Distributed photovoltaic power generation, as an important form of clean energy utilization, is rapidly becoming popular in urban and rural buildings in China. However, due to the wide range of distributed photovoltaic points and complex installation environments, scientific site selection evaluation and standardized installation implementation have become the key to project success.
This article will systematically introduce the site selection principles, installation requirements, and specific methods of distributed photovoltaic power plants, covering the technical points of different types of projects such as household use and industrial and commercial use, providing guidance for practitioners from planning to implementation.
Technical requirements for site selection of distributed photovoltaic power stations
Basic concept and classification
Distributed photovoltaic power plants refer to photovoltaic power generation facilities that are built and operated on or near user sites, with user side self use as the main feature, excess electricity connected to the grid, and balanced and regulated in the distribution network system.
According to different application scenarios and user characteristics, it can be mainly divided into two categories:
Household distributed photovoltaics:
Distributed photovoltaic systems constructed using buildings within the scope of natural person homesteads, such as self owned residences and ancillary facilities. This type of system has a relatively small scale, usually 5-20kW, and is primarily designed for household use.
Industrial and commercial distributed photovoltaics:
Distributed photovoltaic systems built on the roofs, walls, and ancillary areas of fixed buildings such as industrial plants, storage facilities, commercial buildings, and public buildings. For profit oriented distributed photovoltaic projects such as renting someone else's roof, they are also managed according to the industrial and commercial distributed photovoltaic management.
According to different scales, it can be further divided into:
General industrial and commercial distributed photovoltaics: The voltage level at the connection point with the public grid shall not exceed 10 kV (20 kV), and the total installed capacity shall not exceed 6 MW in principle
Large scale industrial and commercial distributed photovoltaics: The voltage level at the connection point with the public grid is 35 kV, and the total installed capacity is generally not more than 20 MW, or the voltage level at the connection point with the public grid is 110 kV (66 kV), and the total installed capacity is generally not more than 50 MW
Site evaluation elements
In the actual site selection process, in addition to avoiding the above-mentioned prohibited areas, a comprehensive evaluation of candidate sites is also necessary, mainly considering the following factors:
1. Evaluation of building structure:
Building age: Buildings with brick and concrete structures exceeding 25 years or brick and wood structures exceeding 25 years should be carefully evaluated
Structural types: distinguish between different types such as concrete roofs, color steel tile roofs, tile roofs, etc
Carrying capacity: Must meet the increased load requirements of the photovoltaic system (detailed in subsequent chapters)
Hazard level: It is strictly prohibited to use buildings with hazard assessment levels of C and D
2. Roof condition assessment:
Roof material and current situation: Check for severe corrosion (color steel tiles), damage, or water leakage
Roof orientation and tilt angle: Priority should be given to roofs facing south with a suitable tilt angle (based on local latitude)
Coverage situation: Evaluate the shadow coverage caused by surrounding buildings, trees, equipment, etc
Available area: Calculate the net available area, excluding areas such as equipment zones, ventilation openings, and lighting belts
3. Electrical condition assessment:
Distance to grid access point: Evaluate the distance to the nearest grid access point, which affects cable costs and voltage drop
Transformer capacity: Check if the remaining capacity of nearby transformers meets the requirements for photovoltaic access
Electricity load characteristics: For "self use" projects, analyze the matching degree between user electricity curves and photovoltaic output
4. Environmental factor assessment:
Pollution source: Assess whether there are nearby factories, transportation arteries, or other sources that may cause surface contamination of components
Meteorological conditions: Pay special attention to historical data on extreme weather such as maximum wind speed, snow pressure, hail, etc
Salt spray corrosion: Coastal areas need to assess the impact of salt spray corrosion on supports and components
5. Property rights and legal factors:
Clear property rights: Ensure that building property rights are clear and undisputed
Service life: Evaluate the matching degree between the remaining service life of the roof and the service life of the photovoltaic system
Neighborhood Relations: Assessing the Potential Impact of Photovoltaic Systems on the Lighting and Landscape of Surrounding Buildings
Through the site selection evaluation of the above system, high-quality sites suitable for building distributed photovoltaic power stations have been selected, laying a solid foundation for subsequent design and installation.
