What is solar irradiation forecast?
Solar irradiation is a key factor in calculating the thermal balance of overhead power lines. While wind provides cooling, solar radiation acts as a primary source of external heating, raising the conductor's temperature even when no electricity is flowing through it. In extreme cases, solar radiation alone can raise a conductor's temperature by more than 10°C above the ambient air temperature.
The Gridraven Approach: Conservative Modeling
Gridraven utilizes a specialized Clear-Sky Radiation Model to estimate the heating effect on every individual span. This approach ensures consistency and safety across the transmission network.
- Deterministic Geometry: The model calculates the exact solar altitude for each specific span based on its precise geographic coordinates, the date, and the time of day.
- Clear-Sky Assumption: As a safety measure, the system intentionally assumes a perfectly clear sky with no cloud cover or aerosols to reduce intensity.
- Safety Margin: By assuming maximum possible solar heating (as if the sun is always shining), Gridraven’s DLR and AAR values are inherently conservative. This prevents overestimating capacity during periods where real-time cloud data might be uncertain.
- Span-Level Resolution: Because the orientation of a power line changes, the angle at which the sun hits the conductor varies; our hyper-local model evaluates this geographic variability for every span.
How it Influences Line Ratings
In the Gridraven Claw, solar irradiation is treated as a critical input for both Ambient Adjusted Ratings (AAR) and Dynamic Line Ratings (DLR).
- Heating Intensity: The model uses a constant solar radiation value of 1361 W/m² (the solar constant at the top of the atmosphere) and adjusts it based on the calculated solar angle.
- Absorption and Emissivity: The calculation accounts for the conductor's physical properties, typically assuming high absorptivity and emissivity coefficients (e.g., 0.9) as conductors darken over time in the field.
- Seasonal Fluctuations: The model captures the significant differences between summer and winter solstices, which can drastically alter the thermal "headroom" available for power transmission.
This graph illustrates the calculated solar heating values for a summer and winter solstice. By integrating these values into the thermal balance equation, Gridraven ensures that the conductor temperature never exceeds its safety limit (e.g., 95°C) due to solar gain.