Improving Optical Qualification of Solar Concentrator by FOCuS Tool

AbstractAn improved tool for the shape qualification of parabolic trough mirror modules used in concentrated solar power plants was developed. The tool is based on the fringe reflection theory, in which sinusoidal fringe patterns are projected on a screen and their reflection over a specular surface is recorded by a camera. The observed distortions in the image are related directly to surface deviations from ideal geometry. Relevant aspects of the technique are its high spatial resolution (more than 1 million points per facet), short measurement time and easy setup. The so called FOCuS tool is capable of calculating the mirror slope deviations from its ideal design and the RMS value as a quality factor. Furthermore, the tool generates a file which can be loaded on CENER'S TONATIUH ray tracing software, through a specially developed plug-in, for mirror modeling and intercept factor calculation with several tube absorber geometries

Modeling of Drift Effects on Solar Tower Concentrated Flux Distributions

A novel modeling tool for calculation of central receiver concentrated flux distributions is presented, which takes into account drift effects. This tool is based on a drift model that includes different geometrical error sources in a rigorous manner and on a simple analytic approximation for the individual flux distribution of a heliostat. The model is applied to a group of heliostats of a real field to obtain the resulting flux distribution and its variation along the day. The distributions differ strongly from those obtained assuming the ideal case without drift or a case with a Gaussian tracking error function. The time evolution of peak flux is also calculated to demonstrate the capabilities of the model. The evolution of this parameter also shows strong differences in comparison to the case without drift

Procesamiento hidrotermal solar de biomasa: operación de reactor y características de los productos

4 figures, 2 tables.[EN] The use of concentrated solar energy to provide heat in the hydrothermal liquefaction is an attractive method to transform biomass into valuable products reducing the environmental impact. However, the coupling of both technologies requires further research. This work analyses the effect of solar fluctuations on the yields, and main characteristics of products obtained in a solar reactor with direct heating method. Results indicate that by direct heating in a solar furnace, at sustained reaction temperatures of 250 ºC, produced a bio-oil and char yield up 24 and 33%, respectively. The results are consistent with conventional heating systems, however direct heating results in higher temperature gradients between the frontal and nonirradiated walls (above 200 ºC), which results in an unstable system, especially at high heating rates and temperatures above 300 ºC, therefore, at the end of this work a modified solar reactor was proposed.[ES] El uso de energía solar concentrada para suministrar calor en el procesamiento hidrotermal de biomasa representa una alternativa atractiva para la transformación de biomasa en productos valiosos con menor impacto ambiental. Sin embargo, el acoplamiento de ambas tecnologías requiere más investigación en el tema. Este trabajo analiza el efecto de las variaciones en la irradiancia solar en los rendimientos y composición de los productos. Los principales resultados muestran rendimientos en el bioaceite y carbón de hasta 24 y 33%, respectivamente. Adicionalmente, se encontró que el tiempo de residencia entre 30-60 min favorece la formación superficial de una estructura porosa en el carbón. Los resultados obtenidos son consistentes con los sistemas de calentamiento convencional, sin embargo, el calentamiento directo del reactor solar genera grandes gradientes térmicos entre la pared frontal y la pared no irradiada (arriba de 200 ºC), lo que resulta en un sistema inestable, especialmente con rampas de calentamiento rápidas y temperaturas arriba de 300 ºC, por lo tanto, al final de este trabajo se propone un reactor mejorado.Authors would like to acknowledge J.J. Quiñones- Aguilar for the design of the modified solar reactor, and the financial support received from Fondo Sectorial CONACYT-SENER-Sustentabilidad Energética through Grant 207450, “Centro Mexicano de Innovación en Energía Solar (CeMIE-Sol)”, within strategic project No. 120 “Tecnología solar para obtención de productos con valor agregado mediante procesamiento hidrotermal” and DGAPA-PAPIITUNAM Project number IN107923: Licuefacción hidrotérmica solar de biomasa residual.Peer reviewe

Annual Optical Performance of a Solar CPC Photoreactor with Multiple Catalyst Support Configurations by a Multiscale Model

In this work, the seasonal and yearly optical performance of supported catalyst CPC solar photocatalytic reactors has been theoretically analyzed. A detailed model for the optical response of the anatase catalyst films is utilized, based on the characteristic matrix method, together with Monte Carlo ray tracing simulations. The catalyst is supported over glass tubes contained inside a larger glass tube that functions as receiver of the CPC reflector. Arrangements with four, five, and six tubes are considered. Overall, the four-tube scenario presents the worst performance of all, followed by the five-tube case. In general, the six-tube configuration is better. Nevertheless, important differences can be observed depending on the specific arrangement of tubes. The six-tube case surpasses the absorption rate of all the other configurations when the distance between tubes is extended. This configuration exhibits 27% increased yearly energy absorption with respect to the reference case and 47% with respect to the worst case scenario

Development of an Elevation–Fresnel Linked Mini-Heliostat Array

Heliostats are critical components of solar tower technology and different strategies have been proposed to reduce their costs; among them diminishing their size to reduce wind loads or linking nearby heliostats mechanically, to reduce the overall number of actuators. This document aims to describe the development of a linked array of mini-heliostats which move together in an elevation–Fresnel configuration. This configuration consists of an array of mirrors rotating around linked parallel axes, in a linear Fresnel style with an added elevation mechanism allowing all axes to incline simultaneously in the plane North–South–Zenith; that is equivalent to an array of N linked mini-heliostats moved by only two drives instead of 2N. A detailed analytical study of the Sun-tracking performance of this kind of heliostat arrays was carried out, and an 8-mirror prototype based on optical and mechanical analyses was designed, built and tested. Even though the mirrors are flat, the array produced a rather compact radiative flux distribution on the receiver. The flux distribution is compatible with a slope error of the order of 1 mrad. Peak and mean concentration ratios reached 6.89 and 3.94, respectively

Experimental Evaluation and Modeling of Air Heating in a Ceramic Foam Volumetric Absorber by Effective Parameters

Reticulate porous ceramic reactors use foam-type absorbers in their operation which must fulfill two essential functions: favoring the volumetric effect and increasing the mass and heat transfer by acting as a support for the reactive materials. Heating these absorbers with highly inhomogeneous concentrate irradiation induces high thermal gradients that affect their thermal performance. Owing to the critical function of these component in the reactor, it is necessary to define a selection criterion for the foam-type absorbers. In this work, we performed an experimental and numerical thermal analysis of three partially stabilized zirconia (PSZ) foam-type absorbers with pore density of 10, 20, and 30 PPI (pores per inch) used as a volumetric absorber. A numerical model and an analytical approximation were developed to reproduce experimental results, and calculate the thermal conductivity, as well as volumetric heat transfer coefficient. The results show that an increase in pore density leads to an increase in the temperature difference between the irradiated face and the rear face of the absorber, this occurs because when pore density increases the concentrated energy no longer penetrates in the deepest space of the absorber and energy is absorbed in areas close to the surface; therefore, temperature gradients are created within the porous medium. The opposite effect occurs when the airflow rate increases; the temperature gradient between the irradiated face and the rear face is reduced. This behavior is more noticeable at low pore densities, but at high pore densities, the effect is less relevant because the internal structure of porous absorbers with high pore density is more complex, which offers obstructions or physical barriers to airflow and thermal barriers to heat transfer. When the steady state is reached, the temperature difference between the two faces of the absorber remains constant if the concentrate irradiation changes slightly, even changing the airflow rate. The results obtained in this work allow us to establish a selection criterion for porous absorbers that operate within solar reactors; this criterion is based on knowledge of the physical properties of the porous absorber, the environment, the working conditions, and the results expected