EP4081699A1

EP4081699A1 - Power plant with energy storage system

Info

Publication number: EP4081699A1
Application number: EP21704418.9A
Authority: EP
Inventors: Jan Rudolf Eggers; Daniel HUCK; Jonathan MEINERT; Jochen OEXMANN; Alexander Zaczek
Original assignee: Siemens Gamesa Renewable Energy GmbH and Co KG
Current assignee: Siemens Gamesa Renewable Energy GmbH and Co KG
Priority date: 2020-02-11
Filing date: 2021-01-25
Publication date: 2022-11-02
Also published as: WO2021160415A1

Abstract

A system is provided that comprises a combined heat and power (CHP) plant (20) that is operable to generate electrical power and to provide a source of heat, wherein the CHP plant (20) is configured to supply heat to a heat consumer (40). The system further includes an energy storage system (30) storing energy in the form of thermal energy, wherein the energy storage system (30) is configured to supply heat to said heat consumer (40). The energy storage system (30) comprises an energy storage device (31) configured to store thermal energy, and a heat exchanger (32) configured to supply heat towards said heat consumer (40). The energy storage system (30) is configured to be operable at least in a charging mode in which a working fluid transfers heat from a heat source (33) to the energy storage device (31) to charge the energy storage device (31) and in a discharging mode in which the working fluid transfers heat from the energy storage device (31) to the heat exchanger (32).

Description

Power plant with energy storage system

FIELD OF THE INVENTION

The invention relates to a system comprising a combined heat and power plant and an energy storage system that stores thermal energy. The invention further relates to a method of operating such system.

BACKGROUND OF THE INVENTION

In combined heat and power (CHP) or cogeneration plants elec tricity (electrical power) and useful heat are generated sim ultaneously. Due to the coupled generation, there are certain disadvantages to CHP plants. Heat and electrical power gener ation cannot be completely decoupled. A shift in the produc tion of one output has an impact on the second output as well. In general, CHP plants can be run in one of two modes. In the heat-driven operation mode, the facility is operated according to the heat demand that it is supplying, while electrical power is a secondary output. In the power-driven operation mode, the electrical power output is controlled as a setpoint while the heat is a resulting by-product.

The working principle of a steam power plant used for CHP generation is to extract steam from the steam turbine, which is then used for heat generation. Two possible implementa tions are shown in Fig. 1 and Fig.2.

Fig. 1 shows an implementation of CHP plant 20 with a back pressure steam turbine 21. The CHP plant 20 further includes a steam generator 23 and a pump 24 that conveys the working fluid (steam/water) in the cycle. The steam turbine 21 is (rotationally) coupled to a generator 25 that generates elec trical power. In the back-pressure steam turbine 21, the steam is only expanded until the required temperature for the heat demand of a heat consumer 40 is reached. This corre sponds to an over-pressure relative to the atmospheric pres sure. The extracted steam is generally still superheated.

This limited expansion reduces the power output of the steam turbine 21 and therefore the net electrical power generation. The steam expanded by steam turbine 21 is condensed in a heat condenser 22 which supplies respective heat to the heat consumer 40, which can for example be a district heating net work 41 or another type of consumer. The heat may be trans ported along a heat transport path 42 from the heat condenser 22 to the heat consumer 40, wherein a heat transfer medium, such as water or steam, can be conveyed along the heat transport path 42 using a pump 43.

Fig. 2 shows an implementation of the CHP plant 20 with an extraction condensing turbine 26. In the extraction condens ing turbine 26, a portion of the steam is extracted from an intermediate stage 27 of the turbine 26 for heat generation, the steam being provided to the heat condenser 22 to supply the heat consumer 40. The rest of the steam is expanded in the steam turbine 26 to a minimum pressure, and is condensed in the condenser 28. The extraction of steam from the inter mediate stage 27 again leads to a reduced turbine work and thus a reduced generation of electrical power.

Auxiliary boilers (not shown) can be used in such CHP plants to cover a constant heat demand in cases where the main steam generator 23 is not operative or not sufficient. The auxilia ry boiler typically uses fossil fuels as a fuel source. Steam accumulators in the district heating network 41 can be used to store steam in order to smooth out peaks and troughs in the heat demand.

It is desirable to be able to independently meet a heat de mand by the heat consumer and to generate and supply electri cal power to the grid by means of such CHP plant. It is also desirable to avoid the burning of fossil fuels to power such auxiliary boilers to meet the heat demand. SUMMARY OF THE INVENTION

Accordingly, there is a need to mitigate at least some of the drawbacks outlined above and to improve the capability of such CHP plant to provide heat and electrical power.

According to an embodiment of the invention, a system com prising a combined heat and power (CHP) plant that is opera ble to generate electrical power and to provide an output of heat is provided, wherein the combined heat and power plant is configured to supply the heat to a heat consumer. The sys tem further comprises an energy storage system storing energy in the form of thermal energy, wherein the energy storage system is configured to supply heat to said heat consumer.

The energy storage system comprises an energy storage device configured to store thermal energy, and a heat exchanger con figured to supply heat towards said heat consumer. The energy storage system is configured to be operable at least in a charging mode in which a working fluid transfers heat from a heat source to the energy storage device to charge the energy storage device and in a discharging mode in which the working fluid transfers heat from the energy storage device to the heat exchanger.

In the embodiment, the heat consumer can be supplied with heat both from the CHP plant and from the energy storage sys tem. If the heat demand of the heat consumer is to be (at least partly or fully) covered by the energy storage system, the heat stored in the energy storage device can be extracted and transferred to the heat consumer through the heat ex changer (HE). The electrical power (also termed electricity herein) generated by the CHP plant may for example be provid ed to a power grid.

The embodiment of the invention may thus provide the integra tion of an energy storage system into the CHP plant to there by allow a decoupling of heat and electricity generation. A demand-oriented and independent generation of electricity and heat in a CHP plant is made possible. The CHP plant no longer has to be run in a heat-driven or electrical power-driven op eration mode, both kinds of output can be delivered constant ly and individually. In periods of high electricity and heat demand, a CHP plant with an attached energy storage system can feed more electricity into the grid than a stand-alone CHP plant since the heat demand can be covered by the energy storage system and no steam has to be extracted from the steam turbine to be used for covering the heat demand. The increased amount of electrical power fed into the grid re sults in increased revenue for the plant operator. In case of a low electricity demand or low price of electricity, if a shut-down of the power plant would result in a higher finan cial loss than continuing electrical power generation, with the addition of the energy storage system, the generated electrical power can be used for charging the storage device instead of feeding the electricity into the grid unprofita- bly. Even when the CHP plant is shut down, a heat supply can still be achieved with the energy storage system. If the heat source, e.g. a heater, of the energy storage system is of sufficient size, it can be used to cover the heat demand in case of low electricity price.

By the embodiment of the invention, heat production and con sumption can be partly decoupled, e.g. in times of high re newable energy production. This allows the CHP plant to react flexibly to changes in electrical power demand.

