Solar Irradiance Research Papers - Academia.edu (original) (raw)

The reflectance characteristics of most natural objects vary with illumination and viewing geometry, i.e. expose a non-Lambertian behaviour. New sensor systems are capable to view at targets quasi-simultaneously from nadir and different... more

The reflectance characteristics of most natural objects vary with illumination and viewing geometry, i.e. expose a non-Lambertian behaviour. New sensor systems are capable to view at targets quasi-simultaneously from nadir and different off-nadir positions. In regard to radiometric corrections the Lambertian assumption has to be overcome by detailed knowledge of the bidirectional reflectance distribution function (BRDF) of targets at the earth surface. In order to obtain bidirectional reflectance factor (BRF) data of naturally illuminated targets a transportable fieldgoniometer system (FIGOS) has been developed. It is operated together with a GER-3700 spectroradiometer. The goniometer consists of an azimuth full-circle and a zenith semi-arc of 2 m radius each. It enables to observe a target from any desired viewing direction. First measurements are taken from a plane meadow under different solar zenith angles over the hemisphere in a resolution of 15° and 30° in zenith and azimuth direction, respectively. A Spectralon panel is measured at the beginning and end of a hemispherical data set. As the position of the sun and the atmospheric conditions cannot be assumed constant over the measurement period of about 18 minutes, the global solar irradiance is monitored simultaneously to the BRF-data acquisition. The obtained results clearly show the non-Lambertian reflectance characteristics of the meadow.

Extraterrestrial total solar irradiance, usually called Solar Constant, is attenuated by the atmosphere in different proportions, depending mainly on solar zenith angle and altitude of the measurement point. In this work, it is presented... more

Extraterrestrial total solar irradiance, usually called Solar Constant, is attenuated by the atmosphere in different proportions, depending mainly on solar zenith angle and altitude of the measurement point. In this work, it is presented very high and extreme horizontal plane measurements of global solar irradiance that in some days overpassed the Solar Constant corrected by the actual SuneEarth distance (CSC). They were obtained at sea level of the intertropical Atlantic coast, in the city of Recife, Brazil, in the period February 2008eJanuary 2009. Extreme total solar irradiance values larger than CSC were measured during 3.4% of the days of the total registered period. This percentage increases to 7.4% for global solar irradiance within 95.1e100% of the CSC and to 15.3% within 90.1e95% of the CSC. The largest extreme total solar irradiance value, 1477 AE 30 W/m 2 , was registered the 28th of March 2008 at 11:34 local time (UT e 3h). It overpassed by 7.9% the CSC value for this day (1369.4 W/m 2) and by 42.3% the estimated value of the clear sky Iqbal C radiation model (1037.7 W/m 2). The observation of extreme values should be taken into account in the study of solar radiation effects related to materials exposed to the outside, UV index and biological effects, among others. Also, the detailed knowledge of this interesting effect may contribute significantly to clarify physical aspects about the interaction of global solar radiation with the ecosystem and climate change.

The effects of solar radiations on physical properties and molecular structures of 200 nm polystyrene nanospheres (PSN) coated on silicon wafer were explored by field emission scanning electron microscope (FESEM) and attenuated total... more

The effects of solar radiations on physical properties and molecular structures of 200 nm polystyrene nanospheres (PSN) coated on silicon wafer were explored by field emission scanning electron microscope (FESEM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometer. It is revealed the particles shape of PSN changed from spherical to dumbbell-like shape after solar irradiation. Reduction of the PSN size as much as 23.79% after 5 minutes exposure was also observed in PSN particles. We believed that some of the phenyl moieties of polystyrene broke down to facilitate carbon-carbon cross linkage bonds intra- as well as inter-PSN particles and were shown by ATR-FTIR spectrums. These results proven the shrinkage of PSN particles were caused by the change of the molecular structure of the irradiated PSN to be much more dense material.

Increasing land use pressure has resulted in increasing suspended solids loading to many African lakes in recent decades, causing concern that littoral habitat may be degraded by sedimentation and light limitation. In a companion paper in... more

Increasing land use pressure has resulted in increasing suspended solids loading to many African lakes in recent decades, causing concern that littoral habitat may be degraded by sedimentation and light limitation. In a companion paper in this issue, we showed that much runoff into Lake Malawi plunges below the euphotic zone and spreads through the lake via the upper metalimnion, thus mitigating nearshore and upper water column impacts. In this study we use data from multiple surveys through two rainy seasons to describe spatio-temporal distributions of suspended solids concentration (SSC) and transparency caused by the flow of runoff through the Linthipe River delta region of Lake Malawi. SSC in interflow at 30-50 m depth was typically an order of magnitude greater than in surface plumes. Seasonal median transparency near the river mouth was inversely proportional to the suspended load in surfacebuoyant inflow, but independent of total loading. This is because storm runoff was more dense (cooler and with higher SSC) than runoff during low-flow periods, so that it was more likely to plunge. The effect was to moderate inter-annual variability in light attenuation near the river mouth because transparency was lower (due to more surface-buoyant inflow of turbid water) in the year when solar irradiance was higher (less cloud cover). The effect was, however, local. Beyond a few kilometers of the river mouth upward mixing of suspended particles carried in interflow reasserted the more intuitive inverse dependence of transparency on total loading.

In this work, a new kind of autonomous solar still is proposed. This construction is used in the arid countries with intense solar irradiation and has shortage of potable water. The goal was to concept and to build a physical and... more

In this work, a new kind of autonomous solar still is proposed. This construction is used in the arid countries with intense solar irradiation and has shortage of potable water. The goal was to concept and to build a physical and mathematical model of solar sea water distiller. The model design and the comparative simulations with the measurement results are carried out offline at the CUTEC Institute GmbH with the arithmetical and technical equipment available there

Knowledge of th,e spectral attenuation associated with clouds is important for accurate estimates of natural irradiance at the Earth's surface. We compare spectral measurements of visible downwelling irradiance, under varying sky... more

