Economic analysis method of photovoltaic hydrogen production exhausted natural gas hydrogen storage system

Abstract

The invention discloses an economical efficiency analysis method for a photovoltaic hydrogen production exhausted natural gas reservoir hydrogen storage system, and the method comprises the following steps: carrying out the construction of a simplified exhausted natural gas reservoir hydrogen storage library physical model according to the gas storage capacity and burial depth distribution of a real exhausted natural gas reservoir; then the maximum hydrogen storage pressure and the maximum hydrogen storage capacity of the hydrogen storage library are calculated according to the assumed model parameters; carrying out overall modeling on the photovoltaic hydrogen production exhausted natural gas hydrogen storage system; in order to achieve the optimal economical efficiency of the photovoltaic hydrogen production exhausted natural gas reservoir hydrogen storage system, capacity configuration optimization adopting mixed integer linear programming is carried out on the photovoltaic hydrogen production exhausted natural gas reservoir hydrogen storage system, and the installation capacity of each module under the target that the annual value cost of the system is minimum is obtained; according to the installation capacity, obtained through capacity configuration optimization, of each module of the system, technical economics analysis under the perspective of the full life cycle is carried out on the photovoltaic hydrogen production exhausted natural gas reservoir hydrogen storage system, and the analysis method comprises net present value analysis, leveling hydrogen cost analysis, single-factor sensitivity analysis and economic index calculation.

Description

Technical Field

[0001] The invention belongs to the field of economic analysis of photovoltaic hydrogen production, and relates to an economic analysis method of a photovoltaic hydrogen production depleted natural gas hydrogen storage system. Background Art

[0002] Hydrogen storage is an important component of photovoltaic hydrogen production projects. The commonly used hydrogen storage method is to use high-pressure gas hydrogen storage in metal hydrogen storage tanks. However, due to the hydrogen embrittlement phenomenon caused by the molecular characteristics of hydrogen and metals, the hydrogen storage tank materials need to use hydrogen embrittlement-resistant materials and interface coatings. The high cost of hydrogen storage leads to an increase in the cost of photovoltaic hydrogen production systems. Therefore, how to reduce the cost of hydrogen storage for large-scale hydrogen storage is a key issue that needs to be solved urgently for the large-scale photovoltaic hydrogen production. Recently, the feasibility assessment of hydrogen geological storage has attracted the attention of research institutions around the world. Common hydrogen geological storage solutions include geological salt caverns and depleted gas reservoirs. Different storage locations have different characteristics to suit different uses.

[0003] Depleted gas reservoirs are also ideal for storing various gases. As deposits of former geological hydrocarbons, these reservoirs have large-scale porous media and impermeable sealed spaces. In addition, the geological characteristics of these reservoirs have been well described, and the existing infrastructure reduces the initial capital investment. At the same time, the residual gas in the reservoir can act as a buffer gas, reducing the amount of buffer gas required. However, many factors must be carefully considered when designing a geological reservoir for hydrogen. The heterogeneity of the reservoir rock mineralogy and the wettability of the rock have a significant impact on the entire hydrogen storage process, including injection rate, extraction rate and storage durability. In addition, the presence of microorganisms may consume hydrogen and produce other gases, thereby reducing the storage volume and reducing the purity of hydrogen. For example, sulfate-reducing bacteria can use sulfate and hydrogen to produce hydrogen sulfide. Methanogens convert CO2 and hydrogen into methane and water. Its consumption efficiency depends on many factors, including temperature, pressure, reaction type, brine salinity, nutrients, pH and inhibitors, which makes the consumption of hydrogen difficult to quantify. Summary of the invention

[0004] 1. Technical problems to be solved:

[0005] This paper provides an economic analysis method for a photovoltaic hydrogen production and depleted natural gas hydrogen storage system, which can optimize the economically optimal capacity configuration of the photovoltaic hydrogen production system using depleted natural gas reservoirs for hydrogen storage, and on this basis, carry out a technical and economic analysis from a full life cycle perspective.

[0006] 2. Technical solution:

[0007] In order to solve the above problems, the present invention provides an economic analysis method for a photovoltaic hydrogen production depleted natural gas reservoir hydrogen storage system, which is characterized by comprising the following steps:

[0008] Step 1: Based on the gas storage capacity and burial depth distribution of actual depleted natural gas reservoirs, a simplified physical model of the hydrogen storage reservoir of depleted natural gas reservoirs is constructed.

[0009] The natural gas reservoir hydrogen storage is represented as a uniform cylinder, including a top safety pillar, a hydrogen storage neck and a cylindrical chamber of the gas storage. The hydrogen pipeline extends from the top of the natural gas reservoir hydrogen storage to the bottom for gas injection. The hydrogen injected at the bottom passes through a large number of pores inside the natural gas layer and is filled into the entire cylindrical chamber. At the same time, another buffer gas pipeline is provided on the top of the gas storage.

[0010] Step 2: After constructing the physical model of the natural gas reservoir hydrogen storage, calculate the maximum hydrogen storage pressure and maximum hydrogen storage capacity of the hydrogen storage according to the assumed model parameters, and on this basis obtain its unit hydrogen storage cost.

[0011] Step 3: Conduct overall modeling of the photovoltaic hydrogen production and depleted natural gas hydrogen storage system, including energy model and cost model.

[0012] Step 4: The capacity configuration of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system is optimized using mixed integer linear programming. The system DC power balance constraints, AC power balance constraints and hydrogen flow balance constraints are set. Under the goal of minimizing the system annual cost, the installed capacity of each module after capacity configuration optimization is obtained.

