Search Results (166)

Spaceborne detection of solar-induced chlorophyll fluorescence (SIF) requires extremely high radiometric accuracy, and the polarization characteristics of an ultra-wide swath spaceborne fluorescence ultraspectral camera directly affect the accuracy of SIF retrieval. This study takes an ultra-wide swath camera based on an off-axis three-mirror anastigmat telescope combined with a Littrow–Offner spectrometer as the research object. A full-field-of-view (FOV), full-spectral, pixel-by-pixel polarization testing system was established based on the Stokes–Muller formalism, achieving for the first time fine characterization and calibration of the pixel-level polarization properties of such a payload. The results show that: (1) polarization sensitivity (LPS) exhibits a strong linear positive correlation with wavelength (R² > 0.97), with good uniformity (fluctuation < 1%) across the full ±15° FOV; (2) the polarization sensitive axis (PSA) shows a symmetric distribution across the FOV and gradually approaches 90° as the wavelength increases, with a clear deviation in the short-wavelength bands and stabilization in the mid-to-long wavelength bands; (3) through multiple sets of cross-validation and Monte Carlo statistics, the calibration accuracy reaches 0.1%, and the system uncertainty is better than 0.05%. This study can provide data support and a reference basis for high-accuracy spaceborne SIF retrieval, payload polarization correction, and optical design optimization. Full article

Heliostats constitute essential elements within concentrating solar power (CSP), where their structure, load profiles, and operational environment render wind loads a critical factor in their design considerations, as these loads directly impact the cost of energy generation. The aerodynamics significantly influence wind-induced effects, resulting in considerable variability in wind loads among different heliostat geometries. This study utilizes the Computational Fluid Dynamics (CFD) methodology to systematically examine the aerodynamic behavior of an isolated pentagonal heliostat. Employing the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations with an atmospheric boundary layer inlet condition, the investigation focuses on the flow field and wind load characteristics at four representative pitch angles: 0° (stow position), 30°, 60°, and 90°. Findings indicate that the pitch angle exerts a decisive impact on flow separation patterns. Specifically, as the elevation angle decreases, the flow regime shifts from being predominantly influenced by the mirror surface to being governed by the support structure, mediated through an interactive coupling between these components. At the 60° operational pitch angle, the pentagonal heliostat’s distinctive corner geometry induces an asymmetric vortex configuration—characterized by a smaller vortex at the top and a larger one at the bottom—thereby disrupting the conventional vortex distribution observed in symmetric heliostat designs. A further analysis of wind load characteristics indicates that, compared to a quadrilateral heliostat, the pentagonal mirror exhibits a significantly lower Elevation Moment Coefficient, despite a slight increase in the normal force coefficient. This reduction is attributed to a balancing mechanism: the “vortex structure asymmetry” creates an upper-large–lower-small distribution of absolute negative pressure on the support surface, while the “stagnation point position” shift with elevation angle produces an upper-small–lower-large distribution of absolute positive pressure on the reflector. The interaction between these opposing trends minimizes the net pressure differential across the mirror height, thereby contributing to superior overall aerodynamic performance. The reduction in the elevation moment coefficient contributes to enhanced structural wind resistance, thereby improving the overall energy efficiency and economic viability of concentrating solar power. Full article

This study presents the design and experimental evaluation of a low-cost parabolic solar concentrator fabricated primarily from recyclable materials. Three reflector configurations—aluminum foil, Plexiglass mirror tiles, and a hybrid design with a peripheral aluminum foil strip—were experimentally assessed to examine their effects on solar concentration performance. A novel foldable and adjustable tripod-mounted receiver was introduced to improve focal alignment, portability, and mechanical stability by isolating the receiver load from the dish structure. Results indicate that Plexiglass mirror tiles significantly enhance thermal performance compared to aluminum foil, while the hybrid configuration achieved the highest receiver temperature of 53 °C under controlled radiation conditions. The findings demonstrate that efficient and portable parabolic solar concentrators can be developed using inexpensive and recyclable materials for small-scale solar thermal applications. Full article