The heat consumer may include a heat transport network con nected to the heat exchanger, i.e. the heat consumer may di rectly receive thermal energy via the heat exchanger. Such heat transport network may further be directly connected to a heat condenser of the CHP plant to be capable of receiving thermal energy of the CHP plant, or a working fluid of the CHP plant may directly be provided into the heat transport network. The heat consumer may for example be a district heating network including such heat transport network. Preferably, the system comprises a first heat transfer medium for transferring heat from the heat exchanger (HE) to the heat consumer, the system being configured to guide the first heat transfer medium from the heat exchanger to the heat con sumer along a first heat transport path. The heat consumer and the first heat transfer medium can thus be distinct and decoupled from the cycle and working medium of the energy storage system.

The first heat transport path may for example be part of a district heating network, and the first heat transfer medium may correspond to a working fluid of such district heating network. The heat consumer may be the district heating net work or the group of individual heat consumers of such net work. The first heat transport path may in another example be a closed path (e.g. an intermediate circuit) that supplies a heat consumer that has an own heat cycle. The first heat transport path may in a further example be part of a steam line that provides heat to a heat consumer in form of an in dustrial process.

In an embodiment, the combined heat and power plant comprises a heat condenser (HC) and a second heat transfer medium for transferring heat from the heat condenser to the heat consum er. The system may be configured to guide the second heat transfer medium from the heat condenser to the heat consumer along a second heat transport path. The second heat transfer medium and the heat consumer can thus be distinct and decou pled from the cycle and working medium of the CHP plant.

For example, the first heat transport path can be separate or distinct from the second heat transport path, they may not be in flow communication. Heat supply of the common heat consum er can thus be entirely separated.

In another example, the first heat transfer medium is the same as the second heat transfer medium, and the first and the second heat transport paths form part of the same common heat transport path that provides heat to the heat consumer. Accordingly, both the heat exchanger and the heat condenser may thus be capable of supplying heat to the same heat transport medium. The common heat transport path may imple ment a single steam cycle or an open path that can either be run by the HC of the CHP plant or by the HE of the storage system. Again, the first and second heat transport paths may form an intermediate circuit that supplies heat to the heat consumer, or they may form part of the heat consumer, e.g. of a district heating network, or they may form part of a steam line.

Preferably, such common heat transport path comprises valves that are controllable to selectively bypass the heat exchang er of the energy storage system and/or the heat condenser of the CHP plant. The inoperative component of both can be by passed by using the respective valves. The other can still efficiently supply heat to the heat consumer, without heat loss in the inoperable HE or the HC.

In both examples, heat supply from either the CHP plant or the energy storage system may thus be entirely decoupled, while allowing the heat consumer to be supplied with heat even if no or only little heat is available from the CHP plant.

In any of these embodiments and examples, the first and/or second heat transfer medium may be steam or CO2. The first and second heat transport paths may implement respective steam cycles/C0₂ cycles, or one or both may implement open paths in which the heat transport medium is discharged after having passed on its thermal energy. The two cycles, the com mon cycle or the open path(s) power the common heat consumer.

In an embodiment, the system further comprises a second heat condenser coupled between the heat exchanger and the heat consumer such that the heat condenser receives a heat trans fer medium that has passed through the heat exchanger to thereby transfer heat from the heat exchanger via the second heat condenser to the heat consumer. The heat transport path via the heat exchanger can thus be decoupled from a cycle, such as a steam cycle, of the heat consumer.

In an embodiment, the heat consumer is connected in a flow path of a working fluid of the CHP plant so as to receive heat via the working fluid of the CHP plant. The CHP plant may use steam as a working fluid. Steam originating from the CHP plant may thus directly be injected into a steam network of the heat consumer, without a heat condenser in between. This may for example be steam that is taken from an interme diate stage of a steam turbine (extraction condensing tur bine) of the CHP plant, or steam that has been partially (not fully) expanded by a steam turbine (back-pressure turbine) of the CHP plant. The working fluid (steam or condensed fluid) that has passed the heat consumer may be recirculated into the CHP plant, e.g. to complete a respective water-steam cy cle. It should be noted that the recirculation of steam into the CHP plant is optional. The steam may also be discharged after having passed the heat consumer.

It is further advantageous if the system can be operated to inject steam generated by the heat exchanger of the energy storage system into a water-steam cycle of the CHP plant. Steam generated using thermal energy stored in the energy storage system can be used in the CHP plant in order to re duce the fuel consumption, e.g. by using the steam from the energy storage system as start-up steam. By providing addi tional steam, the flexibility of the CHP plant during start up and ramping is increased without using fossil fuel fed auxiliary boilers.

The heat consumer may for example be a district heating sys tem or network, an industrial process or the like. The HE and/or the HC may directly heat a working medium (e.g. the first and/or second heat transfer medium) of the heat consum er or further intermediate condensers and/or heat exchangers may be provided. The heat consumer may employ a steam line without return path for supplying plural processes requiring steam.

The energy storage system may comprise the heat source, in particular a heater. The energy storage system may for exam ple comprise an electrical heater as the heat source that is configured to heat the working fluid of the energy storage system at least in the charging mode, wherein the electrical heater is preferably electrically coupled to an electrical power output of the CHP plant so as to enable the supply of electrical power from the CHP plant to the electrical heater. The CHP plant can be used to charge the energy storage system via electrical power generated by the CHP plant. For example in cases where the electricity demand is low (i.e. demand be low a minimum operating load of the CHP plant) but neverthe less critical and thus highly valued, the energy storage sys tem can be used to cover this demand profitably. To realize this, the CHP plant operates at or above the minimum operat ing load and any excess generation of electrical power is used to charge the energy storage device. Additional flexi bility is also added with the electrical heater of the stor age system, since the heater can be used to directly cover a heat demand by converting power to heat even when the storage device itself is not charged. It should be clear that in oth er implementations, the electrical heater may additionally or alternatively be powered from a power grid.

The energy storage system may be a horizontal energy storage system. "Horizontal" means that the main fluid flow through the storage device (chamber) is in horizontal direction. In other implementations, the energy storage device may be a vertical storage device wherein a main flow direction of the heat transfer medium through the storage device is in verti cal direction. The energy storage system may comprise a blow er for conveying the working fluid through the energy storage system. The energy storage device may comprise an insulated housing or chamber that forms an inlet and an outlet. The en- ergy storage device (e.g. the housing/chamber) may contain a heat storage material. The liquid or gaseous working fluid is used to transfer heat to the storage material during the charging mode and to extract heat from the storage material during the discharging mode. The energy storage system may use heated air as a working fluid.

The flow direction of the working fluid through the energy storage device is preferably opposite in the charging mode and the discharging mode (i.e. it is reversed), although it may be the same in some implementations.

For charging the energy storage device, the energy storage system is operated in the charging mode in which the working fluid flows along a charging flow path, which passes the working fluid through the heat source (heater). By passing through the heat source (heater), the temperature of the working fluid inside the energy storage system is increased. Inside the energy storage device, the working fluid transfers its heat to the heat storage material. For discharging the energy storage device, the energy storage system is operated in the discharging mode in which the working fluid flows along a discharging flow path that passes through the energy storage device and the heat exchanger. The working fluid en ters the energy storage device in a low temperature state which results in a heat transfer from the heat storage mate rial to the working fluid. The heated working fluid is then directed to the heat exchanger which transfers the heat from the working fluid to a heat transfer medium, which flows in a separate cycle or path. The heat exchanger is in turn con nected to the heat consumer. The heat consumer receives the heated heat transfer medium from the heat exchanger.

