[GRASS-user] global radiation calculated with r.sun seems to be very high

[Alberto Pettazzi]

Maybe the problem is due to a Linke turbidity coeffcient too low 
(atmosphere too transparent)...


Frank Reekers escribió:
> the global radiation, calculated with r.sun, seems to be very high in 
> comparison to PVGIS (Photovoltaic Geographical Information System).
> - r.sun for 14. Feb: ~2363 Wh/m² per day
> - PVGIS: 1330 Wh/m² per day Irradiation on horizontal plane for 
> february on average
>
> Below the detailed steps I did in GRASS and with PVGIS:
> 1. PVGIS:
> a) http://re.jrc.ec.europa.eu/pvgis/apps3/pvest.php -> search for 
> location 'Osnabrueck, Germany' -> choose monthly radiation -> click 
> calculate -> the output table shows 1330 Wh/m² Irradiation on 
> horizontal plane for february.
>
> 2. GRASS
> a) Take an existing DEM with the resolution of 1m and set all z-values 
> to 68m to have a completely horizontal plane:
> GRASS 6.4.0RC6 (GRASS)> r.mapcalc dsxx94c68=dsxx94c at PERMANENT*0+68.00
>
> b) Set Region
> GRASS 6.4.0RC6 (GRASS)> g.region rast=dsxx94c68
>
> c) Create slope & aspect:
> GRASS 6.4.0RC6 (GRASS)> r.slope.aspect elevation=dsxx94c68 at PERMANENT 
> slope=sdsxx94c68 aspect=adsxx94c68 --overwrite
>
> d) Run r.sun for day 45:
> GRASS 6.4.0RC6 (GRASS)> r.sun elevin=dsxx94c68 at PERMANENT 
> aspin=adsxx94c68 at PERMANENT slopein=sdsxx94c68 at PERMANENT 
> glob_rad=g45phxx94c68  day=45 --overwrite
>
> e) Get global radiation:
> GRASS 6.4.0RC6 (GRASS)> r.what input=g45phxx94c68 
> east_north=3435430.596,5794315.99
> 3435430.596|5794315.99||2362.9213867188
>
>
> Is there a reasonable explanation for this or did I something wrong?
>
> Thanks for your help
> Frank
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>   


-- 

Alberto Pettazzi


MeteoGalicia - Departamento de Climatología y Observación

Consellería de Medio Ambiente, Territorio e Infraestruturas

Rúa de Roma, 6

15707 Santiago de Compostela. A Coruña


Teléfono: +34-881-999646


e-mail: alberto.pettazzi at meteogalicia.es 
<mailto:alberto.pettazzi at meteogalicia.es>