In this study, we present and analyze a fully optically transparent four-port ultra-wideband (UWB) antenna intended for MIMO applications. The antenna’s design is thoroughly described and extensively analyzed, focusing on current distributions across its structure, with all behavioral parameters explained. The proposed antenna design has been validated with both simulations and measurements. The antenna demonstrates excellent performance in terms of port matching, isolation, and efficiency, achieving an efficiency of 40%, which is impressive compared to optically transparent antennas in the literature. The radiation characteristics exhibit peak gains up to 4 dB with stable, symmetric, and linear polarized patterns maintained across the entire UWB range. Regarding diversity performance, the antenna displays outstanding behavior with an envelope correlation coefficient of less than 0.0016 and a diversity gain around 10 dB across the entire operating band. The antenna’s exceptional performance along with its optical transparency makes it suitable for various applications, such as medical non-invasive devices that can be easily integrated into glasses without obstructing vision. It can also be combined with solar cells for energy harvesting and communication purposes. Additionally, its structure is suitable for vehicular settings and can be seamlessly integrated into vehicle mirrors or windows. Full article

Façade systems in hot, high-insolation climates are required to simultaneously mitigate cooling loads, ensure high-quality daylight, and, where feasible, harvest on-site electricity demands that are often in tension. This study assesses and compares two efficient façade strategies for a fully glazed office prototype in Hail, Saudi Arabia: semi-transparent photovoltaic glazing (STPV10–30%VLT) and parametrically tuned split louvers (18 depth–spacing–tilt configurations). Using a unified parametric workflow (Rhino/Grasshopper), Radiance/honeybee for daylight metrics, ASHRAE-55 heat-balance metrics for thermal comfort, and EnergyPlus for end-use and PV yield, to evaluate annual and solstice performance across cardinal orientations. Optimized split louvers maintained UDI_300–1000lx and effectively suppress glare, but incur substantial lighting-energy penalties. In contrast, STPV with 10–20% VLT broadly meets daylight targets while strongly reducing cooling and lighting demand, delivering whole-façade energy savings of up to 50–94% depending on orientation, but could be net-neutral to slightly adverse north 3% when daylight penalties dominate. Thermal comfort responses mirrored these trends: summer PMV was near 0 to +0.5 for both systems, with winter under-heating evident when solar gains are strongly suppressed. Overall, in hot-arid, highly glazed offices, STPV of 10–20%VLT provides the most balanced triad of daylight quality, cooling reduction, and net energy benefit, while optimized louvers excel where glare control is paramount but require careful daylight-control integration. Full article

This study examines the influence of physical biomass pretreatment on the pyrolysis behavior of woody pruning residues of Carya illinoinensis (pecan tree) processed in a stainless-steel batch reactor heated by concentrated radiative energy. Experiments were conducted with 25.5 g of biomass using a solar simulator equipped with a mirror concentrator, operating at three constant thermal power levels (234, 482, and 725 W). As a pretreatment strategy, the woody residues were deliberately processed without drying, while mechanical size reduction and sieving were applied to obtain a controlled particle size range of 1–4 mm. This approach enabled the isolated assessment of the effects of physical pretreatment, particularly particle size and bulk density, on heat transfer, thermal response, and pyrolysis behavior. The pyrolysis performance of the pretreated woody biomass was systematically compared with that of walnut shell biomass and inert volcanic stones subjected to the same particle size control. Two consecutive experimental cases were implemented: Case A (CA), comprising heating, pyrolysis of fresh biomass, and cooling; and Case B (CB), involving reheating of the resulting biochar under identical operating conditions. An improved analytical methodology integrating temperature–time profiles, their derivatives, and gas composition analysis was employed. The results demonstrated the apparently inert thermal behavior of biochar during reheating and enabled clear temporal identification of the main biomass conversion stages, including drying, active pyrolysis of hemicellulose and cellulose, and passive lignin degradation. However, relative to walnut shell biomass of equivalent volume, the woody pruning residues exhibited attenuated thermal and reaction signals, primarily attributed to their lower bulk density resulting from the selected pretreatment conditions. This reduced bulk density led to less distinct pyrolysis stages and a 4.66% underestimation of the maximum reaction temperature compared with thermogravimetric analysis, highlighting the critical role of physical pretreatment in governing heat transfer efficiency and temperature measurement accuracy during biomass pyrolysis. Full article

