Solar Panel Tilt Angle Calculator

How it works

Fixed all year: tilt = 0.76 × latitude + 3.1° (latitude 25°–50°), or 0.87 × latitude below 25° · twice a year: summer 0.93 × lat − 21°, winter 0.875 × lat + 19.2° · four seasons: summer 0.92 × lat − 24.3°, spring/autumn 0.98 × lat − 2.3°, winter 0.89 × lat + 24° · noon sun height = 90° − |latitude − declination|

The tilt that collects the most sunlight over a year is a little flatter than your latitude, because the long summer days carry more energy than the short winter ones. These rules are Charles Landau’s least-squares fits to clear-sky insolation for latitudes 25° to 50°; adjusting the angle twice or four times a year adds a few percent more energy. Point the panels toward the equator — true south in the northern hemisphere, true north in the southern — and use magnetic declination to convert to a compass bearing. The monthly table shows the tilt that would face the noon sun directly on the 21st of each month.

Worked example

At latitude 40° N (Madrid, Philadelphia, Beijing) the best fixed tilt is 0.76 × 40 + 3.1 = 33.5°, facing true south. Adjusting twice a year, use 0.93 × 40 − 21 = 16.2° in summer and 0.875 × 40 + 19.2 = 54.2° in winter; with four adjustments, 12.5° in summer, 36.9° in spring and autumn and 59.6° in winter. The noon sun reaches 73.4° at the summer solstice, 50° at the equinoxes and 26.6° at the winter solstice.

Sources: Charles R. Landau — Optimum tilt of solar panels · NREL — Solar position and tilt (PVWatts documentation)

Frequently asked questions