Standard Analysis of Photovoltaic Bracket


Release time:

Sep 23,2022

Photovoltaic power generation technology with its clean, safe, rich resources and other advantages in the energy revolution gradually play an increasingly important role, the future will become one of the main forms of power supply in China.

Photovoltaic power generation technology with its clean, safe, rich resources and other advantages in the energy revolution gradually play an increasingly important role, the future will become one of the main forms of power supply in China.

 

Photovoltaic industry has become one of the few industries in China that can simultaneously participate in international competition and achieve a leading advantage in industrialization. The production capacity of many links in China's photovoltaic industry chain ranks first in the world, and the installed capacity ranks first in the world for seven consecutive years. Photovoltaic bracket is a supporting device designed to place, install and fix photovoltaic modules in photovoltaic systems.

Compared with the tracking system, the fixed PV bracket still occupies a major position in the global PV support structure market due to its advantages of lower cost, better stability and simple operation and maintenance, especially in China and India, two large PV installed countries, China's PV bracket market share is still above 80% in 2019.

 

As the structural support of the whole photovoltaic system, the bracket should not only bear the component's own load, wind load and snow load, but also bear the erosion of environmental stress such as moisture, light and temperature during its operation. The design life of photovoltaic power generation system is generally more than 25 years, so the quality of the bracket is very important for the long-term reliable operation of the photovoltaic system.

Scope of application

T/CPIA0013-2019 "Photovoltaic Bracket" specifies the relevant terms and definitions, product classification, product marking, raw material requirements (aluminum alloy, steel and hardware, composite), product requirements (appearance, dimensional deviation, allowable slenderness ratio, structural or component deformation requirements, corrosion protection, environmental durability and fire protection requirements of composite support), test methods, inspection rules, marking, packaging, transportation and storage, etc.

This standard is applicable to ground-mounted photovoltaic brackets, including fixed brackets and fixed tilt adjustable brackets. The ground-mounted photovoltaic support in this standard refers to the photovoltaic support directly installed on the surface of plains, mountains, beaches, lakes, etc., excluding the photovoltaic support installed on buildings, but the photovoltaic support used for flat roof installation can be implemented by reference.

The fixed bracket refers to a photovoltaic bracket that usually takes the inclination angle at which the photovoltaic module obtains the largest amount of solar radiation in a year as the installation inclination angle, and the inclination angle is fixed. The fixed tilt angle adjustable bracket refers to the photovoltaic bracket whose tilt angle can be manually adjusted for a limited number of times according to the maximum solar radiation obtained by the photovoltaic module in different time periods.

In addition, according to the material division, the standard is applicable to steel bracket, aluminum alloy bracket and composite bracket.

Analysis of standard points

Dimensional deviation

Whether it is a steel bracket, an aluminum alloy bracket or a composite bracket, the wall thickness of the bracket rod is the basis for ensuring the structural strength of the bracket. Therefore, it is stipulated that the wall thickness of the bracket rod should not have a negative tolerance.

In order to make full use of the solar energy, the structure of the photovoltaic bracket after assembly should be as close to the design value as possible to ensure that the photovoltaic module is at the best inclination angle and the structure is stable and beautiful.

The dimensional deviation in this standard refers to the deviation from the design value after the bracket is pre-assembled before leaving the factory. For the fixed bracket, four key indicators are selected: installation inclination angle, bracket beam elevation, bracket column surface, and rod center line; for the tilt angle adjustable bracket, the deviation between the adjustment angle and the set value (adjustment accuracy) is additionally specified.

Allowable slenderness ratio of members

If the slenderness ratio of the component is too large, it will cause eccentricity due to its own weight deformation, it is easy to bend during transportation and installation, and large vibration occurs under the action of dynamic load, so the slenderness ratio of the component needs to be limited. The adverse effect caused by insufficient stiffness of compression members is far more serious than that of tension members, so the allowable slenderness ratio of compression members is generally smaller than that of tension members (the smaller the allowable slenderness ratio, the higher the deformation resistance). The allowable slenderness ratio of steel bracket components in this standard is determined according to 6.8.9 of the GB50797-2012 Design Code for Photovoltaic Power Stations. The allowable slenderness ratio of aluminum alloy bracket components is determined according to 4.5.4 and 4.5.5 of the GB50429-2007 Design Code for Aluminum Alloy Structures. Composite bracket components are determined according to experience and with reference to the minimum allowable slenderness ratio of steel bracket and aluminum alloy bracket components.

Structural stability (deformation requirements)

The structural stability of the PV bracket was evaluated by static load deformation test. According to the different direction of the load applied on the component plane, it is divided into two types: the vertical horizontal plane static load deformation test and the vertical component surface static load deformation test, with the former being the main one. During the vertical horizontal static load deformation test, the surface load is uniformly applied on the component plane as shown in Figure 1, and the direction is downward along the normal line of the horizontal plane. The surface load value is the standard value of snow load, the unit is kN/m2, and the duration is 1h.

Observe and record the reading of the displacement measuring instrument and the deformation of the specimen. During the vertical assembly surface static load deformation test, the bracket is installed on a fixed inclined surface table with an inclination angle α, α is the installation inclination angle of the bracket assembly, and the surface load is uniformly applied on the assembly plane as shown in Figure 2, with the direction upward along the normal line of the assembly plane, and the surface load value is the standard value of wind load in kN/m2 for 1h. Observe and record the reading of the displacement measuring instrument and the deformation of the specimen.

