1. Essentials of Energy Technology: Sources, Transport, Storage, Conservation;Fricke,2013
2. http://pveducation.org/pvcdrom/2-properties-sunlight/solar-radiation-earths-surface.
3. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810016493.pdf.
4. http://www.nrel.gov/docs/legosti/old/3895.pdf.
5. www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/solar-radiation.