The easiest way to do what you want is to run EnergyPlus for 12 monthly design days, which requires just a DDY file for that location (the EnergyPlus Weather Converter has a file with DDY data taken from ASHRAE for over 8,000 locations around the world). What you will get for each design day of each month would be a fictitious day where the climatic parameters are all manufactured by the ASHRAE Design Day procedure, and the global horizontal and direct normal solar calculated using the 2013 ASHRAE Clear Sky model.

I've never had cause to do this, so I don't know what other switches and settings you'll have to make in your EnergyPlus run, maybe supply a bogus *.EPW for your location, etc., to make it all work.

Having said this, I question the wisdom of evaluating strategies only under clear sky conditions. The power of simulations is to show what happens under multiple conditions over an entire year.

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

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 time series 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.