Knowledge of th,e spectral attenuation associated with clouds is important for accurate estimates of natural irradiance at the Earth's surface. We compare spectral measurements of visible downwelling irradiance, under varying sky conditions at Halifax, Nova Scotia, Canada, with results from a clear-sky model. The spectral effect of clouds is estimated by taking the ratio of the measurements to the modeled irradiances and removing spectrally consistent instrumental effects and errors in the model. Empirical relationships derived between the spectral cloud effect and both CF, the cloud factor (the ratio of measured to modeled irradiances at 490 nm), and f, the fraction of sky covered by cloud, were found to follow a wavelength (•) dependence of the form a(C'F or f)+ b(C'F or f)(•/490) -4 in the 412-700 nm wavelength range. Both this relationship and a previously published linear relationship were found to be inadequate for describing cloudy irradiance data from the Bering Sea, indicating that the spectral effect of clouds can vary with cloud type and location. We show here that the spectral cloud effect can be mimicked by using a clear-sky model and changing the magnitude of the sky reflectivity or the spectral shape and magnitude of the ground albedo within the model. An investigation of the effects of cloud-dependent changes in irradiance spectra on calculations of bio-optical properties is also presented. Estimates of chlorophyll concentration from near-surface radia, nces are found to vary by up to 30%, whereas the effects on estimates of photosynthetically available and usable radiation at the sea surface are negligible. Paper number 1998JC900002. 0148-0227/98/1998JC900002509.00 els. The more complicated representations divide the atmosphere and clouds into several layers, requiring numerous parameters (e.g., LOWTRAN [Kneizys et al., 1983] and SBDART [Ricchiazzi et al., 1998]). Simpler methods compensate for clouds by applying a weighting to the irradiance for the clear-sky case [e.g., A twater and Ball, 1978]. A limited number of studies have shown that in the ultraviolet and visible wavelength regions (from 290 to 700 nm) clouds cause wavelengttldependent attenuation of downwelling solar irradiance [$pinhirne and GreenOnly the study of Siegel et al. [1998] provides a parameterization with coefficients that characterize the spectral effect of clouds on irradiance. However its applicability to a broad range of locations and times of year has not been determined. Different perceptions exist regarding the cause of spectral attenuation by clouds. One hypothesis is that the spectral change in downwelling irradiance is a result of irradiance reflection off the surface of the Earth and clouds [Wang and Lenoble, 1996; h'glling et al., 1997; Frederick, 1997; S. Madronich, personal communication, 1996]. The process is summarized as follows: Downwelling solar irradiance is reflected off the top sur-31,017 31,018 BARTLETT ET AL.: THE SPECTRAL EFFECTS OF CLOUDS face of clouds back to space. Since clouds are generally white or light gray in color, this process is spectrally neutral and simply decreases the magnitude of the downwelling irradiance. Part of this reflected irradiance is then scattered back toward the Earth's surface by the atmospheric constituents. The scattering is greater at shorter (blue) wavelengths than at longer (red) wavelengths, so the resulting downwelling irradiance is bluet relative to irradiance under clear sky.

Land cover estimation with ALOS satellite image using a neural-network AVNIR-2 were adopted as a supervisor signal. There are two reasons for using the classifi cation from AVNIR-2. First, the raw AVNIR-2 data contain much information.... more

Land cover estimation with ALOS satellite image using a neural-network AVNIR-2 were adopted as a supervisor signal. There are two reasons for using the classifi cation from AVNIR-2. First, the raw AVNIR-2 data contain much information. Therefore, the AVNIR-2 data are divided into eight classes in order to reduce it. Second, in the wide-area PALSAR data, more sample data are included in order to enhance the classifi cation accuracy. In the classifi cation with PALSAR, the number of input layers poses a problem because the PALSAR has only one band sensor. We propose that the input signal employs not only single pixels, but also near pixel values.

Marine aerosols produced by bursting bubbles at the ocean surface are highly enriched in organic matter (OM) relative to seawater. The importance of this OM in the photochemical evolution of marine aerosols and particularly as a source of... more

Marine aerosols produced by bursting bubbles at the ocean surface are highly enriched in organic matter (OM) relative to seawater. The importance of this OM in the photochemical evolution of marine aerosols and particularly as a source of reactive oxidants are unknown but likely significant. To investigate oxidant production, nascent aerosols were generated by bubbling zero air through flowing Sargasso seawater and photochemical production of OH radical and hydroperoxide were quantified in aqueous extracts exposed to solar radiation. Extrapolation to ambient conditions indicates that OM photolysis was the primary in situ source for OH (1.1 x10 -8 M s -1 ) and hydroperoxides (1.7 x 10 -8 M s -1 ) in nascent aerosols; NO 3 photolysis was the primary source in aged, acidified aerosols (1.4×10 -7 and 4.1×10 -8 M s -1 , respectively). In situ OH photoproduction was comparable to gas-phase uptake whereas H 2 O 2 photoproduction was slower.

The solar radiation is the fundamental source of energy that drives the EarthÕs climate and sustains life. The variability of this output certainly affects our planet. In the last two decades an enormous advance in the understanding of... more

The solar radiation is the fundamental source of energy that drives the EarthÕs climate and sustains life. The variability of this output certainly affects our planet. In the last two decades an enormous advance in the understanding of the variability of the solar irradiance has been achieved. Space-based measurements indicate that the total solar irradiance changes at various time scales, from minutes to the solar cycle. Climate models show that total solar irradiance variations can account for a considerable part of the temperature variation of the EarthÕs atmosphere in the pre-industrial era. During the 20th century its relative influence on the temperature changes has descended considerably. This means that other sources of solar activity as well as internal and man-made causes are contributing to the EarthÕs temperature variability, particularly the former in the 20th century. Some very challenging questions concerning total solar irradiance variations and climate have been raised: are total solar irradiance variations from cycle to cycle well represented by sunspot and facular changes? Does total solar irradiance variations always parallel the solar activity cycle? Is there a long-term variation of the total solar irradiance, and closely related to this, is the total solar irradiance output of the quiet sun constant? If there is not a long-term trend of total solar irradiance variations, then we need amplifying mechanisms of total solar irradiance to account for the good correlations found between total solar irradiance and climate. The latter because the observed total solar irradiance changes are inconsequential when introduced in present climate models.

