Heliostat’s reflected beam quality has been estimated using the target-camera method for years due to being the only method that can be realistically implemented in a commercial plant. But this methodology is prone to errors such as those derived from target surface flaws and its limited size, and the sensitivity and dynamic range of the camera. To reach a high quality characterization, thus reducing required security margins and boosting plant profitability, a novel system and methodology have been developed. This is a scanner-based methodology in which the spot reflected by a static heliostat, no matter how far it is from the measurement system, is captured simultaneously by two subsystems, a vertical array of detectors and a group of cameras, in order to produce a high quality representation of the reflected beam and a precise characterization of the normal vectors along the whole heliostat reflective surface. The use of optoelectronic detectors allows capturing the solar beam with reduced optical and electronical noise and wider dynamic range with respect to the state-of-the-art methodology. At once, the camera subsystem is used as a scanner to perform an accurate normal vector estimation of the heliostat surface. The combination of both approaches lead to the most precise heliostat characterization to date. This system can be implemented at low cost in any commercial plant, planned, under construction or under exploitation with any size of heliostat field and any number and typology of heliostats.
Solar radiation attenuation in the path from the heliostats to the receiver is one of the main contributions to production estimation uncertainty in the operation of central-receiver concentrated solar plants (CSP). Few systems are commercially available to monitor this phenomenon and those available have high uncertainties due to the non-uniform attenuation pattern across the wavelength range of the useful solar radiation. In this work, we report the results from a 6-month measurement campaign carried out in a commercial CSP tower plant using a prototype system to measure the spectrally-resolved solar radiation attenuation. The system measures the differential spectrum between two pairs of high-resolution spectrometers (VIS and IR) separated approximately 800 meters and each coupled to a telescope system. Both systems are pointed at a white Lambertian target and regularly take a baseline measurement pointing at a black target to eliminate contributions from the diffuse light present in the solar field. The system is calibrated to <1% uncertainty using the reference of a portable spectrometer at both locations. Full-spectrum measurements were taken every 5 minutes. Spectral characteristics of different atmospheric conditions (suspended dust, fog, humidity) and their intra-day and seasonal evolutions are observed and analyzed.
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