What this calculator does
For a fixed-mount solar panel that will not be adjusted through the year, the classic rule of thumb is to set the tilt angle equal to the site's latitude. That angle roughly points the panel face at the sun's average position across the year, balancing summer and winter performance rather than optimising for either.
If a system leans towards one season, the rule adjusts: adding around 15 degrees favours winter output (useful for a heating-season load, since the sun sits lower in the sky and a steeper tilt catches it better), while subtracting around 15 degrees favours summer output, when the sun tracks higher overhead and a shallower tilt performs better.
The formula
The year-round estimate is simply the absolute value of the site latitude. The winter-weighted estimate adds 15 degrees to that figure, and the summer-weighted estimate subtracts 15 degrees, both clamped between 0 and 90 degrees since a tilt angle outside that range is not physically meaningful for a panel facing the sky.
| Term | Meaning |
|---|---|
| Latitude | The site's distance north or south of the equator, in degrees, entered as a positive number. |
| Year-round tilt | Tilt angle ≈ latitude, balancing performance across all seasons. |
| Winter-weighted tilt | Tilt angle ≈ latitude + 15°, favouring output when the sun sits lower in the sky. |
| Summer-weighted tilt | Tilt angle ≈ latitude − 15°, favouring output when the sun sits higher overhead. |
The inputs explained
| Field | What to enter |
|---|---|
| Site latitude (absolute value) (°) | Enter your site's latitude as a positive number of degrees, regardless of whether you are north or south of the equator. You can find this from any map or GPS app. |
When to use it
Setting a fixed rooftop mount
Most residential rooftop installs are not adjusted through the year, so a single compromise angle close to latitude is the practical starting point, subject to whatever the roof pitch itself allows.
Optimising for a winter heating load
A system paired with electric heating, or a household that uses noticeably more power in winter, benefits from the winter-weighted tilt, trading away some summer output for stronger performance when it is needed most.
Optimising for a summer cooling load
The reverse applies to a system feeding heavy summer air-conditioning use, where the summer-weighted tilt captures more of the output when demand peaks.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the three rule-of-thumb tilt angles change with latitude
The three rule-of-thumb tilt estimates across a range of site latitudes.
| Site latitude | Year-round tilt (rule of thumb) | Winter-weighted tilt (heating season) | Summer-weighted tilt (cooling season) |
|---|---|---|---|
| 10° | 10.0° | 25.0° | 0.0° |
| 20° | 20.0° | 35.0° | 5.0° |
| 30° | 30.0° | 45.0° | 15.0° |
| 40° | 40.0° | 55.0° | 25.0° |
| 50° | 50.0° | 65.0° | 35.0° |
| 60° | 60.0° | 75.0° | 45.0° |
Questions
How accurate is this rule of thumb?
It is a widely used starting estimate, not a precise optimum. Actual optimal tilt depends on local weather patterns, typical cloud cover by season and the specific latitude, and can differ from the simple latitude-based figure by several degrees either way. Solar-position software or a professional design uses the sun's actual path at your exact location rather than this shortcut.
Why does the rule break down near the equator or the poles?
Very close to the equator, latitude itself is near zero, so the winter- and summer-weighted adjustments can push the numbers into physically odd territory (a negative tilt, for instance, has no meaning for a panel facing the sky, which is why this calculator floors it at zero). Near the poles, the sun's low angle year-round makes a simple latitude-based rule a poor fit generally, and site-specific analysis matters much more.
Does a steeper or shallower tilt change more than just energy output?
Yes. Tilt also affects how well panels self-clean in rain and shed snow, since a steeper angle sheds both more readily than a nearly flat one, which is worth weighing alongside the pure energy-output estimate.
Should tracking systems use this rule at all?
No. This rule of thumb is only for fixed-tilt mounts. A single or dual-axis tracking system continuously adjusts its angle to follow the sun and is not set to any one fixed figure.
Once a tilt angle is chosen, use the solar energy yield calculator to estimate the output it will actually produce.