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Peak sun hours is arguably the most important number to consider before installing your solar panels. Unlike total sun hours, peak sun hours are calculated by looking at the amount of sunlight hours in a 24 hour period that is strong enough to be absorb by a solar panel. One way to imagine peak sun hours is to think about a solar powered calculator you owned in school. If you covered the solar panel with your finger, or tried to use the calculator in the dark, the calculator would not work. As you slowly exposed the calculator to light the calculator would eventually turn on and be usable. The same is true with peak sun hours; these are the hours that your solar panels receive enough sunlight to work. Looking at the average peak sunlight hours of 4.3 per day can help you determine the amount of solar panels you need to install to power your home or business in Salem, Illinois.

Although you can easily predict sunrise and sunset hours each day to the minute, looking at latitude can help with your solar planning. The closer you get to the equator the closer your latitude gets to zero. Sunlight hours on the equator are consistent throughout the entire year. Places further from the equator can have large variance in daily sunlight. For example higher latitudes can have very long summer days with lots of sunlight and very dark winters. The latitude of Salem is 38.6.

A tracking mount will increase the average peak sun hours for a solar power system. Think about a panel that is tracking the sun in the sky vs a panel that is fixed and not moving: you will see a higher efficiency ratio of productions. A 1-axis mount will track the sun from East to West from sunrise to sunset and move on a single axis of rotation. A 2-axis mount will track the Sun from East to West the same as a 1-axis mount would, but it will also track the angle of the sun in the sky as it slowly varies season to season. A 2-axis mount is more necessary in high latitude regions where the angle of the sun in the sky changes dramatically between each equinox.

There are more variables than latitude that can change average peak sun hours. Weather patterns and geography will influence solar insolation that reaches your system. Thick grey storm clouds for example will block out a lot of the sun to the point where there may be no peak sun hours in the middle of the day when the sun is usually very powerful. Trees and mountains can deflect the sunlight, so be sure your solar panel is selectively placed.

Since we know the latitude of Salem we can take the average amount of total sunlight hours and estimate that with a fixed solar panel there would be an average of 4.3 peak sun hours per day. 5.6 hours per day with a 1-axis tracking mount that tracks the sun from sunrise to sunset, and 5.8 hours with a 2-axis tracking mount that tracks the sun everywhere in the sky.