Energy efficiency optimization strategy for renewable energy hydrogen production system

Abstract

The invention relates to the technical field of renewable energy hydrogen production, and discloses an energy efficiency optimization strategy for a renewable energy hydrogen production system, and the energy efficiency optimization strategy comprises the following steps: S1, evaluating the residual life of equipment in real time and optimizing the operation efficiency of the equipment by dynamically introducing the cycle consumption of a battery and the operation time of an electrolytic cell into a mathematical model of the battery and the electrolytic cell. According to the energy efficiency optimization strategy for the renewable energy hydrogen production system, the service life of a battery and an electrolytic cell is effectively prolonged by optimizing the operation of the electrolytic cell, preferentially guaranteeing hydrogen production, improving the overall hydrogen yield and dynamically introducing cycle consumption and operation time models of the battery and the electrolytic cell to evaluate the residual life of equipment in real time; by constructing an optimization model of four targets of reliability, economy, energy abandoning and environmental protection, the operation cost is reduced while the operation efficiency of the system is ensured, and the energy waste is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of renewable energy hydrogen production, and in particular to an energy efficiency optimization strategy for a renewable energy hydrogen production system. Background Art

[0002] In recent years, with the increasing depletion of traditional fossil energy such as oil and coal, the development and efficient use of renewable energy has gradually become a key research direction in the world. In my country, there are still more than 10 million people without electricity, mainly distributed in remote mountainous areas in the west and coastal border islands. These areas usually have rich wind and solar energy resources, which provide favorable conditions for the application of renewable energy systems. In order to meet the energy needs of such areas, isolated microgrids based on wind power generation, photovoltaic power generation and energy storage units have gradually become important solutions. In addition, hydrogen production technology, as a means of energy storage and conversion, can effectively enhance the flexibility and energy utilization efficiency of microgrid systems, further promoting the development of multi-energy complementary technologies.

[0003] Hydrogen production by water electrolysis can adapt to intermittent energy and provide important support for the production of green hydrogen in the industrial field. Ceylan et al. designed a hybrid renewable energy system, which includes photovoltaic (PV) components for energy supply, PEM electrolyzers for hydrogen production, and PEM fuel cells for power generation. Its goal is to provide a self-sufficient energy solution for independent application scenarios. Ismail et al. studied how to reduce the energy loss of PV components in the hydrogen production process by simulating the PV-PEM electrolyzer system in MATLAB and analyzing its transient behavior. For systems that use PV components to power PEM electrolyzers, DC-DC converters are essential to achieve the required DC voltage. The adjustment of its proportional, integral, and differential parameters is based on the dynamic behavior of the PEM electrolyzer and is regulated based on voltage or current.

[0004] However, the existing renewable energy hydrogen production system has significant technical defects under low input power. Due to the insufficient output power of wind turbines, the electrolyzer cannot operate stably at rated power, resulting in reduced system efficiency and a large hydrogen gap. At the same time, the existing power and hydrogen management strategy (PHMS) fails to effectively utilize the battery energy storage capacity, especially in continuous time periods with low wind speeds. The battery auxiliary function is insufficient, further aggravating the imbalance between hydrogen supply and demand. In addition, during long-term operation, the aging problem of batteries and electrolyzers is not dynamically considered, resulting in an overestimation of the system operating cost and inefficient utilization of the equipment life. Therefore, an energy efficiency optimization strategy for renewable energy hydrogen production system is proposed to solve the above problems. Summary of the invention

[0005] 1. Technical issues to be solved

[0006] In view of the deficiencies in the prior art, the present invention provides an energy efficiency optimization strategy for a renewable energy hydrogen production system, which has the advantages of achieving stable and efficient operation of an electrolyzer under low input power, while reducing the total hydrogen gap, energy abandonment rate and operating costs, and improving the environmental friendliness and sustainability of the system. It solves the significant technical defects of existing renewable energy hydrogen production systems under low input power. Due to power fluctuations in renewable energy power generation equipment, electrolyzers are usually unable to operate stably at rated power, resulting in reduced system efficiency and a large hydrogen gap. At the same time, the existing power and hydrogen management strategy (PHMS) fails to effectively utilize the battery energy storage capacity, especially in continuous time periods with low wind speeds, the battery auxiliary function is insufficient, further aggravating the imbalance between hydrogen supply and demand. In addition, during long-term operation, the aging problem of batteries and electrolyzers is not dynamically considered, resulting in an overestimation of the system operating cost and inefficient utilization of the equipment life.

