Direct Component Of Solar Radiation Research Articles

Empirical modeling of optimum tilt angle for flat solar collectors and PV panels.

A new model has been developed to determine the optimal tilt angle for PV panels and solar collectors on a yearly, seasonal, and monthly basis. The model estimates the diffusion component of solar radiation using Orgill and Holland's model, which relates the diffusion fraction of solar radiation to the sky clearness index. Empirical data on the clearness index is used to derive the relationship between the diffusion and direct components of solar radiation at any global latitude on any given day of the year. By maximizing the total amount of diffused and direct radiation, the optimal tilt angle for each month, season, and year is determined relative to the latitude angle. The model is programmed in MATLAB and is freely available for download from the MATLAB file exchange website. The model shows that small deviations from the optimal inclination angle have only a minor effect on overall system yield. The monthly optimal tilt angles predicted by the model are consistent with experimental data and other published model predictions for various locations around the globe. Importantly, unlike some other models, the present model does not predict negative optimal inclination angles for small northern hemisphere latitudes or vice versa.

Ensemble model output statistics for the separation of direct and diffuse components from 1-min global irradiance

Separation models split diffuse and direct components of solar radiation from the global horizontal radiation. At the moment, all separation models only issue predictions that are deterministic (as opposed to probabilistic). Since the best prediction is necessarily probabilistic, a parametric post-processing framework called the ensemble model output statistics (EMOS) is introduced in this paper, to make probabilistic predictions. EMOS takes the diffuse fractions predicted by an ensemble of existing 1-min separation models, and outputs a predictive distribution, with parameters optimized by maximum likelihood estimation. Clearly, the EMOS-based separation modeling goes beyond the current literature, in terms of uncertainty quantification.Eight popular separation models from the literature, with different architectures, are used to demonstrate the predictive power of EMOS. Using 1-min high-quality radiometric data from seven stations in the USA and four stations in Europe, it is found that Yang2 is the best stand-alone model with an average RMSE of 21.8%, in terms of direct normal irradiance prediction, contrasting the 26.3% of the previously reported best model, namely, Engerer2. On the other hand, the EMOS post-processed predictions have an average RMSE of 20.8%, which is lower than that of the best stand-alone model. Moreover, EMOS is shown superior to simple model averaging, in terms of continuous ranked probability score and ignorance score.

On the use of BRL model for daily and hourly solar radiation components assessment in a semiarid climate

Solar radiation components assessment is a highly required activity for solar energy applications. Despite their importance, diffuse and direct solar radiation components are not available in many locations in the world. This is specifically the case in the studied region due to high fiscal demands and technical limitations. In the present work, our main objective is to estimate the two components using global solar radiation components as the only measured input parameter. Machine learning (ML) techniques seem to be a good solution of such an estimation problem but the main issue of ML techniques is the need of long historical data of both desired outputs, direct and diffuse, to build the optimum model in the training phase. However, in the present study, we adopt the use of the Boland–Ridley–Lauret (BRL) model to deal with the problem of estimation of the direct and diffuse components from the global radiation. The adjusted BRL model was applied on two time scales, daily and hourly components. It was found that the estimated direct and diffuse solar radiation values by the adjusted BRL model are in favorable agreement with the measured data.

Measurements of spectral irradiance during the solar eclipse of 21 August 2017: reassessment of the effect of solar limb darkening and of changes in total ozone

