The annual-optimum tilt for a fixed array is roughly equal to your latitude. At 40° N, tilt the panels 40° from horizontal facing south.
That maximizes the year's total. It is not the best angle for any individual season.
Seasonal optima
- Summer maximum: latitude − 15°
- Winter maximum: latitude + 15°
- Annual maximum: latitude
Adjusting twice a year between those two gains about 4 to 6% over a fixed annual-optimum tilt. Adjusting four times gains perhaps 1% more.
Whether that is worth doing depends entirely on access. On a ground mount you can reach in ten minutes, twice a year, it is free production. On a roof it is not a consideration.
The penalty for being wrong is small
This is the useful part. Production falls off gently around the optimum:
| Deviation from optimum tilt | Annual loss |
|---|---|
| ±5° | under 0.5% |
| ±10° | ~1% |
| ±15° | ~2% |
| ±25° | ~5% |
A 5:12 roof pitch is 22.6°. At 40° latitude that is 17° off optimum — about a 2.5% annual loss. Nobody should re-engineer a roof for that.
Flat and near-flat arrays lose more: a horizontal panel at 40° latitude loses roughly 12% against the optimum, and it also collects dirt, because rain does not run off.
Azimuth matters more
Facing is a bigger lever than tilt. Losses from pointing away from south, at optimum tilt:
- South — reference
- Southeast / southwest, 45° off — about 5% loss
- East / west, 90° off — about 15 to 20% loss
- North — not worth mounting
An east-west split array on a ridge produces about 15% less than the same panels facing south, but it produces it across a broader, flatter curve — more in the morning and evening, less at noon.
Which can be worth more money
Under time-of-use tariffs, a west-facing array produces less electricity and more value, because it is generating into the late-afternoon peak when the retail rate is highest.
Where net metering pays a flat rate, chase total production. Where the tariff has a peak period, chase overlap with it. The optimum orientation is a tariff question as much as a solar one.
Snow, and the reason to steepen
Steeper arrays shed snow. In a snowy climate a shallow tilt can lose weeks of winter production to a covered array — far more than the 2% the tilt table suggests. There, going steeper than latitude is often correct despite the annual arithmetic.
Trackers
Single-axis tracking gains 20 to 30% over a fixed array, dual-axis 30 to 40%. Both add cost, moving parts and maintenance. At current panel prices, adding more fixed panels is usually the cheaper route to the same annual kWh.