Does Roof Pitch Matter for Solar? 20° vs. 30° Compared
Roof pitch changes solar output by only a few percent. See how 20° and 30° compare on south, east, and west roofs, and what it means for payback.
Published 5 min readRoofPayback editorialChecked by automated fact and quality checks
Official data: EIA · DOE · IRS · how we check
In this article · 10 sections
- 01Short answer
- 02What "pitch" means and why it matters
- 03How we measured it
- 0420° vs. 30° on a south-facing roof
- 05Pitch matters even less than direction
- 06What happens when a roof is both steep and east or west facing
- 07What a drop in output means for your payback
- 08Other things that matter as much as pitch
- 09What to ask an installer
- 10Bottom line
Short answer
Roof pitch matters much less than which way the roof faces. In our numbers, moving a south-facing array from a 20° pitch to a 30° pitch changes yearly output by 2.4% on average across states. Facing east or west instead of south costs roughly 14.5% to 14.8% at a 20° pitch. So if your roof is a bit steeper or flatter than ideal, that is rarely a reason to skip solar. A roof that faces the wrong way is a bigger issue.
What "pitch" means and why it matters
Pitch is how steep your roof is. In solar, people usually give it as an angle in degrees. A flat roof is near 0°. A steep roof is far higher.
Panels make the most power when sunlight hits them straight on. In the U.S., the sun sits in the southern half of the sky. A panel tilted toward the south catches more of it over a full year. The best tilt changes with your latitude, but the effect is gentle. A small miss costs little.
How we measured it
We used PVWatts v8, a free solar production estimator from the U.S. Department of Energy's National Laboratory of the Rockies (formerly NREL). The base case is a south-facing array at a 20° pitch with 14% losses, using one reference city per state. Every other case is compared with that base. You can read more on our methodology page.
Numbers below are the average across states, plus the smallest and largest change we found.
20° vs. 30° on a south-facing roof
| South-facing, vs. 20° | Average | Smallest | Largest |
|---|---|---|---|
| 30° pitch | 2.4% | 4.7% (Alaska) | -1.7% (Hawaii) |
Here, "smallest" and "largest" are the labels from our dataset, which is why the table shows 4.7% as the smallest and -1.7% as the largest. The key point is simple: a steeper south-facing roof helps a little in most places. In Hawaii, which is close to the equator, it slightly hurts.
Why would steeper help in Alaska? The sun stays lower in the sky at high latitudes, so a steeper panel faces it better. Near the equator, the sun is higher, so a flatter panel does better.
Pitch matters even less than direction
Now compare direction. All of these are at a 20° pitch, versus south at 20°.
| Direction (20°) | Average | Smallest | Largest |
|---|---|---|---|
| Southeast | -4.1% | -1.8% (Florida) | -7.2% (Alaska) |
| Southwest | -4.3% | -2.2% (Hawaii) | -5.9% (Montana) |
| East | -14.5% | -7.2% (Hawaii) | -20.7% (Alaska) |
| West | -14.8% | -7.6% (Hawaii) | -18.7% (Montana) |
| East and west split | -14.7% | -7.4% (Hawaii) | -18% (Alaska) |
Southeast and southwest roofs lose a few percent. East, west, or a split east-west layout lose much more. Compare that with the 2.4% gain from a steeper south roof. Direction moves your output far more than the pitch change we tested.
What happens when a roof is both steep and east or west facing
Steep roofs that face east or west lose the most in our tests.
| Direction (30°) | Average | Smallest | Largest |
|---|---|---|---|
| East | -17.2% | -11.1% (Hawaii) | -23.3% (Alaska) |
| West | -17.7% | -11.6% (Hawaii) | -21.4% (Montana) |
Compare these with the same directions at 20°. East at 20° averages -14.5%, but east at 30° averages -17.2%. For east and west faces, a steeper pitch makes things worse. The panels point more toward the horizon and less toward the high midday sun.
If your home has an east-west roof, our guide to east-west facing solar panels covers when it can still make sense.
What a drop in output means for your payback
Less output means less electricity from the same hardware. The cost stays about the same, so payback takes longer. Our example home is a good way to see this. It assumes:
- A 7 kW system.
- 10500 kWh a year of household use. A kWh, or kilowatt-hour, is the unit your utility bills you for. See what is a kilowatt hour.
- 40% of use happens while the sun is up.
- Installed cost of $3000 per kW, or $21000 in total, with no incentives.
- $100 a year in maintenance.
- Electricity prices rising 2.5% a year, and panels losing 0.5% of output a year.
- A 25-year horizon.
- Export credits capped at a year of grid purchases, with an annual true-up.
Under those assumptions, a roof that loses 14.5% of output (east at 20°) will pay back slower than one that loses 4.1% (southeast at 20°). To see exact figures for your state, plug your roof into the solar calculator. For background, read solar payback period explained.
Your local electricity price matters too. A high price makes each kWh your panels produce worth more. Check the electricity prices by state page. Prices come from the EIA's July 2026 average residential data.
Other things that matter as much as pitch
- Shade. Trees and chimneys can cost more than any pitch change.
- Roof space. A steeper roof may fit fewer or more panels, depending on layout. See how many solar panels you need.
- Your utility's export rules. Net metering and solar incentive programs vary by state and utility. DSIRE keeps a database of current programs at programs.dsireusa.org. Also see net metering vs. net billing.
- Incentives. The federal Residential Clean Energy Credit (Section 25D) is not available for property placed in service after December 31, 2025, per the IRS. Our example home assumes no incentives. See is solar worth it without the tax credit.
- Mounting. Installers can sometimes tilt panels on a flat roof. On a pitched roof, panels usually follow the roof. Ask what your installer can do.
What to ask an installer
- What output do you expect for my exact roof direction and pitch?
- Which tool did you use, and what loss assumption?
- Are there roof sections that face a better direction?
- How does my utility credit exported power?
Estimates differ by company, so compare more than one quote. You can also run your own roof in PVWatts.
Bottom line
For a south-facing roof, a 30° pitch beats 20° by 2.4% on average. That is a small gain. The direction of your roof matters far more: southeast and southwest lose 4.1% and 4.3% on average, while east and west lose 14.5% and 14.8%. Do not rule out solar because of a pitch that is a little off. Instead, check direction, shade, your utility's rules, and your own price per kWh. Then run the numbers in our solar calculator.
Sources
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