Improved total atmospheric water vapour amount determination from near-infrared filter measurements with sun photometers

International audienceIn this work we explore the effect of the contribution of the solar spectrum to the recorded signal in wavelengths outside the typical 940-nm filter's bandwidth. We use gaussian-shaped filters as well as actual filter transmission curves to study the implications imposed by the non-zero out-of-band contribution to the coefficients used to derive precipitable water from the measured water vapour band transmittance. The moderate-resolution SMARTS radiative transfer code is used to predict the incident spectrum outside the filter bandpass for different atmospheres, solar geometries and aerosol optical depths. The high-resolution LBLRTM radiative transfer code is used to calculate the water vapour transmittance in the 940 nm band. The absolute level of the out-of-band transmittance has been chosen to range from 10?6 to 10?4, and typical response curves of commercially available silicon photodiodes are included into the calculations. It is shown that if the out-of-band transmittance effect is neglected, as is generally the case, then the derived columnar water vapour is systematically underestimated by a few percents. The actual error depends on the specific out-of-band transmittance, optical air mass of observation and water vapour amount. We apply published parameterized transmittance functions to determine the filter coefficients. We also introduce an improved, three-parameter, fitting function that can describe the theoretical data accurately, with significantly less residual effects than with the existing functions. Further investigations will use experimental data from field campaigns to validate these findings

Technical Note: Improved total atmospheric water vapour amount determination from near-infrared filter measurements with sun photometers

International audienceIn this work we explore the effect of the contribution of the solar spectrum to the recorded signal in wavelengths outside the typical 940-nm filter's bandwidth. We employ gaussian-shaped filters as well as actual filter transmission curves, mainly AERONET data, to study the implications imposed by the non-zero out-of-band contribution to the coefficients used to derive precipitable water from the measured water vapour band transmittance. Published parameterized transmittance functions are applied to the data to determine the filter coefficients. We also introduce an improved, three-parameter, fitting function that can describe the theoretical data accurately, with significantly less residual effects than with the existing functions. The moderate-resolution SMARTS radiative transfer code is used to predict the incident spectrum outside the filter bandpass for different atmospheres, solar geometries and aerosol optical depths. The high-resolution LBLRTM radiative transfer code is used to calculate the water vapour transmittance in the 940-nm band. The absolute level of the out-of-band transmittance has been chosen to range from 10?6 to 10?4, and typical response curves of commercially available silicon photodiodes are included into the calculations. It is shown that if the out-of-band transmittance effect is neglected, as is generally the case, then the derived columnar water vapour is mainly underestimated by a few percents. The actual error depends on the specific out-of-band transmittance, optical air mass of observation and water vapour amount. Further investigations will use experimental data from field campaigns to validate these findings

Recherches analytiques du platine dans les Alpes .- Quatriéme mémoire

Mes trois premiers mémoires appartiennent aujourd'hui au domaine public. Le quatrième est connu par ma correspondance particulière avec quelques membres du Corps impérial des mines, plusieurs membres de l'Institut et quelques savants étrangers. J'ai demandé à tous des avis, une direction; Cinq années de laborieuses recherches n'ont pu suffire pour la solution du problème le plus intéressant que les Alpes peuvent offrir. Je vais exposer rapidement les résultats que j'ai obtenus en 1852. Le nombre de pages accordées par le conseil général du département ne me permet pas de donner plus de détails

Recherches analytiques du platine dans les Alpes françaises - 3° mémoire

Mon premier Mémoire sur la découverte du platine, lu à l'Institut le 31 décembre 1849 par M, Arago, donna lieu à une mission scientifique de la part do M. le Ministre des travaux publics. A la suite de divers voyages pour étudier des gîtes, j'ai pris des échantillons sur un grand nombre de points. Je les ai classés par espèces, et j'ai pu commencer mes analyses vers le 1er novembre dernier. Cette division par espèces m'a paru peut-être plus commode pour mes lecteurs, que celle que j'avais adoptée dans mon second Mémoire, en exposant les résultats d'analyses par cantonnements

Recherche analytique du platine dans les Alpes - 2° mémoire

Document publié chez Allier -GrenobleMon premier mémoire sur la découverte du platine a élé lu à l'Institut, le 31 décemhre 1849, paMr Arago. La présence d'un métal si précieux dans nos Alpes fut accueillie avec empressement par tous les savants et de suite le Gouvernement me donna une mission scientifique, en 1850, pour continuer mes études. J 'ai adressé à M. le Ministre des travaux publics, le 18 avril 1851, mes Mémoires sur les recherches faites en 1850. Les résultats obtenus sont d'un grand intérêt scientifique et la mission qui m'avait été confiée continuera en 1851. Je vais donner l'extrait de mes travaux, exécutes au laboratoire du département. Toutefois, je dois indiquer que les frais ont été supportés par l'État. Je suivrai l'ordre de mes Mémoires, dont l'insertion dans les Annales des Mines vient d'être ordonnée par le Ministre des travaux publics

