C. Iriarte-Cornejo, C.A. Arancibia-Bulnes, J.F. Hinojosa, Manuel I. Peña-Cruz

Abstract

The optical characteristics of solar concentrators are key factors influencing the overall efficiency of solar power plants. For instance, heliostats need to be evaluated prior to installation and during its operation lifetime. This guarantees that the optical and thermal performance of these systems is close to design. One methodology that has gained importance due to its potential capabilities has been the Fringe Reflection Technique. This technique uses the reflection of a series of regular stripes to obtain the local slope deviations from a specular surface. Coupled to a ray tracing analysis, these slopes can be used to identify the distortion in concentrated solar spots. The enormous amount of data needed to carry out this analysis difficult its implementation at large scale. In this work, a study for determining the optimal number of sample points for heliostat surface characterization is realized. It has been found that, depending on the level of errors, the number SPFS required to reach convergence in the flux distribution profiles and intercept factors is variable. However, for the wide range of parameters considered in all cases 48 SPFS where enough to reach convergences to 1%. This is equivalent to one point per every 2.5cm of facet side length. For values of slope and canting errors up to 2mrad, half this density is sufficient.

Effect of spatial resolution of heliostat surface characterization on its concentrated heat flux distribution

Publicado en Revistas Arbitradas

E Anguera, CA Estrada

Abstract

In this paper, we present two statistical methods to quantify the heterogeneity of the irradiance flux distribution, in a Concentrator Photovoltaic (CPV) dense-array, based on its operation and the optimization of current-matching. Preventing non-uniform flux distribution from design avoids the generation of hot spots, current mismatch and increases the overall efficiency of the system. This new approach considers the effects of the lowest irradiance values in the performance of the complete array, and its performance was corroborated by the simulations of a CPV array modelled in Matlab/Simulink; the irradiance distribution data as an input parameter was obtained from the images taken in a homogenization experiment, in the HoSIER, an 18,000 X solar furnace. The results are interpreted through the new concept of photovoltaic homogeneity, proven that the methodology successfully predicts the flux distributions, which enhances the efficiency of a series connected CPV array. Additionally, we found that the proposed methodology can also be used to optimize the electrical performance of dense-array CPV systems, working under the effects of non-uniformity illumination by rewiring the series connections into series-parallel configurations.

A new approach for evaluating flux uniformity for dense array concentrator photovoltaic cells

Publicado en Revistas Arbitradas

Alonso, E., Gallo, A., Roldán, M.I., Pérez-Rábago, C.A., Fuentealba, E.

Abstract

Rotary kilns have a long history of use in classical industries. They are able to achieve high temperatures with higher thermal efficiencies than other reactor types. Their performance has been widely studied and classified according to different parameters. Since it is a well-known technology, rotary kilns have been selected for high temperature solar processes. This article initially presents a brief review of the rotary kiln technology and it focuses on the employment of these devices for thermal and thermochemical processes conducted by concentrating solar energy. Among the solar devices, a novel rotary kiln prototype for thermochemical processes is presented and compared with a static solar reactor. Finally, some practical conclusions on the design and operation of solar rotary kilns are remarked and an analysis of their main limitations is presented.

Use of rotary kilns for solar thermal applications: Review of developed studies and analysis of their potential

Publicado en Revistas Arbitradas

D. Riveros-Rosas, J. Herrera-Vázquez, C. Pérez-Rábago,  C.A. Arancibia-Bulnes, S. Vázquez-Montiel, M. Sánchez-González, F. Granados-Agustín, O. Jaramillo, Estrada C.A.

Abstract

Radiative heat transfer in a solar thermochemical reactor for the thermal reduction of cerium oxide is simulated with the Monte Carlo method. The directional characteristics and the power distribution of the concentrated solar radiation that enters the cavity is obtained by carrying out a Monte Carlo ray tracing of a paraboloidal concentrator. It is considered that the reactor contains a gas/particle suspension directly exposed to concentrated solar radiation. The suspension is treated as a non-isothermal, non-gray, absorbing, emitting, and anisotropically scattering medium. The transport coefficients of the particles are obtained from Mie-scattering theory by using the optical properties of cerium oxide. From the simulations, the aperture radius and the particle concentration were optimized to match the characteristics of the considered concentrator.

