태양 광 발전소에 대해 알아야 할 5 가지 그리드 부하

태양광(PV) 발전소는 구조적 사하중, 풍하중, 적설하중, 지진 영향, 온도 변화에 따른 하중 등 다양한 하중을 받습니다.

Here’s a breakdown of the primary load types:

1. Structural Dead Weight: This encompasses the weight of all permanent components, such as PV modules, mounting structures, combiner boxes, cables, and fasteners. It is considered a permanent load.

2. Wind Load: A significant variable load on PV systems, wind load is influenced by geographical location, altitude, terrain, and structure shape.

3. Snow Load: Dependent on geographical location, climate, and season, snow load primarily affects PV plants in regions experiencing snowfall, particularly during winter.

4. Seismic Effects: These are calculated based on the seismic intensity of the region and are categorized as accidental loads.

5. Effects of Temperature Changes: Temperature fluctuations cause materials to expand and contract, leading to stress within the structure.

Wind Load Calculation Example

Consider a rooftop PV system in Beijing with three modules arranged in a row, each with an area of 1.3 square meters. The following steps illustrate the wind load calculation:

1. Determine Basic Wind Pressure: Consult the “Load Code for the Design of Building Structures” (GB50009-2001 or latest edition) to determine the basic wind pressure for Beijing.

2. Calculate Gust Factor (pgz): For a height of 20 meters, assume a gust factor of 1.69 (this value depends on specific height and code requirements).

3. Wind Load Shape Coefficient (ps): Depending on the module arrangement and project specifics, assume a value of 1.3.

4. Wind Pressure Height Variation Coefficient (pz): Use a value of 1.2 to account for wind pressure changes with height.

5. Calculate Wind Load Standard Value (Wk): Use the formula Wk = Pgz × ps × pz × W0, where W0 is the basic wind pressure value.

Assuming a basic wind pressure (W0) of 0.5 kN/m² for Beijing, the wind load standard value is calculated as: 𝑊𝑘=1.69×1.3×1.2×0.5=1.3284𝑘𝑁/𝑚2

This implies a wind load standard value of 1.3284 kN/m² acting on the inclined module surface. In actual design, it’s crucial to consider load combination factors as per the code, convert the standard value to a design value, and verify the load-carrying capacity of the mounting structure, fasteners, and other components.

Snow Load Calculation Example

Snow load calculation usually relies on historical climate data and the “Load Code for the Design of Building Structures” (GB50009). Assuming known values for maximum snow depth and snow density in a specific region, the snow load standard value 𝑆𝑠𝑛𝑜𝑤Ssnow can be calculated using the formula: 𝑆𝑠𝑛𝑜𝑤=𝑐𝑟⋅𝛾𝑠⋅𝑠⋅𝜌𝑠Ssnow=cr⋅γs⋅s⋅ρs
where:
𝑐𝑟cr is the snow load combination factor, typically taken as 0.7;
𝛾𝑠γs is the snow weight per unit volume, approximately 0.2 kN/m³ in northern China;
𝑠s is the maximum snow depth in meters;
𝜌𝑠ρs is the snow density, which varies based on region and climate, generally ranging from 0.15 to 0.35 kN/m³.

Seismic Load Calculation

Calculating seismic effects is relatively complex, involving factors like seismic intensity, site category, structure type, and fundamental period. The response spectrum method, as outlined in the “Code for Seismic Design of Buildings” (GB50011), is commonly employed. This calculation determines the horizontal seismic forces acting on the structure in different directions, as well as the corresponding seismic shears and moments.

Stress Calculation due to Temperature Changes

Thermal expansion and contraction caused by temperature variations induce stress within the structure. During the design phase, this effect is usually mitigated by incorporating appropriate installation gaps and flexible connections. For precise calculations, consider the material’s linear expansion coefficient, structural dimension changes, and constraint conditions. Thermodynamic principles can then be applied to calculate the stress distribution within the structure.

Combined Load Effects

In practical applications, PV plant structures experience the combined action of multiple loads. During design, these loads are combined, considering their most unfavorable effects. Load combinations typically follow code-specified guidelines, such as basic combinations (permanent load + variable load) and special combinations (accounting for accidental loads like earthquakes and explosions).