The transition to renewable energy is essential for mitigating climate change and promoting sustainable development, particularly in Latin America and the Caribbean (LAC). Despite its vast potential, the region faces structural and economic challenges that hinder a sustainable energy transition. Understanding scientific production in this field is key to shaping policy, investment, and technological progress. The primary objective of this study is to conduct a large-scale, data-driven analysis of renewable energy research in LAC, mapping its thematic evolution, collaboration networks, and key research trends over the past three decades. To achieve this, machine learning-based topic modeling and network analysis were applied to examine research trends in renewable energy in LAC. A dataset of 18,780 publications (1994–2024) from Scopus and Web of Science was analyzed using Latent Dirichlet Allocation (LDA) to uncover thematic structures. Network analysis assessed collaboration patterns and regional integration in research. Findings indicate a growing focus on solar, wind, and bioenergy advancements, alongside increasing attention to climate change policies, energy storage, and microgrid optimization. Artificial intelligence (AI) applications in energy management are emerging, mirroring global trends. However, research disparities persist, with Brazil, Mexico, and Chile leading output while smaller nations remain underrepresented. International collaborations, especially with North America and Europe, play a crucial role in research development. Renewable energy research supports Sustainable Development Goals (SDGs) 7 (Affordable and Clean Energy) and 13 (Climate Action). Despite progress, challenges remain in translating research into policy and addressing governance, financing, and socio-environmental factors. AI-driven analytics offer opportunities for improved energy planning. Strengthening regional collaboration, increasing research investment, and integrating AI into policy frameworks will be crucial for advancing the energy transition in LAC. This study provides evidence-based insights for policymakers, researchers, and industry leaders. Full article

This study presents the development and validation of a high-efficiency optical interface designed for ultra-high-concentration photovoltaic (UHCPV) systems, with a focus on enabling clean and sustainable solar energy conversion. A Fresnel lens serves as the primary optical concentrator in a novel system architecture that integrates advanced optical design with system-level thermal management. The proposed modeling framework combines detailed 3D ray tracing with coupled thermal simulations to accurately predict key performance metrics, including optical concentration ratios, thermal loads, and component temperature distributions. Validation against theoretical and experimental benchmarks demonstrates high predictive accuracies within 1% for optical efficiency and 2.18% for thermal performance. The results identify critical thermal thresholds for long-term operational stability, such as limiting mirror temperatures to below 52 °C and photovoltaic cell temperatures to below 130 °C. The model achieves up to 89.08% optical efficiency, with concentration ratios ranging from 240 to 600 suns and corresponding focal spot temperatures between 37.2 °C and 61.7 °C. Experimental benchmarking confirmed reliable performance, with the measured results closely matching the simulations. These findings highlight the originality of the coupled optical–thermal approach and its applicability to concentrated photovoltaic design and deployment. This integrated design and analysis approach supports the development of scalable, clean photovoltaic technologies and provides actionable insights for real-world deployment of UHCPV systems with minimal environmental impact. Full article

