Ratio Of Solar Radiation Research Articles

Performance test of a heliostat field integrated PVT solar collector using organic phase change material and carbon black additives

The rising global awareness of environmental issues has brought about a rise in the adoption of green energy throughout our daily activities in recent decades. The radiation from the sun is utilized for thermal heating, electrical generation, and agriculture by Phase change materials (PCM) integrated PVT collector. However, the lower concentration ratio of solar radiation on flat plate collectors and the lower thermal conductivity of PCMs are the major drawbacks. In this present study, a Heliostat field concentrator was designed to integrate with a hybrid photovoltaic thermal (PVT) collector for the increase of the solar irradiance, and carbon black additives incorporated stearic acid (SA) were used in the underneath PVT collector to enhance the thermal conductivity of SA as well as the thermal efficiency of the system. The performance tests were carried out for both SA with carbon black and SA without carbon black additives for varying water flow rates of 0.0025 kg/s, 0.0035 kg/s, 0.0045 kg/s, and 0.0055 kg/s. The efficiency of the PV panels ranged from 10 % to 13 %. The maximum thermal efficiency was found to be 46.56 % when using SA with carbon black for the water flow rate of 0.0035 kg/s whereas the maximum thermal efficiency was 45.45 % in the case of SA without carbon black for that water flow rate. Especially contrasted with the other flow rates throughout the investigation, the average thermal efficiency increases by 6.83 % for the flow rate of 0.0035 kg/s after integrating carbon black with PCM. The experimented results showed the outlet temperature of water in the range of 50 °C-59 °C throughout the day which is sufficient for domestic hot water applications.

Study of Global Horizontal and Vertical Solar Irradiance Components Under Different Sky Conditions for Sustainable Building Design In Bali Of Indonesia

The study of global and vertical solar irradiance components under different sky conditions is very important for building design applications. This research has been carried out by analyzing the components of solar radiation based on global horizontal irradiance (GHI) data, and global vertical irradiance for east, west, north, and south oriented. Observational data was acquired for one year starting from July 2022 to June 2023 in Jembrana-Bali of Indonesia. The solar radiation component has been analyzed based on sub-diurnal (daytime) and annual patterns. The clearness index (Kt) was calculated based on the ratio of extra-terrestrial solar radiation to global solar radiation measured at the surface. Sun-path analysis was carried out by considering the relationship of the zenith angle, azimuth angle, and the intensity of each solar radiation component to changes in time. The results show that in all-sky conditions, the average monthly maximum global horizontal irradiance occurs in January at 432.4 W/m², while the minimum monthly average global horizontal irradiance occurs in July at 327.9 W/m². The clearness index statistic shows that the hourly average ranges from 0.12 to 0.68 with an average of 0.47. Based on sun-path analysis, east, north, and west orientations receive more solar radiation in the Jembrana-Bali area. The findings from the study provide important information for architects, engineers, and policymakers that can be used for sustainable building design and building energy planning.

A Comparative Study on the Distribution Models of Incident Solar Energy in Buildings with Glazing Facades

The accurate distribution of solar energy on indoor walls is the basis of simulating the indoor thermal environment, and its specific distribution changes all the time due to the influence of solar azimuth and altitude angle. By analyzing the assumptions of each model, the existing solar energy distribution models are eight kinds in all and are divided into three categories. The solar radiation models in TRNSYS, EnergyPlus, and Airpak software all use the absorption-weighted area ratio method, which assumes that a single interior surface is a whole, but the detailed assumptions of the models used in the three software are different. In the Radiosity-irradiation method, the indoor surfaces are discretized into small surfaces for calculation. The calculation accuracy of solar radiation distribution indoors can be controlled by the number of discrete small surfaces. The Radiosity-irradiation method is implemented by using Matlab software programming in this paper. Through the numerical calculation and analysis of typical cases, the solar distribution results of the absorption-weighted area ratio method and the Radiosity-irradiation method all show the asymmetry. The asymmetrical ratio of direct solar radiation varies during the time between 7.96–9.89, and the minimum turns up at 11:30 in the summer solstice. The asymmetrical ratio of diffuse solar radiation is 3.23 constantly. The asymmetrical ratio of total solar energy is mainly influenced by the direct and diffuse solar feat gain and its value changes in the range from 3.4 to 4.45 in the summer solstice. Calculation comparison and error analysis on the solar radiation models used in TRNSYS, EnergyPlus, and Airpak software are conducted. There are significant errors in the simulation results of all three software. TRNSYS has the highest error among the three software as its results do not change over time. For EnergyPlus, the distribution ratio of floor 1 is too large. Airpak has the smallest error, but the solar radiation distribution ratios of the indoor surfaces near the south glazing facade are underrated, especially the indoor surfaces that have not been exposed to direct solar radiation.