The energy storage system may be configured to store thermal energy in the energy storage device at a temperature between 200 °C and 1000 °C, preferably between 400 °C and 1000 °C, more preferably between 500°C and 900°C. For example, the temperature in the energy storage device may be kept between 550 and 800°C. In the discharging flow path, the temperature of the working fluid leaving the energy storage device may lie within the range of about 500°C to 800°C. The pressure of the working fluid in the charging flow path and in the dis charging flow path may be lower than 2 bar, it may be close to atmospheric pressure, e.g. between 0.8 bar and 1.2 bar.

Flow channels may be provided in the heat storage material; they may form due to the structure of the material, e.g. by interspaces, gaps and/or pores in the heat storage material, or they can be built into the heat storage material. Prefera bly, the heat storage material comprises a mesh of heat ex change channels through which the working fluid passes, both along the charging and the discharging flow paths.

The heat storage material may comprise or consist of gravel, rubble, sand and/or grit. It may comprise or consist of rocks, bricks, stone, lava stone, granite, basalt, slag and/or ceramics, or a combination thereof, and can be provid ed as bulk material (it may be configured as pebble bed). The heat storage device can thus be provided cost efficiently while being capable of storing large amounts of thermal ener gy.

The chamber housing the heat storage material may be a space, a cavity, an excavation or a housing (e.g. a concrete struc ture) in which the heat storage material is located. In some configurations, the energy storage device may include several storage chambers placed in series and/or parallel with valves and piping in between, including bypass-lines. This may allow an adaptation of the size of the active storage chamber to the present needs. For example, during charging, the flow of the working fluid and thus the heating may be stopped for one chamber if the specific chamber has been fully charged. This allows the maintaining of a desired temperature gradient within each of the storage chambers. The energy storage system is preferably configured to sequen tially operate in one of plural storage system operating modes, including said charging mode and said discharging mode, depending on heat demand by the heat consumer, availa bility of heat from the heat source (e.g. availabil ity/pricing of electrical power) and status of the energy storage device (fully charged, fully discharged, or in be tween). The storage system operating modes may include fur ther operating modes, such as 'mixed modes' in which heat from the heat source (heater) is supplied both to the energy storage device and the heat exchanger, or only to the heat exchanger (e.g. if the energy storage device is discharged or heat demand is very high); they may further comprise an idle mode in which neither charging nor discharging takes place, and in which the heater may be inactive.

The energy storage system may comprise a storage system control unit configured to operate the energy storage system sequentially in the storage system operating modes, e.g. the charging mode and the discharging mode. The storage system control unit may in particular control respective control valves that are opened and closed so that the working fluid is conveyed along the respective charging or discharging flow path (or another flow path corresponding to the further possible operating modes).

In an embodiment, the system may operate in accordance with an operating mode selected from plural available operating modes (system operating modes). The system may include a re spective controller (system controller) that is configured to control the operation of the system (i.e. of the CHP plant and/or of the energy storage system) in accordance with such operating mode and that may make the selection. In some im plementations, the controller may only control the energy storage system, it may for example perform a respective con trol based on the state of the CHP plant, an energy demand of the heat consumer and may optionally further consider the electricity price. The operating mode determines at least one, preferably all, of the following operating parameters: generation of electrical power by the CHP plant (e.g. deter mines if such generation takes place and/or the amount of generated electrical power), supply of heat provided by the CHP plant (e.g. determines if such supply takes place and/or the amount of heat supplied), and operating mode of the ener gy storage system, the operating mode of the energy storage system being selected from at least said charging mode and said discharging mode. By means of such control, an efficient operation of the system may be ensured.

In some implementations, the controller may for example ob tain as input the generation of electrical power by the CHP plant, the supply of heat provided by the CHP plant, the heat demand of the heat consumer, and optionally the electricity price, and may control the operating mode of the energy stor age system accordingly, e.g. by selecting a respective system operating mode. Such controller may for example be employed if the CHP plant already includes a dedicated controller, and the energy storage system is retrofitted to the CHP plant. In other implementations, a central controller may be provided that controls both, the CHP plant and the energy storage sys tem.

As indicated above, the (storage system) operating modes of the energy storage system may include further storage system operating modes that may be set by the system controller. The system controller may as such include the control unit of the energy storage system or send respective control commands to such control unit if that is implemented as a separate con troller.

The system is preferably configured to operate in accordance with an operating mode of said plural available operating modes that comprises at least the generating of electrical power by the CHP plant (which may be supplied towards a power grid or other power consumer) and the supplying of heat by the energy storage system to the heat consumer. In such oper- ating mode, the generation of electrical power by the CHP plant can be decoupled from the heat demand by the heat con sumer, which is supplied from the energy storage system.

The system is further preferably configured to operate in ac cordance with an operating mode of said plural available op erating modes that comprises at least the generating of elec trical power by the CHP plant and the supplying of electrical power from the CHP plant to the energy storage system to charge the energy storage device with heat generated from the supplied electrical energy, for example by means of an elec trical heater acting as the heat source. In such operating mode, excess electrical power generated by the CHP plant can efficiently be used for increasing the charging level of the energy storage device, thereby making the overall system more energy efficient. It is also conceivable that the electrical power is provided by the CHP plant into a power grid, and the energy storage system uses excess electrical power from the power grid to charge the energy storage device, i.e. there does not need to be a direct transfer of electrical power from the CHP plant to the energy storage system.

In a particular implementation, the system (e.g. the control ler) is configured to select the operating mode of the system based on one or a combination of the following operating con ditions: availability of the energy storage system for discharg ing thermal energy from the energy storage device; availability of the energy storage system for storing thermal energy in the energy storage device; presence of a heat demand of the heat consumer; presence of a demand for electrical power above a demand threshold, the demand threshold preferably being indica tive of a minimum level of electrical power demand at or above which the CHP plant can profitably supply electri cal power or of a minimum level at or above which the CHP plant can generate electricity at its lowest output setting; and a price for electrical power above a price threshold, the price threshold preferably being indicative of a minimum price level for electrical power above which the generation of electrical power by the CHP plant is prof itable.

By considering these operating conditions describing the state of the energy storage system and external parameters, an operating mode can be selected reliably that maximizes the system efficiency and that may further ensure a profitable operation of the system. For example, the first two, the first three or the first four operating conditions may at least be used for making the selection; in some implementa tions, all of these operating conditions are used.