Abstract. Measurements of spectral irradiance between 306 and 1020 nm were performed with a GUVis-3511 multi-channel filter radiometer at Smith Rock State Park, Oregon, during the total solar eclipse of 21 August 2017. The radiometer was equipped with a shadowband, allowing the separation of the global (sun and sky) and direct components of solar radiation. Data were used to study the wavelength-dependent changes in solar irradiance at Earth's surface. Results were compared with theoretical predictions using three different parameterizations of the solar limb darkening (LD) effect, which describes the change in the solar spectrum from the Sun's center to its limb. Results indicate that the LD parameterization that has been most widely used during the last 15 years underestimates the LD effect, in particular at UV wavelengths. The two alternative parameterizations are based on two independent sets of observations from the McMath–Pierce solar telescope. When these parameterizations are used, the observed and theoretical LD effects agree to within 4 % for wavelengths larger than 400 nm and occultation of the solar disk of up to 97.8 %. Maximum deviations for wavelengths between 315 and 340 nm are 7 %. These somewhat larger differences compared to the visible range may be explained with varying aerosol conditions during the period of observations. The aerosol optical depth (AOD) and its wavelength dependence was calculated from measurements of direct irradiance. When corrected for the LD effect, the AOD decreases over the period of the eclipse: from 0.41 to 0.34 at 319 nm and from 0.05 to 0.04 at 1018 nm. These results show that AODs can be accurately calculated during an eclipse if the LD effect is corrected. The total ozone column (TOC) was derived from measurements of global irradiance at 306 and 340 nm. Without correction for the LD effect, the retrieved TOC increases by 20 DU between the first and second contact of the eclipse. With LD correction, the TOC remains constant to within natural variability (±2.6 DU or ±0.9 % between first and second contact and ±1.0 DU or ±0.3 % between third and fourth contact). In contrast to results of observations from earlier solar eclipses, no fluctuations in TOC were observed that could be unambiguously attributed to gravity waves, which can be triggered by the supersonic speed of the Moon's shadow across the atmosphere. Furthermore, systematic changes in the ratio of direct and global irradiance that could be attributed to the solar eclipse were not observed, in agreement with results of three-dimensional (3-D) radiative transfer (RT) models. Our results advance the understanding of the effects of solar LD on the spectral irradiance at Earth's surface, the variations in ozone during an eclipse, and the partitioning of solar radiation in direct and diffuse components.

Experimental Nets for a Protection System against the Vectors of Xylella fastidiosa Wells et al.

The effectiveness of experimental nets in preventing the access of adult meadow spittlebug Philaenus spumarius L., the main vector of Xylella fastidiosa Wells et al. subspecies pauca, sequence type (ST) 53, in olive tree nurseries and orchards was evaluated. To optimize the net design, mesh size, kind of fabric, thread typology, and radiometric properties, six nets with different mesh sizes and kinds of fabric were evaluated in laboratory and in field experiments. Laboratory bioassays evaluating the capability of adult spittlebugs to pass through nets with different mesh sizes (1.2, 1.8, 2.4 mm) showed that all nets with a mesh size equal to or lower than 2.4 mm prevented insect crossing. These results were confirmed in field conditions using an experimental net box apparatus. Further laboratory tests showed a positive correlation between porosity and radiometric properties of the nets. Three prototypes of thermally stabilized flat woven nets made of circular cross-sectional yarns, knitted net with strips, and knitted nets made of yarns were tested after the evaluation of their potential usability in terms of porosity stability. The knitted net features were found to be the most suitable. The net transmissivity of the total and direct component of solar radiation in the photosynthetically active radiation and the infrared ranges increased with the net porosity. A prism-shaped wooden frame with a triangular base covered with the knitted net with a 2.4 mm mesh confirmed the insect’s capability of reaching considerable heights, up to 2.85 m. Hence, based on our results, the monowire knitted net with a 2.4 mm mesh can be used in open field nursery and olive orchards to prevent the access of P. spumarius adults and to shield the openings of greenhouse nurseries.

Generation of the site-adapted clearest-sky year of direct normal irradiance for solar concentrating technologies

Abstract Concentrating photovoltaic and thermoelectric solar facilities base their operation on collecting the direct component of solar radiation. Given that the direct beam that reaches the Earth's surface varies greatly in time and space, it is common to assist the bankability of projects with a solar resource assessment. Sun-tracking collector plants are typically examined via a time series analysis of measured weather data and test reference years. Such analysis, which considers the eventual presence of clouds, may be complemented with the use of the synthetic clear-sky year assuring the maximum theoretical availability of direct normal irradiance at a site. This work introduces for the first time the concept of site-adapted clearest-sky year (CSY) and provides a methodology for its generation. Three methods to build the CSY and one algorithm to detect clear-sky moments are proposed.

