A stable solar power generation method based on photovoltaic expansion and battery energy storage

Abstract

A stable power generation method for solar energy based on photovoltaic expansion and battery energy storage, which relates to the technical field of power systems. In order to solve the problem that it is difficult for existing photovoltaic power stations to achieve stable power generation. The objective function for stable power generation of the photovoltaic-battery hybrid system is given, and the objective function is constrained by using constraint conditions to obtain the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage in the objective function. A photovoltaic-battery hybrid system is established according to the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage, so that the output of the photovoltaic power station and the output of the battery energy storage in the photovoltaic-battery hybrid system cooperate with each other to fully meet the load demand by 100%, realizing the stable power generation of the photovoltaic power station. It is used for stable power generation.

Description

Technical Field

[0001] The invention relates to a solar energy stable power generation method and to the technical field of power systems. Background Art

[0002] Against the backdrop of a deteriorating global environment and depleting resources, countries are vigorously developing green and clean energy such as solar energy. However, large-scale photovoltaic penetration will have an adverse impact on the economic dispatch and safe operation of the power grid because it is inherently characterized by random fluctuations. To solve this problem, battery energy storage, regional leveling, and demand response are introduced to reduce the uncertainty of photovoltaics. These technologies / measures ensure that local loads are met in a timely manner, either by modifying the load curve or by adjusting the photovoltaic power generation. If a photovoltaic power station equipped with certain auxiliary facilities can supply 100% of the local load, the photovoltaic power generation is called "stable power generation." At this point, from this perspective, photovoltaic power stations can be considered to have "dispatchability" similar to traditional thermal power units to a certain extent.

[0003] In order to help photovoltaic power stations become a new type of "thermal power unit", battery energy storage needs to be charged when the photovoltaic output is sufficient during the day, and the stored electricity needs to be released at night or when it is cloudy to supply the load. In other words, battery energy storage can adjust the output plan of the photovoltaic power station to match it with the load curve, achieving the effect of peak shaving and valley filling. Similarly, regional leveling (demand response) also changes the power generation (power consumption) curve on the power generation side (load side) accordingly, thereby reducing the imbalance of power on both sides of the source and load. Although each technology is very attractive in reducing photovoltaic output fluctuations and has become a research hotspot in the scientific research community, people also need to pay attention to some shortcomings. Specifically, the investment cost of battery energy storage is very high. When a photovoltaic power station relies solely on battery energy storage to generate stable solar power, the funds required will far exceed the investor's tolerance. Under the current maturity of battery energy storage technology and market economy, this is not a feasible solution. As for regional leveling, its applicability is affected by the size and spatial distribution of the area where the photovoltaic power station is located. Demand response requires changing consumers' living habits, and there is still a long way to go before it can be truly commercialized. In most cases, it is difficult to meet 100% of local load demand by relying solely on regional leveling and demand response.

[0004] Therefore, a technology that can enable photovoltaic power plants to generate electricity stably is now needed to ensure that the photovoltaic power plants can simultaneously supply 100% of the local load while minimizing the equivalent annual value cost. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that it is difficult to achieve stable power generation in existing photovoltaic power stations, and proposes a solar energy stable power generation method based on photovoltaic expansion and battery energy storage.

[0006] A stable solar power generation method based on photovoltaic expansion and battery energy storage, the method comprising:

[0007] Step 1, give the objective function for stable power generation of the photovoltaic and energy storage hybrid system:

[0008]

[0009] In the formula, C is the equal annual value cost of the photovoltaic and energy storage hybrid system, c s is the unit investment cost of the photovoltaic power station, X s is the expansion multiple of the photovoltaic power station, P s is the original installed capacity of the photovoltaic power station, ξ s is the capital recovery factor of the photovoltaic power station, l s is the equal annual value operation and maintenance cost factor value of the photovoltaic power station; c b is the unit investment cost of the battery energy storage, S b is the rated capacity of the battery energy storage, ξ b is the capital recovery factor of the battery energy storage, l b is the equal annual value operation and maintenance cost factor value of the battery energy storage, P ch,t is the charging power of the battery energy storage at time t; τ is the discount rate, T s and T b are the service lives of the photovoltaic power station and the battery energy storage respectively;

[0010] Step 2, use the constraint conditions to constrain the objective function, obtain the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage in the objective function, establish a photovoltaic and energy storage hybrid system according to the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage, and make the output of the photovoltaic power station and the output of the battery energy storage in the photovoltaic and energy storage hybrid system cooperate with each other to 100% meet the load demand, so as to realize the stable power generation of the photovoltaic power station.

