Quick answer
Solar Panel Tilt is the angle between a panel and the horizontal ground, in degrees: 0° is lying flat and 90° is vertical.
On most homes the panels sit flush with the roof, so tilt equals roof pitch. Across the range of common roof pitches, annual output changes by only a few percent; direction and shade usually matter more.
Quick facts
The key facts about solar panel tilt, with sources:
- Measured as
- Degrees from horizontal, 0° to 90° 2
- DOE guidance
- Slope between 15° and 40° performs best (with a south face) 3
- DOE rule for most yearly energy
- Tilt equal to your latitude, facing due south 4
- Best modelled tilt, Charleston, SC
- About 33° (of the angles we ran) 1
- Flat (0°) vs 33°, Charleston
- About 11% less per year 1
- Roof pitch to degrees
- 4/12 ≈ 18°, 6/12 ≈ 27°, 8/12 ≈ 34°, 12/12 = 45°
Key takeaways
- Tilt is how steeply panels lean. On most homes it simply equals the roof's pitch.
- The DOE rule of thumb for the most yearly energy: face due south and tilt at your latitude.
- Near the best angle, tilt matters little. From 20° to 45°, yearly output in our Charleston model varied by under 3%.
- Flat panels lose more: about 11% a year against the best angle in Charleston. A 10° tilt wins most of that back.
- Steeper panels make more in winter and less in summer. That timing can matter as much as the yearly total.
What tilt means in plain terms
Lay a panel flat on the ground and its tilt is 0°. Stand it straight up like a wall and its tilt is 90°. Every angle in between is a tilt. Installers may also call it the panel angle or array pitch.
On a pitched roof, panels are usually mounted flush, a few inches above the shingles. So the panel tilt is the same as the roof pitch. Roofers describe pitch as rise over run, such as 6/12, meaning the roof rises 6 inches for every 12 inches across. A 6/12 roof is about 27°.
Tilt is one half of the aim. The other half is panel orientation, the compass direction the panels face. The two work together to decide how squarely sunlight hits the panels.
How tilt changes the sunlight panels catch
A panel collects the most when sunlight hits it square on. The sun is high in summer and low in winter. A flat panel faces the June sun well and the December sun badly. A steep panel does the reverse. The best year-round angle sits between the two.
That is why the DOE says panels in the northern hemisphere get the most yearly energy when they point due south and lean at an angle equal to the local latitude. Charleston sits near 33° north, and 33° was the best of the angles we modelled there.
The curve is flat near its top. Missing the best angle by 10° or so costs only a few percent. Missing it by 30° or more costs more, and lying flat costs the most of the common choices.
Tilt vs output: five angles in Charleston
PVWatts V8, 7 October 2026: 7 kW DC facing due south, 14% losses, standard module, fixed roof mount, Charleston (32.78, −79.93). Only the tilt changes 1.
| Tilt | Roughly a roof pitch of | kWh per year | vs best |
|---|---|---|---|
| 0° (flat) | flat roof | 9,148 | −11.0% |
| 10° | about 2/12 | 9,797 | −4.7% |
| 20° | about 4.5/12 | 10,179 | −1.0% |
| 33° | about 8/12 | 10,284 | best of these |
| 45° | 12/12 | 9,993 | −2.8% |
Between 20° and 45°, the whole range of ordinary pitched roofs, the spread is under 3%. Chasing the perfect angle with tilt-up racking on a pitched roof rarely pays.
Steeper favors winter, flatter favors summer
| Tilt | June | December |
|---|---|---|
| 0° | 1,002 | 421 |
| 20° | 962 | 598 |
| 33° | 889 | 674 |
| 45° | 792 | 716 |
Types of tilt by mounting
| Mounting | How tilt is set | Typical use |
|---|---|---|
| Flush roof mount | Equals the roof pitch | Most pitched home roofs |
| Tilt-up rack on a flat roof | Chosen by the designer, often low | Flat or low-slope roofs |
| Fixed ground mount | Chosen once at install | Yards with open sun; see ground mounts |
| Adjustable ground mount | Changed by hand a few times a year | Rare on homes |
| Tracker | Moves through the day to follow the sun 4 | Mostly large ground systems |
Where tilt shows up on your quote
Proposals list tilt for each array, often next to azimuth: "Array 1: 22° tilt, 180° azimuth". If the roof pitch is 5/12, the tilt should read about 23°. A big mismatch is worth a question.
