Power generation performance evaluation method for offshore floating type photovoltaic power generation system

Abstract

The invention provides a power generation performance evaluation method for an offshore floating photovoltaic power generation system, and the method comprises the steps: considering the influence of offshore wind wave fluctuation, researching the inclination angle change characteristics of a photovoltaic module installed on a floating body structure under different sea conditions, and building a single-sided and double-sided photovoltaic module dynamic and static irradiance model considering the influence of sea wave motion; the invention provides a method for generating a scene with uniform and non-uniform irradiance distribution of an offshore floating type photovoltaic array. The irradiance distribution model and the electrical model of the offshore floating photovoltaic array are combined to form a method for simulating the maximum output power Pmax change characteristic of the offshore floating photovoltaic array under the influence of sea wave operation; and evaluating the annual energy output in the target sea area by combining the wind wave data and irradiance distribution in the target sea area and the maximum output power Pmax change characteristics of the floating photovoltaic array. Compared with an existing photovoltaic power generation performance evaluation method, the influence of sea wave fluctuation on the power generation characteristics of the photovoltaic array is considered, and the method is suitable for an offshore floating type photovoltaic power generation scene.

Description

(I) Technical field:

[0001] The invention relates to the technical field of photovoltaic power generation, and in particular to a method for evaluating power generation performance of an offshore floating photovoltaic power generation system. (II) Background technology:

[0002] With the continuous increase in the total installed capacity of new energy, the development and utilization of new energy has encountered obvious constraints such as land resources, and offshore photovoltaics have gradually attracted the attention of the industry. At present, offshore photovoltaics are mainly fixed-bracket near-shore photovoltaics. This structural form is only suitable for shallow water and intertidal areas. As the water depth increases, its cost will increase sharply. The more common development method is offshore floating photovoltaics. Compared with land photovoltaics, offshore floating has sufficient light resources, humid air and more precipitation, which is conducive to the heat dissipation and cleaning of photovoltaic modules. After adopting highly weather-resistant double-sided glass photovoltaic modules, the power generation of offshore floating photovoltaics is theoretically far ahead of inland photovoltaic power stations. However, the power generation of offshore floating photovoltaic power generation systems is not only affected by light resources and the power generation efficiency of photovoltaic modules, but also related to factors such as the wind and wave environment in the sea area.

[0003] Affected by sea breezes, ocean currents, and irregular waves, offshore floating photovoltaic modules move with six degrees of freedom along the floating structure, including translational and rotational movements along all axes. This means that even if the environmental irradiance does not change, the irradiance received by the front and back sides of the offshore floating double-sided glass photovoltaic modules will fluctuate randomly due to the movement of the waves. Therefore, the radiation energy received by the offshore floating double-sided glass photovoltaic modules is not only affected by the weather environment (such as cloud movement) and the inclination angle of the module installation, but is also closely related to the fluctuation of the waves. In practice, the generation of waves at the same time and place, as well as wave properties such as wave height, wavelength, and wave speed, are all random and cannot be accurately predicted. For offshore floating photovoltaic arrays, the distribution and changes of the irradiance they receive are more complex and changeable. It is not only related to the installation angle of the modules and changes in the weather environment, but also closely related to the layout of the photovoltaic strings and the relative orientation of the waves. At present, the research on offshore floating photovoltaic power generation systems is mainly focused on the resource endowment assessment of the target sea area, the economic analysis of combining with other offshore renewable energy sources, and the qualitative research on the power generation output of bifacial glass photovoltaic modules. There is a lack of research on the impact of the operating environment of the engineering sea area on the irradiance of floating bifacial glass photovoltaic modules. In addition, there is still a lack of simulation tools or models specifically for the power generation assessment of offshore floating photovoltaic power generation systems, and key issues related to performance feasibility assessment during project planning are still unclear.

[0004] At present, most researchers are still using performance simulation tools suitable for traditional land-based photovoltaic power stations, which do not take into account the impact of wave action on photovoltaic modules and the irradiance of photovoltaic arrays. A study took the floating photovoltaic power station installed in the inland sea lake as an example to compare and analyze the feasibility of existing simulation evaluation tools. The study monitored the field measurement data of the floating photovoltaic power station and used a variety of mainstream evaluation and analysis methods such as Photovoltaic System Simulation Tool (PVSYST), System Advisory Model (SAM) of the National Renewable Energy Laboratory of the United States, and Helioscope to simulate and evaluate the power generation of the power station. The comparison between the measured data and the simulation evaluation results showed that the energy deviation between the measured value and the simulated value ranged from 18.43% to 38.55%, which shows that the existing simulation tools or models are not suitable for the performance evaluation and planning of offshore floating photovoltaic power station projects. Therefore, in order to promote the large-scale development and utilization of offshore floating photovoltaics and ensure the safe operation and economic production of offshore floating photovoltaic power stations, it is urgent to study a power generation performance evaluation method suitable for offshore floating photovoltaic power generation systems during the development and design of offshore floating photovoltaic power generation systems. On the basis of investigating the light resource endowment of the target sea area, the influence of environmental factors such as waves and wind speed on the irradiance change of floating photovoltaic modules is studied, so as to efficiently and accurately evaluate the photovoltaic power generation performance of the target sea area. (III) Summary of the invention:

[0005] The purpose of the present invention is to provide a method for evaluating the power generation performance of an offshore floating photovoltaic power generation system, which can address the deficiencies of the prior art and is a simple and easy-to-implement evaluation method. This method can ensure that even when the operating sea conditions and the layout of photovoltaic modules change, the photovoltaic power generation performance of the target sea area can still be effectively evaluated.

[0006] The technical solution of the present invention is a method for evaluating the power generation performance of an offshore floating photovoltaic power generation system, characterized in that it comprises the following steps:

[0007] (1) Establish the irradiance model of single-sided and bifacial photovoltaic modules under static sea conditions;

[0008] The installation inclination angle of the single-sided and double-sided photovoltaic modules in step (1) is fixed.

[0009] The step (1) establishes a single-sided and double-sided photovoltaic module irradiance model under static sea conditions, specifically referring to:

[0010] (1-1) Static equivalent irradiance G of bifacial photovoltaic modules E The static irradiance G of the front and back F , GR And the bifaciality of the modules Determine, as shown in formula (1):

[0011]

[0012] (1-2) The total solar radiation received by the front and back of a bifacial photovoltaic module includes three parts: direct radiation, scattered radiation, and reflected radiation. The irradiance G received by the front of a bifacial photovoltaic module with a fixed inclination angle is F As shown in formula (2):

[0013]

[0014] In formula (2), subscript F refers to the front side, G b,F , G d,F , G r,F They are the direct irradiance, scattered irradiance and reflected irradiance on the inclined surface of the front photovoltaic module, in W / m2; B h , D h , G h are horizontal direct irradiance, horizontal scattered irradiance, and horizontal reflected irradiance; θ β,F is the angle between the sunlight and the normal of the front inclined plate, β F is the dihedral angle between the front photovoltaic module and the ground horizontal plane, which is positive towards the south and negative towards the north, and should satisfy the relationship of formula (3):

[0015]

[0016] In formula (3), is the geographic latitude, ω is the hour angle, δ is the declination angle; γ F is the direction angle of the plate, starting from the north and going clockwise is positive;

[0017] (1-3) Horizontal direct irradiance B h Specifically:

[0018] B h =ξ0I SC P m (4)

[0019] In formula (4), I SC The solar constant represents the solar radiation received per unit area per unit time at the upper boundary of the Earth’s atmosphere perpendicular to the sunlight. It is generally taken as 1367W / m 2 ; P is the atmospheric transparency coefficient; m is the atmospheric optical quality, which represents the ratio of the actual distance that sunlight actually passes through the atmosphere to the average total thickness of the Earth's atmosphere, as shown in formula (5):

[0020]

[0021] ξ0 is the Earth orbit eccentricity correction coefficient, as shown in formula (6):

[0022]

[0023] In formula (6), d n is the number of days;

[0024] (1-4) Horizontal diffuse irradiance D h Generally, an empirical calculation formula based on actual measurement is used, as shown in formula (7):

[0025]

[0026] (1-5) After the sun radiates to the ground, the horizontal reflected irradiance G h Horizontal direct irradiance B h and horizontal diffuse irradiance D h The sum of the reflection coefficient ρ, therefore, the reflected radiation energy G h Specifically, as shown in formula (8):

[0027] G h =ρ(B h +D h ) (8)

[0028] (1-6) The irradiance on the back of a bifacial photovoltaic module with a fixed tilt angle is specifically shown in formula (9):

[0029]

[0030] In formula (9), the subscript R refers to the back side, and the back side component irradiance G R Calculation method and frontal irradiance G F The same, the direction angle of the back plate γ R , the dihedral angle β between the back photovoltaic module and the ground level R , the angle θ between the sunlight and the normal of the back tilted plate β,R The opposite of positive, that is:

[0031] γ R =180°-γ F (10)

[0032] β R =180°-β F (11)

[0033]

[0034] (1-7) Direct irradiance G on the inclined surface of the rear moduleb,R The acquisition of G mainly occurs during sunrise or sunset, and the incident angle of direct sunlight is large and the solar altitude angle is small, so b,R It is much smaller than the direct front irradiance, generally less than 5% of the direct front irradiance, so it can be ignored, as shown in formula (13):

[0035]

[0036] From steps (1-2) and (1-7), we can obtain the front and back irradiance G of the single-sided and double-sided photovoltaic modules under static sea conditions respectively. F , G R , we can use (1-1) to get the equivalent irradiance G of single-sided and double-sided photovoltaic modules under static sea conditions E .

