Is my roof good for solar?
A good solar roof has unshaded area facing south, a pitch between 15° and 40°, and at least 10 years of remaining life. Shading matters most — a single badly placed tree can cut output by a third, far more than orientation ever will.
The six factors, in order of impact
1. Shading — the big one
Panels are wired in series, so shade on one panel can drag down a whole string. Trees, chimneys, neighbouring buildings and even a satellite dish matter. Microinverters or optimisers mitigate this but don't eliminate it. Google's imagery accounts for shading, which is why the sunlight hours we report are lower than raw daylight figures.
2. Orientation
In the northern hemisphere, south-facing is best. East and west-facing roofs produce roughly 10–20% less — often still worth doing, and sometimes preferable if your utility pays more during evening peak. North-facing is generally not worth it.
3. Pitch
Between 15° and 40° is ideal. Flat roofs work with tilted mounting frames at extra cost. Very steep roofs raise labour costs and can shade each other at low sun angles.
4. Roof age and material
5. Usable area
You need roughly 21 sq ft per 400W panel, plus fire-code setbacks from ridges and edges — typically 3 ft, which removes more area than people expect on small roofs.
6. Structural condition
An array adds about 2–4 lbs per sq ft. Most roofs handle this fine, but older or damaged framing may need an engineer's sign-off.
Check yours in about ten seconds
Rather than guessing at any of this, enter your address — Google's aerial and 3D imagery reports your roof's usable area, how many panels fit, and its actual measured sunlight hours after shading.
What this looks like in real cities
Measured rooftop data, spanning the range from fastest to slowest payback we have found:
| City | Sun hrs/yr | Rate | Payback |
|---|---|---|---|
| Honolulu, HI | 1,787 | 42.1¢ | 3.1 yrs |
| San Francisco, CA | 1,819 | 31.2¢ | 8.8 yrs |
| Athens, GA | 1,573 | 14.1¢ | 10.9 yrs |
| Swansea, Wales | 1,017 | 26.1¢ | 12.9 yrs |
| Gatineau, QC | 1,291 | 7.9¢ | 33.3 yrs |
Frequently asked
Can I put solar on a north-facing roof?
In the northern hemisphere a north-facing slope is the weakest option and usually not worth using alone. If that is your only aspect, output can fall enough to push payback past the point of being worthwhile. East or west faces lose far less and are usually the better compromise.
Do solar panels damage your roof?
A competent installation should not. Mounts penetrate the roof deck and are sealed; poor flashing is what causes leaks, not the panels themselves. Panels also shelter the covering underneath from UV and weather. If your roof is near the end of its life, replace it before installing.
Can I get solar on a flat roof?
Yes. Panels sit on ballasted or angled frames that tilt them toward the sun, so a flat roof is workable and often easier to access safely. You need more space between rows to stop them shading each other, so a flat roof fits fewer panels than its area suggests.
Related guides
General information, updated 2026-08-22. Not financial, tax or engineering advice.