Solar & battery
Solar Panel Angle Calculator
Works array angle, where orientation usually matters more than tilt.
Result
The loss figures here are an approximation of a cosine relationship, good enough to judge whether a roof is workable. Real modelling uses hourly irradiance data. Solar is also forgiving: most roofs within 30 degrees of south and 15 degrees of optimal tilt lose only a few percent.
Get a Free Business AuditHow the calculation works
The tilt that maximises annual energy is close to the site latitude, with lower tilts favouring summer production and higher tilts favouring winter. The calculation gives the optimum and the penalty for deviating from it, which is the more useful output because most roofs have a fixed pitch.
What moves the number
- Latitude, which sets the annual optimum.
- Whether summer or winter production matters more.
- Roof pitch, which is usually fixed.
- Azimuth, which generally matters more than tilt.
Where this one goes wrong
The penalty for a non-optimal tilt is smaller than people expect over a reasonable range, while the penalty for poor orientation is larger, which means a south-facing roof at the wrong pitch usually beats a correctly pitched roof facing east or west. Spend the effort on orientation and shading. Snow is the exception where a shallow tilt genuinely causes problems, since snow sheds poorly from a low-pitched array and a covered array produces nothing.
Before you quote
- Prioritise orientation and shading over tilt optimisation.
- Accept the roof pitch unless the penalty is genuinely large.
- Consider snow shedding where that applies.
Where the rules come from
Questions
About this calculator
What is the best tilt for solar panels?
Close to the site latitude for maximum annual energy, with lower tilts favouring summer and higher ones favouring winter. The penalty for deviating over a reasonable range is smaller than most people expect, which is why roof pitch is usually acceptable.
Does tilt or orientation matter more?
Orientation, generally. A south-facing roof at a non-ideal pitch usually outperforms a correctly pitched roof facing east or west, which means the effort is better spent on orientation and shading than on tilt optimisation.
Should tilt be adjusted for snow?
It is one case where a shallow tilt causes real problems, since snow sheds poorly from a low-pitched array and a covered array produces nothing at all. In snowy climates that can outweigh the theoretical optimum.
The formula
optimal tilt is roughly the latitude, less 15 degrees for summer or plus 15 for winter
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How to use this calculator
- Latitude (degrees). Enter your own figure; the page starts at 39.
- Optimise for. Enter your own figure; the page starts at Year-round output.
- Tilt you actually have (degrees). Enter your own figure; the page starts at 25.
- Degrees away from true south. Enter your own figure; the page starts at 20.
The result updates as you type, so you can try a figure, see what it does to optimal tilt, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Latitude (degrees) | 39 |
| Optimise for | Year-round output |
| Tilt you actually have (degrees) | 25 |
| Degrees away from true south | 20 |
What comes out
| Result | Value |
|---|---|
| Optimal tilt main result | 39.0 |
| Loss from your tilt | 2.42% |
| Loss from the orientation | 0.99% |
| Combined loss | 3.41% |
| Energy captured | 96.6% |
Optimal tilt here is about 39.0 degrees. At 25 degrees and 20 degrees off south you capture roughly 96.6% of the available energy.
How sensitive the answer is
Holding everything else steady and changing only latitude (degrees), this is what happens to optimal tilt. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Latitude (degrees) | Optimal tilt |
|---|---|
| 19.5 | 19.5 |
| 29.25 | 29.3 |
| 39 example above | 39.0 |
| 58.5 | 58.5 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Latitude (degrees)
- A number, between 0 and 70, starting at 39.
- Optimise for
- Choose from Year-round output, Summer output, Winter output.
- Tilt you actually have (degrees)
- A number, between 0 and 90, starting at 25.
- Degrees away from true south
- A number, between 0 and 180, starting at 20.
What the results tell you
| Result | What it is |
|---|---|
| Optimal tilt | The headline result. A decimal figure. |
| Loss from your tilt | A percentage. |
| Loss from the orientation | A percentage. |
| Combined loss | A percentage. |
| Energy captured | A percentage. |
A design still needs a site visit
Output and sizing figures use the assumptions you enter, not measured irradiance, shading or roof orientation at your address. Real production depends on all three, plus inverter behaviour and local interconnection rules.
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