WO2020153896A1

WO2020153896A1 - Method and system for storing electrical energy in the form of heat and producing a power output using said heat

Info

Publication number: WO2020153896A1
Application number: PCT/SE2020/050054
Authority: WO
Inventors: Joachim KARTHÄUSER
Original assignee: Climeon Ab
Priority date: 2019-01-23
Filing date: 2020-01-23
Publication date: 2020-07-30
Also published as: SE1950081A1

Abstract

The invention relates to a system for storing heat energy and generating a power output in the form of electricity using the heat. The energy system comprising a heat power module (1) operating in accordance with a thermodynamic closed loop cycle process (RC) to generate a first power output (E1) from heat input (HSin) from a geothermal well, a receiver (2) for receiving the first power output (E1) and a second power output (E2) generated by at least one additional intermittent energy source (ES2) selected from solar photovoltaics, wind power, biogas electrification or other renewable energy source arranged to intermittently generate electricity. The energy system also comprises an electricity control system (3) controlling and distributing the first power output (E1) and second power output (E2) via the receiver (2) externally to an electrical grid, at least one flow control system (4) arranged to distribute the flow of a geothermal medium heated by the geothermal heat (HS) in the geothermal well and a controller (5). The controller (5) is arranged to direct the flow control system (4) to regulate the geothermal medium to i) be distributed from the geothermal well to a first thermal storage system (6) when a second power output (E2) is received, and ii) be distributed from the first thermal storage system (6) to be used as heat input (HSin) to the heat power module (1) mainly when a second power output (E2) is not received. The invention also relates to a method for storing electrical energy in the form of thermal energy and producing a power output using the thermal energy.

Description

DESCRIPTION

Title of Invention:

METHOD AND SYSTEM FOR STORING ELECTRICAL ENERGY IN THE FORM OF HEAT AND PRODUCING A POWER OUTPUT USING SAID HEAT

Field of The Invention

This invention relates to the field of power generation, and storage of energy and electricity.

Background and Prior Art

Energy sources, especially solar and wind, are intermittent. Electricity demand is also variable, see e.g. www.energy--cliaits.de/power.htm. Therefore, it is desirable to store electricity, e.g. in chemical form through electrolytic hydrogen production, in batteries, flywheels, magnetic technologies, in pumped hydro storage or in the form of compressed air. This enables the production of electricity at times of high demand, also referred to as“peak shaving” or“time shifting”. An overview of various storage technologies is found at

www.sandia. gov, www.store-proiect.eu, www.purdue.edu, www.irena.org. The references also discuss typical capital and operational costs of the various techniques, as well as application examples, energy densities, round-cycle efficiencies, energy and effect ranges etc.

The invention deals specifically with energy storage in the form of hot water. The following patent disclosures give an impression of the general art:

US 9,331,547 (L. Bronicki, Ormat Technologies) describes an elegant hybrid geothermal power plant where photovoltaic modules and a geothermal Rankine cycle cooperate in order to match electricity production and demand. An electric generator is driven to generate electricity by the turbine of the ORC fluid circuit and/or the DC motor, in turn driven by DC power produced by the PV module.

US 2014/0260246 (U. Fisher, Ormat Technologies) discloses a geothermal power plant comprising an Organic Rankine Cycle, ORC, unit, a geothermal well and a storage tank. The ORC unit uses thermal heat from hot brine in the well to generate electrical energy. In case of low demand for power, the ORC unit is partially or completely stopped, and the hot brine may be stored in storage tank.

US 7,178,337 by Tassilo Pflanz describes a geothermal storage method utilising a compressed gas energy storage system.

WO 2018/102265A1 by J. King et al. (Combined Power LLC) describes a combined geothermal and concentrated-solar-power system which is able to store energy.

US 7,566,980 by G. Fein (Genedics), US 8,005,640 by D. Chiefetz describe the general art, the latter disclosure describing a test system utilising heat and power pulses for testing geothermal reservoirs.

US 3,757,516 by B. McCabe (Magma Energy) gives a general historic overview over low temperature thermodynamic cycles in geothermal power plants.

The general technology to store excess electricity as heat, with possibility to recover at least part of the electricity through a thermodynamic cycle, is being referred to as“Carnot battery”, see htps://iea-eces.org/events/international-workshop-on-camot-batteries/· Heat at any temperature between 100 and 800 °C may be generated directly with resistive heating or by using a heat pump, and the heat may be stored in any medium including hot water (see Climeon WO2017/065683A1), molten salt (Google/Malta proposal), or volcanic stones (Siemens proposal). Heat and cold may be stored in separate containers. Typically, the round- trip-efficiency (RTE = output electricity/input electricity) is determined by the Coefficient of Performance (COP) of the heat pump and the practical thermodynamic efficiency of the thermodynamic cycle, and it is usually in the order of 30-50%.

The prior art does not provide economically attractive methods to store excess electricity in the form of heat and allowing to generate electricity from the heat at a temperature range of 70-120 °C at times of peak electricity demand. Object of the Invention

The object of the invention is to provide a method and a system for storing energy and producing electricity with a high efficiency and profitability.