In an exemplary implementation, the plural available operat ing modes of the system comprise at least one or a combina tion of the following operating modes: a first operating mode (A) in which the CHP plant is op erated to maximize electrical power generation and the energy storage system is operated to supply the heat de mand of the heat consumer; a second operating mode (B) in which the CHP plant gen erates electrical power (e.g. provided towards grid) and supplies heat to the heat consumer while no heat is sup plied to the heat consumer from the energy storage sys tem; a third operating mode (C) in which the CHP plant is op erated to generate electrical power and to supply the generated electrical power at least partially to a heat er of the energy storage system and optionally to other components, e.g. a blower, the energy storage system be ing operated in the charging mode, the CHP plant further supplying heat to the heat consumer; a fourth operating mode (D) in which the CHP plant is inactive and the energy storage system is operated to supply at least partially, preferably fully, the heat demand of the heat consumer; a fifth operating mode (E) in which the CHP plant is op erated to maximize electrical power generation and the energy storage system is not providing heat to the heat consumer (i.e. it may be inoperable); a sixth operating mode (F) in which the CHP plant is op erated to generate electrical power and to supply the generated electrical power at least partially to a heat er of the energy storage system, the energy storage sys tem being operated in the charging mode, wherein the CHP plant does not supply heat to the heat consumer; a seventh operating mode (G) in which the CHP plant and the energy storage system are both inactive; an eighth operating mode (H) in which a heat demand of the heat consumer is covered by electrical power from a power grid, the electrical power preferably being pro vided to an electrical heater of the energy storage sys tem to provide the heat for the heat consumer; a ninth operating mode (I) in which the energy storage system is charged with electrical power from a power grid, and in which optionally, a heat demand of the heat consumer is covered by electrical power from the power grid, wherein electrical power is preferably provided to an electrical heater of the energy storage system for charging of the energy storage device and optionally to provide the heat for the heat consumer; and a tenth operating mode (J) in which the CHP plant is op erated to generate electrical power and to supply the generated electrical power to a heater of the energy storage system, the energy storage system being operated in the charging mode.

Optionally, it is also conceivable that the system is config ured such that the CHP plant can supply heat to the energy storage system for charging the energy storage device (the heat may for example be used to reduce the energy consumption of a heater of the energy storage system when charging the energy storage device). The heat provided by the CHP plant may thus at least partially be stored in the energy storage device. Such operation has advantages in cases where there is no or only little heat demand from the heat consumer.

Optionally, an eleventh operating mode (K) may be provided in which the energy storage system is operated to increase (boost) the generation of electrical power by the CHP plant, for example by providing heat for feedwater preheating. Inac tive with respect to the CHP plant may mean that it neither supplies electrical energy nor heat. Inactive with respect to the energy storage system may mean that it is in an idle mode (no charging or discharging; no operation of the heater).

Preferably, the plural available operating modes of the sys tem comprise at least the first, third and/or sixth operating mode, and may further comprise one or more of the other modes. For example, they may comprise at least the first, second and third operating modes, or the first, third and tenth operating modes. In another example, they may comprise at least the sixth operating mode, the tenth operating mode and/or the eleventh operating mode, and may further comprise one or more of the other operating modes of the system. The controller may operate the system in a respective operating mode.

As indicated above, the energy storage system and/or the pow er plant may be inactive or shut down in operating modes D,

G, H, and I. It should be noted that in these operating modes D, G, H and I, the CHP plant may still continue electrical power generation if the expected penalties for a continued power generation are lower than the cost of a shutdown. If that is the case, operating mode J can be applied if charging of the energy storage device is available.

In a particular implementation, the system is configured to operate in the first operating mode (A) if the price for electrical power is above the price threshold, a heat demand of the heat consumer is present, discharge of the thermal en ergy storage device is available and the demand for electri- cal power is above the demand threshold; and/or in the third operating mode (C) if the price for electrical power is above the price threshold, a heat demand of the heat consumer is present, storage capacity of the thermal energy storage de vice is available and the demand for electrical power is be low the demand threshold; and/or in the sixth operating mode (F) if the price for electrical power is above the price threshold, a heat demand of the heat consumer is not present, storage capacity of the thermal energy storage device is available and the demand for electrical power is below the demand threshold. A more comprehensive selection logic for the operating mode in dependence on the state of the operat ing conditions is explained in more detail further below.

According to a further embodiment of the invention, a method of operating a system is provided, wherein the system com prises a combined heat and power plant that is operable to generate electrical power and to provide an output of heat, wherein the combined heat and power plant is configured to supply the heat to a heat consumer, and an energy storage system storing energy in the form of thermal energy, wherein the energy storage system is configured to supply heat to said heat consumer, the energy storage system comprising an energy storage device configured to store thermal energy, and a heat exchanger configured to supply heat towards said heat consumer, wherein the energy storage system is configured to be operable at least in a charging mode in which a working fluid transfers heat from a heat source to the energy storage device to charge the energy storage device and in a discharg ing mode in which the working fluid transfers heat from the energy storage device to the heat exchanger. The method com prises operating the system in an operating mode in which the heat consumer is supplied with heat from at least one of the combined heat and power plant and the energy storage system. By means of such method, advantages similar to the ones out lined further above may be achieved. The method may be performed by a system having any of the configurations described herein. The method may further com prise any of the steps described herein with respect to the system. Likewise, the system may be configured to carry out the method in any of the implementations disclosed herein.

A further embodiment of the invention provides a computer program for controlling a system comprising a CHP plant and an energy storage system, wherein the computer program com prises control instructions which, when executed by a pro cessing unit of a controller of the system that controls the operation of the CHP plant and the energy storage system, cause the processing unit to perform any of the methods de scribed herein. Such computer program, in particular the con trol instructions, may be provided on a volatile or non volatile storage medium or data carrier.

It is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combina tions or in isolation, without leaving the scope of the pre sent invention. In particular, the features of the different embodiments and examples of the invention can be combined with each other unless noted to the contrary.

BRIEF DESCRIPTION OF THE DRAWINGS

The forgoing and other features and advantages of the inven tion will become further apparent from the following detailed description read in conjunction with the accompanying draw ings. In the drawings, like reference numerals refer to like elements.

Fig. 1 is a schematic drawing showing a CHP plant includ ing a back-pressure turbine.

Fig. 2 is a schematic drawing showing a CHP plant includ ing an extraction condensing turbine. Fig. 3 is a schematic drawing showing a system including a CHP plant and an energy storage system according to an embod iment of the invention, wherein individual steam cycles are provided for the CHP plant heat condenser (HC) and the energy storage system heat exchanger (HE).

Fig. 4 is a schematic drawing showing a system including a CHP plant and an energy storage system according to an embod iment of the invention, wherein the CHP plant HC and the en ergy storage system HE operate a single steam cycle.

Fig. 5 is a schematic drawing showing a system including a CHP plant and an energy storage system according to an embod iment of the invention, wherein the CHP plant provides a di rect steam injection into the steam cycle of the heat consum er, the energy storage system using the HE to provide heat to the steam cycle.

Fig. 6 is a schematic drawing showing a system including a CHP plant and an energy storage system according to an embod iment of the invention.

Fig. 7 is a schematic drawing showing an energy storage device according to an embodiment of the invention.

Figs. 8 and 9 are schematic drawings illustrating a charging mode and a discharging mode, respectively, of an energy stor age system according to an embodiment of the invention.

