METHOD FOR OPERATING SUCH A STORAGE SYSTEM

The invention relates to a storage system for buf fer-storing electric energy . Furthermore , the invention relates to a method for operating such a storage system .

Buf fer-storing electric energy plays an important role in particular in connection with the utilisation for regenerative energy sources . There is a need for storage systems for buf fer-storing electric energy which allow ef ficient buf fer storage of the electric energy .

WO 2013/ 000813 Al discloses a pumped storage power plant . The pump storage power plant comprises a first reservoir, a second reservoir, a flow path for liquid connecting the two reservoirs and a generator for electric energy arranged in the flow path . The generator for electric energy is arranged in the flow path between the two reservoirs in such a manner that the same either separates the two reservoirs from one another or, dependent on whether an energy storage or energy dispensation is to take place , either opens a flow direction from the first reservoir in the direction of the second reservoir or a flow direction from the second reservoir in the direction of the first reservoir .

GN 112727687 A discloses a wind power plant , in which in a tower of the wind power plant a water reservoir is integrated . By way of a pump, seawater for energy storage can be pumped into the tower of the wind power plant . For the energy dispensation, the water stored in the tower is withdrawn from the tower and conducted via a turbine .

There is a need for a more ef ficient storage system for buf fer-storing electric energy and for a method for operating such a storage system . Starting out from this , the present invention is based on the obj ect of creating a new type of storage system for buf fer-storing electric energy and creating a method for operating such a storage system which has a high ef ficiency .

This obj ect is solved through a storage system for buf ferstoring electric energy according to Claim 1 . The storage system according to the invention comprises a liquid-gas pressure reservoir . Further, the storage system according to the invention comprises an energy conversion apparatus , which on the one hand is equipped in order to pump liquid into the liquid-gas pressure reservoir for storing energy in the liquid-gas pressure reservoir while compressing a gas contained in the liquid-gas pressure reservoir, and which on the other hand is equipped in order to conduct liquid out o f the liquid-gas pressure reservoir for dispensing energy from the liquid-gas pressure reservoir while expanding the gas contained in the liquid-gas pressure reservoir . Further, the storage system according to the invention comprises at least one compressor which is equipped for providing in the liquidgas pressure reservoir a cushion of gas with a defined gas pre-pressure . By way of the compres sor, a defined gas prepressure can be provided in the liquid-gas pressure reservoir of the storage system according to the invention . By way of this it is possible to increase the ef ficiency of the storage system .

Preferentially, the compressor is equipped to compensate for a loss of gas in the liquid-gas pressure reservoir . By compensating for a loss of gas in the liquid-gas pressure reservoir, the ef ficiency of the storage system can be increased .

Preferentially, the compressor is equipped to regulate the gas pre-pressure in the liquid-gas pressure reservoir . Regulating the gas pre-pressure in the liquid-gas pressure reservoir via the compressor serves for further increasing the ef ficiency of the storage system . It is possible to adapt the gas pre-pressure .

Preferentially, the liquid-gas pressure reservoir is integrated in a tower of a wind power plant . Preferentially, the invention is employed with a wind power plant .

Preferentially, a connector of the liquid-gas pressure reservoir, via which for dispensing energy liquid can be withdrawn from the liquid-gas pressure reservoir and/or via which for storing energy liquid can be pumped into the liquid-gas pressure reservoir, is designed and arranged in such a manner that the same is permanently covered by liquid . By way of this , a loss of gas in the pressure reservoir can be counteracted . This also serves for increasing the ef ficiency of the storage system .

Preferentially, the energy conversion apparatus comprises at least one pump and at least one turbine . The at least one pump is equipped, for storing energy, to pump liquid from an atmospheric liquid reservoir whi le compressing the gas contained in the liquid-gas pressure reservoir, into the liquid-gas pressure reservoir . By way of the at least one turbine , liquid, for dispensing energy, can be conducted out of the liquid-gas pressure reservoir while expanding the gas contained in the liquid-gas pressure reservoir, in the direction of the atmospheric liquid reservoir . By way of this , a particularly ef ficient storage and dispensation o f energy is possible .

