Quick definition
Azimuth tells you which way a panel points on a compass, expressed in degrees. North is 0, east is 90, south is 180, and west is 270. A roof plane's azimuth is fixed by the direction that section of roof actually faces, unless the array sits on ground mounts or a tracking system that can adjust it.
It's one of two directional measurements that shape how much sun a panel actually captures over a year, alongside tilt angle.
At a glance: a panel within 30 to 45 degrees of true south, so roughly southeast through southwest, typically retains 90% or more of true-south output in most US and Canadian locations.
Why it matters
Most homeowners don't get to choose their roof's azimuth. The house was built facing whatever direction it was built facing, and the roof planes follow from there. What azimuth does is tell you, and your installer, how much of that fixed roof geometry is working for you or against you.
Say a roof has one plane facing true south and another facing due west. The south-facing plane will produce more total energy over a year. But the west-facing plane isn't wasted; it just shifts production later into the afternoon, which can actually line up well with a household's peak usage or with a utility's higher afternoon time-of-use rates, a shift worth checking with the time of use rate savings calculator before writing off a west-facing section as the weaker choice.
This is why azimuth isn't just a technical spec buried in a proposal. It directly shapes how much energy your system produces, when during the day it produces it, and whether a west or east-facing roof section is worth using at all versus leaving off the design. NREL's PVWatts Calculator runs the same azimuth math for a specific address, so you can see the output difference for your own roof.
Where you'll see this
The roof azimuth orientation calculator takes your roof's compass direction and estimates the output impact compared to true south for your location, using the same north-referenced convention NREL's Solar Position Algorithm is built on. For a more precise, location-specific number than a general rule of thumb can give you, NREL's PVWatts Calculator runs the actual math for your address.
If your roof has multiple usable planes, the south-facing vs east-west array calculator compares total output and production timing across different azimuth combinations.
This term comes up in every solar design proposal, in any satellite-based quote tool, and any time an installer explains why one section of your roof produces more than another.
Related terms
Frequently asked
In the northern hemisphere, true south, 180 degrees, usually produces the most total annual output. But a roof facing southwest or southeast, within about 45 degrees of true south, typically only loses a small percentage of output, often not enough to change the economics of installing there.
Yes. East-facing panels produce more in the morning, west-facing panels produce more in the afternoon and evening. Total annual output is lower than a south-facing array, but for homes with high afternoon usage or time-of-use rates, a west-leaning azimuth can sometimes be worth more than raw kWh totals suggest.
The concept is identical, but the ideal direction flips. In the southern hemisphere, true north, not true south, is the azimuth that captures the most sun.
Azimuth is the horizontal compass direction a panel faces. Tilt angle is how steeply the panel is angled up from flat. Both affect output, but they're two separate measurements, and a panel's azimuth is usually fixed by which way the roof plane actually faces.