Structural design and simulation analysis of fixed adjustable photovoltaic support

Abstract

In order to respond to the national goal of “carbon neutralization” and make more rational and effective use of photovoltaic resources, combined with the actual photovoltaic substation project, a fixed adjustable photovoltaic support structure design is designed. By comparing the advantages and disadvantages of the existing support, an innovative optimization design is proposed, and the mechanical structure of the support is analyzed by ANASYS to check the rationality of the design. Saving construction materials and reducing construction costs provide a basis for the reasonable design of photovoltaic power station supports, and also provide a reference for the structural design of fixed and adjustable supports.

Keywords

Photovoltaic support design finite element analysis structural design carbon neutralization

1. Introduction

At the general debate of the 75th session of the General Assembly on September 22, 2020, President Xi Jinping proposed that China should strive to peak its carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060. The plan is to achieve carbon neutrality by 2060. According to the calculations of the Global Energy Internet Partnership, in order to achieve the goal of carbon neutrality, the share of wind power and photovoltaic in China’s total energy generation needs to increase from 8.7% in 2019 to 66% in 2050, representing an 8-fold increase. The development of China’s photovoltaic industry is the most rapid, as of the end of 2020, China’s cumulative grid-connected photovoltaic installed capacity of 253.43 GW to further develop the photovoltaic industry, China proposed to optimize the layout of solar energy development, priority development of distributed photovoltaic power generation plan, planning to the end of 2020 distributed photovoltaic accounted for about 55% of installed solar power. Compared with new power generation technologies such as wind power, biomass power and nuclear power, photovoltaic power generation is a renewable energy generation technology with the most desirable characteristics for sustainable development. Solar energy resources are inexhaustible, available everywhere, can be close to the power supply, no need for long-distance transmission, avoiding the loss of power caused by long-distance transmission lines. Secondly, the energy conversion process of photovoltaic power generation is simple, it is a direct conversion from light energy to electrical energy, there is no intermediate process and mechanical movement, there is no mechanical wear and tear. Photovoltaic power generation itself does not use fuel, does not emit any substances including greenhouse gases and other exhaust gases, does not pollute the air, does not produce noise, is friendly to the environment, does not suffer the impact caused by the energy crisis or the instability of the fuel market, and is a new renewable energy source that is truly green and environmentally friendly. The photovoltaic power generation process does not require cooling water and can be installed on the desert Gobi where there is no water. Photovoltaic power generation can also be easily combined with buildings to form an integrated photovoltaic building power generation system, which does not require separate land occupation and can save valuable land resources. The service life of PV power generation system is more than 30 years, and the solar cell module has a simple structure, small volume and light weight, which is easy to transport and install. The construction period of photovoltaic power generation system is short, and the capacity can be large or small according to the electricity load, so it is convenient and flexible, and extremely easy to combine and expand the capacity.

To achieve the goal of carbon peak, carbon neutral, the core is to achieve two alternatives, that is, in the energy consumption side to achieve the replacement of fossil energy with electricity, in the energy production side to achieve renewable energy generation instead of fossil energy generation, so it is expected that in the power generation side, the future demand for installed photovoltaic will be rapidly increased. Low carbon emission reduction, the development of new energy mainly photovoltaic energy is of great significance.

The most widely used distributed photovoltaic power generation system is built on the rooftop of urban buildings, which must be connected to the public grid power supply is a standard for green buildings, not only to reduce the pressure of the public grid power supply, but also to reduce the cost of electricity for the user. Usually, in the construction of such large photovoltaic power generation projects, the construction and installation costs of photovoltaic mounts account for about 21% of the total investment in the entire project, so a suitable mount structure can significantly save processing costs and post-maintenance costs. The structure form of PV mounting can be usually divided into two categories: fixed tilt type and tracking type. Compared with tracking type PV mounting, fixed tilt type PV mounting has the characteristics of good stability, easy installation and low price. In the tracking type bracket related technology has not reached a very high level, the domestic substation construction projects are mostly installed with fixed tilt type PV bracket [1], because the tilt angle of fixed tilt type PV bracket can not be adjusted according to the local solar energy resources, so it can not maximize its effectiveness, resulting in a large amount of wasted resources.

