EP2777117A2

EP2777117A2 - Method for providing control power

Info

Publication number: EP2777117A2
Application number: EP12781066.1A
Authority: EP
Inventors: Georg Markowz; Carsten Kolligs; Wolfgang SCHWEISSTHAL; Wolfgang Deis; Holger BREZSKI; Michael Igel; Anna FLEMMING; Dennis GAMRAD; Sébastien COCHET
Original assignee: Evonik Degussa GmbH; Evonik Industries AG; Steag Power Saar GmbH
Current assignee: Steag Power Saar GmbH; Evonik Operations GmbH
Priority date: 2011-11-10
Filing date: 2012-10-26
Publication date: 2014-09-17
Also published as: WO2013068244A3; US20140327304A1; WO2013068244A2; DE102011055230A1

Abstract

The invention relates to a method for providing control power for a power network, in which an energy generator connected to the power network supplies energy to the power network as necessary or an energy consumer connected to the power network absorbs energy from the power network as necessary. According to the invention, an energy generator and/or an energy consumer are operated together with an energy store connected to the power network in order to provide the control power, and the energy store at least partially absorbs and/or releases an overshoot energy, the overshoot energy being generated when the power of the energy generator overshoots the nominal power and/or being consumed when the power of the energy consumer overshoots the nominal power. The invention also relates to a device for carrying out such a method, in which the device comprises a control, an energy store and an energy generator and/or energy consumer, wherein the device is connected to a power network, the control is connected to the energy store and to the energy consumer and/or the energy generator and controls the generated and/or absorbed control energy.

Description

"Method of Providing Control Power" Description

The invention relates to a method for providing control power for a power grid in which a power generator connected to the power grid supplies power to the power grid as needed or a power consumer connected to the power grid receives power from the power grid as needed. The invention also relates to a device for carrying out such a method.

Electricity grids are used to distribute electricity from many energy generators in large areas to many users and to supply households and industry with energy. Energy producers mostly in the form of power plants provide the required energy. As a rule, power generation is planned and provided based on the forecasted consumption.

Both the generation and the consumption of energy can lead to unplanned fluctuations. These can arise on the energy producer side, for example, in that a power plant or part of the power grid fails or, for example, in the case of renewable energies such as wind, that the energy production is higher than predicted. Consumers may also experience unexpectedly high or low consumption. For example, the failure of a portion of the grid, which cuts off some consumers from the power supply, can lead to a sudden reduction in power consumption.

This generally results in power network fluctuations due to unplanned and / or short-term variations in power generation and / or consumption. The desired AC frequency is, for example, in Europe 50,000 Hz. This frequency is often referred to as the desired frequency. A reduction in consumption compared to the plan results in an increase in the frequency of planned power generation by the energy producers, as well as an increase in electricity production compared to the planned consumption plan. On the other hand, a reduction in power compared with the energy producers' plan results in a reduction of the network frequency at scheduled consumption, as well as an increase in consumption compared to the planned production plan. For reasons of network stability, it is necessary to keep these deviations within a defined range. For this purpose, depending on the amount and direction of the deviation, it is necessary to provide specifically positive control power by connecting additional generators or switching off consumers, or negative balancing power by shutting down generators or adding consumers. There is a general need for economical and efficient provision of these control powers, where the requirements for the capacities to be kept and the dynamics of the control power sources or sinks can vary depending on the characteristic of the power grid.

In Europe, for example, there is a set of rules (UCTE Handbook) that describes three different categories of control power. This also defines the respective requirements for the control power types. The types of balancing power differ, among other things, in the demands on the dynamics and the duration of the service provision. In addition, they are used differently with respect to the boundary conditions. Primary control power (PRL), regardless of the location of the fault, is to be delivered across Europe from all embedded sources, essentially in proportion to the actual frequency deviation. The absolute maximum power is to be provided at frequency deviations of minus 200 mHz and (absolute) below, the absolute minimum power is to be provided at frequency deviations of plus 200 mHz and above. With regard to dynamics, it is necessary to provide the (maximum) performance within 30 seconds from hibernation. In contrast, secondary control power (SRL) and minute reserve power (MRL) are to be provided in the balancing rooms in which the fault has occurred. Their task is to compensate for the disturbance as quickly as possible and thus to ensure that the grid frequency is back within the desired range as quickly as possible, preferably at the latest after 15 minutes. In terms of dynamics, the SRLs and the MRLs have lower requirements (5 or 15 minutes to full service provision after activation), while at the same time these services must be provided for longer periods than primary control capacity.

In the power grids operated so far, a large part of the control power is provided by conventional power plants, in particular coal and nuclear power plants. Two fundamental problems result from this. On the one hand, conventional power plants providing control power do not become part of the system Full load and thus maximum efficiencies, but slightly operated below the same, in order to provide positive control power if necessary, possibly over a theoretically unlimited period. On the other hand, with increasing expansion and preferential use of renewable energies, fewer and fewer conventional power plants are in operation, which is often the prerequisite for the provision of balancing services.

For this reason, approaches have been developed to increase the use of energy storage in order to store negative control power and to provide it as positive control power when needed.

The use of hydro pumped storage plants to provide control power is state of the art. In Europe, the various types of control are provided by pumped storage. However, hydropumps are also often referred to as the most economical renewable energy storage and retrieval technology today to better match energy supply and demand over time. The potential for expanding storage capacity - especially in Norway - is a matter of controversy, as significant capacity in power lines needs to be approved and installed for use. Consequently, the use for the energy management of load management is in competition with the provision of control power.

Against this background, in the area of primary control power in the recent past, approaches have repeatedly been explored and described for the use of other storage technologies, such as flywheel mass and battery storage, for the provision of control power.

From US 2006/122738 A1 an energy management system is known, which comprises a power generator and an energy store, wherein the energy store can be charged by the power generator. This is intended to enable an energy producer, who in normal operation does not guarantee uniform energy production, such as the increasingly favored renewable energies, such as wind power or photovoltaic power plants, to distribute their energy more evenly into the power grid. The disadvantage of this is that in this way a single power plant can be stabilized, but all other disturbances and fluctuations in the power network can not be intercepted or only to a very limited extent. It is known from WO 2010 042 190 A2 and JP 2008 178 215 A to use energy storage to provide positive and negative control power. When the grid frequency leaves a range around the desired grid frequency, either energy is provided from the energy store or added to the energy store to regulate the grid frequency. DE 10 2008 046 747 A1 also proposes operating an energy store in an island power grid in such a way that the energy store is used to compensate for consumption peaks and consumption minima. The disadvantage hereof is that the energy stores do not have the necessary capacity to compensate for a longer disturbance or a plurality of disturbances rectified with respect to the frequency deviation one after the other.

