Solar Panel Orientation Calculator

How to use this calculator

Enter three numbers:

1. Your latitude — look it up on Google Maps by right-clicking your location.
2. Panel azimuth — the compass direction your roof face points, measured in degrees clockwise from true north (0° = north, 90° = east, 180° = south, 270° = west). Use the compass quick-pick buttons if you don’t have a precise reading.
3. Panel tilt — the angle of your roof from horizontal. A flat roof is 0°, a typical American pitched roof is 18–35° (4/12 to 8/12 pitch).

The calculator returns your production factor — the percentage of optimal production you’ll actually capture — plus the optimal orientation for your latitude and a verdict on whether the array is worth installing as-is.

How orientation affects solar output

Solar panels generate the most power when sunlight hits them perpendicular to their surface. Two angles control how often that happens:

• Azimuth (the compass direction the panel faces) determines whether the sun is in front of, beside, or behind the panel during the day. Equator-facing arrays (south in the N. Hemisphere, north in the S. Hemisphere) capture the sun’s path symmetrically.
• Tilt (the angle from horizontal) determines whether the sun hits the panel from above or at a glancing angle. The right tilt depends on your latitude — see the solar panel tilt calculator for the optimal value.

Get both right and you produce 100% of the array’s nameplate capacity (adjusted for weather and system losses). Get one wrong and you lose 5–20%. Get both wrong and you can lose 30–50%.

How much each orientation produces

The table below shows the approximate annual production factor (relative to optimal, latitude-tilted, equator-facing) for common roof orientations at typical US latitudes (30–45°N). Values are derived from NREL PVWatts v6 reference runs and rounded to the nearest 5%.

Three things to notice:

1. Flat panels lose the same amount regardless of compass direction (they all sit at 88% of an optimally-tilted south array — a fact often missed in ballpark sizing).
2. East and west are nearly identical. Pick the one that matches your time-of-use rate plan if you have one — west catches the afternoon peak, east catches the morning shoulder.
3. North-facing roofs in the N. Hemisphere are workable but expensive. A 30°-tilted north-facing array produces only 60% of an equivalent south-facing one, meaning you need 67% more panels to hit the same kWh.

The formula behind this calculator

The production factor uses a first-order approximation of the projected solar irradiance integrated over a typical year:

factor = cos(Δβ) × (1 − 0.3 × (1 − cos(Δγ)))

Where:

• Δβ = (panel tilt) − (optimal tilt). The optimal tilt is approximated as latitude × 0.76, which weights summer’s longer days slightly more than winter’s lower sun angle. This is the same rule used in the solar panel tilt calculator.
• Δγ = the angular distance between panel azimuth and equator-facing azimuth (180° in the Northern Hemisphere, 0° in the Southern). Wrapped so values stay in 0–180°.
• The 0.3 coefficient in the azimuth term comes from fitting the simple cosine model against PVWatts output. Pure cos(Δγ) over-penalises east/west orientations because it ignores diffuse-light gain.

Limits of the model. It’s a back-of-envelope estimator, not a hour-by-hour simulator. It assumes:

• Clear-sky climate with typical diffuse fraction (15–25%)
• Standard fixed-rack mounting (not single- or dual-axis tracking)
• Tilts ≤ 45° and azimuth deviations ≤ 135°

For pole-facing or steep-tilt arrays, run a free hour-by-hour simulation in PVWatts or SAM rather than relying on this calculator.

When to install at sub-optimal orientation anyway

Solar production is one factor in the decision. The other is cost. A south-facing ground mount might be optimal but cost $4,000 more than tying into your existing east-facing roof. Three rules of thumb:

• >90% of optimal: install as-is. The 5–10% loss is dwarfed by the cost premium of re-orienting.
• 75–90% of optimal: install if your roof is the only sensible option, but oversize the array by 10–20%. Verify the production estimate against PVWatts before signing the contract.
• <75% of optimal: seriously consider an alternative — ground mount, carport, garage roof, or moving to a different house face. The array will work but the payback period stretches significantly.

For the full system economics, use the solar payback calculator once it’s published, or for a sanity check on system size run the solar panel ROI calculator.

Common orientation mistakes

• Reading roof azimuth from a magnetic compass. Magnetic declination is up to 20° east in parts of the western US and up to 20° west in the northeast. Always use a true-bearing source (NOAA’s declination tool or Google Maps measurements).
• Confusing roof pitch with tilt. A 6/12 roof pitch is 26.6° tilt, not 6° or 50°. Pitch is rise/run; tilt is the angle from horizontal.
• Ignoring shading. A perfectly oriented array under a tree will under-perform a poorly oriented array in full sun. Check shading separately with a Solar Pathfinder or any free phone app like Sun Surveyor.
• Mixing orientations on one inverter. If your only option is mixing east-facing and west-facing panels on the same string, use micro-inverters or DC optimisers. String inverters lose more than the calculator predicts when panels in a string face different directions.

Sources

• NREL PVWatts v6 documentation — system performance reference
• NREL Solar Resource Maps — irradiance baselines
• SEIA: Solar Industry Research Data 2026 — installation orientation statistics