About 20% of the final energy consumed in Europe is used in buildings. The active and passive use of solar energy is an approach to reduce the fossil energy consumption and the greenhouse gas emissions originated by buildings.... more

About 20% of the final energy consumed in Europe is used in buildings. The active and passive use of solar energy is an approach to reduce the fossil energy consumption and the greenhouse gas emissions originated by buildings. Consideration of solar energy technologies in urban planning demands accurate information of the available solar resources. This can be achieved by the use of remote sensing data from geostationary satellites which show a very high spatial and a sufficient temporal resolution compared to ground station data. This paper gives a brief introduction to the HELIOSAT method applied to derive surface solar irradiance from satellite images and shows examples of applications: The use of daylight in buildings, the generation of correlated time series of solar irradiance and temperature as input data for simulations of solar energy systems and a short-term forecast of solar irradiance which can be used in intelligent building control techniques. Finally an outlook is given on potential improvements expected from the next generation of European meteorological satellites Meteosat Second Generation (MSG). D

Lifetimes required for greenhouse cover films depend heavily on the country, especially the tradition in the country. They vary from one agricultural season (i.e. 6e9 months) to several years and are strongly dependent on the use of... more

Lifetimes required for greenhouse cover films depend heavily on the country, especially the tradition in the country. They vary from one agricultural season (i.e. 6e9 months) to several years and are strongly dependent on the use of pesticides which destroy the photostabilisers (HALS and nickel quenchers) and on other geographic and climatic factors (solar irradiation, temperature, winds, etc.).

Solar cooling applied to buildings is without a doubt an interesting alternative for reducing energy consumption in traditional mechanical steam compression air conditioning systems. The study of these systems should have a closely purely... more

Solar cooling applied to buildings is without a doubt an interesting alternative for reducing energy consumption in traditional mechanical steam compression air conditioning systems. The study of these systems should have a closely purely fundamental approach including the development of numerical models in order to predict the overall installation performance. The final objective is to estimate cooling capacity, power consumption, and overall installation performance with relation to outside factors (solar irradiation, outside temperature.). The first stage in this work consists of estimating the primary energy produced by the solar collector field. The estimation of this primary energy is crucial to ensure the evaluation of the cooling capacity and therefore the cooling distribution and thermal comfort in the building. Indeed, the absorption chiller performance is directly related to its heat source. This study presents dynamic models for double glazing solar collectors and compares the results of the simulation with experimental results taken from our test bench (two collectors). In the second part, we present an extensive collector field model (36 collectors) from our solar cooling installation at The University Institute of Technology in St Pierre, Reunion Island as well as our stratified tank storage model. A comparison of the simulation results with real scale solar experimental data taken from our installation enables validation of the double glazing solar collector and stratified tank dynamic models.

Module temperature Nominal operating cell temperature Outdoor exposure Modeling of temperature PV-module a b s t r a c t Simple analytical and statistical models for the evaluation of the temperature of PV-modules from climatic data... more

Module temperature Nominal operating cell temperature Outdoor exposure Modeling of temperature PV-module a b s t r a c t Simple analytical and statistical models for the evaluation of the temperature of PV-modules from climatic data (ambient temperature, global solar irradiation, and wind speed) are investigated. The parameters which describe the effects of cell technology and module design were evaluated from outdoor exposure data at different climatic regions. The models were validated by comparison of the simulated module temperatures with measured module temperatures at different test sites. A simplified way to determine a Realistic Nominal Module Temperature (ROMT) instead of the Nominal Operating Cell Temperature (NOCT) is proposed.

This paper presents a neural network based approach for improving the accuracy of the electrical equivalent circuit of a photovoltaic module. The equivalent circuit parameters of a PV module mainly depend on solar irradiation and... more

This paper presents a neural network based approach for improving the accuracy of the electrical equivalent circuit of a photovoltaic module. The equivalent circuit parameters of a PV module mainly depend on solar irradiation and temperature. The dependence on environmental factors of the circuit parameters is investigated by using a set of current-voltage curves. It is shown that the relationship between them is nonlinear and cannot be easily expressed by any analytical equation. Therefore, the neural network is utilized to overcome these difficulties. The neural network is trained once by using some measured current-voltage curves, and the equivalent circuit parameters are estimated by only reading the samples of solar irradiation and temperature very quickly without solving any nonlinear implicit equations that is necessary in conventional methods. To verify the proposed model, an experimental set up is installed. The comparison between the measured values and the proposed model results shows higher accuracy than the conventional model for all operating conditions.

This paper describes a tracking system which can be used with single-axis solar concentrating systems. The position and "status" of the Sun are detected by three light-dependent resistors (LDRs), one of which detects whether the collector... more

This paper describes a tracking system which can be used with single-axis solar concentrating systems. The position and "status" of the Sun are detected by three light-dependent resistors (LDRs), one of which detects whether the collector is focused, whilst a second resistor determines if there is cloud cover, and the third senses whether it is day or night. The resultant signals are fed to an electronic control system which operates a low-speed 12-V d.c. motor which rotates the collector via a speed-reduction gearbox. The tracking system accuracy depends on the magnitude of the solar irradiance. The deviation from zero is 0.2 and 0.05 ° with solar radiation of 100 and 600 W m -2, respectively. Both values suggest that the mechanism can be used satisfactorily for parabolic trough collectors of medium to high concentration ratios.

In moderate climates, short fluctuations in solar irradiance and their impact on the distribution grid will become an important issue with regard to the future large-scale application of embedded photovoltaic systems. Several related... more

In moderate climates, short fluctuations in solar irradiance and their impact on the distribution grid will become an important issue with regard to the future large-scale application of embedded photovoltaic systems. Several related studies from the past are recalled. The approach that is presented here applies a localized spectral analysis to the solar irradiance and derived quantities in order to determine the power content of fluctuations, depending on their characteristic persistence. Pseudorandom time series of solar irradiance, based on measured values of the instantaneous clearness index, are applied as input data. Power-flow calculations are carried out in order to assess the impact of fluctuating solar irradiance on the grid voltage. The "fluctuation power index" is defined as a measure for the mean-square value of fluctuations of a specific persistence. A typical scenario is simulated, and the results are interpreted.