The object of the invention is to provide a method and a system for storing energy and producing electricity with a high cycle turnaround efficiency, i.e. electrical energy produced by the Rankine Cycle (RC) divided by the electrical energy consumed by the device generating heat, >50%, >70% and even >90%. The method is preferably used for storing and time-shifting intermittent renewable electricity from solar and wind power at a scale above 1 MWh and a power effect of 150 kW and above, and it can be used to store any electricity.

The object of the invention is to provide a method and a system for storing energy and producing electricity wherein the method and system is used for quickly, i.e. on the scale of less than one minute, regulating power demand in the electrical grid.

The object of the invention is to provide a method and a system for storing energy and producing electricity wherein full and phase- and frequency-matched power is supplied at within less than one minute.

Summary of Invention

The present invention relates to a system for storing heat energy and generating a power output in the form of electricity using the heat. The energy system comprises a heat power module comprising a turbine generator arranged to generate a first power output in the form of electricity. The heat power module is operating in accordance with a thermodynamic closed loop cycle process being arranged to receive heat input from a geothermal well, wherein the well is functioning as first continuous energy source of geothermal heat, and a cold input from a cold source for phase change of a working medium. The energy system also comprises a receiver for receiving the first power output and a second power output generated by at least one additional intermittent energy source selected from solar photovoltaic s, wind power, biogas electrification or other renewable energy source arranged to intermittently generate electricity. Additionally, the energy system comprises an electricity control system controlling and distributing the first power output and second power output via the receiver externally to an electrical grid, at least one flow control system arranged to distribute the flow of a geothermal medium heated by the geothermal heat in the geothermal well and a controller in electrical communication with the receiver, the electricity control system and the flow control system, wherein the controller is configured to direct the electricity control system and flow control system to regulate electricity distribution and geothermal medium flow and distribution. The energy system is characterised by that the controller is arranged to direct the flow control system to regulate the geothermal medium to: i) be distributed from the geothermal well to a first thermal storage system when a second power output is received by the receiver; and ii) be distributed from the first thermal storage system to be used as heat input to the heat power module mainly when a second power output is not received by the receiver, wherein the heat power module generate the first power output.

When using this method the electricity production is controlled so that the heat power module electricity production is mainly active when the renewable additional intermittent energy sources are not active to produce electricity, and vice versa, so that electricity from the renewable additional intermittent energy sources is stored in the form of geothermal heat in the heat storage tank, and electricity production for the electrical grid can be time-shifted to meet public demand.

In one embodiment, the controller is arranged to direct the electricity control system to distribute selected electricity to operate a geothermal pump arranged to generate a flow of geothermal medium, wherein the selected electricity is the first power output, the second power output or power from the electrical grid.

In one embodiment the receiver is also arranged to detect required power demand from the electrical grid. The selected electricity to operate the geothermal pump is the second power output, when the second power output or the total system power output exceed the detected required power demand from the electrical grid.

Pumping geothermal medium from a well is power consuming and may at some ground conditions be so high that it is difficult to for the heat power module to deliver more power output that power input needed to operate the pump. However, when the energy source selected to deliver the pump power depend on the amount of energy each energy source delivers at that time or at what price electricity is sold the operational efficiency can be improved. For example, during a time period, when wind or solar procedure more electricity than the demand or when electricity is sold at a lower price, the electricity is used to pump hot geothermal medium, e.g. at 90 °C, to the first thermal storage. During a later time period, when electricity is in demand or more expensive, the hot geothermal medium is used to generate electricity by the heat power module. Thus, renewable electricity not required by the market is predominantly used for pump system operation.

In one embodiment the energy system also comprises a first thermal storage system and wherein the first thermal storage system comprises at least one first thermal storage tank arranged below or above ground.

The first thermal storage system is preferably selected to be able to store liquid medium having the temperature range 70-140 °C, preferably at below 100 °C and to maintain the temperature within the range.

In one embodiment the heat storage tank has a volume of at least 50 m³ and/or is large enough to generate a flow of geothermal medium to the heat power module for at least 2 hours of electricity production, preferably at least 4 hours.

In one embodiment the first thermal storage tank is used as a district heating tank or a reservoir.

In one embodiment the first thermal storage tank is a combined storage tank adapted for a layered storage of geothermal medium from the hot source and/or cooling medium from the cold source, wherein the medium is stored in layers according to density and temperature.

The hot storage medium and the cold storage medium may comprise preferably water or geothermal brine, optionally physically decoupled through heat exchangers.

In one embodiment the first thermal storage system comprises a second thermal storage tank arranged to store the geothermal medium exiting the heat power module at a temperature below the first temperature interval.