[0011] Preferably, the constraint conditions include load balance constraint, battery energy storage operation constraint and photovoltaic power station operation constraint.

[0012] Preferably, the photovoltaic power station operation constraint is:

[0013]

[0014] In the formula, P pv,t is the actual output of the photovoltaic power station at time t; P curt,t is the curtailment power of the photovoltaic power station at time t; is the photovoltaic power directly supplied to the load at time t;

[0015] The load balance constraint is:

[0016]

[0017] Wherein, P load,t is the load during period t; P dis,t is the discharge power of the battery energy storage during period t;

[0018] The operating constraints of the battery energy storage are:

[0019] 0 ≤ P ch,t ≤ B ch,t P ch,max Formula 4,

[0020] 0 ≤ P dis,t ≤ B dis,t P dis,max Formula 5,

[0021] B ch,t + B dis,t ≤ 1 Formula 6,

[0022]

[0023] 0 ≤ E b,t ≤ S b Formula 8,

[0024] E b,1 = 0.8S b Formula 9,

[0025] Wherein, P ch,max and P dis,max are respectively the maximum charging power and the maximum discharge power of the battery energy storage; B ch,t and B dis,t respectively represent the binary state variables of the battery energy storage charging and discharging during period t. When its value is 1, the corresponding state is activated, otherwise it is 0; E b,1 、E b,t and E b,t+1 are respectively the available energies of the battery energy storage at t = 1, t, and t + 1; σ b is the self-discharge rate of the battery energy storage; ε b is the charging / discharging efficiency of the battery energy storage; Δt is the time interval.

[0026] Preferably, step 2 further includes;

[0027] Using the constraint conditions to constrain the objective function, and simultaneously obtaining the premium ratio of the equal annual value cost of the photovoltaic-storage hybrid system.

[0028] Preferably, the premium ratio χ is expressed as:

[0029]

[0030] Wherein, κ f is the levelized cost of electricity of the photovoltaic-storage hybrid system during stable power generation; κv is the levelized cost of electricity of a general photovoltaic power station,

[0031] Preferably, in step 2,

[0032] the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage in the objective function are obtained by a solver.

[0033] The beneficial effects of the present invention are:

[0034] This application formulates a load balance constraint, enabling the photovoltaic power station and the battery energy storage to simultaneously meet the load demand, and the load demand must be fully met by 100%, that is, stable power generation is achieved. On the premise of fully meeting the local load demand by 100%, further constraints are imposed on the operation of the battery energy storage and the operation of the photovoltaic power station, enabling the battery energy storage to charge and discharge reasonably and the photovoltaic power station to rationally discard light, thereby achieving stable solar power generation; and this application aims to minimize the equivalent annual cost, achieving the lowest cost while realizing stable power generation. Therefore, the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage finally obtained in this application can not only achieve stable solar power generation but also minimize the cost.

[0035] A method for stable solar power generation based on photovoltaic expansion and battery energy storage proposed in this application combines the advantages of photovoltaic expansion and battery energy storage in stable solar power generation, greatly reducing the capital requirements of investors, and the method used is very easy to expand to the field of "perfect prediction" of solar energy (perfect prediction means that the actual output of solar energy is exactly the same as the predicted output). In addition, this application ensures that the photovoltaic power station supplies 100% of the local load (stable power generation), completely eliminating the uncertainty of photovoltaic output, and has obvious practical significance.

[0036] This application has far-reaching practical and theoretical significance for the deep decarbonization of the power system, the establishment of a zero-carbon society, and even the realization of the grand goal of carbon peaking and carbon neutrality. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flowchart of a method for stable solar power generation based on photovoltaic expansion and battery energy storage;

[0038] Figure 2 is a curve graph of the premium ratio of the equivalent annual cost of the photovoltaic-battery hybrid system under different photovoltaic expansion multiples. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0040] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0041] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but it is not limited to the present invention.

