A method for evaluating power generation performance of a marine floating photovoltaic power generation system

Abstract

The application provides a power generation performance evaluation method of a marine floating photovoltaic power generation system, comprising: considering the influence of marine wave fluctuation, researching the inclination angle change characteristics of photovoltaic components installed on a floating body structure under different sea conditions, and establishing a single / double-sided photovoltaic component dynamic / static irradiance model considering the influence of sea wave motion; a marine floating photovoltaic array irradiance uniform and non-uniform distribution scene generation method is proposed; combining the irradiance distribution model and the electrical model of the marine floating photovoltaic array, a method for simulating the maximum output power P max variation characteristics of the marine floating photovoltaic array under the influence of sea wave motion is formed; combining the wind wave data, irradiance distribution and maximum output power P max variation characteristics of the marine floating photovoltaic array in the target sea area, the annual power generation in the target sea area is evaluated. Compared with the existing photovoltaic power generation performance evaluation method, the application considers the influence of sea wave fluctuation on the power generation characteristics of the photovoltaic array, and is suitable for the marine floating photovoltaic power generation scene.

Description

(I) Technical Field:

[0001] This invention relates to the field of photovoltaic power generation technology, and in particular to a method for evaluating the power generation performance of a floating photovoltaic power generation system at sea. (II) Background Technology:

[0002] With the continuous increase in the total installed capacity of new energy sources, the development and utilization of new energy sources are facing constraints such as significant land resource limitations, gradually attracting the attention of the industry. Currently, most offshore photovoltaic (PV) systems are fixed-support nearshore systems. This structural form is only suitable for shallow water and intertidal areas, and its cost increases dramatically with water depth. A more common development method is floating PV. Compared to terrestrial PV, floating PV systems have abundant sunshine, humid air, and more rainfall, which is beneficial for heat dissipation and cleaning of PV modules. Theoretically, with the use of highly weather-resistant double-sided glass PV modules, the power generation of floating PV systems significantly surpasses that of inland PV power plants. However, the power production of floating PV systems is not only affected by sunshine resources and the power generation efficiency of PV modules, but also by factors such as sea conditions and wind.

[0003] Affected by sea breezes, ocean currents, and irregular waves, floating photovoltaic (PV) modules undergo six degrees of freedom motion along their floating structure, including translational and rotational motions along each axis. This means that even if the ambient irradiance remains constant, the irradiance received by the front and back of the floating bifacial PV modules will fluctuate randomly due to wave motion. Therefore, the radiant energy received by floating bifacial PV modules is not only affected by weather conditions (such as cloud movement) and the installation tilt angle of the modules, but also closely related to wave fluctuations. In reality, the generation of waves and wave properties such as wave height, wavelength, and wave speed at the same time and location are random and cannot be accurately predicted. For floating PV arrays, the distribution and variation of their irradiance are even more complex and variable, related not only to the installation angle of the modules and changes in weather conditions, but also closely related to the arrangement of the PV strings and their relative position to the waves. Current research on offshore floating photovoltaic (PV) power generation systems largely focuses on resource endowment assessments of target sea areas, economic analysis of integration with other offshore renewable energy sources, and qualitative studies on the power generation output of bifacial glass PV modules. There is a lack of research on the impact of the marine operating environment on the irradiance received by floating bifacial glass PV modules. Furthermore, there is still a lack of simulation tools or models specifically designed for assessing the power generation of offshore floating PV power generation systems, and key issues related to performance feasibility assessment during project planning remain unclear.

[0004] Currently, most researchers still use performance simulation tools applicable to traditional onshore photovoltaic (PV) power plants, which do not account for the impact of wave action on the irradiance received by PV modules and arrays. One study, using a floating PV power plant installed on an inland lake as an example, compared and analyzed the feasibility of existing simulation assessment tools. This study monitored on-site measurement data from the floating PV power plant and used various mainstream assessment and analysis methods, such as the Photovoltaic System Simulation Tool (PVSYST), the System Advisory Model (SAM) from the National Renewable Energy Laboratory (NREL), and the Helioscope, to simulate and assess the power generation of the plant. The comparison between measured data and simulation results showed that the energy deviation between the measured and simulated values ​​ranged from 18.43% to 38.55%, indicating that existing simulation tools or models are not suitable for the performance assessment and planning of offshore floating PV power plant projects. Therefore, in order to promote the large-scale development and utilization of offshore floating photovoltaic power plants and ensure their safe operation and economic production, it is urgent to study a power generation performance evaluation method suitable for offshore floating photovoltaic power generation systems during the development and design phase. Based on the survey of the solar resources endowment of the target sea area, the study should investigate the impact of environmental factors such as waves and wind speed on the irradiance changes of floating photovoltaic modules, and efficiently and accurately evaluate the photovoltaic power generation performance of the target sea area. (III) Summary of the Invention:

[0005] The purpose of this invention is to provide a method for evaluating the power generation performance of a floating photovoltaic power generation system at sea. This method overcomes the shortcomings of existing technologies and is a simple and easy-to-implement evaluation method. This method can ensure that the photovoltaic power generation performance of the target sea area can still be effectively evaluated even when the sea conditions and the arrangement of photovoltaic modules change.

[0006] The technical solution of this invention: a method for evaluating the power generation performance of a floating photovoltaic power generation system at sea, characterized by comprising the following steps:

[0007] (1) Establish an irradiance model for single- and double-sided photovoltaic modules under static sea conditions;

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

[0009] Step (1) of establishing the irradiance model of single and double-sided photovoltaic modules under static sea conditions specifically refers to:

[0010] (1-1) Static equivalent irradiance G of bifacial photovoltaic modules E Static irradiance G from the front and back F GR and component bifaciality The decision is as shown in formula (1):

[0011]

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

[0013]

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

[0015]

[0016] In equation (3), ω is the geographical latitude, δ is the hour angle, and γ is the declination angle. F The direction angle of the flat plate is positive when starting from north and rotating clockwise.

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

[0018] B h =ξ0I SC P m (4)

[0019] In equation (4), I SC The solar constant represents the amount of solar radiation received per unit area per unit time at the upper boundary of the Earth's atmosphere perpendicular to sunlight. In engineering calculations, it is typically taken as 1367 W / m². 2 P is the atmospheric transparency coefficient; m is the atmospheric optical quality, which represents the ratio of the actual distance that sunlight travels 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 equation (6), d n Number of days;

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

[0025]

[0026] (1-5) After solar radiation reaches the ground, the horizontal reflected irradiance G h Horizontal direct irradiance B h and horizontal scattered irradiance D h The sum of these factors and the influence 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 specific irradiance received on the back side of a bifacial photovoltaic module with a fixed tilt angle is shown in formula (9):

[0029]

[0030] In equation (9), the subscript R refers to the back side, and the irradiance G of the back side component is... R Calculation method and frontal irradiance G F Similarly, the orientation angle γ of the flat plate on the back side R The dihedral angle β between the rear photovoltaic module and the horizontal plane of the ground R The angle θ between the sunlight and the normal to the inclined plate on the back side β,R The opposite of the front, 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 componentb,R The acquisition of sunlight mainly occurs during sunrise or sunset, and the angle of incidence of direct sunlight is relatively large while the solar altitude angle is relatively small, therefore G b,R It is much smaller than the direct irradiance, generally less than 5% of the direct irradiance, and therefore can be ignored, as shown in formula (13):

[0035]

[0036] Steps (1-2) and (1-7) respectively yield the irradiance G of the front and back sides of the single- and double-sided photovoltaic modules under static sea conditions. F G R Therefore, the equivalent irradiance G of a single- or double-sided photovoltaic module under static sea conditions can be obtained using (1-1). E .

