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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.

Agro-industrial waste valorization is an attractive approach that offers new alternatives to deal with shrinkage and residue problems. One of these approaches is the synthesis of advanced carbon materials. Current research has shown that citrus waste, mainly orange peel, can be a precursor for the synthesis of high-quality carbon materials for chemical adsorption and energy storage applications. A recent approach to the utilization of advanced carbon materials based on lignocellulosic biomass is their use in solar absorber coatings for solar-thermal applications. This study focused on the production of biochar from Citrus aurantium orange peel by a pyrolysis process at different temperatures. Biochars were characterized by SEM, elemental analysis, TGA-DSC, FTIR, DRX, Raman, and XPS spectroscopies. Optical properties such as diffuse reflectance in the UV−VIS−NIR region was also determined. Physical-chemical characterization revealed that the pyrolysis temperature had a negative effect in yield of biochars, whereas biochars with a higher carbon content, aromaticity, thermal stability, and structural order were produced as the temperature increased. Diffuse reflectance measurements revealed that it is possible to reduce the reflectance of the material by controlling its pyrolysis temperature, producing a material with physicochemical and optical properties that could be attractive for use as a pigment in solar absorber coatings.

High flux solar simulators are artificial solar facilities developed to imitate the on-sun operations of concentrating solar power technologies but under a well-controlled lab-scale environment. We report the optical enhancement of different high flux solar simulators for solar thermal and thermochemical applications. The solar simulator enhancement is numerically conducted by optimizing the geometry of ellipsoidal reflectors at focal lengths of 1600, 1800, and 2000 mm. The Monte Carlo ray-tracing technique is employed to evaluate the optical performance of different reflector designs. The typical seven-lamp solar simulator arrangement in hexagonal configuration is modeled to analyze the optical performance at different focal lengths. In addition, different xenon arc lamps are modeled with rated powers of 3000, 4000, 4500, and 5000 W for assessing the radiative flux characteristics of the proposed solar simulators. After the optimization, theoretical results show that peak fluxes and radiative powers of 7.2 − 14 . 3 M W / m 2 and 5.06–10.4 kW, respectively, can be achieved with the proposed designs of solar simulators for the different rated powers. Compared with a commercial reflector, theoretical peak flux and power can be improved up to 36% and 17.9%, respectively, with the proper combination of lamp-reflector units. We provide design alternatives to select a more suitable light source at low-rated powers ( ≤ 5000 W ) and different focal lengths of the reflector, which simplifies the complexity of the design and improves the performance of solar simulators.

One of the problems of designing a solar compound parabolic concentrator (CPC) is related to its manufacturing shape accuracy. The complexity of curving and holding the CPC profile in place is indeed a challenging issue, especially because there are no standardized molds and the process is typically handmade. It is very easy to provoke misalignment on the CPC surface and in consequence, divert the solar incident rays, affecting significantly the optical efficiency of the system. This work presents a novel, inexpensive methodology to manufacture a CPC with accuracy by using basic tools. The design starts with the acquisition of a pair of medium-density fiberboard wooden templates of the CPC profile that are used later to make a Styrofoam CPC mold and then cut with a hot-wire technique. A high-reflectance anodized aluminum sheet is curved to approximate the CPC shape and is then coupled with the temporary Styrofoam mold. The last part consists of the elaboration of a housing system to contain the parts. This is consolidated by a polyurethane resin that expands and fills all enclosure cavities, offering stiffness and stability. A photogrammetry analysis was implemented for the validation of the surface shape accuracy. The results from the optical analysis show that this technique achieved a high degree of accuracy and homogeneity on the CPC surface shape.

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.

In this work the development of a low-cost solar sensor capable of locating the position of the sun through photosensors is presented. In addition, the sensor is integrated with the instrumentation to provide the data for a solar position algorithm. As preliminary results, we present the methodology followed for the development of the sensor, as well as the theoretical characterization carried out through the Tonatiuh software.

Solar resource assessment is a key subject for the viability and implementation of solar power plants. Solar sensors measure irradiance locally, but high cost of these specialized sensors makes their implementation through all the Mexican territory difficult. Satellite images provide a valuable tool for the determination of solar irradiance through image processing. In this work, an algorithm for the estimation of global solar irradiance based on determining the cloud index through pixel analysis is implemented for the central region of Mexico.