In the article "Optimizing a Battery Energy Storage System for Primary Frequency Control" by Oudalov et al., In IEEE Transactions on Power Systems, Vol. 22, No. 3, August 2007, dependency of the capacity of a rechargeable battery of technical and operational It is shown that due to the injection and withdrawal losses in the long term at different time intervals repeatedly charging or discharging the memory is unavoidable, the authors suggest the time periods Although the frequency may be in the deadband (ie in the frequency range where there is no control power available), it may happen temporarily or temporarily that the memory becomes overloaded, and the authors suggest that (limited Use) of loss-generating resistors, which extremal the complete negative nominal regulation record, so have to be interpreted. In addition to the additional investment required for the resistors and their cooling, however, this leads, as already mentioned by the authors, to a more or less undesirable energy depreciation, with the resulting waste heat usually can not be used. The authors point out that a lower utilization of loss production is only possible through a higher storage capacity, combined with higher investment costs.

The price for the provision of control power depends largely on how quickly the control power can be provided after a request, that is, after a frequency deviation outside the tolerance. at Primary control power (PRL) and (secondary control power (SRL) are already compensated for the provision of energy.) In SRL and MR also the work performance is compensated.

As a rule, the stabilization of electricity grids is achieved by technologies that are assigned to different classes in terms of overall capacity and service delivery dynamics. For example, in the European interconnected network, the UCTE is divided into primary control power (PRL), secondary control power (SRL) and minute reserve (MR).

In the area of secondary control power provision, the various requirements for the dynamics of service provision (commissioning and decommissioning) of the sources (or pools of sources) are explained below for the example of the European interconnected network of the UCTE.

1 . The prequalifiable secondary control power (short SR power, SRL or nominal power) results from the power change activated and measured within 5 minutes (each control direction)

2. A short-term overshoot of a maximum of 10% above the secondary control power setpoint is permitted. In any case, a short-term overshoot up to 5 MW is permissible.

3. In the case of secondary control power pools, after 30 seconds at the latest, a reaction of the pool to the transmission system operator shall be measurable.

The compensation for the secondary control power provision consists of a performance fee for the provision of the secondary control power and a remuneration for the actual energy provided in the context of the secondary control power provision.

Such requirements, in particular for groups of energy producers, can be found in the Forum Netztechnik / Netzbetrieb in the VDE (FNN) "TransmissionCode 2007" of November 2009. For this, Annex D2 in particular is relevant for the requirements of SRL pools, in which it is also described It is known from this document to jointly operate several technical units, such as hydraulic and thermal power plants, as a pool to provide control power. Accumulators can absorb or release energy very quickly, making them basically suitable for providing PRL. The disadvantage, however, is that very large capacities of the batteries must be provided in order to deliver the power over a longer period or repeatedly. However, very large capacity batteries are also very expensive.

The problem with using power plants or consumers, such as electrolysis plants to provide control power, is that they can not be ramped up fast enough to provide the required speed for MR or SRL in an emergency. In order to achieve the highest possible increase in power, the energy producer or the energy consumer can be started up with a maximum power increase. The disadvantage of this is that these conventional power generators or energy consumers have a certain inertia, so that the power overshoots after reaching the rated power. An overshoot is only allowed by a small amount. In addition, the energy provided at too high a level is not remunerated. Conventional energy producers or energy consumers must therefore be operated with a lower increase in performance or the increase in power must be stopped early. Both lead to a lower prequalifiable nominal output of the control power supplier.

In order to achieve a certain nominal power with conventional power generators or energy consumers, the control power suppliers must be oversized in order to achieve at least a certain power in the given periods, which can then be ensured as a prequalification performance for the power plant or the consumer as a control power source.

Furthermore, power generators or energy consumers are often not operated at full load and operated only when needed at a higher power, which is at the expense of the efficiency of the power plant or the consumer. In addition, in these cases, only a small proportion of the maximum producible power of the power plant or the consumer can be prequalified as rated power.

The disadvantage of this is that there is currently no way for energy producers or energy consumers to provide control power as efficient as possible, as in operation to provide power without control and thus at Best possible efficiency, and also to operate for a long time to provide control power to stabilize the power grid available. Overdimensioning is in any case uneconomical.

The object of the invention is therefore to overcome the disadvantages of the prior art. In particular, a possibility should be found to provide control power with efficient energy yield of the control power suppliers. As much as possible, the maximum possible output of the control power supplier should be usable. At the same time, energy should not be given away to the grid operator unnecessarily or be sourced from the grid. Furthermore, the fastest possible provision of control power should be possible.

A further object of the invention is to be seen in that, in particular when using galvanic elements, such as accumulators, the capacity of the energy store should be as low as possible in order to provide the required control power.

The objects of the invention are achieved in that a power generator and / or an energy consumer is operated together with an energy storage connected to the power supply to provide the control power and the energy storage at least partially absorbs and / or releases an overshoot energy, wherein the overshoot energy is generated in the overshoot of the power of the power generator beyond the rated power and / or is consumed in the overshoot of the power of the energy consumer over the rated power addition.

In the present case, nominal power is to be understood as the power with which the control power source, which is operated by a method according to the invention, is prequalified.

The control power is delivered to the power grid (positive control power) or taken from the mains (negative control power). The advantage of methods according to the invention is to be seen in particular in the fact that it is possible with the energy store to provide a higher prequalifiable nominal power as a control power source.

This can be done according to the invention and more preferably as often as desired in succession, by the energy storage is recharged or discharged after a control cycle again and again to a second cycle again have the appropriate state of charge. The appropriate state of charge is given when the energy storage is combined only with a power generator, that this has sufficient free charge capacity to absorb the overshoot of the power generator at the previous maximum power increase, or when the energy storage is combined with an energy consumer that this is sufficiently charged, to give the energy for the overshoot of the energy consumer at previous maximum power increase. The appropriate state of charge is approximately half charged when the energy storage is combined with a power generator and an energy consumer. The state of charge corresponds, in particular in the case of accumulators as an energy store, to the state of charge (English: "State-of-charge", SoC) or the energy content ("State-of-energy", SoE). The terms state of charge and state of charge are to be regarded as equivalent according to the invention.