Optical design of a High Radiative Flux Solar Furnece for Mexico

Publicado en Revistas Arbitradas

C. Iriarte-Cornejo, C.A. Arancibia-Bulnes, I. Salgado-Transito, J. Waissman, R.E. Cabanillas, C.A. Estrada.

Abstract

Heliostat image drift is a common phenomenon in central receiver solar power plants. Several geometrical errors produce drift of the heliostat solar spot at receiver surface, increasing radiation spillage. A heuristic drift compensation method is proposed, based on a polynomial approximation to the drift trajectories. Results of the practical implementation of the proposed method for the control of 10 heliostats in a solar tower facility are presented. A substantial improvement of heliostat tracking is observed on the experimental tests. Because heliostat drift experimental monitoring is a time consuming task, a numerical analysis of the yearly behavior of the compensation method, based on simulations of heliostat drift, was carried out. In these simulations, the behavior of the daily RMS deviation of the concentrated solar spot centroid is evaluated for a whole year, as the polynomial correction is applied. The simulations serve also to test the effectiveness of the proposal polynomial method in a wider range of conditions. Thus, heliostats with a variety of primary error values are simulated. Random wind induced vibrations are introduced in the simulation to evaluate the effectiveness of the calibration method under noise conditions. It is found that a very effective calibration can be achieved with a few sampling events of the heliostat behavior during the year, taking only a few minutes. The RMS deviation can be reduced to values of the order of the wind induced noise level. The proposed polynomial compensation looks like a promising alternative to be implemented in heliostat fields.

Compensation of heliostat drift by seasonal sampling

Publicado en Revistas Arbitradas

Elisa Alonso, Carlos Pérez-Rábago, Javier Licurgo, Edward Fuentealba, Claudio A. Estrada.

Abstract

Thermochemical redox processes are currently considered one of the most promising methods for thermal storage of solar energy. Among the different types of materials available for this purpose, metal oxides allow higher operation temperatures in CSP systems. This is in agreement with the new R&D trends that focus on increasing the temperature to augment the efficiency. Copper oxide was previously proposed as a valid metal oxide for thermochemical storage. However, no demonstrative experiments had been carried out so far under solar radiation. In this work, the suitability of copper oxide was proved in a solar furnace. The employed solar reactor was a rotary kiln device with direct radiation absorption on reactive particles, which is a configuration that guarantees higher operation temperatures than other types of solar reactors. Given results include the performance of the CuO reduction in the rotary kiln under argon atmosphere and the cyclability of the pair CuO/Cu2O in air.

First experimental studies of solar redox reactions of copper oxides for thermochemical energy storage

Publicado en Revistas Arbitradas

L.G. Ceballos-Mendivil, R.E. Cabanillas-López, J.C. Tánori-Córdova, R. Murrieta-Yescas, C.A. Pérez-Rábago, H.I. Villafán-Vidales, C.A. Arancibia-Bulnes, C.A. Estrada.

Abstract

Silicon carbide (SiC) has been prepared successfully using concentrated solar energy provided by the IER-UNAM solar furnace. This has led to the development of a low CO2 emissions process for the production of this material via carbothermic reduction of a silica/carbon (SiO2/C) nanocomposite, which has shown a more reactive carbon for formation of composite, being more thermally stable. Silica (obtained by a sol–gel process) and sucrose were used as precursors of silicon and carbon, respectively, at a temperature of 700 °C in controlled atmosphere (nitrogen) for the formation of the SiO2/C composite. This composite was used in a second step to obtain SiC at a temperature of 1500 °C, in argon atmosphere. The experimental setup used a Pyrex® glass spherical vessel designed to work with concentrated solar power and controlled atmospheres. The structure and morphology of the solar obtained SiC were analyzed with FTIR, XRD, TGA/DSC, SEM and TEM techniques. Results show that it is feasible to use concentrated solar energy for the synthesis of SiC. The solar SiC obtained is nanostructured and is mainly β-SiC.

Synthesis of silicon carbide using concentrated solar energy

Publicado en Revistas Arbitradas

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