[0042] Embodiment 1:

[0043] Combined Figure 1 To illustrate this embodiment, a stable solar power generation method based on photovoltaic expansion and battery energy storage, the content includes:

[0044] Obtain the technical parameters and economic parameters of the photovoltaic power station and the battery energy storage, aiming to minimize the equivalent annual cost of the photovoltaic-energy storage hybrid system, and considering the load balance constraint, the battery energy storage operation constraint, and the photovoltaic power station operation constraint, construct a mathematical model for stable power generation of the photovoltaic-energy storage hybrid system; the objective function of the model is:

[0045]

[0046] In the formula, C is the equivalent annual cost of the photovoltaic-energy storage hybrid system, c s is the unit investment cost of the photovoltaic power station, X s is the expansion multiple of the photovoltaic power station, P s is the original installed capacity of the photovoltaic power station, ξ s is the capital recovery factor of the photovoltaic power station, l s is the equivalent annual operation and maintenance cost factor value of the photovoltaic power station; c b is the unit investment cost of the battery energy storage, S b is the rated capacity of the battery energy storage, ξ b is the capital recovery factor of the battery energy storage, l b is the equivalent annual operation and maintenance cost factor value of the battery energy storage, P ch,t is the charging power of the battery energy storage at time t; τ is the discount rate, T s and T b are the service lives of the photovoltaic power station and the battery energy storage respectively;

[0047] Among them, the technical parameters of the photovoltaic power station include the service life T s of the photovoltaic power station, the equivalent annual operation and maintenance cost factor value l s, the unit investment cost c of the photovoltaic power station s and the original installed capacity P of the photovoltaic power station s ; The technical parameters of the battery energy storage include the charge-discharge efficiency ε of the battery energy storage b , the life T of the battery energy storage b , the maximum charging power of the battery energy storage (P ch,max ) and the maximum discharging power (P dis,max ); The equal annual value operation and maintenance cost factor value l of the battery energy storage b and the unit investment cost c of the battery energy storage b ; The economic parameter includes the discount rate τ;

[0048] Solve the model to obtain the optimal expansion multiple of the photovoltaic power station and the optimal rated capacity of the battery energy storage. Establish a photovoltaic-storage hybrid system according to the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage, so that the output of the photovoltaic power station and the output of the battery energy storage in the photovoltaic-storage hybrid system cooperate with each other to meet the load demand by 100%, and realize the stable power generation of the photovoltaic power station.

[0049] In the preferred implementation manner, the constraint conditions include load balance constraint, battery energy storage operation constraint, and photovoltaic power station operation constraint.

[0050] In the preferred implementation manner, the operation constraint of the photovoltaic power station is:

[0051]

[0052] In the formula, P pv,t is the actual output of the photovoltaic power station at time t; P curt,t is the curtailment power of the photovoltaic power station at time t; is the photovoltaic power directly supplied to the load at time t;

[0053] The load balance constraint is:

[0054]

[0055] In the formula, P load,t is the load at time t; P dis,t is the discharging power of the battery energy storage at time t;

[0056] The operation constraint of the battery energy storage is:

[0057] 0 ≤ P ch,t ≤ B ch,t P ch,max Formula 4,

[0058] 0 ≤ P dis,t ≤ B dis,t P dis,max Formula 5,

[0059] Bch,t +B dis,t ≤1 Formula 6,

[0060]

[0061] 0 ≤ E b,t ≤ S b Formula 8,

[0062] E b,1 =0.8S b Formula 9,

[0063] Wherein, B ch,t and B dis,t respectively represent the binary state variables of charging and discharging of the battery energy storage in the t time period. When its value is 1, the corresponding state is activated, otherwise it is 0; E b,1 , E b,t and E b,t+1 are respectively the available energies of the battery energy storage in the t = 1, t, and t + 1 time periods; σ b is the self-discharge rate of the battery energy storage; ε b is the charge / discharge efficiency of the battery energy storage; Δt is the time interval.