[0037] (2) Considering the influence of wind and wave fluctuations at sea, the tilt angle variation characteristics of photovoltaic modules installed on floating structures under different sea conditions are studied, and a dynamic irradiance model of single-sided and bifacial photovoltaic modules considering the influence of wave motion is established;

[0038] The step (2) refers to using the Stokes wave theory applicable to deep ocean waters (where the waves are steeper) to study the impact of offshore wind and wave fluctuations on the dynamic irradiance of single-sided and double-sided photovoltaic modules, specifically including the following contents:

[0039] (2-1) Dynamic equivalent irradiance G of single-sided and double-sided photovoltaic modules E (t) Dynamic irradiance G on the front and back F (t), G R (t) and the bifaciality of the modules Determine, as shown in formula (14):

[0040]

[0041] And G F (t), G R (t) is the dynamic dihedral angle β between the front and back sides of the double-sided glass photovoltaic module and the ground level under the action of waves. F (t), β R (t) and the angle θ between the sunlight and the normal of the front and back inclined plates β,F (t),θ β,R (t) is determined as shown in equations (15) and (16);

[0042]

[0043]

[0044] (2-2) Taking the second-order Stokes wave as an example to design the wave type, the wave surface equation of the second-order Stokes wave is shown in formula (17):

[0045]

[0046] In formula (17), L is the wavelength; d is the water depth; H is the wave height; k is the wave number; w is the wave circular frequency;

[0047] First, the dynamic dihedral angle β between the front and back sides of the bifacial glass photovoltaic module and the ground horizontal plane under the action of the second-order Stokes wave is calculated using equations (18)-(20): F (t), β R (t), the position partial derivative of the wavefront equation of the second-order Stokes wave is taken and the inverse tangent function is taken to obtain the time domain expression function of the Stokes second-order wave inclination angle Δβ(t), which is specifically:

[0048]

[0049] β F (t) = β0 + Δβ(t) (19)

[0050] β R (t) = π - β F (t) (20)

[0051] Then, using β F (t), β R (t) Calculate the angle θ between the sunlight and the normal of the front and back inclined plates β,F (t),θ β,R (t), as shown in equations (21) and (22):

[0052]

[0053]

[0054] In the formula, is the geographic latitude, ω is the hour angle, δ is the declination angle, γ F is the direction angle of the flat panel, which is positive in the clockwise direction starting from the north. Finally, the results of equations (21), (22) and (18)-(20) are substituted into (14)-(16) to calculate the dynamic equivalent irradiance G of the bifacial photovoltaic module. E (t).

[0055] Working principle of step (2): The irradiance received by the positive and negative inclined surfaces of the double-sided glass photovoltaic module and the angles β and θ to the sun βAffected by the fluctuations of wind and waves at sea, the floating structure of the offshore floating photovoltaic power station is constantly moving, which causes the angles of the double-sided glass photovoltaic modules installed on the floating structure to the sun β(t) and θ β (t) fluctuates continuously. Considering that when the size of the floating body is small relative to the wavelength of the wave, the movement of the floating body on the wave surface can be regarded as the movement of the seawater particles on the wave surface, such as Figure 3 As shown. Compared with the wavelength of the sea waves (30-50m), the current offshore photovoltaic structure design is mostly a flexible structure formed by the flexible connection of small-scale floating bodies, and the movement state is basically the same as the wave. Therefore, this article does not target a specific floating structure, and assumes that the floating structure is a fully flexible floating body, that is, the inclination change caused by the movement of the double-sided glass photovoltaic module with the wave is equal to the wave inclination angle, and based on this condition, the angle β(t) and θ of the double-sided glass photovoltaic module to the sun under the action of waves are calculated. β (t).

[0056] Waves are divided into linear waves and nonlinear waves. Linear wave theory, also known as micro-wave theory, is used to describe simple waves in two-dimensional motion. Linear wave theory is only applicable to engineering problems under sea waves whose wave height is smaller than the wavelength. The wave surface shape of nonlinear waves is an asymmetric curve with steep crests and narrow troughs. There are many theories for the study of nonlinear waves, and the commonly used theories are cosine ellipse theory, solitary wave theory and Stokes wave theory. Generally speaking, cosine ellipse theory and solitary wave theory are applicable to shallow water areas of inland lakes, and Stokes wave theory is applicable to deep water areas of the ocean (with steeper waves). Considering that the second-order Stokes wave has high accuracy in simulating waves in limited deep water areas, it is widely used in engineering.

[0057] (3) Analyze the time-varying differences in irradiance of photovoltaic modules installed at different spatial locations in the offshore floating photovoltaic array, and combine the irradiance variation characteristics G of the bifacial photovoltaic modules under the action of waves obtained in step (2) E (t), generate irradiance distribution scenarios for offshore floating photovoltaic arrays;

[0058] The step (3) is based on the installation method of the offshore floating photovoltaic array, the size of the floating structure unit W i The proportional relationship between the irradiance distribution of the offshore floating photovoltaic array and the wave wavelength L is used to divide the irradiance distribution scenario of the offshore floating photovoltaic array into uniform irradiance scenario and non-uniform irradiance scenario. Different photovoltaic array irradiance distribution generation methods are used for different scenarios. The specific contents are as follows:

[0059] (3-1) In actual engineering applications, the topological structure of the photovoltaic array usually adopts a series-parallel (SP) structure, that is, s photovoltaic modules are connected in series to form a photovoltaic string, and then p photovoltaic strings are connected in parallel to form a photovoltaic array, and then connected to the inverter; when the offshore floating photovoltaic array is installed on the same floating structure unit, the irradiance of each photovoltaic module in the floating photovoltaic array is affected by the wave fluctuations in the same way. At this time, the offshore floating photovoltaic array works in a uniform irradiance scenario, that is, the offshore floating photovoltaic array irradiance is consistent with the photovoltaic module irradiance G generated in step (2). E (t) consistent;

[0060] (3-2) When the offshore floating photovoltaic array is installed on i (i≥2) floating structure units, the irradiance of the photovoltaic modules located on the same floating unit in the floating photovoltaic array is affected by the wave fluctuations in a consistent manner, and the irradiance of the photovoltaic modules located on different floating structure units is affected by the wave fluctuations with a phase difference. At this time, the offshore floating photovoltaic array operates in a non-uniform irradiance scenario;

[0061] The offshore floating photovoltaic array installed on i floating structure units in step (3-2) is an s×p group (with s×p photovoltaic arrays installed on i, the irradiance of the photovoltaic components on the wave-facing side of the photovoltaic array changes first, and as time goes by, the waves continue to advance into the photovoltaic array, and the irradiance of the photovoltaic components on the side away from the wave direction changes the most. When the waves come, the irradiance of the photovoltaic components at different spatial positions has the same trend over time, but the phases are different. Therefore, the method for generating the uneven irradiance distribution scene of the offshore floating photovoltaic array is as follows:

[0062] First, based on the size W of the floating structure unit facing the wave in the floating photovoltaic array i The proportional relationship between the wavelength L of the sea waves is used to calculate the time-varying phase difference Δθ of the irradiance of the photovoltaic modules installed in different floating structure units in the offshore floating photovoltaic array. i :

[0063]

[0064] Secondly, using Δθ i Calculate the time-varying initial phase θ of the irradiance of the photovoltaic modules installed on the i floating units i , as shown in formula (24):

[0065] θ1=0, θ2=θ1+Δθ1, θ3=θ2+Δθ2,.....θ i =θ i-1 +Δθ i-1 (twenty four)

[0066] Finally, θ i Substitute into the irradiance variation characteristic model G of the bifacial photovoltaic module under the action of waves in step (2) E (t), generating uneven irradiance scenario G for offshore floating photovoltaic arrays E (t+θ1)-G E (t+θ i ).

