FREDA - An automated field reflectance and degradation assessment system for central receiver systems

The heliostat field of Central Receiver Systems is subject to soiling and degradation, reducing the optical efficiency of the plant. The monitoring of the effects for an optimized cleaning and replacement strategy is a task demanding a high amount of time and effort. This work introduces a novel Field Reflectance and Degradation Assessment system FREDA. The automated monitoring of the condition of heliostat fields supports the operation and maintenance of a Central Receiver System in the aspects of optimized cleaning and replacement strategies as well as yield prediction and reduces the effort for data collection with state of the art reflectometers. The camera based system monitors the reflectance of a homogeneously illuminated Lambertian target or of the sky and relates the gathered data to reference reflectors distributed in the field, equipped with an automated reflectometer measurement. The methodology is outlined in detail including the underlying evaluation scheme. First laboratory tests are presented showing promising results and good agreement with reflectometer measurements. Finally further improvements are discussed and an outlook for the future work is given.