Uncertainty assessment for three-dimensional hydrodynamic and fecal coliform modeling in the Danshuei River estuarine system: The influence of first-order parametric decay reaction

Modeling fecal contamination in water bodies is of importance for microbiological risk assessment and management. This study investigated the transport of fecal coliform (e.g., up to 2.1 × 106 CFU/100 ml at the Zhongshan Bridge due to the main point source from the Xinhai Bridge) in the Danshuei River estuarine system, Taiwan with the main focus on assessing model uncertainty due to three relevant parameters for the microbial decay process. First, a 3D hydrodynamic-fecal coliform model (i.e., SCHISM-FC) was developed and rigorously validated against the available data of water level, velocity, salinity, suspended sediment and fecal coliform measured in 2019. Subsequently, the variation ranges of decay reaction parameters were considered from several previous studies and properly determined using the Monte Carlo simulations. Our analysis showed that the constant ratio of solar radiation (α) as well as the settling velocity (vs) had the normally-distributed variations while the attachment fraction of fecal coliform bacteria (Fp) was best fitted by the Weibull distribution. The modeled fecal coliform concentrations near the upstream (or downstream) stations were less sensitive to those parameter variations (see the smallest width of confidence interval about 1660 CFU/100 ml at the Zhongzheng Bridge station) due to the dominant effects of inflow discharge (or tides). On the other hand, for the middle parts of Danshuei River where complicated hydrodynamic circulation and decay reaction occurred, the variations of parameters led to much larger uncertainty in modeled fecal coliform concentration (see a wider confidence interval about 117,000 CFU/100 ml at the Bailing Bridge station). Overall, more detailed information revealed in this study would be helpful while the environmental authority needs to develop a proper strategy for water quality assessment and management. Owing to the uncertain decay parameters, for instance, the modeled fecal coliform impacts at Bailing Bridge over the study period showed a 25 % difference between the lowest and highest concentrations at several moments. For the detection of pollution occurrence, the highest to lowest probabilities for a required fecal coliform concentration (e.g., 260,000 CFU/100 ml over the environmental regulation) at Bailing Bridge was possibly greater than three.

Two source energy balance maize evapotranspiration estimates using close-canopy mobile infrared sensors and upscaling methods under variable water stress conditions

Mobile infrared thermometers (IRTs) mounted on moving platforms provide one-time-of-day radiometric measurements (Tr), which can be used to calculate instantaneous actual evapotranspiration (ETa) using the two-source energy balance (TSEB) model. However, irrigation scheduling decisions utilize daily ETa estimates, hence the need for time scaling. This study evaluated different upscaling methods to calculate daily maize ETa using one-time-of day Tr under varying water stress conditions. Mobile IRTs were mounted on a high clearance mobile sensing platform and collected Tr in remote locations under full, deficit and rainfed conditions. Seven scaling methods via two pathways were employed to obtain daily ETa. First pathway was scaling one-time-of-day Tr (SC) whereas the second pathway involved use of six upscaling methods of instantaneous ETa including: original and modified evaporative factor ((EF)o, (EF)m) as well as crop coefficient ((Kc)o, (Kc)m), direct canopy resistance (Direct- rc), and solar radiation ratio (Rn/Rs); and all were compared to a neutron-based soil water balance (SWB) determined ETa. From the results, SC outperformed other methods in comparison to SWB ETa across all the selected treatments with smaller discrepancies and lower RMSE (0.9–1.7 mm d−1 vs. 0.7–4.3 mm d−1 for other methods). Furthermore, methods including SC, (EF)o, (EF)m, and Rn/Rs had their daily average ETa values in close agreement to SWB ETa with mean ETa differences ranging between 0.2 and 1.6 mm d−1. Overall, SC method performed better in fully irrigated maize (r2 = 0.52, RMSE = 0.9 mm d−1) than in deficit irrigated maize ( r2 = 0.48, RMSE = 1.4 mm d−1) but worst in rainfed maize (r2 = 0.16, RMSE = 1.7 mm d−1). This implies that SC is more suited for irrigated rather than rainfed settings. Importantly, the choice of any method depends on data requirements, irrigation water management strategy, and ETa estimation accuracy.

