Insolation Data Manual and Direct Normal Solar Radiation Data Manual. Solar Energy Research Institute. A Handbook of Recommended Design Practices. The appendix of this handbook contains monthly estimates of solar radiation striking collectors. These estimates are calculated for different tilts and sun-tracking schemes.
Maps are available that depict long-term average solar radiation data for each month.
This is a convenient way to show variations in the amount of solar radiation and for interpolating data between stations. The Solar Radiation Energy Resource Atlas of the United States was published by the Superintendent of Documents, but is out of print. This atlas is available at some university and city libraries. The University of Lowell compiled an international solar radiation data base for locations outside the Unites States. This data base presents average daily values by month and year for global horizontal solar radiation.