The inventive method ensures that the wishes of the customer, that is, the grid operator can be met for a predictable and defined control power and no regulatory oscillations are generated in the power grid.

It can be provided that the energy storage receives at least 25%, preferably at least 50%, more preferably at least 75% of the overshoot energy and / or releases.

With these shares, the energy storage is worth in two ways. On the one hand, the control power source can be prequalified for a higher rated power, and on the other hand, the stored energy can be used.

In a particularly preferred embodiment of the invention can be provided that the energy storage emits from a first time at least the difference of the power provided by the power generator to a rated power to the power grid or absorbs the power consumed by the consumer power to a rated power from the mains and Energy storage provides at least this difference between the rated power and the power supplied by the power generator or the power consumed by the power consumer, until the power of the power generator or the energy consumer reaches the rated power at a second time. By this measure, the time until which the rated power is provided, can be further shortened. Thus, with sufficient energy storage capacity, even a secondary control power source or a minute reserve can be converted to a primary control power source or a minute reserve to a secondary control power source. As a result, higher revenues can be achieved.

It can be provided that the capacity of the energy storage is chosen at least so large that the energy can be stored in the energy storage, for bridging the rated power to be provided from the first time to reach the rated power by the power generator and / or the energy consumer to the second Time is needed.

Tuning the capacity of the energy storage device on the performance (the maximum power increase) of the energy producer or the energy consumer has the advantage that the energy storage device can be as small as possible and thus dimensioned and constructed inexpensively.

It is particularly preferred if according to the invention it is provided that the energy store absorbs energy from the energy generator at a third time, while the power of the energy generator is reduced and / or the energy store provides energy for the energy consumer from the third time, while the power of the energy consumer is reduced becomes.

This has the advantage that the energy storage is charged or discharged with the energy that can not be sold as control energy. As a result, the energy store can also be placed in the appropriate state of charge for the next control cycle.

Furthermore, it can be provided that a flywheel, a heat accumulator, a hydrogen generator and storage with fuel cell, a natural gas generator with gas power plant, a pumped storage power plant, a compressed air storage power plant, a superconducting magnetic energy storage, a redox flow element and / or a galvanic element is used, preferably an accumulator and / or a battery storage power plant, more preferably a lithium-ion battery. The heat storage must be operated together with a device for producing electricity from the stored thermal energy. In particular, accumulators are particularly suitable for methods according to the invention because of their rapid reaction time, that is, the rate at which the power can be increased or reduced.

The accumulators include in particular lead-acid batteries, sodium-nickel-chloride accumulators, sodium-sulfur accumulators, nickel-iron accumulators, nickel-cadmium accumulators, nickel-metal hydride accumulators, nickel-hydrogen accumulators, nickel-zinc accumulators, tin Sulfur Lithium Ion Accumulators, Sodium Ion Accumulators and Potassium Ion Accumulators.

Here, accumulators are preferred, which have a high efficiency and a high operational and calendar life. As a particularly preferred embodiment of the invention, lithium polymer accumulators, lithium titanate accumulators, lithium manganese accumulators, lithium iron phosphate accumulators, lithium iron manganese phosphate accumulators, lithium iron yttrium Phosphate accumulators, lithium-air accumulators, lithium-sulfur accumulators and / or tin-sulfur lithium-ion accumulators used as lithium-ion accumulators.

It can also be provided that the energy store has a capacity of at least 4 kWh, preferably of at least 10 kWh, particularly preferably at least 50 kWh, very particularly preferably at least 250 kWh.

The capacity of electrochemical energy storage can be at least 40 Ah, preferably about 100 Ah. When using memories based on electrochemical elements, in particular accumulators, this memory can advantageously be operated with a voltage of at least 1 V, preferably at least 10 V and particularly preferably at least 100 V.

It can be inventively provided that the energy storage consists of a pool of several energy storage. The various energy storage can also be arranged at different locations of the power grid. For example, the energy storage may comprise a plurality of rechargeable batteries, for example in electric cars, which are switched as a pool when they are connected to a charging station and thus to the power grid.

Furthermore, it can be provided that the power of the energy store over a period of at least 0.5 s before the first time to the first time is increased, preferably over a period of at least 2 s, more preferably over a period of at least 30 s.

These slower ramps ensure that there are no suggestions of unwanted disturbances or oscillations in the power network or in the connected consumers and generators by a too steep power gradient.

It can also be provided according to the invention that a power plant is used as the energy generator, preferably a coal-fired power station, gas-fired power plant or a hydroelectric power plant and / or a plant for producing a substance is used as energy consumer, in particular an electrolysis plant or a metal plant, preferably one Aluminum plant or a steel plant.

Such energy producers and consumers are well-suited to providing longer-term balancing services. Their inertia can be compensated according to the invention well with energy storage.

Furthermore, it can be provided that the nominal power of the energy generator together with the energy storage and / or the nominal power of the energy consumer together with the energy storage by the method within 15 minutes, preferably within 5 minutes, more preferably within 30 seconds, to at least 95 % is reached.

With these parameters, control power sources operated in such a manner can be used efficiently and with better efficiency as secondary control power sources or even as primary control power sources. In addition, a higher nominal power can be prequalified.

The ratio of rated power of the energy store to maximum power of the power generator and / or energy consumer may preferably be in the range of 1: 10,000 to 10: 1, more preferably in the range of 1: 1000 to 1: 1.

It can also be provided according to the invention that the mains frequency of the power supply network is measured and, given a deviation from a nominal value or a deviation from a tolerance by a nominal value, control power is delivered to the power grid or taken from the power grid and / or at a return of the mains frequency to the setpoint or in the tolerance the control power is reduced.

This allows an automated control of the grid frequency.

According to a further embodiment of the invention, it can be provided that the energy store is charged to at least 50% when reducing the power of the power generator, in particular substantially fully charged and / or the energy storage is discharged at less than 50% in reducing the power of the energy consumer , is essentially completely discharged.

These embodiments of the invention are particularly suitable when the energy storage is operated only with a power generator or only with an energy consumer, since the charge of the energy storage at the beginning of the process according to the invention, that is well prepared for the next cycle.

Alternatively, it can be provided that the energy storage is operated together with a power generator and an energy consumer and the energy storage in reducing the power of the power generator in about half, preferably between 25% and 75%, more preferably between 40% and 60%, completely is particularly preferably charged between 45% and 55% or the energy storage in reducing the power of the energy consumer about half, preferably between 25% and 75%, more preferably between 40% and 60%, most preferably between 45% and 55% discharged becomes.

