Latitude determines tilt — but not by itself
The simplest rule — “tilt = latitude” — is close but not optimal. NREL and MNRE field data show that tilt = latitude × 0.87 + 3.1 produces 1-2% more annual kWh than raw latitude, because weather patterns, diffuse irradiance, and summer high-sun dominance shift the optimum slightly flatter.
Why winter and summer angles differ
The sun's noon altitude swings ±23.5° over the year (solar declination). In December, the sun is low — panels need to tilt steeply (latitude + 15°) to face it directly. In June, the sun is almost overhead — panels should flatten (latitude - 15°). Seasonal adjustment captures both extremes.
When seasonal adjustment is worth it
- Ground-mount installations where labor is cheap and panels are reachable.
- Farms / off-grid sites where every kWh matters and there\'s no grid export.
- Systems where winter demand (space heating) is higher than summer demand.
- Lat > 30°N (Srinagar, Chandigarh) where the seasonal swing is extreme.
For most residential rooftops in south and central India, fixed annual tilt is the right choice. The 5-7% gain from seasonal adjustment doesn't justify climbing on the roof twice a year.
Tilt is only one of three orientation decisions — also check the Panel Azimuth Calculator for direction, Peak Sun Hours for your city's real yield, and the Roof Area Calculator to confirm your tilted panels physically fit.