METHOD FOR OPERATING AN ELECTROLYSIS PLANT

Description

TECHNICAL AREA

[0001] The invention relates to a method for operating an electrolysis plant. Auxiliary systems and an electrolysis unit are required to carry out the method. Furthermore, the method takes into account that the energy available to the electrolysis plant is obtained from a power source that provides varying levels of power at irregular intervals. BACKGROUND TO THE INVENTION

[0002] The auxiliary systems and the electrolysis unit each require a specific time period, dependent on their design, to switch from the off state to their respective on state with constant operation. The auxiliary systems must be started before the electrolysis unit can start. Then, provided sufficient power is available, the electrolysis unit starts.

[0003] It is known that renewable energy sources (solar, wind, etc.) are often available in locations where demand is very low. This necessitates transporting the energy from its point of generation to the point of energy demand. In many cases, renewable energy is generated in the form of electricity, for example, by solar parks or wind turbines. If a large distance needs to be bridged between generation and consumption, it is advantageous to use the renewable electricity to produce storable and more easily transportable hydrogen through electrolysis. A disadvantage of this method is the inconsistent power output provided by the electricity source.

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

[0005] If the power consumption exceeds the power required by the auxiliary systems for a sufficient period of time, these systems are generally ramped up. This is based on the assumption that the electricity is essentially "free" or otherwise unused.

[0006] If, in addition to the auxiliary systems being switched on, sufficient energy is available to operate the electrolysis unit, it is generally switched on immediately. Here, too, every effort is made to use the regeneratively generated electricity for electrolysis as quickly as possible.

[0007] Varela et al., International Journal of Hydrogen Energy, 2021, 46(14), 9303-9313 reveals a planning approach for modeling alkaline water electrolysis for Power-to-X applications. SUMMARY OF THE INVENTION

[0008] Although it is possible to achieve a high hydrogen yield using renewably generated electricity with the known method, it has been found that this operating mode leads to faster aging of the electrolysis unit. Furthermore, maximizing hydrogen production is not always advantageous compared to the costs of operating and maintaining the electrolysis plant.

[0009] The object of the present invention is therefore to enable optimal hydrogen production while taking into account the costs of operating and maintaining the electrolysis plant.

[0010] The problem is solved by a method according to the invention as described in claim 1. Advantageous methods are the subject of the dependent claims.

[0011] First, an electrolysis plant is required. This plant includes, as an essential component, at least one electrolysis unit. The specific design and basic operating principle of this unit are initially irrelevant. At a minimum, the electrolysis unit must be designed to enable the production of hydrogen using an electrical current.

[0012] Furthermore, auxiliary systems are necessary for the operation of the electrolysis unit, and their operation is a prerequisite for the operation of the electrolysis unit itself. The specific type of auxiliary systems is initially irrelevant. Here, too, those skilled in the art can refer to known electrolysis plants and the auxiliary systems used therein. These auxiliary systems can include, for example, controls, pumps, cooling units, and filter devices. Which specific auxiliary systems are required depends, among other things, on the design of the electrolysis unit. These systems are essential for the application of the method according to the invention; however, their precise design is irrelevant, provided their performance data is taken into account. Therefore, those skilled in the art can refer to known designs of electrolysis plants with electrolysis units and auxiliary systems. No further explanation is necessary in this regard.

[0013] Furthermore, a power source is required to supply the energy necessary for operating the electrolysis plant. The power source, as defined in the present invention, refers to a connection to a power generation plant, such as a solar park or a wind turbine (not the power generation plant itself). It is important to consider that the power supplied to the electrolysis plant by the power source may be fluctuating and unreliable. However, the process can also be used even if the power source reliably and continuously provides a usable power output. Therefore, the power output may (but need not) fluctuate in both magnitude and duration, or even drop to zero completely; in other words, the process must be designed so that the power output is not constant.

[0014] Assuming (though this is not a prerequisite for the procedure) that the electrolysis plant is deployed at locations off the grid, a backup power supply is required. This backup power supply must be capable of enabling a controlled shutdown of the electrolysis plant in the event of a power outage. The specific type of backup power supply is initially irrelevant. At a minimum, the backup power must be immediately available to supply the electrolysis plant during operation, allowing for immediate shutdown in case of a power drop or failure. Logically, the backup power supply must be capable of providing the necessary backup power for the duration of the shutdown process until the electrolysis plant is completely switched off.

[0015] Starting from relevant units of the electrolysis plant, the electrolysis unit and the auxiliary systems, different states result.

