Photovoltaic system design is crucial for ensuring efficient and stable operation of the project, requiring comprehensive consideration of resource conditions, investment budget, and long-term benefits:
1. Preliminary assessment and planning
Key points of resource assessment:
Solar radiation:
Annual total irradiance on horizontal surface (H, kWh/m²): determines the system scale and power generation capacity. China is divided into four resource zones
Ratio of direct radiation to diffuse radiation: It affects the selection of components. Areas with high direct radiation are suitable for tracking systems
Meteorological conditions:
Temperature: It affects the efficiency of the component (power decreases by 0.3%-0.5% for every 1℃ increase), so components with a low temperature coefficient should be selected
Wind speed: It affects the design and safety of supports. Coastal areas need to enhance their wind resistance capability (≥28m/s)
Humidity / Salt Spray: Affects equipment selection. Materials with good corrosion resistance should be chosen for humid and coastal areas
Terrain conditions:
Slope and orientation: determining the optimal installation angle and bracket type
Terrain flatness: It affects construction difficulty and cost. If the slope is too steep, special design is required
Grid conditions:
Access point capacity: determines the maximum installed capacity, usually not exceeding 25% of the transformer capacity
Electricity pricing policy: "self-generation and self-consumption, surplus power sold to the grid" or full grid connection, affecting the revenue model
2. System configuration and selection
Component selection decision tree:
Resource conditions → select high-efficiency modules in high-irradiance areas, and select high-yield modules in low-irradiance areas
Application scenarios → choose double-sided components for ground-mounted power stations, lightweight components for rooftop installations, and aesthetically pleasing components for BIPV (Building-integrated Photovoltaics)
Investment budget → For high budget, choose N-type high-efficiency modules; for medium budget, choose PERC + bifacial; for low budget, choose conventional monocrystalline
Temperature conditions → choose low temperature coefficient components (HJT or N-type) for high-temperature regions, and conventional components for cold regions
Key points for inverter selection:
Type selection:
Large-scale ground-mounted solar power plants (≥10MW): Centralized inverters, low cost, high efficiency
Commercial and industrial rooftops (1-10MW): Distributed or string-type, with multiple MPPTs, adaptable to different orientations
Residential system (≤1MW): string or micro-inverter, high safety, easy maintenance
Capacity matching: The rated power of the inverter should be ≥ 0.8 times the total power of the components (taking into account losses), and ≤ 1.2 times the total power of the components (to avoid light load)
Efficiency selection: Give priority to products with European efficiency ≥98%, and choose models with good heat dissipation performance for high-temperature regions
Selection of stent system:
Fixed vs Tracking:
For budget-conscious or low-latitude regions: Fixed type, with the lowest cost
High-latitude or resource-rich regions: Single-axis tracking offers the best cost-performance ratio (with a 15%-25% improvement)
High-value projects or special requirements: dual-axis tracking to maximize power generation (by 25%-40%)
Material selection:
General ground projects: hot-dip galvanized steel supports, high strength, long lifespan, moderate cost
Roof project: aluminum alloy bracket, lightweight, without adding burden to the roof
Coastal areas: Stainless steel or brackets with enhanced anti-corrosion treatment to resist salt spray corrosion
3. System optimization design
Component layout and spacing:
Distance between the north and the south: Ensure there is no obstruction around the winter solstice. Calculation formula: D = L × tan (φ - δ + 23.5°)
L: Module height (m), φ: Local latitude (°), δ: Solar declination (winter solstice - 23.5°)
Distance between east and west: To meet the requirements of maintenance access, it is usually ≥0.8m
Vertical spacing: The pitched roof should be adjusted according to its slope to ensure that the rear row is not blocked by the front row
Cable selection and layout:
DC cable:
Specification selection: Current-carrying capacity ≥ component short-circuit current ×1.25, voltage drop ≤ 2%
Laying method: protected by being laid in pipes to avoid direct sunlight and mechanical damage
Communication cable:
Specification selection: Current-carrying capacity ≥ inverter rated current ×1.25, voltage drop ≤ 3%
Three-phase balance: Ensure balanced three-phase load to reduce system loss
4. System protection and security design
Lightning protection and grounding system:
Lightning rod/strip: protects the entire power station from direct lightning strikes
Surge protection: Install lightning protection modules at the inverter and distribution box to protect the equipment from induced lightning
Grounding grid:
Independent grounding: grounding resistance ≤4Ω, suitable for areas with high soil resistivity
Combined grounding: grounding resistance ≤1Ω, suitable for areas with good soil conditions
Equipotential bonding: All metal parts are reliably connected to eliminate potential differences
Electrical protection:
Overcurrent protection: Each string of components is equipped with a fuse, and a circuit breaker is installed on the input side of the inverter
Overvoltage protection: The inverter is equipped with DC overvoltage protection (disconnected when ≥1.3 times the rated voltage)
Islanding protection: The inverter must possess an islanding effect detection function, with a response time < 200ms
Leakage protection: Residual Current Device (RCD), with an operating current of ≤30mA and an operating time of < 0.1s
5. Design scheme evaluation and optimization
Power generation and revenue assessment:
Annual power generation estimation: E = H × P × η × 365/1000 (kWh)
Earnings calculation:
Self-consumption income: Self-consumption proportion × Electricity generation × Electricity price (Industrial: 0.8-1.2 yuan/kWh)
Surplus electricity on-grid revenue: on-grid proportion × power generation × local desulfurized coal electricity price (0.3-0.45 yuan/kWh)
Total revenue = Self-consumption revenue + Surplus electricity grid-connected revenue - Operation and maintenance costs
Return on investment:
Static payback period: Total investment / annual net income, with high-quality projects having a payback period of ≤6 years
Internal Rate of Return (IRR): Projects with an IRR of ≥8% are considered investment-worthy, and high-quality projects can achieve an IRR of 12% or more
System optimization direction:
Module over-rating: In high-irradiance areas, the module power can be over-rated by 10%-30% compared to the inverter, thereby improving system efficiency
Multiple MPPT configuration: Connect components with different orientations or inclinations to different MPPTs to reduce mismatch losses (up to 5%-10%)
Intelligent monitoring: Equipped with a remote monitoring system, it optimizes operational parameters in real-time, thereby increasing power generation by 3%-5%
Design suggestion: The design of photovoltaic systems should follow the process of "resource assessment → scheme design → equipment selection → system optimization → safety design → benefit assessment", and be tailored to the specific characteristics of the project. For large-scale projects, it is recommended to entrust a professional design institute to conduct a comprehensive feasibility study and system design