Solar Roof Orientation Derate Calculator

Is east/west really that much worse than south?

Yes, roughly 15-20% lower annual production in most US latitudes, though the difference matters less than it used to because panel costs have dropped — many installers now happily use a full east/west roof (splitting panels across both slopes) since it's often the only usable roof space, just sized about 15-20% larger to compensate.

What's the ideal tilt for my location?

As a rule of thumb, tilt roughly equal to your latitude maximizes annual production; a few degrees flatter favors summer production, a few degrees steeper favors winter. Most roof pitches (4/12 to 8/12, roughly 18-34°) fall close enough to optimal for most of the continental US that this isn't usually the biggest factor — azimuth matters more.

Should I avoid a north-facing roof entirely?

In the Northern Hemisphere, yes if you have any other option — a north-facing array can lose 40-45% of potential production, which usually makes the economics much weaker. Ground-mount systems, which let you choose ideal azimuth and tilt regardless of roof shape, become worth strongly considering if your only usable roof plane faces north.

Do these derate factors already account for shading?

No — this tool only covers orientation (azimuth) and tilt geometry. Shading from trees, chimneys, or neighboring structures is a separate, often larger loss that needs a site-specific shading analysis (a Solar Pathfinder or installer's shading report), not a generic table.