[0037] (2) Considering the influence of sea waves, we studied the tilt angle variation characteristics of photovoltaic modules installed on floating structures under different sea conditions and established a dynamic irradiance model for single and double-sided photovoltaic modules that considers the influence of sea wave motion.

[0038] Step (2) refers to using the Stokes wave theory, which is applicable to deep ocean areas (where wave steepness is greater), to study the impact of sea wave fluctuations on the dynamic irradiance of single- and double-sided photovoltaic modules. Specifically, it includes the following:

[0039] (2-1) Dynamic equivalent irradiance G of single- and double-sided photovoltaic modules E (t) Dynamic irradiance G from the front and back sides F (t), G R (t) and component bifaciality The decision is as shown in equation (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 horizontal plane of the ground under the action of ocean waves. F (t), β R (t) and the angle θ between sunlight and the normals of the inclined plates on the front and back sides. 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, the wave type is designed. The wave surface equation of the second-order Stokes wave is shown in equation (17):

[0045]

[0046] In equation (17), L is the wavelength; d is the water depth; H is the wave height; k is the wave number; and 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 second-order Stokes waves is calculated using equations (18)-(20). F (t), β R (t), taking the position partial derivative of the wavefront equation of a second-order Stokes wave and then taking the arctangent function, we can obtain the time-domain expression function of the wave tilt angle of a second-order Stokes wave, Δβ(t), which is as follows:

[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 normals of the inclined plates on the front and back sides. β,F (t), θ β,R (t), as shown in equations (21) and (22):

[0052]

[0053]

[0054] In the formula, ω is the geographical latitude, δ is the hour angle, and γ is the declination angle. F Let G be the orientation angle of the flat plate, with clockwise direction from north being positive. Finally, by substituting the results from equations (21), (22), and (18)-(20) into (14)-(16), the dynamic equivalent irradiance G of the bifacial photovoltaic module can be calculated. E (t).

[0055] The working principle of step (2): The irradiance received by the front and back tilted surfaces of the double-sided glass photovoltaic module and the solar angles β and θ βClosely related. Affected by sea waves, the floating structure in an offshore floating photovoltaic power station is constantly moving, which in turn affects the solar angle β(t) and θ of the bifacial glass photovoltaic modules installed on the floating structure. β (t) fluctuates continuously. Considering that when the size of the floating body is small relative to the wavelength of the wave, the motion of the floating body on the wave surface can be regarded as the motion of seawater particles on the wave surface, such as... Figure 3 As shown. Compared to the wavelength of ocean waves (30-50m), current offshore photovoltaic structure designs are mostly flexible structures formed by small-scale floating bodies connected flexibly, and their motion state is basically consistent with that of the waves. Therefore, this paper does not focus on specific floating body structures, but assumes that the floating body structure is a completely flexible floating body, that is, the change in tilt angle caused by the movement of the double-sided glass photovoltaic module with the waves is equal to the wave tilt angle, and based on this condition, the solar angle β(t) and θ of the double-sided glass photovoltaic module under the action of waves are calculated. β (t).

[0056] Waves are classified into linear waves and nonlinear waves. Linear wave theory, also known as micro-amplitude wave theory, is used to describe simple two-dimensional waves. Linear wave theory is only applicable to engineering problems involving waves with a relatively small wave height relative to their wavelength. Nonlinear waves have a wavefront shape that is an asymmetric curve with steep crests and narrow troughs. Several theories exist for studying nonlinear waves, with commonly used theories including cosine ellipse theory, solitary wave theory, and Stokes wave theory. Generally, cosine ellipse theory and solitary wave theory are suitable for shallow inland lakes, while Stokes wave theory is suitable for deep ocean waters (where waves are steeper). Second-order Stokes waves are considered to have high accuracy in simulating waves in finite-deep waters and are widely used in engineering applications.

[0057] (3) Analyze the time-varying differences in irradiance of photovoltaic modules installed at different spatial locations in a floating photovoltaic array at sea, and combine this with the irradiance variation characteristics G of the bifacial photovoltaic modules under the action of sea waves obtained in step (2). E (t), generating the irradiance distribution scene of a floating photovoltaic array at sea;

[0058] Step (3) is based on the installation method of the floating photovoltaic array at sea and the size W of the floating structure unit. i Based on the proportional relationship between the irradiance distribution of the floating photovoltaic array and the wave wavelength L, the irradiance distribution scenarios are divided into uniform irradiance scenarios and non-uniform irradiance scenarios. Different photovoltaic array irradiance distribution generation methods are adopted for different scenarios, as detailed below:

[0059] (3-1) In practical engineering applications, the topology of photovoltaic arrays 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, which is then connected to an inverter; when the 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 sea. At this time, the floating photovoltaic array works in a uniform irradiance scenario, that is, the irradiance of the floating photovoltaic array is the same as the irradiance G of the photovoltaic module generated in step (2). E (t) consistent;

[0060] (3-2) When the floating photovoltaic array is installed on i (i≥2) floating body structural units, the irradiance of the photovoltaic modules located on the same floating body unit in the floating photovoltaic array is consistent with the influence of sea wave fluctuations, while the irradiance of the photovoltaic modules located on different floating body structural units has a phase difference in the influence of sea wave fluctuations. At this time, the floating photovoltaic array is working in a non-uniform irradiance scenario.

[0061] In step (3-2), the floating photovoltaic array installed on i floating structural units is an s×p group (where s×p photovoltaic arrays are installed on i units). The irradiance of the photovoltaic modules on the wave-facing side of the array changes first. As time goes on, the waves continuously advance into the photovoltaic array, and the irradiance of the photovoltaic modules on the side away from the waves changes the most slowly. When the waves arrive, the irradiance of the photovoltaic modules at different spatial locations changes in the same trend over time, but the phases are different. Therefore, the method for generating the non-uniform irradiance distribution scene of the floating photovoltaic array is as follows:

[0062] First, based on the wave-facing floating body structural unit size W in the floating photovoltaic array i The proportional relationship between the irradiance and the wave wavelength L is used to calculate the time-varying phase difference Δθ of the photovoltaic modules installed in different floating structural units in the floating photovoltaic array at sea using equation (23). i :

[0063]

[0064] Secondly, using Δθ i Calculate the time-varying initial phase θ of the photovoltaic module irradiance installed on i floating units. i As shown in equation (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 ocean waves in step (2) E (t), generating the non-uniform irradiance scene G of a floating photovoltaic array at sea. E (t+θ1)-G E (t+θ i ).