[0007] (II) Technical solution

[0008] To achieve the above object, the present invention provides the following technical solution: an energy efficiency optimization strategy for a renewable energy hydrogen production system, comprising the following steps:

[0009] S1. By dynamically introducing battery cycle consumption and electrolyzer operation time into the mathematical model of batteries and electrolyzers, the remaining life of the equipment is evaluated in real time and the operating efficiency of the equipment is optimized;

[0010] S2. In case of insufficient power generation, the battery-assisted operation strategy is used to prioritize the operation of the electrolyzer at rated power to increase hydrogen production;

[0011] S3, introduce the aforementioned mathematical model into common parameters and modules, and introduce it into the MATLAB program;

[0012] S4. Introduce the possibility of changing the functional form of some input parameters in the mathematical model to make the simulation adjustable;

[0013] S5. Based on the above mathematical model, an optimization model with four objectives including reliability, economy, energy abandonment and environmental protection is constructed, taking into account the operating constraints of different systems and balancing the operating efficiency and economy of the system;

[0014] S6. Based on the comparison between the model simulation data and the real data, the optimal PHMS strategy is obtained.

[0015] Preferably, in the mathematical model in S1, the water transport caused by diffusion described by Fick's law can be expressed as:

[0016]

[0017] Preferably, the dynamic model in S5 includes other additional components such as an electrolyzer, a water pump, a hydrogen and oxygen separator, and a storage tank.

[0018] Preferably, the dynamic model in S5 is used to ensure efficient operation of the electrolytic cell.

[0019] Preferably, the functional form of changing some input parameters in S4 is one of constant value, linear change or exponential change.

[0020] Preferably, the parameters in S4 include temperature, current and pressure.

[0021] Preferably, the electrolytic cell unit voltage is expressed as the sum of the overvoltage caused by all losses and various resistances in the electrolytic cell as shown in the following formula:

[0022] U Ely =U rev +U p +U Aact +U Cact +U Adif +U Cdif +U ohm [V].

[0023] Preferably, the dynamic model in S5 describes the variable reversible voltage through a temperature function, while taking into account the variable exchange current density and transfer coefficient, the diffusion overvoltage of the anode and cathode, and the phenomenon of water passing through the membrane.

[0024] Preferably, the pressure difference between the electrodes causes water to be transferred from the high pressure side to the low pressure side, and its magnitude depends on the permeability of the membrane and can be calculated by Darcy's law as shown below:

[0025]

[0026] Preferably, the total water transport in the membrane is as follows:

[0027]

[0028] (III) Beneficial effects

[0029] Compared with the prior art, the present invention provides an energy efficiency optimization strategy for a renewable energy hydrogen production system, which has the following beneficial effects:

[0030] 1. The energy efficiency optimization strategy for renewable energy hydrogen production system optimizes the operation of the electrolyzer so that it can still operate at rated power under renewable energy input electricity, giving priority to hydrogen production and increasing the overall hydrogen production.

[0031] 2. The energy efficiency optimization strategy for renewable energy hydrogen production system can evaluate the remaining life of the equipment in real time by dynamically introducing the cycle consumption and operation time model of batteries and electrolyzers, effectively extending the service life of batteries and electrolyzers.