The appropriate state of charge of the energy storage is at the beginning of a method according to the invention in about 50% when both a power generator, as well as an energy consumer is operated with the energy storage. This is achieved by these measures for the following cycles.

It can also be provided that the output of the power supply of the power generator or the power absorbed by the power supply of the energy consumer, in particular after the second time, at several times, preferably continuously measured and calculates the difference to the rated power at several times, preferably continuously is adjusted, wherein output or recorded power of the energy storage in response to this difference, preferably any power, the 1 10% of the nominal power, in particular after a time exceeds, received by the energy storage and / or provided and / or at least this difference is set as the power of the energy storage, in particular between the first and second time.

Furthermore, it can be provided that the energy generator and / or the energy consumer has or have a maximum power of at least 1 MW, preferably at least 10 MW, particularly preferably at least 100 MW.

It can also be provided according to the invention that a portion of the overshoot energy dependent on the state of charge of the energy store is absorbed by the energy store and / or emitted, so that the state of charge of the energy store after a control cycle is as close as possible to a setpoint of the state of charge, preferably the entire overshoot Energy is absorbed by the energy storage when the state of charge of the energy storage is below a first limit and only absorbs the portion of the overshoot energy that is above a tolerance above the rated power when the state of charge is above a second limit.

As a result, the state of charge can be kept in the desired state of charge due to the tolerances of the network operator. Then less energy needs to be bought from the power grid or less energy needs to be put into the power grid unnecessarily. At the same time, it ensures that the process remains stable over a long period of time, in particular with automatic control of the process.

The object of the invention is achieved with respect to a device in that the device comprises a controller, an energy storage and an energy generator and / or an energy consumer, wherein the device is connected to a power grid, the controller with the energy storage and the energy consumer and / or Power generator is connected and controls the generated and / or absorbed control power.

Under a control according to the invention is understood in the present case a simple control. It should be noted that each control comprises a control, as in a control, a control in dependence on a difference of an actual value to a desired value takes place. Preferably, the controller is thus designed as a control, in particular with regard to the state of charge. Particularly preferably, the controller is a control system.

It can be provided that the device comprises a frequency meter for measuring the mains frequency of the power network and a memory, wherein in the memory at least one limit value of the network frequency is stored, wherein the controller is adapted to compare the network frequency with the at least one threshold and depending on the comparison to control the performance of the energy storage and the energy consumer and / or the energy generator.

Finally, it can also be provided that the capacity of the energy storage is at least so large that at least the energy is stored in the energy storage, which is necessary for receiving and / or outputting the overshoot energy, preferably the capacity of the energy storage is so large that in Energy storage at least 95% of the overshoot energy can be stored, more preferably 100% to 300%, most preferably 100% to 150%.

The rated power of the device for providing control power is the power achievable within a certain time. It is also spoken of the prequalifiable performance, since this meets the criteria of the customer, that is the network operator.

The invention is based on the surprising finding that the combination of an energy store with at least one conventional control power source makes it possible to improve it in terms of its properties as a control power source. Ideally, a minute reserve may be converted to a secondary control power source or a secondary control power source into a primary control power source. For this purpose, it is sufficient if the energy store is used to pick up unwanted overshoots beyond the agreed nominal output.

Battery storage systems (accumulators) are distinguished from conventional technologies for providing primary and / or secondary control functions, inter alia, in that they can change the services provided more quickly, among other things. In most cases, however, is a disadvantage of battery storage that they have a relatively small storage capacity, so can provide the required services only over a limited period. One to solve the Therefore, the key finding is that the above-mentioned restrictions on the example of the European interconnected network of the UCTE are met by suitable pooling of battery storages with conventional SR sources.

Special and particularly preferred embodiments of the solution approaches are that the energy store is an accumulator or battery store that is used at the same time to provide primary control power. As a rule, such a store still has reserves in terms of both the power and the energy in normal operation.

In a further specific embodiment, the energy taken into the memory in the event of negative SR power can be sold on the spot market if the conditions there are advantageous.

In preferred embodiments of the invention, a plurality of energy stores are pooled and operated in accordance with the method of the invention. The size of the energy storage within the pool can vary. In a particularly preferred embodiment, in the various energy stores of a pool in the use of tolerances, in particular the choice of bandwidth in the deadband, the change from one parameter setting to another not synchronously, but deliberately offset in time to minimize any disturbances in the network or at least tolerable.

The tolerance with regard to the amount of the control power provided and the tolerance in determining the frequency deviation, etc., is to be understood by the network operator to be certain deviations between an ideal nominal power due to technical conditions, such as the measurement accuracy in determining the control power supplied or the grid frequency and the actual control power actually delivered. The tolerance may be granted by the network operator, but could also comply with a legal requirement.

In a further preferred embodiment, the tolerances used in the various methods, in particular the choice of bandwidth in the dead band, vary depending on the time of day, the day of the week or the season. For example, within a period of 5 minutes to 5 minutes after the hour change, tolerances may be more narrowly defined. This is due to the fact that Here often very rapid frequency changes take place. It may be in the interest of transmission system operators that there are lower tolerances and thus the control energy supply is more secure in the sense of sharper.

According to a further embodiment, it may be provided within the scope of the specifications for the provision of control power that, in particular, more energy is absorbed from the network than is fed in by the energy store. This can be done by providing very much negative control power in accordance with the regulations including the procedure outlined above, whereas according to the regulations including the procedure set out above, preferably only the at least guaranteed power is provided at positive control power. Preferably, an average of at least 0.1% more energy is withdrawn from the network than is supplied, in particular at least 0.2%, preferably at least 0.5%, more preferably at least 1.0%, especially preferably 5%, these values being based on a Average measured over a period of at least 15 minutes, preferably at least 4 hours, more preferably at least 24 hours and especially preferably at least 7 days, and refer to the energy fed.

In this case, the control power provision set out above can be used to extract a maximum of energy from the network, whereby the maximum possible negative control power is provided, whereas only a minimum of positive control power is provided.

In the embodiments for the preferred and especially for the maximum energy consumption, the energy thus extracted from the network can be sold via the energy trade described above, preferably at times when the highest possible price is to be achieved. For this purpose, forecasts of the price development based on historical data can be used.

