Solar Spots Research Articles

Optimal multi-layer economical schedule for coordinated multiple mode operation of wind–solar microgrids with hybrid energy storage systems

The aim of this paper is the design and implementation of an advanced model predictive control (MPC) strategy for the management of a wind–solar microgrid (MG) both in the islanded and grid-connected modes. The MG includes energy storage systems (ESSs) and interacts with external hydrogen and electricity consumers as an extra feature. The system participates in two different electricity markets, i.e., the daily and real-time markets, characterized by different time-scales. Thus, a high-layer control (HLC) and a low-layer control (LLC) are developed for the daily market and the real-time market, respectively. The sporadic characteristics of renewable energy sources and the variations in load demand are also briefly discussed by proposing a controller based on the stochastic MPC approach. Numerical simulations with real wind and solar generation profiles and spot prices show that the proposed controller optimally manages the ESSs, even when there is a deviation between the predicted scenario determined at the HLC and the real-time one managed by the LLC. Finally, the strategy is tested on a lab-scale MG set up at Khalifa University, Abu Dhabi, UAE.

Characteristics of Long-Term Spot Activity on Several Late-Spectral-Type Stars

We present our analysis of many-year photometry for several dozens of chromospherically active stars that exhibit solar-type activity (from our own observations as well as from data in the literature). Modeling of the distribution of cool photospheric spots, based on the zonal model, was performed, with several hundred models constructed. We find that, for most stars, their spots are located at intermediate and moderate latitudes and that the largest spotted areas can cover from 7 to 58% of the star’s surface. We demonstrate that a latitude drift of spots can be suspected for a number of stars, towards the equator as well as towards the pole; however, the rate of this drift is several times lower than for solar spots. For 15 stars, we detected the presence of activity cycles from 3 to 28 years long that reveal themselves in variations of the system’s brightness as well as in variations of the total spot coverage of the star. This paper is based on a talk presented at the memorial astrophysical workshop “Novelties in Understanding the Evolution of Binary Stars” dedicated to the 90th birthday of Prof. M.A. Svechnikov.

A proposal for additively manufacturing printed circuits by employing concentrated solar energy

A novel method capable of generating printed circuits using concentrated solar energy (CSE) is proposed. The open literature has reported that no method employs CSE to obtain printed circuits additively. Based on the Mill & Fill method, a conductive material (Sn63Pb37) is deposited inside a trench milled on a thermoplastic substrate (PETG). The concentrated solar beam melts the conductive material to form a solid trace, while the substrate relaxes its structure and allows the inclusion of the path. The resulting hybrid joining between plastic and metal is like those obtained by LAMP (laser-assisted joining of metal-polymer). The 20 conducted tests found that the magnitude of direct solar radiation and the overall system efficiency are the most influential variables on the exposure time of the trace to the solar spot. Each test, with its conditions, was simulated in COMSOL Multiphysics software, and the temperatures obtained experimentally were compared with those obtained by simulation. This proposal is expected to serve as a bridge between both fields of study so that solar concentrators will be considered in the additive manufacturing of printed circuits and expand CSE's potential for developing consumer goods.

Vehicle-Mounted Solar Occultation Flux Fourier Transform Infrared Spectrometer and Its Remote Sensing Application.

For the demand of rapid monitoring of pollution gas disorganized emissions in industrial parks, this paper studies the solar fast tracker system of vehicle-mounted SOF-FTIR (Solar Occultation Flux Fourier Transform Infrared Spectroscopy) system, where the spectrometer directly measures the broadband absorption spectrum of solar radiation light. A fast portable solar tracking system based on PSD (position sensitive detector) is designed, the mathematical model of solar spot position on the PSD surface source is established, and the optimal optical design parameters are simulated using the model. The dead-zone integral separation PID (Proportion Integration Differentiation) control algorithm is used to track the trajectory of the solar, and the light spot position model is used to nonlinearly compensate the output of PID control so that the PID controller has the same control precision and response speed in different error areas. Experimental analysis of the solar tracking performance of the vehicle-mounted SOF-FTIR under static and dynamic conditions, as well as the spectral effects on the measurements under static vehicle, constant speed, and turning driving conditions. The remote sensing application experiment of vehicle-mounted SOF-FTIR pollution gas emission flux was carried out in a tire factory in Hefei City, Anhui Province. A vehicle-mounted SOF-FTIR system realized the qualitative and quantitative analysis of the pollution gas at the boundary of the tire plant and calculated the flux of each component pollution gas. The emission flux of pollution gas was highly consistent with the actual pollution distribution of the tire plant. The results show that the positioning accuracy of PSD in the vehicle tracking experiment can also meet SOF-FTIR requirements for solar tracking. The remote sensing system will be useful in the field of atmospheric environment monitoring, and the mobile monitoring of regional pollutant gases based on solar infrared spectroscopy has application value.