Permit drawings show the roof pitch on the roof plan and in the structural notes. On a flat roof, they show the rack angle and the row spacing too. In PVWatts, tilt is one of the required inputs 2.
Benefits and limits of a steeper or flatter tilt
Steeper (30°–45°)
- More winter output, when the sun is low.
- Snow and rain run off faster.
- Close to the best yearly angle across much of the Southeast.
- Steeper roofs can hold more kW per foot of roof width.
Flatter (0°–15°)
- Less yearly energy; flat lost about 11% in Charleston.
- Weak in winter: December at 0° made 421 kWh against 674 at 33°.
- Snow can sit longer on low-pitch panels 5.
- Strong in summer, which helps only if your summer exports earn well.
Limits: when tilt is a real decision
- Flat or low-slope roofs. Racking can tilt panels up, but rows then shade each other and need wind ballast or attachments. A 10° tilt recovered most of the flat-roof loss in our runs.
- Ground mounts. You choose the angle; see ground mount vs roof mount.
- Very steep or north-facing roofs. Tilt and orientation interact: a steep north face loses much more than a shallow one.
- Pitched roofs. You cannot change the tilt without special racking, and the gain is usually small.
How tilt affects cost
We do not quote dollar prices here. These are the ways tilt moves the price. See cost per watt for current figures.
- Flush mounts are simplest. Panels follow the roof, using standard rails.
- Tilt-up racks add parts. They need extra framing, ballast or attachments, and more spacing between rows.
- Steep roofs add labor. Crews need more safety gear on steep pitches. The DOE builder checklist calls for a permanent roof anchor fall-safety system except on roofs of 3:12 or less 6.
- Lifespan does not change. DOE guidance says systems should produce for at least 30 years, with major parts typically under 25-year warranties 5.
How an installer sets tilt
A licensed installer measures and designs this. Do not go on the roof to measure the pitch yourself.
- Measure the pitch of each roof face during the site survey.
- Model yearly kWh at that tilt and direction in PVWatts or design software.
- On a flat roof, model a few rack angles and check row shading.
- Check the structure can take the panels and, for racks, the wind load.
- Show the tilt on the permit drawings and in the proposal.
Maintenance: how tilt changes upkeep
DOE guidance says rain usually keeps panels clean enough, and that a roof system should need no routine maintenance. It also notes that how fast snow melts off depends partly on the pitch of the roof and the panels.
If you have a low-pitch roof and heavy snow, DOE says you may clear the panels with a long-handled snow rake from the ground. Never climb onto the roof. See our guide to cleaning solar panels for when washing helps.
Sources: [5]
Warning signs: when to call a pro
Call your installer about any of these:
- Panels on a tilt-up rack that move, rattle or have shifted after a storm.
- Rows on a flat roof shading each other in winter.
- Water pooling under low-tilt panels or stains on the ceiling below.
- A tilt on the quote that does not match your roof pitch.
Safety
Steep roofs are dangerous. Do not climb up to check panel angle, clean panels or clear snow. Leave roof work to a trained crew with fall protection.
Rules that affect tilt
No code sets the best angle. Codes cover how the panels are held down. Tilt-up racks catch more wind than flush mounts, so the design must meet the wind and snow loads your building department applies.
Panel data sheets list the loads the panel itself is tested to. One lists a design load of 3,600 Pa push and 1,600 Pa pull 7.
In South Carolina, the 2021 building codes are in force, and the 2024 International Residential Code is scheduled for local use from 1 January 2027 8. Roof mounting must be done by a Residential Builder, a Residential Specialty Contractor with the Roofer classification, or a General Contractor with a roofing classification 9.
Tilt in SC, GA and VA
Using the DOE latitude rule, the starting angle rises as you go north: Charleston, SC sits near 32.8°N, Atlanta, GA near 33.7°N and Richmond, VA near 37.5°N. In practice most homes in all three states mount flush at their roof pitch, which our Charleston runs suggest costs only a few percent.
Size limits still apply: 20 kW AC on Duke Energy Carolinas' SC rider 10, 10 kW for Georgia Power residential systems 11 and 25 kW for residential net metering on Virginia investor-owned utilities 12.
Tilt compared with related terms
| Term | What it describes | Unit |
|---|---|---|
| Tilt | How steeply panels lean | Degrees from flat |
| Orientation | Which way panels face | Degrees from north |
| Mounting system | The racking that sets and holds the tilt | — |
| Irradiance | Strength of sunlight on the panel | W/m² |
| Solar production | Energy the panels make | kWh |
Common misconceptions
- Myth Panels must be at the perfect angle to be worth it.
