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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.

If you open the newspaper in the morning or watch the weather channel on the news you can get an accurate prediction of sunrise and sunset each day for Kailua. However, still knowing that the latitude of Kailua is 21.4 can be a helpful number for your solar panel setup and planning. The closer your latitude is to zero the closer you are to the equator. At the equator you find the most consistent total sunlight hours throughout any given day of the year. As your latitude increases you can see larger discrepancies of daily sunlight hours during the year. For example, having very long summer days and very short and dark winter days

Although most things are out of our control, like the sunrise, sunset or the weather, we can control the angle and the kind of mount we use for a solar panel. The angle of the solar panel, if using a fixed mount, should generally be around the angle that is equal to the latitude of the location to maximize output. In the northern hemisphere, panels angles should be lower in the winter months and higher in the summer months As a fixed mount is set, it is ideal to place it at an angle that will capture the most sunlight during the year. A 1-axis tracking solar mount will track the sun across the sky from sunrise to sunset, but the angle will remain the same throughout the day. A 2-axis solar mount will track the sun throughout the day from East to West, but the angle will also change automatically as the seasons change and the angle of the sun in the sky changes. Thus, a 2-axis will have a higher rating of peak sun hours compared to the 1-axis or fixed.

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.

We can use previous years of data to estimate the amount of peak sun hours in Kailua. A fixed tilt mount for example will receive 5.5 average hours per day. For more efficiency for your system in Kailua you could use a 1-axis tracking mount and increase your daily peak sun average to 7.4 hours, or even further with a 2-axis panel to get an average of 7.6 hours.