[0032] 3. The energy efficiency optimization strategy for renewable energy hydrogen production system, by constructing an optimization model with four goals: reliability, economy, energy abandonment and environmental protection, can reduce operating costs and energy waste while ensuring system operating efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the strategy flow of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] See also Figure 1 , an energy efficiency optimization strategy for a renewable energy hydrogen production system, comprising the following steps:

[0036] S1. By dynamically introducing battery cycle consumption and electrolyzer operation time into the mathematical model of batteries and electrolyzers, the remaining life of the equipment is evaluated in real time and the operating efficiency of the equipment is optimized;

[0037] S2. When photovoltaic and wind power generation is insufficient, the battery-assisted operation strategy is used to prioritize the operation of the electrolyzer at rated power to increase hydrogen production;

[0038] S3, introduce the aforementioned mathematical model into common parameters and modules, and introduce it into the MATLAB program;

[0039] S4. Introduce the possibility of changing the functional form of some input parameters in the mathematical model to make the simulation adjustable;

[0040] S5. Based on the above mathematical model, an optimization model with four objectives including reliability, economy, energy abandonment and environmental protection is constructed, taking into account the operating constraints of different systems and balancing the operating efficiency and economy of the system;

[0041] S6. Based on the comparison between the model simulation data and the real data, the optimal PHMS strategy is obtained.

[0042] Specifically, in the mathematical model in S1, the water transport caused by diffusion described by Fick's law can be expressed as:

[0043]

[0044] Specifically, the dynamic model in S5 includes other additional components such as electrolyzers, water pumps, hydrogen and oxygen separators and storage tanks.

[0045] Specifically, the dynamic model in S5 is used to ensure the efficient operation of the electrolyzer.

[0046] Specifically, in S4, the functional form of changing some input parameters is one of constant value, linear change or exponential change.

[0047] Specifically, the parameters in S4 include temperature, current and pressure.

[0048] Specifically, the cell voltage is the sum of the overvoltage caused by all losses and various resistances in the cell as shown in the following formula:

[0049] U Ely =U rev +U p +U Aact +U Cact +U Adif +U Cdif +U ohm [V].

[0050] Specifically, the dynamic model in S5 describes the variable reversible voltage as a function of temperature, while taking into account the variable exchange current density and transfer coefficient, the diffusion overvoltage of the anode and cathode, and the phenomenon of water passing through the membrane.

[0051] Specifically, the pressure difference between the electrodes causes water to be transferred from the high-pressure side to the low-pressure side, and its magnitude depends on the permeability of the membrane and can be calculated by Darcy's law as shown below:

[0052]

[0053] Specifically, the total water transport in the membrane is shown as follows:

[0054]

[0055] Furthermore, in the dynamic model, it is assumed that the temperature is uniformly distributed throughout the electrolyzer and increases over time. As the hydrogen and oxygen storage tanks are gradually filled, the pressures of the corresponding gases also increase accordingly. Therefore, the pressures of hydrogen and oxygen are variable input parameters that depend on the gas production rate and the tank volume. Among them, the water flow rate is an important factor in calculating the diffusion overvoltage, which depends on the gas production rate and the pump flow rate. The exchange current density and the charge transfer coefficient are temperature-dependent parameters.

[0056] Example 1

[0057] The PHMS strategy is executed based on the following parameters:

[0058] Step 1: When P W = 0, if S o C ht >S o C ht,min , then the hydrogen storage tank fully meets the hydrogen demand; if S o C ht ≤S o C ht,min , the hydrogen in the storage tank cannot meet the demand and the electrolyzer must be shut down.

[0059] Step 2: When 0 <P W <P elz,min There are two situations:

[0060] If a) S o C ht >S o Celz b,min And>m th-2,1elz , the electrolytic cell is completely P W Running, the power provided by the battery is insufficient, this sub-case is combined with all possible sub-cases of the next step, and if b)m th-2,1elz =0, the electrolyzer remains closed.

[0061] Step 3: When P elz,min ≤P W <P elz,max hour

[0062] The electrolyzer fully utilizes PW to produce hydrogen, which is divided into the following five situations and strategies:

[0063] a)m h2,elz <m h2,d And S o C ht >S o C ht,min , then m h2,elz Fully supply hydrogen demand, hydrogen storage tanks make up the gap;

[0064] b)m h2,elz <m h2,d And S o C ht ≤S o C ht,min , then the hydrogen demand cannot be met, m h2,elz is stored in hydrogen tanks;

[0065] c)m h2,elz =m h2,d , then m h2,elzFully supply to meet hydrogen demand;

[0066] d)m h2,elz >m h2,d And S oCht o C ht,max , then the electrolyzer fully meets the hydrogen demand, and the remaining hydrogen is stored in the hydrogen storage tank;

[0067] e)m h2,elz >mh2,d and S o C ht ≥S o C ht,max , the electrolyzer fully meets the hydrogen demand, but the excess hydrogen is discharged into the air.

