Method for operating electrolysis system

Abstract

The invention relates to a method for controlling an electrolysis system having an auxiliary system, an electrolysis unit and a connection to an unreliable power source. To this end, a start-up condition is first determined, which, in order to switch from an idle state to a standby state, requires that sufficient power is expected to be initially present to operate the auxiliary system, followed by operating the electrolysis unit for a longer period of time. Electrolysis begins as the switch to the operating state, which is caused by operating conditions, for which sufficient time and sufficient power are also expected.

Description

Technical Field

[0001] The invention relates to a method for operating an electrolysis device. In order to carry out the method, auxiliary systems and an electrolysis unit are required. In addition, the method takes into account that the energy used for the electrolysis device is drawn from a power source that provides different levels of power at irregular intervals. Background Art

[0002] The auxiliary systems and the electrolysis cells each require a certain time period, which depends on the type of construction, to change from the switched-off state to the corresponding switched-on state with constant operation. Here, before the electrolysis cell is started, the auxiliary systems must be started. Subsequently, the electrolysis cell is started as soon as sufficient power is available.

[0003] It is known that renewable energy (solar energy, wind energy, etc.) is usually available in certain places, but the demand in these places is very low. This leads to the need to transport the energy from the energy acquisition location to the place where the energy is needed. In many cases, the renewable energy is obtained in the form of electrical energy, for example by solar parks or wind power plants. If a large distance needs to be covered between production and consumption, it is suitable to use the renewable electricity to produce storable and easily transportable hydrogen by electrolysis. The disadvantage here is that the power provided by the power source is not constant.

[0004] In known methods for operating an electrolysis system, the expected power of the power supply is therefore continuously determined.

[0005] If the power exceeds the power required by the auxiliary system for a long enough period of time, the auxiliary system will usually be activated. This is based on the assumption that the power is provided to a certain extent "free" or unused.

[0006] Furthermore, if sufficient energy is available to operate the electrolysis cell when the auxiliary system is switched on, the electrolysis cell is usually switched on immediately. Here too, an attempt is made to use the regeneratively generated electricity for the electrolysis as quickly as possible.

[0007] Although it is known that high yields of hydrogen can be achieved using renewable electricity, it has been shown that this method of operation leads to faster aging of the electrolysis cells. In this case, maximizing the hydrogen yield is not always advantageous compared to the costs for operating and maintaining the electrolysis system. Summary of the invention

[0008] It is therefore an object of the present invention to achieve an optimal hydrogen recovery taking into account the costs for operating and maintaining the electrolysis plant.

[0009] This object is achieved by the method according to the invention as taught in claim 1. Advantageous embodiments are the subject matter of the dependent claims.

[0010] First of all, an electrolysis device is required. This electrolysis device comprises at least one electrolysis cell as a basic component. It is currently irrelevant what type of construction it is and what basic operating mode it has. At least the electrolysis cell is designed to be able to obtain hydrogen with the help of supplied electricity.

[0011] In addition, it is necessary for the operation of the auxiliary system that its operation is a prerequisite for the operation of the electrolysis unit. What type of auxiliary system is, it is also not important at present. Here, those skilled in the art can also use known electrolysis equipment, where auxiliary systems are installed. The auxiliary system can, for example, include a control unit, a pump, a cooling unit and a filtering mechanism. Which auxiliary systems are specifically needed depends mainly on the construction type of the electrolysis unit. For adopting the method according to the present invention, these auxiliary systems are necessarily required, but as long as their power data are taken into account, their exact design is irrelevant. In this regard, those skilled in the art can adopt the known design of the electrolysis equipment with electrolysis unit and auxiliary system. In this regard, no further explanation is needed.

[0012] Furthermore, an electrical power source is required to supply the energy required for the operation of the electrolysis system. An electrical power source in the sense of the invention is a connection to a power generation system, such as a solar park or a wind power system (but not the power generation system itself). It should be taken into account for the method that the power supply provided by the electrical power source to the electrolysis system may have a fluctuating and unreliable course. Despite this, the method can also be used even if the electrical power source reliably and permanently provides power that can be advantageously used. In this regard, the power supply may (but not necessarily) fluctuate both in size and in duration, or may completely drop to zero, or in other words, it should be taken into account in the method that the power supply is not constant.

[0013] Assuming (but not a prerequisite for the method) that the electrolysis plant is used at a distance from the normal power grid, a backup unit is required. This backup unit must be able to achieve a controlled shutdown of the electrolysis plant in the event of a failure in the power supply. It is not important at present what type it is. At least, auxiliary power must be immediately available for output when the electrolysis unit is in operation, so that an immediate shutdown can be achieved in the event of a drop or failure in the supply power. Obviously, the backup unit must be able to provide the auxiliary power required during the shutdown period for a period of time until the electrolysis plant is switched off.

