Since it is not economically feasible to build measurement stations at every site where a solar system might be built, Task 9 researchers evaluated a large number of techniques for estimating solar radiation for locations between network sites or where the existing measurements are not adequate. This work expanded on the resource assessment work ofTask 4 and Task 5.

In a major validation exercise, 33 models from various countries were assessed and those having the greatest accuracy identified. Various approaches for deriving needed data were investigated, including classical statistical techniques as well as new methods, such as satellite-based methods. Another activity was concerned with recommending the most appropriate methods for developing "representative design years" as input to solar system and building simulation models.

Finally, the task focussed on demonstrating the improved quality of solar radiation measurements now available with pyranometers and other instruments. Guidelines were also developed for solar energy engineers on proper solar radiation measurement procedures.