Substation roof photovoltaic array design method and photovoltaic power generation system

Abstract

The invention provides a transformer substation roof photovoltaic array design method and a photovoltaic power generation system, and relates to the technical field of new energy power generation and power systems. The method comprises the following steps: acquiring solar radiation data, calculating the total radiation stability of a horizontal plane, and entering a subsequent step if a preset threshold value is met; calculating the annual total solar radiation amount corresponding to different inclination angles of the location, selecting the inclination angle range with the annual total solar radiation amount meeting the maximum interval, and considering the roof area and the distance between the front row and the rear row to determine the optimal fixed inclination angle of the photovoltaic panel; determining the number of photovoltaic panels according to the relationship between the temperature of the photovoltaic panel selected material and the open-circuit voltage of the photovoltaic panel selected material; according to the latitude and longitude coordinates of the location and the local time, the solar altitude angle and the solar azimuth angle are obtained, and the photovoltaic panel spacing is determined; and arranging a photovoltaic panel array on the building roof of the power distribution device of the transformer substation according to the optimal fixed inclination angle of the photovoltaic panels, the number of the photovoltaic panels and the spacing of the photovoltaic panels. The photovoltaic power generation system is built based on the design method, and the technical feasibility and the economic optimality are both considered.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation and power system technology, and in particular to a design method for a rooftop photovoltaic array in a substation and a photovoltaic power generation system. Background Technology

[0002] Installing photovoltaic (PV) power generation systems on the rooftops of substation distribution buildings to supplement station power load and offset grid losses is a key step in building a green and efficient power grid. Currently, distributed PV capacity continues to grow, making its scientific design and benefit assessment increasingly important.

[0003] In existing technologies, research has optimized certain aspects of photovoltaic power generation, for example: Chinese invention patent with publication number CN118747422A discloses a method, device and electronic equipment for evaluating and selecting the location of photovoltaic panels. It provides a method for evaluating and selecting the location of photovoltaic panels, but does not consider the actual sunlight resources at the installation site, and does not provide a method or criterion for evaluating solar energy resources.

[0004] Chinese invention patent with publication number CN116992609A discloses a method for rapid deployment of photovoltaic power in mountainous areas based on GPU computing. It provides a method for rapid deployment of photovoltaic power in mountainous areas based on GPU computing to shorten the design calculation time of photovoltaic power stations. However, it only involves the spatial arrangement of photovoltaic panel supports and does not consider the installation tilt angle design of photovoltaic arrays, series and parallel connection, etc.

[0005] It is evident that existing technologies and research have significant shortcomings: most focus on a single aspect of photovoltaic power generation systems (such as module series connection and tilt angle selection), lacking a holistic, end-to-end design methodology encompassing resource assessment, equipment matching, array layout, grid connection, and life-cycle benefit analysis. Particularly for the specific scenario of substation rooftop photovoltaic power generation systems, with their limited area, unique structure, and clearly defined electricity load characteristics, a comprehensive system design scheme that perfectly matches these needs and simultaneously ensures technical feasibility and economic optimization is required. Summary of the Invention

[0006] Purpose of the invention: To propose a design method for a rooftop photovoltaic array in a substation, and further to propose a photovoltaic power generation system constructed using this design method. Within a limited roof area, by optimizing the tilt angle, spacing, and series-parallel connection design of the photovoltaic array, the system can maximize the utilization of solar radiation energy throughout the year, taking into account both technical feasibility and economic optimization.