The provincial government of Jiangsu Province wants to take the lead in achieving the deployment of carbon peaks, in accordance with the “carbon peak, carbon neutral” action plan of the State Grid Corporation, in order to accelerate the construction of clean, low-carbon, safe and efficient power grid, the construction branch of Jiangsu Electric Power Co.

Ltd. is responsible for the management of the province’s 500 kV and above power grid infrastructure. As one of the specific measures to respond to the action plan of “Carbon Peak, Carbon Neutral”, this project takes the 500 kV substation construction project, which is the most widely used in the company’s work, as the main body of the research, and takes the new energy and new technology more easily used in the engineering temporary area as the entry point, based on the current standardization of 500 kV substation engineering temporary facilities in Jiangsu. On the basis of the standardized construction of 500 kV substation projects in Jiangsu province, the project is studied in the direction of “zero carbon”, this project focuses on the “zero carbon” target direction, with emphasis on the design of PV support structure for distributed PV power generation system. The fixed adjustable photovoltaic bracket designed in this project aims to save the construction cost by manual adjustment, and to improve the power generation capacity of the PV substation by adjusting the tilt angle to a suitable angle several times a year according to the solar resource situation of the substation location. The construction and installation cost of the PV racking accounts for about one-fifth [2] of the investment cost of the whole project, and the success of its racking design is of great significance to the smooth development of the project, so it is necessary to simulate and analyze the racking structure before putting it into construction.

The project proposes to carry out the design derivation of the PV bracket structure scheme, and after selecting the optimal design scheme, focus on the calibration analysis of the main supporting components of the fixed adjustable bracket, using the network cutting of the model and the degradation of the model degradation, to conduct a comprehensive analysis of its mechanical properties, simulate and analyze the force state of the bracket under various loads, and carry out the calibration analysis of the key parts for its installation stability. The calibration analysis is carried out for the key parts. Finally, by comparing the parameters influenced by the force performance of each component, the structural design is optimized to improve the safety and stability of the bracket, while saving construction materials and reducing construction costs, providing a basis for the reasonable design of the bracket of the PV power plant and also providing a reference for the structural design of the fixed adjustable bracket.

2. Current status of domestic and international research

2.1 PV bracket development and fixed adjustable bracket research status

The PV bracket is a support structure for PV modules, which adopts the form of above-ground steel structure and is designed to have a service life of 25 years. The main force members consist of crossbeams, inclined beams, inclined braces and steel columns. The fixed adjustable PV mount studied in this project is a mount system that can continuously adjust the angle between the PV panel and the ground according to the change of sunlight irradiation angle in different seasons and different regions after installation in terms of orientation and angle. Scholars at home and abroad focus their research on the structure of PV mounts mainly on structural optimization, because the structural optimization of mounts can greatly reduce the engineering cost of the foundation construction part. Usually, the research approach is to establish the computational theoretical method according to the requirements of PV mounting design specifications, and to optimize the final design by using the relevant optimization design procedures to derive the optimal numerical simulation.

