

13. The energy handling system (10a; 10b) according to claim 12, further comprising an electronic control system (34) including at least one data processing device (36) and at least one memory (38) having at least one computer program stored thereon, the at least one computer program comprising program code which, when executed by the at least one data processing device (36), causes the at least one data processing device (36) to control of the flow (44) of water (18) through the primary turbine (26).

14. The energy handling system (10a) according to claim 12 or 13, further comprising a primary heat exchanger (48) arranged downstream of the primary turbine (26), the primary heat exchanger (48) including a primary side (50) and a secondary side (52).

15. The energy handling system (10a) according to claim 13 and 14, further comprising a secondary temperature sensor (84) configured to measure a temperature of a secondary fluid (82) at the secondary side (52), wherein the at least one computer program comprises program code which, when executed by the at least one data processing device (36), causes the at least one data processing device (36) to control the flow (44) of water (18) through the primary turbine (26) based on a temperature as measured by the secondary temperature sensor (84).

16. The energy handling system (10a) according to claim 15, further comprising a heat engine system (14) containing the secondary fluid(82), wherein the heat engine system (14) is configured to execute a thermodynamic cycle involving a supercritical state of the secondary fluid (82).

17. The energy handling system (10a) according to claim 15 or 16, wherein the secondary fluid (82) comprises carbon dioxide.

18. The energy handling system (10a) according to any of claims 12 to 17, further comprising an exhaust valve (66a) at a top of the tank (i6a-i6d) for evacuating air from the tank (i6a-i6d).

19. The energy handling system (10a) according to any of claims 12 to 18, wherein the tank (i6a-i6d) is a first tank (16a) and wherein the energy handling system (10a) further comprises:- a second tank (16b, 16c) configured to contain water (18) and to withstand an internal pressure of at least 15 bar;- an energy source (40b, 40c) configured to heat water (18) in the second tank (16b, 16c) to a temperature (112) of at least 100 °C; and- a second outlet valve (42b, 42c) configured to control a flow of water (18) out from the second tank (16b, 16c) and to the primary turbine (26).

20. The energy handling system (10a) according to claim 19, further comprising a tank heat exchanger (y6ab, 76ba) arranged to heat exchange between water (18) in the first tank (16a) and water (18) in the second tank (16b, 16c).

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