[0007] To achieve the above objectives, the present invention provides a design method for a substation rooftop photovoltaic array, comprising the following steps: Obtain the latitude and longitude coordinates and solar radiation data of the location; The total solar radiation stability of the horizontal plane is calculated based on the solar radiation data. If the total solar radiation stability of the horizontal plane meets the preset threshold, the next step is performed; otherwise, the area is considered to have unstable solar radiation and is not suitable for development. Calculate the annual total solar radiation corresponding to different tilt angles at the location, select the tilt angle range that satisfies the maximum range of annual total solar radiation, and determine the optimal fixed tilt angle of photovoltaic panels by considering the roof area and the spacing between the front and rear rows. The number of photovoltaic panels is determined based on the relationship between the temperature of the materials used in the photovoltaic panel and their open-circuit voltage. Based on the latitude and longitude coordinates and local time, the solar altitude angle and solar azimuth angle are determined, and the spacing between photovoltaic panels is determined. Based on the optimal fixed tilt angle of the photovoltaic panels, the number of photovoltaic panels, and the spacing between the photovoltaic panels, a photovoltaic panel array is arranged on the roof of the substation power distribution equipment building.

[0008] As a preferred option, one or more meteorological software programs, such as Meteonorm, SAM, and HelioScope, are used to obtain local solar radiation data, which are then compared and verified with measured data from the nearest weather station.

[0009] As a preferred embodiment, the formula for calculating the total radiation stability (GHRS) of the horizontal plane is as follows:

[0010] In the formula, This indicates the minimum monthly solar radiation in the location; This indicates the maximum monthly solar radiation in the location.

[0011] As a preferred option, the photovoltaic panel is made of materials including monocrystalline silicon, polycrystalline silicon, cadmium telluride, and perovskite.

[0012] As a preferred option, the specific process for determining the number of photovoltaic panels includes: Calculate the actual operating temperature of the photovoltaic panel:

[0013] In the formula, This refers to the actual temperature of the photovoltaic panel. Ambient temperature; NOCT is the nominal operating temperature; G is the real-time irradiance. Calculate the upper limit of the number of photovoltaic panels N, assuming that the open-circuit voltage of the photovoltaic panel string does not exceed the maximum DC input voltage of the inverter at extreme low temperatures:

[0014] In the formula, N is the number of photovoltaic panels connected in series; This is the maximum allowable DC input voltage for the inverter; This is the open-circuit voltage of the photovoltaic panel; t represents the open-circuit voltage temperature coefficient of the photovoltaic panel; t represents the extreme low temperature. With the constraint that the operating voltage of the photovoltaic string at extreme high temperatures is within the range of the inverter's MPPT voltage, calculate the lower limit of the number of photovoltaic panels N:

[0015] In the formula, This represents the minimum MPPT voltage of the inverter. This represents the maximum MPPT voltage of the inverter. This refers to the operating voltage of the photovoltaic panel. Temperature coefficient of photovoltaic panel operating voltage; It is the extreme high temperature.

[0016] As a preferred option, the final number of photovoltaic panels is determined within the upper and lower limits of the number of photovoltaic panels N, taking into account the number of MPPT channels and the maximum number of input channels of the inverter.

[0017] As a preferred option, the specific process for determining the spacing between photovoltaic panels includes: Calculate the projected length L of the front-row photovoltaic array onto the back row:

[0018] In the formula, H is the height of the trailing edge of the photovoltaic array from the ground; The solar altitude angle is the angle between the direction of sunlight incidence and the horizontal plane. , The latitude of the location; The solar declination angle, Solar hour angle; Determine the minimum spacing D between the front and rear rows:

[0019] In the formula, L is the projected length of the front row of photovoltaic panels; The azimuth of the sun. .

[0020] As a preferred option, based on the calculated minimum spacing D, and considering the minimum safety and maintenance distances between each photovoltaic panel and between the photovoltaic panel array and the wall, the photovoltaic panels are arranged in a planar layout on the roof of the substation power distribution equipment building.

[0021] This invention proposes a substation rooftop photovoltaic power generation system, comprising a photovoltaic panel array arranged on the roof of the substation's power distribution building. The optimal fixed tilt angle, number of photovoltaic panels, and spacing of the photovoltaic panel array are all calculated based on the substation rooftop photovoltaic array design method disclosed above. The photovoltaic panel array is connected to an inverter, and the inverter output is directly connected to the substation's 380V station service AC bus via a feeder. When the photovoltaic power generation system's output power exceeds the substation's load, the surplus power is fed back to the grid through the station service transformer to offset grid losses. When the photovoltaic power generation system's output power is insufficient, the grid compensates for the shortfall through the station service transformer.