[0013] Step 5: Based on the installed capacity of each module of the system obtained by capacity configuration optimization, a technical and economic analysis of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system is carried out from the perspective of the entire life cycle. The analysis methods include: net present value analysis, levelized hydrogen cost analysis, single factor sensitivity analysis and economic indicator calculation.

[0014] Furthermore, in step 1, the data for constructing the physical model of the depleted natural gas reservoir hydrogen storage reservoir also includes average air temperature and maximum gas pressure.

[0015] Furthermore, the simplified depleted natural gas reservoir hydrogen storage model uses the following basic assumptions: the pressure gradient and temperature gradient are 0.433psi / ft and 15F / 1000ft respectively; the cumulative production of natural gas under reservoir conditions is equal to the volume of hydrogen stored under reservoir conditions; the buffer gas is hydrogen, and the calculation does not include the hydrogen consumption caused by the presence of microorganisms.

[0016] Furthermore, the calculation method of the maximum hydrogen storage capacity of the natural gas reservoir is:

[0017] Step S21: For a given average depth of the gas field, the average pressure and temperature of the gas field are estimated using the pressure gradient of 0.433 psi / ft and the temperature gradient of 1.5 F / 100 ft, and the formation volume coefficient Bg is calculated after obtaining the hydrogen compression factor z. The specific calculation is shown in formula (1):

[0018]

[0019] Among them, B g The unit of is ft3 / SCF, the unit of P is psia, the unit of T is R, then, use B g Convert the cumulative gas production under standard conditions to reservoir conditions.

[0020] Step S22: The factor 0.8 is used in formula (2), and the buffer gas ratio (UG) of hydrogen stored in the depleted natural gas reservoir is calculated by formula (2):

[0021]

[0022] In the formula, OGIP is the original gas volume in place (m3), RG is the recoverable gas volume (m3), and after determining the volume percentage of the completed buffer gas, the overall hydrogen storage capacity of the natural gas reservoir is determined;

[0023] The unit hydrogen storage capital cost of hydrogen stored in a depleted natural gas reservoir is calculated by modeling the depleted natural gas storage reservoir to obtain the hydrogen storage mass:

[0024]

[0025] Further, in step S3, the energy is photovoltaic, and the photovoltaic hydrogen production system includes a photovoltaic array, an inverter, an electrolyzer, a hydrogen compressor, a battery and a hydrogen storage device. The entire system is an off-grid system and is set to have a fixed hydrogen demand. DC power is provided by photovoltaic modules, part of which is used to power the electrolyzer, and part of which is transmitted to the hydrogen compressor through the inverter. The extra photovoltaic output that meets the above-mentioned DC demand is stored in the battery; the hydrogen production module is an alkaline electrolyzer, and part of the hydrogen produced by the electrolyzer is directly provided to the hydrogen demand, while the extra hydrogen that meets the hydrogen demand is compressed into a high-pressure gas by the hydrogen compressor and stored in the hydrogen storage device. When the hydrogen produced by the electrolyzer is less than the hydrogen demand, the hydrogen in the hydrogen storage device is output to the hydrogen demand side to meet the fixed hydrogen flow demand.

[0026] Further, in step S4, the DC power balance constraint means that part of the DC power output by the photovoltaic system and the DC power output by the battery are all used to meet the energy supply requirements of the two DC devices in the system, namely the inverter and the alkaline electrolyzer:

[0027] P DCtoEly (t)+PDCtoInv (t) = P DischgSt (t)+P PVtoDC (t) (4)

[0028] P pv (t) = P PVtoDC (t)+P ChgSt (t) (5)

[0029] Where: P DCtoEly (t) is the DC power input to the electrolytic cell at time t, kW; P DCtoInv (t) is the DC power input to the inverter at time t, kW; P PVtoDC (t) is the DC power from photovoltaic to DC bus at time t, kW; P pv (t) is the DC output of photovoltaic at time t, kW.

[0030] Furthermore, in step S4, the AC balance constraint condition is:

[0031] The only AC device is the hydrogen compressor. The inverter converts the DC output of the photovoltaic power into AC power and outputs it to the hydrogen compressor. The power constraints of the inverter and the hydrogen compressor are shown in formula (22):

[0032] P ACtoComp (t) = P InvOut (t) (6)

[0033] Where: P InvOut (t) is the AC output power of the inverter, MW, and its value is related to the AC input power of the compressor at that moment, P ACtoComp (t) are equal.

[0034] Furthermore, in step S4, hydrogen production and demand constraints:

[0035] After determining the demand for hydrogen, the system's minimum daily hydrogen production constraint can be determined as shown in Equation 23) and Equation 24). The hydrogen produced by the electrolyzer is either input to the hydrogen storage module via a hydrogen compressor or output to the overall output of hydrogen. The overall output of hydrogen is the sum of the hydrogen output of the hydrogen storage device and the hydrogen output of part of the electrolyzer, and the overall output should meet the hydrogen

[0036] The daily production demand of gas is shown in equations (25) and (26):

[0037]

[0038] Where: is the designed hourly hydrogen production of the hydrogen production system, kg / h; is the annual hydrogen demand, kg; It is the total hydrogen output of the system at time t, i.e. the sum of the hydrogen output of the electrolyzer and the hydrogen output of the hydrogen storage device, kg; is the total hydrogen output of the electrolyzer at time t, kg; is the hydrogen from the electrolyzer to the hydrogen output end at time t, kg; The hydrogen from the electrolyzer to the hydrogen storage device, kg; is the hydrogen stored at the hydrogen output end at time t, kg.

[0039] Furthermore, the meaning of the installed capacity constraint is that the output power of any module in the system cannot be greater than its maximum installed capacity at any time, which is applicable to the installed capacity constraints of photovoltaics, electrolyzers, inverters, hydrogen compressors and batteries:

[0040]

[0041] Where: P modules (t) is the output power of any module in the system at time t, MW; P modulesInstall is the installed capacity of the module, MW.