The aim of this study is to investigate the effects of non-uniform solar irradiation distribution on energy output of different interconnected configurations in photovoltaic (PV) arrays. In order to find which configuration is less... more

The aim of this study is to investigate the effects of non-uniform solar irradiation distribution on energy output of different interconnected configurations in photovoltaic (PV) arrays. In order to find which configuration is less susceptible to mismatch effects, a PV module model is developed. This model can take into consideration the effects of bypass diodes and the variation of the equivalent circuit parameters with respect to operating conditions. The proposed model can provide sufficient degree of precision as well as solar cell-based analysis in analyzing large scale PV arrays without increasing the computational effort. In order to produce more reliable and robust simulations, improved and extended algorithms are presented. Some results are discussed in detail and some recommendations are extracted by testing several shading scenarios.

Evapotranspiration on a regional scale is useful information for agricultural and hydrological practice and can be determined by combining remote sensing data with ground-based measurements. However, estimates of evapotranspiration using... more

Evapotranspiration on a regional scale is useful information for agricultural and hydrological practice and can be determined by combining remote sensing data with ground-based measurements. However, estimates of evapotranspiration using remote sensing data are usually instantaneous values and to obtain daily evapotranspiration at a regional scale, it is necessary to convert these values into daily totals. By using the data obtained during the HAPEX-MOBILHY experiment in southwestern France, two different methods of converting instantaneous evapotranspiration into daily totals were evaluated. The first method is based on the assumption that the diurnal course of evapotranspiration is similar to that of solar irradiance and can be approximated by a sine function. As a result, daily evapotranspiration can be obtained from one instantaneous measurement. The second method assumes that the evaporative fraction, defined as the ratio of the latent heat flux and the available energy flux, is constant during the daytime period. Hence daily evapotranspiration can be determined from the evaporative fraction and daily total available energy. Comparisons of estimated and measured daily evapotranspiration indicated that both the methods are accurate for cloud-free days. However, the first method is preferable for the purpose of estimating regional evapotranspiration using remote sensing data.

This paper presents a systematic analytical approach for the well-being assessment of small autonomous power systems (SAPSs) with wind and solar energy sources. The proposed technique accounts for the uncertainties associated with solar... more

This paper presents a systematic analytical approach for the well-being assessment of small autonomous power systems (SAPSs) with wind and solar energy sources. The proposed technique accounts for the uncertainties associated with solar irradiance, wind speed, demand, and outages of various generating units. The impact of wind power fluctuation on the system stability is also assessed by limiting the wind power dispatch to a certain percentage of system load. Well-being assessment and production costing simulation for SAPS are performed using proposed analytical approach and Monte Carlo simulation (MCS) method, and then, obtained results are compared in terms of accuracy and computational time. The comparison shows that the developed technique requires less computational time than MCS method, with reasonable accuracy, and thus, validates the usefulness of proposed analytical method. The impact of renewable energy penetration on a SAPS is also analyzed using the proposed method.

The need of solar irradiation forecast at a specific location over long time horizons has attained massive importance. In this paper, we study the machine learning techniques to predict solar irradiation in 10 min intervals using data... more

The need of solar irradiation forecast at a specific location over long time horizons has attained massive importance. In this paper, we study the machine learning techniques to predict solar irradiation in 10 min intervals using data sets from Killinochchi district, Faculty of Engineering, University of Jaffna measuring center. The accuracies of the prediction models such as ARIMA, Random Forest Regression, Neural Networks, Linear Regression and Supportive Vector Machine is compared. This study suggests that ARIMA performs well over other approaches.

Accurate pyranometer calibrations, traceable to internationally recognized standards, are critical for solar irradiance measurements. One calibration method is the component summation, where the pyranometers are calibrated outdoors under... more

Accurate pyranometer calibrations, traceable to internationally recognized standards, are critical for solar irradiance measurements. One calibration method is the component summation, where the pyranometers are calibrated outdoors under clear sky conditions, and the reference global solar irradiance is calculated as the sum of two reference components, the diffuse and subtended beam solar irradiances. The beam component is measured with pyrheliometers traceable to the World Radiometric Reference, while there is no internationally recognized reference for the diffuse component. In the absence of such a reference, we present a method to consistently calibrate pyranometers for measuring the diffuse component with an 2 estimated uncertainty of 6(3% of reading11 W/ m ). The method is based on using a modified shade / unshade method, and 2 pyranometers with less than 1 W/ m thermal offset errors. We evaluated the consistency of our method by calibrating three pyranometers four times. Calibration results show that the responsivity change is within 60.52% for the three pyranometers. We also evaluated the effect of calibrating pyranometers unshaded, then using them shaded to measure diffuse irradiance. We calibrated three unshaded pyranometers using the component summation method. Their outdoor measurements of clear sky diffuse irradiance, from sunrise to sundown, showed that the three calibrated pyranometers can be used to measure the 2 diffuse irradiance to within 61.4 W/ m variation from the reference irradiance. Published by (I. Reda).

Résumé -Ce travail concerne l'étude d'un circuit électronique pour le contrôle d'un système suiveur de soleil qui peut suivre le soleil même à puissance d'ensoleillement faible, surtout pour les journées à ciel couvert ou... more

Résumé -Ce travail concerne l'étude d'un circuit électronique pour le contrôle d'un système suiveur de soleil qui peut suivre le soleil même à puissance d'ensoleillement faible, surtout pour les journées à ciel couvert ou complètement couvert de nuages. Une réalisation d'un circuit électronique de contrôle et commande, ainsi qu'une réalisation mécanique d'un héliostat sont traitées. Enfin, une étude de l'éclairement solaire par le modèle de Brichambaut est comparée aux données expérimentales relevés par le système suiveur de soleil réalisé. Abstract -In this paper, we present a new electronic circuit which controls a sun tracker system even then with low solar radiation. An electronic circuit and a mechanical system were realised in the URERMS center of Adrar. A study for the Brichambaut's solar irradiance model is done, and compared with the measured irradiance using the sun tracker.