DETAILED DESCRIPTION

In the following, embodiments of the invention will be de scribed in detail with reference to the accompanying draw ings. It is to be understood that the following description of the embodiments is given only for the purpose of illustra tion and is not to be taken in a limiting sense. It should be noted that the drawings are to be regarded as being schematic representations only, and elements in the drawings are not necessarily to scale with each other. Rather, the representa tion of the various elements is chosen such that their func tion and general purpose become apparent to a person skilled in the art. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, un less the context clearly indicates otherwise. The terms "com prising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted.

Figure 3 illustrates a system 10 including a CHP plant 20 and an energy storage system 30 according to an embodiment. The CHP plant 20 may include a turbine, in particular a steam turbine, a steam generator for providing steam to the steam turbine and a pump for conveying the working fluid in the wa ter-steam cycle of CHP plant 20. CHP plant 20 may in particu lar have any of the configurations described above with re spect to figures 1 and 2. CHP plant 20 includes the heat con denser 22 by means of which heat can be provided to the heat consumer 40.

The energy storage system 30 includes the energy storage de vice 31 that stores thermal energy. An exemplary implementa tion of energy storage device 31 is depicted in figure 7. It comprises an insulated housing or chamber 311 that forms an inlet 314 and an outlet 315. The housing 311 contains the heat storage material 312. As indicated above, the heat stor age material may comprise or consist of rocks, bricks, stone, lava stone, granite, slag, basalt and/or ceramics, or a com bination thereof, which may be provided in the form of grav el, rubble, sand and/or grit, preferably as bulk material.

For example, pebbles of lava rock may be employed. A working fluid in form of a liquid or gaseous heat transfer medium is used to transfer heat to the storage material during the charging mode and to extract heat from the storage material during discharging mode. During charging and discharging, the flow direction through device 31 may be kept the same or may be reversed, as described in more detail further below.

Turning back to figure 3, the energy storage system 30 fur ther comprises the heat exchanger 32 by means of which heat is provided towards the heat consumer 40. It further includes the heat source in form of heater 33 and a blower 34 that conveys a working fluid, in particular air, through the ener gy storage system 30. Operation in a charging mode (i.e. 'charging') is illustrated by the solid arrows in Fig. 3. By passing through the heater 33, the temperature of the working fluid inside the energy storage system 30 is increased. In side the energy storage device 31, the working fluid trans fers its heat to the heat storage material 312. For discharg ing the energy storage device 31, the energy storage system

30 is operated according to the hollow arrows in Fig. 3 (dis charging mode). The working fluid enters the storage device

31 in a low temperature state which results in a heat trans fer from the heat storage material 312 to the working fluid. The heated working fluid is then directed to the heat ex changer (HE) 32, which in turn is connected to the heat con sumer 40. Accordingly, by directing heated working medium through HE 32, the heat consumer 40 can be supplied with heat. A more detailed description of the operation of the heat storage system 30 is provided further below.

Accordingly, the CHP plant and the energy storage system sup ply the same heat consumer 40 with heat, in particular via the heat condenser 22 and the heat exchanger 32, respective ly. In the example of figure 3, individual and separate cy cles are provided for the HC 22 and the HE 32. The HE 32 pro vides heat to a first heat transfer medium that is conveyed along a first heat transport path 51 towards the heat consum er 40. The HE 32 exchanges heat between the working fluid of the energy storage system 30 and the first heat transfer me dium, which are kept separate by the HE 32. The first heat transfer medium can be conveyed along the first heat transport path by a pump, blower or the like (not shown). Similarly, the working fluid of the CHP plant 20 transfers heat to a second heat transfer medium using HC 22, which is conveyed (for example by a pump or blower) along a second heat transport path 52 towards the heat consumer 40. HC 22 likewise provides separation between the working fluid of the CHP plant and the second heat transfer medium. In the example of figure 3, the heat consumer 40 can thus receive heat via the first and/or the second heat transfer medium, which are kept separate.

The heat consumer 40 may for example be a district heating system that receives the heat, or may be an industrial pro cess that receives the heat. The heat consumer may directly receive the respective heated heat transfer medium, or a fur ther heat exchanger or heat condenser may be provided between the respective heat transport path 51, 52 and the heat con sumer 40 (allowing the respective heat transfer medium to circulate in a closed cycle without directly passing through the heat consumer 40).

In some implementations, the first and/or second heat transport path is an open path and the respective heat trans fer medium is discharged at the heat consumer 40 but not re turned (a supply of fresh heat transfer medium may then be provided upstream of the HE 32 or the HC 22). An example of such implementation may include a steam line or steam rail from which plural consumers (e.g. industrial processes) can draw steam. The first and/or second heat transfer medium may be steam or supercritical CO2.

In another exemplary implementation, the heat consumer 40 may be a district heating network (in particular the group of consumers in such network), and the first and/or second heat transport path 51, 52 may form part of such district heating network. The first and/or second heat transfer medium may ac cordingly be a working fluid of such district heating net work. In such implementation, the heat exchanger 32 and the heat condenser 22 provide separation towards a working fluid of the energy storage system and the CHP plant, respectively, but there is no intermediate circuit between the HE/HC and the heat consumer. Rather, the heat consumer is directly con nected to the HE and/or HC.

Electrical power generated by CHP plant 20 may be provided to a power grid (not shown). As indicated by the electrical pow er line 60, electrical power generated by CHP plant 20 may also be provided to the electrical heater 33 for heating the working medium of the energy storage system 30, and may op tionally also be provided to the blower 34 for driving the blower 34. Under which circumstances a fraction or all of the generated electrical power may be provided to the energy storage system 30 is explained in more detail further below. In other implementations, the CHP plant may provide the gen erated electrical power into a power grid, and the heater 33 may receive electrical power from such power grid.

Figure 4 illustrates a further possible implementation of the system 10, which is a modification of the system 10 of figure 3. Accordingly, only differences will be described and the above explanations equally apply to system 10 of figure 4. In figure 4, the first and second heat transport paths are not separate, but they form a common heat transport path 53 that directs the heat transfer medium from the HC 22 and/or the HE 32 to the heat consumer 40. There is accordingly only a sin gle steam cycle (or CO2 cycle) that can either be run by the HC 22 of the CHP plant 20 or the HE 32 of the energy storage system 30. The inoperative component of both is bypassed by using valves, which are indicated in figure 4. It should be clear that also both components 22, 32 can be active and can provide heat to the heat transfer medium and thus to the heat consumer 40. Again, the common heat transfer medium may be the working fluid of a heat consumer in form of a district heating network, and the common heat transport path 53 may form part of such district heating network. In another imple mentation, the single steam cycle may be provided as an open path, wherein the heat transfer medium is not returned but is discharged at heat consumer 40.

Figure 5 illustrates another possible implementation of the system 10, which is a modification of the system 10 of fig ures 3 and 4. Accordingly, only differences will be described and the above explanations equally apply to system 10 of fig ure 5.

In figure 5, the working fluid of the CHP plant 20 is direct ly provided to the heat consumer 40, i.e. there is no inter vening heat condenser 22. For example, steam originating from the CHP plant 20 is directly injected into the steam cycle of the heat consumer, without a heat condenser in between.