[0068] Step 4: When P W ≥P elz,max hour

[0069] The electrolyser uses a wind turbine to generate power equal to P elz,max , which can be divided into the following two cases:

[0070] a)S o C b o C b,max , then the power surplus (P W -P elz,max ) for charging batteries;

[0071] b)S o C b ≥S o C b,max , then the excess power should be discarded and the battery disconnected.

[0072] Example 2

[0073] Step 1: When P W ≥P elz,max When the electrolyzer uses renewable energy to generate power, the power value is equal to P elz,max , which can be divided into the following situations:

[0074] a)S o C b o C b,max , then the remaining power (P W -P elz,max ) is used to charge the battery;

[0075] b)S o C b ≥S o C b,max , the remaining power is discarded.​​​

[0076] Step 2: When P elz,min ≤P W <P elz,max hour

[0077] a) If S o C b ≥S o C elzb,min , then the electrolytic cell fully utilizes P W , the battery provides insufficient power to allow the electrolyzer to operate at P elz,max This subcase is combined with all possible subcases of subcase b in terms of hydrogen flow management.

[0078] b) If S o C b o C elzb,min , then the electrolytic cell only uses P W Produces hydrogen and:

[0079] i) If m h2,elz <m h2,d And S o C ht >S o C ht,min , then m h2,elz Fully supply hydrogen demand, with hydrogen tanks covering the shortfall;

[0080] ii) If m h2,elz <m h2,d And S o C ht ≤S o C ht,min , then the hydrogen demand cannot be met, m h2,elz Stored in hydrogen tanks;

[0081] iii) If m h2,elz =m h2,d , then m h2,elz Complete supply of hydrogen demand;

[0082] iv) If m h2,elz >m h2,d And S o C ht o C ht,max , then the electrolyzer fully supports the hydrogen demand, and the excess is stored in the hydrogen tank;

[0083] v) If m h2,elz >m h2,d And S o C ht ≥S o ​​C ht,max , then the electrolyzer fully supports the hydrogen demand, but the excess hydrogen is released into the air.

[0084] Step 3: When 0≤P W <P elz,min hour

[0085] a) If S o C b >S o C elzb,min And m t-1h2,elz >0, the electrolyzer will not shut down and will continue to operate at P with the support of the battery. elz,max Power operation, this subcase is combined with all possible subcases of subcase b.

[0086] b) If m t-1h2,elz =0, the electrolyzer remains closed and:

[0087] i) If S o C b o C b,max And S o C ht >S o C ht,min , then the battery absorbs P W , the hydrogen tank fully supports the hydrogen demand;

[0088] ii) If S o C b o C b,max And S o C ht ≤S o C ht,min , then the battery absorbs P W , but cannot meet the demand for hydrogen;

[0089] iii) If S o C b ≥S o C b,max And S o C ht >S o C ht,min , then the hydrogen tank fully supports the hydrogen demand, and P W should be discarded;

[0090] iv) If S o C b ≥S o C b,max And S o C ht ≤S o C​​ht,min , then P W Should be disposed of and cannot meet hydrogen demand.

[0091] Furthermore, Example 2 is more suitable for small-scale renewable energy hydrogen production clusters.

[0092] Furthermore, the abbreviations of the symbols in the above content are as follows:

[0093] PHMS: Power and Hydrogen Management Strategy;

[0094] P W : Renewable energy power output;

[0095] S o C ht : Status charge level of hydrogen tank;

[0096] S o C ht,min : minimum charge level of the hydrogen tank;

[0097] P elz,min : Minimum input power of the electrolyzer;

[0098] P elz,max : Maximum input power of the electrolyzer;

[0099] S o C elzb,min : minimum charge level of the electrolyser battery;

[0100] m th-2,1elz : The mass flow rate of hydrogen produced by the electrolyzer in the previous hour;

[0101] m h2,elz : mass flow rate of hydrogen produced by electrolyzer;

[0102] m h2,d : Mass flow rate of hydrogen demand;

[0103] S o C ht,max : Maximum charge level of the hydrogen tank;

[0104] S o C b : The state of charge level of the battery;

[0105] S o C b,max : The maximum charge level of the battery;

[0106] S o C elzb,min : The minimum charge level of the battery that supports electrolyzer operation.

