The European Space Agency's ENVISOLAR project is an ongoing effort to measure and map solar light intensity across the globe. Clouds, ozone, atmospheric aerosols and the like can reduce the amount of sunshine hitting the ground; this information is useful for businesses needing sunlight -- tourism, farming, and particularly solar power generation.

ENVISOLAR takes data from a variety of satellite sources, such as the Heliosat-3 project, as well as the handful of ground-level solar intensity measurement stations. The measurements are akin to those done for the UN Environment Program's SWERA project, which looked at solar and wind potential in the developing world. The resulting solar radiation maps can be used by utilities to calculate best locations for and expected output from solar power facilities.

It's unclear from the ESA site how much of the map data will be made available to the public; the ESA is generally pretty good about making material available, but they're often pretty slow about it. It would be great if the data could be made available in real-time, as an XML feed -- imagine what one could do with that and Google Maps...