[0022] Beneficial Effects: This invention proposes a design method for a substation rooftop photovoltaic array and a photovoltaic power generation system. Based on local solar radiation data, it provides a GHRS-based solar radiation resource evaluation method and criteria, offering a scientific basis for the feasibility of photovoltaic project construction. Through a combination of software simulation and theoretical formula calculations, it provides design and collaborative optimization for key parameters such as photovoltaic devices and inverters, photovoltaic panel tilt angle, number of photovoltaic panel array groups, and photovoltaic panel array spacing. Within a limited roof area, by optimizing the tilt angle, spacing, and series-parallel design of the photovoltaic array, it achieves maximum utilization of annual solar radiation energy, balancing technical feasibility and economic optimization. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method of the present invention.

[0024] Figure 2 This is a schematic diagram illustrating the calculation of the photovoltaic panel array spacing in the embodiment. Detailed Implementation

[0025] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0026] This embodiment discloses a method and process for the overall design and comprehensive benefit evaluation of a substation rooftop photovoltaic power generation system, as shown in the attached document. Figure 1 As shown.

[0027] Step 1: Obtain the latitude and longitude coordinates of the location, use meteorological software (such as Meteonorm, SAM, HelioScope, etc.) to obtain solar radiation data of the project location, and compare and verify it with the measured data of the nearest meteorological station to ensure the reliability of the data.

[0028] Step 2: Obtain the average monthly solar radiation for the entire year in the location, and obtain the maximum monthly solar radiation (G). max ) and monthly minimum solar radiation (G min The total radiation stability (GHRS) of the horizontal plane is calculated as follows:

[0029] The criteria are as follows: when GHRS < 0.28, the region is considered to have unstable solar radiation; when 0.28 ≤ GHRS < 0.36, the region is considered to have moderate solar radiation, and neither region is suitable for solar energy resource development. When 0.36 ≤ GHRS < 0.47, the region is considered to have stable solar radiation; when GHRS ≥ 0.47, the region is considered to have very stable solar radiation, and the region is suitable for solar energy resource development and utilization.

[0030] Step 3: Select high-efficiency photovoltaic panel materials (monocrystalline silicon, polycrystalline silicon, cadmium telluride, perovskite) with low open-circuit voltage temperature coefficient and peak power temperature coefficient to reduce the impact of temperature changes on power generation performance; at the same time, select a suitable inverter to ensure that its output voltage waveform, amplitude, phase and frequency are consistent with the public power grid.

[0031] Step 4: Using PV syst software, simulate and calculate the annual total solar radiation of the tilted surface corresponding to different tilt angles (0° to 90°) at the project site. Select the tilt angle range that maximizes or nearly maximizes the annual total radiation. Taking into account the impact of roof area and the spacing between the front and rear rows on the total installed capacity, determine the optimal fixed tilt angle that balances power generation efficiency and installed capacity.

[0032] Step 5: Since the temperature of the photovoltaic panel affects the open-circuit voltage, the photovoltaic panel array needs to be designed.

[0033] a. Calculate the actual operating temperature of the photovoltaic panel under extreme high and low temperatures according to formula (1).

[0034]

[0035] This refers to the actual temperature of the photovoltaic panel. The ambient temperature is represented by NOCT, which is 45°C, and G is the real-time irradiance.

[0036] b. Based on formula (2), with the constraint that the open-circuit voltage of the string does not exceed the maximum DC input voltage of the inverter at extreme low temperatures, calculate the upper limit of the number of photovoltaic panels.