[0016] A distinction is made between a standby state, in which both the electrolysis unit and the essential auxiliary systems are switched off. Regardless of this, it may be possible to operate individual, low-power auxiliary systems. At the very least, in this state, starting electrolysis is not possible, and energy consumption is reduced to zero or to a very low level.

[0017] The standby state is characterized by the fact that the electrolysis unit can be started virtually at any time. This requires that the necessary auxiliary systems have been started up beforehand. Operating these auxiliary systems consumes power without any electrolysis taking place.

[0018] In operating mode, the electrolysis unit is supplied with operating current and hydrogen is produced by means of electrolysis.

[0019] It is generally not possible to start an electrolysis plant immediately so that hydrogen production begins instantly. Rather, startup processes require a certain amount of time before the electrolysis unit can start and hydrogen production can commence. Depending on the condition of the electrolysis plant when it is to resume operation, different measures are required.

[0020] Before electrolysis can begin and the system can reach operating mode, various auxiliary systems must be activated. It is important to note that each of these auxiliary systems, which must be operational before the actual electrolysis process can start, requires a specific start-up time. This time can be influenced to some extent by the design of the auxiliary systems, but it is also heavily dependent on the design of the electrolysis unit and its operating mode. This results in a specific start-up time for the electrolysis system, which is required to transition from a switched-off, idle state to a ready state during which the electrolysis unit can be started at any time.

[0021] It can be assumed that the startup time will be at least several minutes. On the other hand, the startup time should not exceed 4 hours.

[0022] Similarly, even after the actual electrolysis process has ended, auxiliary systems still need to operate. In particular, it is often necessary to ensure that the electrolysis unit can cool down in a controlled manner. Therefore, there is a shutdown period during which auxiliary systems must remain operational after electrolysis has ceased. This period can also be influenced by the design of the auxiliary systems, but it remains highly dependent on the design of the electrolysis unit and its operating mode.

[0023] It can be assumed that the shutdown period will be at least several minutes. On the other hand, the shutdown period should not exceed 4 hours.

[0024] The various auxiliary systems exhibit individual constant or state-dependent power consumption, depending on the operating state. The relevant factor for consideration is the total power required by all auxiliary systems for the transition from standby to readiness. The readiness state can only be achieved if this specific auxiliary power can be provided. The same applies analogously to the total auxiliary power required by all auxiliary systems for the transition from operating to standby.

[0025] Independently of this, it may be stipulated that, depending on the operating state, individual auxiliary systems are temporarily switched off or their output reduced, while other auxiliary systems continue to operate at full capacity. If a near-instantaneous start of electrolysis and thus a switch to operating mode is possible, this is considered a standby state. This is still considered to be the case if the time until the electrolysis unit can be started is at most 0.1 times the start-up time. For example, the output of pumps could be reduced, which, in contrast, can be very quickly ramped back up to the intended output for starting electrolysis.

[0026] After the electrolysis unit is started, it takes some time before the produced hydrogen can be effectively extracted from the electrolysis system. In particular, a certain amount of time is required to reach a largely stable operating temperature and to establish a suitable pressure within the system. Furthermore, the water circulation and the process of separating oxygen and hydrogen require time to reach a largely stable state (starting from a constant current supply). This start-up process also incurs energy consumption without significant hydrogen production. The duration of this process depends on the design of the electrolysis system and the specific design and operating mode of the electrolysis unit.

[0027] This results in a minimum operating time after which an essentially static state (assuming constant power input) is reached.

[0028] Furthermore, the minimum operating period requires that the ratio between the amount of hydrogen produced and the energy input over that period be at least 50% of the amount produced during continuous operation with the same energy input. This means that at the end of the minimum operating period, at least the amount of hydrogen produced must be equal to the amount produced during continuous operation with half the energy input.

[0029] It is particularly advantageous for the minimum operating period that the ratio of hydrogen produced to energy input at the end of the minimum operating period corresponds to at least 0.8 times the ratio during ongoing operation.

[0030] It can be assumed that the minimum operating time is at least 15 minutes. On the other hand, the minimum operating time should not exceed 4 hours.

[0031] Electrolysis obviously requires a power supply. To ensure a stable process with economical hydrogen production, the power supply must not fall below a certain minimum. Taking into account the power required for the auxiliary systems, this results in a minimum power output that must be available to operate the electrolysis plant.

[0032] Depending on the design and operating mode of the electrolysis unit, there is an operating range in which the electrolysis unit can be operated at a higher power output with a greater hydrogen yield. This range is limited by a maximum power output beyond which no further increase in hydrogen production can be achieved and / or damage to the electrolysis system may occur.