[0042] In addition, the hydrogen storage device must also meet capacity constraints to limit the gas pressure of the hydrogen storage device at each moment:

[0043]

[0044] Where: is the installed capacity of the hydrogen storage device, kg.

[0045] Furthermore, in step 5, the levelized hydrogen production cost is the total life cycle cost of the photovoltaic power generation hydrogen production project divided by the total life cycle hydrogen production. The total cost includes the initial investment cost and operation and maintenance cost, and also takes into account the time value of money and the impact of the residual value of fixed assets. It is used to compare and analyze the comprehensive competitiveness of different hydrogen production technologies and the hydrogen production competitiveness of different photovoltaic power plants. Under the same economic environment, the lower the levelized hydrogen cost, the better the hydrogen production economy of the project.

[0046] 3. Beneficial effects:

[0047] By using photovoltaics as the main energy input, the present invention promotes the application of renewable energy in the field of hydrogen production, helps reduce dependence on fossil fuels, reduces greenhouse gas emissions, and promotes the green transformation of the energy structure. In addition, the use of depleted natural gas reservoirs as hydrogen storage media further enhances the sustainability of the system and provides an environmentally friendly and economical solution for large-scale hydrogen energy storage.

[0048] The present invention optimizes the capacity configuration of the photovoltaic hydrogen production and depleted natural gas hydrogen storage system through a mixed integer linear programming method, ensuring that the system can meet the hydrogen production needs while achieving reasonable resource allocation and cost minimization. This optimization not only reduces energy waste during system operation, but also effectively reduces the overall construction and operation and maintenance costs, and improves the economy of the system.

[0049] The photovoltaic hydrogen production system of the present invention is designed as an off-grid solution with high flexibility and adaptability, and can adapt to different geographical environments and energy needs. The system can dynamically adjust the working status of the photovoltaic array, electrolyzer and hydrogen compressor according to the actual lighting conditions and hydrogen demand, ensuring the stability and reliability of hydrogen supply. At the same time, through sensitivity analysis and economic index calculation, the system can respond to market changes and policy adjustments in a timely manner, and has a strong ability to resist risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The present invention is a flow chart of an economic analysis method for a photovoltaic hydrogen production and depleted natural gas hydrogen storage system taking into account capacity optimization.

[0051] Figure 2 This is a structural diagram of the natural gas hydrogen storage reservoir of the present invention.

[0052] Figure 3 This is a structural diagram of the photovoltaic hydrogen production and depleted natural gas hydrogen storage system of the present invention.

[0053] Figure 4 This is a framework diagram of the MILP model of the photovoltaic hydrogen production and depleted natural gas hydrogen storage system of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with the accompanying drawings.

[0055] The present invention discloses an economic analysis method for a photovoltaic hydrogen production and depleted natural gas hydrogen storage system considering capacity optimization, comprising the following steps:

[0056] Step 1: Based on the gas storage capacity and burial depth distribution of actual depleted natural gas reservoirs, a simplified physical model of the hydrogen storage reservoir of depleted natural gas reservoirs is constructed.

[0057] The present invention adopts a simple depleted natural gas reservoir model, the specific physical structure is as follows Figure 3As shown, the natural gas reservoir hydrogen storage tank is simply represented as a uniform cylinder, and its main structure includes a top safety support, a hydrogen storage tank neck and a cylindrical chamber of the gas storage tank. The hydrogen pipeline extends from the top of the natural gas reservoir hydrogen storage tank to the bottom for gas injection. The hydrogen injected at the bottom is filled into the entire cylindrical chamber through a large number of pores inside the natural gas layer. At the same time, there is another buffer gas pipeline on the top of the gas storage tank, which is used to inject or export buffer gas into the hydrogen storage tank to ensure the gas pressure balance of the entire system and the stability of the geological structure, so as to avoid hydrogen leakage or geological structure collapse caused by too much or too little working gas hydrogen in the hydrogen storage tank.

[0058] Step 2: After the physical model of the natural gas reservoir hydrogen storage is constructed, the maximum hydrogen storage pressure and maximum hydrogen storage capacity of the hydrogen storage reservoir are calculated according to the assumed model parameters, and on this basis, the unit hydrogen storage cost is obtained;

[0059] In estimating the hydrogen storage capacity of depleted gas fields, the following assumptions are made:

[0060] (1) The pressure gradient and temperature gradient are 0.433 psi / ft and 15 F / 1000 ft respectively;

[0061] (2) The cumulative production of natural gas under reservoir conditions is equal to the volume of hydrogen stored under reservoir conditions;

[0062] (3) The buffer gas is hydrogen, and the volume percentage of the buffer gas to the total storage volume is determined by formula (2).

[0063] (4) Due to the large variety of microorganisms and different reservoir conditions, it is difficult to quantify their consumption, so the hydrogen consumption caused by the presence of microorganisms is not included in the calculation.

[0064] For a given average depth of a gas field, the average pressure and temperature of the gas field can be estimated using the pressure gradient (0.433psi / ft) and temperature gradient (1.5F / 100ft). With the average pressure and temperature of the gas field, the formation volume coefficient Bg can be calculated after obtaining the hydrogen compression factor z. The specific calculation is shown in formula (1):

[0065]

[0066] Among them, B g The unit of is ft3 / SCF, the unit of P is psia, and the unit of T is R. Then, use B g The cumulative natural gas production under standard conditions is converted to reservoir conditions. Based on assumption (2) in this section, the amount of hydrogen that can be stored underground can be obtained. The underground hydrogen storage capacity can be converted to the storage capacity under standard conditions by formula (1). The gas compressibility factor z of hydrogen is from the NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP).

