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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 per day can help you determine the amount of solar panels you need to install to power your home or business in Cairo, Illinois.

Knowing the latitude of Cairo will help estimate average peak sun hours for your area. The latitude is used to accurately estimate the time of sunrise and sunset, thus giving you the total hours of daylight each day. Once you know the total hours of daylight, you can estimate the amount of peak sun hours based on a number of variables such as weather, time of year, the angle of the solar panel.

Since a fixed solar panel is set in one position it is ideal to place it at an angle that will expose the panel to the most sunlight throughout the year. This angle is generally the same angle of your latitude which is 37.0 for Cairo. You do not need to strategically place a 1-axis or 2-axis panel as much as you do a fixed panel. A 1-axis panel follows the movement of the sun during the day. Additionally, a 2-axis panel also adjusts for the suns various positions in the sky throughout the year.

The sunrise and sunset is very predictable every day, but things like cloud coverage and weather are less predictable and vary daily and annually. If a location that is usually very sunny experiences a huge increase in storms and cloud coverage in a given year than the average peak sun hours for that day or year will probably decrease. Tall objects such as trees and buildings can block out the sun during high solar insolation times, so be sure to strategically place your solar panels to get better efficiency.

Using the latitude of Cairo along with historical data of sunlight and weather patterns we can estimate that a fixed mounted solar panel will receive an average of 4 hours per day in this area. That number can be increased with better technology including add a 1-axis or 2-axis tracking mount, which would increase the average peak sun hours per day to 5.6 hours and 5.9 hours, respectively.