Weather Data
Weather data forms the foundation of all P90 uncertainty analysis. This section covers supported formats, required variables, and how P90 handles missing or incomplete meteorological data.
Supported Formats
Section titled “Supported Formats”PVW Files (Recommended)
Section titled “PVW Files (Recommended)”PVW files are SunSolve’s optimized weather format that includes pre-calculated solar position data and standardized meteorological variables. These can be exported from SunSolve Yield.
Advantages:
- Pre-validated solar geometry calculations
- Optimized file size and loading performance
- Guaranteed compatibility with P90 analysis
- Includes metadata for timezone and location information
Contents:
- Timestamp data with timezone information
- Solar position (zenith and azimuth angles)
- Global and diffuse horizontal irradiance
- Ambient temperature and wind speed
- Optional time-step specific parameters
CSV Files
Section titled “CSV Files”Standard comma-separated files containing meteorological time series data. The ‘sydney.csv’ file can be used as a template, you must keep all column headers the same.
Requirements:
- Consistent timestamp format and frequency
- All required meteorological variables present
- Proper column headers, following ‘sydney.csv’ template
- Valid numeric data ranges
Supported Variables:
- SolarAzimuth (degrees)
- SolarZenith (degrees)
- AmbientTemp (celsius)
- DHI (W/m2)
- GHI (W/m2)
- DNI (W/m2)
- Wind Speed (m/s)
- Tilt (degrees)
Required Meteorological Variables
Section titled “Required Meteorological Variables”Solar Position Data
Section titled “Solar Position Data”Solar Zenith Angle
- Range: 0° to 180°
- Definition: Angle between sun and vertical (0° = sun directly overhead)
- Units: Degrees
- Usage: Determines direct irradiance component on tilted surfaces
Solar Azimuth Angle
- Range: 0° to 360°
- Definition: Horizontal angle of sun position (0° = North, 90° = East, 180° = South, 270° = West)
- Units: Degrees
- Usage: Calculates irradiance orientation effects
Irradiance Components
Section titled “Irradiance Components”Global Horizontal Irradiance (GHI)
- Range: ≥ 0 W/m²
- Definition: Total solar irradiance on horizontal surface
- Components: Direct + diffuse + reflected irradiance
- Critical for: Overall energy availability assessment
Diffuse Horizontal Irradiance (DHI)
- Range: ≥ 0 W/m²
- Definition: Scattered solar irradiance on horizontal surface
- Relationship: Must be ≤ GHI
- Usage: Determines sky diffuse contribution to tilted surfaces
Environmental Conditions
Section titled “Environmental Conditions”Ambient Temperature
- Units: Kelvin (K)
- Range: Physically reasonable values (typically 200-350 K)
- Usage: Module temperature calculations affecting power output
- Impact: Higher temperatures generally reduce photovoltaic efficiency
Wind Speed
- Range: ≥ 0 m/s
- Definition: Wind velocity at measurement height
- Usage: Convective cooling calculations for module temperature
- Impact: Higher wind speeds improve module cooling
Optional Time-Step Variables
Section titled “Optional Time-Step Variables”These variables can be included in weather files for time-step specific values, or fallback values will be used.
Surface Properties
Section titled “Surface Properties”Albedo
- Range: 0 to 1
- Definition: Ground reflectance fraction
- Typical values: 0.2 (grass), 0.8 (snow), 0.4 (concrete)
- Usage: Calculates reflected irradiance contribution
Soiling Parameters
Section titled “Soiling Parameters”Front Surface Soiling
- Range: 0 to 1
- Definition: Fraction of light transmission through soiled front surface
- Impact: 1.0 = clean, 0.9 = 10% soiling losses
- Variability: Can change seasonally or after cleaning events
Rear Surface Soiling
- Range: 0 to 1
- Definition: Light transmission through soiled rear surface (bifacial modules)
- Application: Only relevant for bifacial installations
- Typically: Lower impact than front surface soiling
Geometric Parameters
Section titled “Geometric Parameters”Module Tilt Angle
- Range: -90° to 90°
- Definition: Angle of module surface from horizontal
- Usage: Overrides system fallback tilt for this time step
- Application: Tracking systems or variable tilt installations
Bifacial Parameters
Section titled “Bifacial Parameters”Rear Transmission Factor
- Range: ≥ 0
- Definition: Light transmission coefficient for rear irradiance
- Usage: Bifacial gain calculations
- Context: Represents module structure transparency
Rear Structural Shading Factor
- Range: 0 to 1
- Definition: Fraction of rear surface unshaded by structural elements
- Impact: Reduces bifacial irradiance collection
- Examples: Mounting rail shadows, frame effects
Data Preprocessing and Validation
Section titled “Data Preprocessing and Validation”Fallback Value Application
Section titled “Fallback Value Application”When time-step specific values are missing, P90 applies fallback values in this order:
- User-specified fallbacks: Values you configure in system settings
- System defaults: Built-in reasonable values for typical installations
Common Fallback Scenarios:
- Albedo: Uses fallback when ground conditions not specified
- Soiling: Applies consistent soiling rates when cleaning schedules unknown
- Tilt: Uses system tilt angle when tracking data unavailable
Time Series Requirements
Section titled “Time Series Requirements”Temporal Resolution
- Typical: Hourly time steps
- Supported: Sub-hourly to daily intervals
- Consistency: All data points must use same interval
Data Completeness
- Minimum: Core meteorological variables for all time steps
- Recommended: Include optional parameters when available
- Missing data: Will use interpolation or fallback values as appropriate
Temporal Coverage
- TMY data: Single representative year, repeated for multi-year analysis
- Actual years: Multiple years of historical data for each analysis year
- Duration: Sufficient data for meaningful statistical analysis