There have been many published articles describing solar position algorithms for solar radiation applications. The best uncertainty achieved in most of these articles is greater than ±0.01°in calculating the solar zenith and azimuth... more

There have been many published articles describing solar position algorithms for solar radiation applications. The best uncertainty achieved in most of these articles is greater than ±0.01°in calculating the solar zenith and azimuth angles. For some, the algorithm is valid for a limited number of years varying from 15 years to a hundred years. This report is a step by step procedure for implementing an algorithm to calculate the solar zenith and azimuth angles in the period from the year À2000 to 6000, with uncertainties of ±0.0003°. The algorithm is described in a book written by Jean Meeus in 1998. This report is written in a step by step format to simplify the complicated steps described in the book, with a focus on the sun instead of the planets and stars in general. It also introduces some changes to accommodate for solar radiation applications. The changes include changing the direction of measuring azimuth angles to be measured from north and eastward instead of being measured from south and eastward, and the direction of measuring the observer's geographical longitude to be measured as positive eastward from Greenwich meridian instead of negative. This report also includes the calculation of incidence angle for a surface that is tilted to any horizontal and vertical angle, as described by Iqbals in 1983.

The use of daylighting in buildings and architecture is not new. Natural lighting became out of vogue due to the availability of cheap electricity, the predictability and the ability to control illumination levels due to artificial... more

The use of daylighting in buildings and architecture is not new. Natural lighting became out of vogue due to the availability of cheap electricity, the predictability and the ability to control illumination levels due to artificial lighting. However, the alarm over rapid depletion of energy resources and the environmental effects of their applications have led designers to reuse daylighting strategies in buildings in order to minimise energy use for lighting and air conditioning as a result of heat gains from the daylight sources and the electrical fixtures. This paper describes a study on the savings achieved by using daylight in passive solar design of buildings and, in this case, the size of windows. Simulated exterior illuminance levels based on long term measured solar irradiation and cloud cover data were used to estimate interior illumination on normal working planes using simple building configurations. Illumination on these planes decreases the need for artificial lighting, thus energy can be saved. A simple algorithm was then used to calculate the overall cooling load to ascertain that the daylighting strategies used do not invoke an increase in thermal gains through walls and glazings. The findings from this study show that at least 10% savings can be produced from simple daylighting strategies.

Nous présentons dans ce papier, une méthode de dimensionnement optimal du générateur photovoltaïque et du banc de batteries dans un système hybride de production d'électricité (éolienphotovoltaïque) totalement autonome. Pour une charge et... more

Nous présentons dans ce papier, une méthode de dimensionnement optimal du générateur photovoltaïque et du banc de batteries dans un système hybride de production d'électricité (éolienphotovoltaïque) totalement autonome. Pour une charge et une probabilité de perte d'énergie données sous le critère d'un prix minimum du système, un nombre optimal de batteries et de modules photovoltaïques a été calculé. Ainsi, à partir de données horaires de l'irradiation solaire, de la température ambiante et de la vitesse du vent, nous avons calculé la puissance horaire produite par l'aérogénérateur et par le générateur photovoltaïque sur une période d'analyse d'une année. Ces données sont issues de mesures au centre de Bouzaréah. Un profil de consommation type a été adopté. Il correspond au profil rencontré généralement dans les sites isolés.

This study evaluates the performance of 12 models to estimate hourly diffuse solar irradiation on inclined surfaces from those measured on horizontal surfaces. Total solar irradiation incident on a tilted surface consists of three... more

This study evaluates the performance of 12 models to estimate hourly diffuse solar irradiation on inclined surfaces from those measured on horizontal surfaces. Total solar irradiation incident on a tilted surface consists of three components including: beam, diffuse and reflected from the ground. On a semi-hourly basis, the beam component can be calculated by the ratio of the incidence angle to the solar zenith angle. The reflected component has a small effect on calculations and may be calculated with an isotropic model. In contrast, models for estimating the diffuse component show major differences, which justify the validation study that this paper discusses. Twelve models were tested against recorded south-and west-facing slope irradiances at Karaj (35155 0 N; 50156 0 E), Iran. The following models were included: Badescu [Ba], Tian et al. [Ti], Perez et al. [P9], Reindl et al. [Re], Koronakis [Kr], Perez et al. [P8], Skartveit and Olseth [SO], Steven and Unsworth [SU], Hay [Ha], Klucher [Kl], Temps and Coulson [TC], and Liu and Jordan [LJ].

Photocatalysis with TiO 2 particles immobilised either on a glass slide or on a non-woven glass fiber fabric has been applied to pure reactive dyes' (azo€ ıc and metal phthalocyanines) solutions as well as textile wastewater containing... more

Photocatalysis with TiO 2 particles immobilised either on a glass slide or on a non-woven glass fiber fabric has been applied to pure reactive dyes' (azo€ ıc and metal phthalocyanines) solutions as well as textile wastewater containing the same dyes under UV and solar irradiation. Decolourization of textile wastewater was in the range 21e74% under solar irradiation, with COD removal rate between 0.2 and 0.9 g COD/h/m 2 . These values are, however, strongly dependent upon the fine chemical structure of the dyes and the global composition of the wastewater. Performance prediction is therefore difficult but the results are encouraging for textile wastewater remediation. The increase of biodegradability is an additional positive factor, as it would improve the efficiency of a biological downstream treatment. No pH adjustment is necessary and wastewater at high pH can be treated directly after suspended solids removal.

a b s t r a c t Highly ordered TiO 2 nanotube arrays generate a considerable interest for hydrogen generation by an electrochemical photocell, since ordered architecture of nanotube arrays provides a unidirectional electric channel for... more

a b s t r a c t Highly ordered TiO 2 nanotube arrays generate a considerable interest for hydrogen generation by an electrochemical photocell, since ordered architecture of nanotube arrays provides a unidirectional electric channel for electron's transport. Here, we report the hydrogen generation by highly ordered TiO 2 nanotube arrays under actual sunlight in KOH electrolyte. The two-electrode electrochemical cell included an adjustable anode compartment capable of tracing the trajectory of the sun and a set of alkaline batteries connected with a rheostat for application of external bias. The results showed that the photocurrent responses of nanotube arrays match well with the intensity of solar irradiance on a clear summer day. Addition of ethylene glycol into KOH electrolyte as a hole scavenger enhanced the rate of hydrogen generation. A maximum photocurrent density of 31 mA/cm 2 was observed at 13:30 h, by focusing the sunlight with an intensity of 113 mW/ cm 2 on the surface of the TiO 2 nanotube arrays in 1 M KOH electrolyte with 10 vol% ethylene glycol under an applied bias of 0.5 V. The observed hydrogen generation rate was 4.4 mL/h cm 2 under the focalized solar irradiance with an intensity between 104 mW/cm 2 and 115 mW/cm 2 from 10:00 to 14:20 h. ª (M. Misra). A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e