In particular when turbine and pump are provided by a common assembly and, further, are operatively connected to an electric machine that can be operated both as a generator and also as a motor, a particularly ef ficient operation o f the storage system with low installation space requirement is possible . Preferred methods for operating a storage system for buf ferstoring electric energy are defined in Claims 10 to 14 .

Preferred further developments of the invention are obtained from the subclaims and the following description . Exemplary embodiments of the invention are explained in more detail by way of the drawing without being restricted to this . There it shows :

Fig . 1 : a diagram of a first storage system according to the invention for buf fer-storing electric energy,

Fig . 2 : a diagram o f a second storage system according to the invention for buf fer-storing electric energy,

Fig . 3 : a diagram of a preferred implementation of the storage system according to the invention for buf fer-storing electric energy .

Fig . 1 shows highly schematically assemblies of a storage system 10 according to the invention for buf fer-storing electric energy . The storage system 10 comprises a liquidgas pressure reservoir 11 . Further, the storage system 10 comprises an energy conversion apparatus 12 . The energy conversion apparatus 12 is equipped on the one hand, for storing energy in liquid-gas pressure reservoir, to pump liquid F, while compressing the gas G contained in the liquid-gas pressure reservoir 11 , into the liquid-gas pressure reservoir 11 . On the other hand, for dispensing energy out of the liquid-gas pressure reservoir 11 , liquid F, while expanding the gas G contained in the liquid-gas pressure reservoir, can be conducted out of the liquid-gas pressure reservoir .

In Fig . 1 , the energy conversion apparatus 12 comprises a pump 13 and a separate turbine 14 . The pump 13 in Fig . 1 is operatively connected to a first electric machine 15 designed as motor . In the exemplary embodiment of Fig . 1 , the turbine 14 is operatively connected to a separate electric machine 16 , which is designed as generator .

For storing energy in the liquid-gas pressure reservoir 11 , the pump 13 can be driven by the electric machine 15 operated as motor while utili sing electric energy El , wherein the pump 13 then draws liquid F out of an atmospheric liquid reservoir 17 and, whi le compres sing the gas G contained in the liquid-gas pressure reservoir 11 , pumps the liquid F into the liquid-gas pressure reservoir 11 .

The liquid-gas pressure reservoir 11 is a closed pressure reservoir in order to prevent that the gas G escapes from the same .

The atmospheric liquid reservoir 17 can be a natural atmospheric liquid reservoir such as a lake or a sea or an arti ficial atmospheric liquid reservoir such as a basin .

For dispensing energy, the liquid F, which is stored in the liquid-gas pressure reservoir 11 , can be withdrawn from the same while expanding the gas G in the liquid-gas pressure reservoir 11 and conducted via the turbine 14 . Starting out from the turbine 14 , the liquid F can be conducted into the atmospheric liquid reservoir 17 , wherein for this purpose the turbine drives the electric machine 16 operated as generator for generating and dispensing electric energy E2 .

Dependent on whether the energy conversion apparatus 12 is operated for storing energy or for dispensing energy, a switching valve 18 , which is connected between the liquidgas pressure reservoir 11 as wel l as the pump 13 and the turbine 14 , assumes a defined switching position . During the energy storage , the switching valve 18 opens a flow path from the pump 13 in the direction of the liquid-gas pressure reservoir 11 , but interrupts a flow path towards the turbine 14 . During the energy dispensation, the switching valve 18 opens a flow path from the liquid-gas pressure reservoir 11 in the direction of the turbine 14 , but interrupts a connection to the pump 13 .

Furthermore , the storage system 10 comprises a compressor 19 for gas . By way of the compressor 19 , a cushion of gas G with a defined gas pre-pressure can be provided in the closed liquid-gas pressure reservoir 11 . Between the compressor 13 and the liquid-gas pressure reservoir 11 , a valve 20 i s connected in order to supply the liquid-gas pressure reservoir 11 with gas G via the compressor 19 i f required . In the event that the liquid-gas pressure reservoir 11 is not gas-tight or in the event that because of other circumstances a loss of gas develops in the liquid-gas pressure reservoir 11 , such los s of gas can be of fset or compensated for by the compressor 13 .