In-situ visualization of powder wrapping behavior in millimeter-scale-beam lunar regolith powder bed fusion

Future lunar base additive manufacturing is accelerated by ground-based technology. Naturally, loosely packed lunar regolith must be directly treated into a solid surface on the first layer of lunar base construction. Solar powder bed fusion (Solar PBF), with huge spot sizes and low energy densities, is the most efficient energy and material usage method on the moon. However, the powder bed's low heat conductivity hinders energy penetration. This investigation used a millimeter-scale laser beam to recreate the solar PBF spot. The beam was directed at the powder bed without substrate. In-situ observation revealed a wrapping mechanism works for multiple parameters. The wrapping process was primarily observed with lunar regolith simulant CUG-1A, and SS316L was used for comparison under a similar spot and no substrate. The periodic wrapping helps to form deeper melt tracks. The wrapping process has the potential to produce a substrate on a loose powder bed directly.

Radiative intensity regulation to match energy conversion on demand in solar methane dry reforming to improve solar to fuel conversion efficiency

The mismatch between radiative intensity field and energy required for solar thermochemical reaction can cause serious heat waste and reduce energy conversion efficiency. To improve the energy conversion efficiency of solar to fuel, the radiative intensity regulation method to match energy conversion on demand in solar methane dry reforming is proposed in this study. The design of solar spots and biomimetic leaf hierarchical porous structures is investigated and optimized, which can realize a better radiative intensity field matching. The experimental and numerical studies show that, by using the method of regulating radiative intensity field to match energy conversion on-demand in solar thermochemical reactor, the methane conversion rate and solar thermochemical energy storage efficiency can be increased by 4.6% and 6.1%, respectively. The ideal synergy between real temperature field distribution and theoretical temperature requirement is perfectly achieved.

Large Sunspot Groups and Great Magnetic Storms: Magnetic Suppression of CMEs

A solar spot group with a large area is not a requirement for a great magnetic storm. Nearly half (14/30) of all storms with a minimum Dst value ≤−300 nT from 1932–2014 originated in spot groups with corrected areas ≤1000 millionths of a solar hemisphere (μsh) on the day of the associated eruption. Over the same interval, spot groups with area 3000–4000 μsh were ∼250 times more likely to give rise to a great storm than those with areas from 100–1000 μsh, with the high percentage of great storms originating in small spot groups attributed primarily to the much higher occurrence frequency of such groups. Above ∼3500 μsh, the ability of a spot group to produce a great storm appears to drop abruptly. For the 1932–2014 interval, we find that for the 71 days when a spot group had a measured daily area of 3000–3500 μsh, five great storms were observed versus none for the 67 times when a group spot with an area from 3500 to ∼6000 μsh was observed on the Sun. This is consistent with recent studies indicating that large spot groups on the Sun and stars can suppress coronal mass ejections.

Faculae Cancel out on the Surfaces of Active Suns

Surfaces of the Sun and other cool stars are filled with magnetic fields, which are either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection and characterization of exoplanets, affecting stellar brightness and spectra, as well as transmission spectra. However, the expected facular and spot signals in stellar data are quite different, for instance, they have distinct temporal and spectral profiles. Consequently, corrections of stellar data for magnetic activity can greatly benefit from the insight on whether the stellar signal is dominated by spots or faculae. Here, we utilize a surface flux transport model to show that more effective cancellation of diffuse magnetic flux associated with faculae leads to spot area coverages increasing faster with stellar magnetic activity than that by faculae. Our calculations explain the observed dependence between solar spot and facular area coverages and allow its extension to stars that are more active than the Sun. This extension enables anticipating the properties of stellar signal and its more reliable mitigation, leading to a more accurate characterization of exoplanets and their atmospheres.