In one embodiment the energy system also comprises a second thermal storage system and wherein the second thermal storage system arranged to store the cooling medium from the cold source. In one embodiment the geothermal pump system and the heat power module are selected to create an energy system operating at a COP of least 10, i.e. one unit of electricity supplied to the geothermal pump produces at least 10 units of heat and later at least 10 units of electricity generated by the heat in the heat power module. The energy system is simple and economic as storage of hot water or hot liquid is

inexpensive. Provided that the geothermal pump produces at least 10 units of thermal energy in the range 80-100 °C using one unit of electrical energy supplied to the pump, thus electrical energy stored in the form of thermal energy can be recovered to 100%.

In one embodiment the heat power module utilises an Organic Rankine Cycle to generate electricity, wherein the Organic Rankine Cycle is operating with a heat input of 70-140 °C, a cold input between 0-30 °C and a net efficiency for conversion of heat to power of at least 5%.

Thus, the heat input of the hot source is from a geothermal medium having a temperature within a first temperature interval. Preferably the first temperature interval are temperatures between 70-140 °C, preferably below 100 °C,

In one embodiment the energy system also comprises at least one additional intermittent energy source selected from solar photovoltaic s, wind power, biogas electrification or other renewable energy source arranged to intermittently generate electricity.

An additional intermittent energy source of that kind typically requires intermediate and temporary storage for 1-120 hours, preferably 4-12 hours, to optimize its power output. The temporary storage is solved by the energy system according to the invention. The additional intermittent energy source may preferably be located in immediate proximity to first continuous energy source, thus the geothermal well and may share certain components such as high voltage connection infrastructure, or where the electricity sources are geographically apart, but linked through the electrical grid.

The invention also relates to a method for storing electrical energy in the form of heat and producing a power output using the heat. The method comprising the steps:

— generating a first power output in the form of electricity from a first continuous energy source in the form of geothermal heat power by using a heat power module comprising a turbine generator arranged to generate a first power output in the form of electricity, wherein the heat power module operating in accordance with a thermodynamic closed loop cycle process being arranged to receive heat input from a geothermal well, functioning as first continuous energy source of geothermal heat and a cold input from a cold source for phase change of a working medium,

— receiving the first power output and a second power output generated by at least one additional intermittent energy source selected from solar photovoltaic s, wind power, biogas electrification or other renewable energy source arranged to intermittently generate electricity,

— controlling and distributing the first power output and second power output via the receiver externally to an electrical grid,

— distributing the flow of a geothermal medium heated by the geothermal heat in the geothermal well,

— directing the electricity control system and flow control system to regulate electricity distribution and geothermal medium flow and distribution, the flow control system is directed to regulate the geothermal medium to

— be distributed from the geothermal well to a first thermal storage system when a second power output is received by the receiver, and

— be distributed from the first thermal storage system to be used as heat input to the heat power module mainly when a second power output is not received by the receiver, wherein the heat power module generates the first power output.

In one embodiment, the electricity control system is directed to distribute selected electricity to operate a geothermal pump arranged to generate a flow of geothermal medium, wherein the selected electricity is the first power output, the second power output or power from the electrical grid.

In a further embodiment the required power demand from the electrical grid is detected in the detection step, and wherein the selected electricity to operate the geothermal pump is the second power output when the second power output or the total system power output exceed the detected required power demand from the electrical grid.

In another embodiment the geothermal pump is controlled to be operated at variable speed depending on the power output from the first continuous energy source and the additional intermittent energy source. In another embodiment, the geothermal pump is controlled to be operated at essentially the same speed, possibly with +/- 10% variations, over extended periods of time.

In another embodiment the method also comprises the step of:

— selecting the geothermal pump and the heat power module to create an energy system operating at a COP of at least 10, i.e. one unit of electricity supplied to the geothermal pump produce at least 10 units of electricity generated by heat in the heat power module, shifted in time.

The method or system according to the above is preferably to be used as a battery for storage of electricity at a capacity scale of 1 MWh electricity and above and a power rating of 150 kW peak electricity and above.

Brief Description of The Drawings

Fig. la and lb show the general first and a second system according to the invention.

Fig. 2a and 2b show schematic view illustrating the energy system and working principle of an exemplary heat power module utilising the phase change energy of a working medium produced in a thermodynamic cycle process RCP.

Fig. 3 shows a schematic view of time-shifting electricity production from renewable energy (RE) using a geothermal well and a pump which is operated at 50-100% of nominal load during the day. Fig. 4 shows data from Fig. 3 in graphical form.

Fig. 5 is a table similar to Fig. 3, but with constant operation of the geothermal pump.

Fig. 6 shows COP 20 geothermal unit, capable of time-shifting intermittent renewable energy production over the day.

Fig. 7 shows storage of 120 a.u. wind energy in geothermal heat storage, and time-shifted electricity production with 100% turnaround efficiency with a COP 10 geothermal well.