New particle formation at a peri-urban agricultural site

New Particle Formation (NPF) is a major source of ultrafine particles that affect both air quality and climate. Despite emissions from agricultural activities having a strong potential to lead to NPF, little is known about NPF within agricultural environments. The aim of the present study was to investigate the occurrence of NPF events at an agricultural site, and any potential relationship between agricultural emissions and NPF events. A field campaign was conducted for 3 months at the FR-Gri-ICOS site (France), at an experimental farm 25 km west of Paris city centre.16 NPF events have been identified from the analysis of particle number size distributions; 8 during the daytime, and 8 during the night-time. High solar radiation and ozone mixing ratios were observed during the days NPF occurred, suggesting photochemistry plays a key role in daytime NPF. These events were also associated with higher levels of VOCs such as isoprene, methanol, or toluene compared to non-event days. However, ammonia levels were lower during daytime NPF events, contributing to the hypothesis that daytime NPF events were not related to agricultural activities.On the other hand, temperature and ozone were lower during the nights when NPF events were observed, whereas relative humidity was higher. During these nights, higher concentrations of NO2 and ammonia were observed. As a result, agricultural activities, in particular the spreading of fertiliser on surrounding crops, are suspected to contribute to night-time NPF events.Finally, all the identified NPF events were also observed at SIRTA monitoring station 20 km from the FR-Gri ICOS site, showing that both night-time and daytime NPF events were regional processes. We hypothesise that night-time NPF may be related to fertiliser spreading over a regional scale, as opposed to the local activities at the farm. To our knowledge, this is the first time night-time NPF has been observed in the agricultural context.

A statistical description method of global sub-grid topography for numerical models

Slope and aspect are important topographic elements for thermodynamics and dynamics of atmospheric circulation, especially for local radiation and topographic precipitation. We propose a simple realistic statistical method based on trigonometric function transformation to calculate sub-grid slope and aspect for describing the orographic characteristics of complex areas over the globe. It is found that the transformed conditional probability density function conforms to the Gaussian distribution in most of the global areas (~ 98%), and this feature is not eliminated with the increasing of horizontal resolution. The reasonability of this method is tested over the Tibetan Plateau. The results show that the improvement ratio of surface solar radiation downward (SSRD) over the Tibetan Plateau improved significantly compared with the results from the grid average scheme, especially in autumn. The improvement of root mean square error is approximately 18.2 W/m2, and the improvement ratio reached 38.4%. The improvements of maximum and regional-averaged SSRD over the whole Tibetan Plateau were ~ 130 W/m2 and ~ 44.3 W/m2 respectively. Although we only consider the effect of sub-grid slope and aspect on solar shortwave radiation, which has a certain bias with the observation data, it is sufficient to prove the rationality of the statistical method compared with the unobstructed horizontal surfaces scheme.

