Tilt & Direction
At which angle and in which direction should solar panels face where you live? Every hour of a typical year is added up: the sun’s position, the direct sunlight and the light from the sky. Find the best angle for the whole year, for summer and winter and month by month, and see what your own roof angle costs.
Why the Best Angle Is Not Simply Your Latitude
A panel catches the most direct sunlight when it faces the sun square-on: the light per square metre drops with the cosine of the angle between the sun’s rays and the panel’s normal. At noon on the equinoxes the sun stands 90° minus your latitude above the horizon, so a panel tilted at your latitude faces it exactly. That is where the old rule “tilt = latitude” comes from.
But summer days are long and bright, winter days short and often cloudy, so the summer sun weighs more and pulls the best angle lower. And part of the light comes from the whole sky, not from the sun: a flatter panel sees more of the sky. In cloudy places like north-west Europe that diffuse light is about half of the total, which is why the best angle there is usually several degrees below the latitude.
From the Sun’s Path to the Best Angle, Step by Step
tiltAssumptions of This Model
| Assumption | In reality… |
|---|---|
| The weather is a typical year: hourly sunshine from PVGIS (a “typical meteorological year” built from 2005–2020 satellite data) | every real year differs; a sunny or dull year moves the yield by several percent, the best angle by a few degrees |
| Sky light follows the Perez model; the ground reflects 20% (grass, roofs) | snow (60–80%) or a white roof makes steep panels gain more; the model is accurate to a few percent |
| No shade from buildings, trees or other panel rows; only the terrain horizon in the PVGIS data | shade in winter mornings and evenings can make a flatter angle better |
| Output follows the sunlight on the panel, times one performance ratio for all losses | reflection at low sun angles, heat and snow cover differ by angle: steep panels shed snow and dirt better, flat ones run warmer |
| The panel keeps the same direction all year; the summer and winter angles assume you change only the tilt (summer: April–September north of the equator, October–March south of it) | trackers that follow the sun gain 25–40% more, but cost more and need maintenance |
| Tilts and directions are searched in whole degrees | near the best angle the yield hardly changes, so this makes no practical difference |
Key Relations
Sun height α from latitude φ, the sun’s declination δ (±23.4° through the year) and the hour angle ω (15° per hour from solar noon). Declination and the equation of time from Spencer (1971).
The beam irradiance times the cosine of the angle between the sun’s direction and the panel’s normal.
Perez model: an even sky, a bright ring around the sun (F₁) and a bright horizon band (F₂), with F₁ and F₂ from the sky’s clearness and brightness each hour. The ground adds ρ·Gh·(1 − cosβ)/2.
A panel rated 1 kWp gives 1 kW at 1000 W/m², so the sunlight on the panel in kWh/m² times the performance ratio is the yield per kWp.
Sources & Verification
- PVGIS 5.2, European Commission Joint Research Centre — typical meteorological year, hourly global, direct and diffuse irradiance. PVGIS © European Union, 2001–2026.
- R. Perez, P. Ineichen, R. Seals, J. Michalsky & R. Stewart, “Modeling daylight availability and irradiance components from direct and global irradiance”, Solar Energy 44(5), 271–289 (1990) — the sky model and its coefficients.
- J. A. Duffie & W. A. Beckman, Solar Engineering of Thermal Processes, 4th ed., Wiley, 2013 — sun position, angle of incidence, irradiance on tilted surfaces.
- J. W. Spencer, “Fourier series representation of the position of the sun”, Search 2(5), 172 (1971) — declination and equation of time.
Frequently Asked Questions
What is the best tilt angle for solar panels?
It depends on your latitude and your climate. From hourly sunshine data of a typical year the best fixed angle is about 39° in Amsterdam, 35° in Madrid, 32° in Phoenix and 35° in Sydney (facing north there). In Amsterdam that gives 18.8% more sunlight than a flat panel. The optimum is broad: 10° more or less costs only about 1–2%.
Should the tilt angle equal my latitude?
It is a reasonable first guess, not the best answer. Long summer days and diffuse light from the clouds pull the best angle lower: in Amsterdam, where about half of the sunlight is diffuse, the best angle is 39°, and tilting at the latitude (52°) gives 98% of the best.
Which direction should solar panels face?
Towards the equator: south in the northern hemisphere, north in the southern hemisphere. Other directions cost more the steeper the panel is: an east-facing roof of 20° in Phoenix still collects about 85% of the best orientation, so east and west roofs are often worth using.
Should I change the tilt between summer and winter?
It helps a little. In Amsterdam the best angle is 28° for April to September and 61° for October to March; changing it twice a year collects 2.6% more than the best fixed angle, and changing it every month 3.7% more. For most home systems a fixed angle is the practical choice.
How much do vertical balcony or facade panels produce?
Less, but more than many expect at high latitudes, because the low winter sun shines almost straight at them. A vertical south-facing panel in Stockholm collects about 76% of the sunlight of the best angle, and in Amsterdam about 72%.
Where does the sunshine data come from?
From PVGIS, the European Commission's solar database: a typical meteorological year built from satellite data of 2005–2020, with the direct and diffuse sunlight for every hour. The calculator works out the sun's position for each hour and the light on the tilted panel with the Perez sky model. For Amsterdam it finds the same best angle as PVGIS itself: 39°.