Two things set how much a solar array harvests: the tilt angle and the direction it faces. The good news is that neither is fussy — being a bit off the ideal costs surprisingly little, so you rarely need to fight your roof. Here are the rules and the numbers behind them.
What tilt angle?
For the best year-round production, tilt panels at roughly your latitude — about 34° for Los Angeles, 40° for New York. To favor winter output (common for backup and off-grid systems) add about 15°; to favor summer, subtract about 15°. Keep at least a 10° minimum so rain washes the panels clean.
Which direction?
Towards the equator: true south in the northern hemisphere (azimuth 180°) and true north in the southern hemisphere (azimuth 0°). Note that is true, not magnetic — a compass reads several degrees off in many places, so correct for your local magnetic declination or sight the roof on a satellite map.
Solar Panel Tilt & Azimuth Calculator
Enter your latitude for the optimal tilt and direction — year-round, winter or summer — and what your roof pitch costs.
How much you lose off-ideal
Less than most people expect. Output falls with the cosine of the error, so being 15° off the optimum tilt typically costs only around 3–4%. Facing the wrong way hurts more: an east- or west-facing roof gives up roughly 15–20% versus facing the equator. That is why it rarely pays to fight your roof’s pitch — but orientation is worth getting right.
Should I adjust seasonally?
On a roof, almost never — the mounting cost and hassle outweigh the few percent gained. Adjustable ground or pole mounts can be worth changing twice a year on off-grid systems where every winter kWh counts. Otherwise set the year-round angle (or the winter angle if your critical loads are in winter) and leave it.
Flat roofs
Use tilt frames at 10–15° minimum rather than laying panels flat — flat panels collect dirt and pond water, losing far more to soiling than the angle math suggests. On a flat roof you can face the frames anywhere, so point them at the equator, and space the rows so they don’t shade each other in winter when the sun is low.