Atmospheric Factors Affecting Global Solar and Photosynthetically Active Radiation Relationship in a Mediterranean Forest Site

Light availability and its composition in components affecting plant growth as photosynthetically active radiation (PAR), are of critical importance in agricultural and environmental research. In this work, radiation data for the period 2009–2014 in a forest site in Greece were analyzed to identify the effect of meteorological variables on the formation of the photosynthetically active to global solar radiation ratio. The temporal changes of the ratio are also discussed. Results showed that the ratio values are higher in summer (0.462) and lower in autumn (0.432), resulting in an annual average of 0.446. In addition, for the investigated site, which was characterized by relatively high water content in the atmosphere, the atmospheric water content and clearness were found to be the most influential factors in the composition of the global solar radiation in the wavelengths of PAR. On the contrary, temperature and related meteorological attributes (including relative humidity, vapor pressure deficit and saturation vapor pressure) were found to have minor effect.

A comprehensive comparative energy and exergy analysis in solar based hydrogen production systems

In the presented paper, energy and exergy analysis is performed for thermochemical hydrogen (H 2 ) production facility based on solar power. Thermal power used in thermochemical cycles and electricity production is obtained from concentrated solar power systems. In order to investigate the effect of thermochemical cycles on hydrogen production, three different cycles which are low temperature Mg–Cl, H 2 SO 4 and UT-3 cycles are compared. Reheat-regenerative Rankine and recompression S–CO 2 Brayton power cycles are considered to supply electricity needed in the Mg–Cl and H 2 SO 4 thermochemical cycles. Furthermore, the effects of instant solar radiation and concentration ratio on the system performance are investigated. The integration of S–CO 2 Brayton power cycle instead of reheat-regenerative Rankine enhances the system performance. The maximum exergy efficiency which is obtained in the system with Mg–Cl thermochemical and recompression S–CO 2 Brayton power cycles is 27%. Although the energy and exergy efficiencies decrease with the increase of the solar radiation, they increase with the increase of the concentration ratio. The highest exergy destruction occurred in the solar energy unit. • Energy and exergy efficiencies of solar based hydrogen production system are investigated. • Low temperature Mg–Cl, H 2 SO 4 and UT-3 cycles are compared. • Reheat-regenerative Rankine or supercritical-CO 2 Brayton power cycle is integrated. • The system with Mg–Cl and s-CO 2 Brayton power cycles has maximum exergy efficiency. • The exergy efficiency increases with the increase of the concentration ratio.

Effects of clouds and aerosols on ecosystem exchange, water and light use efficiency in a humid region orchard

Investigating the patterns of water and carbon dynamics in agro-ecosystems in response to clouds and aerosols can shed new insights in understanding the biophysical impacts of climate change on crop productivity and water consumption. In this study, the effects of clouds and aerosols as well as other environmental factors on ecosystem water and carbon fluxes were examined based on three-year eddy covariance measurements under different sky conditions (quantified as the clearness index, Kt, i.e., the ratio of global solar radiation to extraterrestrial solar radiation) in a kiwifruit plantation in the humid Sichuan Basin of China. Results showed that evapotranspiration (ET) and canopy transpiration (Tc, measured by sap flow sensors) increased, while ecosystem light use efficiency (eLUE) and ecosystem water use efficiency (eWUE) decreased with increasing Kt. GPP presented a parabolic relationship with increasing Kt. The path analysis revealed that surface conductance (Gs) and canopy conductance (Gc) were the most dominant variables directly regulated carbon (GPP) and water (ET and Tc) fluxes. The effect path of Kt on ET and Tc was converted from through diffuse photosynthetic active radiation (PARdif) to direct PAR (PARdir) when the sky became clearer. The effect path of Kt on GPP was primarily through PARdif under different sky conditions. The declined eWUE with increasing Kt was caused by the different responses of GPP and ET to PARdir under clear skies. The declined eLUE resulted from the sharp decrease in GPP/PARdir, which surpassed the slight increase of GPP/PARdif with increasing PAR. The Priestley-Taylor Jet Propulsion Laboratory ET model (PT-JPL) incorporating Kt with an exponential function produced more reliable Tc estimates but minor improvement in ET. Further, the LUE-GPP model incorporating Kt with a linear function obtained much better GPP estimates. Our study shed light on how sky conditions modulate water and carbon dynamics between the biosphere and atmosphere, highlighting the necessity of the inclusion of sky conditions for better modeling regional water and carbon budgets.