Performance Evaluation of Radiation Sensors for the Solar Energy Sector

Rotating Shadowband Irradiometers (RSI) and SPN1 Sunshine Pyranometers allow determining the diffuse and direct components of solar radiation without sun trackers; they can be deployed in networks for continuous field operation with modest maintenance. Their performances are evaluated here by analyzing their errors with respect to well characterized references. The analysis is based on 1‑minute data recorded over a 15‑month period at the Payerne BSRN station in Switzerland. The analysis was applied both to the whole dataset and data subsets reflecting particular conditions to allow a better understanding of how instrument performance depends on such conditions.The overall performance for measuring global horizontal irradiance (GHI) is satisfactory with deviations compatible with an expanded uncertainty of ±25 Wm−2 (±10 %). For diffuse horizontal irradiance (DfHI), RSIs exhibited errors on the order of ±20 Wm−2 (±13 %) with some of them being affected by small systematic negative biases on the order of −5 Wm−2 (median). SPN1s underestimate DfHI by about −10 Wm−2 (median) with a relatively large range of the expanded error distribution between −45 Wm−2 and 20 Wm−2 (−35 % to 13 %). For direct normal irradiance (DNI), the extended error range for RSIs is on the order of ±40 Wm−2 (±5–6 %) with some instruments presenting no bias while others are affected by median biases up to −15 Wm−2. SPN1s exhibit a relatively large median bias of 40 Wm−2, and an extended range of the error distribution between −45 Wm−2 and 125 Wm−2 (−6 % to 19 %). Typical errors on the integrated yearly energy per unit surface area are on the order of a few percent or less (< 5 %) for RSI with negligible errors on DNI for some RSI instruments. SPN1 integrated errors are negligible for GHI, but on the order of −8 % for DfHI, and between 9 % and 11 % for DNI. For RSIs, GHI and DfHI errors showed similar amplitude and dependence on solar elevation, while DNI errors were significantly smaller in relative terms than GHI or DfHI errors. This suggests that RSIs are optimized for providing good estimates of DNI, at the expense of – and resulting in – a correlation between GHI and DfHI errors. RSI uncertainty for DNI is about twice the uncertainty of a good quality pyrheliometer under favorable conditions. SPN1 instruments exhibit the opposite behavior with GHI and DfHI errors of opposite signs, resulting in large DNI errors. While the SPN1 performances for measuring GHI are similar to those of RSI, corrections are required to obtain satisfactory performances for DNI.

The influence of dust storms on solar radiation data, aerosol properties and meteorological variables in Central Arabian Peninsula

Dust storms are one of the natural sources for aerosol particles, especially in desert regions. The arid and semi-arid regions around Saudi Arabia are some of the most important sources of global dust. In this paper, we have quantitatively studied the influence of several dust storms on solar radiation components and meteorological variables. Global, direct and diffuse solar radiation data, in addition to measurements of relative humidity, air temperature, precipitable water vapor, aerosol optical depth and an Angstrom exponent for the period between 1999 and 2002, were used for the purpose of this study. During this period, 34 dusty events were selected, and their effects on these parameters were characterized. We have found that, dust storms significantly increase aerosol optical depth and the diffuse radiation and decrease the global and direct solar radiation components and Angstrom exponent. On the other hand, dusty events affect air temperature, relative humidity and precipitable water vapor differently. They intensify these variables in some events and reduce them in others. We have found that the amount of changes in these variables varies from one event to another. Several possibilities, such as the source of the dust storm and the season in which it occurred, have been suggested to explain these variations.

