Solar panel angle in Tri-Cities
In Tri-Cities, fixed panels collect the most energy over a year tilted 39° from horizontal and facing south. But anything between 30° and 50° is within 2% of the best, so the pitch you already have is probably fine.
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Percentage of the maximum possible annual yield, for each combination of orientation and pitch in Tri-Cities.
| Roof faces | 0° | 15° | 30° | 45° | 60° | 90° |
|---|---|---|---|---|---|---|
| South | 82% | 93% | 99% | 99% | 94% | 70% |
| South-east / south-west | 82% | 89% | 93% | 92% | 86% | 65% |
| East / west | 82% | 80% | 77% | 71% | 65% | 49% |
| North-east / north-west | 82% | 71% | 59% | 48% | 40% | 29% |
| North | 82% | 67% | 51% | 37% | 26% | 19% |
Why "tilt equals your latitude" is wrong here
The rule of thumb says tilt your panels at your latitude — 46° for Tri-Cities. The real optimum is 39°, 7° lower than the rule suggests.
Two reasons, both geometric. Summer days are much longer than winter ones, so the year's energy is weighted toward a higher sun than the annual average. And a low winter sun sends its light through a long slant of atmosphere, arriving weak — tilting to catch it costs more in summer than it wins in winter.
In fairness to the rule: following it here would cost you only 0.7%. It is wrong, but it is not expensive.
Seasonal angles
If you can adjust your panels twice a year, these are the angles to use. Most people should not bother — the gain is small and the ladder is real.
| Setting | Tilt | Facing |
|---|---|---|
| Fixed, all year | 39° | south |
| Summer | 18° | south |
| Winter | 66° | south |
| Flat on the ground | 0° | — |
A flat installation here keeps 82% of the maximum; mounted vertically on a wall, 70%.
Other cities in United States
Assumptions
- These are angles and percentages, never kilowatt-hours. Optimal angles are driven by geometry and are robust. Absolute energy output depends on measured irradiance, cloud, soiling and hardware, none of which are modelled here.
- Clear sky, no shading. Trees, chimneys, neighbouring buildings and terrain are ignored, and they can dominate everything on this page.
- Fixed panels. Trackers follow the sun and change the answer entirely.
- Ordinary ground. Reflectance is taken as 0.2, typical for grass and soil. Snow reflects far more and favours steeper tilts.