[0037]

[0038] N is the number of photovoltaic panels connected in series; This is the maximum allowable DC input voltage for the inverter; This is the open-circuit voltage of the photovoltaic panel; t represents the open-circuit voltage temperature coefficient of the photovoltaic panel; t represents the extreme low temperature.

[0039] c. Based on formula (3), with the constraint of ensuring that the working voltage of the string is within the range of the inverter MPPT voltage under extreme high temperature, calculate the lower limit of the number of photovoltaic panels.

[0040]

[0041] This represents the minimum MPPT voltage of the inverter. This represents the maximum MPPT voltage of the inverter. This refers to the operating voltage of the photovoltaic panel. Temperature coefficient of photovoltaic panel operating voltage; It is the extreme high temperature.

[0042] d. Within this range, determine the final number of photovoltaic panel arrays based on the inverter's MPPT (Multi-Level Photovoltaic Power) and maximum input number. Connect all strings to the selected string inverters, and directly connect the inverter outputs to the substation's 380V AC busbar via feeders. This system enables: when photovoltaic power generation exceeds the substation load, the surplus energy is fed back to the grid through the substation transformer to offset grid losses; when power generation is insufficient, the grid compensates for the shortfall through the substation transformer.

[0043] Step 6: Design the spacing between photovoltaic panel arrays.

[0044] a. Taking the extreme winter solstice in the Northern Hemisphere as the calculation scenario, calculate the projection length L of the front row photovoltaic array on the back row according to formulas (4) to (7), and then determine the minimum spacing D between the front and back rows, such as Figure 2 It is worth noting that a certain margin needs to be left on this basis when making actual arrangements.

[0045]

[0046]

[0047]

[0048]

[0049] The solar altitude angle is the angle between the direction of sunlight and the horizontal plane. The latitude of the project location; This is the solar declination angle, which is -23.45° on the winter solstice in the Northern Hemisphere. It is the solar hour angle, 0° at noon, positive in the morning and negative in the afternoon; The solar azimuth angle is the direction in which the sun is located. L is the projected length of the front row of photovoltaic panels; H is the height of the rear edge of the photovoltaic panel array from the ground; D is the spacing between the front and rear rows of photovoltaic panels.

[0050] b. Based on the above design results, considering the minimum safety and maintenance distances between components and between the array and the wall, the substation power distribution equipment building is arranged in a planar layout.

[0051] Step 7: Calculate the total power generation over the entire life cycle.

[0052] Using PV syst software, input parameters such as system efficiency, component first-year and annual degradation rates, and simulate the total power generation and annual power generation of the system throughout its entire life cycle.

[0053] Step 8: Calculate economic benefits.

[0054] Economic benefit calculation: Based on simulated power generation, unit investment cost, grid connection price / self-consumption price, carbon trading price, and operation and maintenance costs, calculate the project's annual revenue, cumulative revenue, dynamic investment payback period, and net profit, where:

[0055]

[0056]

[0057] Environmental benefit calculation: Based on the total power generation, and according to the standard coal consumption and pollutant emission coefficients, calculate the standard coal saved and the reduction in carbon dioxide, sulfur oxides and nitrogen oxides emissions during the project's entire life cycle.

[0058] The following uses a newly built 110kV substation in a certain city as an example, located at 31°N latitude and 120°E longitude, to specifically illustrate the invention.

[0059] Resource Analysis: Using Meteonorm software, the annual total solar radiation of the area is 1263.6 kWh / m², with the highest solar radiation in July at 541.6 MJ / m² and the lowest in January at 212.2 MJ / m². The calculated GHRS is 0.392, classifying it as a "stable" area B, suitable for development.

[0060] Equipment selection: 540Wp monocrystalline silicon modules and 70kW string inverter (output voltage frequency 50Hz, rated output voltage 220 / 380V) are selected.