Smoldering ignition using a concentrated solar irradiation spot

Ignition of materials by a point source of heating plays an important role in initiating many structure and wildland fires, such as spotting by hot particles, lightning, laser, and concentrated irradiation. Herein, we study the smoldering ignition of tissue paper by a concentrated sunlight spot with heat fluxes up to 780 kW/m2, which is focused by a transparent glass sphere. The diameter of the sunlight spot on the paper sample ranges from 1.5 to 20.0 mm by varying the paper position within the focal length, where a smaller spot has a larger intensity of sunlight irradiation. The measured minimum spot irradiation for smoldering ignition is not a constant and is much higher than 11 kW/m2 measured in a traditional cone-calorimeter test. As the diameter of the irradiation spot decreases from 20 to 1.5 mm, the minimum irradiation for smoldering ignition increases from 17.5 to 205 kW/m2, and the ignition energy increases from 0.084 to 2.0 MJ/m2. A simplified heat transfer analysis reveals that the lateral conductive cooling within the fuel becomes dominant for a smaller spot ignition area. This work ultimately quantifies the potential fire risk from concentrated sunlight spots and helps elucidate the underlying mechanisms leading to smoldering ignition.

Galileo’s revolution and the infancy of meteorology in Padua, Florence and Bologna

This article reconstructs the historical and scientific framework within which modern science, and meteorology in particular, were born and developed beginning in the late XVI century. Scientific knowledge during this period was based on Aristotle’s books and the Holy Bible, and this constituted a serious obstacle for the new astronomical discoveries that contradicted this framework. The paper starts with the earliest experiments made by Galileo, his discoveries, e.g. thermoscope, telescope, solar spots and motion that caused his trial. Galileo facilitated the transition from the middle age to modern science, fighting against the old ideas and separating faith from research. The new science had a strong development with Ferdinand II, grand Duke of Tuscany who founded the Accademia del Cimento (i.e. Experiment Academy), and the first international network of temperature observations in the mid XVII century. The passage from the thermoscope to the modern thermometer is also explained, as well as the pioneering activity at the Universities of Padua and Bologna, and in Florence.

Firefly Algorithm-Based Photovoltaic Array Reconfiguration for Maximum Power Extraction during Mismatch Conditions

This studyaimed at improving the performance and efficiency of conventional static photovoltaic (PV) systems by introducing a metaheuristic algorithm-based approach that involves reconfiguring electrical wiring using switches under different shading profiles. Themetaheuristicalgorithmused wasthe firefly algorithm (FA), which controls the switching patterns under non-homogenous shading profiles and tracks the highest global peak of power produced by the numerous switching patterns. This study aimed to solve the current problems faced by static PV systems, such as unequal dispersion of shading affecting solar panels, multiple peaks, and hot spot phenomena, which can contribute to significant power loss and efficiency reduction. The experimental setup focusedon software development and the system or model developed in the MATLAB Simulink platform. Athorough and comprehensive analysis was done by comparing the proposed method’s overall performance and power generation with thenovel static PVseries–parallel (SP) topology and totalcross-tied (TCT) scheme. The SP configuration is widely used in the PV industry. However, the TCT configuration has superior performance and energy yield generation compared to other static PV configurations, such as the bridge-linked (BL) and honey comb (HC) configurations. The results presented in this paper provide valuable information about the proposed method’s features with regard toenhancing the overall performance and efficiency of PV arrays.

기후, 날씨와도 싸워야 했던 일본제국주의, 그리고 식민지민 - 길었던 한 해, 1939년 조선 대가뭄의 양상과 그 여파 -

Examined in this article is the 1939 Great famine in Joseon, in terms of climatic factors and other issues related to the ecological environment of the time. Such approach revealed three important points.BR First, the 1939 Great famine seems to have been caused most probably by climatic abnormalities, such as volcanic eruptions or changes in solar spot activities. BR Second, the drought that hit Korea at the time caused significant decrease in Joseon’s rice production, which in turn caused severe food shortage throughout the Empire that also undermined Japan’s war efforts against China. In response, Japanese Imperialism employed many counter measures, focusing on minimizing direct aids, emphasizing self-rehabilitation, and increasing food transports.BR Third, the Joseon people actively responded to the colonial authorities’ policy, and acted in various ways. People in distress tried to secure wages through the public works for drought damage relief, and launched local appeal projects to invite the construction work to their areas. People who were spared from direct damages joined donation campaigns, out of their brethren affection. But there were also other people who resorted to believing in superstitions and rumors, after suffering a long hard time of begging and wandering. Such people who remained indifferent to observing the colonial authorities’ policy continued to become a burden, as the authorities still had to uphold and propagate the slogan notion of ‘Japanese Mainland and Joseon being one.’ BR These three points show us that future historical studies of the Asian-Pacific War period should pay more attention to climatic disasters as an ecological environmental element.

