Appropriate models are now widely used to fill gaps in measured data, expand their measurement period (to, e. g., 30 years), and estimate solar radiation either at specific sites where only other meteorological data are available, or at the world or continent scale using gridded satellite data. Although such datasets may contain some measured radiation data, the bulk of their content is always modeled values. However, they are usually merged with other meteorological data, which is highly useful in most applications. Examples of such datasets are given below.
Europe has been very active about collecting measured radiation data, supplementing them with models, and developing solar maps since the late 1970s. Successive editions of the European Solar Radiation Atlas have appeared. Information about the latest edition can be found from HelioClim (http://www. helioclim. org).
Other European-based data sources (for Europe or the world) include SoDa (http:// www. soda-is. com), Satel-Light (http://www. satel-light. com), DLR-ISIS (http:// www. pa. op. dlr. de/ISIS), SOLEMI (http://www. solemi. com), and Meteonorm (http:// www. meteonorm. com). (Note that some of them are of a commercial nature.) Radiation datasets and maps for other continents have been recently developed through the international SWERA project (http://swera. unep. net). Daily solar radiation maps are also available for Australia (http://www. bom. gov. au/ reguser/by_prod/radiation) and Scandinavia (http://produkter. smhi. se/strang).
In North America, the most important sources of data and maps are from NREL (http://rredc. nrel. gov/solar/old_data/nsrdb; http://www. nrel. gov/gis/solar. html),
NASA (http://earth-www. larc. nasa. gov/solar; http://power. larc. nasa. gov; http://data. giss. nasa. gov/seawifs; http://eosweb. larc. nasa. gov/PRODOCS/srb/table_srb. html; http://flashflux. larc. nasa. gov), and Environment Canada (http:// www. ec. gc. ca).
Finally, convenient sites centralize links to various sources of world weather data for building applications (http://www. eere. energy. gov/buildings/energyplus/cfm/ weather_data. cfm) or photovoltaic applications (http://re. jrc. cec. eu. int/pvgis/solrad/ index. htm).