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EP-4505128-B1 - ENERGY STORAGE DEVICE AND METHOD FOR STORING ENERGY USING SERIALLY CONNECTED THERMAL ENERGY STORAGE UNITS

EP4505128B1EP 4505128 B1EP4505128 B1EP 4505128B1EP-4505128-B1

Inventors

  • Pancheshnyi, Sergey
  • NENADIC, ZORAN
  • SAVIC, SASHA

Dates

Publication Date
20260506
Application Date
20230403

Claims (12)

  1. Energy storage device comprising a plurality of thermal energy storage units (1) which each comprise a thermal storage element (3) made of a solid material, for storing thermal energy; and a conduit (41) which is adapted to guide a fluid (W, S) through or along the thermal storage element (3), in order to transfer thermal energy from the thermal storage element (3) to the fluid (W, S); wherein at least two of the thermal energy storage units (1) are connected in series, such that the fluid (W, S) can be guided serially through the conduits (41) of these thermal energy storage units (1), wherein a bypass conduit (16) is provided which allows the fluid (W, S) to bypass at least one thermal energy storage unit (1) of the at least two serially connected thermal energy storage units (1), characterized in that each of the thermal energy storage units comprises an electrical heating device (5) for heating the thermal storage element (3) by means of electric energy, which electrical heating device (5) comprises a ceramic tube (52) with a main longitudinal center axis (54) and an electric wire (51), which is spirally wound around the main longitudinal center axis (54) inside or outside of the ceramic tube (52) .
  2. The energy storage device of claim 1, wherein the at least one thermal energy storage unit (1) which is allowed to be bypassed by the fluid (W, S) by means of the bypass conduit (16) is arranged upstream of at least another thermal energy storage unit (1) of the at least two serially connected thermal energy storage units (1).
  3. The energy storage device of claim 1 or 2, wherein at least one thermal energy storage unit (1) is connected in parallel to at least one thermal energy storage unit (1) of the at least two serially connected thermal energy storage units (1).
  4. The energy storage device as claimed in one of the preceding claims, comprising three or four serially connected thermal energy storage units (1), which can be bypassed by means of the bypass conduit (16) in such a way that, in the case of three serially connected thermal energy storage units (1), both one and two thermal energy storage units (1) can be bypassed as required, or, in the case of four serially connected thermal energy storage units (1), both one, two and three thermal energy storage units (1) can be bypassed as required.
  5. The energy storage device as claimed in one of the preceding claims, additionally comprising a heat exchanger (17), which is arranged serially downstream of the at least two serially connected thermal energy storage units (1), and which serves to cool the fluid (W, S) that is output from the at least two serially connected thermal energy storage units (1).
  6. The energy storage device of claim 5, wherein the heat exchanger (17) is adapted to cool the fluid (W, S) that is output from the at least two serially connected thermal energy storage units (1) by means of at least a part of the fluid (W, S) that is input to the at least two serially connected thermal energy storage units (1).
  7. The energy storage device as claimed in one of the preceding claims, additionally comprising a fluid tank (19) for storing heated or partially heated fluid (W, S) that is output from one of the plurality of thermal energy storage units (1), in order to use the stored heated or partially heated fluid (W, S) for cogeneration and/or for inputting the stored heated fluid (W, S) to at least one of the plurality of thermal energy storage units (1).
  8. The energy storage device as claimed in one of the preceding claims, additionally comprising a heat transfer material (7), which is arranged between the conduit (41) and the thermal storage element (3) of one or more of the plurality of thermal energy units (1), and which is adapted to dimensionally compensate for differential thermal expansions of the conduit (41) and the thermal storage element (3).
  9. The device as claimed in one of the preceding claims, wherein a field shield (53) partially or completely surrounding the ceramic tube (52) is provided in the region of each end of the spirally wound electric wire (51).
  10. Method for storing energy by means of an energy storage device, as claimed in one of the preceding claims, with a plurality of thermal energy storage units (1) each comprising a thermal storage element (3) made of a solid material, an electrical heating device (5) and a conduit (41) which is adapted to guide a fluid (W, S) through or along the thermal storage element (3), wherein at least a first thermal energy storage unit (1) and a second thermal energy storage unit (1) of the plurality of thermal energy storage units (1) are connected in series, and wherein each electrical heating device (5) comprises a ceramic tube (52) with a main longitudinal center axis (54) and an electric wire (51), which is spirally wound around the main longitudinal center axis (54) inside or outside of the ceramic tube (52), the method comprising the steps of - heating the thermal storage element (3) of the second thermal energy storage unit (1) by means of electric energy; and - guiding a fluid (W, S) through the conduit (41) of the second thermal energy storage unit (1), in order to transfer thermal energy from the thermal storage element (3) of the second thermal energy storage unit (1) to the fluid (W, S), while bypassing the first thermal energy storage unit (1) using a bypass conduit (16).
  11. The method of claim 10, further comprising the steps of - heating the thermal storage element (3) of the first thermal energy storage unit (1) by means of electric energy, when the thermal storage element of the second thermal energy storage unit (1) has reached a certain temperature; and - closing the bypass conduit (16) and guiding the fluid (W, S) serially through the conduits (41) of the first and the second thermal energy storage units (1).
  12. The method of claims 10 and 11, wherein the second thermal energy storage unit (1) is arranged downstream of the first thermal energy storage unit (1), wherein the energy storage device additionally comprises a heat exchanger (17), which is arranged serially downstream of the second thermal energy storage unit (1), and wherein the method further comprises the step of - cooling the fluid (W, S) that is output from the second thermal energy storage unit (1) by means of the heat exchanger (17), when the thermal storage element (3) of the second thermal energy storage unit (1) exceeds a certain temperature.