The valve 20 is for example a non-return valve , as a result of which the pressure storage system can be merely supplied with gas via the compressor . In addition, a safety valve as well as a gas discharge regulating valve can be provided in order to discharge gas from the reservoir in a regulated manner in order to avoid overpres sures and damage in the pressure storage system .

Furthermore , it is possible to regulate the gas pre-pressure in the liquid-gas pressure reservoir 11 via the compressor 19 to a set-point value . Thi s set-point value can be variable . For this purpose it is possible , with the help of a pressure sensor that is not shown, to measure an actual value of the gas pre-pressure in the closed liquid-gas pressure reservoir 11 at a defined liquid filling level in the liquid-gas pressure reservoir 11 , compare the actual value with a set-point value , and dependent on the comparison between the actual value and the set-point value , regulate the gas pre-pressure via the compressor 19 to the set-point value . As already explained, the set-point value for the gas pre-pressure in the liquid-gas pressure reservoir 11 can change for example dependent on operating conditions of the storage system 10 .

As already explained, the liquid-gas pressure reservoir 11 is connected via a line 21 for the liquid F, dependent on the switching position of the switching valve 18 , either to the pump 13 or to the turbine 14 . A connector 22 of the liquid-gas pressure reservoir 11 to this line 21 , via which for dispensing energy liquid can be withdrawn from the liquid-gas pressure reservoir 11 and via which for storing energy liquid can be supplied to the liquid-gas pressure reservoir 11 , is designed and arranged in such a manner that the same is permanently covered by liquid . Thus , a loss of gas of gas G from the liquid-gas pressure reservoir 11 can be counteracted .

In the exemplary embodiment of Fig . 1 , pump 13 and turbine 14 are provided by separate assemblies . Likewise , the electric machine 15 operatively connected to the pump 13 and the electric machine 16 operatively connected to the turbine 14 are provided in the exemplary embodiment of Fig . 1 by separate electric machines .

In contrast with this , Fig . 2 shows a modi fication of the storage system 10 , in which both the pump 13 and also the turbine 14 are provided by a common assembly and in which the two electric machines 15 , 16 are also provided by a common electric machine , which is operated either as motor or as generator, namely during the energy storage as motor and during an energy dispensation as generator . In Fig . 2 , the switching valve 18 can be omitted .

A mixed form of the exemplary embodiments of Fig . 1 and 2 is also possible . Accordingly it is conceivable in Fig . 1 that the pump 13 and the turbine 14 are operatively connected to a common electric machine which is operated either as motor or as generator, namely as motor during the energy storage for driving the pump 13 and emanating from the turbine 14 as generator during the energy dispensation .

In Fig . 1 and 2 , preferentially water and preferentially air are used as liquid F and gas G respectively . In this case , the liquid-gas pressure reservoir 11 is a water-air pressure reservoir and the compressor 19 an air compressor .

As already explained above , the atmospheric liquid reservoir 17 can be a natural or arti ficial liquid reservoir . As liquid-gas pressure reservoir 11 , an above-ground or subterranean storage space can be utilised, for example a tunnel , a cavern, a cave or another geological formation .

Preferentially, an arti ficial pressure reservoir is employed as liquid-gas pressure reservoir 11 which, as shown in the exemplary embodiment of Fig . 3 , is integrated in a tower 23 of a wind power plant 24 . The wind power plant 24 generates electric energy which can be fed either via an electrical assembly 25 into a power grid 26 or which in particular when this is not desired or required, can be utilised to drive the pump 13 and draw liquid F from the atmospheric liquid reservoir 17 pumping it into the liquid-gas pressure reservoir 11 integrated in the tower 23 of the wind power plant 24 , namely while compressing the gas G in the liquidgas pressure reservoir 11 .