[0061] Tilt Angle Selection: PV system simulations show that the maximum annual solar radiation is achieved at a tilt angle of 22°-25°, where the tilted surface receives the maximum total annual solar radiation. As the tilt angle of the photovoltaic array increases, the spacing between the front and rear rows of photovoltaic arrays must also increase, leading to a decrease in the total installed capacity within a limited site. Considering factors such as the total annual solar radiation of the tilted surface and the spacing between the front and rear rows, the photovoltaic array is installed facing due south, with a fixed installation tilt angle of 15°. The total annual solar radiation of the tilted surface is 1331 kWh / m².

[0062] Number of strings: Calculations show that under extreme low temperatures of -11.3℃ and extreme high temperatures of 41.2℃, the number of strings ranges from 5.8 to N, which is 20 modules per string. A total of 160 modules, totaling 86.4 kW, are connected in 8 strings to the aforementioned 70kW inverter. The system is connected to the 380V bus within the substation. This inverter has 6 MPPTs and can connect up to 12 strings, meeting the requirements.

[0063] Photovoltaic panel spacing: Based on the above photovoltaic panel fixed installation tilt angle of 15°, the length of a single module along the installation direction is 2279 mm, the number of rows of modules in the same array is 2, the solar hour angle is 45°, and the height of the front edge of the photovoltaic panel from the ground is 600 mm, the calculated spacing between the front and rear rows of photovoltaic panels is D=2356 mm. Considering a certain margin, the spacing between the front and rear rows of photovoltaic panels is taken as 2400 mm.

[0064] Power generation benefit assessment: The PV syst software was used to simulate the rooftop photovoltaic power generation project. The total efficiency of the photovoltaic power generation system is 0.82, with a 2% degradation in the first year and a 0.55% degradation in each subsequent year. The simulated total power generation over 25 years is 2.1547 million kWh.

[0065] Economic Benefit Assessment: The project has a total installed capacity of 86.4 kWp, with a unit investment cost of 5,000 yuan / kW and a total investment of 432,000 yuan. The electricity price is 0.7 yuan / kWh, the carbon trading price is 72.12 yuan / ton, and the annual operation and maintenance cost is 200 yuan / kW. Calculations show that over 25 years, the cumulative electricity cost savings will be 1,508,300 yuan, carbon trading revenue will be 126,500 yuan, and the total revenue will be 1,634,800 yuan. The dynamic investment payback period for the rooftop photovoltaic power generation system is 8.45 years. Over the planned 25-year lifespan, the net profit will be 770,800 yuan.

[0066] Environmental benefit assessment: Based on the coal consumption of the power generation group, it is calculated that every 1 kWh of electricity generated and fed to the grid requires 301 g of standard coal, and emits 814 g of carbon dioxide, 6.2 g of sulfur oxides (data before desulfurization), and 2.1 g of nitrogen oxides (data before denitrification). Over 25 years, the cumulative savings will be 648.56 tons of standard coal, a reduction of 1753.92 tons of carbon dioxide emissions, a reduction of 13.36 tons of sulfur oxide emissions, and a reduction of 4.52 tons of nitrogen oxide emissions.

[0067] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A design method for a rooftop photovoltaic array in a substation, characterized in that, Includes the following steps: Obtain the latitude and longitude coordinates and solar radiation data of the location; The total solar radiation stability of the horizontal plane is calculated based on the solar radiation data. If the total solar radiation stability of the horizontal plane meets the preset threshold, the next step is performed; otherwise, the area is considered to have unstable solar radiation and is not suitable for development. Calculate the annual total solar radiation corresponding to different tilt angles at the location, select the tilt angle range that satisfies the maximum range of annual total solar radiation, and determine the optimal fixed tilt angle of photovoltaic panels by considering the roof area and the spacing between the front and rear rows. The number of photovoltaic panels is determined based on the relationship between the temperature of the materials used in the photovoltaic panel and their open-circuit voltage. Based on the latitude and longitude coordinates and local time, the solar altitude angle and solar azimuth angle are determined, and the spacing between photovoltaic panels is determined. Based on the optimal fixed tilt angle of the photovoltaic panels, the number of photovoltaic panels, and the spacing between the photovoltaic panels, a photovoltaic panel array is arranged on the roof of the substation power distribution equipment building.

