Solar panel tilt angle.

How this works

The sun's elevation in the sky varies through the year because Earth's axis is tilted 23.45° from its orbital plane. For maximum power output, a solar panel should be perpendicular to incoming sunlight — but that direction changes daily and seasonally.

Fixed tilt (year-round):    angle = |latitude|
Summer-optimized:           angle = |latitude| − 15°
Winter-optimized:           angle = |latitude| + 15°

Per-month optimal tilt:
   angle = |latitude| − solar_declination(month)

Solar declination on the 15th of each month (approx):
   Jan:  −21°   Feb:  −13°   Mar:  −2°
   Apr:  +10°   May:  +19°   Jun:  +23°
   Jul:  +22°   Aug:  +14°   Sep:  +3°
   Oct:  −10°   Nov:  −20°   Dec:  −23°

Azimuth: face true south (or true north)

Tilt angle is only half the equation. The other half is azimuth — which compass direction the panel faces.

• Northern hemisphere: Face true south (azimuth = 180°).
• Southern hemisphere: Face true north (azimuth = 0°).
• Equatorial regions (within ±5° of equator): Either direction works; near-flat tilt.

True south/north, not magnetic. Magnetic declination varies — in the US it ranges from ~15° west (east coast) to ~15° east (west coast). For installation, use a compass corrected for declination, or use a smartphone's compass with declination applied.

Fixed vs adjustable vs tracker

• Fixed tilt at latitude: Simplest, cheapest. Captures ~95% of the energy that a single-axis tracker would.
• Seasonal adjust (2 positions): Adjust twice a year — summer (lat − 15°) and winter (lat + 15°). Gains ~5% over fixed.
• Monthly adjust (12 positions): Gains ~3% over seasonal. Rarely worth the labor.
• Single-axis tracker: Pivots east-to-west through the day. Gains 25-35% over fixed.
• Dual-axis tracker: Adjusts tilt and azimuth. Gains 35-45% over fixed, but mechanical complexity adds cost and maintenance.

Why latitude is a good first approximation

If you tilt the panel up at exactly your latitude, then at solar noon on the equinoxes (March 21 and September 21), the sun is exactly perpendicular to the panel. Averaged over the year, this orientation captures the most energy from a fixed panel — though it's optimal for spring/fall and slightly off for summer (sun too high) and winter (sun too low).

When this rule breaks down

• Snow / albedo regions: Steeper tilt sheds snow better. In snowy regions, latitude + 5° to + 10° is common.
• Mountainous / shaded sites: Local horizon obstruction matters more than tilt. A panel shaded for 2 hours/day loses far more than a sub-optimal tilt.
• Off-grid winter loads: If your winter loads dominate (heating, more hours of darkness), bias toward winter tilt — even at the cost of summer harvest.
• Tropical sites (latitude < 15°): Tilt becomes very flat; debris and water shedding may matter more than energy capture. A minimum tilt of 10° is recommended for self-cleaning.
• Bifacial panels: Some ground-reflected light hits the rear, so a steeper tilt over a reflective surface (white gravel, snow) can capture more.

Sources

• Solar declination formula: NASA / NOAA solar position algorithms.
• Optimal tilt research: NREL (National Renewable Energy Laboratory) PVWatts methodology.
• Practical design: SunPower, SolarEdge installation guides.

Disclaimer. Optimal tilt also depends on local weather patterns (sunny vs cloudy seasons), shading, roof structure constraints, and electricity rate structure. For a serious installation, use NREL's PVWatts tool or consult a solar designer.

See also