Dear all i need to estimate the real-sky radiation for inclined surfaces (tilt 25° degrees) throw using r.sun. I followed this procedure to evaluate the two parameters coefbh and coefdh. Below I explain how I get these two maps (I hope the procedure is correct... in negative case please alert me) so other people can use it.
1) go to this page http://www.soda-is.com/eng/services/services_radiation_free_eng.php and download data for the interested location using horizontal radiation, for a long period using HC1month data 2) the ratio between Irradiance (monthly mean) and the clear-sky gives you the Kc for each month. You should get the mean of Kc using all year you have (ie using data pilot in libre office). 3) run this script http://www.grassbook.org/scripts3rd/rsun_crop_grass6.sh that gives you for each day in year the value of W/m2 for beam ,diffuse, reflected and global radiation. 4) summarise all daily maps for each month in order to have monthly global radiation map, beam radiation map and diffuse radiation map (i prepared a python script to do this if someone is interested...). 5) multiply the global radiation for each month to the corresponding monthly Kc to have the real sky global radiation for horizontal plane 6) at the same website http://www.soda-is.com/eng/services/services_radiation_free_eng.php get the monthly inclined value for beam, diffuse and global for the location of interest using the tilt you need (25° in my case) (Note that the website provide only values for year 2005) and make the ratio between Diffuse horizon and Global horizon for each month (Dhs/Ghs). 7) The monthly diffuse horizontal radiation under overcast condition (Dh) is computed as the monthly real sky global radiation (from 5) by Dhs/Ghs (from 6) 8) The monthly beam horizontal radiation under overcast condition (Bh) is computated as the monthly real sky global radiation (from 5) minus Dh map (from 7) 9) the monthly coefdh map is the ratio of Dh map (from 7) and the monthly corresponding map of Diffuse radiation computed from r.sun and summarised in 4 10) the monthly coefbh as above is the ratio of Bh (from8) and the direct radiation If this procedure is correct I can write a better howto in a wiki elsewhere... I have one more question: once I have coefbh and coefdh maps in order to evaluate the global real sky radiation map for tilt 25 degrees in slopein parameters I should create a raster map with the value of 25? Is this correct? Thanks in advance Pierluigi -- ________________________________________________________________________ Ing. Pierluigi De Rosa (PhD) Studio Associato GFOSSERVICES Via Tilli 58 - 06127 Perugia (PG) tel: 075 7825101 / fax: 075 7823038 cel: 3497558268 web: www.gfosservices.it skype: pierluigi.derosa _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user