Macular Thickness in Cameroonians Sickle Cell Patients

Introduction: Sickle cell disease is the most common genetic disease in the world. It is particularly prevalent in Africa south of the Sahara. In Cameroon. Several authors have described morphological changes from the macula to Optical Coherence Tomography-Spectral Domain (SD OCT) including the thinning of the predominant inner layers in the temporal area. Methodology: This is a prospective analytic study. It was conducted mainly at the specialized ophthalmology department of the Army Military Application and Reference Hospital of Yaounde (HMARAY) in Cameroon. Clinical ophthalmologic exam was done and biological parameters (rate of hemoglobin, electrophoretic quantification of S hemoglobin) registered from October 2016 to June 2017.We included: Any AS patient or Cameroonian SS patient who is 20 years of age or older; sickle cell patients AS or SS without intercurrent retinal pathology (strong myopia, diabetic retinopathy, vitreoretinal interface pathology). Results: In our study the average age is 31 years. There is a predominance of female versus male sex ratio H/F=0.56. 84% of eyes had retinal lesions suggestive of non-proliferative retinopathy in the retina. The solar black spots were the most found retinal lesions (66.66%). Lesions were more localized temporally. In the OCT measurement, 60% of the eyes showed a decreased retinal thickness SD with 53% concerning the temporal retina. An hemoglobin level between 7 and 10 g/dl was found in 40% of our patients, 24% has severe anemia (hemoglobin<7 g/dl). All our patients had a percentage of hemoglobin S greater than 80%. No decrease in visual acuity in our patients who had a decrease in retinal thickness at OCT SD. Conclusion: There is a thinning of the retinal layers in SS Cameroonian sickle cell patients in the temporal region of the macula. Patients with retinal thinning are asymptomatic with preserved visual acuity.

Study on Optimized Dispatch and Operation Strategies for Heliostat Fields in a Concentrated Solar Power Tower Plant

Concerning solar flux densities during the operation of a concentrated solar power tower plant, their uneven distribution on a central receiver not only leads to abrupt variations of thermal gradient on the receiver surface but also makes it possible for the receiver to break down. Specific to such problems, a “concentrating-receiver” coupling system of a 1 MWe concentrated solar power tower plant in Yanqing was selected as the research object. On this basis, a spliced heliostat model was firstly established in this paper. The model was used to investigate solar flux distribution on the receiver surface. Considering that heliostats in different positions make diverse contributions to receiver surface energy and the incidence cosines of adjacent heliostats are similar to each other, a new grouping method for heliostat fields was subsequently proposed; moreover, focal point selection criteria were designed for the receiver surface according to solar spot sizes. Finally, an optimized dispatch and operation strategy was established based on the genetic algorithm for the heliostat field. Therefore, a standard deviation of solar flux distribution can be minimized. To verify the reliability of the established model and the proposed strategy, a small-scale heliostat field was adopted to check the simulation results by means of experiments. It has been demonstrated that a heliostat field subjected to optimized dispatch makes solar flux densities distribute more uniformly on the receiver surface. Hence, the safe and steady operation of the receiver is guaranteed.

Analysis and Adjustment of Positioning Error of PSD System for Mobile SOF-FTIR.

A PSD-based solar spot position detection system is developed for solar tracking closed-loop control of mobile SOF-FTIR (Solar Occultation Flux method based on Fourier Transform Infrared spectrometer). The positioning error factors of PSD (position sensitive detector) are analyzed in detail. A voltage model for PSD signal conditioning circuit has been established to investigate the noise factors. The model shows that the positioning error is mainly related to PSD dark current and circuit gain. A static voltage deduction calibration method based on genetic algorithm is proposed to eliminate the effect of dark current. The gain ratio between channels is calculated based on the fitting curve slope of discrete position data of PSD center point with different light intensity for circuit gain calibration. The positioning accuracy and precision are greatly enhanced, especially when the light intensity is weak, compared with uncalibrated results. The positioning accuracy of center, middle and edge areas of PSD can reach 0.14%, 0.49%, and 1.09%, respectively, after correction in the range of light intensity voltage from 40 mV to 20 V. The corresponding standard deviations of each region are 0.005, 0.009, and 0.014, respectively. The adjustment methods proposed in this paper improve both measurement accuracy and detection limit. The results demonstrate that the calibrated PSD positioning accuracy can meet the requirements of SOF-FTIR for solar tracking.