Maximum power point tracking (MPPT) techniques are employed in photovoltaic (PV) systems to make full utilization of PV array output power which depends on solar irradiation and ambient temperature. Among all the MPPT strategies, the... more

Maximum power point tracking (MPPT) techniques are employed in photovoltaic (PV) systems to make full utilization of PV array output power which depends on solar irradiation and ambient temperature. Among all the MPPT strategies, the incremental conductance (INC) algorithm is widely used due to the high tracking accuracy at steady state and good adaptability to the rapidly changing atmospheric conditions. In this paper, a modified variable step size INC MPPT algorithm is proposed, which automatically adjusts the step size to track the PV array maximum power point. Compared with the conventional fixed step size method, the proposed approach can effectively improve the MPPT speed and accuracy simultaneously. Furthermore, it is simple and can be easily implemented in digital signal processors. A theoretical analysis and the design principle of the proposed method are provided and its feasibility is also verified by simulation and experimental results.

We present highly resolved, annually dated, calibrated proxies for atmospheric circulation from several Antarctic ice cores (ITASE (International Trans-Antarctic Scientific Expedition), Siple Dome, Law Dome) that reveal decadal-scale... more

We present highly resolved, annually dated, calibrated proxies for atmospheric circulation from several Antarctic ice cores (ITASE (International Trans-Antarctic Scientific Expedition), Siple Dome, Law Dome) that reveal decadal-scale associations with a South Pole ice-core 10 Be proxy for solar variability over the last 600 years and annual-scale associations with solar variability since AD 1720. We show that increased (decreased) solar irradiance is associated with increased (decreased) zonal wind strength near the edge of the Antarctic polar vortex. The association is particularly strong in the Indian and Pacific Oceans and as such may contribute to understanding climate forcing that controls drought in Australia and other Southern Hemisphere climate events. We also include evidence suggestive of solar forcing of atmospheric circulation near the edge of the Arctic polar vortex based on ice-core records from Mount Logan, Yukon Territory, Canada, and both central and south Greenland as enticement for future investigations. Our identification of solar forcing of the polar atmosphere and its impact on lower latitudes offers a mechanism for better understanding modern climate variability and potentially the initiation of abrupt climate-change events that operate on decadal and faster scales.

One of the most important steps to make use of any renewable energy is to perform an accurate estimation of the resource that has to be exploited. In the designing process of both active and passive solar energy systems, radiation data is... more

One of the most important steps to make use of any renewable energy is to perform an accurate estimation of the resource that has to be exploited. In the designing process of both active and passive solar energy systems, radiation data is required for the site, with proper spatial resolution. Generally, a radiometric stations network is used in this evaluation, but when they are too dispersed or not available for the study area, satellite images can be utilized as indirect solar radiation measurements. Although satellite images cover wide areas with a good acquisition frequency they usually have a poor spatial resolution limited by the size of the image pixel, and irradiation must be interpolated to evaluate solar irradiation at a sub-pixel scale. When pixels are located in flat and homogeneous areas, correlation of solar irradiation is relatively high, and classic interpolation can provide a good estimation. However, in complex topography zones, data interpolation is not adequate and the use of Digital Terrain Model (DTM) information can be helpful. In this work, daily solar irradiation is estimated for a wide mountainous area using a combination of Meteosat satellite images and a DTM, with the advantage of avoiding the necessity of ground measurements. This methodology utilizes a modified Heliosat-2 model, and applies for all sky conditions; it also introduces a horizon calculation of the DTM points and accounts for the effect of snow covers. Model performance has been evaluated against data measured in 12 radiometric stations, with results in terms of the Root Mean Square Error (RMSE) of 10%, and a Mean Bias Error (MBE) of þ2%, both expressed as a percentage of the mean value measured.

Efficient use of solar radiation needs detailed knowledge of its spatial and temporal variations. Such information can be achieved using interpolating measured irradiance by ground stations. But more reliable results can be obtained by... more

Efficient use of solar radiation needs detailed knowledge of its spatial and temporal variations. Such information can be achieved using interpolating measured irradiance by ground stations. But more reliable results can be obtained by processing geostationary satellite images. Heliosat is an algorithm which has been developed to estimate global horizontal irradiance at ground level from images taken in the visible band by the Meteosat satellites.

A two-dimensional numerical study of combined heat transfer (laminar and turbulent natural convection, surface thermal radiation and conduction) in a square cavity with a glass wall is presented. The cavity is modeled as one vertical... more

A two-dimensional numerical study of combined heat transfer (laminar and turbulent natural convection, surface thermal radiation and conduction) in a square cavity with a glass wall is presented. The cavity is modeled as one vertical isothermal wall, two horizontal adiabatic walls and one vertical glass wall. Numerical results in the cavity are obtained by means of a control volume approach where the conditions are set as: 21 • C uniform temperature in the isothermal wall, 35 • C outside ambient temperature and 750 W/m 2 constant direct normal solar irradiation over the glass wall. The Rayleigh number was varied between the range 10 3 Ra 10 12 . Results show that the flow pattern is not symmetric due to the combined effect of non-isothermal glass wall and radiative exchange inside the cavity. A correlation for the total Nusselt number was obtained for both laminar and turbulent flow considering conjugate heat transfer.

