Durability of anti-reflective coatings for parabolic trough receivers

Anti-reflective coatings are employed on both sides of the glass envelope tube of evacuated parabolic trough receiver tubes to minimize reflectance losses. This paper reports the measured initial transmittance values of seven different receiver tube manufacturers as well as the degradation rates after accelerated aging, outdoor exposure and inservice testing. The presented data represents a summary of measurements carried out in the OPAC laboratory at Plataforma Solar de Almería in the period between 2013 and 2019

Airborne soiling measurements of entire solar fields with Qfly

Concentrating Solar Power (CSP) plants are often being built in regions with high dust loads such as the Middle East and North Africa. Current soiling measurement methods in solar fields are labor and cost intensive and they only cover small measurement spots. Even a high number of manual measurements can only cover a minimal portion of the total solar field mirror surface. Airborne measurement solutions such as QFly have been developed in recent years to measure the geometry and tracking accuracy of the large CSP mirror areas. Soiling on solar mirrors is qualitatively visible in raw QFly measurement images. In this study we present a method to automatically derive the mirror cleanliness from aerial images taken with QFly. We present scattering investigations that correct for the directional particle scattering, illumination and camera viewing angles. A promising correlation was found between the thus corrected camera RGB signals and reference reflectance measurements that shows an RMSD of 3% for the investigated dust

SolarPACES Task III Project: Analyze Heliostat Field

In recent years, great efforts have been made to reach a consensus on heliostat testing best practices. A specific SolarPACES task was launched to provide a Heliostat Testing Guidelines document for single heliostat evaluation with a focus on prototype validation and qualification. Such guidelines are not well-suited for heliostat evaluation in operating commercial heliostat fields. The commercial implementation of the Central Receiver technology is burdened by the lack of a demonstrated cost-effective methodology to test solar fields, particularly during the commissioning and operation phases of the plant. To address heliostat characterization challenges, the SolarPACES funded Project Analyze Heliostat Field aims to set the basis towards a SolarPACES guideline for Heliostat Field Performance testing under a common framework. This is by means of a review of the existing methodologies, R&D and industrial stakeholders information sharing and preparation of a future quantitative comparison and validation plan. As part of the development of this project, several meetings and a workshop involving the SolarPACES community was organized to share knowledge and experience in the measurement and characterization of heliostat fields using a range of technologies and procedures. Research centers and companies from 5 different and distant countries have actively participated in these meetings, sharing their experiences, needs and interests. This paper summarizes the outcome of this international collaborative effort and the prospects for future close collaborations sustained over time

CSP component performance: Mirrors

The solar mirror (solar reflector) is the first key component in the nergy conversion process; any solar Radiation that is not reflected by it in the direction of the Receiver impolies a loss of System efficienca. In Addition, this component represents an crucial aspect in the construction and further operation of a concentrated solar power (CSP) plant because it involves a significantly large surface area. As a consequence, the feasibility strongly depends on the material and manufacturing process used to achieve a suitable solar concentrator. This chapter includes a description of solar mirros for concentrating solar applications, their fundamentals, types, specifications, meaurement and assessment of performance parameters, and future trends expected in the coming year

Soiling and Degradation Analysis of Solar Mirrors

The degradation and the soiling of the mirrors are dependent of the solar field and the mirrors technologies, the local climate, the meteorological events, the O&M tasks and the human activities around the site. In the frame of the European project SFERA II, the SODAM project has been the opportunity to compare the soiling and the degradation mechanisms on a Fresnel solar field installed in the South of France and on a parabolic-through solar field installed in the South of Spain. The analysis of the soiling has shown equivalent maximum weekly reflectance loss due to soiling in both sites but a double mean weekly reflectance loss in Spain respect to France, as well as typical meteorological events to be taken into account to adapt the cleaning strategies. Among the meteorological parameters mainly influencing the soiling, the study has revealed the effect of the rain and of the DNI. In parallel, the analysis of the degradation mechanisms has highlighted a common chalking of the protective back paint layers due to the irradiation. This chalking being associated to a leaching of the paint layers in the site of Cadarache due to the high presence of liquid water. A difference in the speed of corrosion of the silver layer has been also noticed, leading to a difference in the mechanisms of delamination of the paints layers

Airborne Soiling Measurements in Operating Solar Fields

Soiling is an issue receiving increased attention over the last years. Currently solar field soiling levels are measured with handheld reflectometers that need a technician to operate and are limited to measuring small sections of the vast mirror surfaces present in CSP solar fields. Earlier we presented a method to determine the soiling levels over parabolic trough solar fields using a drone and image analysis techniques in combination with particle scattering simulations [1]. This previous method evaluated those areas of a mirror that showed the black absorber tube in the direct reflection. The light reaching a given pixel of the camera sensor consists of light scattered by the dust on the mirror and the so-called “background contribution” showing the object reflected in the observed section of the mirror. As the reflections of the absorber tube were used in [1] the background contribution could be neglected. Then scattering simulations were used to correct for the effect of different incidence and viewing angles on the intensity of the scattering signal. A good agreement between the scattering corrected RGB camera signal and reference reflectometer measurements could be shown. In operating power plants the parabolic trough field needs to de-focus in order to realize the black absorber tube background. In tower plants a black target would be required. In this study we present an enhancement of the method that allows evaluation of mirror areas that show the sky as a background. Thus, the enhanced method facilitates soiling measurements during full solar field operation and for all CSP technology options. The approach to determine the sky background to be subtracted from the scattering signal is presented and a feasibility study using a test dataset including reference soiling levels will be given

Homogeneous equivalent model coupled with P1-approximation for dense wire meshes volumetric air receivers

International audienc

Standards For Components In Concentrating Solar Thermal Power Plants - Status Of The Spanish Working Group

Today Spain is still the worldwide leader in the use of Concentrating Solar Power (CSP) technology with more than 2300 MW installed solar thermal power rated in 2015, compared to the 4600 MW installed worldwide. In order to improve the quality of current plants and require the best quality for future plants, the subcommittee AEN/CTN 206/SC “Thermoelectric Solar Energy Systems” works on different aspects of the plants since 2010. This paper aims to give an overview of the state of the publications in draft to qualify the performance and the durability of the main components of the solar field (receiver tubes, solar tracking systems, reflectors, heat transfer fluids, collectors and specific sensors). A summary of the main tests set for each component in the future spanishstandards is presented