TREND-RUN model application of surface temperature and its implications for South African forestry and reforestation using local weather services data

Temperature can directly and indirectly impact the livelihood of inhabitants of a country and the natural environment as a whole. The surface temperature trend approximations for South Africa (SA) were calculated using a linear-regression fitting model. The model was adapted at The University of Reunion Island and was referred to as the Trend-Run model. The geophysical signal of the model was split into a sum of oscillations, which was used to clarify most of its variability. The trend values were calculated from the residual terms as a linear function. The model used atmospheric oscillations, which included Annual (AO), Semi-Annual (SAO), Quasi-Biennial Oscillations (QBO), El Niño-Southern Oscillation (ENSO), the 11-years solar cycle-Sun Spot Number (SSN) and Indian Ocean Dipole (IOD). The South African Weather Service (SAWS) data were used for the study. Data sets over a 31-year period, from March 1980 to December 2011, were used to measure the validity of the Trend-Run model, to determine the contribution and effect of this particular oscillation, and the validity of the model. The Trend-Run model showed very high applicability to the surface temperatures in all provinces across the SA region under investigation. High coefficient of determination values between (0.70-0.91) were recorded for surface temperatures across all provinces in the country with minor variations. The AO, ENSO and SAO were the highest contributing forcings in the model, thereby showing their high relevance to the success of this model in the study area. The temperature increases are expected to negatively impact on the biomes of SA, including the forest biome. Selected tree species of Acacia, Eucalyptus and Pinus could be impacted negatively with rising temperatures, which would negatively impact on the forestry industry in SA. As expected, the model did obtain a high success rate that ranged from 70% to 91% in the areas under study, however, there was still room for improvement by the possible inclusion of additional atmospheric forcings to the model that maybe be applicable to the weather and forestry distribution in SA.

Relación entre capturas del tiburón Rhizoprionodon terraenovae al sur del Golfo de México y el número de manchas solares

Background. The Antillean or sharpnose shark is one of the main exemplars of shark species in the commercial catch in southern Gulf of Mexico. Oceanic dynamics on the planet Earth varies year-on-year due to the oscillation of solar radiation; fish abundances (and catches) likely respond to these oscillations. Goals. This study focuses on the analysis of landings variability of the antillean sharpnose shark (Rhizoprionodon terraenovae) in the Mexican coast of the Gulf of Mexico, from 1940 to 2006, and its possible connection with solar activity as assessed by the average sunspot number (Zurich Index). Methods. A polynomial curve by least-squares best fitting was used to eliminate the tendency from the sharpnose shark landings time series. Spectral techniques of Maximum Entropy (ME) and Fast Fourier Transform (FFT) were used to analyze the time series of sharpnose shark landings and the Zurich Index. Results. The time series of sharpnose shark landings showed a remarkable spectral peak with a period of about 12.8 years, while the Zurich Index showed a marked peak at a period of 11.6 years. Cross-correlation revealed a delay between the average number of solar spots and sharpnose shark landings. Conclusions. This work is the first to report such a low frequency variability for landings of the Rh. terraenovae fishery in the Gulf of Mexico, using a particular methodology that can provide information for the design of predictive models in the future. The analyzed landing volumes of the sharpnose shark Rh. terraenovae showed as a result a periodical behavior in coincidence with Wolf’s solar activity cycle of 10.6 years.