[0033] The method according to the invention first requires the definition of a starting condition. The electrolysis plant is assumed to be in a standstill state. Initially, it is necessary that the output power exceeds the auxiliary power, at least for the duration of the ramp-up time. Since the output power is not uniquely determined with an unreliable power source, it is necessary to use a predicted output power that is subject to probabilities.

[0034] The probability of the predicted output can be determined in different ways. On the one hand, one can use the probability assigned to the given energy source, for example, the expected wind speed. On the other hand, a probability can be determined based on historical data, comparing past forecasts with actual values. At the very least, a person skilled in the art is readily able to determine meaningful probability values ​​that can be used as a basis for conducting a procedure.

[0035] Since the predicted delivery output ultimately contains an assumption, but actual output must be provided for starting up the auxiliary systems, the starting condition still requires that the predicted delivery output is sufficiently likely to exceed the required auxiliary output.

[0036] A sufficient probability is assumed to exist if it exceeds 80%. It is particularly advantageous if a sufficient probability is required to exceed 90%.

[0037] In contrast, when a high probability is mentioned, it is assumed that this is above 95%.

[0038] It should be noted that when considering probability, it is important to take into account that a check is being carried out to determine whether limit values ​​are being exceeded. That is, the relevant factor is not the probability that the actual delivery performance will correspond to the previously forecasted delivery performance. Rather, the assessment must be made as to whether the actual delivery performance exceeds the respective limit value under consideration.

[0039] Following the ramp-up phase, during the transition from standby to standby mode, it is necessary that the predicted delivery output continues to exceed the auxiliary output. The duration of this period is initially irrelevant.

[0040] Furthermore, the existence of the start condition requires that, following the ramp-up period or from a later point in time, the minimum power is reached without an expected interim drop in the predicted power below the auxiliary power.

[0041] Firstly, it is necessary to determine the period for which the predicted delivery performance can be expected to exceed the minimum performance.

[0042] Secondly, the probability that the predicted performance will be above the minimum performance must be taken into account.

[0043] Based on these two considerations—the duration of the expected sufficient delivery performance and the probability of it being sufficient—the initial condition requires that the period with a projected delivery performance above the minimum performance, multiplied by the probability, corresponds to at least 1.5 times the minimum operating time. That is, if it can be assumed with a high probability that the projected delivery performance is above the minimum performance, the required period is slightly more than 1.5 times the minimum operating time. However, if the probability is only 50%, the period with the projected delivery performance above the minimum performance must already last three times the minimum operating time.

[0044] This means that the starting condition assumes that, as expected (since the delivery output is only predicted and not precisely defined), after the electrolysis plant is started and the auxiliary systems are switched on, these can be operated continuously until the electrolysis unit starts, and subsequently the electrolysis can take place continuously beyond the minimum operating time.

[0045] Furthermore, defining an operating condition is necessary. In this case, it is assumed that the electrolysis plant is in standby mode, meaning the necessary auxiliary systems are operational, while the electrolysis unit itself is switched off. Compared to the start-up condition, the only initial requirement is that the predicted output for the minimum operating time exceeds the minimum output. However, a sufficient probability of this is required.

[0046] When examining the operating conditions, the immediately following period is assessed to determine whether the forecasted delivery performance exceeds the minimum performance. It is assumed that the probability of this exceeding the minimum performance is higher than the probability of the forecasted delivery performance for the same period when examining the initial conditions.

[0047] The underlying assumption here is that if the auxiliary systems are already in operation, it is useful if electrolysis can take place for the minimum operating time, especially if the energy comes from renewable sources and cannot be used in any other meaningful way.

[0048] The electrolysis plant is operated under defined start and operating conditions, logically based on the predicted delivery output. If the electrolysis plant is in standby mode, it switches to standby mode and starts the auxiliary systems when the start conditions are met.

[0049] If the electrolysis system is in standby mode and the operating conditions are met, it switches to operating mode and starts electrolysis.

[0050] The new method with delayed start conditions, while foregoing the most comprehensive use of renewable energies, prevents the electrolysis plant from starting unless a sufficient period for continuous operation can be foreseen. This reduces the detrimental effects on the electrolysis plant caused by frequent on / off cycles. As a result, the reliability and lifespan of the electrolysis plant can be improved, even if the hydrogen yield is slightly lower. Considering the maintenance costs of the electrolysis plant, it should therefore be possible to produce hydrogen at a lower cost – although this always depends on the actual output.

[0051] When designing the auxiliary systems and assuming that a longer period of sufficient power supply from the unreliable power source can be expected to start the electrolysis plant, it is not necessary to aim for a minimum start-up time. Rather, it should be assumed that a start-up time of less than half an hour would cause unnecessary additional effort and costs for the auxiliary systems.