[0067] (4) Establish an electrical model for offshore floating photovoltaic arrays and combine it with the irradiance distribution model G E (t+θ1)-G E (t+θ i ), and the ambient temperature information T em (t), simulate the PV curve of the offshore floating photovoltaic array under the influence of wave operation at each moment, and find the maximum power output point of the offshore floating photovoltaic array at each moment based on the PV curve of the photovoltaic array;

[0068] The step (4) specifically refers to:

[0069] (4-1) The electrical model is established to describe the electrical characteristics and power output of the photovoltaic module. A five-parameter single diode circuit model is used to simulate the electrical performance of the bifacial photovoltaic module, taking into account both simplification and accuracy. The relevant mathematical model of the photovoltaic cell based on the Shockley diode equation is shown in formula (25):

[0070]

[0071] In formula (25), I ph is the photocurrent of the photovoltaic module, I d is the diode current, I sh is the current through the parallel resistance of the photovoltaic module, I sat is the reverse saturation current of the photovoltaic module diode, V is the output voltage of the photovoltaic module, I is the output current of the photovoltaic module, R sh is the parallel resistance of the photovoltaic module, R s is the series resistance of the photovoltaic module, q is the electron charge (1.602E-19C), A is the diode ideality factor, K is the Boltzmann constant (1.381E-23J / K), and T is the battery temperature;

[0072] (4-2) For a photovoltaic array composed of multiple photovoltaic modules connected in series and parallel, its electrical mathematical model is specifically shown in formula (26):

[0073]

[0074] In formula (26), V t =AKT / q is the diode thermal voltage, Ns N is the number of components in a single series-parallel group. p is the number of array groups connected in series and parallel;

[0075] (4-3) The electrical mathematical model of photovoltaic cells under standard test conditions is obtained from formula (27):

[0076]

[0077] (4-4) Under standard test conditions (STC), the key parameters of the electrical model are as follows:

[0078] Diode thermal voltage V under STC t,STC As shown in formula (28):

[0079]

[0080] In formula (28), μ sc is the short-circuit current temperature coefficient, μ oc is the open circuit voltage temperature coefficient, E g is the bandgap width (1.7936e-19J);

[0081] Photocurrent I under STC ph,STC As shown in formula (29):

[0082] I ph,STC ≈I sc,STC (29)

[0083] Diode reverse saturation current I under STC sat,STC As shown in formula (30):

[0084]

[0085] (4-5) Based on the key parameters of the electrical model under STC, the temperature of the photovoltaic module T em (t) and the equivalent irradiance G of the components in the photovoltaic array E (t+θ i ) can calculate the key characteristic parameters of the electrical model under non-STC conditions, as shown in formulas (31)-(33):

[0086]

[0087]

[0088]

[0089] (4-5) The key characteristic parameter I in the electrical model under non-STC ph ,I sat 、Vt Substituting into equations (25) and (26), the PV curve of the offshore floating photovoltaic array under the influence of wave operation at each moment can be simulated and generated. For the scenario of uniformly distributed irradiance, there is only one maximum power point in the PV curve of the offshore floating photovoltaic array at each moment, while for the scenario of non-uniform irradiance, there are multiple local maximum power points. By traversing the PV curve, the maximum power output value P of the offshore floating photovoltaic array at each moment can be obtained. max .

[0090] (5) Combining the wind and wave data in the target sea area, the irradiance distribution of the floating photovoltaic array obtained in step (3), and the maximum power output value P of the offshore floating photovoltaic array at each moment in step (4) max , evaluate the annual power generation in the target sea area.

[0091] The step (5) specifically refers to:

[0092] (5-1) Theoretical power generation of offshore floating photovoltaic arrays under uniform irradiance scenario;

[0093] From step (3), it can be seen that when the offshore floating photovoltaic array is installed on the same floating structure unit, the irradiance of each photovoltaic module in the floating photovoltaic array is affected by the wave fluctuations in the same way. At this time, the offshore floating photovoltaic array works in a uniform irradiance scene, that is, the irradiance of the offshore floating photovoltaic array is equal to the irradiance of the photovoltaic module generated in step (2). E (t) is consistent; therefore, in engineering, the components are usually concentrated on the same floating unit, and the component layout direction is perpendicular to the direction of normal waves and strong waves in the sea area, so as to eliminate the irradiance difference of photovoltaic components connected to the same inverter to a certain extent, reduce the local power maximum point of the PV curve, and the offshore floating photovoltaic array works approximately in a uniform irradiance scene. At this time, the theoretical power generation of the offshore floating photovoltaic array is mainly determined by the irradiance change G of the photovoltaic components under the action of waves. E (t) determine:

[0094]

[0095] Where CI is the rated installed capacity of the photovoltaic array, in kilowatts (kW); G E (t) is the instantaneous value of the equivalent irradiance on the inclined surface of the photovoltaic array, in kilowatt-hours per square meter (kWh / m 2 ); G0 is the irradiance under standard conditions, G0 = 1, and the unit is kilowatt-hour per square meter (kWh / m 2 ).

[0096] (5-2) Theoretical power generation of offshore floating photovoltaic arrays under uneven irradiance scenarios;

[0097] It can be seen from step (3) that when the offshore floating photovoltaic array is installed on i (i≥2) floating structure units, the irradiance of the photovoltaic modules located on the same floating unit in the floating photovoltaic array is affected by the wave fluctuations in a consistent manner, and the irradiance of the photovoltaic modules located on different floating structure units is affected by the wave fluctuations with a phase difference. At this time, the offshore floating photovoltaic array operates in a non-uniform irradiance scenario; and with the movement of the waves, the irradiance and change trend of the modules in the photovoltaic string unit are inconsistent, resulting in rapid random changes in the PV multi-peak curve of the photovoltaic string unit. Combined with the wind and wave data in the target sea area, the irradiance distribution of the floating photovoltaic array obtained in step (3) and the maximum power output value P of the offshore floating photovoltaic array at each moment in step (4), max , we can get the theoretical power generation of offshore floating photovoltaic array under non-uniform irradiance scenario, that is:

[0098]

[0099] In the formula, E out is the theoretical annual power generation of the photovoltaic power generation system, in kilowatt-hours (kWh); P max (t) is the instantaneous value of the inverter AC side output power, in kilowatts (kW).

[0100] Advantages of the present invention:

[0101] (1) The method for evaluating offshore floating photovoltaic power generation proposed in the present invention can make up for the defects of traditional simulation methods, simulate the rapid random changes of the multi-peak curve of the photovoltaic array of the offshore floating photovoltaic power generation system in a complex and changeable marine environment, study the influence of environmental factors such as waves and wind speed on the irradiance change of the floating photovoltaic module, evaluate the photovoltaic power generation performance of the target sea area, and is conducive to the promotion and commercial operation of offshore floating photovoltaic power generation.

[0102] (2) Compared with the prior art method of simulating the irradiance of single-sided and double-sided photovoltaic modules at a fixed inclination angle, the present invention proposes to design the wave type using multi-order Stokes waves as an example, and realizes the simulation of the irradiance change curve of single-sided and double-sided photovoltaic modules under different sea conditions by analyzing the influence of different levels of waves on the inclination angle of photovoltaic modules.

[0103] (3) Compared with the method of simulating the uneven irradiance distribution of photovoltaic arrays in the prior art, the present invention takes into account that the uneven irradiance of offshore floating photovoltaic arrays is not only related to parameters such as wave direction, wave height, wavelength, and period, but also related to the layout of the photovoltaic array, thereby realizing a method for generating uniform and uneven irradiance distribution scenes suitable for offshore floating photovoltaic systems.

[0104] (4) Relying on the above-mentioned non-uniform irradiance generation scenario of the offshore floating photovoltaic array and the irradiance change curve of the photovoltaic module, the temporal and spatial variation characteristics of the irradiance of the offshore floating photovoltaic power generation system are simulated. Combined with the electrical model of the photovoltaic array, the present invention proposes a method for simulating the PV output characteristics of the offshore floating photovoltaic array. (IV) Description of the drawings:

[0105] Figure 1 The present invention is a schematic flow chart of a method for evaluating power generation performance of an offshore floating photovoltaic power generation system.

[0106] Figure 2 The present invention is a schematic diagram of a double-sided photovoltaic module irradiance model for a method for evaluating power generation performance of an offshore floating photovoltaic power generation system.