Fig. 8 shows a graphical representation of Fig. 7. Detailed Description

The Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into mechanical work. An Organic Rankine cycle (ORC) is a Rankine cycle using other working fluids than water/steam, in particular organic fluids. Moreover, in the present invention, the term“ORC” is meant as any power generation process capable of converting 50-150 °C heat streams to electricity. The applicant uses the process termed“Heat Power” as described in WO 2012/128715, WO 2014/042580, WO 2015/034418, WO 2015/112075, WO 2015/152796, and WO 2016/068778, and related documents in the patent families, all hereby incorporated by reference. Essentially, the heat power module is a particularly efficient power generation system operating at low pressures and capable of utilising heat of low

temperatures, e.g. 70-120 °C, for power generation. Other ORC processes may be used as well in the embodiments of the present invention.

The present invention relates to an energy system and method which allow the reversible storage of electricity at a scale exceeding 1 Megawatt-hour (MWh).

Fig. la shows the general system for storing heat energy and producing electricity using the heat according to a first embodiment of the invention.

In the context of the present invention, the term‘receiver’ is to be interpreted as any device, structure or system configured to receive, control, convert and/or deliver electric power to and from different sources of electric power supply, including an electrical grid. To this end, the receiver may comprise one or more power electronic devices such as rectifiers, inverters, DC- to-DC and/or AC-to-AC converters and transformers for conversion between direct current (DC) and alternating current (AC), stepping up or down between different voltages and/or changing the frequency of current. The receiver may further include associated components such as capacitors, voltage regulators, reactors, switchgears and/or circuit breakers as known in the art. An electrical substation represents one example of a receiver that may be employed in the energy system according to the present invention.

The energy system according to the first embodiment comprises at least one heat power module 1 comprising a turbine generator 300, 400 arranged to continuously generate first power output El in the form of electricity. The energy system also comprises a receiver 2 for receiving the first power output El and a second power output E2, wherein the second power output E2 is generated by at least one additional intermittent energy source ES 1 selected from solar photovoltaic s, wind power, biogas electrification or other energy sources arranged to intermittently generate electricity. The energy system also comprises an electricity control system 3 controlling and distributing the first power output El and second power output E2 via the receiver 2 externally to an electrical grid, represented by the transmission tower supporting overhead power lines at the top of Figs la and lb, as well as at least one flow control system 4 arranged to distribute the flow of a geothermal medium heated by the geothermal heat HS in the geothermal well.

In one embodiment, the receiver 2 may be a collector substation, collecting the first power output El and second power output E2 from multiple power sources as defined herein (e.g. solar, thermal, wind etc.), for further delivery to a connected electrical grid. In a further embodiment, the receiver 2 and electricity control system 3 together act as a switching station in connecting and disconnecting transmission lines or other components to and from the energy system.

The flow is generated by an electricity powered geothermal pump 7. The energy system may also comprise a system of pipes and valves connecting the pump 7 with the heat power module 1 and the first thermal storage system 6. The geothermal medium is distributed to and from the first thermal storage system 6 by the system of pipes and valves controlled by signals sent by the flow control system 4.

The energy system also comprises a controller 5 in electrical communication with the receiver 2, the electricity control system 3 and the flow control system 4. The controller 5 is configured to direct the electricity control system 3 and flow control system 4 to regulate electricity distribution and geothermal medium flow and distribution. The controller 5 may comprise a processor and a non-transitory computer-readable medium, configured to store instructions, which when executed by the processor, causes the controller 5 to receive the instructions from the electricity control system 3 and the flow control system 4 and to generate a signal to distribute electricity and flow of geothermal medium accordingly. Preferably the geothermal medium is distributed to flow from the geothermal well to the first thermal storage system 6 when the least one additional intermittent energy source ES2 is generating a power output E2 and to flow from the first thermal storage system 6 to be used as heat input HSin to the heat power module 1 mainly when the least one additional intermittent energy source ES2 is not generating a power output E2.

The geothermal medium is controlled to be distributed on the basis of mainly the following input parameters, a) amount of generated electricity by the additional intermittent energy source ES2, b) available heat input HSin stored in the first thermal storage system 6, c) power demand of the geothermal pump 7, and d) marked required first power output El from the first continuous energy source ESI.

The electricity control system is arranged to distribute power to a geothermal pump 7 either from the intermittent energy source ES2 and/or from the heat power module 1 and/or from the electrical grid.

In one embodiment the receiver 2 also detect signals about the present required power demand from the electrical grid. The power demand varies over the day, see for example Fig. 4. When the second power output E2 or the total system power output E1+E2 exceed the required power demand from the electrical grid the selected electricity to operate the geothermal pump 7 is the second power output E2. Detection of power demand from the electrical grid is possible e.g. by detecting changes in the frequency of the electrical grid, i.e. deviations from e.g. 50 or 60 Hz.

The energy system may also include the at least one additional intermittent energy source ES2. However, the energy system may also be connected to an already existing power plant producing energy from the additional intermittent energy source ES2.

The first thermal storage system 6 comprises at least one first thermal storage tank 6A arranged below or above ground. The energy system for storing heat energy may be connected to or include the first thermal storage system 6. The first thermal storage system 6 is preferably selected to be able to store liquid medium having the temperature range 70-140 °C, preferably at below 100 °C and to maintain the temperature within the range. The heat storage tank 6A preferably has a volume of at least 50 m³ and/or is large enough to generate a flow of geothermal medium to the heat power module for at least 2 hours of electricity production, preferably at least 4 hours.