The earliest research on photovoltaics began with the “photovoltaic effect”, which was discovered by the French scientist Becqurel discovered in the 19th century that light causes a potential difference between inhomogeneous semiconductors or different parts of the semiconductor-metal bond [3]. This phenomenon is known as the “photovoltaic effect”. The American scientists Chapin and Pearson made the first practical monocrystalline silicon solar cells in Bell Labs in the United States, and in 1954, photovoltaic power generation technology was created. Compared with domestic, foreign countries in the mid-20th century has formed a certain range of photovoltaic power generation system, while scholars also began to care about how to ensure the safety of the equipment while working properly. In 1960, Brosens conducted a study on the wind resistance and stability of photovoltaic system mounts, and at the same time [4]. Hoyer also put forward the same view on wind response. After the 1980s [5], J.A. obtained a design solution to reduce the wind response of PV modules by wind tunnel experiments [6]. Koteras. J.R. used the finite element method to calculate the displacement and stress inclination errors of PV mounting systems under wind loads, and also analyzed The force effects were analyzed [7]. While Naeeni. N. studied the wind load patterns at different angles and wind speeds. The more developed PV mounting systems were formed in the 1990s, i.e. Grassl and Chwieduk D studied the introduction of common design forms of solar mounting structures. JM Barker, J Shingleton, and JC Underwood [8] investigated an improved solution for PV panel support assemblies in 1993, which consisted of a single selectively operable actuator to rotate all panels simultaneously with the same angular displacement. Based on the safety and stability of well-established PV mounting systems, in the 21st century, foreign research has focused more on structural improvements to existing PV mounts to enable PV systems to adapt to different weather and terrain conditions while being as cost effective as possible. In the last 20 years, research has focused on the optimization of PV mounting systems [9]. Hausner Martin and Schletter Ludwig present a design proposal for a mounting system for the assembly of photovoltaic zone-free module brackets in the form of a permanently adjustable support bracket in the form of a triangular truss, as well as a method for a mounting system for the assembly of support brackets for photovoltaic open space installations [10]. In the same periodM Hausner andL Schletter also conducted research on bracket mounting, proposing in 2013 a mounting system for PV open-space mounting brackets and a method for assembling this type of mounting system that facilitates the generation of solar energy for PV devices in open spaces with linear bearings. And nowadays, foreign research has shifted from the fixed tilt type to the more costly tracking type, which is ahead of the domestic research in tracking type PV mounts.

Compared with the research in foreign developed countries, the domestic research on fixed adjustable PV mounts started late, and most of the preliminary research was mainly focused on the structural design and application level of PV mounts. From the structural form of fixed adjustable PV bracket is mainly divided into three types: push-pull rod type, semi-circular arc type and jack type [11]. The composition of the bracket structure mainly includes structural beams, inclined beams, inclined braces, columns, support systems, connectors and fixings. The form is relatively simple and only needs to be modified on the basis of the original fixed bracket structure, while taking into account the advantages of strong wind stability of the fixed bracket and high average daily power generation of the trackingbracket [12].

Jian Shi and Aning Li [13] conducted the first study on seasonal adjustable mounts (seasonal condition mounts), based on the characteristics of seasonal changes in solar altitude angle in Xinbei District, Changzhou, and obtained the optimal tilt angle of the mounts in different seasons. It was concluded that the application research of fixed adjustable PV mounts in China was initiated. By establishing a solar radiation database and optimizing the height angle of PV plant mounts, Ju Zhenhe [14] studied a 10 MW grid-connected power plant in Shenyang area to improve the power generation efficiency of the PV plant, and obtained the highest economic benefit by adjusting the tilt angle four times a year through economic and technical analysis. Mou Juan [15] further studied on this basis, using the control variable method to analyze the effect of different latitudes and altitudes on the radiation output of PV mounts. Through the economic benefit analysis, it was suggested that adjustable mounts (adjusted 4 times a year) should be used in areas with high latitude, high altitude and low land cost, and fixed mounts with the best angle should be used in areas with low latitude and low altitude. It provides an important reference for the economic benefit analysis of fixed adjustable PV mounts in other regions.

2.2 Status of domestic structural optimization design and simulation analysis research

With the continuous research on photovoltaic brackets, the optimal design of the structure is particularly important to ensure the structural stability of fixed adjustable brackets. Compared with the traditional design, the optimized design of the structure can reduce the overall project cost by 5% to 30% compared with the traditional design [16]. The optimized design of the engineering structure can be divided into section (or size) optimization, shape optimization, topology optimization, layout optimization and type optimization according to the difficulty of the study. Commonly used structural optimization design paths are PKPM, SAP2000 and ANSYS [14].