Determination of direct normal irradiance including circumsolar radiation in climate/NWP models

An issue in the determination of the direct component of solar radiation involving the circumsolar contribution in numerical weather prediction (NWP) and climate models is discussed. The direct solar radiation has multiple definitions in different applications, but this ambiguity has not always been clearly identified and has therefore sometimes caused confusion. The confusion arises from a fact that the photons that are scattered into the direct solar beam path by atmospheric particles are no different from the non‐scattered photons travelling in the same direction. Therefore there is a question whether these scattered photons should be included in the direct flux calculation or whether they should be excluded. Different definitions of the direct solar radiation in a wide range of applications have been discussed by Blanc et al. (2014). We further discuss it in terms of its relation to NWP and climate models. The short‐wave radiation schemes used in NWP and climate models can be classified into two groups: those that calculate the direct solar radiation without including scattering contributions and those which include the scattering contribution in terms of the delta‐Eddington approximation. We assess the two treatments by comparing modelled direct solar radiation with observations. It is found that the use of delta‐Eddington scaling results in positive errors in the direct solar flux at the surface, while neglecting the delta‐scaling leads to negative errors. The important result is that the positive error from using the delta‐Eddington scaling is at least 1 order of magnitude larger than the absolute negative error due to neglecting it. In order to include properly the scattering contribution in the direct flux calculation, a simple parametrization for dust aerosol is developed which can be used to consider the scattering contribution due to the particular case of dust aerosol to the direct solar radiation within the circumsolar region.

Prismatic TIR (total internal reflection) low-concentration PV (photovoltaics)-integrated façade for low latitudes

Low-concentration Façade-integrated Photovoltaic system in the form of TIR (total internal reflection) prismatic segmented façade could play an effective role in reducing the direct component of solar radiation transmitting through buildings, hence reducing both cooling and artificial lighting load on such buildings. A prismatic segmented façade is capable of allowing diffused skylight to transmit through it to the building interior, while preventing most of the direct solar radiation and converting it into clean energy by means of the integrated PV (​photovoltaics) cells. A range of prismatic TIR segmented façades with different head angles has been designed based on the geographical latitude of the chosen location. Each façade configuration is simulated by ray-tracing technique and its performance is investigated against realistic direct solar radiation data in two clear sky days representing summer and winter of the targeted location. Ray tracing simulations revealed that all of the selected configurations could collect most of the direct solar radiation in summer. In contrary, larger head angle of the segmented façade could collect wider intervals around the noon time till reaching a head angle of 23° at which most of the incident direct solar radiation could be collected.

Estimativas das componentes da radiação solar incidente em superfícies inclinadas baseadas na radiação global horizontal

Foram avaliadas equações estatísticas de estimativas com agrupamentos de dados anuais e mensais e suas respectivas validações, para as componentes global, direta e difusa da radiação solar incidente em superfícies inclinadas a 12,85, 22,85 e 32,85º, com face para o Norte, nas condições climáticas e geográficas de Botucatu, SP. Empregou-se as frações das três componentes da radiação a do topo da atmosfera em correlação com o coeficiente de transmissividade atmosférica do plano horizontal, em uma base de dados de abril/1998 a dezembro/2007, cujas medidas nas três inclinações ocorreram em diferentes períodos, todavia concomitantes ao plano horizontal. O aumento do ângulo de inclinação da superfície propiciou aumento do espalhamento dos valores diários do índice de claridade para superfícies inclinada e horizontal. Nos agrupamentos anuais os piores desempenhos foram verificados na estimativa da radiação difusa diária para superfície inclinada, com valores máximos de espalhamentos iguais a 3,89 MJ m-2 d-1 (43,65%) e ajustamento em torno de 62%. Na estimativa das componentes global e direta da radiação solar nos planos inclinados, podem ser aplicadas, tanto as equações anuais como as mensais, com desempenhos dependentes das condições climáticas.

Global and diffuse solar irradiances in urban and rural areas in southeast Brazil