[0052] However, the ramp-up time should not be unnecessarily long. After all, this delays the potential start of the electrolysis plant if it becomes apparent that sufficient power will subsequently be available to begin electrolysis. Therefore, it is advantageous if the ramp-up time does not exceed two hours.

[0053] A lower limit for the minimum operating time is determined, on the one hand, by the proportion of hydrogen produced relative to the energy input. On the other hand, it is expected that a substantially stable process with virtually constant water flows will have been established. A certain degree of design flexibility remains, and the minimum operating time can also be set higher. Accordingly, it is advantageous if the minimum operating time is at least half an hour, although effective hydrogen production and stable processes may already be in place before then.

[0054] To avoid unnecessary delays in starting the electrolysis unit, care should be taken to ensure that the minimum operating time does not exceed 2 hours.

[0055] Depending on the possible connection of the electrolysis plant to, for example, a public grid or, conversely, its absence, as well as depending on the required safety, it can be stipulated for the start-up condition that the predicted delivery output is highly likely to exceed the auxiliary output for at least the ramp-up period.

[0056] Furthermore, it is obvious that the state of readiness requires continuous support. Although – as previously noted – the required level of assistance is not fixed at all times, the necessary (possibly slightly fluctuating) assistance must nevertheless be provided for the state of readiness.

[0057] Therefore, it remains advantageous to require, as a starting condition, that the necessary auxiliary power is also guaranteed for continued operation beyond the standby state. This can be achieved simply by requiring that the predicted delivery power, at least for the ramp-up period, is sufficiently or highly likely to exceed the auxiliary power. If an alternative or supplementary energy supply is available, it is advantageously taken into account as a backup power source.

[0058] Although the forecast shows that the predicted delivery output is sufficient for switching from standby to readiness, and that at a later point in time the minimum output can be expected for a longer period without the predicted delivery output falling below the required auxiliary output, an unnecessarily long operation of the auxiliary systems is also not optimal.

[0059] Therefore, it is advantageous to specify the start condition such that the period between reaching standby mode with auxiliary systems switched on and the expected start of electrolysis is at most three times the ramp-up time. In this respect, the forecast for reaching the minimum output before the electrolysis plant starts should ideally not be further than four times the ramp-up time. Alternatively, the start condition can be specified that the forecasted output will reach the minimum output no later than three times the ramp-up time. As previously stated, it is essential that the start condition assumes electrolysis can be carried out for the required duration.

[0060] The basic idea of ​​the invention is to protect the electrolysis system from unnecessary aging and thus premature maintenance, even if this means that potentially available renewable energy remains unused. Particularly in difficult local conditions for carrying out maintenance and supplying the necessary materials and spare parts, it is advantageous to achieve the longest possible service life or service interval.

[0061] It is therefore advantageous to tighten the start-up condition by requiring, after a ramp-up period and continued power supply at the level of the auxiliary power until the switch to operating mode, that the predicted delivery power, or its expected value, enables continuous operation of the electrolysis unit for a longer period than the minimum operating time and, accordingly, is expected to at least reach the minimum power output for that period. The probability of the predicted delivery power can, in turn, be taken into account.

[0062] Firstly, it is advantageous to establish the same requirement for the operating condition regarding the required period in which the forecasted delivery performance exceeds the minimum performance as for the starting condition.

[0063] Furthermore, the operating condition advantageously requires that the period during which the forecasted delivery output exceeds the minimum output be multiplied by the probability and that the product of this probability be at least twice the minimum operating time. That is, if it can be assumed with a high probability that the forecasted delivery output will exceed the minimum output, the required period is slightly more than twice the minimum operating time. However, if the probability is only 50%, the period during which the forecasted delivery output exceeds the minimum output must already be four times the minimum operating time.

[0064] Furthermore, it is particularly advantageous if it is required that the operating condition can be predicted to be maintained at least over the period weighted with the probability of 3 times the minimum operating time.

[0065] The same applies to the determination of the operating conditions as to the starting conditions, whereby the start of electrolysis is also advantageously delayed in favor of a longer service life.

[0066] The reserve unit is required to enable a controlled shutdown of the electrolysis plant in the event of an unexpected reduction in delivery capacity or its complete absence.

[0067] A reserve unit could initially be implemented as a power connection to a regular power grid. This design can be advantageous in locations where auxiliary power necessary for shutting down the plant can be provided, but the power connection is unable to supply any or any significant amount of energy generated by the power source or to provide the electrolysis plant with energy at the minimum required output.