[0107] Figure 3 The present invention is a schematic diagram of the effect of sea wave action on the swing of photovoltaic modules around the Y-axis in a method for evaluating power generation performance of an offshore floating photovoltaic power generation system.

[0108] Figure 4 The present invention is a schematic diagram of wave parameters and waveforms in a method for evaluating power generation performance of an offshore floating photovoltaic power generation system.

[0109] Figure 5 The present invention is a schematic diagram of a non-uniform irradiance scenario of an offshore floating photovoltaic array in a power generation performance evaluation method of an offshore floating photovoltaic power generation system.

[0110] Figure 6 The invention relates to an electrical model of an offshore floating photovoltaic array in a method for evaluating the power generation performance of an offshore floating photovoltaic power generation system.

[0111] Figure 7 It is a schematic diagram of PV curve characteristics under uniform irradiance and non-uniform irradiance scenarios of an offshore floating photovoltaic array in a power generation performance evaluation method of an offshore floating photovoltaic power generation system involved in the present invention.

[0112] Figure 8 It is a schematic diagram of PV curve changes under uneven irradiance scenarios of an offshore floating photovoltaic array in a power generation performance evaluation method of an offshore floating photovoltaic power generation system involved in the present invention.

[0113] Fig. 9 This is a wave rose diagram of the target sea area throughout the year in the embodiment of the present invention.

[0114] Fig.10 A schematic diagram of irradiance variation of an offshore floating photovoltaic array in a uniform irradiance scenario according to an embodiment of the present invention;

[0115] Fig.11A schematic diagram of the irradiance of an offshore floating photovoltaic array in a non-uniform irradiance scenario according to an embodiment of the present invention; (V) Specific implementation methods:

[0116] Embodiment: A method for evaluating power generation performance of an offshore floating photovoltaic power generation system, such as Figure 1 As shown, it is characterized in that it includes the following steps:

[0117] (1) Establish the irradiance model of single-sided and double-sided photovoltaic modules with fixed installation angles under static sea conditions:

[0118] (1-1) Static equivalent irradiance G of bifacial photovoltaic modules E The static irradiance G of the front and back F , G R And the bifaciality of the modules Determine, as shown in formula (1):

[0119]

[0120] (1-2) The total solar radiation received by the front and back of a bifacial photovoltaic module includes three parts: direct radiation, scattered radiation, and reflected radiation. Figure 2 As shown in the figure, the irradiance G received by the front side of the bifacial photovoltaic module with a fixed tilt angle is F As shown in formula (2):

[0121]

[0122] In formula (2), subscript F refers to the front side, G b,F , G d,F , G r,F They are the direct irradiance, scattered irradiance and reflected irradiance on the inclined surface of the front photovoltaic module, in W / m2; B h , D h , G h are horizontal direct irradiance, horizontal scattered irradiance, and horizontal reflected irradiance; θ β,F is the angle between the sunlight and the normal of the front inclined plate, β F is the dihedral angle between the front photovoltaic module and the ground horizontal plane, which is positive towards the south and negative towards the north, and should satisfy the relationship of formula (3):

[0123]

[0124] In formula (3), is the geographic latitude, ω is the hour angle, δ is the declination angle; γ F is the direction angle of the plate, starting from the north and going clockwise is positive;

[0125] (1-3) Horizontal direct irradiance Bh Specifically:

[0126] B h =ξ0I SC P m (4)

[0127] In formula (4), I SC The solar constant represents the solar radiation received per unit area per unit time at the upper boundary of the Earth’s atmosphere perpendicular to the sunlight. It is generally taken as 1367W / m 2 ; P is the atmospheric transparency coefficient; m is the atmospheric optical quality, which represents the ratio of the actual distance that sunlight actually passes through the atmosphere to the average total thickness of the Earth's atmosphere, as shown in formula (5):

[0128]

[0129] ξ0 is the Earth orbit eccentricity correction coefficient, as shown in formula (6):

[0130]

[0131] In formula (6), d n is the number of days;

[0132] (1-4) Horizontal diffuse irradiance D h Generally, an empirical calculation formula based on actual measurement is used, as shown in formula (7):

[0133]

[0134] (1-5) After the sun radiates to the ground, the horizontal reflected irradiance G h Horizontal direct irradiance B h and horizontal diffuse irradiance D h The sum of the reflection coefficient ρ, therefore, the reflected radiation energy G h Specifically, as shown in formula (8):

[0135] G h =ρ(B h +D h ) (8)

[0136] (1-6) The irradiance on the back of a bifacial photovoltaic module with a fixed tilt angle is specifically shown in formula (9):

[0137]

[0138] In formula (9), the subscript R refers to the back side, and the back side component irradiance G R Calculation method and frontal irradiance G F The same, the direction angle of the back plate γR , the dihedral angle β between the back photovoltaic module and the ground level R , the angle θ between the sunlight and the normal of the back tilted plate β,R The opposite of positive, that is:

[0139] γ R =180°-γ F (10)

[0140] β R =180°-β F (11)

[0141]

[0142] (1-7) Direct irradiance G on the inclined surface of the rear module b,R The acquisition of G mainly occurs during sunrise or sunset, and the incident angle of direct sunlight is large and the solar altitude angle is small, so b,R It is much smaller than the direct front irradiance, generally less than 5% of the direct front irradiance, so it can be ignored, as shown in formula (13):

[0143]

[0144] From steps (1-2) and (1-7), we can obtain the front and back irradiance G of the single-sided and double-sided photovoltaic modules under static sea conditions respectively. F , G R , we can use (1-1) to get the equivalent irradiance G of single-sided and double-sided photovoltaic modules under static sea conditions E .

[0145] (2) Using the Stokes wave theory applicable to deep ocean waters (where waves are steeper), the influence of offshore wind and wave fluctuations on the dynamic irradiance of single-sided and bifacial photovoltaic modules is studied. Considering the influence of offshore wind and wave fluctuations, the inclination angle variation characteristics of photovoltaic modules installed on floating structures under different sea conditions are studied, and a dynamic irradiance model of single-sided and bifacial photovoltaic modules considering the influence of wave motion is established:

[0146] (2-1) Dynamic equivalent irradiance G of single-sided and double-sided photovoltaic modules E (t) Dynamic irradiance G on the front and back F (t), G R (t) and the bifaciality of the modules Determine, as shown in formula (14):

[0147]

[0148] And G F (t), G R(t) is the dynamic dihedral angle β between the front and back sides of the double-sided glass photovoltaic module and the ground level under the action of waves. F (t), β R (t) and the angle θ between the sunlight and the normal of the front and back inclined plates β,F (t),θ β,R (t) is determined as shown in equations (15) and (16);

[0149]

[0150]

[0151] (2-2) Taking the second-order Stokes wave as an example, the wave type is designed. Figure 4 As shown, the wavefront equation of the second-order Stokes wave is shown in formula (17):

[0152]

[0153] In formula (17), L is the wavelength; d is the water depth; H is the wave height; k is the wave number; w is the wave circular frequency;

[0154] First, the dynamic dihedral angle β between the front and back sides of the bifacial glass photovoltaic module and the ground horizontal plane under the action of the second-order Stokes wave is calculated using equations (18)-(20): F (t), β R (t), the position partial derivative of the wavefront equation of the second-order Stokes wave is taken and the inverse tangent function is taken to obtain the time domain expression function of the Stokes second-order wave inclination angle Δβ(t), which is specifically:

[0155]

[0156] β F (t) = β0 + Δβ(t) (19)

[0157] β R (t) = π - β F (t) (20)

[0158] Then, using β F (t), β R (t) Calculate the angle θ between the sunlight and the normal of the front and back inclined plates β,F (t),θ β,R (t), as shown in equations (21) and (22):

[0159]

[0160]

[0161] In the formula, is the geographic latitude, ω is the hour angle, δ is the declination angle, γ F is the direction angle of the flat panel, which is positive in the clockwise direction starting from the north. Finally, the results of equations (21), (22) and (18)-(20) are substituted into (14)-(16) to calculate the dynamic equivalent irradiance G of the bifacial photovoltaic module. E (t).