The heat storage tank 6A may also be at least 100 m³, 1000 m³, 10 000 m³ or at least 100 000 m³. For storages of at least 5 000 m³, the storage tank may be a heat storage tank/reservoir as used in the district heating industry. Underground caverns are suitable reservoirs for both heat and cold storage.

The heat power module 1 is arranged to continuously generate first power output El in the form of electricity. The heat power module operating in accordance with a thermodynamic closed loop cycle process RCP being arranged to receive heat input HSin from a geothermal well, functioning as first continuous energy source ES 1 of geothermal heat HS, and a cold input CSin from a cold source CS. The heat and cold inputs are used for phase change of a working medium. The hot source is geothermal well comprising a geothermal medium and the cold source may for example be a cooling tower, radiator, a large water body (from a nearby river, lake or sea) or underground well. The heat power module 1 is further described in Fig. 2a and 2b.

In one additional embodiment of the invention, the hot side heat exchanger of the heat power module 1 is kept at an operational temperature by circulating hot water through the hot side heat exchanger and by idling the heat power module, and where after the heat power module may be started up within less than one minute to provide full and phase- and frequency- matched power supply. Moreover, the cycle turnaround efficiency, i.e. electrical energy produced by the heat power module divided by the electrical energy consumed by the heat pump, is at least 50%.

Fig. lb shows the general system for storing heat energy and producing electricity using the heat according to a second embodiment of the invention. The general system is similar to the energy system in Fig. la however here additional thermal storage systems have been added.

In this second embodiment the first thermal storage system 6 also comprises a second thermal storage tank 6B arranged to store the geothermal medium exiting the heat power module. I.e. at a temperature below the first temperature interval. Further, the energy system in Fig. lb also comprises a second thermal storage system 8. The second thermal storage system 8 is arranged to store the cooling medium from the cold source CS.

Moreover, the cold second thermal storage system 8 and/or the hot first thermal storage system 6 may either comprise two separate storage tanks or a combined storage tank. The combined storage tank may be a stratified tank which may have a separating layer such as a floating separating layer. In a combined storage tank, the colder storage medium is collected at the bottom and the hot storage medium is collected at the top of the combined storage due to difference in densities of the cold and warm media.

Thus, the complete energy system provides electrical energy partly by continuous electrical energy from heat power and generated in the heat power module and partly by intermittent electrical energy from wind power or solar power. The purpose of the energy system is to store especially intermittent energy until such time when electrical energy is needed by a utility or customers.

Fig. 2a shows a schematic view illustrating the working principle of an exemplary heat power module. The power generation module is arranged to convert low temperature heat into electricity by utilising the phase change energy of a working medium produced in a thermodynamic cycle process RCP. The thermodynamic closed loop cycle may be a Rankine cycle, Organic Rankine Cycle, Kalina cycle or any other known thermodynamic closed loop power generating processes converting heat into power. The heat power module of the invention is arranged to continuously generate thermal power output in the form of electricity by a thermodynamic closed loop cycle process utilising the temperature difference between a heat input of a hot source and a cold input from a cold source. The hot source HS is a geothermal medium flow from a geothermal well. The heat power module is cooled by a cooling medium flow which may come from a cold source CS in the form a cooling tower, radiator, a large water body (from a nearby river, lake or sea) or underground well. The temperature of the cooling flow entering the heat power module is within a second temperature interval of 0-30 °C, preferably 5-20 °C. The temperature of the cooling medium when exiting the heat power module is preferably 20-40 °C. The cooling medium may circulate in a closed loop. The hot storage medium and the cold storage medium may comprise preferably water or geothermal brine, optionally physically decoupled through heat exchangers.

The power generation module comprises a turbine 300, a generator 400, a hot source heat exchanger 200, a condensation device 500, for example in the form of a cold source heat exchanger, and a pump 600, and a working fluid is circulated through the module. The working fluid is heated in the hot source heat exchanger 200, also called evaporator, to vaporisation by an incoming hot source HSin, e.g. the hot geothermal fluid. The hot gaseous working fluid is then passed through the turbine 300 which drives the generator 400 for production of electrical energy. The expanded hot working fluid, still in gaseous form, is then fed into the condensation device 500 to be by the cold input from the cold source CSin, converted back to liquid form before being recirculated to the hot source heat exchanger 200 to complete the closed-loop cycle 100, as shown on the left-hand side of Fig. 2a. Thus, the condensation of the working medium takes place directly in the cold source heat exchanger 500 which then can be the to be the condensation device. In this embodiment, the stream of liquid medium Q may be pumped directly back to the hot source heat exchanger 200 by the pump 600.

The condensation device may in one embodiment, as illustrated in Fig. 2b, 1 be a separate vessel 100 or container 100 and a cold source heat exchanger 500.

