Area Solar Calculation What Exactly is Wh/m^2

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02-21-2013 04:56 AM
FredKellner
New Contributor
I am attempting to use the Area Solar tool. However I am having a difficult time understanding what exactly any of the solar outputs represent. I would like to calculate the daily integrated solar value for any given pixel within a DEM's domain. But with an output of Wh/m^2, what does this value represent? Is this truly the integrated daily solar radiation value or something else? If the tool is actually calculating integrated insolation shouldn't the output simply be in W/m^2?

Cheers,

Fred
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4 Replies
DanPatterson_Retired
MVP Emeritus
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FredKellner
New Contributor
Thanks Dan, That does clear things up a little bit. I guess I was thinking about what those units meant incorrectly.

As a follow up. Does anyone know why my solar values would be lower on the few days on and around Summer solstice than the few days previous and after this time period?

My DEM has a central latitude of 46.1487398830322 it seems that this should be the period of peak insolation. I have tried adjusting the sky size, but this failed to significantly change the results. I have not adjusted any of the other default settings.

Fred
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DanPatterson_Retired
MVP Emeritus
I don't know if the software accounts for the fact that the summer solstice isn't a fixed date and time but occurs within a small range about the average.  How significant is the difference?  Could it be a terrain artifact?  Do you get similar results when calculating values for a uniform flat surface?
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FredKellner
New Contributor
The Solar value appears to be lower for all pixels across the entire DEM for a several day period. I tired using the "special day" function in the tool which calculates solar for Summer solstice. This value is low is well. Attached is a plot where I'm comparing bulk radiation on N and S facing slopes and you can see around day 174 the value dips and then returns back to previous levels a few days later.

I have rerun the tool several times, thinking I made an error when setting up the tool, but get the same result every time.
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