Solar Panel Efficiency Vs. Sun Angle

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Solar Panel Efficiency Vs. Sun Angle
Solar panels need to have their angles changed in spring and fall. (Solar Panels image by alessbonaventura from

The position at which a solar panel derives maximum energy from the sun is when the panel surface is perpendicular to the rays of the sun. This infuses the silicon with maximum solar energy. The process is the same as a person getting a sunburn on the skin that was perpendicular to the sun, but not the skin with closer exposure. More solar energy per square inch enters when a surface is at 90 degrees to the direction of the rays.

Daily Adjustment

When solar panels are mounted on a rooftop or on a rack, they are positioned so they will be perpendicular to the sun when the sun is at its highest point. You would get more energy if you constantly adjusted the panel throughout the day, but this is an impractical solution.

Seasonal Adjustment

Because the height of the sun in the sky is so different in the summer and the winter, it is worth the trouble to adjust the angle of the panels in the spring and fall. The panels are laid closer to horizontal in the summer so the rays from the higher sun will hit them more or less perpendicularly, and they are raised to a higher angle to catch the winter sun, which lies lower in the sky. The panels can be changed on the spring equinox and fall equinox, March 21 and September 21, respectively.

Panel Location

Panels need to be located in a place where they can gain maximum solar input and be kept more or less perpendicular to the sun. They should not be in a place where they are shadowed by trees or other buildings at any time of the day.


Trackers are mobile racks that are fitted with solar panels and are designed to track the sun as it moves across the sky, keeping the panel faces perpendicular to the sun's rays. In some situations, where the location of the panels is wide and flat, with very broad sky exposure, this application makes sense. In other situations, the added cost of the tracker is not warranted by the energy gain. Sometimes it is just as efficient or more efficient to simply add another panel to the array.

Water Panels

Water panels, which are used for hot water and space heating, are not as flexible as electric panels when mobility is a factor. Because they are much larger and heavier, and attached to the system with plumbing, they need to be installed in a single position and remain in that position. Their permanent position is the most efficient compromise between the summer and winter positions of the sun.

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