One of the challenges facing investment in photovoltaic (PV) energy is the accumulation of dust on the surface of the PV panels due to frequent dust storms in many countries, including Iraq. Surface dust particles reduce solar irradiance... more

One of the challenges facing investment in photovoltaic (PV) energy is the accumulation of dust on the surface of the PV panels due to frequent dust storms in many countries, including Iraq. Surface dust particles reduce solar irradiance which declining the electrical performance of the PV solar systems. Therefore, this paper proposes an experimental study to analyze and evaluate the power efficiency of a PV system installed in Baghdad city, Iraq. The performance of dusty solar PV array is compared with that of the clean array of the same PV system. The clean solar array is equipped with an automatic-sprayer cleaning system that is powered by the PV system. The automatic cleaning system utilized in the test system reduces human effort by cleaning the PV array using closed-cycle water with low energy consumption (less than 10 Wh). The PV array under test is part of a 15 kW grid-tied PV system. The experimental results show significant improvement in the performance parameters of efficiency, performance ratio, and the energy gain compared to the clean array. Furthermore, the experimental study contributes to a reduction in CO2 emission, which is substantial for the Iraqi environment that suffers from predominate fossil-fuel power plants.

Photovoltaic systems have been increasingly used in the generation of electrical energy, either as a means of providing electricity in areas where there is no grid connection (stand alone systems), or by providing electricity to the grid... more

Photovoltaic systems have been increasingly used in the generation of electrical energy, either as a means of providing electricity in areas where there is no grid connection (stand alone systems), or by providing electricity to the grid (grid connected systems). In a deregulated energy market, the cost of energy produced from fossil fuels is rising and the photovoltaic energy becomes a promising alternative source. Yet it still suffers from problems that need to be resolved in order to be widely accepted as an equivalent alternative to fossil fuels. Firstly the more direct problem of efficiency and cost needs to be overcome and secondly the indirect problem of the quality of power provided by photovoltaic technology has to be addressed. In this work 14 different grid connected PV systems have been considered and power quality measurements have been taken. Results for low and average irradiance cases are presented and analyzed in order to determine how power quality quantities are affected by changes in solar irradiance.

Values of downward and upward flux densities of solar and terrestrial radiation were continuously recorded between 1 December 2001 and 30 November 2002 using a four-components radiometer at S. Pietro Capofiume (SPC) in northern Italy... more

Values of downward and upward flux densities of solar and terrestrial radiation were continuously recorded between 1 December 2001 and 30 November 2002 using a four-components radiometer at S. Pietro Capofiume (SPC) in northern Italy (44j39VN, 11j37VE, alt. 11 m a.m.s.l.), which is characterized by a weakly-reflective surface. The aim of the study was to investigate the effects of clouds on surface radiation balance (SRB); the cloud fraction (N) has been retrieved through the inverted form of the parameterization proposed by Kasten and Czeplak [Solar Energy 24 (1980) 177] and cloud types estimated following the methodology of Duchon and O'Malley [J. Appl. Meteorol. 38 (1999) 132]. The cloud radiative forcing (CRF) was evaluated through the Bintanja and Van den Broeke [Int. J. Climatol. 16 (1996) 1281] formula and then associated with cloud type. Experimental results showed that during the measuring period the net shortwave (Sw) balance always decreased with increasing N, whereas the net longwave (Lw) balance increased in all seasons. The net radiation available at the surface decreased with increasing N in all seasons except in winter, where no significant dependency was detected.

A macromodel is developed for estimating the year-long biomass productivity of outdoor cultures of microalga in tubular photobioreactors. The model evaluates the solar irradiance on the culture surface as a function of day of the year and... more

A macromodel is developed for estimating the year-long biomass productivity of outdoor cultures of microalga in tubular photobioreactors. The model evaluates the solar irradiance on the culture surface as a function of day of the year and the geographic location. In a second step, the geometry of the system is taken into account in estimating the average irradiance to which the cells are exposed. Finally, the growth rate is estimated as a function of irradiance, taking into account photoinhibition and photolimitation. The model interconnects solar irradiance (an environmental variable), tube diameter (a design variable), and dilution rate (an operating variable). Continuous cultures in two different tubular photobioreactors were analyzed using the macromodel. The biomass productivity ranged from 0.50 to 2.04 g L −1 d −1 , and from 1.08 to 2.76 g L −1 d −1 , for the larger and the smaller tube diameter photobioreactors, respectively. The quantum yield ranged from 1.1 to 2.2 g E −1 ; the higher the incident solar radiation, the lower the quantum yield. Simultaneous photolimitation and photoinhibition of outdoor cultures was observed. The model reproduced the experimental results with less than 20% error. If photoinhibition was neglected, and a growth model that considered only photolimitation was used to fit the data, the error increased to 45%, thus reflecting the inadequacy of previous outdoor growth models that disregard photoinhibition.

The experiments were commenced in March 2003 and repeated in June 2003 at Sutton Bonington Campus, the University of Nottingham, UK, to investigate the effect of irradiance on plant growth and volatile oil content and composition in... more

The experiments were commenced in March 2003 and repeated in June 2003 at Sutton Bonington Campus, the University of Nottingham, UK, to investigate the effect of irradiance on plant growth and volatile oil content and composition in plants of basil. Four levels of irradiance were provided in the glasshouse, i.e. no shade (control), 25, 50 and 75% glasshouse irradiance. It suggested that basil grows well in full sun, however it can tolerate light shade. Heavy shading (75%) to provide a light integral of 5.3 moles m −2 d −1 resulted in shorter plants, lower weight, smaller leaf area, less shoots and higher specific leaf area, and also strongly reduced the rate of photosynthesis. There was no difference in CO 2 assimilation rate between 24.9 moles m −2 d −1 light integrals (no shading) and 13.5 moles m −2 d −1 light integrals (25% shading). Shading effectively reduced leaf temperature when air temperature was less than 30 • C, but heavy shading (75%) could not reduce leaf temperature when air temperature was above 36 • C due to a limitation of free air convection. Consequently, leaf temperature increased. Heavy shading strongly reduced total volatile oil content in fresh leaves, especially in older plants (shading treatment applied at the 3 leaf-pair growth stage). There were three chemical compounds in basil leaves, namely linalool, eugenol and methyl eugenol, influenced by the shading treatments. Linalool and eugenol, which contribute to the characteristic taste of basil, were significantly increased by high daily light integrals, whereas methyleugenol was increased by lower daily light integrals. No differences in the relative content of 1,8-cineole, one of the key aromatic compounds of Ocimum species, were observed.