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.

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.

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.

This study presents the optical improvement of a high flux solar simulator (HFSS) with controllable flux-spot capabilities developed for researching solar thermal and thermochemical processes. The HFSS is comprised of seven 2.5 kWel Xenon arc lamps coupled with ellipsoidal reflectors, a servo-controlled attenuator curtain, and three-axes linear test bench. Different attenuators were designed and tested in order to identify the best curtain geometry to improve the HFSS modulation with the lowest possible radiative losses. The optical design improvement was performed with the aid of TracePro, a Monte Carlo ray-tracing software. From simulation results, radiative peak flux from 1700 to 480 kWm−2 from the focal plane to 300 mm further back was estimated without curtains. By using the attenuators, flux levels from 1570 to 92 kWm−2 at the focal plane were also estimated. An experimental validation was achieved with a single lamp-reflector unit obtaining peak flux distributions from 200±20 kWm−2 to 97±9.7 kWm−2 from the focal plane to 300 mm behind. Flux modulation from 170 to 1.5 kWm−2 was also measured at the focal plane using a servo-controlled curtain from fully-open slats (0°) to partially closed (60°). With this attenuator, introduced as the shutter of the system, the use of several lamps or electronic rectifiers is avoided and the radiative flux is modulated with high resolution in an optomechatronical form.

Solar resource assessment is fundamental to reduce the risk in selecting the solar power-plants&rsquo, location, also for designing the appropriate solar-energy conversion technology and operating new sources of solar-power generation. Having a reliable methodology for solar irradiance forecasting allows accurately identifying variations in the plant energy production and, as a consequence, determining improvements in energy supply strategies. A new trend for solar resource assessment is based on the analysis of the sky dynamics by processing a set of images of the sky dome. In this paper, a methodology for processing the sky dome images to obtain the position of the Sun is presented, this parameter is relevant to compute the solar irradiance implemented in solar resource assessment. This methodology is based on the implementation of several techniques in order to achieve a combined, fast, and robust detection system for the Sun position regardless of the conditions of the sky, which is a complex task due to the variability of the sky dynamics. Identifying the correct position of the Sun is a critical parameter to project whether, in the presence of clouds, the occlusion of the Sun is occurring, which is essential in short-term solar resource assessment, the so-called irradiance nowcasting. The experimental results confirm that the proposed methodology performs well in the detection of the position of the Sun not only in a clear-sky day, but also in a cloudy one. The proposed methodology is also a reliable tool to cover the dynamics of the sky.

Compound parabolic concentrators are relevant systems used in solar thermal technology. With adequate tailoring, they can be used as an efficient and low-cost alternative in residential water heating applications. This work presents a simulation study using a ray tracing analysis. With this technique, we simulate the interaction between solar rays and solar concentrator to quantify the amount of energy that impinges on the receiver at a particular time. Energy availability is evaluated in a comparison of two configurations throughout the year: static setup at 21° and multi-position setup; tilted with respect to the horizontal, depending on three seasonal positions: 0° for summer, 16° for spring/autumn, and 32° for winter, with the aim to evaluate the amount of available energy in each season. The fact that a tracking system can be dispensed with also represents an economical option for the proposed application. The results showed that at 21°, the proposed solar Compound Parabolic Concentrator (CPC) works satisfactorily; however, by carrying out the selected angular adjustments, the overall energy availability increased by 22%, resulting in a more efficient option. The most effective design was also built and analyzed outdoors. The obtained thermal efficiency was of ~43%. The optical design and its evaluation developed herein proved to be a valuable tool for prototype design and performance evaluation.

In the framework of the National Laboratory of Solar Concentrating and Solar Chemistry Systems (LACYQS, for its Spanish acronym), a Heliostat Test Field (HTF) was built in México. This research facility is located 10 km away from the city of Hermosillo, in the state of Sonora. The main purpose of the HTF, at the present stage, is to serve as platform for the development and testing of heliostat technology. In order to evaluate the performance of heliostats, various optical tests have been implemented. In the sun tracking test, the heliostat is operated as a solar tracker. A camera is attached to the heliostat, which is pointed directly to the sun. Images are captured throughout the day to quantify the wandering of the solar disc in the image. In the reflected spot test, the image produced on the Lambertian target by the concentrating heliostat, due to the reflection of the sun, is recorded by a CCD camera throughout the day. Image processing algorithms calculate the centroid of energy of the image and evaluate the position and wandering across the white screen at all times. After this information is gathered, and the influence of wind and external factors eliminated, data are interpreted to characterize the behavior of solar projection algorithms and mechanical components. In the fringe projection analysis, also known as deflectometry, fringe patters are projected at night on a Lambertian target. The image of the pattern reflected by the heliostat is recorded with a camera. Distortions in the fringes, due to mirror stress and canting, allows the characterization of the surface error of the facets.