[0014] The different states result from the relevant units of the electrolysis system, the electrolysis unit and the auxiliary systems.

[0015] Here, an idle state is distinguished, in which the electrolysis unit and important auxiliary systems are switched off. In addition, it can be provided that the individual auxiliary systems are operated with low power. At least in this state, the electrolysis cannot be started and the energy consumption is reduced to zero or a very low level.

[0016] The standby mode is characterized by the fact that the electrolysis unit can be started at almost any time. To do this, the necessary auxiliary systems must be started beforehand. By running the auxiliary systems, power is drawn for their operation when no electrolysis is taking place.

[0017] In the operating state, the electrolysis unit is supplied with operating current and generates hydrogen by electrolysis.

[0018] It is usually not possible to start up the electrolysis system immediately in order to produce hydrogen immediately. Rather, the switch-on process requires a certain amount of time before the electrolysis unit can start up and produce hydrogen. Depending on the state of the electrolysis system when it is put back into operation, different measures are required.

[0019] Before the electrolysis is started and thus the operating state is reached, various auxiliary systems are switched on. It must be taken into account that the various auxiliary systems which must be ready for operation before the actual electrolysis begins each require their own time period. This time period is influenced to some extent by the design of the auxiliary systems, but depends largely on the type of construction of the electrolysis unit and its operating mode. This results in an electrolysis-specific start-up time period which is required in order to switch the switched-off electrolysis unit from an idle state to a standby state in which the electrolysis unit can be started at any time.

[0020] It can be assumed that the startup period is at least a few minutes. On the other hand, the startup period should not exceed 4 hours.

[0021] Likewise, when the actual electrolysis is over, the operation of the auxiliary systems is still necessary. In particular, it is usually necessary to ensure that the electrolysis cell can cool down in a controlled manner. In this respect, there are switch-off periods during which the auxiliary systems must continue to operate after the electrolysis has ended. This period can also be influenced by the design of the auxiliary systems, but still depends largely on the type of construction of the electrolysis cell and its mode of operation.

[0022] It can be assumed that the cut-off period is at least a few minutes. On the other hand, the cut-off period should not exceed 4 hours.

[0023] The individual auxiliary systems have their own constant or state-dependent power depending on the operating state. It is important to consider the power that the auxiliary systems require overall in order to switch from the idle state to the standby state. The standby state can only be achieved if this specific auxiliary power can be provided to the auxiliary systems. This applies similarly to the auxiliary power that the auxiliary systems require overall in order to switch from the standby state to the idle state.

[0024] In any case, it can be provided that, depending on the operating state, individual auxiliary systems are temporarily switched off or their power is reduced, while other auxiliary systems continue to operate without hindrance. If the electrolysis can be started at almost any time and thus switched to the operating state, this is considered to be a standby state. This is still considered to be the case if the time period before the electrolysis unit can be started is at most 0.1 times the start-up time period. For example, the power of a pump can be reduced, which power is increased again to the specified power for starting the electrolysis very quickly.

[0025] After the electrolysis unit is started, it takes some time before the hydrogen produced can also be effectively discharged from the electrolysis device. This requires, in particular, a certain amount of time to reach a substantially stable operating temperature and to build up a favorable pressure in the device. In addition, the water circulation and the separation process of oxygen and hydrogen require some time to reach a substantially stable state (assuming a constant power supply). In addition, this startup process causes energy consumption, but does not produce a large amount of hydrogen. The duration depends on the design of the electrolysis device on the one hand and on the type of construction of the electrolysis unit and its operating mode on the other hand.

[0026] This specifies the minimum operating time required to reach a substantially steady state (assuming a constant power supply).

[0027] Furthermore, for the shortest operating time, it is required that the ratio between the amount of hydrogen obtained and the energy introduced during the shortest operating time is at least 50% of the amount of hydrogen obtained in continuous operation with the same energy input. This means that at the end of the shortest operating time, the amount of hydrogen produced is at least equivalent to the amount of hydrogen produced in continuous operation with half the energy input.

[0028] It is particularly advantageous for the shortest operating time if the ratio of hydrogen obtained to energy input at the end of the shortest operating time is at least 0.8 times the ratio in continuous operation.

[0029] Assume that the minimum run time is at least 15 minutes. On the other hand, the minimum run time should not exceed 4 hours.

[0030] Obviously, electrolysis requires an electricity supply. In order to ensure a stable production process and economical hydrogen production, the electricity supply must not fall below a certain lower limit. Taking into account the power required by auxiliary systems, the total minimum power that must be provided in order to operate the electrolysis equipment in the operating state is generated.

[0031] Depending on the type of construction of the electrolysis unit and its mode of operation, there is an operating range in which the electrolysis unit can be operated at a higher power and achieve a greater hydrogen production. This is limited by a maximum power, beyond which no increase in hydrogen production can be achieved and / or damage to the electrolysis system may occur.