For fixed supports, the displacement of the column top shall not be greater than 1/60 of the column height; for fixed tilt adjustable supports, the displacement of the column top shall not be greater than 1/80 of the column height.

 

 

The deflection of the bending member is the key to ensure the stability of the overall structure of the bracket. According to the provisions of GB50797-20126.8.8 and GB50429-20074.4.1, the allowable deflection value of the main beam of the steel bracket and the aluminum alloy bracket is l/250, and the allowable deflection value of the secondary beam is l/250 (installation of frameless photovoltaic modules) and l/200 (installation of other components). The allowable deflection values of flexural members in this standard are determined with reference to the above design specifications and in combination with actual project experience.

Anti-corrosion

The design life of the photovoltaic system is generally 25 years, and the photovoltaic bracket is placed outdoors for a long time to withstand the wind, sun and rain. At present, the materials used for photovoltaic support mainly include steel, aluminum alloy and composite materials.

As the most widely used type, steel bracket is also the most prone to corrosion, so anti-corrosion treatment must be carried out. For carbon structural steel low-alloy high-strength structural steel, alloy structural steel and other steel brackets, hot-dip galvanizing is usually used for corrosion protection.

The standard ensures the corrosion resistance of the steel bracket through the thickness of the galvanized layer and the salt spray corrosion resistance test. The minimum thickness of the galvanized layer is given according to different application scenarios, and the time and protection rating requirements for copper accelerated acetic acid salt spray corrosion test are specified for weak corrosion environment, medium corrosion environment and strong corrosion environment (Table 1).

Table 1 Requirements for Salt Spray Corrosion Resistance of Steel Bracket

Corrosion grade Neutral salt spray test time/h Protection Rating RP
weak corrosion 96 ≥ 9
Moderate corrosion 240 ≥ 9
strong corrosion 480 ≥ 9

 

Aluminum alloy profile surface anti-corrosion treatment technology mainly adopts anodic oxidation method for surface treatment. The standard is aimed at the application environment of three different corrosion levels of weak corrosion, medium corrosion and strong corrosion, and gives the minimum thickness of the surface treatment layer of aluminum alloy profiles and the time and protection rating requirements for copper accelerated acetic acid salt spray corrosion test (Table 2) to ensure the long-term corrosion resistance of aluminum alloy brackets.

Table 2 Salt spray corrosion resistance of aluminum alloy bracket

Corrosion grade Copper accelerated acetic acid salt spray test time/h Protection ratingRP
weak corrosion 32 ≥ 9
Moderate corrosion 56 ≥ 9
strong corrosion 72 ≥ 9

 

The composite material support is generally made of fiber reinforced composite materials, such as polyester glass fiber reinforced plastic, epoxy glass fiber reinforced plastic, phenolic glass fiber reinforced plastic, etc., which has excellent corrosion resistance. However, polymer matrix composites are easy to age, so for composite scaffolds, water resistance test, alkali resistance test, ultraviolet durability test and freeze-thaw cycle durability test requirements are proposed according to the existing GB/T31539-2015 "Structural Fiber Reinforced Composite Materials pultruded profiles" to ensure the long-term environmental durability of composite scaffolds.

Fire protection requirements for composite supports

During the operation of photovoltaic power generation system, arc may be generated and there is a fire hazard, so the polymer matrix composite support is required to have a certain degree of flame retardancy. The standard selects two indicators of combustion performance and glow wire finished product test to ensure the flame retardancy of composite materials.

The combustion performance shall conform to the HB level requirements specified in 8.4 of GB/T2408-2008-Determination of Flammability of Plastics by Horizontal and Vertical Methods.

Glow wire finished product test should comply with GB/T5169.11-2017 "electrical and electronic products fire hazard test part 11: Glow wire/hot wire basic test method Glow wire flammability test method of finished product (GWEPT)", the test temperature is 750 ℃. According to the actual test situation, the composite support that meets the two indicators of combustion performance and glow wire finished product test has excellent flame retardancy, can meet the fire protection requirements of photovoltaic system applications, and can reduce the rapid spread of fire.

Standard implementation significance and future prospects

The formulation of T/CPIA0013-2019 is based on ensuring the safe and reliable operation of the photovoltaic system, based on the principles of scientific rationality and operability, and based on the technical level of domestic photovoltaic bracket design and production, it is the first group standard on bracket products in China's photovoltaic industry.

The formulation of this standard provides a technical basis for reducing the assembly error of photovoltaic support, ensuring the overall carrying capacity of the support, improving the anti-corrosion ability (or environmental durability) of the support, and ensuring the quality level of photovoltaic support products.

In 2019, for photovoltaic tin-coated solder tape, ethylene-vinyl acetate copolymer (EVA) adhesive film, copolyolefin (PO) adhesive film and other three photovoltaic material products to carry out the standard and user-end promotion catalog work, in promoting the implementation of standards, improve product quality, brand building and other aspects to achieve obvious results.

In the next step, based on T/CPIA0013-2019, we will carry out the work of benchmarking and standard catalogue of photovoltaic support, comprehensively promote the quality improvement of photovoltaic support products, build a bridge of quality assurance for the upstream and downstream of the industrial chain, reduce the cost of product selection, and provide guarantee for the low-cost and high-quality development of photovoltaic industry.

Source: Network Resources

 

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