How the sun hits your solar electric panels and any shadows created by the sun is arguably the most important design consideration for your solar electric system.  This should always be carefully thought out during any design and before starting any installation. 

Daily Sun Motion
The location of the sun is as it moves across the sky every day is crucial.  You might be saying "of course" by now, but please read on.  There's more. 

Your solar electric system only produces significant power when it has direct sunlight is hitting it.  As the sun comes up and runs its course across the sky, shadows form and move as the sun moves.  If these shadows move across your solar panels they will significantly reduce the power output. 

Seasonal Sun Motion
Equally important is how the Sun's location changes throughout the year.  It changes quite a bit throughout the four seasons.  Because of this, shadows can be very different in Summer as compared to Winter. 

Shadows are typically longer in the winter and shorter in the summer.  They may also shade different locations because their orientation can change.  A shadow that does not shade your solar panels in the Summer could cause problems in the Winter.  Again, if these shadows encroach on you solar system they can significantly reduce your energy production. 

Seasonal Changes in Number of Sunny Hours Each Day
Summer days are longer (unless you're on the Equator) and so there are more hours of sunlight.  In the winter,the days will be shorter and have fewer hours of usable sunlight.  So noticeably more electricity is normally produced  in the summer months. 

How to Know If a Shading Problem Exists
If you have good trigonometry skills, you can use some math and charts that provide the Sun's path throughout the year for your approximate location.  That's beyond the scope of this article. 

A much easier way is to ask your solar design professional to provide a detailed shading analysis and determine if you have any shading problems.  Sometimes it's very obvious and sometimes it will take detailed measurements to figure out the severity of problems. 

Catch Shading Problems in the Design Phase
Every solar electric system design should include a thorough attempt to minimize any shading on your solar panels.  And always remember how much shadows can change throughout the day and throughout the year. 


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Robert Morse
BSEE, MSEE
SunCal Solar, Incorporated
www.SunCalSolar.com