[0032] The method according to the invention requires first determining the start-up conditions. It is assumed that the electrolysis device is in an idle state. First, it is required that the supply power exceeds the auxiliary power at least during the start-up period. Since the supply power cannot be clearly determined when the power supply is unreliable, it is necessary to consider using an estimated supply power with probability.

[0033] The probability of the predicted power can be determined in different ways. On the one hand, the probability provided for the current energy source, for example for the expected wind speed, can be used. On the other hand, the probability between past predictions and actual values ​​can be determined with the help of historical data. At least a person skilled in the art can easily determine a reasonable value of the probability based on which a certain method can be implemented.

[0034] Since the predicted supply power ultimately contains assumptions, but actual power must be provided to start the auxiliary system, the start-up condition still requires that the predicted supply power is higher than the required auxiliary power with sufficient probability.

[0035] If the probability is above 80%, then a sufficient probability is considered to have been generated. It is particularly advantageous if a sufficient probability is above 90%.

[0036] Whereas, if a high probability is mentioned, it is assumed to be above 95%.

[0037] It should be noted that when considering probabilistic issues, it is checked whether a limit value is exceeded. In other words, it is not of interest whether the later actually occurring supply power corresponds to the previously estimated supply power. Rather, it is assessed whether the later actually occurring supply power exceeds the respectively considered limit value.

[0038] After the startup period that accompanies the switch from the idle state to the standby state, it is necessary to be able to expect that the estimated supply power continues to exceed the auxiliary power. How long this period lasts is currently unimportant.

[0039] Furthermore, the presence of the start-up condition requires that the minimum power be reached after the start-up period or from a later point in time, and the power is not expected to be sometimes lower than the auxiliary power.

[0040] On the one hand, it is necessary to determine the time periods during which the estimated supplied power can be expected to be higher than the minimum power.

[0041] On the other hand, the probability that the expected power is higher than the minimum power should be considered.

[0042] Based on these two considerations - the expected duration of sufficient supplied power and the probability of sufficient magnitude, for the start condition, it is required that the period of time during which the expected supplied power is higher than the minimum power multiplied by the probability corresponds to at least 1.5 times the shortest operating time. In other words, if it can be assumed with a high probability that the expected supplied power is higher than the minimum power, a little more than 1.5 times the shortest operating time is required. However, if the probability is only 50%, the period of time during which the expected supplied power is higher than the minimum power must have lasted for three times the shortest operating time.

[0043] This means that under the start-up conditions it is assumed that, as expected (because the supplied power is only estimated and not precisely determined), after starting the electrolysis equipment and connecting the auxiliary systems, these auxiliary systems can operate uninterruptedly until the electrolysis unit starts, after which the electrolysis can be carried out uninterruptedly for the shortest operating time.

[0044] Furthermore, the operating conditions must be determined. In this case, it is assumed that the electrolysis plant is in standby mode, i.e. the necessary auxiliary systems are in operation, whereas the electrolysis units are switched off. Compared to the start-up conditions, initially only the expected supply power must be above the minimum power for the shortest operating time. However, sufficient probability is required here.

[0045] When checking the operating conditions, the immediately subsequent time period is evaluated to determine whether the predicted supplied power exceeds the minimum power. It is assumed that this probability is higher than the probability of the predicted supplied power in the same time period when checking the start-up conditions.

[0046] The assumption here is also that if the auxiliary system is already in operation anyway, it is useful that the electrolysis can be carried out as intended within the shortest operating time, especially if the energy comes from renewable energy sources and cannot be used beneficially in any other way.

[0047] The use of the electrolysis equipment is obviously based on the estimated supply power, provided that the start-up conditions and operating conditions are determined. If the electrolysis equipment is in idle state, it switches to standby state when the start-up conditions exist and starts the auxiliary systems.

[0048] If the electrolysis device is in the standby state and meets the operating conditions, it switches to the operating state and starts electrolysis.

[0049] Although the new method with delayed start-up conditions does not make the most comprehensive use of renewable energy, this approach does not allow the electrolysis system to be started if it is not foreseeable that there will be enough time for the electrolysis to continue to operate. This will reduce the adverse effects on the electrolysis system caused by switching on and off processes. This will increase the reliability and service life of the electrolysis system, although the hydrogen production will be slightly lower. Taking into account the costs for maintaining the electrolysis system, which always depends on the actual supply power, it should be possible to produce hydrogen at a lower cost.

[0050] When designing the auxiliary systems and assuming that a longer period of sufficient power supply from an unreliable power source can be expected for starting the electrolysis plant, it is not necessary to strive for a minimum start-up period. Rather, it can be determined that a start-up period of less than half an hour would impose unnecessary additional burden or additional costs on the auxiliary systems.

