Help on the Area Solar Radiation tool say "It is recommended to have your data in a projected coordinate system with units of meters."
My input data is in a projected coordinate system (Ohio State Plane North Feet) and my Z units are feet. Will my output results be WH per square feet?
The output radiation rasters will always be floating-point type and have units of watt hours per square meter (WH/m2). The direct duration raster output will be integer with unit hours.
It is recommended to have your data in a projected coordinate system with units of meters. If you choose to run the analysis with a spherical coordinate system, you will need to specify an appropriate z-factor for that latitude.
perhaps they have abandoned feet.
As a check, run with your 'feet', run with the same in a projected coordinate system which is in meters and run a test with the data in decimal degrees and the appropriate z-factor.
If the help topic needs clarification at that point, you would be advised to report it using the Feedback on this topic at the bottom of the help file.