[0162] (3) Analyze the time-varying differences in irradiance of photovoltaic modules installed at different spatial locations in the offshore floating photovoltaic array, and combine the irradiance variation characteristics G of the bifacial photovoltaic modules under the action of waves obtained in step (2) E (t), generate the irradiance distribution scenario of the offshore floating photovoltaic array; based on the installation method of the offshore floating photovoltaic array and the size of the floating structure unit W i The proportional relationship between the irradiance distribution of the offshore floating photovoltaic array and the wave wavelength L is used to divide the irradiance distribution scenario of the offshore floating photovoltaic array into uniform irradiance scenario and non-uniform irradiance scenario. Different photovoltaic array irradiance distribution generation methods are used for different scenarios. The specific contents are as follows:

[0163] (3-1) In actual engineering applications, the topological structure of the photovoltaic array usually adopts a series-parallel structure, that is, s photovoltaic modules are connected in series to form a photovoltaic string, and then p photovoltaic strings are connected in parallel to form a photovoltaic array, and then connected to the inverter; when the offshore floating photovoltaic array is installed on the same floating structure unit, the irradiance of each photovoltaic module in the floating photovoltaic array is affected by the wave fluctuations in the same way. At this time, the offshore floating photovoltaic array works in a uniform irradiance scenario, that is, the offshore floating photovoltaic array irradiance is consistent with the photovoltaic module irradiance G generated in step (2). E (t) consistent;

[0164] (3-2) When the offshore floating photovoltaic array is installed on i (i≥2) floating structure units, the irradiance of the photovoltaic modules located on the same floating unit in the floating photovoltaic array is affected by the wave fluctuations in a consistent manner, and the irradiance of the photovoltaic modules located on different floating structure units is affected by the wave fluctuations with a phase difference. At this time, the offshore floating photovoltaic array operates in a non-uniform irradiance scenario;

[0165] In this embodiment, the offshore floating photovoltaic array installed on i floating structure units is an s×p group (taking the s×p photovoltaic array installed on i (i≥2) floating units as an example), and the irradiance distribution of the offshore floating photovoltaic array is as follows: Figure 5As shown in the figure, the irradiance of the photovoltaic modules on the wave-facing side of the photovoltaic array changes first. As time goes by, the waves continue to advance into the photovoltaic array, and the irradiance of the photovoltaic modules on the side away from the waves lags behind. When the waves come, the irradiance of the photovoltaic modules at different spatial positions has the same trend over time, but the phases are different. Therefore, the method for generating the uneven irradiance distribution scene of the offshore floating photovoltaic array is as follows:

[0166] First, based on the size W of the floating structure unit facing the wave in the floating photovoltaic array i The proportional relationship between the wavelength L of the sea waves is used to calculate the time-varying phase difference Δθ of the irradiance of the photovoltaic modules installed in different floating structure units in the offshore floating photovoltaic array. i :

[0167]

[0168] Secondly, Δθi is used to calculate the time-varying initial phase θ of the irradiance of the photovoltaic modules installed on the i floating units. i , as shown in formula (24):

[0169] θ1=0, θ2=θ1+Δθ1, θ3=θ2+Δθ2,…θ i =θ i-1 +Δθ i-1 (twenty four)

[0170] Finally, substitute θi into the irradiance variation characteristic model G of the bifacial photovoltaic module under the action of waves in step (2): E (t), generating uneven irradiance scenario G for offshore floating photovoltaic arrays E (t+θ1)-G E (t+θ i ).

[0171] (4) Establish an electrical model for offshore floating photovoltaic arrays and combine it with the irradiance distribution model G E (t+θ1)-G E (t+θ i ), and the ambient temperature information T em (t), simulate the PV curve of the offshore floating photovoltaic array under the influence of wave operation at each moment, and find the maximum power output point of the offshore floating photovoltaic array at each moment based on the PV curve of the photovoltaic array;

[0172] (4-1) The electrical model is established to describe the electrical characteristics and power output of the photovoltaic module. A five-parameter single diode circuit model is used to simulate the electrical performance of the bifacial photovoltaic module, taking into account both simplification and accuracy. The equivalent circuit is as follows Figure 6As shown, the relevant mathematical model of the photovoltaic cell based on the Shockley diode equation is specifically shown in formula (25):

[0173]

[0174] In formula (25), I ph is the photocurrent of the photovoltaic module, I d is the diode current, I sh is the current through the parallel resistance of the photovoltaic module, I sat is the reverse saturation current of the photovoltaic module diode, V is the output voltage of the photovoltaic module, I is the output current of the photovoltaic module, R sh is the parallel resistance of the photovoltaic module, R s is the series resistance of the photovoltaic module, q is the electron charge (1.602E-19C), A is the diode ideality factor, K is the Boltzmann constant (1.381E-23J / K), and T is the battery temperature;

[0175] (4-2) For a photovoltaic array composed of multiple photovoltaic modules connected in series and parallel, its electrical mathematical model is specifically shown in formula (26):

[0176]

[0177] In formula (26), V t =AKT / q is the diode thermal voltage, N s N is the number of components in a single series-parallel group. p is the number of array groups connected in series and parallel;

[0178] (4-3) The electrical mathematical model of photovoltaic cells under standard test conditions is obtained from formula (27):

[0179]

[0180] (4-4) Under standard test conditions STC, the key parameters of the electrical model are as follows:

[0181] Diode thermal voltage V under STC t,STC As shown in formula (28):

[0182]

[0183] In formula (28), μ sc is the short-circuit current temperature coefficient, μ oc is the open circuit voltage temperature coefficient, E g is the bandgap width (1.7936e-19J);

[0184] Photocurrent I under STC ph,STC As shown in formula (29):

[0185] I ph,STC ≈I sc,STC (29)

[0186] Diode reverse saturation current I under STC sat,STC As shown in formula (30):

[0187]

[0188] (4-5) Based on the key parameters of the electrical model under STC, the temperature of the photovoltaic module T em (t) and the equivalent irradiance G of the components in the photovoltaic array E (t+θ i ) can calculate the key characteristic parameters of the electrical model under non-STC conditions, as shown in formulas (31)-(33):

[0189]

[0190]

[0191]

[0192] (4-5) The key characteristic parameter I in the electrical model under non-STC ph ,I sat 、V t Substituting into equations (25) and (26), the PV curve of the offshore floating photovoltaic array under the influence of wave operation at each moment can be simulated and generated. For the scenario of uniformly distributed irradiance, there is only one maximum power point in the PV curve of the offshore floating photovoltaic array at each moment, while for the scenario of non-uniform irradiance, there are multiple local maximum power points, such as Figure 7 As shown in Figure 2, the PV curve of the photovoltaic array changes rapidly and randomly with the movement of the waves, as shown in Figure 2. Figure 8 As shown; by traversing the PV curve, the maximum power output value P of the offshore floating photovoltaic array at each moment can be obtained max .

[0193] (5) Combining the wind and wave data in the target sea area, the irradiance distribution of the floating photovoltaic array obtained in step (3), and the maximum power output value P of the offshore floating photovoltaic array at each moment in step (4) max , evaluate the annual power generation in the target sea area:

[0194] (5-1) Theoretical power generation of offshore floating photovoltaic arrays under uniform irradiance scenario;

[0195] From step (3), it can be seen that when the offshore floating photovoltaic array is installed on the same floating structure unit, the irradiance of each photovoltaic module in the floating photovoltaic array is affected by the wave fluctuations in the same way. At this time, the offshore floating photovoltaic array works in a uniform irradiance scene, that is, the irradiance of the offshore floating photovoltaic array is equal to the irradiance of the photovoltaic module generated in step (2). E (t) is consistent; therefore, in engineering, the components are usually concentrated on the same floating unit, and the component layout direction is perpendicular to the direction of normal waves and strong waves in the sea area, so as to eliminate the irradiance difference of photovoltaic components connected to the same inverter to a certain extent, reduce the local power maximum point of the PV curve, and the offshore floating photovoltaic array works approximately in a uniform irradiance scene. At this time, the theoretical power generation of the offshore floating photovoltaic array is mainly determined by the irradiance change G of the photovoltaic components under the action of waves. E (t) determine:

[0196]

[0197] Where CI is the rated installed capacity of the photovoltaic array, in kilowatts (kW); G E (t) is the instantaneous value of the equivalent irradiance on the inclined surface of the photovoltaic array, in kilowatt-hours per square meter (kWh / m 2 ); G0 is the irradiance under standard conditions, G0 = 1, and the unit is kilowatt-hour per square meter (kWh / m 2 ).

