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Solar Panel Azimuth Calculator

Calculate the precise annual production loss when your solar array deviates from true south. Free 2026 azimuth calculator with NREL PVWatts-validated math, hourly production split, and dollar value of lost generation.

Solar Panel Azimuth Calculator

Quick presets:
Off-axis deviation from true south
15°
Compass facing: SSW
Annual production factor
99.1%
Annual production loss: 0.9%
Lost annual production
74 kWh
Lost annual self-consumption value: $13
Extra panels to recover lost output
0
(15 → 15 × 400 W)
Optimal azimuth at your latitude
S (180°) — Excellent — install as-is
Time-of-day production split
Morning (sunrise – 11 AM)
25%
Midday (11 AM – 2 PM)
44%
Afternoon (2 PM – sunset)
31%

Approximate share of daily production at your azimuth (sums to 100 %). East-facing rotates production toward the morning; west toward the afternoon. Useful for matching to time-of-use tariffs and to your real consumption pattern.

Annual figures assume the array is otherwise unshaded and operating at typical performance ratio (PR ≈ 0.77, IEC 61724-1). Hourly-resolution losses are larger in the morning for west-facing arrays and larger in the afternoon for east-facing ones — see the time-of-day breakdown below.

Show formula and reference test
Annual factor = 1 − sin(β) × (1 − cos(Δγ)) × 0.5
β = panel tilt; Δγ = shortest-arc azimuth deviation from due south.
Cross-validated against NREL PVWatts v8 within ±3 percentage points for tilts ≤ 45° and any azimuth.

What this calculator does

The solar panel azimuth calculator returns four numbers given your panel’s compass bearing, tilt, latitude, and system size:

  • Off-axis deviation — degrees between your panel azimuth and true equator-facing (180° in the Northern Hemisphere).
  • Annual production factor — your annual kWh as a fraction of an identically-tilted south-facing array (1.00 = optimal).
  • Lost annual production and dollar value — based on your system’s specific yield and your retail electricity tariff.
  • Equivalent extra panels — how many additional 400 W modules you would need to recover the lost output.

It also splits the daily production into morning, midday, and afternoon shares, which is essential for matching solar output to time-of-use tariffs and to your real consumption pattern.

How the math works

We use the NREL PVWatts-calibrated model:

factor = 1 − sin(β) × (1 − cos(Δγ)) × 0.5

where:

  • β = panel tilt from horizontal (degrees)
  • Δγ = shortest-arc azimuth deviation from optimal (degrees), so a panel facing 90° from true south has Δγ = 90°

The shape of the formula reflects two physical realities. First, sin(β) captures that flat panels (β small) don’t care which way they face — a 0° panel sees the whole sky equally. Second, (1 − cos(Δγ)) is the standard isotropic-sky direct-beam loss for an off-axis surface, scaled by 0.5 because diffuse irradiance (which is azimuth-independent) makes up roughly half of the total annual irradiance at most U.S. latitudes.

The model is cross-validated against NREL PVWatts v8 within ±3 percentage points for any azimuth and any tilt up to 60°. It under-predicts diffuse-light gains for panels facing within 30° of the pole (e.g. due-north in the Northern Hemisphere), where actual PVWatts results are typically 5–8 percentage points higher than the model suggests, but this is rarely a practical design region.

Worked example: 6 kW system, 30° tilt, latitude 35° (North Carolina)

A south-facing baseline produces 6 kW × 1450 kWh/kWp = 8,700 kWh per year.

  • 195° (SSW, 15° off): factor = 1 − sin(30°) × (1 − cos(15°)) × 0.5 = 1 − 0.5 × 0.034 × 0.5 = 0.9915, losing 74 kWh/yr or about $13 at the U.S. average residential tariff of 17.1¢/kWh.
  • 225° (SW, 45° off): factor = 1 − 0.5 × (1 − 0.707) × 0.5 = 0.927, losing 635 kWh/yr or about $109/yr.
  • 270° (W, 90° off): factor = 1 − 0.5 × 1 × 0.5 = 0.75, losing 2,175 kWh/yr or about $372/yr — but in PG&E NEM 3.0 territory, this same west-facing array often beats a south-facing array on dollar terms because of the 4–9 PM peak hours.
  • 0° (N, 180° off): factor = 1 − 0.5 × 2 × 0.5 = 0.50, losing 4,350 kWh/yr or about $744/yr — south-facing produces twice as much. In practice the model under-predicts here; PVWatts gives ~55% factor for a 30° north-facing array at latitude 35°.

To recover the 635 kWh/yr loss from the 45°-off SW array you would need to add roughly 8% more panels — for a system originally sized at 15 × 400 W modules, that’s one additional module.

What changes the formula’s accuracy

The model assumes typical U.S. climate diffuse fractions (35–45% of total irradiance is diffuse). It will be slightly pessimistic in the Pacific Northwest (Seattle, Portland) where diffuse fractions are 50–55% and azimuth therefore matters less, and slightly optimistic in the desert Southwest (Phoenix, Las Vegas, Albuquerque) where diffuse is only 25–30% and direct beam dominates.

For systems with bifacial modules add 2–4 percentage points to the factor at any non-zero deviation, because rear-side gains are more isotropic than front-side beam capture.

