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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.

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 Stratford is 42.3.

You will notice the difference in peak sunlight hours depending on the panel type. The more flexibility the solar panel has the efficient it can be throughout the day and the year. A fixed solar panel remains in the same position at all times. A 1-axis panel follows the sun throughout the day as it moves through the sky and eventually sets. A 2-axis panel not only tracks the daily movement, but also adjusts based on the sun's changing position in the sky throughout the year as the seasons change.

The sun is a great ball of gas that rises and sets every day that the earth rotates while in orbit around the sun. Barring any major disasters this is a very predictable occurance every day. Latitude helps predict this even more, narrowing it down to the minute for sunrise and sunset. But some things aren’t as predictable that will greatly influence the efficiency of solar panels. Weather and cloud coverage for example can greatly diminish peak sun hours on any given day. Thick storm clouds will block a high percentage of the sun's rays, resulting in lower output of your solar panels. Weather needs to be factored into deciding when to use your system, or how much output one expects to get.

In Stratford the average yearly peak sun hours for a fixed tilt non-tracking solar panel mount is 4.7. 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 6.2 hours if you are using a 1-axis panel, and to 6.7 hours if you upgrade to a 2-axis solar panel.