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Posted on 12-02-2016

IMPACT OF ROOF ANGLE ON ELECTRICITY PRODUCTION

by Shen Ge

Introduction

Seasonal Tilt of Solar Array

Although the orientation of solar panels have greater effect than the tilt angle on your roof, it’s still important to understand how your roof angle can affect solar panels’ production levels and hence the amount of money you’re saving or making. By orientation, we mean the direction your roof faces which in the northern latitudes should optimally be true south. However, there is also the consideration of the tilt angle of the solar panels relative to a flat surface. For a roof-mounted system, if your roof is not at the optimal tilt angle, you have to ask yourself if the extra cost in the racking system to change the tilt angle justifies the increase in performance.

What’s the optimal tilt angle?

If you’re in the north latitudes between 25 and 50 degrees (which covers the entire US except for Alaska), if you wish to have the most direct sunlight on your solar panels for a direct south orientation, you’ll wish to have a tilt angle that is your latitude multiplied by 0.76 plus 3.1 degrees.  Some companies will tell you that you should match the tilt angle with the latitude but that just maximizes the performance at noon when the sun is directly overhead.

To make life simpler for you, we have a table of common cities in the United States with the optimal tilt angle for greatest annual production:

City

Latitude

Optimal Angle (Annual)

Key West, Florida

25°

22.1°

Houston, Texas

30°

25.9°

Atlanta, GeorgiaLos Angeles, California

34°

28.9°

Albuquerque, New Mexico

35°

29.7°

San Francisco, California

38°

32.0°

Washington D.C.

39

32.7°

New York City, New York

41°

34.3°

Boston, MassachusettsChicago, Illinois

42°

35.0°

Seattle, Washington

48°

39.6°

What is the performance loss?

Things are not as bad as it seems if your roof is not at the right angle! If you have a flat roof with a tilt angle of only 5 degrees, this decreases production by about 10%. The alternative with a steeper roof is barely noticeable. For instance, if the optimal tilt is 30 degrees and your roof is at 40 degrees, your production decrease is only 1%.  In other words, if you have a relatively flat roof, you may want to consider increasing the tilt angle. Talk to us and see how much more expensive this may be. However, if you have a steep roof, you’re probably perfectly fine without adding extra hardware.

Our Verdict

An angle between 25 degrees and 45 degrees should work well. If you’re in the southern states, you’ll want between 25 – 32 degrees while if you’re in the northern states, you’ll want 32 – 45 degrees. If the pitch of the roof doesn’t match your optimal tilt angle, you may consider using a racking system to achieve the right angle. However, the extra cost may not justify the minor gains you would see in efficiency.

With this information, you may feel ready to commit to a residential solar panel. Allow Simplify Solar to help you save up to 30% in residential solar installation costs. Furthermore, our turnkey solution saves you a lot of time — typically one to two months is sufficient for you to get a system up on your roof. Start with Simplify Solar and see how well you can benefit from solar.

Interested in more of Shen Ge’s posts on solar energy and other energy-related posts? Follow the author on Twitter @shenge86

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