Why tilt matters
Solar panels produce the most power when sunlight hits them squarely. The sun’s path changes with your latitude and with the seasons: high in summer, low in winter. A well-chosen tilt captures more of that light over the year. Fortunately, output is not very sensitive to small errors, so a good rule of thumb is all most homeowners need.
Rules of thumb used by the calculator
Fixed panels, year-round
- Latitude below 25°: tilt ≈ latitude × 0.87
- Latitude 25° to 50°: tilt ≈ latitude × 0.76 + 3.1°
Adjusted twice a year
- Summer: latitude × 0.93 − 21°
- Winter: latitude × 0.875 + 19.2°
Adjusted four times a year: in spring and fall, use about latitude − 2.5°.
These formulas come from simulations of yearly output; they tilt panels a little flatter than the latitude because more sunshine arrives in the long summer days.
Worked example: New York (40.7° N)
| Setting | Tilt |
|---|---|
| Fixed, year-round | 34.0° |
| Summer | 16.9° |
| Spring and fall | 38.2° |
| Winter | 54.8° |
The year-round angle corresponds to a roof pitch of about 8.1/12. At noon, the sun climbs to 72.7° at the June solstice and only 25.9° at the December solstice.
Ideal fixed tilt in other US cities
| City | Latitude | Fixed tilt |
|---|---|---|
| Miami | 25.8° | 22.7° |
| Los Angeles | 34.1° | 29.0° |
| Denver | 39.7° | 33.3° |
| Seattle | 47.6° | 39.3° |
How much does the exact angle matter?
Not much. Panels within 10° to 15° of the ideal tilt usually lose only a few percent of yearly output. That is why most residential systems are mounted flush with the roof: the savings on racking and wind loading outweigh the small loss. Tilting is worth more on flat roofs and ground mounts.
Direction
Face panels toward true south in the Northern Hemisphere (true north in the Southern). True south differs from magnetic south by the local magnetic declination. East- or west-facing arrays typically produce 15% to 20% less, but can still pay off, especially with time-of-use rates that value afternoon power.
Other factors
- Snow slides off more easily at steeper angles, which can favor a winter-friendly tilt in snowy regions.
- Shading from trees or chimneys costs far more than a non-ideal angle.
- For a detailed estimate at your address, the free PVWatts calculator, developed for the US Department of Energy, models tilt, azimuth and local weather.