Distributed photovoltaic (PV) power generation specifically refers to PV power generation facilities built near user sites, operating with the user's own consumption of generated electricity and surplus electricity fed into the grid, and characterized by balancing and regulating the power distribution system. Distributed PV power generation follows the principles of adapting to local conditions, clean and efficient operation, decentralized layout, and local utilization, making full use of local solar energy resources to replace and reduce fossil fuel consumption.
The most widely used distributed photovoltaic (PV) power generation system currently is the PV power generation project built on the rooftops of urban buildings. This type of project must be connected to the public power grid to supply electricity to nearby users.
What does distributed photovoltaic (PV) power generation equipment include?
The basic configuration of distributed photovoltaic power generation equipment includes: solar panels, inverters, brackets, cables and installation accessories, etc. Large power plants also require other auxiliary equipment such as transformers and distribution cabinets.
Technical requirements for main equipment in distributed photovoltaic power stations:
I. Photovoltaic support system
The roof support system uses hot-dip galvanized carbon steel brackets, and the components are installed on aluminum alloy purlins using back plates or clamps. Fasteners are made of stainless steel. The support system is designed to withstand winds of 30 meters per second, ensuring long-term outdoor use.
1. Material and performance requirements:
1) Material requirements: The main steel structure material is Q235B, and the welding rod is E43 series welding rod.
2) Mechanical performance requirements: The tensile strength, elongation, yield point, cold bending test and other mechanical performance requirements of the selected steel structural materials must comply with the relevant provisions of "Carbon Structural Steel" (GB/T700-2007).
3) Chemical composition requirements: The content of chemical elements such as carbon, sulfur, and phosphorus in the main steel structure materials selected must comply with the relevant provisions of "Carbon Structural Steel" (GB/T700-2007).
2. Rust removal methods and rust removal grade requirements
1) Steel components must undergo surface treatment. The rust removal method and rust removal grade shall comply with the relevant provisions of the current national standard "Rust Grades and Rust Removal Grades of Steel Surfaces Before Painting" (GB8923-88).
2) Rust removal methods: Steel components can be rust removed by sandblasting or shot blasting. If chemical rust removal is used, a treatment liquid with two or more functions such as rust removal, phosphating and passivation should be selected, and its quality should meet the requirements of the current national standard "General Technical Conditions for Multifunctional Steel Surface Treatment Liquid" (GB/T 12612-2005).
3) Rust removal grade: The rust removal grade should meet the Sa2 1/2 requirement.
3. Corrosion prevention requirements:
1) Steel components are protected against corrosion using a metal protective layer. All steel structure supports are hot-dip galvanized. The hot-dip galvanizing must meet the relevant requirements of "Technical Requirements and Test Methods for Hot-Dip Galvanized Coatings of Steel Components with Metallic Coatings" (GB/T13912-2002), and the thickness of the galvanized layer shall not be less than 80μm.
2) Zinc plating thickness test: The zinc plating thickness shall be tested in accordance with the methods provided in "Technical Requirements and Test Methods for Hot-dip Galvanized Coatings of Steel Components".
3) Hot-dip galvanizing anti-deformation measures: Adopt a reasonable anti-deformation galvanizing scheme to prevent the components from undergoing significant deformation after hot-dip galvanizing.
4. Aluminum alloy material
1) Material requirements: The material is generally selected as 6061 or 6063, etc.
2) Mechanical performance requirements: The quality, chemical composition, and mechanical properties of the selected aluminum profiles must comply with the relevant provisions of GB5237.1.
3) Surface treatment must meet the technical requirements and comply with GB5237.2-2004 "Aluminum Alloy Building Profiles Part 2: Anodized and Colored Profiles".
4) The appearance quality of the profiles shall conform to the requirements of GB5237.2-2004. The surface of the profiles shall be clean and smooth, and serious defects such as cracks, peeling, corrosion and bubbles shall not be allowed.
II. Cement Foundation
The cement foundation uses grade C30/20 and undergoes a 20-day curing period. Reinforcing bars or embedded parts are added to the dimensions according to the design drawings.
III. Photovoltaic Modules
1. The service life of photovoltaic modules under normal conditions shall not be less than 25 years, and the module power standard shall strictly comply with the relevant requirements of TUV IEC61215 and IEC61730. The output power shall not be less than 80% of the standard power within the 25-year service life.
2. The power of a single polycrystalline silicon module provided shall not be less than 255W. Simultaneously, the photovoltaic module should have a high area ratio, with a power-to-area ratio of not less than 143.5W/m². The power-to-weight ratio should be greater than 12W/kg, and the fill factor (FF) should be greater than 0.70.
3. The module uses Grade A standard cell packaging (EL imaging shows no defects), the cell surface of the module has a uniform color, no mechanical damage, and no oxide spots on the solder joints.
4. Each cell and interconnecting strip of the module should be neatly arranged, and the module frame should be clean and free of corrosion spots.
5. Bubbles or delamination are not allowed in the encapsulation layer of the module to form a path between a cell and the edge of the module. The geometry and number of bubbles or delaminations should comply with the relevant product specifications.
6. The insulation resistance of the components under normal conditions shall not be lower than 200MΩ.
7. The light-receiving surface of photovoltaic cells should have good self-cleaning ability; the surface corrosion resistance and wear resistance should meet the relevant national standards.