[0107] In summary, the energy efficiency optimization strategy for renewable energy hydrogen production system optimizes the operation of the electrolyzer so that it can still work at rated power under fluctuating renewable electricity, prioritizes hydrogen production, and improves the overall hydrogen production. By dynamically introducing the cycle consumption and operating time model of the battery and electrolyzer, the remaining life of the equipment is evaluated in real time, and the service life of the battery and electrolyzer is effectively extended. By constructing an optimization model for four goals: reliability, economy, energy abandonment, and environmental protection, the operating cost is reduced while ensuring the system operation efficiency, and energy waste is reduced. The significant technical defects of the existing renewable energy hydrogen production system under low input power are solved. Due to the power fluctuation of renewable energy power generation equipment, the electrolyzer is usually unable to operate stably at rated power, resulting in a decrease in system efficiency and a large hydrogen gap. At the same time, the existing power and hydrogen management strategy (PHMS) fails to effectively utilize the battery energy storage capacity, especially in continuous time periods with low wind speeds, the battery auxiliary function is insufficient, which further aggravates the imbalance between hydrogen supply and demand. In addition, during long-term operation, the aging problem of batteries and electrolyzers is not dynamically considered, resulting in an overestimation of the system operation cost and inefficient utilization of the equipment life.

[0108] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0109] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An energy efficiency optimization strategy for a renewable energy hydrogen production system, characterized by: The following steps are involved: S1. By dynamically introducing battery cycle consumption and electrolyzer operation time into the mathematical model of batteries and electrolyzers, the remaining life of the equipment is evaluated in real time and the operating efficiency of the equipment is optimized; S2. In case of insufficient power generation, the battery-assisted operation strategy is used to prioritize the operation of the electrolyzer at rated power to increase hydrogen production; S3, introduce the aforementioned mathematical model into common parameters and modules, and introduce it into the MATLAB program; S4. Introduce the possibility of changing the functional form of some input parameters in the mathematical model to make the simulation adjustable; S5. Based on the above mathematical model, an optimization model with four objectives including reliability, economy, energy abandonment and environmental protection is constructed, taking into account the operating constraints of different systems and balancing the operating efficiency and economy of the system; S6. Based on the comparison between the model simulation data and the real data, the optimal PHMS strategy is obtained.

2. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 1, characterized in that: In the mathematical model of S1, water transport caused by diffusion described by Fick's law can be expressed as:

3. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 1, characterized in that: The dynamic model in S5 includes other additional components such as electrolyzer, water pump, hydrogen and oxygen separator and storage tank.

4. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 1, characterized in that: The dynamic model in S5 is used to ensure efficient operation of the electrolyzer.

5. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 1, characterized in that: The functional form of changing some input parameters in S4 is one of constant value, linear change or exponential change.

6. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 1, characterized in that: The parameters in S4 include temperature, current and pressure.

7. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 3, characterized in that: The cell voltage is expressed as the sum of the overvoltage caused by all losses and various resistances in the cell as shown in the following formula: IN Ely =U rev +U p +U Aavt +U Cact +U Adif +U Cdif +U ohm [V].

8. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 1, characterized in that: The dynamic model in S5 describes the variable reversible voltage as a function of temperature, while taking into account the variable exchange current density and transfer coefficient, the diffusion overvoltage of the anode and cathode, and the phenomenon of water passing through the membrane.

9. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 8, characterized in that: The pressure difference between the electrodes causes water to be transported from the high pressure side to the low pressure side, and its magnitude depends on the permeability of the membrane and can be calculated by Darcy's law as shown below:

10. The energy efficiency optimization strategy for a renewable energy hydrogen production system according to claim 8, characterized in that: The total water transport within the membrane is given by the following formula:

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