The domestic structural optimization design for fixed adjustable PV bracket was first proposed by Chen Yuan [17] in 2013, taking the domestic code as a guide and also referring to the foreign design code requirements,analyzing from the economic perspective of PV bracket structure design, establishing the theoretical method of PV bracket structure calculation, and developing the related optimization design procedure, which provides the theoretical basis for the subsequent optimization design of PV bracket structure. Yongjun Zhao [18] used SAP2000 and ANSYS for numerical simulation and analysis to analyze and optimize some components of the bracket, integrated the two optimization methods of zero-order and first-order of ANSYS for verification, and obtained the best optimization results of the bracket structure. Yang Tao, Fan Jiuchen et al. [19] completed a project of Science and Technology Development Plan of Jilin Science and Technology Bureau in cooperation with Liaoning Hongyanhe Nuclear Power Co. In the course of executing the project, a design process of column-type dual-axis light-tracking bracket structure was proposed, And the finite element model was established by the conceptual modeling method of finite element software ANSYS Workbench, and the stress and displacement clouds were derived, and the maximum stress was found and compared with the yield stress of the material to find the most material-saving practice, which reduced the design cost to some extent.The expression of the mathematical model for structural optimization in an optimal design solution, which is often adjusted only for specific parameters, is generally as follow [20]:

$\displaystyle\textit{Objective function}:F(X)\to\min,X={\{}X1,X2\ldots,Xn{\}}$ (1) $\displaystyle\textit{satisfy the conditions}:hi(X)=0,i={\{}1,2\ldots,p{\}}$ (2) $\displaystyle gi(X)\leqslant 0,j={\{}1,2\ldots,m{\}}$ (3)

where $X$ is the design variable; $F(X)$ is the objective function, and $hi(X)$ and $gi(X)$ are the constraints.

PV mounts are usually at a certain angle to the ground, and wind becomes an important factor affecting the stability of the mounts. Both the requirement of bracket strength in downwind and the requirement of bracket resistance to overturning in upwind are the basic requirements for the structural design of PV brackets. Therefore, the reasonable wind load taking value in the numerical simulation analysis is the key to the optimal design of PV bracket. Zengping Guo [21] further explores the optimal design of PV brackets based on previous studies, and through simulation and testing, it is concluded that the current optimal design of PV bracket structure takes the wind load value of 42 meters per second as appropriate. Chunpeng Wang [22] taking 76 m ${}^{2}$ solar PV system bracket as the research object, the bracket structure was optimized by comparing the wind load design codes of China, Japan and the United States, and simulating the windward side of the research object with the hydrodynamic calculation software, so that the weight of the optimized north bracket was reduced by more than 50%, which provides a reference for the design and optimization of the fixed adjustable PV bracket structure. Hongxing Teo [23] studied the coefficient taking problem of PV square array bracket structure under wind load, proposed a reasonable bracket structure load taking method, and assembled the standard units formed after optimization into standard unit combinations, which in turn formed a standardized product library, and combined with the existing structure design software, the optimal solution selected quickly and improved the efficiency of the whole process. Ying Zhao [24] studied the differential yield analysis of the economic inclination angle, height above ground, and optimal capacity ratio of photovoltaic power generation system in combination with actual engineering projects, so as to improve the project revenue by optimizing the system design.

3. Project overview

The project is located in Sheyang County, Yancheng City, Jiangsu Province, where the average value of climatic average total solar radiation from January to December 1961–2008 is 4832 MJ/(m ${}^{2}$ .a) [25], which is a region rich in terrestrial energy resources in Jiangsu Province and suitable for laying PV mounts on a large area. The elevation of Sheyang area is about 2 m, the building site category is II, the seismic intensity is 7 degrees, the design basic seismic acceleration value is 0.10 g, the response spectrum characteristic period is 0.4 s. The maximum wind speed range of the construction site is 32.7 $\sim$ 36.9 m/s. The project constructs 500 kV temporary substation and lays down the floor bracket.