[0051] However, the start-up time period should not be selected to be unnecessarily long. If it is clear that there will be enough supply power to start the electrolysis later, this start-up time period will always delay the possible start-up of the electrolysis plant. In this respect, it is advantageous if the start-up time period does not exceed 2 hours.

[0052] On the one hand, the lower limit of the minimum operating time is determined by the ratio of hydrogen obtained to energy input. On the other hand, it is expected that a substantially stable process with a quasi-constant water flow has already been produced. A certain design flexibility is retained here, and the minimum operating time can also be selected to be longer. It is therefore advantageous if the minimum operating time is at least half an hour, although there can already be effective hydrogen production and a stable process beforehand.

[0053] In order to avoid unnecessary delays in the start-up of the electrolysis unit, care should be taken that the minimum operating time does not exceed 2 hours.

[0054] Depending on whether the electrolysis plant is connected to a public grid, for example, or not connected to a public grid, and on the required safety, it can be determined for the start-up conditions that the expected supply power is with high probability higher than the auxiliary power, at least during the start-up period.

[0055] It is also obvious that the standby state requires a continuous supply of power. Although - as mentioned above - the amount of auxiliary power required is not always constant, the necessary auxiliary power is still provided for the standby state (which may fluctuate slightly over time).

[0056] It is therefore also advantageous that the auxiliary power necessary for further operation in the standby state is also guaranteed for the startup condition requirement. Here, it can be required in a simple manner that the expected supply power is higher than the auxiliary power with sufficient probability or with a high probability at least in the startup time period. If an alternative or supplementary energy supply is available, it will advantageously be taken into account as an alternative power.

[0057] Even though estimates show that the expected supplied power is sufficient to switch from idle to standby mode and that at a later point in time minimum power can be expected for a longer period of time without the expected supplied power falling below the required auxiliary power, unnecessarily long operation of the auxiliary system is not optimal.

[0058] It is therefore advantageous to specify the start-up conditions in such a way that there is a period of at most three times the start-up time period between reaching the standby state with the auxiliary system switched on and the expected start of electrolysis. In this respect, the time at which the minimum power is expected to be reached before starting the electrolysis device is advantageously no more than four times the start-up time period. Alternatively, it can be determined for the start-up conditions that the expected supply power reaches the minimum power no later than after three times the start-up time period. Here - as already mentioned - it is required that under the start-up conditions it can be assumed that the electrolysis can be carried out for the desired duration.

[0059] The basic idea of ​​the invention is to protect the electrolysis system from unnecessary aging and thus from premature maintenance, even if the renewable energy that could be made available is not used. In particular, when carrying out maintenance and supplying corresponding materials and spare parts under difficult local conditions, it is advantageous to be able to achieve the longest possible service life or the longest possible maintenance intervals.

[0060] It is accordingly advantageous that the start-up conditions are tightened, i.e. after the start-up period, the power is continuously supplied at the level of the auxiliary power until the switchover to the operating state, assuming that the expected supply power or its expected value for a period longer than the shortest operating time enables the electrolysis unit to be operated continuously and that at least the minimum power is achieved as expected in this period. The probability of the expected supply power can also be taken into account.

[0061] Firstly, it is advantageous to set the same requirements for the operating conditions as for the start-up conditions for the required period of time during which the estimated supplied power is above the minimum power.

[0062] Furthermore, it is advantageously required for the operating condition that the period of time during which the estimated supplied power is higher than the minimum power is multiplied by the probability, and the product is at least equal to twice the minimum operating time. That is, if it can be considered with a high probability that the estimated supplied power is higher than the minimum power, the required time is slightly more than twice the shortest operating time. However, if the probability is only 50%, then the period of time during which the estimated supplied power is higher than the minimum power must have lasted for four times the shortest operating time.

[0063] Furthermore, it is particularly advantageous if the required operating state is expected to be maintained at least for a period of time weighted with a probability of three times the shortest operating time.

[0064] The operating conditions are determined analogously to the start-up conditions, wherein here too the start-up of the electrolysis is advantageously delayed in order to increase the service life.

[0065] The backup unit is necessary in order to be able to achieve a controlled shutdown of the electrolysis plant in the event of an unexpected reduction in the supplied power or its failure. The manner in which the backup unit achieves this is currently unimportant.

[0066] Thus, the backup unit may initially represent an electrical connection to the conventional grid. This design is particularly advantageous in places where, although the auxiliary power required by the auxiliary systems for shutting down the equipment can be provided, the electrical connection is unable or barely able to transfer the energy generated by the power supply or to provide the minimum power level to the electrolysis equipment.

