To get the most from solar panels, you need to point them in the direction
that captures the most sun. But there are a number of variables in figuring
out the best direction. This page is designed to help you find the best placement
for your solar panels in your situation.
This advice applies to any type of panel that gets energy from the sun; photovoltaic, solar hot water, etc. We assume that the panel is fixed, or has a tilt that can be adjusted seasonally. (Panels that track the movement of the sun throughout the day can receive 10% (in winter) to 40% (in summer) more energy than fixed panels. This page doesn't discuss tracking panels.)
Solar panels should always face true south. (If you are in the southern hemisphere, they should face north.) The question is, at what angle from horizontal should the panels be tilted? Books and articles on solar energy often give the advice that the tilt should be equal to your latitude, plus 15 degrees in winter, or minus 15 degrees in summer. It turns out that you can do better than this - about 4% better.
| Latitude | Angle | % of optimum |
| 25° (Key West, Taipei) | 51.5° | 85% |
| 30° (Houston, Cairo) | 56° | 86% |
| 35° (Albuquerque, Tokyo) | 60.5° | 88% |
| 40° (Denver, Madrid) | 65° | 89% |
| 45° (Minneapolis, Milano) | 69.5° | 91% |
| 50° (Winnipeg, Prague) | 74° | 93% |
These angles are about 10° steeper than what is commonly recommended. The reason is that in the winter, most of the solar energy comes at midday, so the panel should be pointed almost directly at the sun at noon.
The third column of the table shows how well this orientation will do compared with the best possible tracker that always keeps the panel pointed directly at the sun.
| Winter | October 13 to February 27 |
| Spring | February 27 to April 20 |
| Summer | April 20 to August 22 |
| Autumn | August 22 to October 13 |
| Season | Insolation on panel | % of winter insolation |
| Winter | 5.3 | 100% |
| Spring, Autumn | 5.6 | 106% |
| Summer | 4.5 | 85% |
| Season | Insolation on panel | % of winter insolation |
| Winter | 4.3 | 100% |
| Spring, Autumn | 5.3 | 123% |
| Summer | 4.5 | 105% |
| Season | Insolation on panel | % of winter insolation |
| Winter | 2.9 | 100% |
| Spring, Autumn | 4.9 | 169% |
| Summer | 4.5 | 155% |
The optimum angle of tilt for the spring and autumn is the latitude minus
2.5°. The optimum angle for summer is 52.5° less than the winter
angle. This table gives some examples:
| Latitude | Spring/Autumn angle | Insolation on panel | % of optimum | Summer angle | Insolation on panel | % of optimum |
| 25° | 22.5 | 6.5 | 75% | -1.0 | 7.3 | 75% |
| 30° | 27.5 | 6.4 | 75% | 3.5 | 7.3 | 74% |
| 35° | 32.5 | 6.2 | 76% | 8 | 7.3 | 73% |
| 40° | 37.5 | 6.0 | 76% | 12.5 | 7.3 | 72% |
| 45° | 42.5 | 5.8 | 76% | 17.0 | 7.2 | 71% |
| 50° | 47.5 | 5.5 | 76% | 21.5 | 7.1 | 70% |
If you want to adjust the tilt of your panels four times a year, you can use these figures to keep capturing the most energy year-round.
Note that the summer angles are about 12 degrees flatter than is usually recommended. In fact, at 25° latitude in summer, the panel should actually be tilted slightly to the north.
It is interesting to note that all the temperate latitudes bask almost equally in the warmth of summer.
The efficiency of a fixed panel, compared to optimum tracking, is lower in the spring, summer, and autumn than it is in the winter, because in these seasons the sun covers a larger area of the sky, and a fixed panel can't capture as much of it. These are the seasons in which tracking systems give the most benefit.
The following graph shows the effect of adjusting the tilt. The blue line
is the amount of solar energy you would get each day if the panel is fixed
at the winter angle. The red line shows how much you would get by adjusting
the tilt four times a year as described above. For comparison, the green
line shows the energy you would get from two-axis tracking, which always
points the panel directly at the sun. These figures are calculated for 40°
latitude.
You may need to make adjustments for your situation. For example, if you have trees to the east but not the west, it may be better for you to aim your solar panels slightly to the west. Or if you often have clouds in the afternoon but not the morning, you might aim your panels slightly to the east.
The calculations also assume that you are near sea level. At high altitude, there is less atmosphere to absorb light, so it is more important to capture sunlight near sunrise and sunset. At high altitude it might be better to lower the angle of tilt a little.
intensity in kw/m2 = 1.35 * (1.00/1.35) sec(angle of sun from zenith)
These factors, and the angle of the sun with respect to the panel, then determine the insolation on the panel. An iterative method then determined the angles that give the maximum total insolation during each season. Given those angles, the beginning and ending dates of the season were then adjusted to the optimum, then the angles recalculated, until the process converged. After the optimum dates and angles were calculated, it was determined that a linear formula approximates the optimum closely.
Other published articles on tilt angles have used less accurate calculations. For example, Richard Perez and Sam Coleman, in "PV Module Angles", Home Power n.34 p.14-16, 1993 , recommend an angle that puts the panel perpendicular to the sun's rays at noon. That is indeed the best angle at noon on that day, but it does not take into account the best angle for capturing solar energy at other times of the day. That article also leaves it to the reader to estimate the best angle over the period until the next time the tilt is adjusted.
Percentages may not be exact due to rounding.
This page was last updated on 9 December 2002.