Measured Solar Radiation Over Illinois

Shortwave solar radiation has been measured and recorded at 19 sites in Illinois since the late 1980s and early 1990s by the Illinois State Water Survey (ISWS). Mean monthly and annual analyses are provided to show the distributions over the state. The monthly distributions are uniform, showing minimum values in the northeast reaching south along the Indiana border and maximum values in the southwest. The 21.5 years of individual monthly and annual totals vary slightly from the long-term monthly and annual averages, suggesting that solar radiation in Illinois would be temporally dependable. Such measurements should be beneficial when evaluating the economic benefits derived from this alternative energy source.