4. Design solutions for brackets

There are five types of PV mounts in PV projects: fixed mounts, fixed adjustable mounts, flat single-axis tracking mounts, inclined single-axis tracking mounts and dual-axis tracking mounts. The cost of the equipment is 0.35, 0.5, 0.7, 1.0, 1.4 Yuan/Wp. The Tianjin Panshan PV project is calculated to cost 0.2769 Yuan/k Wh if 35 ${}^{\circ}$ fixed bracket is used. The cost of power generation is about 0.2778 Yuan/k Wh, which is 0.31% higher; the cost of power generation is about 0.3023 Yuan/k Wh, which is 9.17% higher; the cost of power generation is about 0.3236 Yuan/k Wh, which is 16.86% higher, if a double-axis tracking bracket is used.

From the above calculation and analysis, although the use of fixed adjustable brackets and tracking brackets can significantly improve the power generation of PV power plants, but, due to the significant increase in equipment investment costs and land costs, converted to the cost of power generation, if the tracking bracket is used, the cost of power generation will increase rather than decrease, if the fixed adjustable bracket is used, the cost of power generation will slightly decrease. If we take into account the higher height of the tracking bracket, higher cleaning and maintenance difficulties, resulting in increased operation and maintenance costs, higher self-consumption of electricity and higher failure rate, the economy of using tracking brackets will be even lower.

Combined with the situation of this project, we decided to design the most cost-effective fixed adjustable bracket. The fixed part is toward the base of the adjustment mechanism toward the adjustment base. Adjustable part is there are three parts, one is the jack adjustment mechanism, including the bracket – jack connection flange and jack shear – base plate used to adjust the angle of the photovoltaic plate, the second is the photovoltaic plate bracket mechanism, using the pin fixed hole way to adjust, toward the adjustable angle range of 0 ${}^{\circ}$ $\sim$ 30 ${}^{\circ}$ . Third, the orientation adjustment mechanism of the orientation adjustment disc, rotating mounted on the fixed base by connecting bearings, the fixed base is provided with a limit hole, the orientation adjustment disc is connected with a rotating limit mechanism, the rotating limit mechanism matches the limit hole and can adjust the bracket direction.

In order to facilitate the disassembly of photovoltaic panels, can be reused, while improving the angle adjustment freedom of the photovoltaic panels, the project design mechanism uses a shear jack structure, the use of pin fixing holes to adjust the direction of the adjustable angle range of 0 ${}^{\circ}$ $\sim$ 30 ${}^{\circ}$ , greatly improving the utilization of solar energy photovoltaic panels.

As shown in Figs 1 and 2, the design bracket structure is mainly composed of three major parts: PV bracket structure, jack adjustment structure and orientation adjustment structure.

Figure 1.

Design structure 1.

Figure 2.

Design structure 2.

PV panel bracket mechanism, as shown in Figs 3 and 4, by setting locking screws and fixing pins on both sides of the PV panel bracket clamping left and PV panel bracket clamping right, it ensures the convenience of PV panel installation while better ensuring the stability of the installation. Its size is 2350 mm long and 2000 mm wide, and it can install 2 pieces of 430 w monocrystalline silicon photovoltaic panels, and fix the photovoltaic panels through the bracket clamping structure with the fixing pins.

Figure 3.

Photovoltaic panel bracket structure 1.

Figure 4.

Photovoltaic panel bracket structure 2.

The directional adjustment structure, as shown in Fig. 5. Fixed in the flat ground, the jack adjustment structure and the orientation adjustment structure is relatively fixed, when the orientation adjustment structure towards the angle adjustment, the jack adjustment structure then rotate, the rotation limit mechanism of the orientation adjustment mechanism, the use of only through the handle to limit the pin upwards, in the photovoltaic plate to adjust to the appropriate angle, release the handle, through the spring return force makes the pin inserted into the lower limit hole can It is more convenient to use. In addition, the bottom of the bracket structure is provided with an orientation adjustment mechanism, which can be more convenient to achieve the adjustment of the orientation of the photovoltaic panel in the horizontal direction.