[0067] The use of the method according to the invention is particularly suitable if there is no reliable power connection. Under these conditions, it is generally not possible to assume that a sufficient power connection for the backup unit can be guaranteed. In this regard, the use of battery storage is advantageously suitable. Thus, in extreme cases, the electrolysis plant can be operated autonomously using renewable energy sources and a safe shutdown can be ensured in the absence of energy.

[0068] If the backup unit is a rechargeable energy storage device, i.e., in particular a battery storage device, the startup condition further advantageously requires that after the electrolysis device has been put into operation, sufficient energy is (predictably) additionally provided by the power supply in the operating state over a minimum operating time in order to be able to fully charge the energy storage device or the battery storage device. A sufficient charge state of the energy storage device thus enables a safe shutdown in the event of a loss of energy from the energy source. This is of course dependent on the corresponding charge state of the energy storage device or the battery storage device when the startup condition is checked.

[0069] When designing a backup unit with a rechargeable energy store, the charge level and the probability of the expected delivery power occurring are advantageously taken into account in the operating conditions. If the probability of the expected delivery power is considered high, it may be sufficient to fully charge the backup unit at the end of the minimum operating time.

[0070] If only a sufficient probability of an expected supply power is given (as required by the start-up conditions), it is advantageously required that a sufficient charge level of the backup unit can already be reached in half the shortest operating time.

[0071] The energy storage device or battery storage device can be charged during continuous operation according to the expected supply power. If the expected supply power is only slightly higher than the minimum power, it may be necessary to first charge the energy storage device or battery storage device before starting the electrolysis unit, because the expected supply power may not be sufficient to output the minimum power to the electrolysis unit and charge the backup unit at the same time. If the expected power is sufficiently higher than the minimum power, it can also be provided that the electrolysis unit is started, switched to the operating state, and the energy storage device or battery storage device is charged at the same time.

[0072] The backup unit is necessary as a safeguard against a sudden failure of the supplied power. In contrast, it may also be advantageous to provide an electrical storage device which can store the energy provided by the power supply.

[0073] This enables in particular that energy which cannot be used by the auxiliary system or in the electrolysis unit can be stored for later use. The extension of the time period resulting from the provision of the start-up conditions and operating conditions almost necessarily results in that the energy provided by the power supply can be stored before the start-up conditions or the operating conditions exist.

[0074] Since the backup unit is fundamentally required and, if further advantageously, the energy storage device is required, they can in principle be provided as separate units. Obviously, the operation of the backup unit is different from the energy storage device (storage in the backup unit as a prerequisite for operation; storage in the energy storage device only in the case of excess energy).

[0075] Advantageously, the backup unit is integrated in the energy storage device. In this respect, the energy storage device is charged first with a higher priority for the integrated backup unit in order to ensure a safe shutdown of the electrolysis unit. The energy storage device is only further charged if there is excess energy or the power supplied by the power source is not consumed in the electrolysis unit and is not consumed by the auxiliary system.

[0076] Furthermore, the presence of the energy storage device creates further operating possibilities, so that the use of the electrolysis cell can continue unimpeded, in particular when the energy storage device is charged and briefly falls below a minimum power.

[0077] If it is particularly advantageous to be able to compensate for brief dips below the minimum power by the actual supplied power, it is particularly advantageous if the charged energy storage device can provide at least half of the minimum power for at least half of the minimum operating time. This allows the electrolysis unit to continue to operate uninterruptedly even if brief dips below the minimum power occur.

[0078] It is also advantageous if the charged energy storage device can provide a minimum power. Thus, even if there is a brief or complete interruption in the power supply, the operating state can still be maintained. This means that when designing the energy storage device, it is therefore advantageous to take into account that the energy storage device can store the energy required for operating the auxiliary systems and the electrolysis unit.

[0079] In order to enable the electrolysis unit to operate for as long as possible, it is also provided that the charged power storage device can provide at least half of the minimum power during at least the shortest operating time. Thus, even if the actual supplied power drops below the minimum power for a longer period of time, electrolysis can still continue.

[0080] Since the power supply is expected to be an unreliable power supply, it is advantageous to determine which measures are to be taken if the estimated supply power is lower than the supply power required for the continued operation of the electrolysis system.

[0081] If the standby state is reached or provided, the question arises: how long will the expected supply power be lower than the necessary auxiliary power? This time period is defined as the permitted downtime period. Based on this, a downtime condition is advantageously defined, when which the switch from the standby state to the idle state takes place.

[0082] As a first condition, it is advantageously provided that the shutdown period weighted by probability is longer than the startup period X times. This is based on the assumption that, for a longer period of time, it is possible to switch first to the idle state and then to the standby state, during which auxiliary power can be saved. Therefore, if the time period until the expected supply power increases again multiplied by the startup period with probability greater than X times, a shutdown condition (as a triggering event for the switch-off) is generated.

