Actually in V.V.Nagar , SPRERI work on solar energy , so u will have to find research organisation , in baroda or some industry , who work on solar energy
I think Trnsys (meteonorm) data is better , but one have to purchase. NREL have maps and data but you have to authenticate it whether they have hourly data (its free). RETScreen provide daily data (free) which can be converted to hourly one (r factor duffie).
While more simple is to find research article on science direct.
There are different ways to generate such data by modeling, but nothing exists that is both free and accurate. Meteonorm would be the least costly source, but with an unknown accuracy. It's possible to obtain high-quality hourly data from satellite for the last 15+ years, which is the usual method used for resource assessment of large solar projects, but it's costly. Let me know how you want to pursue this,
Yes, it is possible to generate data by modeling, but the big question is accuracy: if you need good accuracy, particularly in direct hourly irradiance, and long time series (>15 years), the method is complex and must rely on satellite data. This translates into higher costs. So you need to be give more details about what you need exactly (which component, time step and time frame, acceptable uncertainty...)