Again, it is noted that the recirculation of steam into the CHP plant 20 is optional. Heat consumer 40 is thus directly supplied with heat from CHP plant 20. Further, the CHP plant 20 can also be bypassed using the indicated valves, and heat can be supplied from the energy storage system 30. Also in this implementation, the heat consumer 40 can be supplied with heat from either the CHP plant 20 or the energy storage system 30. Such configuration also allows the injection of additional steam into the steam cycle of the CHP plant 20 by means of HE 32.

Figure 6 shows a generalized schematic overview of system 10, of which the exemplary systems of figures 3, 4, and 5 are possible implementations. The heater and the blower of the energy storage system 30 are indicated at reference signs 33, 34 and they receive electrical power from the power grid 65, which can for example be a renewable energy source grid (e.g. wind farm grid) or the utility grid. As indicated by solid arrows, heat is provided to storage device 31 during charg ing. During discharging, heat is provided from the storage device 31 to the heat exchanger 32, which is implemented as a stream generator. As indicated by dashed arrows, the steam generator can supply steam (and thus heat) to the heat con sumer 40. Likewise, the CHP plant 20 can supply steam to the heat consumer 40, e.g. using a separate steam cycle, a common steam cycle or by direct steam injection.

As indicated by electrical power line 60 (dotted line), elec trical power can be provided for charging the energy storage device 31 (as indicated above, the electrical power may also be provided from a power grid). This charging can occur via a separate electrical heater or via heater 33. Furthermore, in some operating modes, the storage device 31 may be bypassed via bypass 35 and the heater 33 may supply heated working fluid directly to the heat exchanger 32 (i.e. the steam gen erator) to generate steam. Heat supply to consumer 40 can thus be ensured even if the storage device 31 is already dis charged or cannot be discharged (e.g. because it is finan cially not attractive). Such bypass can be implemented in the examples of figures 3-5 by simply circulating the working fluid in the outer flow conduits (piping) of the energy stor age system 30 (thus bypassing storage device 31). Hybrid op eration is also conceivable, in which the heater is operating and the energy storage device is discharged simultaneously.

In operation, the energy storage device 31 can for example be charged with hot working fluid, wherein the fluid is heated via the electrical heater 33, set on hold/idle, discharged for uprating of CHP plant 20, discharged for CHP plant 20 start up, and discharged for steam supply to consumer 40.

Turning back to figure 3, a controller 70 is schematically illustrated that controls the system 10. It should be clear that controller 70 may not need to be implemented as a single physical unit, but may for example be implemented as plural units, e.g. computing systems, that are distributed and that are in communication with each other. The controller 70 com prises a processing unit 71 and a memory 72. Processing unit 71 may be any kind of processor, such as a microprocessor, or may be a digital signal processor, an ASIC or the like.

Memory 72 may include volatile and non-volatile memory, such as RAM, ROM, flash memory, a hard disc drive, cloud memory and the like. Memory 72 may store control instructions which when executed by processing unit 71 execute any of the meth ods described herein. Controller 70 may comprise further com ponents that are common to such controller, such as in put/output interfaces, a user interface, communication hard ware, e.g. a network card and the like.

Controller 70 controls the operation of the CHP plant 20 and the energy storage device 30 in accordance with the control instructions. It may for example implement a separate con troller 74 for controlling the operation of energy storage system 30 in accordance with respective storage system oper ating modes, as disclosed herein. It may further implement a controller that controls the electrical power output and the heat output of the CHP plant 20. The controller 70 may for example monitor, in particular obtain, measure or receive re spective operating conditions that can relate to states or the operating environment of the system 10 and can determine an operating mode for the system 10. Such operating mode may set the storage system operating mode, the electrical power output of the CHP plant, and the heat output of the CHP plant. Although the controller is only shown in the system 10 of figure 3, it should be clear that a respective controller can be present in any of the systems disclosed herein, in particular in the system of figures 4-6. The controller 70 may in some implementations control both, the CHP plant and the energy storage system. In other implementations, the con troller 70 may only control the energy storage system 30, yet may make use of information indicating the operating state of the CHP plant 20. For example, it may select the system oper ating mode based on such information, e.g. based on the gen eration of electrical power provided by the CHP plant and the supply of heat provided by the CHP plant.

The table below shows possible operation cases (corresponding to monitored operating conditions) of the system 10 and the resulting operating mode of the system. The following operat ing conditions can be considered, from which the different cases indicated in the table arise: - Electricity price above profit threshold: To fulfill this condition, the price per unit of electrical power fed into the power grid has to be above the margin at which the generation of electricity is profitable for the plant operator.

- Heat demand of consumer: To fulfill this condition, there has to be a heat demand of the consumer(s) 40 con nected to the CHP plant 20.

- Storage discharging available: To fulfill this condi tion, the energy storage system 30 has to contain a sub stantial amount of energy and be able to discharge this energy (no condition preventing the discharge, such as maintenance etc., must be present).

- Storage charging available: To fulfill this condition, the charging level of the energy storage system has to be below 100% and the charging mode has to be operation al in order to allow a further charging.

- demand for electrical power in the power grid above min imum load or above minimum profitable level (demand threshold): To fulfill this condition, the demand for electrical power in the power grid has to be at or above the level at which the CHP plant 20 can generate elec tricity at its lowest output setting or the level at which the CHP plant can profitably supply electrical power to the grid.

In the last column of the table, an operating mode identified by the letters A-K is assigned to each of the 18 cases. In some of these cases, more than one operating mode is feasi ble. The operating modes of the system are:

- A: In this operating mode, the CHP plant 20 is config ured for maximum electricity generation, there is no bleed steam for the heat supply necessary in the CHP plant 20 as the energy storage system 30 covers the heat demand by discharging its available stored energy (to heat consumer 40). - B: Since no discharging of the energy storage system 30 is available, the CHP plant 20 has to cover both the electrical power and the heat demand and a portion of the steam has to be taken from the steam turbine 21, 26 to cover the heat demand.

- C: Despite the electrical power demand being below the corresponding minimum load for the operation of the CHP plant 20 or below the minimum profitable level, the CHP plant 20 is still operational to cover both the heat and electrical power demand, the surplus of generated elec trical power is used to charge the energy storage system 30.

- D: The electrical power demand is below the minimum load for the operation of the CHP plant 20 and the energy storage system 30 cannot be charged or the electricity price is below the profit threshold in general. The pow er plant is shut down.(*) The stored thermal energy in the energy storage system 30 can be used to cover the heat demand.

- E: The CHP plant 20 is configured for maximum electrical power generation. The energy storage system 30 is not active since there is no heat demand.

- F: Despite the electrical power demand being below the minimum load for the operation of the CHP plant 20, the CHP plant 20 is still operational to cover the low but profitable electrical power demand, the surplus of gen erated electrical power is used to charge the energy storage system 30.

