Solar-Tilt-Calculator

Calculate solar radiation on tilted surfaces for wind and solar energy analysis. Based on NASA POWER climatology data and Hay's anisotropic sky-diffuse model.

Trigger

User provides:

1. Input Excel file path (from metdata-nasa-access)
2. Tilt angle (β) in degrees
3. Azimuth angle (γ) in degrees (optional, default: 0 = facing equator)

Example:

• "帮我计算倾角30°，方位角0°的辐射量"
• "使用 /path/to/metdata.xlsx，倾角25°"
• "30度倾角，正南朝向"

Workflow

Step 1: Read Input Excel

Read the Excel file generated by metdata-nasa-access:

python3 scripts/calculate_tilt_radiation.py \
  --input <INPUT_EXCEL> \
  --tilt <TILT_ANGLE> \
  --azimuth <AZIMUTH_ANGLE> \
  --output <OUTPUT_EXCEL>

Input Excel structure (from metdata-nasa-access):

• Sheet "气象数据": Contains monthly radiation data
  • Columns: T2M, T10M, ALLSKY_SRF_ALB, ALLSKY_SFC_SW_DNI, ALLSKY_SFC_SW_DIFF, ALLSKY_SFC_SW_DWN
  • Rows: 1月-12月 + 年度均值

Step 2: Calculate Tilted Surface Radiation

Use Hay's anisotropic model (from paper: 不同方位倾斜面上太阳辐射量及最佳倾角的计算):

HT = Hb × Rb + Hd × [(Hb/H0) × Rb + (1/2)(1 - Hb/H0)(1 + cosβ)] + (1/2)ρH(1 - cosβ)

For equator-facing surfaces (γ = 0):

Rb = [sin(φ - β) × sinδ + cos(φ - β) × cosδ × cosωs] / [sinφ × sinδ + cosφ × cosδ × cosωs]

For tilted surfaces with azimuth (γ ≠ 0): Use Bushell's improved formula for sunrise/sunset hour angles:

ωs1 = min{ωs, arccos[(A - B)/C]}
ωs2 = max{-ωs, arccos[(A + B)/C]}

Where:

• A = sinδ(sinφ cosβ - cosφ sinβ cosγ)
• B = cosδ(cosφ cosβ + sinφ sinβ cosγ)
• C = cosδ sinβ sinγ
• ωs = arccos(-tanφ tanδ)

Step 3: Generate Output Excel

Output Excel with 3 sheets:

1. 基本信息 - Location, tilt angle, azimuth angle, input data source
2. 倾斜面辐射数据 - Monthly mean daily radiation on tilted surface
3. 参数说明 - Calculation model, parameters, formulas

Step 4: Report to User

Confirm the file path and summarize key findings:

• 年均可用辐射量（水平面 vs 倾斜面）
• 最佳辐射月份
• 辐射增益/损失百分比

Output Format

Excel with 3 sheets:

基本信息:

• 输入数据源
• 当地纬度
• 倾斜角度
• 方位角度
• 计算模型

倾斜面辐射数据:

参数说明:

• Hay 模型说明
• 公式来源
• 符号对照表

Notes

• Based on Hay's anisotropic sky-diffuse model
• Input data should be from metdata-nasa-access (NASA POWER climatology)
• Tilt angle (β): 0-90° (0° = horizontal)
• Azimuth angle (γ): -90° to +90° (0° = facing equator, negative = east, positive = west)
• Ground reflectance (ρ): default 0.2 (typical for most surfaces)
• Units: MJ/(m²·day)
• Calculation method: Monthly mean daily radiation

References

• 杨金焕, 毛家俊, 陈中华. 不同方位倾斜面上太阳辐射量及最佳倾角的计算[J]. 上海交通大学学报, 2002, 36(7): 1032-1035.
• Hay J E. Calculation of monthly mean solar radiation for horizontal and inclined surfaces[J]. Solar Energy, 1979, 23(4): 301-307.
• Bushell R H. A solution for sunrise and sunset hour angles on a tilted surface without a singularity at zero[J]. Solar Energy, 1982, 28(4): 359.