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I am trying to run Solar analysis in ArcGIS Desktop and it is an enormous DEM of a very mountainous region. I am going to have to split the DEM.

Are there any issues with doing this?

For example, if you analyze a section separately from an adjacent mountain that would have shaded this section.

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Surrounding topography does have an effect on each pixel as it is analyzed using the solar analysis tools. From ESRI's own documentation:

...accounts for atmospheric effects, site latitude and elevation, steepness (slope) and compass direction (aspect), daily and seasonal shifts of the sun angle, and effects of shadows cast by surrounding topography.

More specifically: How the viewshed is calculated

Since radiation can be greatly affected by topography and surface features, a key component of the calculation algorithm requires the generation of an upward-looking hemispherical viewshed for every location in the digital elevation model (DEM).

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It would seem that if you are in a mountainous region and you remove some of those mountains, the nearby pixels will be affected. The documentation doesn't mention anything about these edge effects. A test or possible solution to this issue would be to create overlapping clipped regions. You could recombine these clipped regions based on a rule-set (e.g. use the overlapping region that has the lowest pixel values).

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You are also going to want to split the DEM at the pixel line, rather than sub splitting the pixels. Splitting a pixel can provide interpolation and rounding errors with algorthimns.

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