[0067] The values ​​of the buffer gas percentage in the literature vary. According to AAmid's research on hydrogen storage and reuse in natural gas fields on a cross-seasonal scale, the value was found to be 0.55 to 0.45. However, another limiting factor must be considered, that part of the buffer gas in the system is not the gas that is circulating. The working gas type (i.e., hydrogen) must account for at least 20% of the buffer gas, that is, for hydrogen storage, at least 20% of the buffer gas must be hydrogen. This constraint is explained by the 0.8 factor in equation (2). When the recoverable gas volume of the gas field exceeds 62.5% of the OGIP, the present invention assumes that the hydrogen storage working gas accounts for 50% of the original gas storage volume. However, if the original in-place gas volume that can be recovered from the reservoir is less than 62.5%, the recoverable part is multiplied by 0.8 as the working gas volume, and the rest is used as buffer gas, that is, the second term of the minimum statement in equation (2). Therefore, the buffer gas percentage (UG) of hydrogen storage in depleted natural gas reservoirs used in the present invention is calculated by equation (2):

[0068]

[0069] Where, OGIP is the original gas volume in place (m3), RG is the recoverable gas volume (m3)

[0070] After determining the volume percentage of the completed buffer gas (H2), the total volume of the buffer gas and the working gas, that is, the total hydrogen storage capacity of the natural gas reservoir, can be determined.

[0071] When natural gas is not mined, the natural gas reservoir has good air tightness. When natural gas is mined and exhausted, a large number of pores are formed inside the natural gas reservoir. The depleted natural gas reservoir also has a relatively stable internal structure and is a good container for gas storage. The cost structure of the depleted natural gas reservoir is shown in Table 1:

[0072] Table 1 Cost composition of depleted natural gas reservoirs

[0073]

[0074] The total capital cost (TCC) of the depleted natural gas reservoir is calculated from the above table. The unit hydrogen storage capital cost of the depleted natural gas reservoir is calculated by modeling the depleted natural gas reservoir to obtain the hydrogen storage mass:

[0075]

[0076] Step 3: Conduct overall modeling of the photovoltaic hydrogen production and depleted natural gas hydrogen storage system, including energy model and cost model;

[0077] The key components of the photovoltaic hydrogen production system include photovoltaic arrays, inverters, electrolyzers, hydrogen compressors, batteries and hydrogen storage devices. The entire system is an off-grid system that is set to have a fixed hydrogen demand. DC power is provided by photovoltaic modules, part of which is used to power the electrolyzer, and part of which is transmitted to the hydrogen compressor through the inverter, while the extra photovoltaic output that meets the above DC demand is stored in the battery; the hydrogen production module of the system is an alkaline electrolyzer, part of the hydrogen produced by the electrolyzer is directly provided to the hydrogen demand, and the extra hydrogen that meets the hydrogen demand is compressed into a high-pressure gas by the hydrogen compressor and stored in the hydrogen storage device. When the hydrogen produced by the electrolyzer is insufficient to meet the hydrogen demand, the hydrogen in the hydrogen storage device is output to the hydrogen demand side to meet the fixed hydrogen flow demand.

[0078] The energy model and cost model of each module are as follows:

[0079] Photovoltaic

[0080] The photovoltaic power generation module is the energy supply end of the photovoltaic hydrogen production system. In this off-grid scenario, the power supply of the entire system is provided by the photovoltaic power generation module. Considering the characteristics of photovoltaic power generation, the photovoltaic power generation used in the present invention is simulated using formula (4). The calculation model uses the derating factor and temperature correction coefficient to correct the power generation. pv Taking into account the loss and aging of the line, the default f pv is 0.9.

[0081]

[0082] Where: Y pv is the rated power of the PV array under standard test conditions, MW; f pv is the derating factor; G TI is the solar radiation intensity currently received by the photovoltaic array, kW / m 2 ; G T,STC The incident light intensity under standard test conditions is defined as 1 kilowatt per square meter, kW / m 2 ; T c is the current temperature of the photovoltaic cell, ℃; T c,STC is the surface temperature of the photovoltaic array under standard test conditions, ℃; usually defined as 25℃; α p The reference value of the temperature correction coefficient is 0.4%.

[0083] The cost structure of photovoltaic arrays mainly includes the capital cost per unit installed capacity and the operation and maintenance cost of photovoltaic components. In order to facilitate the unified calculation of the cost model, the equal annual value method is used to convert the capital cost of the components into annual value for calculation. The equal annual value of photovoltaic cost is calculated by multiplying its capital cost by the capital recovery coefficient CCF. PVTherefore, the total annual cost of the photovoltaic module is equal to the annual value of the capital cost plus the annual operation and maintenance cost. The model is shown in equations (5) and (6):

[0084] C PV =C PVCAPEX ×P PV ×CCF PV +C PVOPEX (17)

[0085]

[0086] Where: C PVCAPEX is the unit capital cost of the photovoltaic array; P PV is the photovoltaic installed capacity; C PVOPEX is the photovoltaic operation and maintenance cost; r is the social discount rate, assuming the social discount rate is 0.05; n is the project operation life.

[0087] Inverter

[0088] The DC inverter converts DC power into AC power to meet the power supply needs of the compressor and other on-site equipment. In this off-grid photovoltaic power generation model, the DC output of the photovoltaic power plant is used to power the electrolyzer, and the other part is converted into AC power by the inverter to power the hydrogen compressor. The power model of the inverter is shown in formula (7):

[0089] P Inv (t) = P DCtoInv (t)×η inv (19)

[0090] Where P DCtoInv (t) is the DC output from PV to inverter, kW; η inv is the energy efficiency of the inverter.

