# Understanding the TimeWholeYear configuration in ArcGIS Area Solar Radiation

I am a bit confused with the interpretation of my results and it would be great to have some clarification!

I used the TimeWholeYear configuration (without choosing the {each-interval} option, so the result should be a single output for the whole year) for the 'Area Solar Radiation' tool in ArcGIS10. I set the analysis to run with intervals of 14 days, and 0.5 hours.

With that I understand that every 14 days, and every 0.5 hours of those days, the tool will measure the radiation that falls on each cell of the raster.

Now that I have the results, I am a little bit confused as to what they mean. Basically, I have 2 questions regarding how to interpret the results:

1. Is the result value in each cell an average or the sum of the radiation received by that cell in the whole year?

2. If I go to layer properties > statistics in the output raster, I can see the minimum, mean and maximum value of the global radiation. How do I interpret that?

a) it refers to the minimum, mean, and maximum radiation measured during the year (i.e. measured on one occasion every 14 days and 0.5 hours)?...

...or b) it is the min, mean, and max values amongst all the cells of the raster?

I'm sorry if these are a very basic questions!!

Thanks, JJ

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## 1 Answer

1. The result value in each cell is the sum of the radiation (global) received by that cell (presumably 1mx1m) in the whole year. This will be expressed in kWh / m2, which is a unit of energy, not a rate. See here: Kilowatt-Hour - Wiki

2. Those statistics are referring to the min, mean, and max of global radiation "amongst all the cells of the raster". Global refers to the sum of all wavelengths of radiation, which in terms of solar irradiance refer to two types:

• direct (or "beam" radiation. Unimpeded ray from the solar disc)
• diffuse (or "skylight". Radiation that has been refracted, reflected, and re-emitted from atmospheric constituents).

Speaking of atmospheric conditions, the transmissivity and diffuse fraction are parameters in the Solar Radiation Tool that should be given great consideration. The atmosphere is the most influential factor in how much radiation reaches the Earth's surface. Atmopsheric Attenuation - Google Scholar

I would caution you to consider how "representative" your raster output of radiation might be given that you are running the tool using the same two atmospheric parameters for an entire year.

If this answers your question, please indicate so by checking the checkmark. Thanks.

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