In terms of material selection, solar mounts require steel with strong tensile strength to make the structure more secure and reliable. In addition, the higher the yield point of steel, the smaller the cross-section, the more material and cost savings. China’s solar PV mounts are mainly made of light structural steel and carbon structural steel. The former is suitable for small-scale PV projects and the latter is suitable for large-scale PV projects. After comparing several papers of the same type, this project is suitable for carbon structural steel. The tensile strength and bending strength values of Q235B steel are 375 MPa and 235 MPa, which is also the commonly used structural steel in bracket design, corrosion resistant and with strong load bearing stability.

In order to reduce costs, the design does not have a motor, for manual adjustment, adjustment structure in the design process to minimize the screw fixing method, easy to disassemble, conducive to recycling. Jack and photovoltaic bracket contact point for the key strength check calculation part.

Figure 5.

Jack structure and orientation adjustment structure diagram.

5. Load calculation

5.1 Permanent load

The permanent load consists of two parts of the PV module and the PV bracket self-weight, the project uses model CEC6-72 monocrystalline wafer, a single PV module weight 24.2 kg. PV module single self-weight 24.2 kg, Gsingle component $=$ 0.237 KN, bracket weight 349.51 kg, Gsteel bracket $=$ 3.425 kn, bracket supported by the PV module part of the surface area S $=$ 2 * 2.35 $=$ 4.7 m ${}^{2}$ . Permanent load G $=$ (2Gsingle component $+$ Gsteel bracket)/S $=$ 0.829 kN/m ${}^{2}$ .

5.2 Snow load

According to GB 50009-2012 “Code of Structural Loads for Buildings” [26], the standard formula for snow load calculation is $s_{k}=\mu_{r}s_{0}$ , where $s_{0}$ is the basic snow load, the 50-year basic snow load value recorded in Sheyang where the project is located is 0.2 kN/m ${}^{2}$ , and $\mu_{r}$ , the snow distribution coefficient, the project takes the value of 0.8. snow load standard value ${}_{k}$ $=$ 0.8 $\times$ 0.2 $=$ 0.16 kN/m ${}^{2}$ .

5.3 Wind load

According to GB 50009-2012 “Code for Structural Loads of Buildings”, the standard formula for wind load calculation is $W_{k}=\beta_{z}\mu_{s}\mu_{z}w_{0}$ , we can check that the basic wind pressure of the project location in 50 years, $w_{0}$ take the value of 0.4 kN/m ${}^{2}$ . $\beta_{z}$ , the vibration wind coefficient take the value of 1.0, the roughness of the ground of the solar photovoltaic power station is B class, the distance of the top of the bracket from the ground is less than 5 m, refer to the table of design specifications, $\mu_{z}$ , the wind pressure height change factor take the value of 1.09, $\mu_{s}$ , wind load body type coefficient, take the value of 1.3. $W+k=$ 1 $\times$ 1.3 $\times$ 1.09 $\times$ 0.40 $=$ 0.55 kN/m ${}^{2}$ .

5.4 Combined load

Photovoltaic bracket in the use of the process is not only subject to a load pressure, bad weather will be subject to wind and snow double load pressure, so to consider the combination of load, according to GB 50009-2012 “building structure load code”, the combination of load calculation standard formula is $F=1.2G_{1}\cos\theta+1.4W_{k}\sin\theta+1.4\times 0.7s_{k}$ , bringing in the permanent load, wind load and snow load of the project location to get $F=1.2\times 0.829+1.4\times 0.55+1.4\times 0.7\times 0.16=$ 1.92 kN/m ${}^{2}$ .

