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If you put your solar powered math calculator in your backpack it will turn off from the lack of sunlight needed to power the device. As you slowly open your backpack and begin to let sunlight in, the calculator will eventually turn on when the amount of sunlight is enough to power the calculator. Similarly, peak sun hours refer to the hours of they day where the sunlight is strong enough to power a solar panel. This is different from total sunlight hours, which is simply the amount of hours in a day when there is any sunlight.

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 Limestone is 36.2.

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.

Weather is a big determinate of average peak sun hours each day. There are many aspects of weather that can increase or lessen the peak sun hours in a day in a particular location. For example cloud coverage is a crucial variable. And more importantly, what type of cloud coverage; thin scattered clouds will have less diminishing power on the solar insolation than thick rainy storm clouds. Sometimes long periods of sunny days are rare in certain locations, this would increase average peak sun hours for that time-frame

By taking the latitude of Limestone one can get a close estimate of the amount of average peak sun hours per day for the geographical area. It varies with technology and the type of solar panel mount you use, but for a fixed mount solar panel in Limestone one can expect close to 4.7 average peak sun hours per day. With a 1-axis tracking mount you would get 6 hours per day, and 6.3 hours per day with a 2-axis tracking mount that tracks the sun everywhere in the sky.