Examples

Example 1

In one embodiment, hot working fluid is produced from a geothermal well using a pump to pump geothermal fluid. Figs. 3 and 4 give schematic details:

Fig. 3 shows a schematic view of time-shifting electricity production from renewable energy (RE) using a geothermal well and a pump which is operated at 50-100% of nominal load during the day. RE, in this case solar PV, produces a total of 120 a.u. = arbitrary units (e.g. kWh) during the day. Operating the geothermal pump partly by RE and partly by the power output of the heat power module, the“Total Delivery to grid” can be time-shifted. In effect, solar PV electricity has been stored by means of the geothermal well and heat storage. Fig. 4 shows data from Fig. 3 in graphical form. In this example, renewable energy (RE) is produced mainly around mid-day, i.e. in the hours 9-16 and peaking at noon. A total of 120 a.u. (e.g. kWh) is produced. The actual demand from the market is shown in the line“Total delivery to grid”, this is also set to be 120 a.u. The geothermal pump consumes 240 a.u. for the production of 2400 a.u. thermal energy corresponding to a COP of 10. The thermal energy is stored in a tank of suitable size. The operation of the heat power module is variable during the day, as is apparent from the line“El from Heat Power”. The total daily consumption and production of electricity from the heat power module is 240 a.u. In combination, the RE production around noon has been spread out over the day to match demand, thus in effect the electrical energy has been stored. Provided the geothermal well works like a heat pump with a COP of 10, 100% of the electrical energy is recovered. Higher COP means that in excess of 100% can be produced.

The pump is operated variably. At night time, the pump uses 6 a.u. whereas at noon, 14 a.u. are consumed. This mode is possible but not preferred. In general, geothermal pumps are preferably operated at the same speed for longer periods, leading to example 2.

Example 2:

In this example, the geothermal pump is constantly using 10 a.u. The electrical energy is supplied by operation of the heat power module especially at night time, and from RE around noon. Even in this case, the RE production can be“smeared out” over the day. The thermal energy reservoir is built up during the day and depleted in the evening/night and morning hours.

Fig. 5 shows a table similar to Fig. 3, but with constant operation of the geothermal pump. Typically, geothermal pumping is more efficient than corresponding to a COP of 10. The next example describes a system with a COP of 20.

Example 3:

In this example, as visualized in Fig. 6, a smaller geo pump is operated at the same speed at all times. Due to the high efficiency of the geothermal system, 240 a.u. energy can be delivered to the electrical grid, and the delivery profile can be adjusted widely. Delivery of about 200 a.u. electricity from afternoon to the next morning requires about 2000 a.u. thermal energy. For a commercial 150 kW heat power module, this equates to 150 kW*20 hours = 3000 kWh electricity, requiring 30 000 kWh thermal energy at 10% net efficiency. This corresponds to about a 2000 m³ tank containing 90 °C water, and a cooling source of about 20 °C of similar dimensions (or a nearby river or other cooling). The 2000 m³ tank may be filled with water at all times, but early afternoon the tank may contain only 90 °C water, and the next morning, when 30 000 kWh thermal energy has been used for nighttime electricity production (3 000 kWh) using the heat power module, the temperature may have dropped to 75 °C (15 °C temperature difference and 2000 m³ equate to 33 000 kWh thermal energy).

Fig. 6 shows a COP 20 geothermal unit, capable of time-shifting intermittent renewable energy production over the day.

For simplicity, the typical production profile of solar PV (photovoltaics) has been used. It is conceivable, that intermittent wind energy or any electricity source is used to partly operate the geothermal pump, as shown in the following example:

Example 4: Here, wind is assumed to supply a total of 120 a.u. energy, stochastically distributed over the day. Wind energy is used as solar energy to drive the geothermal pump to the degree possible given market demand, as shown in Figs. 5 and 6.

Fig. 7 shows a graph presenting storage of 120 a.u. wind energy in geothermal heat storage, and time-shifted electricity production with 100% turnaround efficiency with a COP 10 geothermal well.

Fig. 8 shows a graphical representation of Fig. 7.

It should be understood that above embodiments described in the present invention are merely examples of useful sequences to achieve the objective of the invention, namely to generate and store heat for electricity generation, and thereby to enable the storage of electricity, achievable through a combination of a geothermal well, a geothermal pump, a preferably renewable source of electricity, a heat power module and a heat storage tank. All

embodiments are simplified. Obviously, the source of electricity, be it wind, solar or any other electricity source, may be a single source or a plurality of sources. The source may be in direct proximity, or it may be geographically far away. In the latter case electricity supply would be physically through the electrical grid, and legally through a Power Purchase

Agreement (PPA). If the source such as a solar park is in proximity, the geothermal facility and the solar park may share certain components such as HV generation, AC/DC converters and the like for grid feed-in. The cooling devices creating the cooling flow necessary to operate the heat power module may be utilising the space occupied by the solar park. The cooling devices, for example air cooled heat exchangers, could be placed under solar panels, as an example. These and other engineering solutions are well known and obvious. Certain practical solutions, such as use of direct current generated in solar cells for operation of e.g. pumps are also considered rather obvious.