Outdoor Characterization of a Plasmonic Luminescent Solar Concentrator

Plasmonic luminescent solar concentrators (PLSCs) have been shown to enhance the optical performance and power conversion efficiency of LSCs, due to added plasmonic gain in the medium. Despite the promising outlook of a PLSC through plasmonic coupling, device characterization and performance have not been verified in the real outdoor conditions, with varying direct and diffuse solar irradiation. In this work, characterization of a PLSC device of dimensions 4.5 \(\times\) 4.5 \(\times\) 0.3 cm3 embedded with Lumogen Red 305 dye and plasmonic gain medium of gold core silver shell nano cuboids was carried out in outdoor conditions of Dublin, Ireland. Optimized PLSC device power output at different solar insolation was compared to a reference photovoltaic (PV) cell and an optimized luminescent solar concentrator (LSC) device. The effect of the solar disc position, solar insolation, PV cell surface temperature, diurnal, and seasonal variation on the performance of the PLSC device is studied. The key observation was that PLSC average power conversion efficiency was 1.4 times more than the PV cell in cloudy and diffuse solar conditions. The PLSC device performed 45% better than a PV cell in December than July, as December has higher diffuse solar irradiation. Even though the PLSC device absorbs only 31% and transmits 69% incident solar irradiation in the concerned visible range of 380–750 nm. The preliminary outdoor characterization on a small-scale PLSC establishes its viability in a diffuse to direct solar radiation ratio throughout the year as well as establishing its benefits for integration in buildings.

Mechanism and influence of different colors of opaque outdoor surfaces on cooling demand of malls

ABSTRACT The present study investigated a specific mall in Chengdu with diverse opaque outdoor surface colors (black, dark grey, dark green, navy blue and yellow). It was revealed that different colors had a variation effect and energy-saving mechanism on the cooling energy saving ratio in hourly, daily, monthly and annual dimensions. These results revealed that for the whole year, the annual cooling load exhibited a differential change. For the whole day, as affected by meteorological factors, especially wind speed, and when the solar radiation is the same, the daily cooling energy saving amounts presented two branches. The global horizontal radiation has a significant positive influence on the daily cooling energy saving amount, but the daily cooling energy saving ratio was not significant. At the hourly level, due to the leading role of wind speed and the diffuse radiation-to-global solar radiation ratio, the hourly cooling energy-saving amount and hourly cooling energy-saving rate presented different branches. When the hourly horizontal solar radiation was the same, the lower the wind speed, the greater the cooling energy savings. Furthermore, the higher the diffuse radiation-to-global solar radiation ratio, the greater the cooling energy savings.

Nitrogen oxides (NO and NO2) pollution in the Accra metropolis: Spatiotemporal patterns and the role of meteorology

Economic and urban development in sub-Saharan Africa (SSA) may be shifting the dominant air pollution sources in cities from biomass to road traffic. Considered as a marker for traffic-related air pollution in cities, we conducted a city-wide measurement of NOx levels in the Accra Metropolis and examined their spatiotemporal patterns in relation to land use and meteorological factors. Between April 2019 to June 2020, we collected weekly integrated NOx (n = 428) and NO2 (n = 472) samples at 10 fixed (year-long) and 124 rotating (week-long) sites. Data from the same time of year were compared to a previous study (2006) to assess changes in NO2 concentrations. NO and NO2 concentrations were highest in commercial/business/industrial (66 and 76 μg/m3, respectively) and high-density residential areas (47 and 59 μg/m3, respectively), compared with peri-urban locations. We observed annual means of 68 and 70 μg/m3 for NO and NO2, and a clear seasonal variation, with the mean NO2 of 63 μg/m3 (non-Harmattan) increased by 25–56% to 87 μg/m3 (Harmattan) across different site types. The NO2/NOx ratio was also elevated by 19–28%. Both NO and NO2 levels were associated with indicators of road traffic emissions (e.g. distance to major roads), but not with community biomass use (e.g. wood and charcoal). We found strong correlations between both NO2 and NO2/NOx and mixing layer depth, incident solar radiation and water vapor mixing ratio. These findings represent an increase of 25–180% when compared to a small study conducted in two high-density residential neighborhoods in Accra in 2006. Road traffic may be replacing community biomass use (major source of fine particulate matter) as the prominent source of air pollution in Accra, with policy implication for growing cities in SSA.

