You could try to find solar radiation data for your location (USA) at the following website: National Solar Radiation DatabaseSODA solar radiation data,

or for locations in Europe: SODA-IS solar radiation data. Some of the data at SODA-IS can be downloaded free of charge. Downloadable data are You would get general irradiation time series data in hourly steps, containing e.g.

direct normal irradiation, 
diffuse horizontal irradiation

etc.. I have tested this for a location in Europe.

With some additional calculations you should be able to derive incident solar radiation for your application.