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The design and location of solar energy technologies are based chiefly on the availability of solar resource. Specialized measurement equipment and solar resource assessment techniques are mandatory in order to identify appropriate locations for deploying solar systems while minimizing risk and increasing the return rate of the site. These needs have given the scientific community a motivation to design highly reliable and cost-competitive sensors. This work presents a novel methodology to estimate solar irradiance components using a low-cost sky-imager system. Captured images are processed to correct the spherical aberration of the dome and to achieve a pixel-radiance model, allowing each pixel of the image to be considered as an individual source of irradiation. The performance of the proposed model is analyzed and compared in four different weather scenarios against a secondary standard solarimetric station, obtaining a normalized mean bias error for direct normal irradiance, global horizontal irradiance and diffuse horizontal irradiance of 4.53%, −6.55% and 19.62% for a sunny day, 0.79%, −6.13% and 7.00% for a partially sunny day, 1.96%, −6.58% and −0.73% for a partially cloudy day, 100%, −10.48% and −0.65% for a cloudy day, respectively. According to the experimental results, the system stands out for its performance, easy setup, low-cost components and a robust estimation in all possible weather scenarios.

It is well known that concentrating solar power and concentrating photovoltaic technologies require high accuracy and high precision solar tracking systems in order to achieve greater energy conversion efficiency. The required tracking precision depends primarily on the acceptance angle of the system, which is generally tenths of a degree. Control algorithms applied to active solar tracking systems command and manipulate the electrical signals to the actuators, usually electric motors, with the goal of achieving accurate and precise solar tracking. In addition, a solar tracking algorithms system must provide robustness against disturbances, and it should operate with minimum energy consumption. In this work, a systematic review of the control algorithms implemented in active solar tracking systems is presented. These algorithms are classified according to three solar tracking control strategies: open-loop, closed-loop and combined open- and closed-loop schemes herein called hybrid-loop. Their working principles as well as the main advantages and disadvantages of each strategy are analyzed. It is concluded that the most widely used solar tracking control strategy is closed-loop, representing 54.39% of all the publications consulted. On–off, fuzzy logic, proportional-integral-derivative and proportional-integral are the control algorithms most applied in active solar tracking systems, representing 57.02%, 10.53%, 6.14% and 4.39%, respectively.

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 2.5 cm of facet side length. For values of slope and canting errors up to 2 mrad, half this density is sufficient.

A new High Flux Solar Simulator (HFSS) has been designed and built for the research of medium/ high-temperature solar material testing and solar thermochemical processes in Mexico. The HFSS was designed using seven 2.5 k W el Xenon short arc lamps, each close-coupled to a 2 m focal length truncated ellipsoidal specular reflector made of polished aluminum. A Monte Carlo (MC) ray tracing technique was employed to design the shape of the ellipsoidal reflectors. The estimated radiative flux obtained with the MC ray-tracing was 1700 kW m−2 peak flux for all the seven lamps in a flux spot of 100 mm in diameter. A peak flux of 267 kW m−2 was obtained for a single lamp-reflector unit. The design, dimensions and material specifications are presented. The control system is composed of an attenuator curtain and a servo-controlled dynamic test bench that allows variation of the spot size and irradiance incident in the focal plane. A study to compare the theoretical design and the real ellipsoidal reflector surface was conducted with the use of the photogrammetry technique. This was done in order to know if differences in the theoretical flux compared to that of the measured flux come from defects in manufacturing of the reflector. A data acquisition module and an artificial vision system provide information and allow for a monitoring flux spot. Obtaining an experimental peak flux of 194 kW m−2 and a flux spot diameter of 120 mm per lamp, the results were consistent with the desired design. In addition, in order to quantify the risk of our own installation and implement a safety protocol, an experimental campaign of ultraviolet radiation monitoring was conducted; the assessment of ultraviolet radiation shows that the recommended dose per 8 h is exceeded in a few seconds when close to the focal plane (∼0.2 m). In this paper, due to extension, preliminary design, construction, and validation of the HFSS are presented.