Performance analysis of an improved solar dryer with hybrid system

This study describes the development of a solar dryer system by using the hybrid photovoltaic solar dryer. The study also compares the conventional solar dryer collector system and the solar dryer hybrid system. Measurements under the same conditions of temperature, humidity, solar radiation, and moisture ratio were performed for both systems. The results showed that drying by using the hybrid solar dryer collector system is 10 % faster than by using conventional solar dryer system. The result of current study is beneficial to increase the drying performance of the solar dryer on the future.

Capricious basins of attraction in photogravitational magnetic binary problem

The present paper deals with the magnetic binary problem in the framework of restricted problem of three bodies. The bigger primary is taken as the source of radiation pressure and smaller primary is taken as point mass. The parametric evolution of the position and existence of libration points are explored. The study of zero velocity curves and the stability of libration points are one of the critical aspects of this investigation. A systematic probe to find out the influence of solar radiation pressure q, ratio of magnetic moments λ and mass ratio μ on the geometry of basins of attraction is carried out. The shape of the basins of attraction is significantly affected by the variation of these parameters. It is also found that the presence of solar radiation pressure and ratio of magnetic moments increase the unpredictability of basins of attraction. Variation of the mass ratio μ also affects the evolution of libration points as well as the geometry of basins of attraction.

Evaluation of satellite-retrieved evapotranspiration based on a nonparametric approach over an arid region

ABSTRACT Daily evapotranspiration (ET) controlled by latent energy (LE) is an important variable used in the study of hydrology, meteorology, and ecology. A constant solar radiation ratio approach was introduced to the LE retrieval algorithm based on a nonparametric ET approach to upscale instantaneous LE temporally. On the basis of the proposed algorithm, this study retrieved the daily and eight-day LE using Moderate-resolution Imaging Spectroradiometer (MODIS) and China Meteorological Administration Land Data Assimilation System products and evaluated the daily and eight-day LE retrieval by using the ground observations and MOD16 product in Zhangye City during 25 June to 15 September 2012. Results show that the temporal-spatial distribution of retrieved result was reliable. The retrieved daily/eight-day LE could capture the dynamic change of ground observations, whereas the MOD16 LE was invalid. The retrieved daily (eight-day) LE was underestimated at all four (two) sites, with bias, root mean square error, and R2 of −7.9 to −2.2 W m−2 (approximately −5 W m−2), 19.8 to 39.0 W m−2 (approximately 10 W m−2), and 0.72 to 0.84 (approximately 0.9), respectively. The proposed approach showed more satisfactory performance than the triangle approach under clear sky condition. The eight-day LE retrieval was considerably better than MOD16 LE and had (no/slight) influence on MOD16 LE (eight-day retrieval). In addition, the accurate estimation of net radiation, soil heat flux, land surface temperature, and air temperature could aid in improving LE retrieval. Future studies would focus on the improvement of the retrieval algorithm, input accuracy, and residuals.

MODELLING PHOTOSYNTHETICALLY ACTIVE RADIATION: A REVIEW

Photosynthetically active radiation (PAR) is important in applications related to plant physiology or the carbon cycle. However, despite its importance, a global network for its measurement has not yet been established. This work consists of the revision of a series of works related to the development of empirical models for the estimation of PAR in places where it is not regularly measured, using for this purpose measurements of meteorological and radiation parameters available in weather stations. A list of the models developed, the study site, the results obtained, and the nomenclature used in each of them is made. The most common way to develop empirical estimation models is by studying spatio-temporal changes in the relationship between PAR and global solar radiation. Other estimation methods include the use of satellite-derived products such as MODIS-derived products and the use of artificial neural networks. Despite being more efficient for estimating PAR, the use of artificial neural networks is not as widespread because its use is more complex than the development of empirical models. The PAR to global solar radiation ratio reached its maximum in the summer months and the minimum in the winter months; in addition, the daily values per hour reached their maximum at sunrise and sunset, and their minimum around noon.