When the wind power plant 24 as a consequence of insuf ficient wind cannot generate electric energy, but electric energy is required, the liquid F contained in the liquid-gas pressure reservoir 11 of the tower 23 can be conducted via the turbine 14 in the direction of the atmospheric liquid reservoir 17 and in the process electric energy be generated which can then be supplied to the power grid 26 . The electric energy, which in the exemplary embodiment of Fig . 3 can be generated in the region of the turbine 14 depends on the mass flow of liquid F conducted via the turbine 14 , on the geodetic head di f ference between the liquid F in the liquid-gas pressure reservoir 11 and the turbine 14 and on the gas pre-pressure of the gas G in the liquid-gas pressure reservoir 11 . The gas pre-pressure within the liquid-gas pressure reservoir 11 integrated in the tower 23 of the wind power plant 24 can be adj usted or regulated via the compressor 19 .

Furthermore , the invention relates to methods for operating a storage system 10 according to the invention . Preferentially, the actual value of the gas pre-pressure in the closed liquid-gas pressure reservoir 11 is measured with the help of a sensor at a defined liquid filling level in the liquid-gas pressure reservoir 11 , wherein this actual value is compared with a set-point value , and wherein with the compressor the gas pre-pressure in the liquid-gas pressure reservoir is regulated to the set-point value . The set-point value can be variable .

When storing energy, the pressure reservoir 10 can be operated in a constant power mode of the pump 13 . For this purpose , the pump 13 is operated by the electric machine 15 driving the pump 13 in such a manner that with constant drive power of the electric machine 15 driving the pump 13 at a relatively low pressure in the liquid-gas pressure reservoir 11 , a relatively large mass flow of liquid F and at a relatively high pressure in the liquid-gas pressure reservoir 11 , a relatively small mass flow of liquid F is pumped into the liquid-gas pressure reservoir 11 . At the start of storing energy in the liquid-gas pressure reservoir 11 , the pressure in the pressure reservoir 11 is low which is why, with constant drive power of the electric machine 15 driving the pump 13 , a high mass flow of liquid F can be pumped into the liquid-gas pressure reservoir 11 . Towards the end of storing the energy, this mass flow of liquid F decreases with the same drive power of the electric machine 15 driving the pump 13 .

Such a constant power mode is also possible during the dispensation of energy . In this case , the turbine 14 , interacting with the electric machine 16 driven by the turbine 14 , generates a constant electric power, wherein at a high pressure in the liquid-gas pressure reservoir a relatively small mass flow of liquid F then flows via the turbine 14 into the atmospheric liquid reservoir 17 while at a low pressure a relatively large mass flow of liquid f lows via the turbine 14 .

In contrast with this it is also possible , both when storing and also when dispensing energy, to utilise a constant mass flow mode . In this case , the mass flow of liquid F via the pump 13 or the turbine 14 is then constant , but the drive power utilised during the storing and the electric power generated during the dispensing is variable .

It is obviously also possible to util ise a mixed mode between a constant power mode and a constant mass flow mode ; namely both during the storing of energy and also during the dispensing of energy .

For the storage system 10 the compressor 19 is of fundamental importance . The same serves for providing a defined gas prepressure in the closed liquid-gas pressure reservoir 11 . It is possible to compensate for a loss of gas in the liquidgas pressure reservoir 11 . The storage system can always be operated with high ef ficiency .

Although in Fig . 1 to 3 merely one pump 13 and turbine 14 is shown, multiple pumps 13 and turbines 14 can also be present . Thus , multiple pumps 13 can be connected in series for building-up in steps a pressure level in the closed liquidgas pressure reservoir 11 .

Likewise , multiple pumps 13 or turbines 14 can be connected in parallel in order to activate or deactivate individual pumps 13 or turbines 14 in steps upon a constant power mode with changed mass flow .

LIST OF REFERENCE NUMBERS

Storage system

Liquid-gas pressure reservoir

Energy conversion apparatus

Pump

Turbine

Electric machine , motor

Electric machine , generator

Atmospheric liquid reservoir

Switching valve

Compressor

Valve

Line

Connector

Tower

Wind power plant

Electrical assembly

Power grid