Abstract. 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.
For the evaluation of functional material developments in the EU-project RAISELIFE, a tool chain of ray tracing, thermal FEM simulation and dynamic system simulation has been created. Multi-year simulations allow considering degradation of optical parameters. With this tool chain, the thermal energy output of a reference plant with one non-selective and one generic selective coating was simulated. The LCOE (Levelized Cost of Electricity) was calculated based on these results. The LCOE of the selective coating is 2.6 % lower, if the same costs are assumed. Furthermore, the ideal recoating interval for the reference system was identified. Finally, it was demonstrated that dynamic system simulation shows benefits to evaluate in-service performance of functional materials as dynamic behavior of solar thermal power plants can change quite significantly, if another coating is used.
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