The maximum force surface that the PV panel will come into contact with is 4.7 m ${}^{2}$ . The worst case that the bracket will bear is the combined load of $F=$ 9034 N, that is, the ultimate force that the PV panel will receive is 9034 N. Then use the finite element analysis tool to analyze and calculate the structural deformation in the most extreme case, and if the simulation value in this case meets the design requirements, the rest of the case will certainly meet the requirements.

6. PV bracket structure strength calculation

The strength calculation of PV bracket structure is divided into three modules, and the modules are divided into PV bracket panel structure, jack adjustment structure and orientation adjustment structure according to the structure. The PV bracket panel design of this project is further improved on the basis of the beam unit, so the analysis type refers to the beam unit combination analysis, the material is structural steel, its Poisson’s ratio is $v=$ 0.3, the elastic modulus $E=$ 2e05 MPa, after using digital simulation to finely divide the mesh, restrain the degrees of freedom of the part connected with the bracket panel and the jack, and apply a combined load of $F=$ 9034 N to the frame involved in fixing the solar PV panel. After applying a combined load of $F=$ 9034 N to the bracket panel, the static structural analysis was carried out, and the analysis results are shown in Figs 6 and 7.

Representation of the picture in the form of a data table is shown in Table 1.

Table 1
Static mechanical analysis of photovoltaic support structure

Structure	Displacement value max.	Minimum displacement value	Minimum stress	Maximum stress
Photovoltaic racking panel	0.32036 mm	0.06849 mm	0.016631 Mpa	21.811 Mpa

Figure 6.

Photovoltaic support panel displacement diagram.

The key parameters in the finite element analysis are the maximum displacement value and stress value of the bracket. The displacement value can determine the size of the deformation, and the data of the stress value corresponds to the maximum force that the structure is subjected to. Steel deformation within 0.2% can be restored to the original, more than 0.2% deformation can not be restored to the original steel scrap, do the simulation analysis of the bracket force. It can be known whether the design meets the requirements, if the design of the selected materials and material thickness is not appropriate, will cause a large amount of maintenance costs later.

According to the information in Table 1, the maximum deformation of the photovoltaic support panel is 0.32036 mm, and the maximum deformation occurs in the middle of the panel, which is connected with the jack part and also the center of gravity of the structure. The deformation volume meets the practical requirements. The maximum stress is concentrated in the middle edge on both sides, about 22 Mpa, the structural steel allowable stress is: 235/1.4 (safety factor) $=$ 168 MPa; ultimate stress is 235 MPa, the value is less than the maximum bearing capacity limit of the material, and the part of the structure to ensure the safety of the actual project using part of the separate analysis, the calculated value will be larger than the actual value, the large value In line with the design requirements, the actual use of safe and stable.

The jack adjusting structure is the main supporting part of this design, the screw nut material is selected as 45 steel, the pin is made of 50 steel, and the rest of the material selection is mainly Q235 structural steel, with a turbo ratio of 0.3 and a modulus of elasticity of 200 GPa, whose load case is affected by its own gravity, the PV module and the PV panel gravity. Considering the extreme condition case, the combined load is applied with the uppermost connection panel, and after restraining the fixed base and jack to adjust the two ends of the screw degrees of freedom, the analysis results are shown in Figs 8 and 9.

Representation of the picture in the form of a data table is shown in Table 2.

Table 2

Static mechanical analysis of the jack structure

Structure	Displacement value max.	Minimum displacement value	Minimum stress	Maximum stress
Jack	2.7575 mm	0 mm	4.4125e-7 Mpa	75.274 Mpa

Figure 7.

Photovoltaic support panel stress diagram.

Figure 8.

Jack structure displacement diagram.

Figure 9.

Jack structure stress diagram.

According to the information in Table 2, the maximum displacement of the jack structure part is 2.7575 mm, the maximum deformation is located in the top plate, the deformation of the structure in addition to the top plate and the two jack shear upper plate structure part linked below.

Figure 10.

Base displacement diagram.

Figure 11.