[0064] Explanation of this embodiment:

[0065] Formula 2 shows that the photovoltaic output in the t time period is divided into three parts: the curtailed power, the charging power of the battery energy storage, and the photovoltaic power directly supplied to the load.

[0066] Formula 3 indicates that the photovoltaic power station and the battery energy storage can simultaneously meet the load demand, and the load demand must be fully met; Δt is the time interval, which is defaulted to one hour.

[0067] Formulas 4 and 5 prevent the charge / discharge power of the battery energy storage from exceeding its limit; Formula 6 ensures that the battery energy storage cannot charge and discharge simultaneously; Formula 7 gives the power balance constraint of the battery energy storage, that is, the available capacity of the battery energy storage in the t + 1 time period plus the discharge power in the t time period is equal to the available capacity in the t time period plus the discharge power in the t time period. At the same time, the self-discharge rate and charge / discharge efficiency of the battery energy storage are also taken into account; Formula 8 shows that the available capacity of the battery energy storage should be less than its rated capacity; Formula 9 determines the initial available capacity of the battery energy storage. It should be noted that 0.8 is randomly selected, but it is best not to choose too small a value.

[0068] The preferred embodiment further includes;

[0069] Using the constraint conditions to constrain the objective function, and at the same time obtaining the premium ratio of the equivalent annual cost of the hybrid photovoltaic and energy storage system.

[0070] In the preferred embodiment, the premium ratio χ is expressed as:

[0071]

[0072] where κ f is the levelized cost of electricity (LCOE) when the hybrid PV-storage system generates electricity stably; κ v is the LCOE of a conventional PV power plant,

[0073] Preferred embodiment,

[0074] The expansion multiple of the PV power plant and the rated capacity of the battery energy storage in the objective function are obtained using a solver.

[0075] In this preferred embodiment, the Gurobi commercial solver can be called on Spyder to solve the model, and the optimal expansion multiple of the PV power plant and the optimal rated capacity of the battery energy storage can be obtained.

[0076] This embodiment significantly reduces the capital requirements of investors. In addition, this application ensures that the PV power plant supplies 100% of the local load, completely eliminates the uncertainty of PV output, and has obvious practical significance.

[0077] Experimental verification:

[0078] The hybrid PV-storage system of Example 1 is applied to Harbin, Heilongjiang Province, China (45.76°N, 126.64°E). The original installed capacity of the PV power plant is 1 MW, and the purpose of building the power plant is to meet the demand of a local constant load of 0.17 MW. Assume that the tilt angle of the PV panels is 45.76° and the azimuth angle is 180°. The actual output of the PV power plant is simulated using a PV physical model chain. The PV physical model chain consists of a solar positioning model, a separation model, a conversion model, a temperature model, a DC model, an AC model, a loss model, etc. Its inputs include time, location, global radiation, direct radiation, diffuse radiation, and air temperature. Relevant data can be downloaded from the National Solar Radiation Database of the United States. Set the discount rate (τ) to 8%, and the maximum charging power (P ch,max ) and the maximum discharging power (P dis,max ) of the battery energy storage are equal to 1 / 4 times of the rated capacity (S b ) of the battery energy storage. The economic and technical parameters of the PV power plant and the battery energy storage are shown in Table 1.

[0079] Table 1 Economic and technical parameters of the PV power plant and the battery energy storage in this embodiment

[0080]

[0081] The Gurobi commercial solver is called to solve the established model, and the optimal expansion multiple of the PV power station is obtained as 1.80 - that is, it is necessary to expand the rated PV by 0.8 MW, and the optimal rated capacity of the PV-battery energy storage is 1.86 MWh. At this time, the premium ratio of the equivalent annual cost of the PV-ES hybrid system is 3.66. To more clearly demonstrate the advantages of this application in reducing the cost of stable PV power generation, Figure 2 The premium ratios of the equivalent annual costs of the PV-ES hybrid system under different PV expansion multiples are given, where the values of the PV expansion multiples are in the range of [1, 5] with an interval of 0.1. It can be seen from the figure that as the PV expansion multiple increases, the premium ratio first rapidly decreases to the lowest point and then slowly rises, and when the PV expansion multiple is 1.8, the premium ratio is the lowest at 3.66. Obviously, Figure 2 the numerical value of the ordinate of the lowest point in [ ] is equal to the optimal premium ratio result directly solved by this application, indicating the superiority of this application. It should be noted that at each specific PV expansion multiple, it is necessary to call the solver again to solve the premium ratio.