[0083] As to what is a particularly favorable factor, a balance must be struck between the unnecessary continued operation of the auxiliary system, which prevents electrolysis from being carried out in time, and the time wasted in shutting down and restarting the auxiliary system. A limit value of the downtime period multiplied by the probability of being between 2 and 10 times the start-up period, for example 3 or 5 times, has proven to be favorable.

[0084] It is particularly advantageous to consider as a first condition that the weighted downtime period is longer than 4 times the start-up period. This allows for a faster start-up while improving the prediction for the electrolysis unit to resume operation, i.e. when operating conditions are present again. However, if this defect exceeds a longer period of time, it is advantageous to switch to an idle state (i.e. to generate a downtime condition).

[0085] Furthermore, it only makes sense to skip the downtime period if it can be expected that the electrolysis can be put back into operation after the downtime period and thus produce hydrogen. This advantageously results in a second condition for the downtime condition. Thus, a downtime condition is generated if it is expected that the operating conditions will not be met after the downtime period.

[0086] In the event of insufficient supply power, the auxiliary system can only continue to operate if the missing energy is supplied in another way. This is advantageously achieved by means of an electrical storage device. However, this is obviously only possible if the electrical storage device is sufficiently charged for this purpose. This results in the third condition of the shutdown condition. Thus, a shutdown condition occurs when the energy stored in the electrical storage device is insufficient to continue to operate the auxiliary system during the shutdown period.

[0087] Due to the presence of the power storage device and the determination of the shutdown condition, the following behavior is advantageously produced: the auxiliary system is shut down when the shutdown condition exists, in this regard, switching from the standby state to the idle state. In other cases, the auxiliary power lacking in the power supply is provided by the power storage device.

[0088] Furthermore, it is advantageous to consider what needs to be done in the operating state (ie, electrolysis takes place) if the actual supplied power drops below the minimum power. If there is no other way to supply the missing power, this will immediately lead to the need to switch to the standby state.

[0089] If an electricity storage device of sufficient size is available, this not only enables the temporary operation of auxiliary systems, but also the temporary partial or complete supply of the minimum power required for the operation of the electrolysis unit.

[0090] It is therefore further advantageous to determine a stop condition, when the stop condition exists, to switch from the operating state to the standby state. In this case, the expected supply power and its probability are similarly taken into account. For this purpose, a shortage period is determined, wherein the stop condition is met when the power falls below a minimum for the shortage period.

[0091] Firstly, if the operating condition is not met after the shortage period, a stop condition is considered to have occurred. This means that if after the shortage period, the electrolysis unit cannot be operated for the minimum operating time with sufficient probability by power supply from the power supply, a stop condition has occurred.

[0092] In terms of the time period that needs to be spanned, the shortage time period is advantageously determined according to the capacity and power level of the power storage device. Based on this, it is necessary to limit the shortage time period to a time period in which the power storage device can proportionally provide the minimum power missing from the power supply or the minimum power missing.

[0093] However, it should be avoided that the energy storage device is completely emptied as planned. In this respect, it is advantageous to limit the shortage period as soon as the charge level of the energy storage device falls below a limit value.

[0094] Two different parameters can advantageously be considered as the basis for the limit value. In a first variant, the first limit value is advantageously set in dependence on the storage capacity of the storage device.

[0095] In a second variant, it may be advantageous to use the second limit value as a function of the respective charge level of the energy storage device at the beginning of the shortage period.

[0096] In both the first variant and the second variant, these limit values ​​are preferably between 5% and 25%. If, in the event of a power shortage or a power shortage of the power source, the power storage device supplies the missing minimum power during the shortage period, then at the end of the shortage period, the power level of the power storage device should not be lower than the relevant limit value absolutely (first variant) or relatively (second variant).

[0097] If the charge level of the storage device before the shortage period is, for example, 50%, then at the end of the shortage period the charge level of the storage device should not be lower than between 5% and 25% - the first variant, or between 2.5% and 12.5% ​​- the second variant.

[0098] This obviously results in a procedure in which, when a shortage condition exists, the electrolysis unit is switched off and switched from the operating state to the standby state, while in other cases the missing minimum power is supplied by the power storage device.

[0099] The above statements about the method according to the invention and the advantageous use of the required electrolysis device are basically independent of the number of electrolysis units. However, the descriptions about the start-up conditions, operating conditions, advantageously stop conditions and advantageous shutdown conditions refer to the first electrolysis unit.

[0100] Advantageously, the electrolysis device has two or more electrolysis cells. In this case, conditions need to be set for each individual electrolysis cell. In this case, these conditions can be the same or different, depending on whether the electrolysis devices are designed to be the same or different. For this purpose, the relevant time period must also be determined for each electrolysis cell.