[0198] (5-2) Theoretical power generation of offshore floating photovoltaic arrays under uneven irradiance scenarios;

[0199] From step (3), it can be seen that when the offshore floating photovoltaic array is installed on i (i≥2) floating structure units, the irradiance of the photovoltaic modules located on the same floating unit in the floating photovoltaic array is affected by the wave fluctuations in a consistent manner, and the irradiance of the photovoltaic modules located on different floating structure units is affected by the wave fluctuations with a phase difference. At this time, the offshore floating photovoltaic array operates in a non-uniform irradiance scenario; and with the movement of the waves, the irradiance and change trend of the modules in the photovoltaic string unit are inconsistent, which leads to rapid random changes in the PV multi-peak curve of the photovoltaic string unit, such as Figure 7 Combined with the wind and wave data in the target sea area, the irradiance distribution of the floating photovoltaic array obtained in step (3), and the maximum power output value P of the offshore floating photovoltaic array at each moment in step (4), max , we can get the theoretical power generation of offshore floating photovoltaic array under non-uniform irradiance scenario, that is:

[0200]

[0201] In the formula, Eout is the theoretical annual power generation of the photovoltaic power generation system, in kilowatt-hours (kWh); P max (t) is the instantaneous value of the inverter AC side output power, in kilowatts (kW).

[0202] In order to make the purpose, technical scheme and advantages of the present invention clearer, the embodiments of the present invention are further described in detail below. It should be noted that the embodiments described below are only some embodiments of the present invention, not all embodiments. In the absence of conflict, the embodiments and embodiment features in the present invention can be combined with each other.

[0203] Specifically, an embodiment of the present invention provides a method for evaluating power generation performance of an offshore floating photovoltaic power generation system. Figure 1 As shown, the method includes the following steps: calculating the irradiance changes of single-sided and double-sided photovoltaic modules in the target sea area under the influence of wave movement; constructing uniform and uneven distribution scenarios of irradiance of offshore floating photovoltaic arrays; simulating the PV curve changes of offshore floating photovoltaic arrays under the influence of wave movement; and evaluating the annual power generation in the target sea area.

[0204] 101: Study the irradiance changes of single-sided and double-sided photovoltaic modules in the target sea area under the influence of wave motion;

[0205] Collect data such as water depth d(t), wave height H(t), wavelength L(t), period T(t), wave number k(t) of the target sea area, and calculate the wave circular frequency w=2π / T(t);

[0206] Calculate the impact of waves in the target sea area on the installation angle of photovoltaic modules. Based on the wave statistics of the target sea area, simulate the waves in the limited deep water area based on the second-order Stokes wave, and analyze the impact of the wave environment on the installation inclination of photovoltaic modules throughout the year, that is, Δβ(t). Based on the static installation inclination angle β0 between the photovoltaic panel and the floating body, calculate the dihedral angle β between the front and back of the photovoltaic module and the horizontal plane of the ground under the action of waves. F (t), β R (t), the angle θ between the sunlight and the normal of the front and back tilted plates of the photovoltaic module β,F (t), θ β,R (t), as shown in formulas (18)-(22), where is the geographic latitude, ω is the hour angle, δ is the declination angle, γ F is the direction angle of the plate, which is positive in the clockwise direction starting from the north.

[0207] The proposed offshore floating bifacial photovoltaic module irradiance model is used to calculate the irradiance variation characteristics of bifacial photovoltaic modules in the target sea area under the action of waves. The Earth orbit eccentricity correction coefficient ξ0 and the atmospheric optical mass m in the target sea area are calculated, and the solar constant I is obtained through local meteorological data. SC Based on the PV module plane irradiance model, the horizontal plane direct irradiance B is calculated according to formulas (4)-(8) throughout the year. h , horizontal diffuse irradiance D h , horizontal reflected irradiance G h .

[0208] The inclination variation characteristic data of the bifacial photovoltaic modules installed on the floating structure under different sea conditions in the target sea area and the horizontal direct irradiance B of the photovoltaic modules are used. h , horizontal diffuse irradiance D h , horizontal reflected irradiance G h , and further calculate the irradiance G on the front and back sides of the bifacial photovoltaic modules affected by the wave motion in the target sea area using formulas (9)-(14) F (t), G R (t) and equivalent irradiance G E (t)Change.

[0209] 102: Constructing scenarios of uniform and uneven irradiance distribution of offshore floating photovoltaic arrays;

[0210] Based on the installation method of offshore floating photovoltaic array and the size of floating structure unit W i The proportional relationship between the offshore floating photovoltaic array and the wave wavelength L divides the irradiance distribution scenario of the offshore floating photovoltaic array into uniform irradiance scenario and non-uniform irradiance scenario, and different photovoltaic array irradiance distribution generation methods are used for different scenarios. When the offshore floating photovoltaic array is installed on the same floating structure unit, the offshore floating photovoltaic array works in a uniform irradiance scenario, that is, the offshore floating photovoltaic array irradiance is proportional to the photovoltaic module irradiance G in 101. E (t)Consistent.

[0211] When the offshore floating photovoltaic array is installed on i (i≥2) floating structure units, the offshore floating photovoltaic array works in a non-uniform irradiance scenario. Based on the size W of the floating structure unit facing the wave in the floating photovoltaic array i The proportional relationship between the wavelength L of the ocean waves can be used to calculate the time-varying phase difference Δθ of the irradiance of photovoltaic modules installed in different floating structure units in the offshore floating photovoltaic array. i , as shown in formula (23). i Calculate the time-varying initial phase θ of the irradiance of the photovoltaic modules installed on the i floating units i, as shown in formula (24). Finally, θ i Substitute into the irradiance variation characteristic model G of the bifacial photovoltaic module under the action of waves in 101 E (t), generating uneven irradiance scenario G for offshore floating photovoltaic arrays E (t+θ1)-G E (t+θ i ).

[0212] 103: Using the electrical model of the offshore floating photovoltaic array, simulate the PV curve of the offshore floating photovoltaic array under the influence of waves at each moment, and find the maximum power output point P of the offshore floating photovoltaic array at each moment. max ;

[0213] Using the electrical model of the offshore floating photovoltaic array, based on the irradiance distribution model G provided by 102 E (t+θ1)-G E (t+θ i ) and ambient temperature information T em (t), simulating the PV curve of the offshore floating photovoltaic array under the influence of wave operation at each moment. In order to describe the electrical characteristics and power output of the photovoltaic array, the electrical model of the offshore floating photovoltaic module is first established, and then the electrical model of the module is connected in series and parallel to form the electrical model of the photovoltaic array.

[0214] A five-parameter single diode circuit model is used to simulate the electrical performance of the bifacial photovoltaic module, taking into account both simplification and accuracy. The relevant mathematical model of the photovoltaic cell based on the Shockley diode equation is shown in formula (25); V t =AKT / q is the diode thermal voltage.

[0215] Diode thermal voltage V under standard test conditions t,STC , as shown in formula (28). sc is the short-circuit current temperature coefficient, μ oc is the open circuit voltage temperature coefficient, E g is the bandgap width (1.7936e-19J). Photocurrent I under standard test conditions ph,STC As shown in formula (29), the diode reverse saturation current I under standard test conditions is sat,STC The details are shown in formula (30).

[0216] Based on the key parameters of the electrical model under STC, the temperature of the photovoltaic module T em (t) and the equivalent irradiance G of the components in the photovoltaic array E (t+θ i ) The key characteristic parameters of the electrical model under non-STC can be calculated as shown in formulas (31)-(33).

[0217] The key characteristic parameters I in the electrical model under non-STC ph ,I sat 、V t Substituting into formula (16), the PV curve of the offshore floating photovoltaic array under the influence of wave operation at each moment can be simulated and generated. By traversing the PV curve, the maximum power output value P of the offshore floating photovoltaic array at each moment can be obtained. max .

[0218] 104: Assess the annual power generation in the target sea area.

[0219] Theoretical power generation of offshore floating photovoltaic array under uniform irradiance scenario. Usually, the local maximum power point of the PV curve is reduced by arranging the components in a centralized manner. At this time, the offshore floating photovoltaic array works approximately in a uniform irradiance scenario. At this time, the irradiance variation characteristics G of the bifacial photovoltaic module under the action of waves calculated by 101 are E (t), the theoretical power generation of the offshore floating photovoltaic array under the uniform irradiance scenario is calculated as shown in formula (34).

[0220] Theoretical power generation of offshore floating photovoltaic array under uneven irradiance scenario. The uneven irradiance scenario G generated by 102 for offshore floating photovoltaic array E (t+θ1)-G E (t+θ i ), and the maximum power output value P of the offshore floating photovoltaic array at each moment provided by 103 max , and then the theoretical power generation of the offshore floating photovoltaic array under the uneven irradiance scenario is calculated as shown in formula (34).