Comparative analysis of thermoelectric elements optimum geometry between photovoltaic-thermoelectric and solar thermoelectric

The optimization of the thermoelectric (TE) device geometry is one of the significant ways to improve its efficiency and power output. However, the complex relationship between the Photovoltaic and the thermoelectric device necessitates the need for the study of the optimum geometry of the thermoelectric device in a hybrid Photovoltaic-thermoelectric device. Therefore, this study investigates the optimum thermoelectric geometry for optimum performance of a Photovoltaic-thermoelectric (PV-TE) device and a solar thermoelectric generator (STEG). A three-dimensional finite element method is used to model the PV-TE and the STEG with different thermoelectric leg geometries. The performance of the PV-TE with two different PV cells and different TE leg geometries is investigated and compared with that of the STEG, and the optimum leg geometry for each device is identified. In addition, the effects of solar radiation and concentration ratio on the optimized device geometry performance are presented. Results obtained showed that the optimum thermoelectric geometry in a hybrid PV-TE device is dependent on the PV cell type and this is different from that of the STEG under the same conditions. The PV-TE device with cell 1 has an improved overall efficiency when a symmetrical (rectangular) thermoelectric leg is used however, this is different when the PV cell type is changed. In fact, the PV-TE device with cell 2 has an improved overall efficiency when a trapezoidal thermoelectric leg is used instead of a rectangular leg and this is the same as is the same trend observed in the case of the STEG. Therefore, the optimum geometry for a stand-alone solar thermoelectric generator cannot be directly used as a reference for the PV-TE device as the characteristics of the PV cell affects the PV-TE optimum geometry. Results from this study will indicate the different optimum geometries of STEG and PV-TE, and also provide a solid basis for optimization efforts in hybrid PV-TE devices.

A new model to evaluate solar spectrum impacts on the short circuit current of solar photovoltaic modules

Solar spectrum plays an important role on electrical performance of PV modules via affecting their short circuit current. In this study, a new model combining the impacts of both air mass and diffuse solar radiation ratio is developed to evaluate the solar spectrum impacts on the short circuit current of photovoltaic (PV) modules. A new method, named air mass cumulative distribution function method (AMCDF), is introduced to represent the relationship between air mass and solar spectrum effect. The experimental data shows that when air mass is less than 4.5, the relationship between the normalized short-circuit current and the air mass cumulative distribution function can be well represented by a five-order polynomial. However, when air mass is larger than 4.5, the relationship becomes irregular. Further study on the irregular data indicates that the chaotic relationship is caused by the impact of diffuse solar radiation ratio (Rd). Based on these findings, the new model which combines the air mass cumulative distribution function and the diffuse solar radiation ratio is developed to evaluate the spectrum effect. Compared to conventional models, the proposed model has higher prediction accuracy and it also can predict short circuit current even when the air mass is high.

Application of a Three-Dimensional Radiative Transfer Model to Retrieve the Species Composition of a Mixed Forest Stand from Canopy Reflected Radiation

The paper introduces a three-dimensional model to derive the spatial patterns of photosynthetically active radiation (PAR) reflected and absorbed by a non-uniform forest canopy with a multi-species structure, as well as a model algorithm application to retrieve forest canopy composition from reflected PAR measured along some trajectory above the forest stand. This radiative transfer model is based on steady-state transport equations, initially suggested by Ross, and considers the radiative transfer as a function of the structure of individual trees and forest canopy, optical properties of photosynthesizing and non-photosynthesizing parts of the different tree species, soil reflection, and the ratio of incoming direct and diffuse solar radiation. Numerical experiments showed that reflected solar radiation of a typical mixed forest stand consisting of coniferous and deciduous tree species was strongly governed by canopy structure, soil properties and sun elevation. The suggested algorithm based on the developed model allows for retrieving the proportion of different tree species in a mixed forest stand from measured canopy reflection coefficients. The method accuracy strictly depends on the number of points for canopy reflection measurements.