[0082] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not depart from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. A method for stable solar power generation based on photovoltaic expansion and battery energy storage, characterized in that, the method includes: Step 1: Give the objective function for stable power generation of the photovoltaic and energy storage hybrid system: Where C is the equivalent annual value cost of the hybrid PV and energy storage system, and c s is the unit investment cost of the PV power station, X s is the expansion multiple of the PV power station, P s is the original installed capacity of the PV power station, ξ s is the capital recovery factor of the PV power station, l s is the equivalent annual value operation and maintenance cost factor value of the PV power station; c b is the unit investment cost of the battery energy storage, S b is the rated capacity of the battery energy storage, ξ b is the capital recovery factor of the battery energy storage, l b is the equivalent annual value operation and maintenance cost factor value of the battery energy storage, P ch,t is the charging power of the battery energy storage at time t; τ is the discount rate, T s and T b are the service lives of the PV power station and the battery energy storage respectively; Step 2: Use the constraint conditions to constrain the objective function, obtain the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage in the objective function, establish a photovoltaic and energy storage hybrid system according to the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage, and make the output of the photovoltaic power station and the output of the battery energy storage in the photovoltaic and energy storage hybrid system cooperate with each other to fully meet the load demand by 100%, so as to achieve stable power generation of the photovoltaic power station.

2. The method for stable solar power generation based on photovoltaic expansion and battery energy storage according to claim 1, characterized in that, the constraint conditions include load balance constraint, battery energy storage operation constraint and photovoltaic power station operation constraint.

3. The method for stable solar power generation based on photovoltaic expansion and battery energy storage according to claim 2, characterized in that, the operation constraint of the photovoltaic power station is: where, P pv,t is the actual output of the PV power station in period t; P curt,t is the curtailment power of the PV power station in period t; is the PV power directly supplied to the load in period t; the load balance constraint is: where P load,t is the load in period t; P dis,t is the discharge power of the battery energy storage in period t; the operation constraint of the battery energy storage is: 0 ≤ P ch,t ≤ B ch,t P ch,max Formula 4 0 ≤ P dis,t ≤ B dis,t P dis,max Formula 5 B ch,t +B dis,t ≤ 1 Formula 6 0 ≤ E b,t ≤ S b Formula 8 E b,1 = 0.8S b Formula 9 Wherein, P ch,max and P dis,max are respectively the maximum charging power and the maximum discharging power of the battery energy storage; B ch,t and B dis,t respectively represent the binary state variables of the battery energy storage charging and discharging in the t time period. When its value is 1, the corresponding state is activated, otherwise it is 0; E b,1 , E b,t and E b,t+1 are respectively the available energies of the battery energy storage at t = 1, t, and t + 1 time periods; σ b is the self-discharge rate of the battery energy storage; ε b is the charge / discharge efficiency of the battery energy storage; Δt is the time interval.

4. The method for stable solar power generation based on photovoltaic expansion and battery energy storage according to claim 3, characterized in that, Step 2 further includes; Use the constraint conditions to constrain the objective function, and at the same time obtain the premium ratio of the equivalent annual cost of the photovoltaic and energy storage hybrid system.

5. The method for stable solar power generation based on photovoltaic expansion and battery energy storage according to claim 4, characterized in that, the premium ratio χ is expressed as: where κ f is the levelized cost of electricity (LCOE) of the hybrid PV and energy storage system during stable power generation; κ v is the LCOE of a conventional PV power plant, 6. The method for stable solar power generation based on photovoltaic expansion and battery energy storage according to claim 1, characterized in that, in Step 2, use a solver to obtain the expansion multiple of the photovoltaic power station and the rated capacity of the battery energy storage in the objective function.

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