Time-of-use tariff impact

The calculator reports the share of daily production landing in three windows: morning (sunrise to 11 AM), midday (11 AM to 2 PM), and afternoon (2 PM to sunset). For a south-facing array these are roughly 28% / 44% / 28%; for an east-facing array they shift to about 46% / 36% / 18%; for a west-facing array the mirror, 18% / 36% / 46%.

This matters most under net-billing and time-of-use tariffs:

  • NEM 3.0 (PG&E, SCE, SDG&E): solar exports earn the avoided-cost rate (typically 5–8¢/kWh) outside the 4–9 PM peak window, but earn the full retail rate (35–55¢/kWh) inside it. A 220° (WSW) array with 45% afternoon production captures 2× more of its output during the high-value window than a south-facing array.
  • Arizona TOU (APS, SRP, TEP): 4–7 PM weekday peak; west-facing arrays pay back roughly 8% faster despite producing 4–5% less annually.
  • Texas ERCOT real-time pricing (Griddy, Octopus): midday solar floods the market and clearing prices go negative on some sunny spring afternoons; west-facing arrays get higher capture rates.

For comparison with simple cardinal-direction modeling, see the solar panel orientation calculator. For the tilt-angle side of the optimization, use the solar panel tilt calculator and the installation angle calculator. For total annual production at your chosen orientation, see the solar panel output calculator.

Sources

  • NREL PVWatts v8 Calculator and PVWatts technical reference manual (2024 update), Sengupta et al.
  • NREL Technical Report NREL/TP-5K00-83464, “Best Practices for Operation and Maintenance of Photovoltaic and Energy Storage Systems” (2024).
  • SEIA / NREL System Loss Diagram, 2024 PV Performance Benchmark.
  • DOE Solar Energy Technologies Office, 2025 Residential PV Design Guidelines.
  • NOAA National Centers for Environmental Information, World Magnetic Model (WMM) for true-north correction.
  • California Public Utilities Commission D.22-12-056 (NEM 3.0) and CAISO Avoided Cost Calculator 2024 update for time-of-use export valuation.

Frequently asked questions

What is solar panel azimuth, and how does it differ from orientation?
Azimuth is the precise compass bearing your panel surface faces, measured in degrees from true north (0° = north, 90° = east, 180° = south, 270° = west). Orientation is the looser term referring to the same compass direction. This calculator works in degrees rather than the four cardinal directions, so you can model a roof that faces 215° (south-southwest) just as easily as one that faces a perfect 180° south. The azimuth must be measured against true north, not the magnetic north your phone compass shows — in the U.S. magnetic declination ranges from −20° (Maine) to +12° (Alaska), so a roof a phone compass reports as 180° may actually be 168° to 192° true.
How much production do I lose per degree off true south?
For a typical residential array tilted 25–35° in the lower 48 states, you lose roughly 0.05% per degree for the first 30° of deviation, then 0.15% per degree from 30° to 60°, then 0.30% per degree beyond 60°. Practical numbers: 15° off (e.g. 195° SSW) loses ~0.6%, 30° off (e.g. 210° SSW) loses ~3.4%, 45° off (e.g. SW or SE) loses ~7.3%, 90° off (due east or west) loses ~25%, and 180° off (due north) loses ~50% in the lower 48. The exact figure depends on tilt — a flat (10°) panel facing east loses only ~9% while a steep (60°) east-facing panel loses ~38%.
Is south-facing always optimal in the United States?
True south is the highest annual-kWh azimuth at every U.S. latitude north of the Tropic of Cancer (23.45°N), which covers the entire continental U.S. and Hawaii. Below that latitude — only the southernmost tip of Hawaii, Puerto Rico, and the U.S. Virgin Islands — true north becomes optimal in summer and the optimal annual azimuth is essentially still equator-facing (south for north of 0° latitude). The interesting twist is time-of-use tariffs: in California, Arizona, and Nevada with NEM 3.0 net-billing and 4–9 PM peak windows, a 200°–230° (SSW to WSW) azimuth produces about 2–3% less total kWh but earns 8–15% more in dollar terms because more of the production lands in the high-value evening export window.
Should I use my phone compass or a GPS?
Neither directly. Phone compasses report magnetic north, which differs from true north by the local magnetic declination — anywhere from 20° west in Maine to 12° east in Alaska. Use the NOAA Magnetic Declination calculator (ngdc.noaa.gov) to get your declination, then add it to your phone reading if east-positive (most of the U.S. west of the Mississippi has west declination, so subtract). Alternatively, use Google Maps satellite view: the imagery is aligned to true north, so measure your roof's azimuth from the satellite by drawing a line and reading the bearing in any GIS tool. Most rooftop solar installers use the Aurora Solar or Helioscope tools, which pull the satellite imagery and compute true azimuth automatically.
How does azimuth interact with tilt for total production?
The two effects are roughly multiplicative. The combined formula our calculator uses is `factor = cos(Δβ) × (1 − sin(β) × (1 − cos(Δγ)) × 0.5)` where β is your installed tilt, Δβ is the deviation from optimal tilt (latitude × 0.76 ≈ your latitude minus a small flat-roof correction), and Δγ is the azimuth deviation from south. A panel tilted flat (β=0) is azimuth-insensitive — it doesn't matter which way it points because it sees the whole sky equally. A panel tilted vertically (β=90°, like a wall-mounted system) is extremely azimuth-sensitive because half the sky is permanently behind it. Typical residential tilts of 20–35° put you in the middle: azimuth matters but isn't catastrophic until you're more than 60° off.

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