Heliostat image drift is defined as the wandering of the irradiance spot produced by a heliostat on a receiver or observation screen. Two factors producing heliostat image drift have been analyzed theoretically in the present paper: errors in reference position, and time delay. Some regular behavior is found in the drift curves. Maximum deviations from target tend to be linearly dependent with either angular error, or time delay. In particular, the curves produced by this later effect are circular or elliptical. Heliostats at different distances from a tower have been analyzed. For heliostats far from the tower the drift curves due to errors in reference position also have a more or less elliptical shape. Results are presented as dimensionless quantities. Some practical implications of these results are discussed.

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 × 106 points per mirror facet), short measurement time and easy setup. The developed tool (called FOCuS) is capable of calculating the local 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 into CENER's TONATIUH ray tracing software, through a specially developed plug-in, for mirror modeling and intercept factor calculation with several tube absorber geometries.

"Solar technologies, such as concentrating solar power (CSP) systems, are one of the most promising technologies for covering the future global energy demand, achieving a low-carbon economy and mitigating environmental problems (greenhouse effect). Typically, outdoor solar facilities are implemented for evaluating solar receivers and prototypes, but the intermittent nature of solar radiation and weather constrains are the main challenges in offering stable testing environments. Solar simulators have been identified as key facilities for carrying out high-quality indoor assessments under a controlled lab-scale environment. This PhD thesis is aimed to the optical design and characterization of a high flux solar simulator (HFSS) for researching solarthermal and thermochemical processes. To do so, a 17.5 kWe HFSS was developed along with a calorimetric test bench for the assessment of solar-thermal materials. The design of the 7 xenon lamps based solar simulator was numerically analyzed through the Monte Carlo ray-tracing method and characterized with the indirect flux mapping technique, an optical technique that involves the use of a high resolution camera and a diffusely reflective flat target plate. Characterization results showed a total peak flux of up to 1327±58 kW/m2 having an intercepted radiative power of 5.11±0.22 kW over a flux spot distribution of 120 mm in diameter, and conversion efficiency of 33%. Regarding the calorimetric test bench, its design was based on a flat-plate calorimeter which provides the versatility to replace test samples as interchangeable cartridges. By coupling the test bench with the HFSS, solar-thermal assessments of 4 different commercial solar absorber coatings and a new soot of forest biomass based coating were experimentally evaluated and compared under the same operating conditions. The presented approach for evaluating commercial and new solar-thermal materials provides critical information about their optical-thermal capabilities. Accordingly, the flux acceptance of suitable materials for their usage in solar-based industrial process heating can be effectively determined, and further progress in the improvement of solar-thermal technologies can be accomplished."

"En este documento se describe el diseño, construcción y desarrollo de un sistema de visión artificial terrestre de bajo costo (ViSoN-Vision Solar Nowcasting) como una alternativa para la predicción de valores de irradiancia solar en horizontes de tiempo corto. El documento comprende un desarrollo progresivo de las diversas etapas que inicia desde la documentación bibliográfica hasta los resultados del procesamiento de las imágenes obtenidas por el prototipo. El método usado en este trabajo de investigación es efectivo ya que los resultados obtenidos de las componentes GHI y DNI de la irradiancia solar son confiables y se comportan de manera similar a los datos adquiridos con radiómetros comerciales de alta calidad, pero a bajo costo computacional y con altas resoluciones tanto temporales como espaciales. Además, ViSoN tiene la capacidad de detectar y realizar seguimiento de las nubes más próximas al sol sobre las imágenes, gracias a los algoritmos desarrollados e implementados en el prototipo, permitiendo así obtener sus posiciones, trayectorias, velocidad y tiempo que tardaría la nube en hacer contacto con el sol."