[0067] (4) Establish an electrical model for a floating photovoltaic array at sea, combined with an irradiance distribution model G. E (t+θ1)-G E (t+θ i ), and ambient temperature information T em (t) simulates the PV curve of the floating photovoltaic array at each moment under the influence of sea waves. Based on the PV curve of the photovoltaic array, the maximum power output point of the floating photovoltaic array at each moment is found.

[0068] 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 and calculate the electrical performance of the bifacial photovoltaic module, which takes 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 equation (25), I ph For the photocurrent generated by the photovoltaic module, I d I is the diode current. sh I is the current flowing through the parallel resistance of the photovoltaic module. sat R 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, and R is the reverse saturation current of the photovoltaic module diode. sh R is the parallel resistance of the photovoltaic module. s q 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 cell temperature.

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

[0073]

[0074] In equation (26), V t =AKT / q is the diode thermal voltage, Ns N represents the number of serial-parallel components in a single group. p 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 equation (28):

[0079]

[0080] In equation (28), μ sc Let μ be the temperature coefficient of the short-circuit current. oc E is the open-circuit voltage temperature coefficient. g The bandgap width is 1.7936e-19J.

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

[0082] I ph,STC ≈I sc,STC (29)

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

[0084]

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

[0086]

[0087]

[0088]

[0089] (4-5) The key characteristic parameter I in the electrical model under non-STC is... ph I sat Vt Substituting into equations (25) and (26), the PV curve of the floating photovoltaic array at each moment under the influence of sea waves can be simulated. For the scenario of uniform irradiance, there is only one maximum power point in the PV curve of the 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 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 floating photovoltaic array at each moment in step (4). max Assess the annual power generation within the target sea area.

[0091] Step (5) specifically refers to:

[0092] (5-1) Theoretical power generation of a floating photovoltaic array at sea under uniform irradiance;

[0093] As can be seen from step (3), when the 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 floating photovoltaic array is working in a uniform irradiance scenario, that is, the irradiance of the floating photovoltaic array is the same as the irradiance G of the photovoltaic module generated in step (2). E (t) is consistent; therefore, in engineering, the components are usually arranged in a concentrated manner in the same floating unit, and the arrangement direction of the components is perpendicular to the direction of normal and strong waves in the sea area. This can eliminate the difference in irradiance of photovoltaic components connected to the same inverter to a certain extent, reduce the local power maximum point of the PV curve, and at this time, the floating photovoltaic array at sea is approximately working in a uniform irradiance scenario. At this time, the theoretical power generation of the floating photovoltaic array at sea is mainly determined by the change in irradiance G of the photovoltaic components under the action of sea waves. E (t) determines, that is:

[0094]

[0095] In the formula, CI represents the rated installed capacity of the photovoltaic array, in kilowatts (kW); G E (t) represents the instantaneous value of the equivalent irradiance received by the tilted surface of the photovoltaic array, in kilowatt-hours per square meter (kWh / m²). 2 G0 represents the irradiance under standard conditions, G0 = 1, and the unit is kilowatt-hours per square meter (kWh / m²). 2 ).

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

[0097] As can be seen from step (3), when the floating photovoltaic array is installed on i (i≥2) floating structural units, the irradiance of the photovoltaic modules located on the same floating structural unit in the floating photovoltaic array is consistent under the influence of wave fluctuations. The irradiance of the photovoltaic modules located on different floating structural units is affected by wave fluctuations with a phase difference. At this time, the floating photovoltaic array is working in a non-uniform irradiance scenario. Moreover, with the movement of waves, the irradiance and the trend of change of the modules in the photovoltaic string unit are inconsistent, which leads to the rapid and random change of the PV multi-peak curve of the photovoltaic string unit. 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 floating photovoltaic array at each moment in step (4), max Thus, the theoretical power generation of a floating photovoltaic array at sea under non-uniform irradiance conditions can be obtained, namely:

[0098]

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

[0100] Advantages of the present invention:

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

[0102] (2) Compared with the existing technology for simulating the irradiance of single and double-sided photovoltaic modules under a fixed tilt angle, this invention proposes to design wave types using multi-order Stokes waves as an example. By analyzing the influence of different wave levels on the tilt angle of photovoltaic modules, the irradiance variation curves of single and double-sided photovoltaic modules under different sea state levels are simulated.

[0103] (3) Compared with the existing methods for simulating the non-uniform irradiance distribution of photovoltaic arrays, the present invention takes into account that the non-uniformity of irradiance of floating photovoltaic arrays at sea is not only related to parameters such as wave direction, wave height, wavelength, and period, but also to the arrangement of photovoltaic arrays, and realizes a method for generating uniform and non-uniform irradiance distribution scenarios applicable to floating photovoltaic systems at sea.

[0104] (4) Based on the above-mentioned scenario of uneven irradiance generation of floating photovoltaic array at sea and the irradiance variation curve of photovoltaic module, the spatiotemporal variation characteristics of irradiance of floating photovoltaic power generation system at sea are simulated. Combined with the electrical model of photovoltaic array, this invention proposes a method to simulate the PV output characteristics of floating photovoltaic array at sea. (iv) Description of the attached drawings:

[0105] Figure 1 This is a flowchart illustrating a method for evaluating the power generation performance of a floating photovoltaic power generation system at sea, as described in this invention.

[0106] Figure 2 This is a schematic diagram of the irradiance model of a bifacial photovoltaic module for evaluating the power generation performance of a floating photovoltaic power generation system at sea, as described in this invention.

[0107] Figure 3 This is a schematic diagram illustrating the effect of ocean waves on the oscillation of photovoltaic modules around the Y-axis in a method for evaluating the power generation performance of a floating photovoltaic power generation system according to the present invention.

[0108] Figure 4 This is a schematic diagram of wave parameters and waveforms in a method for evaluating the power generation performance of a floating photovoltaic power generation system at sea, as described in this invention.

[0109] Figure 5 This is a schematic diagram of the uneven irradiance scenario of a floating photovoltaic array in a method for evaluating the power generation performance of a floating photovoltaic power generation system according to the present invention.

[0110] Figure 6 This is the electrical model of the floating photovoltaic array in the power generation performance evaluation method of the floating photovoltaic power generation system involved in this invention.

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

[0112] Figure 8 This is a schematic diagram of the PV curve variation under the non-uniform irradiance scenario of a floating photovoltaic array in the power generation performance evaluation method of a floating photovoltaic power generation system involved in this invention.

[0113] Figure 9 This is a year-round wave rose diagram for the target sea area in an embodiment of the present invention.

[0114] Figure 10 This is a schematic diagram of the irradiance variation of a floating photovoltaic array at sea under a uniform irradiance scenario, as described in an embodiment of the present invention.

