The table to the right lists the solar insolation data collected over a period of years from monitoring stations acrosss the united states. The numbers represent the sun hours per day, with the high being at summer solstice, low at winter solstice and average the average over the year. The data is also correlated to the weather, giving an accurate annual estimation of available solar irradance at each location.
How to use the chart
Sun hours is a common unit of measurement in the solar field. More often you want to know the amount of energy in terms of annual killowatt hours or annual BTUs. The conversion guide below lets you easily convert sun hours into kilowatt hours. As an example, let us use the data for Fairbanks, Alaska, which is the first entry in the table. It receives an average of 3.99 sun hours per day. The total for year is the sum of two numbers:
3.99 x 365 kWh/(m2·y)= 1456 kWh/(m2·y)
So a solar panel 1 m2
would have 1456KWh falling upon it in a year. However, this is not a measure of the total energy that is available, since only a portion is converted to useful energy, typically 15% with a photovoltaic, and 60% with a solar thermal panel.
1456kWh x 15%= 218 kWh/(m2·y)
Solar Thermal Panel:
1456 x 60%= 873 kWh/(m2·y)
These are rough estimates and will vary on the angle a panel is mounted and its orientation toward the sun. It does highlight, however, the primary determinate of ouput energy is highly dependent upon solar collector area and solar collector efficiency.