Furthermore, the state of charge of the energy store at the time of a planned sale of energy may preferably be at least 70%, particularly preferably at least 80% and particularly preferably at least 90% of the storage capacity, the state of charge after sale preferably not exceeding 80%, in particular not more than 70% and especially preferably at most 60% of the storage capacity amounts. Embodiments of the invention will be explained below with reference to five schematically illustrated figures, without, however, limiting the invention. Showing:

Figure 1 is a schematic P-t diagram of a conventional secondary control power source and a conventional pool as a secondary control power source;

FIG. 2 shows a schematic P-t diagram of a control power source operated using a method according to the invention and conventional control power sources;

FIG. 3 shows a second schematic P-t diagram of a control power source operated with a method according to the invention;

FIG. 4 shows a flow chart for a method according to the invention; and

Figure 5: a schematic representation of a device according to the invention for the provision of control power.

Figure 1 shows a graph of power (P) versus time (t) of a conventional single secondary control power source (solid line) and a secondary control power source pool (dashed line) comprising a hydroelectric plant and a thermal power plant (e.g., a nuclear power plant). The hydraulic hydropower plant provides a contribution to the balancing power right from the start. In addition, the energy added by the hydropower station can be sold and ensures that the pool's response as a secondary control power source to the customer, ie the grid operator, is readily apparent.

The above, in the context of the example of the European interconnected network of the UCTE, leads to limitations of the marketable potential for many market participants. This is due, for example, to the fact that the marketable power is limited by a low power gradient, or a higher power can be provided in principle within 5 minutes, but these lead due to control technology to excessively high overshoots over the rated power (P _SO II).

Not only that, both in the pool and when using a single conventional power generator or energy consumer, the performance over the permissible level over the rated power (Psoii) overshoots, moreover, the energy that is provided by such a power is not remunerated. The energy corresponds to the area which lies above the straight line of the nominal power (Psoii) and between this straight line and the curves.

If an overshoot in the power increase or reduction is limiting, according to the invention a single or multiple energy stores connected in a pool can be used to limit the overshoot by targeted, ie opposite performance. This is schematically outlined in the diagram of Figure 2. For example, if only the overshoot of the nominal power P _{2 of} a control power source by a maximum of 10% of the prequalified power P _{2 is allowed} by the grid operator, the energy store may be used to pick up any excess energy or, in the event, overshoot while providing a negative power Control power enters, deliver.

Figure 2 shows how a conventional power generator or energy consumer must be operated to provide control power (lower graph) if it would overshoot at maximum power increase (over 10%) above the prequalified rated power P ₂ (upper graph). Although a higher prequalifiable power P ₂ could generally be achieved with maximum power increase, such an increase in power can not be offered due to excessively high overshoot. The lower curve shows how much power the conventional power generator or energy consumer can still operate to limit the overshoot to 10% over a lower prequalified rated power Pi. As a result, within the prescribed control period of 5 minutes, only a lower prequalifiable rated power Pi is possible. It is only with the help of the energy storage, which absorbs or releases an overshoot energy E, which is generated or consumed at too high power, it is possible to operate the power generator or energy consumer with maximum performance increase, without the provided power by more than 10% over the maximum control power P ₂ overshoots. The overshoot energy E is shown in the diagram of Figure 2 as a diagonally hatched area. As a result, a higher prequalified power P ₂ can be offered with the same energy consumer or power generator than without the combination with the energy store and without the inventive method in which only a lower prequalified power Pi could be offered.

It may also be preferred, unlike in FIG. 2, that any excess balancing energy is absorbed or discharged by the energy store, since the energy contributions are not compensated for up to 10% above the prequalified power, or must be paid for.

Likewise, however, it may also be provided that the excess output power of the energy producer in the range of 0% to 10% of the prequalified power is only absorbed by the energy store or the surplus absorbed power of the energy consumer in the range of 0% to 10% of the prequalified power is only given by the energy storage, if the state of charge of the energy storage makes sense sense. If, for example, the energy store is already charged to more than 50% or to two-thirds, it may be useful to absorb the surplus energy of an energy producer only if it provides a power of more than 10% above the prequalified power P ₂ . This is done to maintain the state of charge of the energy store in a desired state suitable for the following control cycles.

Conversely, if the energy store is less than 50% or less than one-third loaded, it can absorb any excess energy of the energy producer that is above the prequalified power P ₂ . When the energy store is powered by an energy consumer, the energy store can provide the energy consumed beyond the rated power. Whether this already happens from reaching the nominal power P ₂ or only when reaching 10% above the rated power P ₂ , in turn, can be made dependent on the state of charge of the energy storage. If the charge of the energy store is to be reduced more, because the charge of the energy store is, for example, in the range of the maximum charge of the energy store, the energy store will already provide its power as soon as the nominal power P _{2 has been reached} . If the charge of the energy storage is to be reduced less, because the charge of the energy storage is small, for example, less than half or less than one third of the maximum possible charge of the energy storage is the energy storage only provide its power from reaching 10% above the nominal power P ₂ .

The energy store, which is preferably a rechargeable battery, in this way allows the conventional SR technology to be prequalified with a higher power than if it were operated alone.

Furthermore, the overshoot energy E provided or consumed may not be sold to the grid operator since this power can not be sustainably provided. Instead, it is taken up in the energy storage or provided by the energy storage, so that the overshoot energy E can remain with the operator of the control power system, or does not have to be purchased from the power grid.

In a commissioning phase in everyday operation, the energy storage can be used to close the difference between power demand (target value) and current service provision and thus to achieve additional operating revenue. In the diagram of FIG. 1 already shown, this would mean that the energy associated with the area above the solid curve could additionally be marketed according to FIG. 1, thereby achieving additional revenue. In a specific embodiment, the decision as to whether this energy is additionally provided could be made dependent on the current working prices or the current state of charge of the battery storage.

Even with a given and marketed balancing power, considerable potential often remains unused. This applies in particular to the energy provided or the labor income. After a call to secondary control (SR) power (SRL), the dynamics of the SR technologies, or technical units in a pool providing SRLs, determines how much revenue can be generated. In the diagram according to FIG. 1, for example, the potential work proceeds, which corresponds to the area above the dashed curve, remain unused due to technical limitations.

Therefore, to improve the economics of SR technologies, there is a need for technical alternatives to override or at least significantly reduce the limitations of conventional SR technologies.

