How roof tilt and direction affect solar output
Last updated October 2026
Two numbers describe how a roof plane meets the sun: its tilt (how steeply it slopes) and its azimuth (the compass direction it faces). Together they decide how directly sunlight hits the panels over a year, and they're the two numbers SolPan asks you to confirm for each roof plane.
Direction (azimuth)
In the U.S. the sun spends most of the day in the southern half of the sky, so panels facing south usually produce the most over a year. SolPan uses the standard convention where 180° is due south, 90° is east, 270° is west, and 0° is north.
- South-facing (about 180°): usually the best annual output.
- Southeast or southwest (about 135° or 225°): a small drop, often only a few percent.
- East or west (about 90° or 270°): commonly somewhere around 10 to 20 percent less than south, depending on tilt and location. Production shifts toward morning or afternoon.
- North-facing (about 0°): often well below the other directions in the U.S., which is why installers usually favor other planes first.
Tilt
For a fixed panel, the annual sweet spot is roughly a tilt equal to your latitude, which is about 25° to 50° across the lower 48 states. Production is forgiving, though. A tilt within a few tens of degrees of the ideal usually costs only a few percent a year, so a normal roof pitch is rarely a deal-breaker.
Common roof pitches and their tilt in degrees:
- 4:12 pitch — about 18°
- 6:12 pitch — about 27°
- 9:12 pitch — about 37°
- 12:12 pitch — 45°
Flat roofs have a tilt near 0°, but panels on a flat roof are normally mounted on racks that tilt them toward the sun.
Why a hip roof or dormers change the picture
A roof with several planes can have panels facing different ways. Each plane produces differently, so SolPan estimates each one separately at its own tilt and direction and adds the results. That is why the tool lets you outline several roof planes instead of one.
Shade matters too
Tilt and direction assume an unshaded roof. Trees, chimneys, and neighboring buildings can cut output more than a less-than-ideal direction does, and they're the main thing an on-site assessment will check.
These are rules of thumb. For your own roof, enter its numbers into the estimator to see the effect, and read how SolPan arrives at its figures.