8. For modules encapsulated using EVA, glass, etc., the cross-linking degree of EVA should be 75-85%, and the peel strength between EVA and glass should be greater than 50 N/cm. The peel strength between EVA and the module backsheet should be greater than 40 N/cm.
9. The contractor shall provide photovoltaic module test data, TUV-calibrated standard parts for calibrating test equipment, and test standard S:TC (T=25℃, 1000W/㎡, AM1.5).
IV. Cables
1. Photovoltaic cables must be certified by domestic or international certification bodies, possessing TUV or UL certification certificates;
2. The selection of DC side cables should be based on the principle of reducing line loss and preventing external interference. Double-insulated, UV-resistant, flame-retardant copper core cables should be selected, and the cable performance should meet the performance test requirements of GB/T18950-2003. Z-PFG type DC cables are recommended.
3. For AC side, the installation method and safety need to be considered when selecting a cable; multi-strand copper core fire-resistant and flame-retardant cable is recommended; the recommended model is ZR-YJVR.
V. Photovoltaic Inverters
The photovoltaic grid-connected inverter (hereinafter referred to as the inverter) is the core equipment in a photovoltaic power generation system, and high-quality, high-performance, mature products must be used. The inverter converts the direct current (DC) generated by the photovoltaic array into single-phase sinusoidal alternating current (AC), outputting electrical energy that meets the grid requirements.
Inverters should meet the following requirements:
1. The power factor and power quality of the grid-connected inverter should meet the requirements of the China Power Grid, and all performance indicators should meet the requirements of the "Technical Regulations for Photovoltaic Power Plant Grid Connection" issued by the State Grid Corporation of China in May 2011.
2. The installation of the inverter should be simple and have no special requirements.
3. The inverter should adopt maximum power point tracking (MPPT) technology for solar cell modules.
4. All inverters used have a proven track record of safe operation for more than 3 years.
5. The inverter is required to operate automatically with a high degree of visibility into its operating status. The display screen should clearly show real-time operating data, real-time fault data, historical fault data, total power generation data, and historical power generation data (queried by month and year).
6. The inverter is required to have an automatic fault data recording and storage function with a storage time of more than 10 years.
7. The inverter body must have a DC input disconnect switch and an emergency stop operation switch.
8. The inverter should have short circuit protection, islanding protection, over-temperature protection, AC overcurrent and DC overcurrent protection, DC bus overvoltage protection, grid power failure protection, grid over/under voltage protection, grid over/under frequency protection, and grounding detection and protection functions for the photovoltaic array and the inverter itself. The conditions and operating conditions for each protection function to operate should be given accordingly (i.e., when the protection operates, the protection time, the self-recovery time, etc.).
9. The inverter must be certified by a nationally approved certification body in accordance with the certification technical specifications of CNCA/CTS0004:2009.
10. The mean time between failures (MTBF) of the inverter shall not be less than 10 years and its service life shall not be less than 25 years.
11. The warranty period for the entire inverter shall not be less than 5 years.
12. The inverter should have low voltage ride-through capability.
VI. AC combiner box and grid connection cabinet
1. The switch cabinet adopts a standard modular design, consisting of various standard units with a module of E=25mm. Units of the same specification have good interchangeability.
2. All primary equipment and components shall withstand short-circuit dynamic and thermal stability currents not less than the busbar's dynamic and thermal stability current value without damage. All electrical components shall be CCC certified, and the distribution cabinet shall provide full-type testing/partial-type testing and have sufficient operational performance.
3. Both the main busbar and branch busbars are made of copper with high conductivity. When bolted connections are used, each joint should have no fewer than two bolts.
4. The rated voltage of the secondary terminal blocks shall not be less than 1000V and the rated current shall not be less than 10A. They shall have partitions, labeled wire sleeves, and terminal screws. Each terminal block shall be labeled with a number.
5. Selection of main components
Our frame circuit breakers, molded case circuit breakers, contactors, thermal relays, and other components utilize high-quality international and domestic products, all of which possess domestic certifications. We also select high-quality components such as ABB circuit breakers and Phoenix Contact surge arresters.
The frame circuit breaker is equipped with a built-in intelligent protection unit; the protection unit has complete three-stage protection and upper/lower level coordination functions. Feeder molded case circuit breakers should use electronic trip units or thermomagnetic electronic trip units.
All control and display components in the switch cabinet, such as selector switches, buttons, indicator lights, relays, and current transformers, should be high-quality products with operational experience.
VII. Photovoltaic Construction Auxiliary Materials
1. Cable Trays: All screws used are made of stainless steel or treated with rust prevention measures. The zinc coating thickness shall not be less than 65μm for thin plates less than 5mm and not less than 86μm for thick plates.
2. Lightning protection grounding flat iron: The flat iron used is hot-dip galvanized flat iron with parameters of 25*4mm and 4*40mm, which is welded together.
3. PVC power cable conduit: mainly used for cable laying on the AC side of photovoltaic systems. All the fixed conduits used are made of stainless steel 304 screws.
4. Screws, nuts, and bolts: All materials used are made of 304 stainless steel to ensure both fixing strength and rust prevention.
