Central Receiver Systems use up to thousands of heliostats to concentrate solar radiation. The precise control of heliostat aiming points is crucial not only for efficiency but also for reliable plant operation. Besides the calibration of open loop control systems, closed loop tracking strategies are developed to address a precise and efficient aiming strategy. The need for cost reductions in the heliostat field intensifies the motivation for economic closed loop control systems. This work introduces an approach for a closed loop heliostat tracking strategy using image analysis and signal modulation. The approach aims at the extraction of heliostat focal spot position within the receiver domain by means of a centralized remote vision system decoupled from the rough conditions close to the focal area. Taking an image sequence of the receiver while modulating a signal on different heliostats, their aiming points are retrieved. The work describes the methodology and shows first results from simulations and practical tests performed in small scale, motivating further investigation and deployment.

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.