[0068] The use of the method according to the invention is advantageous when a reliable power supply is not available. Under these circumstances, it often cannot be assumed that a sufficient power supply for a backup unit can be guaranteed. Therefore, the invention provides for the use of a battery storage system. This allows the electrolysis plant to be operated autonomously using renewable energy and ensures a safe shutdown in the event of a power outage.

[0069] Since the reserve unit is a rechargeable energy storage device, i.e., a battery storage system, it is further advantageous for the start-up conditions that, after an assumed operation of the electrolysis plant for the minimum operating time (forecasted), sufficient additional energy is available from the power source to adequately charge the energy storage device or battery storage system. A sufficient state of charge in the energy storage system thus enables a safe shutdown in the event of a power outage at the power source. This is obviously dependent on the respective state of charge of the energy storage device or battery storage system when the start-up conditions are checked.

[0070] When designing the reserve unit with a rechargeable energy storage device, the state of charge and the probability of achieving the predicted delivery output are advantageously considered with regard to operating conditions. If a high probability of achieving the predicted delivery output can be assumed, it may be sufficient for the reserve unit to be sufficiently charged by the end of the minimum operating period.

[0071] Provided that there is a sufficient probability of predicted delivery performance (as required for the starting condition), it is advantageously required that a sufficient state of charge of the reserve unit can be achieved at half the minimum operating time.

[0072] Charging the energy storage system or battery can occur during operation, depending on the predicted power output. If this is only slightly above the minimum power output, it may be necessary to charge the energy storage system or battery before starting the electrolysis unit (as the predicted power output may not be sufficient to deliver the minimum power to the electrolysis unit and simultaneously charge the reserve unit). If the predicted power output is significantly above the minimum power output, it may also be possible to start the electrolysis unit and switch to operating mode while simultaneously charging the energy storage system or battery.

[0073] The reserve unit is necessary as a safeguard against a sudden power outage. Conversely, it can also be advantageous to provide a storage device that can store the energy supplied by the power source.

[0074] This makes it possible, in particular, to store energy that cannot be used by the auxiliary systems or in the electrolysis unit for later use. The extended time periods resulting from the definition of start-up and operating conditions almost inevitably mean that energy supplied by the power source can be stored before the start-up or operating conditions are met.

[0075] Since a reserve unit is generally required, and if a storage device is also advantageously required, these can in principle be provided as separate units. In this case, it is logical that the reserve unit is operated differently from the storage device (storage in the reserve unit is a prerequisite for operation; storage in the storage device only occurs in the event of energy surplus).

[0076] Advantageously, the reserve unit is integrated into the storage device. Therefore, charging the storage device with the integrated reserve unit initially takes place with higher priority to ensure the safe shutdown of the electrolysis unit. Further charging of the storage device only occurs in the event of an energy surplus or power supply from the power source that is not being consumed by the electrolysis unit or by the auxiliary systems.

[0077] Furthermore, the presence of a storage device offers additional operating possibilities, so that the electrolysis unit can continue to be used without interruption, especially when the storage device is charged and the minimum power is briefly undershot.

[0078] Given that it is particularly beneficial if short-term drops below the minimum power output can be compensated for by the actual delivery output, it is especially advantageous if the charged storage device can deliver at least half the minimum power output for at least half the minimum operating time. This enables continued uninterrupted operation of the electrolysis unit, even if short-term fluctuations below the minimum power output occur.

[0079] Furthermore, it is advantageous if the charged storage device can provide the minimum power output. This ensures that the operating state can be maintained even in the event of a brief, complete drop in power supply. Therefore, when designing the storage device, it is advantageous to consider that it should be able to store energy required for the operation of the auxiliary systems and the electrolysis unit.

[0080] To enable the electrolysis unit to operate for as long as possible, the charged storage device is designed to provide at least half of its minimum power output for at least the minimum operating time. This allows electrolysis to continue even if the actual power output drops below the minimum for an extended period.

[0081] Since the power source is expected to be unreliable, it is advantageous to determine what measures should be taken if the predicted delivery output is lower than what is required for the continued operation of the electrolysis plant without changes.

[0082] Once the readiness state is reached or established, the question arises as to how long the predicted delivery output will fall below the required auxiliary output. This period is defined as the permissible downtime. Based on this, a failure condition is advantageously defined, under which the system switches from the readiness state to the standby state.

[0083] As a first condition, it is advantageously defined that a probability-weighted downtime period is longer than X times the ramp-up time. This is based on the assumption that, over a longer period, it is possible to first switch to standby mode and subsequently back to standby mode, thereby saving auxiliary power in the meantime. Thus, the downtime condition (as a trigger for shutdown) is met when the time until the predicted delivery output increases again, multiplied by the probability, is longer than X times the ramp-up time.

