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Looking at the average peak sunlight hours in Washington is a valuable number for determining your solar power setup. Peak sunlight hours are only the hours a day in which the sunlight is strong enough for the solar panels to do their job. Not every hour of sunlight was created equal. For example, solar panels do not provide much use during early sunrise and sunset, and therefore you should not look at total hours of sunlight in a day, but instead focus on peak sunlight hours. Using this number will provide a much better estimate of your needs for setting up panels in Washington, California.

The latitude at the equator of the earth is zero degrees. This is where sunlight strikes the earth most directly. Due to the earth's curved shape, sunlight hits at a various angles depending on location. As latitude increases, the further you are located from the equator and more variance you see in sunlight hours. The latitude of Washington is 39.4.

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.

Peak sun hours are greatly affected by weather patterns. Cloud coverage is a huge factor in peak sun hours per day because heavy cloud coverage will diminish the power of the solar insolation. You can use historical climate data to estimate average cloud and weather coverage, but it will obviously vary slightly from year to year.

By taking the latitude of Washington one can get a close estimate of the amount of average peak sun hours per day for the geographical area. It varies with technology and the type of solar panel mount you use, but for a fixed mount solar panel in Washington one can expect close to 5.1 average peak sun hours per day. With a 1-axis tracking mount you would get 6.5 hours per day, and 8.3 hours per day with a 2-axis tracking mount that tracks the sun everywhere in the sky.