High-precision measurements of direct solar radiation spectra are crucial for the development of solar resources, climate change research, and agricultural applications. However, the current measurement systems all rely on a moving two-axis tracking system with a complex structure and many error transmission links. In response to the above problems, a polar-axis rotating solar direct radiation spectroscopic measurement method is proposed, and an overall architecture consisting of a rotating reflector and a spectroradiometric measurement system is constructed, which simplifies the system’s structural form and enables year-round, full-latitude solar direct radiation spectroscopic measurements without requiring moving tracking. The paper focuses on the study of its optical system, optimizes the design of a polar-axis rotating solar direct radiation spectroscopy measurement optical system with a spectral range of 380–780 nm and a spectral resolution better than 2 nm, and carries out spectral reconstruction of the solar direct radiation spectra as well as the assessment of measurement accuracy. The results show that the point error distribution of the AM0 spectral curve ranges from −9.05% to 13.35%, and the area error distribution ranges from −0.04% to 0.09%; the point error distribution of the AM1.5G spectral curve ranges from −9.19% to 13.66%, and the area error distribution ranges from −0.03% to 0.11%. Both exhibit spatial and temporal uniformity exceeding 99.92%, ensuring excellent measurement performance throughout the year. The measurement method proposed in this study enhances the solar direct radiation spectral measurement system. Compared to the existing dual-axis moving tracking measurement method, the system composition is simplified, enabling direct solar radiation spectrum measurement at all latitudes throughout the year without the need for tracking, providing technical support for the development and application of new technologies for solar direct radiation measurement. It is expected to promote future theoretical research and technological breakthroughs in this field. Full article

To improve the optical concentrator ratio of space solar power stations (SSPSs), this paper proposes a deployable segmented solar concentrator (DSSC) based on an afocal reflective system. First, a novel concept of an afocal reflective concentrator composed of segmented primary and secondary mirrors is introduced, and the deployable mechanism for the segmented primary mirror is described in detail. Subsequently, a model for the comprehensive error of the deployable mechanism with 3D revolute joint clearances and link length errors is established based on the “massless link” equivalent model of the clearance in revolute joints and the homogeneous transfer matrix. Sensitivity analysis evaluates the impact of various geometric errors of the deployable mechanism on the comprehensive error. Finally, a prototype experimental system is built to verify the concentration ratio of the concentrator and the pose error of the deployable mechanism. The experimental results show that the DSSC geometric concentration ratio reaches 5.36 to 6, and the optical concentration ratio reaches 24.7 to 32.2. The repeatability of the deployable mechanism is ±50 µm and ±1.2′, meeting the tolerance requirements of the optical system. The proposed afocal reflective DSSC can be used for solar energy concentration, improving the utilization of solar energy. Full article

Access to clean cooking remains a major challenge in rural and off-grid areas where traditional fuels are costly, harmful, or scarce. Solar cooking offers a sustainable solution, but many existing systems suffer from fixed positioning and low efficiency. This study presents a low-cost, dual-axis solar tracking parabolic dish cooker designed for such regions, featuring adjustable pot holder height and portability for ease of use. The system uses an Arduino UNO, LDR sensors, and a DC gear motor to automate sun tracking, ensuring optimal alignment throughout the day. A 0.61 m parabolic dish with ≥97% reflective silver-coated mirrors concentrates sunlight to temperatures exceeding 300 °C. Performance tests in April, June, and November showed boiling times as low as 3.37 min in high-irradiance conditions (7.66 kWh/m²/day) and 6.63 min under lower-irradiance conditions (3.86 kWh/m²/day). Compared to fixed or single-axis systems, this design achieved higher thermal efficiency and reliability, even under partially cloudy skies. Built with locally available materials, the system offers an affordable, clean, and effective cooking solution that supports energy access, health, and sustainability in underserved communities. Full article

A novel total internal reflection solar end-pumped laser system has been introduced for the first time, aimed at enhancing the solar-to-laser conversion efficiency. Utilizing a conical solid or cavity reflector, this system refocuses sunlight from a 0.2818 $m^2$ parabolic mirror into a single Ce (0.05 at.%): Nd (1 at.%): YAG crystal rod, measuring 4 mm in diameter and 10 mm in length, thereby promoting total internal reflection and extending the pumping path. Simulation results indicate that under the same solar input power conditions (249.05 W), the conversion efficiencies of the conical solid reflector and cavity reflector systems are 1.2 times and 1.33 times higher than the current highest recorded efficiency of single-rod systems, respectively. At 950 ${W/m}^2$, the conical reflector reaches 5.48% efficiency, while the cavity reflector attains 6.09%. Their collection efficiencies are 52.03 ${W/m}^2$ and 57.90 ${W/m}^2$, with slope efficiencies of 6.65% and 7.72%. Full article

