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Looking at the average peak sunlight hours in Alton is a valuable number for determining your solar power setup. Peak sunlight hours are only the hours a day in which the sunlight is strong enough for the solar panels to do their job. Not every hour of sunlight was created equal. For example, solar panels do not provide much use during early sunrise and sunset, and therefore you should not look at total hours of sunlight in a day, but instead focus on peak sunlight hours. Using this number will provide a much better estimate of your needs for setting up panels in Alton, Illinois.

Your latitude is an indicator of when the sunrises and sunsets and certain times of the year. If you live near the equator with a latitude of near zero, the sun will rise and set close to the same time all year resulting in consistent total sunlight hours per day. If you live near the poles, the time of sunrise and sunset will vary dramatically with each season, resulting in long days for part of the year and very short days at other times. So, locations closer to the equator will have more consistent amounts of peak sun hours throughout the year than locations closer to the poles.

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.

Another reason to consider average peak sun hours is because weather can dramatically affect the day-to-day output of solar panels. It goes without saying that a dark stormy day will produce less output than a clear sunny day. Looking at a yearly average helps account for these daily variables.

In Alton the average yearly peak sun hours for a fixed tilt non-tracking solar panel mount is 4.2. This is for a fixed panel mounted at an angle that is equal to the latitude of the location for the entire year. The amount of peak sun hours increases to 5.6 hours if you are using a 1-axis panel, and to 6.2 hours if you upgrade to a 2-axis solar panel.