[0221] To verify the effectiveness of the method proposed in this invention, a simulation is performed using a floating photovoltaic power generation system at sea as an example. Based on the wave observation station in the target sea area, regional wave statistical information can be obtained, such as Fig. 9 As shown in the figure, the common wave direction in this sea area is NE, with a frequency of 25.2%, the second common wave direction is NNE, with a frequency of 17.3%, and the strong wave direction is NNE, with a frequency of 0.6%. The capacity of the offshore floating photovoltaic array is about 30kW, and the photovoltaic array N s is 26, N p =2, and the parameters of the bifacial photovoltaic modules are shown in Table 1. Under the uniform irradiance scenario, the irradiance variation curve of the offshore floating photovoltaic array at an installation angle of 15° during a certain period is shown in Table 1. Fig.10 As shown. Fig.10As shown in the figure, 0-10s is the ideal situation, that is, the wave height H is less than 0.2m, 10-30s is light waves, that is, the wave height H is about 1m, 30-50s is medium waves, that is, the wave height H is about 2m, and 50-70s is large waves, that is, the wave height H is about 4m. It can be seen that with the increase of wave fluctuations, the irradiance of the photovoltaic array changes more dramatically. In the non-uniform irradiance scenario, the irradiance distribution of the offshore floating photovoltaic array at a certain moment when the installation angle is 15° is as follows: Fig.11 As shown in the figure, the irradiance of photovoltaic modules at different phases is different. The maximum irradiance difference of modules at different phases is nearly 600W / m 2 , the peak and valley values ​​of irradiance are approximately 1000W / m 2 、800W / m 2 、600W / m 2 , 400W / m 2 In a certain period of time under the non-uniform irradiance scene, with the movement of waves, the multi-peak PV curve of the photovoltaic array changes rapidly and randomly. max The range is between 13.82kW and 24.59kW, as shown below: Figure 8 As shown. Through simulation calculation, it can be seen that under the action of waves, the annual power generation of the uniform irradiance scenario is about 2.3% higher than that of the non-uniform irradiance scenario. Therefore, in engineering applications, the wave conditions in the target sea area should be investigated, and the occurrence of non-uniform irradiance scenarios should be reduced by centrally arranging photovoltaic arrays, thereby increasing the power generation of offshore floating photovoltaic power generation systems.

[0222] Table 1 Bifacial photovoltaic module parameters

[0223]

[0224]

[0225] Those skilled in the art will appreciate that the accompanying drawings are merely schematic diagrams of an embodiment and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating the power generation performance of an offshore floating photovoltaic power generation system, characterized in that It includes the following steps: (1) Establish the irradiance model of single-sided and bifacial photovoltaic modules under static sea conditions; (2) Considering the influence of wind and wave fluctuations at sea, the tilt angle variation characteristics of photovoltaic modules installed on floating structures under different sea conditions are studied, and a dynamic irradiance model of single-sided and bifacial photovoltaic modules considering the influence of wave motion is established to obtain the irradiance variation characteristics G of bifacial photovoltaic modules under the action of waves. E (t); (3) Analyze the time-varying differences in irradiance of photovoltaic modules installed at different spatial locations in the offshore floating photovoltaic array, and combine the irradiance variation characteristics G of the bifacial photovoltaic modules under the action of waves obtained in step (2) E (t), generate irradiance distribution scenarios for offshore floating photovoltaic arrays; (4) Establish an electrical model for offshore floating photovoltaic arrays and combine it with the irradiance distribution model G E (t+θ1)-G E (t+θ i ), and the ambient temperature information T em (t), simulate the PV curve of the offshore floating photovoltaic array under the influence of wave operation at each moment, and find the maximum power output point P of the offshore floating photovoltaic array at each moment based on the PV curve of the photovoltaic array max ; (5) Combining the wind and wave data in the target sea area, the irradiance distribution of the floating photovoltaic array obtained in step (3), and the maximum power output value P of the offshore floating photovoltaic array at each moment in step (4) max , evaluate the annual power generation in the target sea area.

2. According to claim 1, a method for evaluating power generation performance of an offshore floating photovoltaic power generation system is characterized in that The installation inclination angle of the single-sided and double-sided photovoltaic modules in step (1) is fixed.

3. The method for evaluating power generation performance of an offshore floating photovoltaic power generation system according to claim 1, characterized in that The step (1) establishes a single-sided and double-sided photovoltaic module irradiance model under static sea conditions, specifically referring to: (1-1) Static equivalent irradiance G of bifacial photovoltaic modules E From the front static irradiance G F , Back static irradiation G R And the bifaciality of the modules Determine, as shown in formula (1): (1-2) The total solar radiation received by the front and back of a bifacial photovoltaic module includes three parts: direct radiation, scattered radiation, and reflected radiation. The irradiance G received by the front of a bifacial photovoltaic module with a fixed inclination angle is F As shown in formula (2): In formula (2), subscript F refers to the front side, G b,F , G d,F , G r,F They are the direct irradiance, scattered irradiance and reflected irradiance on the inclined surface of the front photovoltaic module, in W / m2; B h , D h , G h are horizontal direct irradiance, horizontal scattered irradiance, and horizontal reflected irradiance; θ β,F is the angle between the sunlight and the normal of the front inclined plate, β F is the dihedral angle between the front photovoltaic module and the ground horizontal plane, which is positive towards the south and negative towards the north, and should satisfy the relationship of formula (3): In formula (3), is the geographic latitude, ω is the hour angle, δ is the declination angle; γ F is the direction angle of the plate, starting from the north and going clockwise is positive; (1-3) Horizontal direct irradiance B h Specifically: B h =ξ0I SC P m (4) In formula (4), I SC is the solar constant, which indicates the solar radiation received per unit area per unit time at the upper boundary of the Earth's atmosphere perpendicular to the sunlight; P is the atmospheric transparency coefficient; m is the atmospheric optical quality, which indicates the ratio of the actual distance that sunlight actually passes through the atmosphere to the average total thickness of the Earth's atmosphere, as shown in formula (5): ξ0 is the Earth orbit eccentricity correction coefficient, as shown in formula (6): In formula (6), d n is the number of days; (1-4) Horizontal diffuse irradiance D h Generally, an empirical calculation formula based on actual measurement is used, as shown in formula (7); (1-5) After the sun radiates to the ground, the horizontal reflected irradiance G h Horizontal direct irradiance B h and horizontal diffuse irradiance D h The sum of the reflection coefficient ρ, therefore, the reflected radiation energy G h The specific formula is as shown in formula (8); G h =ρ(B h +D h ) (8) (1-6) The irradiance on the back of a bifacial photovoltaic module with a fixed tilt angle is specifically shown in formula (9); In formula (9), the subscript R refers to the back side, and the back side component irradiance G R Calculation method and frontal irradiance G F The same, the direction angle of the back plate γ R , the dihedral angle β between the back photovoltaic module and the ground level R , the angle θ between the sunlight and the normal of the back tilted plate β,R The opposite of positive, i.e.; c R =180°-c F (10) β R ＝180°-β F (11) (1-7) Direct irradiance G on the inclined surface of the rear module b,R The acquisition of G mainly occurs during sunrise or sunset, and the incident angle of direct sunlight is large and the solar altitude angle is small, which makes G b,R It is much smaller than the direct irradiance from the front and can be ignored. Then the static irradiance from the back is G R Arranged as shown in formula (13): From steps (1-2) and (1-7), we can obtain the front and back irradiance G of the single-sided and double-sided photovoltaic modules under static sea conditions respectively. F , G R , we can use (1-1) to get the equivalent irradiance G of single-sided and double-sided photovoltaic modules under static sea conditions E .

4. The method for evaluating power generation performance of an offshore floating photovoltaic power generation system according to claim 1, characterized in that The step (2) refers to using the Stokes wave theory applicable to deep ocean waters with large wave steepness to study the influence of offshore wind and wave fluctuations on the dynamic irradiance of single-sided and double-sided photovoltaic modules, specifically including the following contents: (2-1) Dynamic equivalent irradiance G of single-sided and double-sided photovoltaic modules E (t) is determined by the front dynamic irradiance G F (t), back dynamic irradiance G R (t) and the bifaciality of the modules Determine, as shown in formula (14): The front dynamic irradiance G F (t) and back dynamic irradiance G R (t) The dynamic dihedral angle β between the front surface of the double-sided glass photovoltaic module and the ground level under the action of waves F (t), dynamic dihedral angle β between the back surface and the geoid R (t), the angle θ between the sunlight and the normal of the front inclined flat plate β,F (t) and the angle θ between the sunlight and the normal of the back tilted plate β,R (t) is determined as shown in equations (15) and (16) respectively; (2-2) Taking the second-order Stokes wave as an example to design the wave type, the wave surface equation of the second-order Stokes wave is shown in formula (17): In formula (17), L is the wavelength; d is the water depth; H is the wave height; k is the wave number; w is the wave circular frequency; (2-3) Using equations (18)-(20) to calculate the dynamic dihedral angle β between the front surface of the bifacial glass photovoltaic module and the ground horizontal plane under the action of the second-order Stokes wave F (t), dynamic dihedral angle β between the back surface and the geoid R (t), the position partial derivative of the wavefront equation of the second-order Stokes wave is taken and the inverse tangent function is taken to obtain the time domain expression function of the Stokes second-order wave inclination angle Δβ(t), which is specifically: b F (t)=β0+Δβ(t) (19) b R (t)=π-β F (t) (20) (2-4) Using the dynamic dihedral angle β between the front of the double-sided glass photovoltaic module and the ground level F (t) and the dynamic dihedral angle β between the back surface and the geoid R (t), calculate the angle θ between the sunlight and the normal of the front inclined plate β,F (t) and the angle θ between the sunlight and the normal of the back tilted plate β,R (t), as shown in formula (21) and (22) respectively: Finally, the results of equations (21) and (22) obtained in step (2-4) and the results of equations (18)-(20) obtained in step (2-3) are substituted into equations (14)-(16) in step (2-1) to calculate the dynamic equivalent irradiance G of the bifacial photovoltaic module. E (t).

