Please visit the website of the Department of Energy and you will find many computational tools for solar radiation probability distribution and stochastic models that you can download at no cost. Here is the URL:

www.doe.gov

Also visit the websites of Sandia National Laboratory (SNL) and the National Renewable Energy Laboratory (NREL):

www.snl.gov

www.NREL.gov

Hope this helps answer your question.

Professor Yehia Khalil

Yale University

USA

For theoretical models, I suggest you to read the attached papers

Article Evaluation and comparison of hourly solar radiation models

Article Comparison of long-term broad band model results with experi...

Article Evaluation of the SolarCalc model for simulating hourly and ...

 Thank you Prof. Yehia and Mohammed for the helpful references. 

I would like suggest you the following papers:

Hybrid solar/wind power system probabilistic modelling for long-term performance assessment

G Tina, S Gagliano, S Raiti

Solar Energy 80 (5), 578-588

Probabilistic analysis of weather data for a hybrid solar/wind energy system

G Tina, S Gagliano

International Journal of Energy Research 35 (3), 221-232

Fill free to contact me for any enquiry

The best reference: (Includes other references)

www.NREL.gov