Yield as a share of the best fixed angle at this site. Click a cell to try it.
The best tilt for each month, and what changing the tilt through the year adds.
Panels flush on a roof, as a share of the best angle for flush panels here. Hover for energy per kW.
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The best angle for solar panels is the tilt and facing that collect the most energy over a year where they stand. It depends on more than latitude: how cloudy the winters are, how clear the summer mornings or afternoons are, and how hot the panels run. This page works it out from every hour of a typical year at the place, with the same model as the array planner.
SolarPlan is a free, independent project, developed by enginerds from the University of Southern California and the University of Pennsylvania.
The rule of thumb sets the tilt equal to the latitude. Computed, the best tilt in these twelve US cities comes out 1° to 15° flatter: least in sunny southern cities like Miami and Phoenix, most in cloudy northern ones like Seattle and Chicago, where much of the year’s light comes from an overcast sky rather than the low winter sun. Long summer days, with the sun high overhead, pull the best tilt flatter too. The yield is forgiving near the top: in every city, a band of tilts about 25° wide stays within 2% of the best.
| City | Latitude | Best tilt | Facing | kWh/kWp | Within 2% | Flat | 4/12 east | 4/12 west |
|---|---|---|---|---|---|---|---|---|
| Seattle | 47.6° | 33° | 190° | 1,085 | 20–45° | 87% | 83% | 87% |
| San Francisco | 37.8° | 33° | 190° | 1,650 | 21–45° | 86% | 83% | 86% |
| Los Angeles | 34.1° | 31° | 190° | 1,721 | 19–44° | 87% | 83% | 87% |
| Phoenix | 33.4° | 32° | 180° | 1,803 | 20–44° | 87% | 85% | 85% |
| Denver | 39.7° | 36° | 170° | 1,584 | 24–49° | 84% | 84% | 79% |
| Dallas | 32.8° | 30° | 184° | 1,506 | 18–42° | 89% | 86% | 87% |
| Minneapolis | 45.0° | 38° | 180° | 1,346 | 26–50° | 82% | 81% | 81% |
| Chicago | 41.9° | 33° | 180° | 1,351 | 21–46° | 86% | 85% | 85% |
| Atlanta | 33.7° | 30° | 178° | 1,448 | 18–43° | 88% | 87% | 86% |
| Miami | 25.8° | 25° | 172° | 1,568 | 13–37° | 92% | 91% | 89% |
| New York | 40.7° | 33° | 180° | 1,315 | 21–45° | 86% | 84% | 84% |
| Boston | 42.4° | 36° | 178° | 1,339 | 24–49° | 83% | 82% | 81% |
A roof’s pitch and facing are fixed, so the useful question is how much a given roof gives up. Panels flush on a roof run warmer than panels on an open rack, which costs about 1% at the same angle. East and west roofs lose less than many expect: at 4/12, they keep 79% to 91% of the best roof angle in these cities, and a flat roof keeps 82% to 92%. North faces lose more the steeper they are.
A rack whose tilt can change gains a few percent a year: twice a year, at the equinoxes, captures most of what monthly changes would. The seasons here are centered on the solstices and equinoxes (winter is November to January), and swap south of the equator.
Every tilt and facing is run through the model PVWatts version 8 uses (National Laboratory of the Rockies), on the typical meteorological year from the National Solar Radiation Database in the Americas or from PVGIS elsewhere: sun position, direct and sky light on the tilted panel (Perez), reflection off the glass, spectrum, cell temperature, a single-diode module model, PVWatts’ 14.08% system losses and the inverter. Energy is AC, per kW of panels. Flush panels use PVWatts’ roof-mount temperatures; open racks its rack temperatures. Shade from trees, buildings and other rows is not included; for rows on the ground, see Row spacing.
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