A mathematical model to estimate the solar irradiance profile and average light intensity inside a tubular photobioreactor under outdoor conditions is proposed, requiring only geographic, geometric, and solar position parameters. First,... more

A mathematical model to estimate the solar irradiance profile and average light intensity inside a tubular photobioreactor under outdoor conditions is proposed, requiring only geographic, geometric, and solar position parameters. First, the length of the path into the culture traveled by any direct or disperse ray of light was calculated as the function of three variables: day of year, solar hour, and geographic latitude. Then, the phenomenon of light attenuation by biomass was studied considering Lambert-Beer's law (only considering absorption) and the monodimensional model of Cornet et al. (1900) (considering absorption and scattering phenomena). Due to the existence of differential wavelength absorption, none of the literature models are useful for explaining light attenuation by the biomass. Therefore, an empirical hyperbolic expression is proposed. The equations to calculate light path length were substituted in the proposed hyperbolic expression, reproducing light intensity data obtained in the center of the loop tubes. The proposed model was also likely to estimate the irradiance accurately at any point inside the culture. Calculation of the local intensity was thus extended to the full culture volume in order to obtain the average irradiance, showing how the higher biomass productivities in a Phaeodactylum tricornutum UTEX 640 outdoor chemostat culture could be maintained by delaying light limitation.

The temperature independent thermal infrared spectral indices (TISI) method is employed for the separation of land surface temperature (LST) and emissivity from surface radiances (atmospherically corrected satellite data). The daytime... more

The temperature independent thermal infrared spectral indices (TISI) method is employed for the separation of land surface temperature (LST) and emissivity from surface radiances (atmospherically corrected satellite data). The daytime reflected solar irradiance and the surface emission at ~3.8 µm are comparable. Using surface radiances and a combination of day-night 2channel TISI ratios, the ~3.8 µm reflectivity is derived. For implementing the TISI method, coefficients for NOAA 9-16 AVHRR channels are obtained. A numerical analysis with simulated surface radiances shows that for most surface types (showing nearly Lambertian behavior) the achievable accuracy is ~0.005 for emissivity (AVHRR channel 5) and ~1.5 K for LST. Data from the European Centre for Medium-Range Weather Forecasts (ECMWF) is used for calculation of atmospheric attenuation. Comparisons are made over a part of central Europe on two different dates (seasons). Clouds pose a major problem to surface observations, hence, monthly emissivity composites are derived. Additionally, using TISI-based monthly composites of emissivities, a normalized difference vegetation index (NDVI)-based method is tuned to the particular study area and the results are intercompared. Once the coefficients are known, the NDVI-method is easily implemented but holds well only for vegetated areas. The error of the NDVI-based emissivities (with respect to the TISI results) ranges between -0.038 and 0.032, but for vegetated areas the peak of error-histogram is at ~0.002. The algorithm for retrieving emissivity via TISI was validated with synthetic data. Due to the different spatial scales of satellite and surface measurements and the lack of homogeneous areas, which are representative for low resolution pixels and ground measurements, ground-validation is a daunting task.

Ni-based catalysts a b s t r a c t Supercritical water gasification (SCWG) of wet biomass is a very promising technology for hydrogen energy and the utilization of biomass resources. Ni-based catalysts are effective in catalyzing SCWG of... more

Ni-based catalysts a b s t r a c t Supercritical water gasification (SCWG) of wet biomass is a very promising technology for hydrogen energy and the utilization of biomass resources. Ni-based catalysts are effective in catalyzing SCWG of original biomass and organic compounds for hydrogen production.

In order for quantitative applications to make full use of the ever-increasing number of Earth observation satellite systems, data from the various imaging sensors involved must be on a consistent radiometric scale. This paper reports on... more

In order for quantitative applications to make full use of the ever-increasing number of Earth observation satellite systems, data from the various imaging sensors involved must be on a consistent radiometric scale. This paper reports on an investigation of radiometric calibration errors due to differences in spectral response functions between satellite sensors when attempting cross-calibration based on near-simultaneous imaging of common ground targets in analogous spectral bands, a commonly used post-launch calibration methodology. Twenty Earth observation imaging sensors (including coarser and higher spatial resolution sensors) were considered, using the Landsat solar reflective spectral domain as a framework. Scene content was simulated using spectra for four ground target types (Railroad Valley Playa, snow, sand and rangeland), together with various combinations of atmospheric states and illumination geometries. Results were obtained as a function of ground target type, satellite sensor comparison, spectral region, and scene content. Overall, if spectral band difference effects (SBDEs) are not taken into account, the Railroad Valley Playa site is a "good" ground target for cross calibration between most but not all satellite sensors in most but not all spectral regions investigated. "Good" is defined as SBDEs within ± 3%. The other three ground target types considered (snow, sand and rangeland) proved to be more sensitive to uncorrected SBDEs than the RVPN site overall. The spectral characteristics of the scene content (solar irradiance, surface reflectance and atmosphere) are examined in detail to clarify why spectral difference effects arise and why they can be significant when comparing different imaging sensor systems. Atmospheric gas absorption features are identified as being the main source of spectral variability in most spectral regions. The paper concludes with recommendations on spectral data and tools that would facilitate cross-calibration between multiple satellite sensors.

The integrated aquaculture of the tetrasporophyte of Asparagopsis armata Harvey (Falkenbergia rufolanosa) using fish farm effluents may be viable due to the species high capacity of removing nutrients and its content of halogenated... more

The integrated aquaculture of the tetrasporophyte of Asparagopsis armata Harvey (Falkenbergia rufolanosa) using fish farm effluents may be viable due to the species high capacity of removing nutrients and its content of halogenated organic compounds with applications on the pharmaceutical and chemical industries. In order to optimize the integrated aquaculture of F. rufolanosa, we followed the daily variation of the potential quantum yield (F v /F m ) of PSII on plants cultivated at different biomass densities and different total ammonia nitrogen (TAN) fluxes to check if they are photoinhibited at any time of the day. Moreover, the photoinhibition under continuous exposure to highly saturating irradiance and its potential for subsequent recovery in the shade was assessed. The potential for year round cultivation was evaluated by measuring rates of O 2 evolution of plants acclimated at temperatures ranging from 15 to 29°C, the temperature range of a fish farm effluent in southern Portugal where an integrated aquaculture system of F. rufolanosa was constructed.