[0101] At least when there are at least two electrolysis units, it is advantageous to switch these on or off sequentially, so that when the expected supply power fluctuates, the available energy can be advantageously utilized for the production of hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0102] The following figure shows by way of example a graph of a possible course of the supply power. For example, this can be the supply power generated by a wind power plant, which is accordingly supplied to the power supply of the electrolysis plant. DETAILED DESCRIPTION

[0103] Here the supplied power (P) 01 (ordinate 03) is plotted against time (t) (abscissa 02). The lower limit line represents the auxiliary power required by the auxiliary system 05. Above this there is another limit line, which is the minimum power 06 of the electrolysis unit together with the auxiliary system.

[0104] Assume that this is the expected supply power, which occurs with a probability of 80%, for example.

[0105] In practice, the probability obviously often depends on the time interval, ie the probability of the correctness of the estimated supplied power usually always gets lower and lower as the time interval increases.

[0106] The starting point is that the electrolysis plant is in idle state. With the estimated supply power determined, the start-up conditions are first checked.

[0107] Based on the exemplary depicted course of the predicted supply power 01 , there is a time period in which the predicted supply power 01 is with sufficient probability higher than the assistance power 05 and is longer than the start time period 07 .

[0108] However, if the probability of the estimated supply power 01 being higher than the auxiliary power 05 is required to be high, and here the probability is 80%, then this condition is not met. However, it can be expected that the probability of exceeding the limit value is significantly higher than the probability of the estimated course of the supply power.

[0109] In the subsequent period of time, there is a process in which the predicted supply power 01 is higher than the minimum power 06. Here, the coefficient obtained by multiplying the exemplary predicted supply power 01 higher than the minimum power 06 by the exemplary probability 80% is greater than 1.5 times the shortest operation time 08.

[0110] As a result, the activation condition is met (at the beginning of the illustrated time period 07 ) and the auxiliary system is to be activated, ie switched from the idle state to the standby state.

[0111] When the auxiliary system is in standby mode, it is constantly checked whether the operating conditions are met. This is obviously the case because these operating conditions already exist when the start conditions are checked for this exemplary process.

[0112] With the emergence of operating conditions (at the beginning of time period 08), a switch is made from the standby state to the operating state. That is, the electrolysis unit starts to perform electrolysis.

[0113] It can be considered that the course of the expected supplied power changes over time depending on the probability, and the shorter the distance in the future, the greater the probability. When the start condition exists, it is considered that the operating condition also occurs at a later point in time. However, it may happen directly that the course of the expected supplied power changes unfavorably and the operating condition is not achieved as expected.

[0114] In the exemplary process, some relevant time points are shown for example for further explanation. It is important here whether there is an electrical storage device and what the charge level of the backup unit and the assumed electrical storage device is.

[0115] First, in the standby state (after the start time period 07), there is a short drop below the auxiliary power - time period 11. If there is no power storage device and if it is not possible or desired to use the backup unit for the bridge instead, this will lead to an immediate failure of the auxiliary system (at least partially) (due to the lack of necessary power).

[0116] However, advantageously, an electrical storage device is present so that it is first checked whether a fault situation exists. Assuming that the electrical storage device is at least partially charged, it can easily supply the missing auxiliary power. In addition, the time period until the expected operating condition is reached is short, so that the auxiliary system does not have to be switched off, i.e. kept in standby mode.

[0117] In the further course of events, the supply power 01 is increased above the minimum power - time period 12. However, when checking the start conditions, it can be seen that the expected supply power does not exceed the minimum power 06 within the shortest operating time - see time period 13. Therefore, the standby state is maintained. In this case, the excess energy exceeding the auxiliary power is advantageously supplied to the power storage device.

[0118] After the start of electrolysis, ie after the minimum operating time 08, a short drop below the minimum power occurs - time period 14. As in time period 11, this shortfall of energy can advantageously be provided by an electrical storage device.

[0119] In the further course of things, the supplied power 01 drops below the minimum power 06 again - time period 15. It is now advantageous to check whether the stop condition for shutting off the electrolysis has occurred. The shortage period starts from the drop below the minimum power 06 until the minimum power 06 is exceeded again. It is assumed that the operating conditions are then met again. The key question now is whether the energy storage device can supply the energy missing in the supplied power during the shortage, up to the minimum power. If this is the case, the operating state remains unchanged and the electrolysis can continue. However, if the energy storage device is, for example, discharged, it is necessary to shut off the electrolysis unit and switch to the standby state.