TiO2 and iron-doped TiO2 microsized powder is prepared by sol–gel method combined with hydrothermal treatment as an alternative to obtain high specific area under controlled conditions. Synthesis parameters such as temperature of hydrothermal treatment (125 °C–210 °C), calcination temperature (500 °C–900 °C), and calcination time (1 h–9 h) along with operational parameter as solution pH (3, 7 and 9) in the solar photocatalytic reaction are assessed. TiO2 and iron-doped TiO2 micro powders are characterized by XRD studies, FE-SEM, specific area BET and photocatalytic activity by basic orange 2 (BO2) mineralization under solar irradiation. Results showed that ultrafine anatase microspheres are generated by sol-gel/hydrothermal treatment. Iron-doped TiO2, prepared by consecutive steps such as sol-gel/hydrothermal treatment at 200 °C, washed with ethanol, followed by calcination at 600 °C and dried with a rotary evaporator, showed the highest discoloration and mineralization of BO2. Outstanding performance is observed when compared with commercial TiO2 (Hombikat).

Solar simulators are key facilities for conducting solar research and certification tests under a well-controlled environment. This study presents the optical design optimization of a modular low flux solar simulator to improve solar technology qualification testing. The optical system was designed as a multi-lamp array of 26 subunits. Each subunit consists of a 575 W e metal halide lamp and a parabolic reflector. The Monte Carlo ray tracing technique was used for analyzing the optical performances of the proposed design. Reflector design parameters were analyzed in detail for optimizing the uniformity of the flux distribution on the target. Results show that an average flux of 1198 W/ m 2 over a target area of 2000 mm × 1000 mm, with a conversion efficiency of 25.7% and a sustained non-uniformity of only 1.4% was numerically achieved, predicting a Class A solar simulator for large target areas. A shutter curtain was modeled and introduced between the light source and the target for flux regulation, achieving average flux levels ranging from 1162 to 105 W/ m 2 with a resolution of approximately 100 W/ m 2 . The modular nature of this design has the great advantage that it could be easily scaled according to the test requirements of potential solar systems.

A multiscale model is presented to describe the radiation absorption field in photocatalytic reactors with supported catalyst. The characteristic matrix method is applied at the photocatalyst layer scale, and is embedded within a Monte Carlo ray tracing method, applied at the photoreactor scale. This approach allows to account for important design parameters, such as photocatalyst layer thickness, location of supporting surfaces, and incoming radiation profiles, among others. To resolve the validity of the characteristic matrix method for the description of the optical properties of the catalyst, modeled transmittance and reflectance of the supported films is compared to experimental data. This comparison is carried out for different wavelengths and film thicknesses. Afterwards, the model is applied to a solar reactor with anatase TiO 2 catalyst films supported on multiple surfaces. The reactor consists of a compound parabolic concentrator with a tubular borosilicate glass receiver. Smaller glass tubes coated with the catalyst are located inside this receiver. With the developed model, a study is conducted to analyze the reactor optical performance as a function of two important design variables: TiO 2 film thickness and radius of the absorber tubes. The results of the model indicate directions for the improvement of the current design.

The optical quality of concentrators has a direct impact on the thermal efficiency of concentrating solar power plants. There is a need to evaluate the quality of the mirrors before installation and during operation. A review of the optical characterization techniques that have been developed for solar concentrators is presented. A brief description of the operation and methodology of each technique is done. The strengths and possible vulnerabilities of the techniques are also discussed. A classification of the different techniques in families according to their underlying principles of operation is proposed. Finally an analysis of the available information about the accuracy and precision of the different methods is carried out.

Solar cavity receivers are key components in point-focus concentrating solar power technologies due to their benefits of high efficiency and operating temperature. Accordingly, the enhancement of the optical performance can yield to significant improvements in the whole thermal power system. In this study, a geometrical optimization of an axial type impinging receiver for a solar dish Brayton system was analytically accomplished through Monte Carlo ray tracing method. By modeling a reference cylindrical cavity, optical surface properties and geometrical parameters were analyzed by dividing the cavity into three zones: front wall, middle wall and back wall. Simulation results show that the light flux peaking on the cylindrical wall can be significantly reduced when the cavity front wall is modified by changing the inclination angle; the light flux distribution over the absorber surface can be flattened by increasing the cavity radius; the irradiance distribution over the absorber can be efficiently adjusted by modifying the cavity back wall. After the cavity geometry optimization, the optical efficiency of the receiver can be enhanced by 3.34%, the material volume can be reduced by 20.1% and the peak flux on the cavity wall can be reduced by 38.6%, from 30 to 18.4 kW/m2.

An 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.