- Reality Near the best angle the curve is flat. From 20° to 45° our Charleston model varied by under 3%.
- Myth Flat panels do not work.
- Reality They work, at a cost: about 11% less over a year in Charleston, and much less in winter.
- Myth Steeper is always better.
- Reality Past the best angle, summer output falls faster than winter output rises. 45° made less than 33° in our model.
- Myth You should tilt panels up on a pitched roof.
- Reality The gain is usually small and the racking adds wind load and cost.
When tilt matters to you
Use these rules:
- If your roof is pitched between about 4/12 and 12/12, mount flush and move on.
- If your roof is flat, ask for a modelled comparison of a few rack angles.
- If you are building a ground mount, start near your latitude and model it.
- If winter bills matter most, a steeper angle helps more than the yearly total suggests.
- Next step: size the system with the system size calculator, then compare quotes in the proposal analyzer.
Questions about solar panel tilt
What is the best angle for solar panels in South Carolina?
In our Charleston runs, about 33° produced the most of the angles tested. But 20° was only 1% behind and 45° under 3% behind. On a pitched roof, mount flush and accept the roof's angle. On a ground mount, starting near your latitude is a sound choice.
Is the best tilt equal to my latitude?
It is the DOE's rule of thumb for the most yearly energy, with panels facing due south. Charleston sits near 33° north, and 33° performed best in our runs there. Local weather shifts the best angle slightly, so check with PVWatts for your address.
Should I adjust my panels' tilt by season?
Fixed roof panels cannot be adjusted. On an adjustable ground mount, a steeper winter angle raises winter output, as the December figures above show. Most homeowners do not find the labor worth it, because the yearly gain is small.
How do I convert roof pitch to degrees?
Divide the rise by the run, then take the arctangent. A 6/12 roof is arctan(0.5), about 27°. A 4/12 roof is about 18°, an 8/12 roof about 34° and a 12/12 roof exactly 45°. Your installer measures this during the site survey.
Do solar panels work on a flat roof?
Yes. Flat-mounted panels made about 11% less over a year than the best angle in our Charleston model. Many installers tilt them up a little on racks. A 10° tilt won back most of the loss in our runs, but rows then need spacing so they do not shade each other.
Is a steep roof bad for solar?
Not for output. A 45° (12/12) roof made under 3% less than the best angle in our Charleston model, and it does well in winter. Steep roofs are harder and slower to work on, so installation can take more safety gear and time.
Does tilt matter more than direction?
Usually not, on pitched roofs. In our Charleston runs, moving from 20° to 45° tilt cost under 2%, while turning from south to east cost about 13%. Direction and shade usually decide more than tilt does.
What tilt angle is best for winter?
A steeper one. In our Charleston model, December output rose from 421 kWh lying flat to 598 kWh at 20°, 674 kWh at 33° and 716 kWh at 45°. The trade-off is lower summer output, so the yearly total peaks at a middle angle.
Sources
- PVWatts V8 API runs by HyreSolar, 7 October 2026 (Charleston SC, 7 kW, standard module, roof mount, azimuth 180°, tilt varied, losses 14%, NSRDB PSM V3 TMY), retrieved .
- NLR (formerly NREL), PVWatts V8 API documentation, retrieved .
- U.S. DOE Solar Energy Technologies Office, Homeowner's Guide to Going Solar, retrieved .
- US DOE Solar Energy Technologies Office, Solar Photovoltaic System Design Basics, retrieved .
- US DOE Weatherization Assistance Program, Solar Frequently Asked Questions, retrieved .
- U.S. DOE Building America, Renewable Energy Ready Home Solar Photovoltaic Checklist, retrieved .
- Qcells, Q.TRON BLACK (Q.TRON BLK S-G3R.12+/BFG 435–450) data sheet, 2025-08 Rev04, retrieved .
- SC Building Codes Council, code adoption, retrieved .
- SC LLR, Residential Specialty Contractor registration (Solar Panel Installer), retrieved .
- Duke Energy Carolinas (SC), Rider RSC Residential Solar Choice, retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Output figures are PVWatts V8 results for the stated inputs; percentages and pitch conversions are computed.
Slope and latitude guidance from DOE; snow and maintenance from the DOE Weatherization FAQ; fall-safety threshold from the DOE RERH checklist; design load from the Qcells data sheet. SC code and licensing facts from sc-local/facts.js.
Suggest a correction. We fix errors and say what changed.