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

[Frank Reekers]

Thanks for the hint.
I did the calculations with the default value of the linke Linke 
turbidity coeffcient, which is 3.0
In the output table of PVGIS the Linke turbidity coeffcient is in 
february 2.7, so I think this should be okay.
Any other ideas?


Alberto Pettazzi schrieb:
> 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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>>   
>
>
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