[0115] Figure 11This is a schematic diagram of the irradiance of a floating photovoltaic array at sea under a non-uniform irradiance scenario, as described in an embodiment of the present invention. (V) Specific Implementation Methods:

[0116] Example: A method for evaluating the power generation performance of a floating photovoltaic power generation system at sea, such as... Figure 1 As shown, it is characterized by comprising the following steps:

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

[0118] (1-1) Static equivalent irradiance G of bifacial photovoltaic modules E Static irradiance G from the front and back F G R and component bifaciality The decision is as shown in formula (1):

[0119]

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

[0121]

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

[0123]

[0124] In equation (3), ω is the geographical latitude, δ is the hour angle, and γ is the declination angle. F The direction angle of the flat plate is positive when starting from north and rotating clockwise.

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

[0126] B h =ξ0I SC P m (4)

[0127] In equation (4), I SC The solar constant represents the amount of solar radiation received per unit area per unit time at the upper boundary of the Earth's atmosphere perpendicular to sunlight. In engineering calculations, it is typically taken as 1367 W / m². 2 P is the atmospheric transparency coefficient; m is the atmospheric optical quality, which represents the ratio of the actual distance that sunlight travels 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 equation (6), d n Number of days;

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

[0133]

[0134] (1-5) After solar radiation reaches the ground, the horizontal reflected irradiance G h Horizontal direct irradiance B h and horizontal scattered irradiance D h The sum of these factors and the influence 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 specific irradiance received on the back side of a bifacial photovoltaic module with a fixed tilt angle is shown in formula (9):

[0137]

[0138] In equation (9), the subscript R refers to the back side, and the irradiance G of the back side component is... R Calculation method and frontal irradiance G F Similarly, the orientation angle γ of the flat plate on the back sideR The dihedral angle β between the rear photovoltaic module and the horizontal plane of the ground R The angle θ between the sunlight and the normal to the inclined plate on the back side β,R The opposite of the front, 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 component b,R The acquisition of sunlight mainly occurs during sunrise or sunset, and the angle of incidence of direct sunlight is relatively large while the solar altitude angle is relatively small, therefore G b,R It is much smaller than the direct irradiance, generally less than 5% of the direct irradiance, and therefore can be ignored, as shown in formula (13):

[0143]

[0144] Steps (1-2) and (1-7) respectively yield the irradiance G of the front and back sides of the single- and double-sided photovoltaic modules under static sea conditions. F G R Therefore, the equivalent irradiance G of a single- or double-sided photovoltaic module under static sea conditions can be obtained using (1-1). E .

[0145] (2) Using Stokes wave theory, which is applicable to deep ocean areas (with steeper waves), to study the influence of sea wave fluctuations on the dynamic irradiance of single- and double-sided photovoltaic modules. Considering the influence of sea wave fluctuations, the tilt angle variation characteristics of photovoltaic modules installed on floating structures under different sea states are studied, and a dynamic irradiance model of single- and double-sided photovoltaic modules considering the influence of sea wave motion is established:

[0146] (2-1) Dynamic equivalent irradiance G of single- and double-sided photovoltaic modules E (t) Dynamic irradiance G from the front and back sides F (t), G R (t) and component bifaciality The decision is as shown in equation (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 horizontal plane of the ground under the action of ocean waves. F (t), β R (t) and the angle θ between sunlight and the normals of the inclined plates on the front and back sides. β,F (t), θ β,R (t) is determined as shown in equations (15) and (16);

[0149]

[0150]

[0151] (2-2) Taking second-order Stokes waves as an example, design ocean wave types, such as... Figure 4 As shown, the wave surface equation of a second-order Stokes wave is given by equation (17):

[0152]

[0153] In equation (17), L is the wavelength; d is the water depth; H is the wave height; k is the wave number; and 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 second-order Stokes waves is calculated using equations (18)-(20). F (t), β R (t), taking the position partial derivative of the wavefront equation of a second-order Stokes wave and then taking the arctangent function, we can obtain the time-domain expression function of the wave tilt angle of a second-order Stokes wave, Δβ(t), which is as follows:

[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 normals of the inclined plates on the front and back sides. β,F (t), θ β,R (t), as shown in equations (21) and (22):

[0159]

[0160]

[0161] In the formula, ω is the geographical latitude, δ is the hour angle, and γ is the declination angle. F Let G be the orientation angle of the flat plate, with clockwise direction from north being positive. Finally, by substituting the results from equations (21), (22), and (18)-(20) into (14)-(16), the dynamic equivalent irradiance G of the bifacial photovoltaic module can be calculated. E (t).

[0162] (3) Analyze the time-varying differences in irradiance of photovoltaic modules installed at different spatial locations in a floating photovoltaic array at sea, and combine this with the irradiance variation characteristics G of the bifacial photovoltaic modules under the action of sea waves obtained in step (2). E (t), generating an irradiance distribution scene for a floating photovoltaic array at sea; based on the installation method of the floating photovoltaic array at sea and the size W of the floating structure unit. i Based on the proportional relationship between the irradiance distribution of the floating photovoltaic array and the wave wavelength L, the irradiance distribution scenarios are divided into uniform irradiance scenarios and non-uniform irradiance scenarios. Different photovoltaic array irradiance distribution generation methods are adopted for different scenarios, as detailed below:

[0163] (3-1) In practical engineering applications, the topology of photovoltaic arrays 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, which is then connected to an inverter; when the 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 sea. At this time, the floating photovoltaic array works in a uniform irradiance scenario, that is, the irradiance of the floating photovoltaic array is the same as the irradiance G of the photovoltaic module generated in step (2). E (t) consistent;

[0164] (3-2) When the floating photovoltaic array is installed on i (i≥2) floating body structural units, the irradiance of the photovoltaic modules located on the same floating body unit in the floating photovoltaic array is consistent with the influence of sea wave fluctuations, while the irradiance of the photovoltaic modules located on different floating body structural units has a phase difference in the influence of sea wave fluctuations. At this time, the floating photovoltaic array is working in a non-uniform irradiance scenario.

[0165] In this embodiment, the floating photovoltaic array installed on i floating structural units is an s×p group (taking an s×p photovoltaic array installed on i (i≥2) floating units as an example). The irradiance distribution of the floating photovoltaic array is as follows. Figure 5As shown, the irradiance of photovoltaic modules on the wave-facing side of the photovoltaic array changes first. As time progresses, the waves continuously advance into the photovoltaic array, and the irradiance of photovoltaic modules on the side away from the waves changes the most slowly. When the waves arrive, the irradiance of photovoltaic modules at different spatial locations changes in the same trend over time, but the phases differ. Therefore, the method for generating the non-uniform irradiance distribution scenario of a floating photovoltaic array at sea is as follows:

[0166] First, based on the wave-facing floating body structural unit size W in the floating photovoltaic array i The proportional relationship between the irradiance and the wave wavelength L is used to calculate the time-varying phase difference Δθ of the photovoltaic modules installed in different floating structural units in the floating photovoltaic array at sea using equation (23). i :

[0167]

[0168] Secondly, the time-varying initial phase θ of the photovoltaic module irradiance installed on the i floating units is calculated using Δθi. i As shown in equation (24):

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

[0170] Finally, θi is substituted into the irradiance variation characteristic model G of the bifacial photovoltaic module under the action of ocean waves in step (2). E (t), generating the non-uniform irradiance scene G of a floating photovoltaic array at sea. E (t+θ1)-G E (t+θ i ).