[0084] When considering what constitutes a particularly advantageous factor, a balance must be struck between the unnecessary continued operation of auxiliary systems, preventing timely electrolysis, and the time lost due to shutdown and restart of these systems. Threshold values ​​for the downtime multiplied by the probability, ranging from two to ten times (e.g., three or five times) the start-up time, have proven advantageous.

[0085] It is particularly advantageous to consider, as a first condition, that the weighted downtime is longer than four times the start-up time. This allows for a faster start-up if the prognosis for restarting the electrolysis unit improves, i.e., if the operating condition is met again. Conversely, if the deficiency exceeds a longer period, it is advisable to switch to standby mode (i.e., if the failure condition is met).

[0086] Furthermore, bridging a downtime period only makes sense if it can be expected that electrolysis, and thus hydrogen production, can be restarted after the downtime. This leads advantageously to the second condition for the downtime condition. Accordingly, the downtime condition is met if the predicted operating condition is not fulfilled after the downtime.

[0087] Continued operation of the auxiliary systems is only possible in the event of insufficient power supply if the missing energy is supplied by another source. This is advantageously achieved through the storage device. However, this is only possible if the storage device is sufficiently charged for this purpose. This leads to the third condition for the failure condition. Accordingly, the failure condition is met if the storage device does not contain sufficient energy to continue operating the auxiliary systems for the duration of the failure.

[0088] With the presence of a storage device and the definition of a failure condition, the advantageous procedure is that the auxiliary systems are shut down when the failure condition occurs, thus switching from standby to idle mode. Otherwise, the auxiliary power missing from the power source is provided by the storage device.

[0089] Furthermore, it is advantageous to consider what procedure is necessary during operation, i.e., when electrolysis is taking place, if the actual delivery output falls below the minimum output. If no other supply of the missing power is possible, this immediately necessitates switching to standby mode.

[0090] Provided that a sufficiently large storage device is available, this not only enables the temporary operation of the auxiliary systems, but can also temporarily supply part or all of the minimum power required for the operation of the electrolysis unit.

[0091] Consequently, it remains advantageous to define a stop condition, the occurrence of which triggers a switch from operating to standby mode. Similarly, the predicted delivery output and its probability must be considered. For this purpose, a shortage period is determined, and the stop condition is met if the minimum output is not met beyond this shortage period.

[0092] First of all, the shutdown condition is considered to be met if the operating conditions are not fulfilled after the shortage period. That is, the shutdown condition is met if, after the shortage period has expired, it is not possible to operate the electrolysis unit with sufficient probability for the minimum operating time using the power supply from the power source.

[0093] Regarding the time period to be bridged, the shortfall period is advantageously defined as a function of the capacity and state of charge of the storage device. Based on this, the shortfall period should be limited to the period during which the storage device is able to supply a portion of the minimum power lacking or the minimum power not being supplied by the power source.

[0094] However, it should be avoided that the storage device is completely discharged on purpose. Therefore, it is advantageous to limit the period of depletion as soon as the charge level of the storage device falls below a certain threshold.

[0095] Advantageously, two different parameters can be considered as the basis for the limit value. In a first variant, a first limit value is advantageously set in relation to the storage capacity of the storage device.

[0096] In a second variant, it may be advantageous to use a second limit value in relation to the respective state of charge of the storage device at the beginning of the shortage period.

[0097] These limit values, in both the first and second variants, are preferably between 5% and 25%. If, in the event of a lack of or insufficient power supply from the power source, the missing minimum power is supplied by the storage device over the period of the shortage, then at the end of the shortage period the state of charge of the storage device should not be below the corresponding limit value, either absolutely (first variant) or relatively (second variant).

[0098] 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 be no less than between 5% and 25% - first variant - or no less than between 2.5% and 12.5% ​​- second variant.

[0099] This naturally leads to the procedure whereby, if the deficiency condition is present, the electrolysis unit is switched off and changed from the operating state to the standby state, while otherwise the missing minimum power is supplied by the storage device.

[0100] The preceding descriptions of the inventive and advantageous methods with the required electrolysis system are fundamentally independent of the number of electrolysis units. However, the information regarding the start condition, the operating condition, and advantageously the stop condition and the failure condition, refers to a first electrolysis unit.

[0101] An electrolysis system advantageously has two or more electrolysis units. It is necessary to define the conditions for each individual electrolysis unit. These conditions can be identical or different, depending, among other things, on whether the electrolysis systems are identical or different in design. The corresponding time periods for each electrolysis unit must also be determined.

