Knowledge of the mean reflectance of solar thermal central receiver system heliostat fields is highly relevant for both operation and component evaluation. Calculation of the mean reflectance becomes essential to establishing a procedure by which its value can be found without measuring each and every one of the facets that make up the field, since this is a long, time-consuming and not very productive task. This article reports on the results of a statistical reflectance study of the Plataforma Solar de Almeria Central Receiver Systems (CRS) heliostats field. (c) 2005 Elsevier Ltd. All rights reserved.