How We Forecast Solar Energy Using GTI
GTI quantifies the solar irradiance incident on a plane tilted at the same angle and azimuth as our photovoltaic (PV) array. It is derived from the Global Horizontal Irradiance (GHI), which is then decomposed into its direct (beam) and diffuse components using established radiative transfer models (e.g., the Perez or Hay-Davies model). These components are then transposed from the horizontal plane to the panel tilt angle using geometric and atmospheric corrections, accounting for the sun’s position, air mass, and local shading effects.
To generate the 24-hour production forecast, the GTI time series is integrated over the day to compute the expected irradiance profile. This profile is then scaled using our inverter’s capacity (7.0 kWp) and adjusted for system-specific performance factors like temperature coefficient, inverter efficiency, soiling losses, and wiring losses. The result is a high-fidelity prediction of energy yield (in kWh) for each hour of the day — not just under ideal conditions, but in response to actual and forecasted weather dynamics.