The seasonal evolution of daily and hourly values of global and diffuse solar radiation at the surface are compared for the cities of Sao Paulo and Botucatu, both located in Southeast Brazil and representative of urban and rural areas, respectively. The comparisons are based on measurements of global and diffuse solar irradiance carried out at the surface during a six year simultaneous period in these two cities. Despite the similar latitude and altitude, the seasonal evolution of daily values indicate that Sao Paulo receives, during clear sky days, 7.8% less global irradiance in August and 5.1% less in June than Botucatu. On the other hand, Sao Paulo receives, during clear sky days, 3.6% more diffuse irradiance in August and 15.6% more in June than Botucatu. The seasonal variation of the diurnal cycle confirms these differences and indicates that they are more pronounced during the afternoon. The regional differences are related to the distance from the Atlantic Ocean, systematic penetration of the sea breeze and daytime evolution of the particulate matter in Sao Paulo. An important mechanism controlling the spatial distribution of solar radiation, on a regional scale, is the sea breeze penetration in Sao Paulo, bringing moisture and maritime aerosol that in turn further increases the solar radiation scattering due to pollution and further reduces the intensity of the direct component of solar radiation at the surface. Surprisingly, under clear sky conditions the atmospheric attenuation of solar radiation in Botucatu during winter – the biomass burning period due to the sugar cane harvest – is equivalent to that at Sao Paulo City, indicating that the contamination during sugar cane harvest in Southeast Brazil has a large impact in the solar radiation field at the surface.

Humidity: A factor in the appropriate positioning of a photovoltaic power station

Humidity is an ambient parameter which refracts, reflects and diffracts the direct visible solar radiation. This dispersion effect results in deterring the reception of the direct component of solar radiation by water vapour particles present in the atmosphere. Tropical Sudan Savannah region is known to be a hot climatic area with a highly humidified atmosphere. This paper investigates the effect of humidity on the reception of solar radiation and the resulting effect on the generated electrical power in this climatic region. A monocrystalline silicon photovoltaic module containing 33 cells connected in series was used for the investigation. The module open-circuit voltage (V OC) and short-circuit current (I SC) variations with irradiance level have been established. The variation of solar radiation intensity with humidity has also been analysed. Result indicates a little variation of the V OC with irradiance. On the other hand, the I SC has been observed to vary largely with the irradiance level. Also, the analysis of the variation of humidity with irradiance level reveals a non-linear relationship. This shows the dependence of photovoltaic module efficiency not only on the type of cell structure but also on the maximum irradiance and consequently the humidity of the surrounding.

Different methods for separating diffuse and direct components of solar radiation and their application in crop growth models

Influence of the diffuse proportion of solar radiation on the simulation of gross assimilation and dry matter production in leaf canopies is evaluated under different climatic conditions. Four methods to estimate daily and hourly values of direct and diffuse radiation from measurements of global radiation are compared both in terms of accuracy of incoming solar component estimates and of their suitability for incorporation into 2 wheat growth-simulation models (NWHEAT and SUCROS 90). Comparison showed that ( l ) the accuracy of direct and diffuse component estimates tends to decrease with increasing temporal resolution and varies under different climatic conditions and (2) the final grain yield calculated by the models is slightly but significantly influenced by the method used to calculate the components of incoming radiation.

Monthly average solar radiation in panama—Daily and hourly relations between direct and global insolation

Regressions are developed to estimate daily global and direct radiation and the hourly distribution of direct radiation for Barro Colorado Island, Panama from monthly mean values observed 35 km away at Chiva-Chiva. The ratio model of Liu and Jordan and the logarithmic model of Anderson for estimating direct from global radiation are compared. Both gave satisfactory results after accounting for “seasonal” variation, but the ratio model was preferred in this case for the smaller number of separate regressions required. The ratio model fitted for diffuse radiation at Chiva-Chiva agreed closely with regressions for stations at similar latitude. For a given value of the clearness index, the direct component of solar radiation was relatively (but not absolutely) reduced during the dry season compared with the wet season. A likely explanation for this unexpected result is increased marine and terrestrial aerosol during the dry season when offshore winds are stronger and burning of crop and wasteland occurs. The models of Whillier and of Garnier and Ohmura, which assume constant atmospheric transmittance throughout the day, gave unsatisfactory fits to the hourly distribution of direct radiation. They were also unable to mimic an observed morning/afternoon asymmetry that was strongest in the wet season. Hourly direct radiation was accurately estimated from hourly global radiation by quadratic polynomials fitted separately to the morning and afternoon data. The resulting regressions will enable estimation of radiation in forest understory from measurements of insolation in the open by computerized image analysis of hemispherical canopy photos.