- G: Contrary to operation mode F, energy storage system charging is not available. Both, the CHP plant 20 and the energy storage system 30 are therefore inactive.(*)

- H: If present, the heat demand is covered by the availa ble electrical power in the power grid. The energy stor age system 30 and the CHP plant 20 are inactive.(*)

I: If present, the heat demand is covered by the availa ble electrical power in the power grid. The energy stor age system 30 is charged with electricity from the power grid. The CHP plant 20 is inactive.(*) - J: The CHP plant 20 is operative and only used for charging the energy storage system 30.

- K: The stored heat in the energy storage system 30 is used to boost the electrical power generation of the CHP plant 20, e.g. via feedwater preheating (i.e. the feed- water provided to the steam generator of the steam tur bine), evaporation, superheating, reheating or a combi nation thereof. It should be noted that in the cases marked with (*), it can still be reasonable to continue power generation of the CHP plant 20 if the expected penalties for a continued power gen eration are lower than the cost of a shutdown. If that is the case, operating mode J can be applied if charging of the en- ergy storage system 30 is available.

Table 1 - Exemplary cases for selecting the operating mode of system 10 based on given operating conditions

The controller 70 may for example be configured to select a respective operating mode of system 10 based on the above conditions. The controller 70 may for example use a logic that corresponds to table 1 shown above, it may for example employ a respective look-up table. Where plural possible op erating modes exist, the operator may specify the desired op erating mode in advance, or the operating mode may be dynami cally selected, for example based on an optimization parame ter, such as revenue maximization or lifetime maximization.

A more detailed description of the operation and possible im plementations of the energy storage system 30 is now given.

The storage system 30 may contain a non-pressurized air cycle (working fluid is air). The storage device 31 itself is part of the air cycle. During charging, the temperature of an air flow is increased by the heater 33, preferably an electrical resistance heater. The resulting hot air flows (horizontally) through the storage chamber device 31 and leaves with lower temperature at the other side of the storage device 31. A preferred storage chamber comprises or consists of a packed bed of volcanic stones in an isolated container (e.g. 311). Due to the high temperature difference between air and stones and the large surface area of the stones, the enthalpy dif ference is transferred to the stones directly after the entry (assuming a cold storage). The hot and warm part of the stor age device, each part with a uniform temperature distribu tion, is separated by a temperature transition area called thermocline. Further charging shifts the thermocline towards the warm side. Mixing effects as well as heat transfer mecha- nisms may lead to decreasing temperature gradients in the thermocline (e.g. during a longer standstill or after multi ple cycles without complete discharge) which enlarge the tem perature transition width. In avoidance of a lower amount of exergy in the storage because of the lower average tempera ture, small thermoclines are desirable. To overcome the pres sure loss within the storage chamber and to realize a running closed cycle, the air flows to a blower 34 after exiting the storage device 31.

Figure 8 illustrates the charging mode, and controllable valves 39 which direct the flow of working fluid (air) along the charging flow path (solid lines) are indicated. Due to the closed valve 39 (at bottom of figure 8) towards the heat exchanger 32, only the air cycle is active during charging. The inactive flow lines of the system 30 are shown as dashed lines in figure 8.

The discharging is illustrated in figure 9. For the discharg ing mode, the valve 39 towards the HE 32 is opened, the heat er 33 is switched off (therefore not shown in figure 9), and the flow direction through the storage device 31 is reversed. Therefore, the blower 34 leads the majority of warm air di rectly to the storage device 31. The air flow enters the storage device 31 at the warm side and exits with higher tem perature at the hot side. But contrary to charging, discharg ing shifts the temperature transition area in the storage chamber towards the hot side of the storage which is the rea son for a decreasing air temperature at the steam generator inlet as soon as the temperature transition reaches the hot side. To stay in operating range and avoid degraded efficien cy in the water-steam cycle at the heat consumer 40, a set air temperature at the warm side of the storage device 31 is used as a discharge stopping criteria. Consequently, a short er temperature transition area leads to longer discharging and therefore higher usable storage capacity. After transfer ring its heat to the heat exchanger 32, the air flows back to the blower 34. The system 30 preferably supplies heat to a heat consumer 40 in form of a district heating system, industrial heat consum er or the like. However, the energy storage system 30 of the above embodiments may also supply additionally heat to a fur ther (different) heat consumer, which may for example gener ate electricity from the heat.

By embodiments of the system, a demand-oriented and independ ent generation of electricity and heat in a CHP plant is made possible. The plant no longer has to be run in a heat-driven or power-driven operation mode, both kinds of output can be delivered constantly and individually. In periods of high electrical power and heat demand, a CHP plant with an at tached energy storage system can feed more electricity into the grid than a stand-alone CHP plant since the heat demand can be covered by the energy storage system and no steam has to be extracted from the steam turbine to be used for cover ing the heat demand. The increased amount of electricity fed into the grid results in increased revenue for the plant operator. If a shut-down of the power plant would result in a higher financial loss than continuing power generation, with the addition of the energy storage system, the generated pow er can be used for charging the storage instead of feeding the electricity into the grid unprofitably. Even when the CHP plant is shut down, a heat supply can still be achieved with the energy storage system. If the heater of the energy stor age system is of sufficient size, it can be used to cover the heat demand in case of low electricity price and/or to charge the storage device. Furthermore, in cases where the electric ity demand is low (i.e. demand below the minimum operating load) but nevertheless critical and thus highly valued the energy storage can be used to cover this demand profitably.

To do this, the power plant operates at or above the minimum operating load and any excess generation is used to charge the storage. Additional flexibility is added also with the heater of the energy storage system since the heater can be used to directly cover a heat demand by converting power to heat even when the storage device itself is not charged. The option of injecting steam generated in the energy storage system into the CHP plant cycle increases the flexibility of the CHP plant and can reduce the amount of fuel used in the CHP plant. The energy storage system can substitute fossil fuel auxiliary boilers. Some or all of the advantages de scribed above may be achieved by embodiments of the inven tion, in particular by connecting an energy storage system to the CHP plant and connecting the energy storage system to the same heat consumer as the CHP plant.

While specific embodiments are disclosed herein, various changes and modifications can be made without departing from the scope of the invention. The present embodiments are to be considered in all respects as illustrative and non- restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims

1. A system, comprising: a combined heat and power, CHP, plant (20) that is operable to generate electrical power and to provide an output of heat, wherein the combined heat and power plant (20) is con figured to supply the heat to a heat consumer (40); and an energy storage system (30) storing energy in the form of thermal energy, wherein the energy storage system (30) is configured to supply heat to said heat consumer (40), the en ergy storage system (30) comprising: an energy storage device (31) configured to store ther mal energy, and a heat exchanger (32) configured to supply heat towards said heat consumer (40), wherein the energy storage system (30) is configured to be operable at least in a charging mode in which a working fluid transfers heat from a heat source (33) to the energy storage device (31) to charge the energy storage device (31) and in a discharging mode in which the working fluid transfers heat from the energy storage device (31) to the heat exchanger (32).

2. The system according to claim 1, wherein the system com prises a first heat transfer medium for transferring heat from the heat exchanger (32) to the heat consumer (40), the system being configured to guide the first heat transfer me dium from the heat exchanger (32) to the heat consumer (40) along a first heat transport path (51).

