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What is the panel wattage and what does it mean?


About 35 years ago, an international standard was created to rate all solar panel outputs. This was a result of manufacturers playing games with the figures in their marketing. This is called STD or standard test conditions. STD can only be mimicked in a laboratory setting on a specific machine that does a flash test in a controlled environment. This is because panel output varies dramatically depending on the temperature outside, how hazy the day is, and how intense the sun is.

A 310w panel can produce from zero watts to over 400w depending upon these factors. The output increases as the ambient temperature falls, as the sun becomes more intense and the skies become clearer. Those days when it is below zero ‘F’ has the best potential. This is why the wire sizing of a solar array is dependent upon these items. A solar array in a warmer climate can get away with smaller wires than we can in Michigan. At zero degrees ‘F’ a 310w solar array can produce over 356w, with all else being equal. The STD panel wattage listed on the placard, of any panel sold in the United States, is at an ambient temperature of 77°F (25 degrees c), 1000 W per square meter of sun intensity, and 1.5 atmospheres. When any of these factors change, so will the output.

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