Question About DNI Classifications
This SSE question was submitted on behalf of the User
I need to classify a global raster of annual direct normal irradiation - DNI (values in the range 27–3865 KWh/m2) in varying degrees of potential (e.g. extremely low, very low, low, medium, high, very high and extremely high). There is a specialized source in which different types of DNI potential are concretely classified in certain intervals? If no, the best method is the natural breaks (Jenks classification method) for delimitation of classes of interest?
We don't provide a discrete classification. My best recommendation is to go to our SSE web site, click on "Solar Meteorology and Solar Energy" => "Global Data Sets" and then download the data set entitled, "Direct Normal Radiation (kWhr/m^2/day)". The is our best estimate for the 22 year climatology we currently use for DNI. The file provides the monthly and annual averaged DNI for every 1x1 grid area for the globe. The annual average is in the last column. You'll have to convert to your units above by multiplying by the average number of days in a year. However, strictly speaking you may want to consider converting each month separately then re-averaging the 12 months to get the annual average since every month has a different number of days. Then you'll have to devise a method to determine a proper classification. Our recommendation is to first plot a histogram for all the annual averages to see the distribution before trying a classification scheme. Please let us know if you have any additional questions.