Understanding orientation's effect on output
Why south-facing remains the reference point
At 35 degrees latitude, an east or west facing array produces around 82% of what an identical south-facing array produces. An 11,000 kWh/year south-facing system would produce roughly 9,070 kWh/year facing due east or west. South-facing arrays in the Northern Hemisphere track the sun's path most directly across the full day, which is why installers default to it whenever roof geometry allows. A DOE federal PV performance report models orientation-driven differences as part of its standard performance calculation methodology.
North-facing roofs still have a place
Sometimes, especially if it's the only usable roof space or if south, east, and west sections are already shaded or full. A north-facing array still produces meaningful power, typically 60% to 70% of a south-facing system in the Northern Hemisphere. For homes with limited south-facing roof area, a north-facing section can still be worth adding if the alternative is no panels at all. NLR's PVWatts documentation defines this same azimuth convention used across the solar industry, with 180 degrees representing true south in the Northern Hemisphere and 0 degrees representing true north. Check the shading loss estimator too if trees or structures limit your south-facing options.
How latitude changes the penalty
Yes, slightly. Higher latitude locations see a bit more output penalty for non-south orientations than locations closer to the equator, since the sun's path arcs lower and more directly overhead varies more with latitude. This is a smaller effect than the orientation choice itself, but it's worth accounting for at latitudes above 45 degrees. The peak sun hours by latitude tool shows this same latitude sensitivity applied to a different metric. The array tilt angle optimizer finds the tilt that makes the most of that difference.
When splitting orientations makes sense
Not necessarily. Splitting panels across east and west facing roof sections can better match a household's morning and evening usage pattern, even if the combined annual total is slightly lower than an all-south array. This approach, sometimes called an east-west split, produces a flatter output curve across the day rather than one sharp midday peak. Compare this against the flat roof vs pitched roof comparison if your roof geometry limits which orientations are even possible. If your utility bills you differently by time of day, the time of use rate savings calculator can help show whether that flatter production curve actually saves more money than a higher annual total would.
What to do with this number next
Compare your best orientation option against the tilt angle comparison tool, since tilt and orientation work together to determine your total output.