5. The method for evaluating power generation performance of an offshore floating photovoltaic power generation system according to claim 1, characterized in that The step (3) specifically refers to: based on the installation method of the offshore floating photovoltaic array, the size W of the floating structure unit i Based on the proportional relationship between the wavelength L of the ocean waves, the irradiance distribution scenario of the offshore floating photovoltaic array is divided into a uniform irradiance scenario and an uneven irradiance scenario. Different photovoltaic array irradiance distribution generation methods are used respectively. The specific contents are as follows: (3-1) In actual engineering applications, the topological structure of the photovoltaic array usually adopts a series-parallel structure, that is, s photovoltaic modules are connected in series to form a photovoltaic string, and then p photovoltaic strings are connected in parallel to form a photovoltaic array, and then connected to the inverter; when the offshore floating photovoltaic array is installed on the same floating structure unit, the irradiance of each photovoltaic module in the floating photovoltaic array is affected by the wave fluctuations in the same way. At this time, the offshore floating photovoltaic array works in a uniform irradiance scenario, that is, the offshore floating photovoltaic array irradiance is consistent with the photovoltaic module irradiance G generated in step (2). E (t) consistent; (3-2) When an offshore floating photovoltaic array is installed on i (i≥2) floating structure units, the irradiance of photovoltaic modules located on the same floating unit in the floating photovoltaic array is affected by the wave fluctuations in a consistent manner, while the irradiance of photovoltaic modules located on different floating structure units is affected by the wave fluctuations with a phase difference. At this time, the offshore floating photovoltaic array operates in a non-uniform irradiance scenario.

6. A method for evaluating power generation performance of an offshore floating photovoltaic power generation system according to claim 5, characterized in that In the step (3-2), the offshore floating photovoltaic array installed on the i floating structure units is an s×p group. The irradiance of the photovoltaic components on the wave-facing side of the photovoltaic array changes first. As time goes by, the waves continue to advance into the photovoltaic array, and the irradiance of the photovoltaic components on the side away from the wave direction changes the most. Therefore, the method for generating the uneven irradiance distribution scene of the offshore floating photovoltaic array is as follows: First, based on the size W of the floating structure unit facing the wave in the floating photovoltaic array i The proportional relationship between the wavelength L of the sea waves is used to calculate the time-varying phase difference Δθ of the irradiance of the photovoltaic modules installed in different floating structure units in the offshore floating photovoltaic array. i : Secondly, using Δθ i Calculate the time-varying initial phase θ of the irradiance of the photovoltaic modules installed on the i floating units i , as shown in formula (24): θ1=0,θ2=θ1+Δθ1,θ3=θ2+Δθ2,.....θ i =θ i-1 +Δθ i-1 (24) Finally, θ i Substitute into the irradiance variation characteristic model G of the bifacial photovoltaic module under the action of waves in step (2) E (t), generating uneven irradiance scenario G for offshore floating photovoltaic arrays E (t+θ1)-G E (t+θ i ).

7. The method for evaluating power generation performance of an offshore floating photovoltaic power generation system according to claim 1, characterized in that The step (4) specifically refers to: (4-1) The relevant mathematical model of photovoltaic cells based on the Shockley diode equation is shown in formula (25): In formula (25), I ph is the photocurrent of the photovoltaic module, I d is the diode current, I sh is the current through the parallel resistance of the photovoltaic module, I sat is the reverse saturation current of the photovoltaic module diode, V is the output voltage of the photovoltaic module, I is the output current of the photovoltaic module, R sh is the parallel resistance of the photovoltaic module, R s is the series resistance of the photovoltaic module, q is the electron charge, A is the diode ideality factor, K is the Boltzmann constant, and T is the battery temperature; (4-2) For a photovoltaic array composed of multiple photovoltaic modules connected in series and parallel, its electrical mathematical model is specifically shown in formula (26): In formula (26), V t =AKT / q is the diode thermal voltage, N s N is the number of components in a single series-parallel group. p is the number of array groups connected in series and parallel; (4-3) The electrical mathematical model of photovoltaic cells under standard test conditions is obtained from formula (27): (4-4) Under standard test conditions STC, the key parameters of the electrical model are as follows: Diode thermal voltage V under STC t,STC As shown in formula (28): In formula (28), μ sc is the short-circuit current temperature coefficient, μ oc is the open circuit voltage temperature coefficient, E g is the bandgap width; Photocurrent I under STC ph,STC As shown in formula (29): I ph,STC ≈I sc,STC (29) Diode reverse saturation current I under STC sat,STC As shown in formula (30): (4-5) Based on the key parameters of the electrical model under STC, the temperature of the photovoltaic module T em (t) and the equivalent irradiance G of the components in the photovoltaic array E (t+θ i ) can calculate the key characteristic parameters of the electrical model under non-STC conditions, as shown in formulas (31)-(33): (4-5) The key characteristic parameter I in the electrical model under non-STC ph ,I sat 、V t Substituting into equations (25) and (26), the PV curve of the offshore floating photovoltaic array under the influence of wave operation at each moment can be simulated and generated. For the scenario of uniformly distributed irradiance, there is only one maximum power point in the PV curve of the offshore floating photovoltaic array at each moment, while for the scenario of non-uniform irradiance, there are multiple local maximum power points. By traversing the PV curve, the maximum power output value P of the offshore floating photovoltaic array at each moment can be obtained. max .

8. The method for evaluating power generation performance of an offshore floating photovoltaic power generation system according to claim 1, characterized in that The step (5) specifically refers to: (5-1) Theoretical power generation of offshore floating photovoltaic arrays under uniform irradiance scenario; In engineering, each photovoltaic module of the offshore floating photovoltaic array is usually centrally arranged on the same floating structure unit, and the module arrangement direction is perpendicular to the direction of normal waves and strong waves in the sea area, so as to eliminate the irradiance difference of photovoltaic modules connected to the same inverter to a certain extent, and reduce the local power maximum point of the PV curve. At this time, the offshore floating photovoltaic array works approximately in a uniform irradiance scene. At this time, the theoretical power generation of the offshore floating photovoltaic array is mainly determined by the irradiance change G of the photovoltaic modules under the action of waves. E (t) determine: Where CI is the rated installed capacity of the photovoltaic array, in kilowatts; G E (t) is the instantaneous value of the equivalent irradiance on the inclined surface of the photovoltaic array, in kilowatt-hours per square meter; G0 is the irradiance under standard conditions, in kilowatt-hours per square meter; (5-2) Theoretical power generation of offshore floating photovoltaic arrays under uneven irradiance scenarios; The irradiance of photovoltaic modules located on different floating structure units has a phase difference due to the influence of wave fluctuations. At this time, the offshore floating photovoltaic array operates in a non-uniform irradiance scene. Moreover, with the movement of waves, the irradiance and change trend of the modules in the photovoltaic string unit are inconsistent, which leads to rapid random changes in the PV multi-peak curve of the photovoltaic string unit. Combined with the wind and wave data in the target sea area, the irradiance distribution of the floating photovoltaic array obtained in step (3) and the maximum power output value P of the offshore floating photovoltaic array at each moment in step (4), max , we can get the theoretical power generation of offshore floating photovoltaic array under non-uniform irradiance scenario, that is: In the formula, E out is the theoretical annual power generation of the photovoltaic power generation system, in kilowatt-hours; P max (t) is the instantaneous value of the inverter AC side output power, in kilowatts.

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