Sources of information Solar, temperature, degree day, humidity and wind was obtained from The Solar Radiation Data Manual for Buildings, produced by the National Renewable Energy Laboratory's (NREL's) Analytic Studies Division under the Resource Assessment Program, which is funded and monitored by the U.S. Department of Energy's Office of Solar Energy Conversion. For more detailed information please visit : http://rredc.nrel.gov/solar/pubs/bluebook/ , Interpreting the Data Tables. Precipitation data was obtained from the National Climatic Data Center, a program of the National Atmospheric and Oceanic Administration. Select historical data by location from:http://cdo.ncdc.noaa.gov/cgi-bin/climatenormals/climatenormals.pl Definition of Terms Incident Solar Radiation - Global Radiation (Btu/sq.ft./day) "Global radiation is the total radiation received by the window and is the sum of the direct beam radiation component, sky radiation, and radiation reflected from ground in front of the surface." Data is provided for five windows, horizontal and north, south, east and west facing vertical windows. The annual average is comprised of 30 years (1961 - 1990) of average annual data. Degree Days - "A degree day gauges the amount of heating or cooling needed for a building using 65 degrees as a baseline.  Heating Degree Days are the number of days below 65 degrees Fahrenheit in winter multiplied by the number of degrees below 65 (cooling degree days are the number of days above 65 in summer). For example: 10 days at 55 degrees (10 under 65 degrees) multiplied by 10 degrees = 100 degree days" Clearness Index (Kt) - "The clearness index (Kt) is the station's global horizontal solar radiation divided by its extraterrestrial horizontal radiation. Because clouds decrease the amount of solar radiation reaching the earth, stations in cloudy regions will have lower values for Kt than stations in regions will fewer clouds." Precipitation - Based on 30-year (1971 - 2000) Normal.