[0171] (4) Establish an electrical model for a floating photovoltaic array at sea, combined with an irradiance distribution model G. E (t+θ1)-G E (t+θ i ), and ambient temperature information T em (t) simulates the PV curve of the floating photovoltaic array at each moment under the influence of sea waves. Based on the PV curve of the photovoltaic array, the maximum power output point of the floating photovoltaic array at each moment is found.

[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, balancing simplification and accuracy. The equivalent circuit is as follows: Figure 6As shown, the relevant mathematical model of photovoltaic cells based on the Shockley diode equation is specifically shown in formula (25):

[0173]

[0174] In equation (25), I ph For the photocurrent generated by the photovoltaic module, I d I is the diode current. sh I is the current flowing through the parallel resistance of the photovoltaic module. sat R 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, and R is the reverse saturation current of the photovoltaic module diode. sh R is the parallel resistance of the photovoltaic module. s q 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 cell temperature.

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

[0176]

[0177] In equation (26), V t =AKT / q is the diode thermal voltage, N s N represents the number of serial-parallel components in a single group. p 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 the standard test condition STC, the key parameters of the electrical model are as follows:

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

[0182]

[0183] In equation (28), μ sc Let μ be the temperature coefficient of the short-circuit current. oc E is the open-circuit voltage temperature coefficient. g The bandgap width is 1.7936e-19J.

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

[0185] I ph,STC ≈I sc,STC (29)

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

[0187]

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

[0189]

[0190]

[0191]

[0192] (4-5) The key characteristic parameter I in the electrical model under non-STC is... ph I sat V t Substituting into equations (25) and (26), the PV curve of the floating photovoltaic array at each moment under the influence of sea waves can be simulated. For a uniform irradiance scenario, there is only one maximum power point in the PV curve of the floating photovoltaic array at each moment, while for a non-uniform irradiance scenario, there are multiple local maximum power points, such as... Figure 7 As shown, and with the movement of the waves, the PV curve of the photovoltaic array changes rapidly and randomly, such as... Figure 8 As shown; by iterating through the PV curves, the maximum power output value P of the 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 floating photovoltaic array at each moment in step (4). max Assess the annual power generation in the target sea area:

[0194] (5-1) Theoretical power generation of a floating photovoltaic array at sea under uniform irradiance;

[0195] As can be seen from step (3), when the 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 floating photovoltaic array is working in a uniform irradiance scenario, that is, the irradiance of the floating photovoltaic array is the same as the irradiance G of the photovoltaic module generated in step (2). E (t) is consistent; therefore, in engineering, the components are usually arranged in a concentrated manner in the same floating unit, and the arrangement direction of the components is perpendicular to the direction of normal and strong waves in the sea area. This can eliminate the difference in irradiance of photovoltaic components connected to the same inverter to a certain extent, reduce the local power maximum point of the PV curve, and at this time, the floating photovoltaic array at sea is approximately working in a uniform irradiance scenario. At this time, the theoretical power generation of the floating photovoltaic array at sea is mainly determined by the change in irradiance G of the photovoltaic components under the action of sea waves. E (t) determines, that is:

[0196]

[0197] In the formula, CI represents the rated installed capacity of the photovoltaic array, in kilowatts (kW); G E (t) represents the instantaneous value of the equivalent irradiance received by the tilted surface of the photovoltaic array, in kilowatt-hours per square meter (kWh / m²). 2 G0 represents the irradiance under standard conditions, G0 = 1, and the unit is kilowatt-hours per square meter (kWh / m²). 2 ).

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

[0199] As can be seen from step (3), when the floating photovoltaic array is installed on i (i≥2) floating structural units, the irradiance of the photovoltaic modules located on the same floating structural unit is uniformly affected by the wave fluctuations, while the irradiance of the photovoltaic modules located on different floating structural units has a phase difference due to the wave fluctuations. At this time, the floating photovoltaic array operates in a non-uniform irradiance scenario. Moreover, with the movement of the waves, the irradiance and the trend of change of the modules within the photovoltaic string unit are inconsistent, resulting in rapid and random changes in the PV multi-peak curve of the photovoltaic string unit, such as... Figure 7 As shown. 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 floating photovoltaic array at each moment in step (4). max Thus, the theoretical power generation of a floating photovoltaic array at sea under non-uniform irradiance conditions can be obtained, namely:

[0200]

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

[0202] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. It should be noted that the embodiments described below are only some embodiments of the present invention, and not all embodiments. Where there is no conflict, the embodiments and features described in the present invention can be combined with each other.

[0203] Specifically, embodiments of the present invention provide a method for evaluating the power generation performance of a floating photovoltaic power generation system at sea, as shown in the attached figure. Figure 1 As shown, the method includes the following steps: calculating the irradiance change of single and double-sided photovoltaic modules in the target sea area under the influence of wave movement; constructing scenarios of uniform and non-uniform irradiance distribution of floating photovoltaic arrays at sea; simulating the PV curve change of floating photovoltaic arrays at sea under the influence of wave movement; and evaluating the annual power generation in the target sea area.

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

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

[0206] The impact of ocean wave activity on the installation angle of photovoltaic (PV) modules in the target sea area was calculated. Based on wave statistics of the target sea area, and using second-order Stokes waves to simulate waves in a finite-depth area, the influence of the annual ocean wave environment on the installation tilt angle of the PV modules, Δβ(t), was analyzed. Based on the static installation tilt angle β0 between the PV panel and the floating body, the dihedral angle β between the front and back of the PV module and the horizontal plane of the ground under the action of ocean waves was calculated. F (t), β R (t), the angle θ between sunlight and the normals of the tilted flat plates on the front and back sides of the photovoltaic module. β,F (t), θ β,R (t), as shown in formulas (18)-(22), where, ω is the geographical latitude, δ is the hour angle, and γ is the declination angle. F The direction angle of the flat plate is positive when starting from the north and moving clockwise.

[0207] The proposed irradiance model for floating bifacial photovoltaic (PV) modules at sea was used to calculate the irradiance variation characteristics of these modules under wave action in the target sea area. The Earth orbital eccentricity correction factor ξ0 and atmospheric optical mass m for the target sea area were calculated, and the solar constant I was obtained using local meteorological data. SC With atmospheric transparency coefficient P. Based on the photovoltaic module planar irradiance model, the annual and seasonal horizontal direct irradiance B is calculated according to formulas (4)-(8). h Horizontal scattered irradiance D h Horizontal reflected irradiance G h .