In detail, according to the invention can be proceeded as follows. If the dynamics of service delivery of conventional SR technology is limited, then An energy storage device is used for support. This is outlined in a schematic power-time diagram according to FIG. Conventionally, due to the limited power gradient, only 13 MW could be prequalified here, even though higher performance could be achieved after more than 5 minutes. In the pool with a suitable battery storage (accumulator), the prequalifiable power can be increased to 18 MW. The battery storage closes the corresponding gap until the expiry of 7 minutes. The high performance combined with a comparatively short service life is very accommodating for certain storage technologies, such as lithium-ion battery technology and flywheels.

The solid line A shows the maximum increase in output of a conventional power plant, such as a coal power plant or a gas power plant. After 7 minutes, the power plant reaches its maximum output of 18 MW. However, this is too slow to provide SRL. For example, the provision of SRLs requires that the pre-qualifiable power of an SR power source should be achieved within 5 minutes. As a result, the conventional power plant can only provide a prequalifiable power of 13 MW, or can only be prequalified for a SR power of 13 MW.

In a further embodiment of a method according to the invention, the conventional power plant is now combined with an accumulator. As soon as a request for the provision of SR power is received, not only the conventional power plant is started up, but the accumulator is switched on. The capacity of the accumulator is increased up to the time ti = 5 minutes. At this point in time ti, the accumulator provides 5 MW of power, which is precisely the difference in power that the conventional power plant provides due to its maximum time gradient after 5 minutes, to the maximum power of the conventional power plant.

The device according to the invention, namely the combination of a conventional power plant and an accumulator and a controller for implementing such a method according to the invention, is thus able to apply a power of 18 MW after only 5 minutes, ie the maximum power of the conventional power plant. As a result, the device for providing SR power can be prequalified to 18 MW.

The capacity of the accumulator can be steadily reduced from time ti to the extent that increases the power of the conventional power plant. For this purpose, a controller may be provided which measures the lack of power of the conventional power plant to its maximum power and provides this power from the accumulator. The power of the accumulator is thus reduced to zero until time t ₂ , since from this time t ₂ the entire control power can be applied by the conventional power plant.

During the provision of the SR power, an energy E ₂ must therefore be applied by the accumulator, which corresponds to the left diagonally hatched area E ₂ in FIG. The energy E ₂ is equal to the integral of the accumulator's power over time, from which the integral of the conventional power plant's output is subtracted over time. The capacity of the accumulator should therefore be chosen at least approximately so large that the energy E _{2 can be} absorbed or released. If only a prequalifiable power of the control power source according to the invention is offered, which is smaller than the maximum power of the power generator / power plant and / or the energy consumer, the capacity of the accumulator can be selected correspondingly smaller.

From the time t _2, the power of the power generator / power plant is sufficient to provide the complete control power. However, due to the inertia of the power plant, the power continues to increase over the rated power of 18 MW in the short term. Since this overshoot is not desirable and is not allowed to a certain extent, since it can lead to control oscillations of various control power sources and thus the grid frequency in the power grid, the excess overshoot energy E is absorbed by the energy storage. Since the charge of the energy storage has previously been reduced, the energy storage has enough capacity to absorb the overshoot energy E. The right diagonal hatched area between the straight line at 18 MW and the curve above 18 MW corresponds exactly to the energy E and can be calculated by integration. If from a time t ₃ no more control power is needed, the conventional power plant usually can not be easily turned off, but the power is reduced over a certain period of time to zero. The energy E ₃ provided by the conventional power station in this period from the time t ₃ , characterized in Figure 3 by the horizontally dashed surface, no longer needs to be fed into the network, but instead according to the invention can be used for further charging or recharging of the battery. If necessary, the charging process can be terminated when the output state of charge of the energy storage is reached again before the request for control power.

By means of the described method according to the invention and the device according to the invention discussed, it is thus possible to provide an optimum control power profile, which is shown in FIG. 3 by the dashed curve. The weaknesses of conventional methods, represented by the solid line in FIG. 3, could be overcome according to the invention.

The principle discussed in this exemplary embodiment with reference to FIG. 3 is readily applicable to an energy consumer and a rechargeable battery or to an energy consumer and another energy store. For example, instead of providing a maximum output of 18 MW, it can also be provided that a maximum output of 18 MW is consumed by a plant (energy consumer). The plant can produce, for example, methane or ethane or even hydrogen. Until the maximum power of 18 MW of the energy consumer is reached at time t ₂ after 7 minutes, the energy store, for example a flywheel to which electrical energy is supplied, can absorb the missing power, that is, in the energy store between the first times t ₁ and the second time t _2, the energy E _{2 is} stored. As a result of this measure, the device according to the invention comprising the energy consumer and the energy store can be prequalified not only to 13 MW but to 18 MW.

It is particularly advantageous if the energy storage can deliver energy very quickly and is particularly responsive. Therefore, accumulators and to some extent flywheels are particularly well suited as energy storage, while pumped storage power plants or gas generators in particular with memory and Gas power plant as an energy storage are not so well suited for implementing inventive method.

Just when in a Verfahrender invention, the energy storage has just been emptied or filled, a, as also explained in Figure 2, opposite charge or discharge of the energy storage in a subsequent overshoot be welcome to keep the state of charge of the energy storage in a desired range.

A device according to the invention can also comprise an energy consumer, an energy store and an energy generator and thereby implement a method according to the invention in which both positive and negative control power can be provided and all three components are used.

FIG. 4 shows a flow chart for a method according to the invention. In the method, an energy storage, a power generator and an energy consumer are used. In step 1, the grid frequency of the power grid is measured. Decision step 2 then checks whether the grid frequency is within a tolerance, or above or below it. Alternatively, it is also possible to respond to a request from the network operator. This would then indicate whether he needs positive or negative control power.

If the grid frequency is within the tolerance, proceed to step 1. If the grid frequency is above the tolerance, the grid must be deprived of energy. For this purpose, the energy consumer is started in step 3 and the power of the energy consumer is increased. In the process, the difference power to the prequalified power can optionally be taken up by the energy store from the time ti agreed with the network operator, by charging the energy store. Then, the pool of energy consumers and energy storage supplies the prequalified nominal control power, that is, the prequalified power is taken from the power grid. If, for example, the pool is prequalified as a primary power source, the nominal power must be consumed as early as ti = 30 seconds. If, for example, the pool is prequalified as a secondary control power source, the nominal power must be consumed only after ti = 5 minutes. Especially with the use of accumulators, the control energy can be absorbed very quickly, that is, that the performance can be increased very quickly. As the power consumer's power increases, the power consumption of the energy store may optionally be reduced.