[0102] At least when at least two electrolysis units are available, a method is advantageous in which the electrolysis units are switched on and off successively. This allows the available energy to be used more efficiently for hydrogen production if the predicted delivery output fluctuates. DESCRIPTION OF THE EXECUTION FORMS

[0103] The following figure illustrates a possible curve for the power output. For example, it could represent power generated by a wind turbine, which is then supplied to the electrolysis plant's power source.

[0104] Here, the power output (P) 01 - ordinate 03 - is plotted against time (t) - abscissa 02. A lower boundary line outlines the required auxiliary power 05 of the auxiliary systems. Above this is another boundary line representing the minimum power 06 of the electrolysis unit together with the auxiliary systems.

[0105] It is assumed that this is a forecasted delivery performance and that, as an example, a probability of 80% is given.

[0106] In practice, the probability will likely depend on the time horizon, i.e., the probability of the predicted delivery performance being correct usually decreases further and further with increasing time intervals.

[0107] The starting point is the electrolysis plant in its idle state. The initial step involves determining the predicted delivery output by verifying the starting conditions.

[0108] Based on the exemplary course of the predicted delivery performance 01, there is a period over which the predicted delivery performance 01 is with sufficient probability higher than the auxiliary performance 05 and longer than the ramp-up time span 07.

[0109] If, however, it were required that the predicted delivery output 01 be highly likely to be higher than the assistance output 05, and a probability of 80% were given, this condition would not be met. However, it can be expected that the probability of exceeding a limit is significantly higher than the probability of the predicted delivery output occurring as expected.

[0110] In a subsequent period, there is a trend where the predicted delivery output 01 exceeds the minimum output 06. The factor derived from the time period, multiplied by the exemplary predicted delivery output 01 above the minimum output 06 and the exemplary probability of 80%, is greater than 1.5 times the minimum operating time 08.

[0111] As a result, the starting conditions are met (at the beginning of the depicted time period 07) and the auxiliary systems would have to be started up, i.e., the switch from the idle state to the standby state takes place.

[0112] For auxiliary systems in standby mode, continuous checks are performed to ensure that the operating conditions are met. This is evidently the case, as these conditions were already present during the initial testing of the starting conditions for this exemplary scenario.

[0113] Once operating conditions are met (at the beginning of time period 08), the system switches from standby to operating mode. This means the electrolysis unit starts the electrolysis process.

[0114] It can be assumed that the course of the predicted delivery performance will change over time depending on the probability, with the probability increasing the closer the future date approaches. Given the initial conditions, it is assumed that the operating conditions will also be met at a later point in time. Conversely, it is entirely possible that the course of the predicted delivery performance will change adversely and that the operating conditions will not be met as expected.

[0115] The following example illustrates several relevant points in time for further explanation. It is important to consider whether a storage device is present or not, and what the charge level of the reserve unit and the assumed storage device is.

[0116] Initially, in standby mode (following the start-up period 07), there is a short-term drop below the auxiliary power output - time period 11. Without a storage device and if the reserve unit cannot or does not want to be used as a substitute for bridging, an immediate failure of the auxiliary systems (at least partially) would be the consequence (since the necessary power is lacking).

[0117] However, the presence of a storage device is advantageous, allowing for an initial check to determine if the failure conditions are present. Assuming the storage device is at least partially charged, it should readily be able to supply the missing auxiliary power. Furthermore, the time until operating conditions are expected to be reached is short, meaning the auxiliary systems do not need to be shut down; the standby state is maintained.

[0118] Subsequently, the delivery output 01 increases above the minimum output – time period 12. However, upon checking the start-up condition, it is determined that the predicted delivery output does not exceed the minimum output 06 for the minimum operating time – see time period 13. Therefore, the system remains in standby mode. The energy surplus above the auxiliary output is advantageously fed into the storage device.

[0119] After the start of electrolysis, i.e., the minimum operating time 08, there is a brief drop below the minimum power output - time period 14. Likewise, as with time period 11, this lack of energy can be advantageously provided by the storage device.

[0120] Subsequently, the delivery output 01 again falls below the minimum output 06 – time period 15. It is now advantageous to check whether the stop conditions for switching off the electrolysis have been met. The shortfall period extends from the drop below the minimum output 06 until the minimum output 06 is exceeded again. It is assumed that the operating condition is subsequently met again. The crucial question now is whether the storage device is capable of supplying the energy missing from the delivery output over the shortfall period until the minimum output is reached. If this is the case, the operating state remains unchanged and the electrolysis can continue. However, if the storage device is, for example, discharged, it is unavoidable that the electrolysis unit be switched off and put into standby mode.