[0208] Using data on the tilt angle variation characteristics of bifacial photovoltaic modules installed on a floating structure under different sea conditions in the target sea area, and the horizontal direct irradiance B of the photovoltaic modules, this study investigated the effects of these tilt angle variations. h Horizontal scattered irradiance D h Horizontal reflected irradiance G h Furthermore, the irradiance G received by the front and back sides of the bifacial photovoltaic module under the influence of ocean wave motion in the target sea area is calculated using formulas (9)-(14). F (t), G R (t) and equivalent irradiance G E (t) change.

[0209] 102: Constructing scenarios with uniform and non-uniform irradiance distribution for floating photovoltaic arrays at sea;

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

[0211] When a floating photovoltaic array is installed on i (i≥2) floating structural units, it operates under non-uniform irradiance conditions. This is based on the wave-facing floating structural unit size W in the floating photovoltaic array. i The proportional relationship between the irradiance and the wave wavelength L allows for the calculation of the time-varying phase difference Δθ of the photovoltaic modules installed in different floating structural units within a floating photovoltaic array at sea. i As shown in equation (23). Secondly, using Δθ i Calculate the time-varying initial phase θ of the photovoltaic module irradiance installed on i floating units. iAs shown in equation (24). Finally, θ i Substituting into the irradiance variation characteristic model G of 101 bifacial photovoltaic modules under the action of ocean waves E (t), generating the non-uniform irradiance scene G of a floating photovoltaic array at sea. E (t+θ1)-G E (t+θ i ).

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

[0213] Using the electrical model of a floating photovoltaic array at sea, 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) simulates the PV curve of a floating photovoltaic array at each moment under the influence of ocean waves. To describe the electrical characteristics and power output of the photovoltaic array, an electrical model of the floating photovoltaic module is first established, and then the electrical models of the module are 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 bifacial photovoltaic modules, balancing 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 equation (28). μ sc Let μ be the temperature coefficient of the short-circuit current. oc E is the open-circuit voltage temperature coefficient. g The bandgap is 1.7936e-19J. The photocurrent I under standard test conditions. ph,STC Specifically, as shown in equation (29), the diode reverse saturation current I under standard test conditions sat,STC Specifically, as shown in equation (30).

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

[0217] The key characteristic parameter I in the electrical model under non-STC conditions ph I sat V t Substituting into equation (16) allows for the simulation of the PV curve of the floating photovoltaic array at each moment under the influence of ocean waves. By traversing the PV curve, the maximum power output value P of the floating photovoltaic array at each moment can be obtained. max .

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

[0219] The theoretical power generation of a floating photovoltaic array at sea under uniform irradiance. Typically, by centrally arranging the modules, the local power maxima on the PV curve are reduced, allowing the floating photovoltaic array to approximate a uniform irradiance scenario. The irradiance variation characteristic G of the bifacial photovoltaic module under wave action is calculated using 101. E (t), the theoretical power generation of the floating photovoltaic array at sea under uniform irradiance is calculated as shown in formula (34).

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

[0221] To verify the effectiveness of the method proposed in this invention, a simulation was conducted using a floating photovoltaic power generation system at sea as an example. Based on wave observation stations in the target sea area, regional wave statistics can be obtained, such as... Figure 9 As shown, the most common wave direction in this sea area is NE (northeast), with a frequency of 25.2%; the next most common wave direction is NNE (northeast-northeast), with a frequency of 17.3%; and the strongest wave direction is NNE (northeast-northeast), with a strong wave frequency of 0.6%. The floating photovoltaic array has a capacity of approximately 30kW. s For 26, N p The parameters of the bifacial photovoltaic module are shown in Table 1. Under uniform irradiance conditions, the irradiance variation curve of a floating photovoltaic array at an installation tilt angle of 15° over a certain period is shown in Table 1. Figure 10 As shown. Figure 10As shown, 0-10s represents the ideal situation (wave height H < 0.2m), 10-30s represents light waves (wave height H approximately 1m), 30-50s represents moderate waves (wave height H approximately 2m), and 50-70s represents large waves (wave height H approximately 4m). It can be seen that the irradiance received by the photovoltaic array changes more drastically with increasing wave fluctuations. Under non-uniform irradiance conditions, the irradiance distribution of a floating photovoltaic array at a certain moment with an installation tilt angle of 15° is shown below. Figure 11 As shown, the irradiance of photovoltaic modules at different phases varies, with the maximum difference in irradiance between modules at different phases approaching 600 W / m². 2 The peak and valley values ​​of irradiance are approximately 1000 W / m. 2 800W / m 2 600W / m 2 400W / m 2 In a non-uniform irradiance scenario, over a certain period of time, the multi-peak PV curve of the photovoltaic array changes rapidly and randomly with the movement of waves. max The range is between 13.82kW and 24.59kW, specifically as follows: Figure 8 As shown in the figure. Simulation calculations show that under the influence of ocean waves, the annual power generation in a uniform irradiance scenario is about 2.3% higher than that in a non-uniform irradiance scenario. Therefore, in engineering applications, it is necessary to investigate the wave conditions of the target sea area and reduce the occurrence of non-uniform irradiance scenarios by centrally arranging photovoltaic arrays, thereby increasing the power generation of offshore floating photovoltaic power generation systems.

[0222] Table 1 Parameters of Bifacial Photovoltaic Modules

[0223]

[0224]

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

Claims

1. A method for evaluating the power generation performance of a floating photovoltaic power generation system at sea, characterized in that... It includes the following steps: (1) Establish an irradiance model for single- and double-sided photovoltaic modules under static sea conditions; (2) Considering the influence of sea waves, the tilt angle variation characteristics of photovoltaic modules installed on the floating structure under different sea conditions are studied. A dynamic irradiance model of single and double-sided photovoltaic modules considering the influence of sea wave motion is established to obtain the irradiance variation characteristics G of double-sided photovoltaic modules under sea wave action. E (t); (3) Analyze the time-varying differences in irradiance of photovoltaic modules installed at different spatial locations in a floating photovoltaic array at sea, and combine this with the irradiance variation characteristics G of the bifacial photovoltaic modules under the action of sea waves obtained in step (2). E (t), generating the irradiance distribution scene of a floating photovoltaic array at sea; (4) Establish an electrical model for a floating photovoltaic array at sea, combined with an irradiance distribution model G. E (t+θ1)-G E (t+θ i ), where θ i The initial phase of the time-varying irradiance of the photovoltaic module, i = 1, 2, 3..., is related to the ambient temperature information T. em (t) simulates the PV curve of the floating photovoltaic array at each moment under the influence of sea waves. Based on the PV curve of the photovoltaic array, the maximum power output point P of the floating photovoltaic array at each moment is found. 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 floating photovoltaic array at each moment in step (4). max Assess the annual power generation within the target sea area.

2. The method for evaluating the power generation performance of a floating photovoltaic power generation system at sea according to claim 1, characterized in that... The installation tilt angle of the single- or double-sided photovoltaic modules in step (1) is fixed.