In step 4, the pre-qualified rated power of the energy consumer is reached at time t ₂ and is consumed by the consumer. In step 5, the power of the energy consumer oscillates beyond the prequalified power due to its inertia. The energy storage provides the consumed excess energy E available.

In decision step 6, it is finally checked whether the mains frequency is still above the tolerance. If so, the energy consumer continues to run and absorb energy, and the energy storage supplies the energy E that exceeds the prequalified power rating. If not, the power of the energy consumer is reduced in step 7 from time t ₃ . At the same time, optionally in step 7, the power for the energy consumer can be supplied by the optional energy storage device loaded in step 3 and the charge of the energy storage device can be further reduced.

Then the mains frequency is measured again in step 1. The measurement of the mains frequency can also be carried out according to the invention in parallel to steps 3, 4, 5 and 7, the power of the energy consumer being increased whenever the mains frequency is above the tolerance.

Steps 1 to 7 together already provide a method according to the invention for an energy store and an energy consumer, wherein in step 2 it is only decided whether the grid frequency is below the tolerance or not.

If the grid frequency in decision step 2 is below the tolerance, step 13 is continued. In this step 13, the power of a power generator such as a coal power plant is increased. At the latest from the time ti, at which the rated power must be provided, optionally the energy storage device can provide the missing power of the energy generator. The power of the power generator will increase and the power of the energy storage accordingly reduced, until finally in step 14 at time t _{2 of} the power generator reaches the rated power and the energy storage no longer needs to provide energy. The power of the power generator will increase beyond the prequalified power rating. The additionally generated Energy, or the excess power is absorbed by the energy storage in step 15.

It is then determined whether the mains frequency is still below the tolerance. In decision step 16 this is checked. If the grid frequency is still below the tolerance, the power generator simply keeps running. If not, the process continues to step 17, in which the power of the power generator is reduced, that is, the power generator is shut down, the energy storage from this time t ₃ receives and stores the energy generated by the power generator.

Steps 1, 2 and 13 to 17 thus provide, analogously to steps 1 to 7, a method according to the invention for an energy store and a power generator, wherein in step 2 it is only decided whether the grid frequency is above the tolerance or not. The method can also be considered in decision step 2 deciding whether the energy store forms a pool for the following control with the energy producer or the energy consumer.

Also in the right bank of the flowchart (steps 1, 2 and 13 to 17) can be continuously checked whether the grid frequency is below the tolerance or not and then reacted accordingly. Here, too, can be waited for a request from the network operator instead of their own measurement of the grid frequency. In the European power grid, a grid frequency of 50.00 Hz is set, the tolerance is currently ± 10 mHz.

FIG. 5 shows, in a schematic view, a device 20 according to the invention comprising a power generator 21 or energy consumer 21, which is connected to an energy store 22. A controller 23 is connected to the power generator 21 or consumer 21 and to the energy store 22 so that the controller 23 can adjust the power of the power generator 21 or consumer 21 and the power consumption and output of the energy store 22.

The power generator 21 or consumer 21 and the energy storage 22 are connected to a power grid 24 and can absorb and / or deliver power from the power grid 24. If there is a need for control power - positive or negative control power - the controller 23 receives a signal. Subsequently the power of the power generator 21 or consumer 21 is increased. From the time ti, for example after 30 seconds, or shortly before the power of the energy storage device 22 is switched on, that is, energy is absorbed into the energy storage 22 or discharged from the energy storage 22.

The controller 23 determines the currently provided by the power generator 21 or consumer 21 control power and ensures that the difference is provided by the energy storage 22. If the power of the energy generator 21 or consumer 21 from the time t ₂ is sufficient to provide the entire rated power of the device 20, the energy storage 22 can be disconnected by the controller 23 from the power supply 24, or switched off.

Due to the inertia of the systems of the power generator 21 and the energy consumer 21 there is an overshoot of the control power after reaching the rated power. The energy store 22 then absorbs the excess energy or provides the excess energy. The control is also used for this. Since the energy store 22 has just been discharged or charged in the other direction, this leads to a desired charge state of the energy store 22 for subsequent control cycles.

At a time t ₃ , the controller 23 receives the signal that the control power is no longer needed. The power of the power generator 21 or consumer 21 is reduced. So that no unnecessary energy is fed into or taken out of the power network 24, the controller 23 again switches on the energy store 22, which can receive the energy of the energy generator 21 or can provide it to the energy consumer 21. This measure also leads to a medium state of charge of the energy store 22, so that it has a suitable state of charge for the next control cycle.

The controller 23 can charge or discharge the energy storage 22 in an intelligent manner, so that a certain desired state of charge is desired. For example, tolerances in the overshoot or the times ti, t ₂ and / or t ₃ can be used to develop the state of charge in the desired direction. For example, the power of the energy storage 22 may be provided earlier than ti to charge or discharge the energy storage 22 when deemed necessary. Similarly, an overshoot of up be tolerated to 10% or be intercepted by the energy storage 22 to regulate the state of charge of the energy storage 22.

In particular, in such cases, a particularly fast-reacting and easy to charge and discharge energy storage 22 is required. Batteries are best suited for this purpose. In particular, Li-ion batteries are quickly and frequently charged and discharged without damaging influences on the battery, so that they are particularly suitable and preferred for all embodiments according to the invention. This requires the provision of Li-ion accumulators of considerable capacity. For example, these are easily accommodated in one or more 40-foot ISO containers.

A device 20 according to the invention is therefore particularly well suited as a primary or secondary control power source.

For details on the regulation of control power and the exchange of information with network operators, please refer to the Forum Network Technology / Network Operation in VDE (FNN) "TransmissionCode 2007" of November 2009. In particular, Annex D2 on the pooling of control power units is interesting to obtain the implementation of inventive method.

The features of the invention disclosed in the foregoing description, as well as the claims, figures and embodiments may be essential both individually and in any combination for the realization of the invention in its various embodiments.

