Solar Panel Azimuth & Orientation Loss Calculator
Enter a roof plane’s true-north azimuth, tilt, and local annual sun resource to estimate its annual orientation penalty. The result also separates morning from afternoon production and searches for the best fixed direction under the same assumptions.
Orientation factor96.84%
- Orientation loss
- 3.16%
- Estimated annual production
- 10,165.5
- Equator-facing production
- 10,497.03
- Annual kWh difference
- 331.53
- Morning production share
- 38.94%
- Afternoon production share
- 59.99%
- Best modeled fixed orientation
- Tilt 31°, azimuth 180° (true south)
Annual production is shown in kWh/year and uses horizontal peak sun hours, a constant diffuse-light fraction, and the entered non-orientation losses.
The best fixed orientation is a one-degree annual scan using the same five-minute solar-hour-angle intervals as the entered orientation.
How to use this calculator
- Enter latitude as positive north or negative south, then enter the roof plane’s true-north bearing and tilt.
- Use annual-average horizontal peak sun hours rather than a value already adjusted for a tilted array.
- Choose a diffuse-light fraction and ground reflectance that reasonably describe the site.
- Enter the array’s DC size and losses other than orientation, then compare annual production with the equator-facing reference.
How solar orientation loss is calculated
Azimuth is the compass direction a panel faces, measured here from true north: 90 degrees is east, 180 degrees is south, and 270 degrees is west. North of the equator, a fixed array normally gets its highest annual direct exposure while facing south; south of the equator, the reference direction is north. A west-facing roof may still be a sensible choice when later electricity production has more value, but it usually receives less annual beam energy than the equator-facing reference.
The calculator represents every day of a 365-day year and samples the solar hour angle every five minutes. For each sun-above-horizon interval, it first calculates the horizontal zenith cosine q = sin(phi) sin(delta) + cos(phi) cos(delta) cos(omega). It then calculates the panel-incidence cosine c from latitude, declination, panel tilt, azimuth, and hour angle. The direct part of the panel weight is max(c, 0), so the front of the panel cannot collect direct light from behind.
The interval plane-of-array weight is:
p = (1 - f) max(c, 0) + f q (1 + cos(beta)) / 2 + rho q (1 - cos(beta)) / 2
- f is the diffuse-light fraction.
- beta is panel tilt above horizontal.
- rho is ground reflectance, also called albedo.
Summing p and dividing by the summed horizontal weights gives the transposition ratio R = sum(p) / sum(q). Annual horizontal irradiation is H = 365 x PSH, so modeled plane-of-array irradiation is H_POA = H x R. Annual production is E = array kW x H_POA x (1 - losses). Orientation factor is the entered production divided by production from the same tilt facing the equator; orientation loss is max(0, 1 - factor).
What moves the result most
Azimuth matters most for steep panels and dry, beam-dominated climates. A high diffuse fraction softens the difference between east, south, and west because sky light arrives from many directions. Tilt also changes the balance: flat panels have no azimuth preference in this model, while a steeper roof gains and loses more from its facing. The morning and afternoon shares show timing, not electricity value; a west-facing array can shift more energy into the afternoon even when its annual total falls.
What this calculator leaves out
This is an annual geometry estimate, not an hourly weather or financial model. It uses one annual diffuse fraction and a synthetic solar-year distribution. It does not model trees, buildings, a raised horizon, snow, row shading, bifacial rear gain, inverter clipping, module mismatch, or the way temperature and weather vary through the day. Use measured hourly weather data and a professional design when a system decision depends on the final production number.
Worked example
For a 6 kW DC array at latitude 35 degrees, facing 225 degrees at a 25 degree tilt, with 5.0 peak sun hours per day, 30% diffuse light, 20% ground reflectance, and 14% other losses, the orientation factor is 96.84%. The model estimates 10,165 kWh/year, compared with 10,497 kWh/year for a 180 degree, same-tilt reference: a 332 kWh/year difference. It converts 5.0 daily peak sun hours to 1,825 kWh/m²/year before applying the modeled plane-of-array ratio and the 86% remaining system factor.
The southwest-facing plane assigns 38.94% of modeled irradiation to morning and 59.99% to afternoon. Under these assumptions, the one-degree search finds a 31 degree tilt at 180 degrees as the best fixed orientation; that result can use a tilt different from the roof plane.
Common questions
What azimuth should solar panels face?
For the highest annual direct exposure, fixed panels generally face true south in the Northern Hemisphere and true north in the Southern Hemisphere. The best roof direction can differ when a utility pays more for late-day energy, when roofs limit the layout, or when local shading favors another plane. This calculator reports annual quantity, not time-of-use value.
Is solar azimuth measured from true north or magnetic north?
This calculator uses true-north bearings. A magnetic compass reading must be corrected for local magnetic declination before entry, because magnetic north and true north are not usually the same direction. Mapping tools and professional solar software commonly report true bearings.
How much output do east- or west-facing panels lose?
The loss depends on latitude, tilt, diffuse light, and the exact azimuth, so there is no reliable single percentage. East and west roofs often lose less in cloudy places because diffuse sky light is less directional. They also move production earlier or later in the day, which may matter more than annual kWh for some tariffs.
Are southwest-facing panels better for afternoon electricity use?
Usually, a southwest-facing array produces a larger share of its energy after solar noon than a south-facing array. Whether that is better depends on your electricity rate, battery behavior, and demand profile. The annual total can be lower even when the timing is more useful.
Do flat solar panels have an azimuth?
A horizontal panel has a compass bearing physically, but its front surface is the same in every azimuth. In this model a zero-degree tilt has an orientation factor of 100% because azimuth does not change its plane-of-array irradiation. Mounting details and drainage considerations are separate design questions.
Why can this estimate differ from PVWatts or an installer proposal?
PVWatts and design proposals can use weather stations, hourly weather files, module temperature models, horizon data, and equipment-specific loss assumptions. This calculator intentionally isolates annual sun geometry using a constant diffuse fraction. Use it to compare orientations consistently, then use a site-specific model for a production forecast.