Description

TECHNICAL FIELD The present invention relates to an energy storage device comprising a plurality of thermal energy storage units of which at least two are connected in series. The invention also concerns a method for storing energy by means of such an energy storage device. PRIOR ART For generating electricity, renewable sources such as wind and solar power are increasingly used. The problem, however, very often associated with renewable energy sources is the continuous availability of the generated electric power. For example, wind has an intermittent nature and is not blowing constantly for 24 hours and seven days a week. Solar energy is only available during daylight and is highly dependent on weather conditions, in particular the amount of clouds. Therefore, to make renewable energy sources more attractive and to increase the availability of the electric energy generated from such sources, energy needs to be stored. Today, there are different energy storage technologies available, ranging from batteries, pump storage systems, compressed air storages and various versions of energy storage using heat, either at high or at low end. By means of these energy storage technologies, energy is stored in the form of e.g. thermal energy, pressurized air or chemical energy in times when a surplus of the renewable source is available and is later converted into electric energy and used during times of high demand and/or low availability of the renewable source. The main issues that today's energy storage systems are facing are their efficiency and their relatively low energy storage density (stored energy per unit of surface or volume). Systems in which energy is stored based on compressed air are for example disclosed in WO 2004/072452 A1, DE 10 2011 112 280 A1, US 2012/0085087 A1, DE 44 10 440 A1, WO 2016/176174 A1 and CN 103353060 A. In WO 2019/149623 A1 of the same applicant, an energy storage device is proposed in which thermal storage elements made of a solid material are arranged within a gas receptacle. The thermal storage elements can be heated up by means of an electrical heating device. Thus, the device allows the combined storage of both thermal energy and compressed gas. The stored compressed gas is already heated and, as a result, can directly be used to e.g. drive a gas turbine. With regard to large-scale applications, molten salt energy storage systems are known which are based on the heating of liquid salt. In these systems, salt is heated during times of high energy availability and used during times, when energy is needed, to create heated steam for driving a steam turbine. Most of the currently available energy storage systems for the generation of steam have the common drawback, that an intermediate medium is used for charging the thermal storage and/or for extracting heat for steam production. The intermediate medium (e.g. air, molten salt, etc.) is heated by an independent energy source and the heat accumulated in the storage is used for generating steam by means of a heat transfer process. Thus, the intermediate medium is heated by means of heat transfer from the thermal storage and then transfers the obtained thermal energy to the steam in a heat exchanger. These indirect processes for transferring the energy from the storage device to the steam provide additional parasitic losses and significantly reduce system efficiency. Moreover, the additional equipment needed for circulating the intermediate medium makes the system complicated and less robust. Recently, energy storage devices have been proposed which use solid storage materials in the form of stones or concrete, in order to store thermal energy. The stored thermal energy can be used in times of high demand to generate steam for heating or for driving a steam power plant, in order to convert the stored thermal energy back to electric energy. In several publications, solid materials such as graphite (WO 2005/088218 A1; US 4,136,276 A), metals (iron - EP 1 666 828 A2, steel - WO 91/14906 A1) or MGA (WO 2014/063191 A1) are proposed as storage materials. In several publications, it is suggested to heat the solid storage materials by electric resistive heaters (WO 2005/088218 A1, WO 91/14906 A1 and WO 2012/038620 A1) or by induction (US 4,136,276 A). For generating steam based on the stored thermal energy, it is proposed in WO 2005/088218 A1 to provide pipes, in order to guide water along the storage material. In the device as disclosed by EP 1 666 828 A2, a conduit is provided within the metallic storage material. In WO 91/14906 A1, separate blocks with baffle plates are used. The difficulty with pipes is the thermal contact resistance between the pipes and the storage material, which may require an overheating of the storage material, in order to achieve the required steam parameters. The provision of a conduit formed by the storage material itself is only applicable with metallic storage materials that have a moderate thermal capacity. Th