Your optimal angle
Average daily irradiation at the optimal angle
How much does the wrong angle cost?
Photovoltaic yield changes slowly near the optimum and quickly far from it. The tables below are computed for the coordinates you entered, so they show your real penalties rather than generic ones. Anything above about 95% is usually not worth re-engineering a roof for.
| Tilt | Relative yield | kWh/m²/year |
|---|
| Orientation | Relative yield | kWh/m²/year |
|---|
Practical rules that survive contact with a real roof
Follow the roof, not the textbook
Rebuilding a roof pitch to gain 3% of yield never pays. Mount flush with the tiles, check the loss in the tables above, and spend the money on one more panel instead — an extra module usually beats a perfect angle.
Winter is where the shading loss hides
A chimney that clears the array in June can black it out in December, when the sun is more than 40° lower. Model the obstacle on the sun position map and look at the 21 December figure: a string inverter can lose far more to one shaded module than to a suboptimal tilt.
Steeper tilts for winter-heavy loads
If a heat pump or an off-grid battery drives your December demand, tilt toward latitude plus 10–15°. You give up a little in June, when you are exporting anyway, and gain when it counts. Steeper glass also sheds snow, which in a snowy climate is worth more than the geometry.
East-west arrays
Two rows facing east and west at 10–15° fit more panels on a flat roof than one south-facing row with shading gaps, and they flatten the production curve. Total yield per panel drops, total yield per roof often rises.
Check the numbers against measured data
This page models a clear-sky spectrum modified by a clearness index, which is excellent for comparing orientations but is not a climate dataset. Before you sign a contract, put the same coordinates into PVGIS (Europe, Africa, Asia) or NREL's PVWatts (Americas) and compare the annual figure.
How the optimum is computed
For your coordinates the tool walks through a full year in fifteen-minute steps, computes the sun's position for each step, converts it into direct and diffuse irradiance with the Erbs correlation for the chosen clearness index, and projects both onto a candidate plane together with ground reflection. It then searches the tilt and azimuth grid for the maximum. That is thousands of sun positions per candidate angle, which is why the answer for your latitude differs from the textbook rule of thumb.
Questions
Frequently asked questions
What is the best angle for solar panels?
For a fixed array the yearly optimum is a tilt roughly equal to your latitude minus 10 to 15 degrees, facing the equator. At 52 degrees north the optimum is close to 35 degrees facing south; near the equator it is nearly flat. The calculator on this page computes the exact value for your coordinates instead of using a rule of thumb.
Which direction should solar panels face?
True south in the northern hemisphere and true north in the southern hemisphere. Note that this is true north, not magnetic north: a compass can be off by ten degrees or more. Turning the array up to 30 degrees away from the optimum azimuth typically costs only a few percent, so an east or west facing roof is often still worth using.
Should I change the tilt between summer and winter?
A two-position seasonal adjustment gains a few percent a year compared with a fixed optimum, which rarely pays for the extra hardware on a roof. It matters more for off-grid systems that must survive December, where a steeper winter tilt near latitude plus 15 degrees collects noticeably more from a low sun and sheds snow better.
How much does east or west orientation cost?
At mid latitudes an east or west facing array at a typical roof pitch collects roughly 15 to 25 percent less over a year than a south facing one. That is often acceptable: an east-west split array spreads production across the morning and evening, which can raise self-consumption and reduce grid export.
Do flat roofs need tilted mounts?
Tilting a flat array to about 10 to 20 degrees gains energy, keeps rain washing the glass and reduces soiling. Higher tilts need more spacing between rows to avoid mutual shading, so on a crowded flat roof a shallower tilt with more panels usually beats a steeper tilt with fewer.