Claims

1. A method for controlling an electrolysis device having an idle state, a standby state and an operating state, the electrolysis device comprising: - an auxiliary system, which has a specific auxiliary power as a whole, is turned on in the standby state and the operating state, has a specific start-up time period for switching from the idle state to the standby state and a specific cut-off time period for switching from the standby state to the idle state, and is designed so that the start-up time period is a maximum of 4 hours and the cut-off time period is a maximum of 4 hours; and at least one electrolysis unit having a certain minimum power including said auxiliary power and producing hydrogen and oxygen in said operating state and having a specified minimum operating time of between 0.25 hours and 4 hours; and - at least one power source allowing to provide electrical power at a varied supply power at varied times and for varied time periods; and at least one backup unit, which is capable of providing energy for outputting at least the auxiliary power during at least the cut-off period; Wherein, for sufficient probability, the determined probability exceeds 80%, and for high probability, the determined probability exceeds 95%; a) wherein, starting from the idle state, a start condition is determined, under which: - at least during the start-up period, the estimated supply power is higher than the auxiliary power with sufficient probability, and - subsequently, the estimated time period during which the supplied power is higher than said minimum power is multiplied by a probability at least equal to 1.5 times said shortest operating time; b) wherein, starting from the standby state, an operating condition is determined, under which: - the estimated supply power is higher than the minimum power within the shortest operating time with sufficient probability; c) wherein, starting from the currently available supply power, a forecast of the expected course of the estimated supply power is continuously generated; d) wherein, in the idle state, when the start condition exists, switching to the standby state; and e) Wherein, in the operating state, when the operating conditions exist, switching to the operating state is performed.

2. The method according to claim 1, in, The start-up time period is at least 0.5 hours and at most 2 hours; and / or Wherein, the shortest running time is between 0.5 hours and 2 hours.

3. The method according to claim 1 or 2, a') Among them, Determine a start condition under which - the estimated supply power exceeds the auxiliary power with a high probability at least during the startup time period; and / or - the estimated supply power, supplemented by the alternative power as necessary until the minimum power is reached, exceeds the auxiliary power with a high probability; and / or - the supply power is expected to reach the minimum power for the required duration at most after 4 times the start-up time period; and / or - Subsequently, the estimated time period during which the supplied power is above the minimum power is multiplied by a probability which corresponds to at least 2.5 times the shortest operating time.

4. The method according to any one of claims 1 to 3, b') Among them, Determine operating conditions under which - the estimated supplied power has a high probability of exceeding the minimum power within the shortest operating time; and The time period during which the estimated supplied power is above the minimum power multiplied by the probability is at least twice as large as the shortest operating time.

5. The method according to any one of claims 1 to 4, in, The backup unit includes a battery storage device, a″) wherein the start condition further requires that the battery storage device is sufficiently charged at the latest by the end of the minimum operating time.

6. The method according to any one of claims 1 to 5, in, The backup unit includes a battery storage device, b”) where: The operating conditions further require that the battery storage device can be sufficiently charged with a sufficient probability at the latest by the end of half the shortest operating time.

7. The method according to any one of claims 1 to 6, in, The electrolysis equipment further includes an electricity storage device capable of being charged and discharged according to an electricity storage state, and the electricity storage device particularly includes the backup unit.

8. The method according to claim 7, in, Energy provided by the power source and not consumed by the auxiliary system or the electrolysis unit is delivered to the power storage device.

9. The method according to claim 7 or 8, in, The charged power storage device is capable of supplying energy for at least half of the shortest operating time or at least half of the minimum power level or at the minimum power level during the shortest operating time.

10. The method according to any one of claims 7 to 9, f) wherein, starting from the standby state, a shutdown condition is determined, under which the estimated supply power is less than the auxiliary power during the shutdown period, -in, The probability-weighted downtime period is longer than 3 or 5 times the uptime period; or - wherein said operating condition is not met after said downtime period; or - wherein the energy stored in the electrical storage device is insufficient to operate the auxiliary system during the downtime period.

11. The method according to any one of claims 7 to 10, g) Among them, In the shutdown condition, the auxiliary system switches to the idle state, and otherwise the missing auxiliary power is supplied by the power storage device.

12. The method according to any one of claims 7 to 11, h) wherein, starting from the operating state, a stop condition is determined, under which the estimated supply power is lower than the minimum power during the shortage period, -in, the operating condition is not met after the shortage period has elapsed; or -Wherein, the permitted shortage period is limited by the power supply capacity of the power storage device at the minimum power level, which is limited to a lower limit value at the end of the shortage period, which is between 5% and 25% of the storage capacity and / or between 5% and 25% of the power level generated before the shortage period.

13. The method according to claim 12, i) wherein, under the stop condition, the electrolysis unit switches to the standby state, and in other cases the missing minimum power is supplied by the power storage device.

14. The method according to any one of claims 1 to 13, in, The electrolysis device comprises at least two or more electrolysis cells, wherein the preceding conditions relate to a first electrolysis cell and each further electrolysis cell has a start condition and / or an operating condition and / or a stop condition and / or a shutdown condition with a respectively assigned time period assigned to the respective electrolysis cell.

15. The method according to claim 14, in, The electrolysis units are sequentially switched on or off according to the estimated supply power and / or the capacity and charge level of the power storage device.

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