Solar
Solar Panel Angle Calculator
Annual fixed tilt starts at absolute latitude, with simple 15-degree seasonal adjustments. The angle-loss comparison uses cosine geometry and does not replace site production modeling. Production inputs follow the dated NLR PVWatts, EIA, and Census-derived sources documented on the Solar Data Sources page.
Estimate a fixed or seasonal solar-panel tilt from latitude and compare the direct-beam geometry at an entered installation angle.
Calculated result
Panel tilt estimate
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
Data provenance: NLR PVWatts v8 grid awaiting its first private-key refresh; the visible peak-sun-hours fallback is active. EIA residential state averages updated 2026-08-13. ZIP centroids use the 2025 Census Gazetteer. Calculator lookups use checked-in data rather than sending inputs to those source agencies; information submitted through quote or email forms is handled under the Privacy policy. Read the solar data provenance and limitations.
What this calculator returns
Use the angle as a transparent starting point for fixed-rack planning, then account for roof pitch, azimuth, shade, snow, wind, access, and structural requirements.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Annual fixed tilt = absolute latitude; summer tilt = latitude − 15°; winter tilt = latitude + 15°, each limited to 0–90°. Relative direct irradiance = cos(angle difference).
- φ
- Absolute site latitude in degrees.
- θopt
- Simple annual or seasonal target tilt from horizontal.
- θactual
- Entered planned panel tilt from horizontal.
- cos(Δθ)
- Relative direct-beam incidence factor for the angle difference only.
Latitude and tilt are angles from the horizontal. The cosine comparison isolates only incidence-angle geometry.
Worked example
| Input | Value |
|---|---|
| U.S. ZIP Code | 80202 |
| Tilt period | Annual fixed |
| Planned panel tilt | 30 ° |
At 40° latitude, annual fixed tilt is 40°. A 30° panel differs by 10°, corresponding to about 1.5% direct-beam geometric loss before weather and system effects.
Reference table
| U.S. latitude band | Annual fixed | Summer adjustment | Winter adjustment |
|---|---|---|---|
| 25°–30° N | 25°–30° | 10°–15° | 40°–45° |
| 30°–35° N | 30°–35° | 15°–20° | 45°–50° |
| 35°–40° N | 35°–40° | 20°–25° | 50°–55° |
| 40°–45° N | 40°–45° | 25°–30° | 55°–60° |
| 45°–50° N | 45°–50° | 30°–35° | 60°–65° |
Frequently asked questions
How is seasonal tilt calculated?
The tool starts from absolute latitude, subtracts 15 degrees for summer, or adds 15 degrees for winter, limited to 0–90 degrees.
Does the angle result account for roof direction?
No. The cosine comparison isolates tilt difference and does not model azimuth, shading, weather, or diffuse light.
Is latitude always the best roof angle?
No. It is a simple annual fixed-tilt starting point; actual production and installation constraints need site-specific modeling.
Assumptions and limitations
- Geometry only; not a production forecast or mounting design.
- Terrain, horizon, diffuse light, weather, azimuth, tracking, bifacial gain, and obstruction losses are excluded.
- Verify mounting and structural requirements with qualified professionals.
Method and sources
Review the solar data sources, calculation methodology, and electrical formulas for the references most relevant to this calculation. The broader technical sources index records source scope and provenance. Content release .
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