Stress diagram of the base.

Table 3

Static mechanical analysis of the base structure

Structure	Displacement value max.	Minimum displacement value	Minimum stress	Maximum stress
Base	2.5281 mm	0 mm	2.1454e-7 Mpa	2.1454e-7 Mpa

From Fig. 9 can be seen that the jack adjusting screw to bear a larger load, is the main stress bearing parts, the maximum stress is concentrated in the jack shear part and each part of the connection part of 75.274 Mpa, the same use of partial split analysis, the large value is less than the maximum load bearing limit of the material, in line with the design requirements.

The base part is made of cast iron with high wear resistance and good machinability, density of 7 340 kg/m ${}^{3}$ , modulus of elasticity is 120 GPa, Poisson’s ratio is 0. 25. If partial analysis is used for this part of the structure, the difference between the value and the actual is too large due to the distance from the main load-bearing support, and there is no reference value. Therefore, the whole analysis is adopted, and the analysis results are shown in Figs 10 and 11 after the base is fixed and restrained to the ground connection part and the combined load is applied.

Representation of the picture in the form of a data table is shown in Table 3.

According to the information in Table 3, the maximum displacement of the base structure part is 2.5281 mm, the maximum deformation is located towards the edge of the adjustment support surface, and the part supported by the base connection structure.

It can be seen from Fig. 11 that the base bears the same maximum and minimum stress with a small value of 2.1454e-7 Mpa, which is uniformly distributed among the four seats. The maximum load bearing limit of cast iron is 200 MPa, the value is much smaller than the maximum load bearing limit of the material, in line with the design requirements.

The fasteners of the design structure are M10 bolts and nuts, which are international standard parts with nominal tensile strength of 800 MPa, yield strength of 640 MPa, shear force $=$ (0.6 $\sim$ 0.8)*800 MPa $=$ 480 $\sim$ 640 MPa. The stress cross-sectional area of M10 bolts is 58 mm ${}^{2}$ , and the calculated ultimate force of the fasteners is 37120 N, while the bracket as a whole will The maximum force is $F=$ 9034 N, which is much less than the ultimate stress of the fastener and meets the design requirements.

7. Summary and outlook

At present, the main ways of domestic structure design are: online numerical simulation analysis and experimental research. As the numerical simulation design in the pre-design stage, its reasonable and reliable analysis can truly reflect the stress situation of different material structures, provide reliable data reference, shrink the design cycle, reduce the waste of material caused by modification in the later stage, and improve the overall process efficiency. In the field of PV bracket design, the stress analysis of the bracket is a necessary part of the whole engineering design. This paper designs a fixed adjustable PV bracket structure according to the actual project and performs finite element analysis on the main structure of the bracket, the analysis process considers the bracket application scenario and multiple load application, and the load under the limit condition is applied to the bracket for comprehensive numerical analysis. The analysis process considers the bracket application scenario and multiple load application, applies the load under ultimate conditions to the bracket for comprehensive numerical analysis, and the analysis results refer to the "Table of Allowable Stress and Modulus of Elasticity of Commonly Used Steel in China" to compare the yield stress of the material, check the design conforms to the specification, ensure the design is safe and reliable, and provide reference for the design of fixed adjustable bracket structure and online digital simulation. The article only analyzes the online digital simulation part, the complete analysis also includes the experimental research part, and the later work will focus on the actual model feasibility study.

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Structural design and simulation analysis of fixed adjustable photovoltaic support

Abstract

Keywords

1. Introduction

2. Current status of domestic and international research

2.1 PV bracket development and fixed adjustable bracket research status

2.2 Status of domestic structural optimization design and simulation analysis research

4. Design solutions for brackets

5.1 Permanent load

5.2 Snow load

5.3 Wind load

5.4 Combined load

6. PV bracket structure strength calculation

Table 1 Static mechanical analysis of photovoltaic support structure

References

Table 1
Static mechanical analysis of photovoltaic support structure