3. The method for evaluating the power generation performance of a floating photovoltaic power generation system according to claim 1, characterized in that... Step (1) of establishing the irradiance model of single and double-sided photovoltaic modules under static sea conditions specifically refers to: (1-1) Static equivalent irradiance G of bifacial photovoltaic modules E From the frontal static irradiance G F Static irradiation of the back side G R and component bifaciality The decision is as shown in formula (1): (1-2) The total solar radiation received by the front and back sides of a bifacial photovoltaic module includes three parts: direct radiation, diffuse radiation, and reflected radiation. The irradiance G received by the front side of a bifacial photovoltaic module with a fixed tilt angle is... F As shown in formula (2): In equation (2), the subscript F refers to the front side, and G... b,F G d,F G r,F These represent the direct irradiance, diffuse irradiance, and reflected irradiance on the tilted surface of the front photovoltaic module, respectively, in W / m². 2 B h D h G h These are, respectively, the direct horizontal irradiance, the horizontal diffuse irradiance, and the horizontal reflected irradiance; θ β,F β is the angle between the sunlight and the normal to the inclined plate. F The dihedral angle between the front photovoltaic module and the horizontal plane of the ground is defined as positive for south and negative for north, and should satisfy the relationship of formula (3): In equation (3), ω is the geographical latitude, δ is the hour angle, and γ is the declination angle. F The direction angle of the flat plate is positive when starting from north and rotating clockwise. (1-3) Horizontal direct irradiance B h Specifically: B h =ξ0I SC P m (4) In equation (4), I SC is the solar constant, representing the amount of solar radiation received per unit area per unit time at the upper boundary of the Earth's atmosphere perpendicular to sunlight; P is the atmospheric transparency coefficient; m is the atmospheric optical mass, representing the ratio of the actual distance sunlight travels 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 equation (6), d n Number of days; (1-4) Horizontal diffuse irradiance D h Generally, empirical calculation formulas based on actual measurements are used, as shown in formula (7), where α is the solar altitude angle; (1-5) After solar radiation reaches the ground, the horizontal reflected irradiance G h Horizontal direct irradiance B h and horizontal scattered irradiance D h The sum of these factors and the influence of the reflectance coefficient ρ, therefore, the horizontal reflected irradiance G h Specifically, as shown in formula (8); G h =ρ(B h +D h ) (8) (1-6) The specific irradiance received on the back side of a bifacial photovoltaic module with a fixed tilt angle is shown in formula (9); In equation (9), the subscript R refers to the back side, and the irradiance G of the back side component is... R Calculation method and frontal irradiance G F Similarly, the orientation angle γ of the flat plate on the back side R The dihedral angle β between the rear photovoltaic module and the horizontal plane of the ground R The angle θ between the sunlight and the normal to the inclined plate on the back side β,R The opposite of positive, that is; c R =180°-c F (10) β R ＝180°-β F (11) (1-7) Direct irradiance G on the inclined surface of the rear component b,R The acquisition of sunlight mainly occurs during sunrise or sunset, and the angle of incidence of direct sunlight is relatively large while the solar altitude angle is relatively small, resulting in G... b,R Much smaller than the direct frontal irradiance, it can be ignored; therefore, the static back irradiance G... R Rearranged into the form shown in formula (13): Steps (1-2) and (1-7) respectively yield the irradiance G of the front and back sides of the single- and double-sided photovoltaic modules under static sea conditions. F G R Therefore, the equivalent irradiance G of a single- or double-sided photovoltaic module under static sea conditions can be obtained using (1-1). E .

4. The method for evaluating the power generation performance of a floating photovoltaic power generation system at sea according to claim 1, characterized in that... Step (2) refers to using the Stokes wave theory, which is applicable to deep-sea areas with steep waves, to study the impact of sea wave fluctuations on the dynamic irradiance of single- and double-sided photovoltaic modules. Specifically, it includes the following: (2-1) Dynamic equivalent irradiance G of single- and double-sided photovoltaic modules E (t) From the frontal dynamic irradiance G F (t), Backside dynamic irradiance G R (t) and component bifaciality The decision is as shown in equation (14): The frontal dynamic irradiance G F (t) and back dynamic irradiance G R (t) The dynamic dihedral angle β between the front side of the double-sided glass photovoltaic module and the ground horizontal plane under the action of ocean waves. F (t), the dynamic dihedral angle β between the back side and the horizontal plane of the earth. R (t) Angle θ between sunlight and the normal to the inclined plate. β,F (t) and the angle θ between the sunlight and the normal to the inclined plate on the back side. β,R (t) is determined as shown in equations (15) and (16) respectively; In the formula, G b,F G d,F G r,F These are the direct irradiance, diffuse irradiance, and reflected irradiance on the tilted surface of the front photovoltaic module, respectively; G b,R G d,R G r,R These are the direct irradiance, diffuse irradiance, and reflected irradiance on the inclined surface of the rear component, respectively; B h D h G h These are, respectively, the direct horizontal irradiance, the horizontal diffuse irradiance, and the horizontal reflected irradiance; (2-2) Taking the second-order Stokes wave as an example, the wave type is designed. The wave surface equation of the second-order Stokes wave is shown in equation (17): In equation (17), L is the wavelength; d is the water depth; H is the wave height; k is the wave number; w is the wave circumferential frequency; η is the height of the wave surface; and x is the horizontal position of the wave in the coordinate system. (2-3) By taking the position partial derivative of the wavefront equation of the second-order Stokes wave in equation (17) and then taking the arctangent function, we can obtain the time-domain expression function Δβ(t) of the wave tilt angle of the second-order Stokes wave, which is as follows: Using the time-domain expression function Δβ(t) of the wave tilt angle of the second-order Stokes wave calculated by equation (18), and the initial installation dihedral angle β0 between the front side of the bifacial photovoltaic module and the horizontal ground plane, the dynamic dihedral angle β between the front side of the bifacial photovoltaic module and the horizontal ground plane under the action of the second-order Stokes wave can be calculated. F (t), the dynamic dihedral angle β between the back side and the horizontal plane of the earth. R (t), specifically: b F (t)=β0+Δβ(t) (19) b R (t)=π-β F (t) (20) (2-4) Utilizing the dynamic dihedral angle β between the front side of the bifacial photovoltaic module and the ground horizontal plane F (t) and the dynamic dihedral angle β between the back side and the horizontal ground plane. R (t), calculate the angle θ between the sunlight and the normal to the inclined plate. β,F The cosine value of (t) is cosθ β,F (t) and the angle θ between the sunlight and the normal to the inclined plate on the back side. β,R The cosine value of (t) is cosθ β,R (t), as shown in equations (21) and (22) respectively: In equations (21) and (22), ω is the geographical latitude, δ is the hour angle, and γ is the declination angle. F With γ R The front and back angles of the flat panel are defined as follows: clockwise direction from north is positive. Finally, by substituting the results of equations (21) and (22) obtained in step (2-4) and the results of equations (18)-(20) obtained in step (2-3) into formulas (14)-(16) in step (2-1), the dynamic equivalent irradiance G of the bifacial photovoltaic module can be calculated. E (t).