Any geothermal well may be used for the invention. Practically, it is sufficient to utilize geothermal sources providing a flow within the temperature range 80-140 °C and even below 100 °C. Those sources are more common in many countries, and cheaper to utilize. The heat may come from depths such as 1-3 km. It is usual that pumping power is needed to produce the thermal flow, and the thermal power output divided by the pumping power can be defined as a COP or coefficient of performance for heat production. If 1 kWh electrical energy is required for production of 10 kWh of thermal energy, e.g. water in the temperature range of 70-90 °C, then these 10 kWh of thermal energy can be re-converted to 1 kWh electrical energy using the heat power module. Such a geothermal well is obviously not suitable for electricity production as net production would be zero. However, if 1 kWh renewable electricity is used to build up a thermal storage of the flow in the temperature range 70-90 °C, then this 1 kWh could be recovered time-shifted to 100%. Surprisingly thus, the combination of a - as such not particularly useful - geothermal well with high flow resistance (COP 10) and a renewable electricity source requiring time-shifting is thus a highly useful combination, enabling 100% recovery or storage of the electricity. In practice, many geothermal wells perform much better than COP 10, thus increasing the performance of the new battery according to this invention.

In the embodiments, different scenarios regarding the pumping operation were discussed. In general, for the performance of a geothermal reservoir, it is preferred to operate the geothermal pump at a constant speed with little and slow variations. For the invention, it is preferred to increase the pump speed when cheap electricity is available e.g. from sun and wind, and to decrease the speed when electricity is in high demand, but a compromise needs to be struck between the reservoir characteristics and the power demand. In practice, variations in the order of +/- 20% within hours may be a good compromise.

When not operational, the hot side heat exchanger of the heat power module may be kept at an operational temperature by circulating hot water through the hot side heat exchanger and by idling the heat power module, where after the heat power module may be started up within less than one minute to provide full and phase- and frequency-matched power supply.

The geothermal well can be considered an essentially closed loop of geothermal fluid, compared to a traditional geothermal well comprising an additional volume of water stored in a tank or underground reservoir. Supply of electricity from the renewable electricity source, while the heat power module is not or only partly operating, leads to increased heat energy content in the tank, which later can be re-converted to electricity when demand is high. The essentially closed loop may also comprise further use of water at e.g. 75 °C and below for district heating or heating of agricultural areas such as greenhouses, as the case may be using intermediate heat exchangers according to known art. Finally, the water is reinjected into the geothermal well.

In summary, a simple solution is disclosed for storing electricity in the form of a hot medium. The solution is cheap in construction and operation, and therefore provides a useful method to store intermittent electricity at attractive“levelized costs of storage” or LCOS, significantly below the LCOS of electrochemical batteries.

Claims

1. An energy system for storing thermal energy and generating a power output in the form of electricity using the thermal energy, comprising:

— a heat power module (1) comprising a turbine generator arranged to generate a first power output (El) in the form of electricity, wherein the heat power module operating in accordance with a thermodynamic closed loop cycle process (RC) being arranged to receive heat input (HSin) from a geothermal well, functioning as first continuous energy source (ESI) of geothermal heat (HS), and a cold input (CSin) from a cold source (CS) for phase change of a working medium,

— a receiver (2) for receiving the first power output (El) and a second power output (E2) generated by at least one additional intermittent energy source (ES2) selected from solar photovoltaic s, wind power, biogas electrification or other renewable energy source arranged to intermittently generate electricity,

— an electricity control system (3) controlling and distributing the first power output (El) and second power output (E2) via the receiver (2) externally to an electrical grid,

— at least one flow control system (4) arranged to distribute the flow of a geothermal medium heated by the geothermal heat (HS) in the geothermal well,

— a controller (5) in electrical communication with the receiver (2), the electricity control system (3) and the flow control system (4), wherein the controller (5) is configured to direct the electricity control system (3) and flow control system (4) to regulate electricity distribution and geothermal medium flow and distribution,

characterised in that the controller (5) is arranged to direct the flow control system (4) to regulate the geothermal medium to:

— be distributed from the geothermal well to a first thermal storage system (6) when the second power output (E2) is received by the receiver (2), and

— be distributed from the first thermal storage system (6) to be used as heat input (HSin) to the heat power module (1) mainly when the second power output (E2) is not received by the receiver (2), wherein the heat power module (1) generates the first power output (El).

2. The energy system according to claim 1, wherein the controller is arranged to direct the electricity control system (3) to distribute selected electricity to operate a geothermal pump (7) arranged to generate a flow of geothermal medium, wherein the selected electricity is the first power output (El), the second power output (E2) or power from the electrical grid.

3. The energy system according to claim 1 or 2, wherein the receiver (2) is also arranged to detect required power demand from the electrical grid, and wherein the selected electricity to operate the geothermal pump (7) is the second power output (E2) when the second power output (E2) or the total energy system power output (E1+E2) exceeds the required power demand from the electrical grid.

