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The average peak sun hours of Johnston is a crucial measurable component needed to efficiently implement a solar power system in a home or business. Put simply, peak sun hours are the hours of sunlight a day that are strong enough to be efficiently absorbed by solar panels and eventually turned into usable electricity. Not every minute of sunlight during a day is strong enough to be useful to a solar power system. Think about just minutes after the sunrises, which officially counts towards total hours of sunlight, but is usually too weak to be counted in peak sun hours because the strength of the solar insolation is not strong enough near the horizon to be absorbed and turned into electricity at an efficient rate. Times during the day like this, where the sun is out but not strong enough, are not counted as peak sun hours. In other words, the amount of peak sun hours in a location will theoretically always be less than total sunlight hours for a given day.

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 Johnston is 41.8.

You will notice that the average peak sun hours for Johnston change based on the type of panel being used. The reason for this is quite simple. A fixed panel does exactly what it sounds like, remains fixed in one position at all times. A 1-axis and 2-axis panels have axis that allow them to rotate. The 1-axis rotates with the sun's daily east to west movement while a 2-axis also adjusts for seasonal changes.

Climate in your geographical region is a major factor that will influence average peak sun hours per year. If you live in a region that does not have a lot of completely sunny days, then cloud coverage will greatly influence solar insolation on any given day. Mountains and trees may also contribute to lower solar insolation if they block the sun from your panels at any given point of the day.

For a fixed mounted solar panel in Johnston, meaning that the solar panel will not track the sun in the sky, once can expect about 4 average peak sun hours per day. A 1-axis mount would increase this number to 5.3 hours per day because the panel would be facing the sun throughout the day. A 2-axis system that tracks the sun in the sky every day of the year would get approximately 5.8 hours per day in Johnston.