To enable accurate evaluation of satellite laser communication terminals under solar outage interference, this paper presents the design and implementation of a solar radiation simulation system targeting the 1540–1560 nm communication band. The system reconstructs co-propagating interference conditions through standardized and continuously tunable output, based on high irradiance and spectral uniformity. A compound beam homogenization structure—combining a multimode fiber and an apodizator—achieves 85.8% far-field uniformity over a 200 mm aperture. A power–spectrum co-optimization strategy is introduced for filter design, achieving a spectral matching degree of 78%. The system supports a tunable output from 2.5 to 130 mW with a 50× dynamic range and maintains power control accuracy within ±0.9%. To suppress internal background interference, a BRDF-based optical scattering model is established to trace primary and secondary stray light paths. Simulation results show that by maintaining the surface roughness of key mirrors below 2 nm and incorporating a U-shaped reflective light trap, stray light levels can be reduced to 5.13 × 10⁻¹² W, ensuring stable detection of a 10⁻¹⁰ W signal at a 10:1 signal-to-background ratio. Experimental validation confirms that the system can faithfully reproduce solar outage conditions within a ±3° field of view, achieving consistent performance in spectrum shaping, irradiance uniformity, and background suppression. The proposed platform provides a standardized and practical testbed for ground-based anti-interference assessment of optical communication terminals. Full article

In order to provide a theoretical basis for the thermal analysis and management of spacecraft/payload interstellar pointing attitudes, which are used for inter-satellite communication, this paper develops an analytical method for solar heat flux under pointing attitudes. The key to solving solar heat flux is calculating the angle between the sun vector and the normal vector of the object surface. Therefore, a method for calculating the included angle is proposed. Firstly, a coordinate system was constructed based on the pointing attitude. Secondly, the angle between the coordinate axis vector and solar vector variation with a true anomaly was calculated. Finally, the reaching direct solar heat flux was obtained using an analytical method or commercial software. Based on the proposed method, the direct solar heat flux of relay satellites in commonly used lunar orbits, including Halo orbits and highly elliptic orbits, was calculated. Thermal analysis on the payload of interstellar laser communication was also conducted in this paper. The calculated temperatures of each mirror ranged from 16.6 °C to 21.2 °C. The highest temperature of the sensor was 20.9 °C, with a 2.3 °C difference from the in-orbit data. The results indicate that the external heat flux analysis method proposed in this article is realistic and reasonable. Full article

Parabolic trough collector (PTC) systems, often deployed in arid regions, are vulnerable to dust accumulation (soiling), which reduces mirror reflectivity and energy output. This study presents a physically based soiling forecast algorithm (SFA) designed to estimate soiling levels. The model was calibrated and validated using three meteorological data sources—numerical forecasts (YR), METAR observations, and on-site measurements—from a PTC facility in Limassol, Cyprus. Field campaigns covered dry, rainy, and red-rain conditions. The model demonstrated robust performance, particularly under dry summer conditions, with normalized root mean square errors (NRMSE) below 1%. Sedimentation emerged as the dominant soiling mechanism, while the contributions of impaction and Brownian motion varied according to site-specific environmental conditions. Under dry deposition conditions, the reflectivity change rate during spring and autumn was approximately twice that of summer, indicating a need for more frequent cleaning during transitional seasons. A red-rain event resulted in a pronounced drop in reflectivity, showcasing the model’s ability to capture abrupt soiling dynamics associated with extreme weather episodes. The proposed SFA offers a practical, adaptable tool for reducing soiling-related losses and supporting seasonally adjusted maintenance strategies for solar thermal systems. Full article