[0091] The cost structure of the inverter includes capital cost and operation and maintenance cost:

[0092] C Inv =C InvCAPEX ×P Inv ×CCF+C InvOPEX (20)

[0093] Where: C Inv is the unit capital cost of the inverter, RMB 10,000 / MW; P Inv is the inverter installed capacity, MW; C InvOPEX The operation and maintenance cost of the inverter is RMB 10,000.

[0094] Battery

[0095] The battery component in the system is to provide a stable DC input to the electrolyzer in response to the period when the photovoltaic array is not supplying power. Since the solar illumination conditions fluctuate with the seasons throughout the year, and the photovoltaic array has the characteristic of not generating electricity at night, when the excess photovoltaic power generation makes it difficult to store the hydrogen produced by the electrolyzer of the hydrogen production module, the electricity will be stored in the battery; and when the light conditions are insufficient, such as at night, in order to meet the output demand of hydrogen, the electrolyzer needs to continue to produce hydrogen to meet the hydrogen demand when the hydrogen in the hydrogen storage device is difficult to supply. At this time, the battery can provide power supply for the electrolyzer. Therefore, when the hydrogen storage capacity is large, the battery quota will be reduced accordingly. The battery storage state balance model is shown in formula (9):

[0096] S ocSt (t) = S ocSt (t-1)+η Chg P ChgSt (t)-P DischgSt (t) / η DisChg (twenty one)

[0097] Where: S ocSt (t) is the storage state of the battery at time t; η Chg is the battery charging efficiency, which is 0.96; P ChgSt (t) is the input power of the battery at time t; P DischgSt (t) is the output power of the battery at time t; η DisChg is the battery discharge efficiency, which is 0.96.

[0098] The cost structure model of the battery is shown in formula (10):

[0099] C Storage =C StCAPEX ×P St,power ×C CFSt +C EnCAPEX ×P St,energy ×CCF+C StOPEX (twenty two)

[0100] Where: C StCAPEX is the unit installation cost of the battery, RMB / MW; P St,power is the installed capacity of the battery, in MW; C EnCAPEX is the unit energy storage cost of the battery, RMB / MWh; P St,energy is the energy storage capacity of the battery, MWh; C StOPEX is the annual operation and maintenance cost of the battery, in ten thousand yuan.

[0101] Electrolyzer

[0102] The electrolyzer is a hydrogen production device. The electrolyzers currently used for large-scale hydrogen production mainly include ALK alkaline water electrolyzers and PEM proton exchange membrane electrolyzers. The production cost of PEM electrolyzers is relatively high compared to ALK electrolyzers. Currently, large-scale water electrolysis projects mostly use alkaline water electrolysis as a hydrogen production solution. Therefore, alkaline water electrolyzers are used to reduce the overall capital cost of the system. The hydrogen production model of the electrolyzer is shown in formula (11):

[0103]

[0104] Where: is the hydrogen production of the electrolyzer at time t, kg; P DCtoEly (t) is the DC input to the electrolytic cell at time t, kW; η Ely is the unit energy consumption of the electrolyzer, kWh / kg.

[0105] The cost structure of the electrolyzer includes the electrolyzer capital cost, operation and maintenance cost, and water consumption cost:

[0106] C Ely =C FixEly +C Water (twenty four)

[0107] C FixEly =P Ely ×C ElyCAPEX ×CCF+C ElyOPEX (25)

[0108]

[0109] Where: C FixEly is the fixed cost of the electrolytic cell; C Water is the water consumption cost of the electrolytic cell; P Ely is the installed capacity of the electrolyzer; C ElyCAPEX is the unit installation cost of the electrolyzer; CCF is the capital recovery factor; C ElyOPEX The operation and maintenance cost of the electrolyzer; is the total annual hydrogen production of the electrolyzer; m water is the unit water consumption of hydrogen production in electrolyzer; p water The unit water price.

[0110] compressor

[0111] The hydrogen compressor is used to compress the hydrogen produced by the electrolyzer to the pressure conditions that the hydrogen storage device needs to meet. According to the hydrogen storage scheme adopted, the hydrogen needs to be compressed to 1.2-70 MPa. The energy consumption of the compressor required for the same gas to be compressed to different pressures is also different. According to the principles of gas thermodynamics and compressor energy consumption, the energy consumption of the compressor used is calculated as shown in formula (15):

[0112]

[0113] Where: η m is the mechanical efficiency of the compressor; e is the compressor energy efficiency; c pH2 is the constant pressure specific heat capacity of hydrogen before compression; β is the compression ratio of the gas; T1 and T2 are the temperatures of hydrogen before and after compression, respectively, ΔT 12 is the difference between T2 and T1; γ is the inherent adiabatic index of the gas, which is 1.41 for hydrogen.

[0114] The cost structure of hydrogen compressor includes compressor capital cost and compressor operation and maintenance cost:

[0115] C Comp =P Comp ×C CompCAPEX ×CCF+C CompOPEX (28)

[0116] Where: C Comp is the compressor cost; P Comp is the installed capacity of the hydrogen compressor; C CompCAPEX is the unit installed capacity of the compressor; C CompOPEX The operation and maintenance cost of the compressor.

[0117] Depleted natural gas reservoirs

[0118] The hydrogen storage module in this hydrogen production model is set to have a fixed hydrogen storage efficiency and hydrogen release efficiency, that is, the hydrogen injection rate into the hydrogen storage device is a fixed value, and the hydrogen flow output by the hydrogen storage device is a fixed value. The gas balance model of the hydrogen storage device is shown in formula (17):

[0119]

[0120] Where: is the amount of hydrogen stored in the hydrogen storage device at time t; and are the hydrogen flow rates entering and leaving the hydrogen storage device at time t respectively.