LIST OF REFERENCE NUMBERS

A Service provision with a conventional power plant

B Service provision with a method according to the invention

E, overshoot energy

E2, E3 energy

P performance

t time

ti First time

t ₂ Second time

t ₃ Third time

1 ; 3; 4; 5; 7 process step

2; 6; 16 decision step

13; 14; 15; 17 process step

20 Device for providing control power

21 energy producers / energy consumers

22 energy storage

23 control

24 power grid

Claims

claims

1 . Method for providing control power for a power grid (24), in which a power generator (21) connected to the power grid (24) supplies energy to the power grid (24) or an energy consumer (21) connected to the power grid (24) Power grid (24) absorbs energy as needed, characterized in that

a power generator (21) and / or an energy consumer (21) together with an energy store (22) connected to the power grid (22) for providing the control power is operated and the energy storage (22) at least partially absorbs an overshoot energy (E) and the overshoot energy (E) is generated when the power of the power generator (21) overshoots the rated power and / or is consumed when the power consumer (21) overshoots the rated power.

2. The method according to claim 1, characterized in that

the energy store receives at least 25%, preferably at least 50%, particularly preferably at least 75% of the overshoot energy (E) and / or releases.

3. The method according to claim 1 or 2, characterized in that

the energy store (22) from a first time (ti) delivers at least the difference of the power provided by the power generator (21) at a rated power to the power grid (24) or the power consumed by the power consumer (21) to a rated power from the power grid (24) and the energy store (22) at least provides this difference between the rated power and the power supplied by the power generator (21) or the power consumed by the power consumer (21) until the power of the power generator (21) or of the power consumer ( 21) reaches the rated power at a second time (t ₂ ).

4. The method according to any one of the preceding claims, characterized in that

the energy store (22) receives energy (E ₃ ) of the energy generator (21) from a third point in time (t ₃ ) while the power of the energy generator (21) is reduced and / or the energy store (22) is operated from the third time point (t ₃ ) Provides energy (E ₃ ) to the energy consumer (21) while reducing the power of the energy consumer (21).

5. The method according to any one of the preceding claims, characterized in that

a flywheel, a heat accumulator, a hydrogen generator and storage with fuel cell, a natural gas generator with gas power plant, a pumped storage power plant, a compressed air storage power plant, a superconducting magnetic energy storage, a redox flow element and / or a galvanic element is used as energy storage (22) preferably an accumulator and / or a battery storage power plant, particularly preferably a lithium-ion accumulator.

6. The method according to any one of the preceding claims, characterized in that

the energy store (22) has a capacity of at least 4 kWh, preferably of at least 10 kWh, particularly preferably at least 50 kWh, very particularly preferably at least 250 kWh.

7. The method according to any one of the preceding claims, characterized in that

a power plant is used as energy generator (21), preferably a coal-fired power station, gas-fired power plant or a hydroelectric power station and / or as energy consumer (21) a plant is used for producing a substance, in particular an electrolysis plant or a metal plant, preferably an aluminum plant Plant or a steel plant.

8. The method according to any one of the preceding claims, characterized in that the rated power of the energy generator (21) together with the energy store (22) and / or the rated power of the energy consumer (21) together with the energy store (22) by the method within 15 minutes, preferably within 5 minutes, more preferably within 30 Seconds, at least 95% is achieved.

9. The method according to any one of the preceding claims, characterized in that

the network frequency of the power network (24) is measured and in case of a deviation from a nominal value or a deviation from a tolerance by a setpoint control power to the power grid (24) delivered or from the power grid (24) is added and / or with a return of the grid frequency for Setpoint or in the tolerance the control power is reduced.

10. The method according to any one of the preceding claims, characterized in that

the energy store (22) is charged to at least 50% when reducing the power of the power generator (21), in particular substantially fully charged and / or the energy store (22) discharges less than 50% in reducing the power of the power consumer (21) is discharged substantially completely.

1 1. Method according to one of claims 1 to 9, characterized in that the energy store (22) is operated together with a power generator (21) and an energy consumer (21) and the energy store (22) in reducing the power of the power generator (21) in approximately in half, preferably between 25% and 75%, more preferably between 40% and 60%, even more preferably between 45% and 55% is charged or the energy store (22) in reducing the power of the energy consumer (21) about half, preferably between 25% and 75%, more preferably between 40% and 60%, most preferably between 45% and 55%.

12. The method according to any one of the preceding claims, characterized in that

the output of the power generator (21) or the power of the energy consumer (21) received from the power grid (24), in particular after the second time (t ₂ ), is measured at several times, preferably continuously, and the difference the rated power is calculated at several points in time, preferably continuously, with the output or absorbed power of the energy store (22) being set as a function of this difference, preferably any power exceeding 1 10% of the rated power, in particular after a time t ₂ , by Energy storage (22) is received and / or provided and / or at least this difference as a power of the energy storage device (22), in particular between the first and second time ti and t _{2 is} set.

13. The method according to any one of the preceding claims, characterized in that

the energy generator (21) and / or the energy consumer (21) has or has a maximum power of at least 1 MW, preferably at least 10 MW, particularly preferably at least 100 MW.

14. The method according to any one of the preceding claims, characterized in that

a proportion of the overshoot energy (E) dependent on the state of charge of the energy store (22) is received and / or emitted by the energy store (22) so that the state of charge of the energy store (22) after a control cycle is as close as possible to a desired state of charge state, Preferably, the entire overshoot energy (E) from the energy storage device (22) is received when the state of charge of the energy storage device (22) is below a first limit and only absorbs the portion of the overshoot energy (E), which is above a tolerance above the rated power is when the state of charge is above a second limit.

15. A device for carrying out a method according to one of the preceding claims, characterized in that

the device (20) comprises a controller (23), an energy store (22) and a power generator (21) and / or an energy consumer (21), wherein the device is connected to a power grid (24), the controller (23) the energy store (22) and the power consumer (21) and / or the power generator (21) is connected and controls the generated and / or recorded control energy.

16. The apparatus according to claim 15, characterized in that

the device (20) comprises a frequency meter for measuring the mains frequency of the power network (24) and a memory, wherein at least one limit value of the network frequency is stored in the memory, wherein the controller (23) is adapted to the network frequency with the at least one limit value and, depending on the comparison, to control the performance of the energy storage device (22) and the energy consumer (21) and / or the energy producer (21).

17. The apparatus of claim 15 or 16, characterized in that

the capacity of the energy store (22) is at least so large that at least the energy which is necessary for receiving and / or delivering the overshoot energy (E), preferably the capacity of the energy store (22), can be stored in the energy store (22) it is great that at least 95% of the overshoot energy (E) can be stored in the energy store (22), particularly preferably 100% to 300%, very particularly preferably 100% to 150%.