The results of a new theoretical approach to the calculation of annual utilizability are illustrated and validated against utilizabilities that are based on detailed meteorological data. The theory is applied to concentrating solar collectors with tracking about two axes, the polar axis, the horizontal east-west axis, and the horizontal north-south axis, for a wide range of clearness index values. A new simple analytic formula for annual utilizability and its accuracy for the case of concentrating collectors are presented. The ultimate power of the theoretical results lies in the fact that with a knowledge of the annual average clearness index only, one can accurately predict utilizability curves for concentrating solar collectors in any climate. This would be particularly valuable for geographical locations and climates which are not covered by existing correlations or for which years of detailed meteorological data do not exist.