2. The substation rooftop photovoltaic array design method according to claim 1, characterized in that, Solar radiation data of the location was obtained using one or more meteorological software programs, such as Meteonorm, SAM, and HelioScope, and compared with the measured data from the nearest meteorological station for verification.

3. The substation rooftop photovoltaic array design method according to claim 1, characterized in that, The formula for calculating the total radiation stability (GHRS) of the horizontal plane is as follows: In the formula, This indicates the minimum monthly solar radiation in the location; This indicates the maximum monthly solar radiation in the location.

4. The substation rooftop photovoltaic array design method according to claim 1, characterized in that, The photovoltaic panels are made of materials including monocrystalline silicon, polycrystalline silicon, cadmium telluride, and perovskite.

5. The substation rooftop photovoltaic array design method according to claim 1, characterized in that, Determining the number of photovoltaic panels specifically includes: Calculate the actual operating temperature of the photovoltaic panel: In the formula, This refers to the actual temperature of the photovoltaic panel. Ambient temperature; NOCT is the nominal operating temperature; G is the real-time irradiance. Calculate the upper limit of the number of photovoltaic panels N, assuming that the open-circuit voltage of the photovoltaic panel string does not exceed the maximum DC input voltage of the inverter at extreme low temperatures: In the formula, N is the number of photovoltaic panels connected in series; This is the maximum allowable DC input voltage for the inverter; This is the open-circuit voltage of the photovoltaic panel; t represents the open-circuit voltage temperature coefficient of the photovoltaic panel; t represents the extreme low temperature. With the constraint that the operating voltage of the photovoltaic string at extreme high temperatures is within the range of the inverter's MPPT voltage, calculate the lower limit of the number of photovoltaic panels N: In the formula, This represents the minimum MPPT voltage of the inverter. This represents the maximum MPPT voltage of the inverter. This refers to the operating voltage of the photovoltaic panel. Temperature coefficient of photovoltaic panel operating voltage; It is the extreme high temperature.

6. The substation rooftop photovoltaic array design method according to claim 5, characterized in that, Within the upper and lower limits of the number of photovoltaic panels N, the final number of photovoltaic panels is determined by combining the number of MPPT channels and the maximum number of input channels of the inverter.

7. The substation rooftop photovoltaic array design method according to claim 1, characterized in that, Determining the spacing between photovoltaic panels specifically includes: Calculate the projected length L of the front-row photovoltaic array onto the back row: In the formula, H is the height of the trailing edge of the photovoltaic array from the ground; The solar altitude angle is the angle between the direction of sunlight incidence and the horizontal plane. , The latitude of the location; The solar declination angle, Solar hour angle; Determine the minimum spacing D between the front and rear rows: In the formula, L is the projected length of the front row of photovoltaic panels; The azimuth of the sun. .

8. The substation rooftop photovoltaic array design method according to claim 7, characterized in that, Based on the calculated minimum spacing D, and considering the minimum safety and maintenance distances between each photovoltaic panel and between the photovoltaic panel array and the wall, the substation power distribution equipment building is arranged in plan.

9. A rooftop photovoltaic power generation system for a substation, characterized in that, The photovoltaic array, which is arranged on the roof of the power distribution equipment building of the substation, is provided. The optimal fixed tilt angle, number of photovoltaic panels, and spacing of the photovoltaic array are all calculated according to the design method of the substation roof photovoltaic array according to any one of claims 1 to 8. The photovoltaic array is connected to the inverter, and the inverter output is directly connected to the 380V AC bus of the substation via a feeder. When the power generation of the photovoltaic power generation system is greater than the load in the station, the surplus power is fed back to the grid through the station transformer to offset the grid loss. When the power generation of the photovoltaic power generation system is insufficient, the grid makes up the shortfall through the station transformer.

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