Area solar radiation - wrong results

[EleniAmpatzi]

Dear All,

Is there anyone with experience in the Area Solar radiation tool of the Spatial Analyst? I was getting some seriously unreliable results so I run a simple analysis using a flat DEM and then compared these with average values based on measurements.

I have included a word file explaining the problem, along with the flat DEM (please use the latitude shown on the word file if you re-run the analysis to check results I provide). I am running the analysis for two days, one typical for winter (16/2) and one for summer (11/6). I also use complete transmission and totally clear sky conditions to compute a value that can be compared to the Extraterrestrial/exo-atmospheric irradiance on horizontal. The results for the Global, Beam and Diffuse irradiances are entirely inaccurate (as an indication, the annual results underestimated the Global horizontal irradiance by 75%) and I would appreciate any help on this.

Keep in mind that I am new in GIS, so please excuse me if I have done something really stupid:).  I am also confused with the name of the tool, what is the difference between the Area Solar Radiation Tool and the Solar Analyst or TopoView that I usually come across in the literature?

Thank you in advance,

Kind Regards

Eleni

[MarkEllis]

In case you are not already familiar with the background of the ArcGIS tools, they are covered in a white paper:
http://proceedings.esri.com/library/userconf/proc99/proceed/papers/pap867/p867.htm

I've not used these tools in a long time, so will not hazard a guess about what might explain the differences you see.  Hopefully the paper will provide something to trigger an idea... Good luck!

How many of the optional parameters did you use in the process, and did the 'other source' results use the same set of variables?

[Anonymous User]

Original User: Ampatzi

Dear Mark,

Thank you very much for the reply, yes I am aware of this paper. The reason for including the 'other sources' in the table is to highlight that the estimation of the extraterrestrial irradiation (E) is not inaccurate and to reveal how the average atmospheric transmissivity (�?=B/E) and diffuse to global ratios (D/G) that are input for Solar Analyst were calculated for this location . The rest is simple mathematics, isn't it? It should be B=E x �?, D + B=G.

[RyanDeBruyn]

Dear All,

Is there anyone with experience in the Area Solar radiation tool of the Spatial Analyst? I was getting some seriously unreliable results so I run a simple analysis using a flat DEM and then compared these with average values based on measurements.

I have included a word file explaining the problem, along with the flat DEM (please use the latitude shown on the word file if you re-run the analysis to check results I provide). I am running the analysis for two days, one typical for winter (16/2) and one for summer (11/6). I also use complete transmission and totally clear sky conditions to compute a value that can be compared to the Extraterrestrial/exo-atmospheric irradiance on horizontal. The results for the Global, Beam and Diffuse irradiances are entirely inaccurate (as an indication, the annual results underestimated the Global horizontal irradiance by 75%) and I would appreciate any help on this.

Keep in mind that I am new in GIS, so please excuse me if I have done something really stupid:).  I am also confused with the name of the tool, what is the difference between the Area Solar Radiation Tool and the Solar Analyst or TopoView that I usually come across in the literature?

Thank you in advance,

Kind Regards

Eleni

Please note, the Solar Radiation tools available in ArcGIS are built upon the Solar Analyst/ Topoview extension so essentially they should produce similar results.  Some enhancements and bug fixes were done at this time. 

The results in question may be related to the settings you are using when running the tool.  For single day analyisis you can try increasing the skysize to 400 (max 1000). As well there is an option to specify FLAT surface for surface paramaters rather than calculated aspect and slope from the input DEM.  

If you are still having quesitons or problems I would recommend contacting esri support to work with a support analyst to identify any issues and provide further input to the developement team.

Perhaps the help topic for calculating the incoming radiation might be of some help. http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/How_solar_radiation_is_calculated/009z...
Regards,
-Ryan

[Anonymous User]

Original User: Ampatzi

Dear Ryan,

Thank you for the reply. The sky resolution does not affect the results, I have tried it. I am aware of all the relevant publications/helpfiles but unfortunately I have found no solution. Let's see if ESRI can help me with this.

Regards

Eleni