Technical requirements before installation of distributed photovoltaic power plants
Safety assessment of building structures
Before installing a distributed photovoltaic system, a comprehensive safety assessment of the building structure must be conducted, which is the foundation for ensuring the long-term safe operation of the power station. The evaluation should focus on the following aspects:
1. Structural type identification:
Concrete structures: including cast-in-place concrete and precast slabs, their bearing characteristics need to be evaluated separately
Steel structure: commonly found in industrial plants, requiring evaluation of steel type, degree of corrosion, and connection node condition
Wooden structure: commonly seen in traditional buildings, special attention should be paid to the aging of wood and the firmness of connections
Hybrid structure: A building that combines multiple materials requires a comprehensive evaluation of the load-bearing capacity of each part
2. Load capacity calculation:
Constant load (permanent load): including the self weight of equipment such as photovoltaic modules, brackets, cables, etc
Live load (variable load): including wind load, snow load, weight of construction and maintenance personnel, etc
Special loads: additional stresses caused by seismic action, temperature changes, etc
Taking a common concrete roof as an example, the load of the newly added photovoltaic system is generally controlled within the range of 0.15-0.25kN/m2, and the specific load needs to be determined based on structural calculations. For color steel tile roofs, it is also necessary to consider the concentrated loads during construction and operation.
3. Professional evaluation requirements:
Evaluation must be conducted by a qualified structural engineer
For B-class buildings, strict evaluation and assessment must be conducted, and structural components that are in a dangerous state must be avoided
The evaluation report should include structural calculations, on-site inspection data, and reinforcement recommendations (if necessary)
Fire safety requirements
The fire safety of distributed photovoltaic power plants is crucial, and the following requirements must be met before installation:
1. Classification of Building Fire Hazards:
It is strictly prohibited to use buildings with fire hazard categories of Class A and Class B to construct distributed photovoltaic projects
When using other buildings or sites near such buildings for construction, the fire separation distance should not be less than 30 meters
2. Firefighting equipment configuration:
According to the "Code for Design of Fire Extinguisher Configuration in Buildings" (GB50140), fire-fighting equipment and facilities shall be equipped
Suggest installing an intelligent fire alarm system, especially in densely populated areas around
Ensure that fire exits are unobstructed and do not block existing fire exits due to the installation of photovoltaic systems
3. Fire isolation measures:
When cables pass through roofs or walls, fireproof sealing materials must be used for sealing
Fire barriers should be installed around electrical equipment
Inverters, distribution cabinets, and other equipment should be installed in well ventilated areas to avoid heat accumulation
Electrical safety requirements
The electrical safety assessment before the installation of distributed photovoltaic systems should include:
1. Lightning protection grounding system:
The photovoltaic system installed on buildings should take lightning protection measures and be included as part of the building's electrical lightning protection design
The classification of lightning protection levels and lightning protection measures should be implemented in accordance with the relevant provisions of GB 50057
The grounding resistance should not exceed 10 Ω (for lightning protection purposes)
2. Selection of electrical equipment:
Photovoltaic modules, inverters and other equipment should be certified by relevant national certification agencies
Grid connected inverters should have the ability to withstand abnormal frequency and voltage in the power grid as specified in GB/T 37408
The relevant electrical components should be made of flame-retardant materials
3. System protection device:
Anti islanding devices or components with corresponding functions must be installed
For projects with a series circuit layout, install a main circuit breaker at the output end of the component array
Install arc fault circuit breakers or use components with corresponding functions
Preparation work before installation
Before formal installation, the following preparations need to be completed:
1. Procedure handling:
Project filing: Submit the filing to the competent department according to the principle of "whoever invests, who files"
Grid Connection Application: Submit a grid connection application to the local power supply company and obtain a confirmation form for the access system plan
2. On site preparation:
Construction area isolation: Install protective nets and set up prominent safety signs
Material and equipment entry: Check the model, quantity, and quality of components, brackets, and other materials
Construction equipment inspection: Ensure that lifting equipment, safety protection equipment, etc. are in good condition
3. Technical preparation:
Construction drawing review: Organize design, construction, owner and other units to conduct drawing review
Construction plan preparation: including lifting plan, safety protection measures, etc
Technical briefing: Detailed explanation of technical points and safety precautions to construction personnel