[0121] Unit capital cost of hydrogen storage module for depleted natural gas It needs to be calculated by formula (20). The overall capital cost of hydrogen storage in depleted natural gas reservoirs is calculated as shown in formula (18):

[0122]

[0123] Where: The hydrogen storage capacity of depleted natural gas, kg; The unit hydrogen storage cost of the depleted natural gas hydrogen storage module is 10,000 yuan / kg·H2; The operation and maintenance cost of hydrogen storage for depleted natural gas is 10,000 yuan.

[0124] Step 4: In order to optimize the economic efficiency of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system, the capacity configuration optimization is carried out using mixed integer linear programming, and the system DC power balance constraints, AC power balance constraints and hydrogen flow balance constraints are set. Under the goal of minimizing the annual cost of the system, the installation capacity after the capacity configuration optimization of each module is obtained;

[0125] Mixed-integer linear programming (MILP) is a mathematical programming method that combines integer variables and continuous variables for optimization. Its main components include: objective function, constraints, model parameters, integer variables and continuous variables. The MILP model framework of photovoltaic hydrogen production system is as follows: Figure 4 As shown. It can be seen from the figure that the objective function of the MILP optimization model is to minimize the overall annual cost of the system; the constraints include equality constraints and inequality constraints, which are used to constrain the model solution boundary to meet the convergence requirements; and the optimization of decision variables is the core purpose of the optimization model, where the integer variables include the number of hydrogen storage tanks and the system operating status. The system operating status variable is used for hydrogen production calculations. This variable represents: 1 when the system is running and 0 when the system is stopped. Continuous variables include the installed capacity of photovoltaics, inverters, electrolyzers, and hydrogen compressors. The present invention uses the Gurobi professional solver to solve the model, and finally determines the optimal capacity configuration of photovoltaic power generation and water electrolysis to produce hydrogen, so as to minimize the cost of the entire system.

[0126] The capital cost of each component of the system is summarized in the form of equal annual value using the equal annual value method, and the objective function is set to minimize the sum of the annual values ​​of the system cost:

[0127]

[0128] After determining the objective function to be minimized, the mixed integer programming model needs to set constraints to facilitate model optimization. The main constraints in the photovoltaic hydrogen production model include:

[0129] (1) DC power balance:

[0130] The constraint means that part of the DC power output by photovoltaic power and the DC power output by battery are all used to meet the energy supply needs of the two DC devices in the system, namely the inverter and the alkaline electrolyzer.

[0131] P DCtoEly (t)+P DCtoInv (t) = P DischgSt (t)+P PVtoDC (t) (32)

[0132] P pv (t) = P PVtoDC (t)+P ChgSt (t) (33)

[0133] Where: P DCtoEly (t) is the DC power input to the electrolytic cell at time t, kW; P DCtoInv (t) is the DC power input to the inverter at time t, kW; P PVtoDC (t) is the DC power from photovoltaic to DC bus at time t, kW; P pv (t) is the DC output of photovoltaic at time t, kW.

[0134] (2) AC power balance:

[0135] The only AC device in the system is the hydrogen compressor. Since the photovoltaic output in the system is DC power, an inverter is required to convert the DC output of the photovoltaic power into AC power and output it to the hydrogen compressor. The power constraints of the inverter and the hydrogen compressor are shown in formula (22):

[0136] P ACtoComp (t) = P InvOut (t) (34)

[0137] Where: P InvOut (t) is the AC output power of the inverter, MW, and its value is related to the AC input power of the compressor at that moment, P ACtoComp (t) are equal.

[0138] (3) Hydrogen production and demand constraints:

[0139] The minimum hydrogen production constraint is used to formulate the minimum hydrogen production of the system. This value is related to the hydrogen demand. After determining the hydrogen demand, the daily minimum hydrogen production constraint of the system can be determined, as shown in formula (23); the meaning of formula (24) is that the hydrogen produced by the electrolyzer is either input to the hydrogen storage module through the hydrogen compressor or output to the overall output of hydrogen. The overall output of hydrogen is the sum of the hydrogen output of the hydrogen storage device and the hydrogen output of part of the electrolyzer, and the overall output should meet the daily production demand of hydrogen, as shown in formulas (25) and (26):

[0140]

[0141] Where: is the designed hourly hydrogen production of the hydrogen production system, kg / h; is the annual hydrogen demand, kg; It is the total hydrogen output of the system at time t, i.e. the sum of the hydrogen output of the electrolyzer and the hydrogen output of the hydrogen storage device, kg; is the total hydrogen output of the electrolyzer at time t, kg; is the hydrogen from the electrolyzer to the hydrogen output end at time t, kg; The hydrogen from the electrolyzer to the hydrogen storage device, kg; is the hydrogen stored at the hydrogen output end at time t, kg.

[0142] (4) Installed capacity constraints

[0143] The constraint means that the output power of any module in the system cannot be greater than its maximum installed capacity at any time. This formula is applicable to the installed capacity constraints of photovoltaics, electrolyzers, inverters, hydrogen compressors and batteries.

[0144]

[0145] Where: P modules (t) is the output power of any module in the system at time t, MW; P modulesInstall is the installed capacity of the module, MW.

[0146] In addition, the hydrogen storage device must also meet capacity constraints to limit the gas pressure of the hydrogen storage device at each moment:

[0147]

[0148] Where: is the installed capacity of the hydrogen storage device, kg.

[0149] After optimizing the capacity configuration of the photovoltaic hydrogen production and depleted natural gas hydrogen storage system, further technical and economic analysis is required.