3. The system according to claim 1 or 2, wherein the combined heat and power plant (20) comprises a heat condenser (22) and a second heat transfer medium for transferring heat from the heat condenser (22) to the heat consumer (40), the system be ing configured to guide the second heat transfer medium from the heat condenser (22) to the heat consumer (40) along a second heat transport path (52).

4. The system according to claims 2 and 3, wherein the first heat transfer medium is the same as the second heat transfer medium, the first and the second heat transport paths (51,

52) forming part of the same common heat transport path (53) that comprises the heat consumer (40).

5. The system according to claim 4, wherein the common heat transport path (53) comprises valves that are controllable to selectively bypass the heat exchanger (32) of the energy storage system (30) and/or the heat condenser (22) of the CHP plant (20).

6. The system according to any of the preceding claims, wherein the heat consumer (40) is connected in a flow path of working fluid of the CHP plant (20) so as to receive heat via the working fluid of the CHP plant (20).

7. The system according to any of the preceding claims, wherein the energy storage system (30) comprises an electri cal heater (33) as the heat source that is configured to heat the working fluid of the energy storage system (30) at least in the charging mode, wherein the electrical heater (33) is preferably electrically coupled to an electrical power output of the CHP plant (20) so as to enable the supply of electri cal power from the CHP plant (20) to the electrical heater (33).

8. The system according to any of the preceding claims, wherein the system (10) is configured to operate in accord ance with an operating mode selected from plural available operating modes, wherein the operating mode determines at least one, preferably all, of the following operating parame ters: generation of electrical power by the CHP plant (20), supply of heat provided by the CHP plant (20), and operating mode of the energy storage system (30), the operating mode of the energy storage system (30) being selected from at least said charging mode and said discharging mode.

9. The system according to claim 8, wherein the system (10) is configured to operate in accordance with an operating mode of said plural available operating modes that comprises at least the generating of electrical power by the CHP plant (20) and the supplying of heat by the energy storage system (30) to the heat consumer (40).

10. The system according to claim 8 or 9, wherein the system (10) is configured to operate in accordance with an operating mode of said plural available operating modes that comprises at least the generating of electrical power by the CHP plant (20) and the supplying of electrical power from the CHP plant (20) to the energy storage system (30) to charge the energy storage device (31) with heat generated from the supplied electrical power.

11. The system according to any of claims 8-10, wherein the system (10) is configured to select the operating mode based on one or a combination of the following operating condi tions: availability of the energy storage system (30) for dis charging thermal energy from the energy storage device (31); availability of the energy storage system (30) for stor ing thermal energy in the energy storage device (31); presence of a heat demand of the heat consumer (40); presence of a demand for electrical power above a demand threshold, the demand threshold preferably being indica tive of a minimum level of electrical power demand above which the CHP plant (20) can profitably supply electri cal power or of a minimum level at or above which the CHP plant (20) can generate electrical power at its low est output setting; and a price for electrical power above a price threshold, the price threshold preferably being indicative of a minimum price level for electrical power above which the generation of electrical power by the CHP plant (20) is profitable .

12. The system according to any of claims 8-11, wherein the plural available operating modes of the system comprise at least one or a combination of the following operating modes: a first operating mode in which the CHP plant (20) is operated to maximize electrical power generation and the energy storage system is operated to supply the heat de mand of the heat consumer (40); a second operating mode in which the CHP plant (20) gen erates electrical power and supplies heat to the heat consumer (40) while no heat is supplied to the heat con sumer (40) from the energy storage system (30); a third operating mode in which the CHP plant (20) is operated to generate electrical power and to supply the generated electrical power at least partially to a heat er (33) and/or to a blower of the energy storage system (30), the energy storage system (30) being operated in the charging mode, the CHP plant (20) further supplying heat to the heat consumer (40); a fourth operating mode in which the CHP plant (20) is inactive and the energy storage system (30) is operated to supply at least partially, preferably fully, the heat demand of the heat consumer (40); a fifth operating mode in which the CHP plant (20) is operated to maximize electrical power generation and the energy storage system (30) is not providing heat to the heat consumer (40); a sixth operating mode in which the CHP plant (20) is operated to generate electrical power and to supply the generated electrical power at least partially to a heat er (33) of the energy storage system (30), the energy storage system (30) being operated in the charging mode, wherein the CHP plant (20) does not supply heat to the heat consumer (40); a seventh operating mode in which the CHP plant (20) and the energy storage system (30) are both inactive; an eighth operating mode in which a heat demand of the heat consumer (40) is covered by electrical power from a power grid (65), the electrical power preferably being provided to an electrical heater (33) of the energy storage system (30) to provide the heat for the heat consumer (40); a ninth operating mode in which the energy storage sys tem is charged with electrical power from a power grid (65), and in which optionally, a heat demand of the heat consumer (40) is covered by electrical power from the power grid, wherein electrical power is preferably pro vided to an electrical heater (33) of the energy storage system for charging of the energy storage device and op tionally to provide the heat for the heat consumer (40); and a tenth operating mode in which the CHP plant (20) is operated to generate electrical power and to supply the generated electrical power to a heater (33) of the ener gy storage system (30), the energy storage system (30) being operated in the charging mode.

13. The system according to claims 11 and 12, wherein the system (10) is configured to operate in the first operating mode if the price for elec trical power is above the price threshold, a heat demand of the heat consumer (40) is present, discharge of the thermal energy storage device (31) is available and the demand for electrical power is above the demand threshold; and/or to operate in the third operating mode if the price for elec trical power is above the price threshold, a heat demand of the heat consumer (40) is present, the energy storage system (30) is available for storing thermal energy in the energy storage device (31), and the demand for electrical power is below the demand threshold; and/or to operate in the sixth operating mode if the price for elec trical power is above the price threshold, a heat demand of the heat consumer (40) is not present, the energy storage system (30) is available for storing thermal energy in the energy storage device (31), and the demand for electrical power is below the demand threshold.

14. A method of operating a system (10), wherein the system (10) comprises a combined heat and power plant (20) that is operable to generate electrical power and to provide an output of heat, wherein the combined heat and power plant (20) is configured to supply the heat to a heat consumer (40); and an energy storage system (30) storing energy in the form of thermal energy, wherein the energy storage system (30) is configured to supply heat to said heat consumer (40), the energy storage system (30) comprising an ener gy storage device (31) configured to store thermal ener gy, and a heat exchanger (32) configured to supply heat towards said heat consumer (40), wherein the energy storage system (30) is configured to be operable at least in a charging mode in which a working fluid trans fers heat from a heat source to the energy storage de vice (31) to charge the energy storage device (31) and in a discharging mode in which the working fluid trans fers heat from the energy storage device (31) to the heat exchanger (32); wherein the method comprises operating the system (10) in an operating mode in which the heat consumer (40) is supplied with heat from at least one of the combined heat and power plant (20) and the energy storage system (30).

15. A computer program for controlling a system comprising a CHP plant (20) and an energy storage system (30), wherein the computer program comprises control instructions which, when executed by a processing unit (71) of a controller (70) of the system (10) that controls the operation of the CHP plant (20) and of the energy storage system (30), cause the pro cessing unit (71) to perform the method of claim 14.