Claims

1. A method for controlling an electrolysis plant having an idle state and a ready state and an operating state, comprising - auxiliary systems which have a total specific auxiliary power and are switched on in the ready state and in the operating state, and have a specific start-up period for switching from the idle state to the ready state and a specific switch-off period for switching from the ready state to the idle state, and are designed for a start-up period of a maximum of 4 hours and a switch-off period of a maximum of 4 hours; and - at least one electrolysis unit which has a specific minimum power including the auxiliary power and generates hydrogen and oxygen in the operating state and has a defined minimum operating time between 0.25 hours and 4 hours; and - at least one current source which supplies current at changing times and changing time periods with changing supply power; and - at least one storage device; and - at least one backup unit integrated in the storage device, comprising a battery storage; wherein sufficient charging of the battery storage is provided if energy for outputting at least the auxiliary power can be made available over at least the switch-off period; wherein, in case of a sufficient probability, the determined probability is above 80%, and, in case of a high probability, is above 95%; a) wherein, starting from the idle state, a start condition is defined in which - a projected supply power is sufficiently likely to exceed the auxiliary power for at least the start-up period, and - then that time period with a projected supply power above the minimum power multiplied by its probability corresponds to at least 1.5 times the minimum operating time, and - the battery storage can also be sufficiently charged with sufficient probability until the end of the minimum operating time; b) wherein, starting from the ready state, an operating condition is defined in which - the projected supply power is sufficiently likely to exceed the minimum power for the minimum operating time, and - in case of a sufficient probability, the battery storage can be sufficiently charged at the latest by the end of half the minimum operating time, or, in case of a high probability, at the latest by the end of the minimum operating time; c) wherein, based on the current available supply power, a forecast of the expected course of a projected supply power continuously created; d) wherein, in the idle state, the ready state is switched into if the start condition is met, and e) wherein, in the ready state, the operating state is switched into, if the operating condition is met; and f) wherein energy supplied by the current source and not consumed by the auxiliary system or the electrolysis unit is supplied to the battery storage.

2. The method according to claim 1, wherein the start-up period is at least 0.5 hours and at most 2 hours; and / or wherein the minimum operating time is between 0.5 hours and 2 hours.

3. The method according to claim 1 or 2, a') wherein a start condition is defined in which - the projected supply power is highly likely to exceed the auxiliary power for at least the start-up period; and / or - the projected supply power, optionally supplemented by a compensatory power until surpassing the minimum power, is highly likely to exceed the auxiliary power; and / or - reaching the minimum power with the required duration is achieved by the projected supply power at the latest after 4 times the start-up period; and / or - then that time period with a projected supply power above the minimum power multiplied by its probability corresponds to at least 2.5 times the minimum operating time.

4. The method according to any one of claims 1 to 3, b') wherein an operating condition is defined in which - the projected supply power is highly likely to exceed the minimum power for the minimum operating time, and - the time period with a projected supply power above the minimum power multiplied by its probability corresponds to at least 2 times the minimum operating time.

5. The method according to any one of claims 1 to 4, wherein the charged storage device can supply energy at the level of at least half the minimum power over at least half the minimum operating time.

6. The method according to any one of claims 1 to 5, f) wherein, starting from the ready state, a failure condition is defined in which the projected supply power for a failure period is lower than the auxiliary power, - wherein the failure period weighted with the probability is longer than 3 times or 5 times the start-up period; or - wherein the operating condition is not met after the failure period, or - wherein the energy stored in the storage device is not sufficient for operating the auxiliary systems over the failure period; g) wherein, in case of the failure condition, the auxiliary system switches to the idle state, and otherwise a missing auxiliary power is supplied from the storage device.

7. The method according to any one of claims 1 to 6, h) wherein, starting from the operating state, a stop condition is defined in which the projected supply power for a shortage period is lower than the minimum power, - wherein the operating condition is not met after the shortage period, or - wherein the allowable shortage period is defined by the supply capability of the storage device at the level of the minimum power limited to a lower threshold at the end of the shortage period of between 5% to 25% of the storage capacity and / or between 5% to 25% of the state of charge prior to the shortage period; i) wherein, in case of the stop condition, the electrolysis unit switches to the ready state, and otherwise a missing minimum power is supplied from the storage device.

8. The method according to any one of claims 1 to 7, wherein the electrolysis plant comprises at least two or more electrolysis units, wherein the previous conditions relate to a first electrolysis unit and each further electrolysis unit has a start condition and / or operating condition and / or stop condition and / or failure condition associated with the respective electrolysis unit with corresponding associated time periods.

9. The method according to claim 8, wherein the electrolysis units are successively switched on or off as a function of the projected supply power and / or the capacity and the state of charge of the storage device.