ДОСЛІДЖЕННЯ ЦИКЛІЧНОСТІ МАГНЕТИЗМУ СОНЦЯ В МЕЖАХ ТЕОРІЇ МАКРОСКОПІЧНОЇ МАГНІТОГІДРОДИНАМІКИ

Since the mid-70s of the last century, a new direction in theoretical studies of the evolution of the global magnetism of the Sun in the framework of macroscopic MHD has been launched at the Astronomical Observatory of the Taras Shevchenko National University of Kyiv. The paper presents the results of a study of the processes of generation and restructuring of a large-scale (global) magnetic field based on the αΩ-dynamo model, taking into account new turbulent effects discovered in the theory of macroscopic MHD and data of helioseismological experiments on the internal rotation of the Sun. It was established that a sharp radial gradient of turbulent velocity in the lower half of the solar convective zone (SCZ) leads to a change in the sign of the azimuthal component of the helicity parameter α, resulting in the formation of a relatively thin layer of negative α-effect near the bottom of the SCZ. It was found that the layer of negative α-effect, together with the sign of the radial gradient of the angular velocity, detected in helioseismological experiments, makes it possible to explain the direction of migration of dynamo-waves on the solar surface. The magnetic saturation of the α-effect (alpha-quenching) in the deep layers of the SCZ was calculated. An explanation of the protracted duration of the 23rd solar cycle of about 13 years is proposed. For this, we used the observed data on a significant increase of the annual module of the magnetic fields of sunspots in the 23rd cycle. The calculated north-south asymmetry of the structure of the global magnetic field provides an opportunity to explain the phenomenon of the seeming magnetic “monopole”, which is observed during reversal of polar magnetism. It was found that the values of turbulent electrical conductivity and turbulent magnetic permeability of the solar plasma are significantly less than the corresponding gas-kinetic parameters. Therefore, the turbulent dissipation of solar magnetic fields is enhanced by 4–9 orders of magnitude compared with classical ohmic dissipation. Macroscopic turbulent diamagnetism of solar plasma was investigated. It has been found that in the lower part of the SCZ, turbulent diamagnetism acts against magnetic buoyancy, thus fulfilling the role of “negative magnetic buoyancy”. As a result of the balance of the effects of magnetic buoyancy and turbulent diamagnetism, a layer of blocked magnetic field of magnitude ≈ 3000 G is formed in the depths of the SCZ. The turbulent advection of a magnetic field in an inhomogeneous plasma density of the SCZ was studied. It was found that in the lower half of the SCZ of the equatorial domain, turbulent advection is directed upwards. As a result of the combined action of magnetic buoyancy and turbulent advection, deep strong toroidal fields are carried to the surface of the Sun in the latitudinal “royal zone” of sunspots. The role of horizontal turbulent diamagnetism in ensuring the long-term stability of sunspots was noted. To explain the observed phenomenon of double maxima of the solar spot cycle, a scenario was developed containing the generation of a magnetic field in the tachocline at the bottom of the SCZ and subsequent removal of this magnetic field from the depth layers to the surface in the latitudinal “royal zone”. The role of the radial omega-effect in the radiant zone in explaining the observed asymmetry in the amplitude of two neighbouring 11-years sunspot cycles was noted.

On a Magnetic Anomaly in the Umbra of the Following Spot of an NOAA 12192 Active Region

This paper examines the evolution and morphology of a magnetic anomaly: the appearance and disappearance of a longitudinal magnetic flux with opposite polarity at an area of about 10 arc seconds in the umbra of the following sunspot of an NOAA 12192 active region, which was observed from 21 to 26 October 2014 in the SDO/HMI and SOLIS/VSM magnetograms. Information collected by spacecraft and under on-ground observations including data from the Sun Service of the Crimean Astrophysical Observatory of the Russian Academy of Sciences are analyzed. Based on the methods of observation and determination of longitudinal magnetic fields in SDO/HMI in line FeI 6173.34 A it was revealed, that combinations of contours appearing due to magnetic force lines inclinations relative to the line-of-sight and line-of-sight velocities can cause a significant undervalue of the magnetic field intensity in magnetograms, but polarity does not reverse. The fine spatial structure, evolution features, close correlation with ultraviolet loops system in SDO/AIA images, “moustaches”, and no temporal and spatial correlation with flares point to a connection between the detected anomaly and the new magnetic flux emergence of opposite polarity in a spot’s umbra at an earlier decay stage. We analyze magnetic force lines reconnection and show that annigilation of the magnetic fields of opposite polarities can take place for many hours at small (~30 km) scales and this fact is verified by observation results. There are additional facts in favor of the cluster model of a solar spot by Severny-Parker.

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

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.