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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.

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.

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 42.3 for Wellesley. 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.

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

For a fixed mounted solar panel in Wellesley, meaning that the solar panel will not track the sun in the sky, once can expect about 4.6 average peak sun hours per day. A 1-axis mount would increase this number to 5.7 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 5.9 hours per day in Wellesley.