[0150] Step 5: Based on the installed capacity of each module of the system obtained by capacity configuration optimization, a technical and economic analysis of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system is carried out from the perspective of the entire life cycle. The analysis methods include: net present value analysis, levelized hydrogen cost analysis, single factor sensitivity analysis and economic indicator calculation.

[0151] (1) Levelized cost of hydrogen

[0152] The levelized hydrogen production cost is the total life cycle cost of the photovoltaic power generation hydrogen production project divided by the total life cycle hydrogen production. The total cost includes the initial investment cost and operation and maintenance cost, and also takes into account the time value of money and the impact of the residual value of fixed assets. It is used to compare and analyze the comprehensive competitiveness of different hydrogen production technologies, and can also compare the hydrogen production competitiveness of different photovoltaic power plants. Under the same economic environment, the lower the levelized hydrogen cost, the better the hydrogen production economy of the project. The calculation of LCOH is shown in formula (29):

[0153]

[0154] Where: CAPEX is the initial investment; V R A is the residual value of fixed assets; n is the operating cost in the nth year; E n is the energy consumption cost in the nth year; C R is the replacement cost of the electrolytic cell; Y n is the hydrogen production in the nth year; T is the project life cycle, and r is the discount rate.

[0155] (2) Net present value

[0156] Net Present Value (NPV) is an important indicator for evaluating the economic feasibility of a project. The net present value is the difference between the cash inflow and outflow of an investment project. The final net present value of the project can be obtained by discounting the cash flow in the last year of the operation life of the photovoltaic hydrogen production project to the year of initial investment and then subtracting the initial investment of the project. This indicator measures the difference between the total present value of the project's future cash flow and the initial investment. Only when the net present value is greater than zero, it means that the investment is feasible. When the net present value of the photovoltaic hydrogen production project is positive, it means that the cash inflow of the project exceeds the initial investment cost, which also shows that the project is economically feasible; conversely, if the net present value is negative, it means that the cash inflow of the project is not enough to cover the investment cost, and the photovoltaic hydrogen production project may not be economically feasible. The net present value calculation formula for hydrogen revenue is shown in formula (30):

[0157]

[0158] Where: NPV is the net present value; B n is the cash inflow in the nth year; C n is the cash outflow in the nth year; r is the discount rate.

[0159] (3) Internal rate of return

[0160] Internal Rate of Return (IRR) is an important economic evaluation indicator for evaluating project profitability. It is defined as the discount rate when the net present value is equal to zero. The calculation formula of internal rate of return is shown in formula (31):

[0161]

[0162] Among them, IRR is the internal rate of return. If the internal rate of return is greater than the benchmark rate of return, it means that this plan is feasible, and the higher the internal rate of return, the better the plan.

[0163] (4) Net present value

[0164] The payback period (PBP) refers to the number of years it takes to recover the investment through the return of funds. It can usually be divided into static payback period and dynamic payback period. The static payback period refers to the time required to recover the entire investment with the net income of the project without considering the time value of money. The dynamic payback period takes the time value of money into consideration, and calculates the payback period after converting the net cash flow of each year into present value according to the benchmark rate of return. The dynamic payback period is the year when the cumulative present value of the net cash flow is equal to zero. Its calculation formula is shown in formula (32):

[0165]

[0166] Where T is the dynamic investment payback period; t' is the year when the cumulative net present value is greater than zero for the first time.

Claims

1. An economic analysis method for a photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system, characterized by: The steps include: Step 1: Based on the gas storage capacity and burial depth distribution of actual depleted natural gas reservoirs, a simplified physical model of hydrogen storage in depleted natural gas reservoirs is constructed; The natural gas reservoir hydrogen storage is represented as a uniform cylinder, including a top safety pillar, a hydrogen storage neck and a cylindrical chamber of the gas storage. A hydrogen pipeline extends from the top of the natural gas reservoir hydrogen storage to the bottom for gas injection. The hydrogen injected at the bottom is filled into the entire cylindrical chamber through a large number of pores inside the natural gas layer. At the same time, another buffer gas pipeline is provided on the top of the gas storage; Step 2: After the physical model of the natural gas reservoir hydrogen storage is constructed, the maximum hydrogen storage pressure and maximum hydrogen storage capacity of the hydrogen storage reservoir are calculated according to the assumed model parameters, and on this basis, the unit hydrogen storage cost is obtained; Step 3: Conduct overall modeling of the photovoltaic hydrogen production and depleted natural gas hydrogen storage system, including energy model and cost model; Step 4: Optimize the capacity configuration of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system using mixed integer linear programming, set the system DC power balance constraints, AC power balance constraints and hydrogen flow balance constraints, and obtain the installation capacity after the capacity configuration optimization of each module under the goal of minimizing the system annual value cost; Step 5: Based on the installed capacity of each module of the system obtained by capacity configuration optimization, a technical and economic analysis of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system is carried out from the perspective of the entire life cycle. The analysis methods include: net present value analysis, levelized hydrogen cost analysis, single factor sensitivity analysis and economic indicator calculation.

2. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system according to claim 1 is characterized by: In step 1, the data for constructing the physical model of the depleted natural gas reservoir hydrogen storage facility also includes average temperature and maximum gas pressure.

3. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system according to claim 1 is characterized by: In step 2, the simplified depleted natural gas reservoir hydrogen storage model adopts the following basic assumptions: the pressure gradient and temperature gradient are 0.433psi / ft and 15F / 1000ft respectively; the cumulative production of natural gas under reservoir conditions is equal to the volume of hydrogen stored under reservoir conditions; the buffer gas is hydrogen, and the calculation does not include the hydrogen consumption caused by the presence of microorganisms.

4. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system according to claim 3, characterized in that: The calculation method for the maximum hydrogen storage capacity of natural gas reservoirs is: Step S21: For a given average depth of the gas field, the average pressure and temperature of the gas field are estimated using the pressure gradient of 0.433 psi / ft and the temperature gradient of 1.5 F / 100 ft, and the formation volume coefficient Bg is calculated after obtaining the hydrogen compression factor z. The specific calculation is shown in formula (1): Among them, B g The unit of is ft3 / SCF, the unit of P is psia, the unit of T is R, then, use B g Converting the cumulative gas production under standard conditions to reservoir conditions; Step S22: The factor 0.8 is used in formula (2), and the buffer gas ratio (UG) of hydrogen stored in the depleted natural gas reservoir is calculated by formula (2): In the formula, OGIP is the original gas volume in place (m3), RG is the recoverable gas volume (m3), and after determining the volume percentage of the completed buffer gas, the overall hydrogen storage capacity of the natural gas reservoir is determined; The unit hydrogen storage capital cost of hydrogen stored in a depleted natural gas reservoir is calculated by modeling the depleted natural gas storage reservoir to obtain the hydrogen storage mass:

5. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system according to claim 1 is characterized by: In step S3, the energy is photovoltaic, and the photovoltaic hydrogen production system includes a photovoltaic array, an inverter, an electrolyzer, a hydrogen compressor, a battery and a hydrogen storage device. The entire system is an off-grid system and is set to have a fixed hydrogen demand. DC power is provided by photovoltaic modules, part of which is used to power the electrolyzer, and part of which is transmitted to the hydrogen compressor through the inverter. The extra photovoltaic output that meets the above-mentioned DC demand is stored in the battery; the hydrogen production module is an alkaline electrolyzer, and part of the hydrogen produced by the electrolyzer is directly provided to the hydrogen demand, while the extra hydrogen that meets the hydrogen demand is compressed into a high-pressure gas by the hydrogen compressor and stored in the hydrogen storage device. When the hydrogen produced by the electrolyzer is less than the hydrogen demand, the hydrogen in the hydrogen storage device is output to the hydrogen demand side to meet the fixed hydrogen flow demand.

6. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system according to claim 1, characterized in that: In step S4, DC power balance: The constraint means that part of the DC power output by the photovoltaic system and the DC power output by the battery are all used to meet the energy supply requirements of the two DC devices in the system, namely the inverter and the alkaline electrolyzer: P DCtoEly (t)+P DCtoInv (t)=P DischgSt (t)+P PVtoDC (t) (4) P pv (t)=P PVtoDC (t)+P ChgSt (t) (5) Where: P DCtoEly (t) is the DC power input to the electrolytic cell at time t, kW; P DCtoInv (t) is the DC power input to the inverter at time t, kW; P PVtoDC (t) is the DC power from photovoltaic to DC bus at time t, kW; P pv (t) is the DC output of photovoltaic at time t, kW.

7. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system according to claim 1, characterized in that: In step S4, the AC balance constraint is: The only AC device is the hydrogen compressor. The inverter converts the DC output of the photovoltaic power into AC power and outputs it to the hydrogen compressor. The power constraints of the inverter and the hydrogen compressor are shown in formula (22): P ACtoComp (t)=P InvOut (t) (6) Where: P InvOut (t) is the AC output power of the inverter, MW, and its value is related to the AC input power of the compressor at that moment. P ACtoComp (t) are equal.

8. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system according to claim 1, characterized in that: In step S4, hydrogen production and demand constraints: After determining the demand for hydrogen, the daily minimum hydrogen production constraint of the system can be determined as shown in Equation 23) and Equation 24). The hydrogen produced by the electrolyzer is either input to the hydrogen storage module through the hydrogen compressor or output to the overall output of hydrogen. The overall output of hydrogen is the sum of the hydrogen output of the hydrogen storage device and the hydrogen output of part of the electrolyzer, and the overall output should meet the daily production demand of hydrogen, as shown in Equation (25) and (26): Where: is the designed hourly hydrogen production of the hydrogen production system, kg / h; is the annual hydrogen demand, kg; It is the total hydrogen output of the system at time t, i.e. the sum of the hydrogen output of the electrolyzer and the hydrogen output of the hydrogen storage device, kg; is the total hydrogen output of the electrolyzer at time t, kg; is the hydrogen from the electrolyzer to the hydrogen output end at time t, kg; The hydrogen from the electrolyzer to the hydrogen storage device, kg; is the hydrogen stored at the hydrogen output end at time t, kg.

9. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system as described in claim 1 is characterized by: The meaning of installed capacity constraint is that the output power of any module in the system cannot be greater than its maximum installed capacity at any time. It is applicable to the installed capacity constraints of photovoltaic, electrolyzer, inverter, hydrogen compressor and battery: Where: P modules (t) is the output power of any module in the system at time t, MW; P modulesInstall is the installed capacity of the module, MW; In addition, the hydrogen storage device must also meet capacity constraints to limit the gas pressure of the hydrogen storage device at each moment: Where: is the installed capacity of the hydrogen storage device, kg.

10. The economic analysis method of the photovoltaic hydrogen production and depleted natural gas reservoir hydrogen storage system according to claim 1, characterized in that: In step 5, the levelized hydrogen production cost is the total life cycle cost of the photovoltaic power generation hydrogen production project divided by the total life cycle hydrogen production. The total cost includes the initial investment cost and operation and maintenance cost, and also takes into account the time value of money and the impact of the residual value of fixed assets. It is used to compare and analyze the comprehensive competitiveness of different hydrogen production technologies and the hydrogen production competitiveness of different photovoltaic power plants. Under the same economic environment, the lower the levelized hydrogen cost, the better the hydrogen production economy of the project.

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