5. The method for evaluating the power generation performance of a floating photovoltaic power generation system according to claim 1, characterized in that... Step (3) specifically refers to: the installation method of the floating photovoltaic array at sea, and the size W of the floating structure unit. i Based on the proportional relationship between the irradiance distribution of the floating photovoltaic array and the wave wavelength L, the irradiance distribution scenario is divided into a uniform irradiance scenario and a non-uniform irradiance scenario. Different photovoltaic array irradiance distribution generation methods are used for each scenario, as detailed below: (3-1) In practical engineering applications, the topology of photovoltaic arrays 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, which is then connected to an inverter; when the 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 sea. At this time, the floating photovoltaic array works in a uniform irradiance scenario, that is, the irradiance of the floating photovoltaic array is the same as the irradiance G of the photovoltaic module generated in step (2). E (t) consistent; (3-2) When the floating photovoltaic array is installed on i floating structural units, the irradiance of the photovoltaic modules located on the same floating structural unit in the floating photovoltaic array is consistent with the influence of sea wave fluctuations, while the irradiance of the photovoltaic modules located on different floating structural units has a phase difference due to the influence of sea wave fluctuations. At this time, the floating photovoltaic array is working in a non-uniform irradiance scenario; where i≥2.

6. The method for evaluating the power generation performance of a floating photovoltaic power generation system according to claim 5, characterized in that... In step (3-2), the floating photovoltaic array installed on the i floating structural units is an s×p group. The irradiance of the photovoltaic modules on the wave-facing side of the 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 changes the most slowly. Therefore, the method for generating the non-uniform irradiance distribution scene of the floating photovoltaic array is as follows: First, based on the wave-facing floating body structural unit size W in the floating photovoltaic array i The proportional relationship between the irradiance and the wave wavelength L is used to calculate the time-varying phase difference Δθ of the photovoltaic modules installed in different floating structural units in the floating photovoltaic array at sea using equation (23). i : Secondly, using Δθ i Calculate the time-varying initial phase θ of the photovoltaic module irradiance installed on i floating structural units. i As shown in equation (24): θ1=0,θ2=θ1+Δθ1,θ3=θ2+Δθ2,.....θ i =θ i-1 +Dθi i-1 (24) Finally, θ i Substitute into the irradiance variation characteristic model G of the bifacial photovoltaic module under the action of ocean waves in step (2) E (t), generating the non-uniform irradiance scene G of a floating photovoltaic array at sea. E (t+θ1)-G E (t+θ i ).

7. The method for evaluating the power generation performance of a floating photovoltaic power generation system according to claim 1, characterized in that... Step (4) specifically refers to: (4-1) The relevant mathematical model of photovoltaic cells based on the Shockley diode equation is shown in Equation (25): In equation (25), I ph For the photocurrent generated by the photovoltaic module, I d I is the diode current. sh I is the current flowing through the parallel resistance of the photovoltaic module. sat R 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, and R is the reverse saturation current of the photovoltaic module diode. sh R is the parallel resistance of the photovoltaic module. s Where q is the series resistance of the photovoltaic module, A is the electron charge, K is the diode ideality factor, and T is the cell temperature. Equation (4-2) (25) is the mathematical model for the output current of a single photovoltaic module. For a photovoltaic array consisting of s photovoltaic modules connected in series to form a photovoltaic string, and p such strings connected in parallel, the output current I of the photovoltaic array is... s,p The mathematical model is shown in formula (26): In equation (26), V t =AKT / q is the diode thermal voltage, N s N represents the number of serial-parallel components in a single group. p The number of array groups connected in series and parallel; (4-3) The electrical mathematical model of the photovoltaic cell under the standard test condition STC can be obtained from formula (27). The variable subscript "STC" specifically refers to the value defined for the variable under the standard test condition; where the standard test condition STC refers to an irradiance of 1000W / m 2 The module cell temperature is 25℃ and the atmospheric mass is AM1.5; (4-4) Under the standard test condition (STC), the key parameters of the electrical model are as follows: Diode thermal voltage V under standard test conditions STC t,STC As shown in equation (28): In equation (28), μ sc Let μ be the temperature coefficient of the short-circuit current. oc E is the open-circuit voltage temperature coefficient. g For the bandgap width, T STC The standard test condition (STC) for photovoltaic modules is the operating temperature, typically 25℃; V oc,STC The open-circuit voltage of the photovoltaic module under standard test conditions (STC); Photocurrent I under standard test conditions STC ph,STC As shown in equation (29): I ph,STC ≈I sc,STC (29) Among them, I sc,STC This refers to the short-circuit current of the photovoltaic module under standard test conditions (STC). Diode reverse saturation current I under standard test conditions STC sat,STC As shown in equation (30): (4-5) Key parameters of the electrical model under standard test conditions STC and photovoltaic module temperature T em (t) and the equivalent irradiance G of the modules in the photovoltaic array E (t+θ i The key characteristic parameters in the electrical model under non-STC conditions can be calculated, as shown in formulas (31)-(33): (4-5) The key characteristic parameter I in the electrical model under non-standard test conditions STC is... ph I sat V t Substituting into equations (25) and (26), the PV curve of the floating photovoltaic array at each moment under the influence of sea waves can be simulated. For the scenario of uniform irradiance, there is only one maximum power point in the PV curve of the 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 floating photovoltaic array at each moment can be obtained. max .

8. The method for evaluating the power generation performance of a floating photovoltaic power generation system according to claim 1, characterized in that... Step (5) specifically refers to: (5-1) Theoretical power generation of a floating photovoltaic array at sea under uniform irradiance; In engineering practice, floating photovoltaic (PV) arrays typically employ a centralized arrangement of each PV module within the same floating structural unit, with the module orientation perpendicular to the direction of normal and strong waves in the sea area. This mitigates, to some extent, the irradiance differences among PV modules connected to the same inverter, reducing local power maxima on the PV curve. In this configuration, the floating PV array operates approximately under uniform irradiance, and its theoretical power generation E is [value missing]. MPP,i The main factor is the change in irradiance G of photovoltaic modules under the action of ocean waves. E (t) determines, that is: In the formula, CI represents the rated installed capacity of the photovoltaic array, in kilowatts; G E (t) represents the instantaneous value of the equivalent irradiance received by the tilted surface of the photovoltaic array, in kilowatt-hours per square meter; G0 represents 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 structural units is affected by the wave fluctuations and has a phase difference. At this time, the floating photovoltaic array at sea is working in a non-uniform irradiance scenario. Moreover, with the movement of the waves, the irradiance and the trend of the modules in the photovoltaic string unit are inconsistent, which leads to the rapid and random change of the PV multi-peak curve of the photovoltaic string unit. 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 floating photovoltaic array at each moment in step (4), the irradiance of the floating photovoltaic array at sea is affected by the wave fluctuations and has a phase difference. max Thus, the theoretical power generation of a floating photovoltaic array at sea under non-uniform irradiance conditions can be obtained, namely: In the formula, E out P represents the theoretical annual power generation of the photovoltaic power generation system, expressed in kilowatt-hours. max (t) represents the instantaneous value of the AC output power of the inverter, in kilowatts.

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