4. The energy system according to any one of the preceding claims, further comprising a first thermal storage system (6) comprising at least one first thermal storage tank (6A) arranged below or above ground.

5. The energy system according to claim 4, wherein the thermal storage tank (6A) has a volume of at least 50 m³ and/or is large enough to generate a flow of geothermal medium to the heat power module (1) for at least 2 hours of electricity production, preferably at least 4 hours.

6. The energy system according to claim 4 or 5, wherein the first thermal storage tank (6A) is used as a district heating tank or a reservoir.

7. The energy system according to any one of claims 4-6, wherein the thermal storage tank (6A) is a combined storage tank adapted for a layered storage of geothermal medium from the hot source (HS) and/or cooling medium from the cold source (CS), wherein the mediums are stored in layers according to density and temperature.

8. The energy system according to any one of claims 4-7, wherein the first thermal storage system (6) comprises a second thermal storage tank (6B) arranged to store the geothermal medium exiting the heat power module.

9. The energy system according to any one of claims 4-8, further comprising a second thermal storage system (8) comprising at least one third storage tank (8A) arranged to store the cooling medium from the cold source (CS).

10. The energy system according to any one of claims 2-9, further comprising a geothermal pump (7), wherein operating parameters of the geothermal pump (7) and the heat power module (1) are selected such that the energy system operates at a coefficient of performance, COP, of at least 10, i.e. one unit of electrical energy supplied to the geothermal pump (7) produces at least 10 units of thermal energy which may be converted to electrical energy by the heat power module (1).

11. The energy system according to any one of the preceding claims, wherein the heat power module (1) utilises an Organic Rankine Cycle to generate electricity, wherein the Organic Rankine Cycle is operating with a heat input (HSin) of 70-140 °C, a cold input (CSin) between 0-30 °C and a net efficiency for conversion of heat to power of at least 5%.

12. The energy system according to any one of the preceding claims, further comprising at least one additional intermittent energy source (ES2) selected from solar photovoltaic s, wind power, biogas electrification or other energy source arranged to intermittently generate electricity.

13. A method for storing electrical energy in the form of heat and producing a power output using the heat, comprising the steps:

— generating a first power output (El) in the form of electricity from a first continuous energy source (ESI) in the form of geothermal heat power by using a heat power module (1) comprising a turbine generator arranged to generate a first power output (El) in the form of electricity, wherein the heat power module operating in accordance with a thermodynamic closed loop cycle process (RC) being arranged to receive heat input (HSin) from a geothermal well, functioning as first continuous energy source (ESI) of geothermal heat (HS), and a cold input (CSin) from a cold source (CS) for phase change of a working medium,

— receiving the first power output (El) and a second power output (E2) generated by at least one additional intermittent energy source (ES 1) selected from solar photovoltaic s, wind power, biogas electrification or other renewable energy source arranged to intermittently generate electricity by means of a receiver (2), — controlling and distributing the first power output (El) and second power output (E2) via the receiver (2) externally to an electrical grid by means of an electricity control system

(3),

— distributing the flow of a geothermal medium heated by the geothermal heat (HS) in the geothermal well by means of a flow control system (4),

— directing the electricity control system (3) and flow control system (4) to regulate electricity distribution and geothermal medium flow and distribution, the flow control system

(4) is directed to regulate the geothermal medium to

— be distributed from the geothermal well to a first thermal storage system (6) when a second power output (E2) is received by the receiver (2), and

— be distributed from the first thermal storage system (6) to be used as heat input (HSin) to the heat power module (1) mainly when a second power output (E2) is not received by the receiver (2), wherein the heat power module (1) generates the first power output (El).

14. The method according to claim 13, wherein the electricity control system (3) is directed to distribute selected electricity to operate a geothermal pump (7) arranged to generate a flow of geothermal medium, wherein the selected electricity is the first power output (El), the second power output (E2) or power from the electrical grid.

15. The method according to claim 13 or 14, wherein required power demand from the electrical grid is detected, and wherein the selected electricity to operate the geothermal pump (7) is the second power output (E2) when the second power output (E2) or the total system power output (E1+E2) exceed the required power demand from the electrical grid.

16. The method according to claim 14 or 15, wherein the geothermal pump (7) is controlled to be operated at variable speed depending on the power output from the first continuous energy source (ESI) and the additional intermittent energy source (10).

17. The method according to any one of claims 14-16, wherein the geothermal pump

(7) is controlled to be operated at essentially the same speed, possibly with +/- 10% variations, over extended periods of time.

18. The method according any one of claims 13-17, further comprising the step of: — selecting the operating parameters of the geothermal pump (7) and the heat power module (1) to create an energy system operating at a coefficient of performance, COP, of at least 10, i.e. one unit of electrical energy supplied to the geothermal pump (7) produces at least 10 units of thermal energy which may be converted to electrical energy by the heat power module (1).