☀ Panel Angle

Your tilt target comes from real measured sunlight, not just theory: 20-year NASA satellite irradiance and ECMWF reanalysis for your exact coordinates are cross-checked, then a clear-sky physics model (sun declination, hour angle, air-mass haze) is weighted by each month's real cloud cover to find the angle that collects the most energy over your chosen period. Cloudy seasons count for less. Where it snows, measured snowfall for your spot is folded in too — shallow tilts that hold snow are penalized, so snowy climates get steeper recommendations automatically. Offline, it falls back to the physics model. Headings use true north, so "south" already accounts for magnetic declination.