This site provides web tools of solar irradiance algorithms for photovoltaic (PV) system modelling.
The tools are free to use, and we are glad if you use them, but please cite the corresponding papers.
Feel free to have a look at the new API here
Generate one-minute global irradiance time series from data with one-hour resolution.
Calculate the diffuse irradiance from global irradiance input (in one-hour and one-minute resolution)