Shading evaluations with general three-dimensional models

The SHADOWPACK package of computer programs has been developed to facilitate shading evaluations, for the direct component of solar radiation, with general 3D models. An interactive solid modelling program allows the user to construct and view the 3D model before saving it for further analysis and display. Other programs permit the graphical display of the shading situation throughout the year, the quantitative assessment of energy received on different faces of the model, and the display of the distribution of energy received on particular faces by means of contour plots. The use of the computer graphics approach has proved particularly convenient because of the similarity between the techniques used for graphical and numerical algorithms.

Estimating clear-day solar radiation: An evaluation of three models

Three models for estimating clear-day solar radiation were compared to one another and to values of solar radiation measured at Ft Collins, Colo. The models of Campbell (1977), Gates (1962) and McCullough and Porter (1971) all correlate closely with measurements of clear-day solar radiation. The Campbell and the Gates models require less technical expertise and less expensive computations to produce estimates of the direct component of solar radiation. All of the models appear to require calibration in order to correct estimates of the input variables to measured values of irradiance so that accurate calculations of direct solar radiation can subsequently be made. The best estimates of the diffuse component of solar radiation are obtained from the model of McCullough and Porter. The easiest and most accurate predictions of total solar radiation can be obtained from the direct-radiation models of Campbell (1977) and Gates (1962) and a modification of the diffuse-component model of McCullough and Porter (1971).

Estimating clear-day solar radiation: An evaluation of three models

Three models for estimating clear-day solar radiation were compared to one another and to values of solar radiation measured at Ft Collins, Colo. The models of Campbell (1977), Gates (1962) and McCullough and Porter (1971) all correlate closely with measurements of clear-day solar radiation. The Campbell and the Gates models require less technical expertise and less expensive computations to produce estimates of the direct component of solar radiation. All of the models appear to require calibration in order to correct estimates of the input variables to measured values of irradiance so that accurate calculations of direct solar radiation can subsequently be made. The best estimates of the diffuse component of solar radiation are obtained from the model of McCullough and Porter. The easiest and most accurate predictions of total solar radiation can be obtained from the direct-radiation models of Campbell (1977) and Gates (1962) and a modification of the diffuse-component model of McCullough and Porter (1971).

The luminous efficiency of direct solar radiation

Through the knowledge of luminous efficiency of solar radiation it is possible to derive the values of illumination from the known values of solar radiation. This is important in view of the scarcity of luminous data and easy availability of radiation data. In this paper the author presents the computed results of luminous efficiency for the direct component of solar radiation over varied solar altitudes and atmospheric turbidity conditions.&#x0D; This will enable the computation of the externally reflected daylight in buildings which is considerable in tropics. The luminous efficiency of diffuse radiation will be dealt with in a later paper.

A New Thermal Rating Approach: The Real Time Thermal Rating System for Strategic Overhead Conductor Transmission Lines Part III Steady State Thermal Rating Program Continued-Solar Radiation Considerations

For the first time, equations and computer programs are developed to show how the solar radiation received by an overhead transmission line is dependent on the conductor sag or slope. In the past, the overhead line has been assumed to lie in a horizontal plane with respect to the earth for the entire span length. Mathematical relationships for determining the sun's position in terms of solar azimuth and solar altitude, as a function of latitude, declination and hour angle are formulated and a polar plot is constructed to show the apparent path of the sun during the day for each month. Two different methods are presented to determine the angle of incidence between the sun's ray and the normal to any sloped cylindrical surface oriented at any azimuth angle. Plots are provided to indicate the variation in the angle of incidence and the direct component of solar radiation absorbed as a function of solar time for four general transmission line azimuths and five slopes at one latitude and declination. In addition, plots are drawn for the total solar radiation received by a conductor on a typical clear day as a function of both the span length and any sag or slope for both minimum and maximum diffuse radiation conditions for four general transmission line azimuths at one latitude and declination. It is shown that the conductor slope can have as much of an effect on the total radiation as does the solar adsorption constant.