A bankable method of assessing the performance of a CPV plant

Concentrating Photovoltaics (CPV) is an alternative to flat-plate module photovoltaic (PV) technology. The bankability of CPV projects is an important issue to pave the way toward a swift and sustained growth in this technology. The bankability of a PV plant is generally addressed through the modeling of its energy yield under a baseline loss scenario, followed by an on-site measurement campaign aimed at verifying its energy performance. This paper proposes a procedure for assessing the performance of a CPV project, articulated around four main successive steps: Solar Resource Assessment, Yield Assessment, Certificate of Provisional Acceptance, and Certificate of Final Acceptance. This methodology allows the long-term energy production of a CPV project to be estimated with an associated uncertainty of ≈5%. To our knowledge, no such method has been proposed to the CPV industry yet, and this critical situation has hindered or made impossible the completion of several important CPV projects undertaken in the world. The main motive for this proposed method is to bring a practical solution to this urgent problem. This procedure can be operated under a wide range of climatic conditions, and makes it possible to assess the bankability of a CPV plant whose design uses any of the technologies currently available on the market. The method is also compliant with both international standards and local regulations. In consequence, its applicability is both general and international

An all-sky radiative transfer method to predict optimal tilt and azimuth angle of a solar collector

This paper describes a radiative transfer method for calculating radiances in all-sky conditions and performing an integration over the view hemisphere of an arbitrary plane to calculate tilted irradiance. The advantage of this method is the combination of cloud parameters inside the radiative transfer model with a tilt procedure. For selected locations this method is applied with cloud, ozone, water vapour and aerosol input data to determine tilted irradiance, horizontal irradiance and optimal tilt angle. A validation is performed for horizontal and tilted irradiance against high-quality pyranometer data. For 27 sites around the world, the annual horizontal irradiation predicted by our model had a mean bias difference of +0.56% and a root-mean-squared difference of 6.69% compared to ground measurements. The difference between the annual irradiation estimates from our model and the measurements from one site that provides tilted irradiance were within ±6% for all orientations except the north-facing vertical plane. For European and African sites included in the validation, the optimal tilt from our model is typically a few degrees steeper than predictions from the popular PVGIS online tool. Our model is generally applicable to any location on the earth’s surface as the satellite cloud and atmosphere data and aerosol climatology data are available globally. Furthermore, all of the input data are standard variables in climate models and so this method can be used to predict tilted irradiance in future climate experiments

Stochastic generation of synthetic minutely irradiance time series derived from mean hourly weather observation data

Synthetic minutely irradiance time series are utilised in non-spatial solar energy system research simulations. It is necessary that they accurately capture irradiance fluctuations and variability inherent in the solar resource. This article describes a methodology to generate a synthetic minutely irradiance time series from widely available hourly weather observation data. The weather observation data are used to produce a set of Markov chains taking into account seasonal, diurnal, and pressure influences on transition probabilities of cloud cover. Cloud dynamics are based on a power-law probability distribution, from which cloud length and duration are derived. Atmospheric transmission losses are simulated with minutely variability, using atmospheric profiles from meteorological reanalysis data and cloud attenuation derived real-world observations. Both direct and diffuse irradiance are calculated, from which total irradiance is determined on an arbitrary plane. The method is applied to the city of Leeds, UK, and validated using independent hourly radiation measurements from the same site. Variability and ramp rate are validated using 1-min resolution irradiance data from the town of Cambourne, Cornwall, UK. The hourly irradiance frequency distribution correlates with R2=0.996 whilst the mean hourly irradiance correlates with R2=0.971, the daily variability indices cumulative probability distribution function (CDF), 1-min irradiance ramp rate CDF and 1-min irradiance frequency CDF are also shown to correlate with R2=0.9903, 1.000, and 0.9994 respectively. Kolmogorov-Smirnov tests on 1-min data for each day show that the ramp rate frequency of occurrence is captured with a high significance level of 99.99%, whilst the irradiance frequency distribution and minutely variability indices are captured at significances of 99% and 97.5% respectively. The use of multiple Markov chains and detailed consideration of the atmospheric losses are shown to be essential elements for the generation of realistic minutely irradiance time series over a typical meteorological year. A freely downloadable example of the model is made available and may be configured to the particular requirements of users or incorporated into other models

Selection of cloudless sky conditions by applying solar globalultraviolet irradiance measurements

Taking advantage of UV (295 385 nm) irradiance measurements is one of the objectives of this paper. A newindex termed kt″ is established for this band. This newindexworks as a zenith angle independent clearness index for band measurements and has similar applications to those of kt′ for broadband measurements. The new index may be applied to identify cloudless instants from UV band measurements. Both indexes were correlated throughout the period 1998 2004 with a R2 of 0.85. A selection criterion of kt″UV >1.1 classified cloudless sky conditions with a probability of 95% in comparison with a selection that two criteria-applying broadband measurements would make. This index may be of interest for classifying cloudless sky conditions when only UV band measurements are available. An estimation method from the literature was applied to the period 1998 2004. This method was previously validated for the UV band with a measurement campaign made in Valencia (Spain) in the summer season.This work was supported by the Spanish Government through MEC grant MAT2006-02279, and was a part of the activities of the Grup d'Optoelectronica i Semiconductors of the Universitat Politecnica de Valencia, Spain.Serrano, M.; Boscá Berga, JV. (2013). Selection of cloudless sky conditions by applying solar globalultraviolet irradiance measurements. Atmospheric Research. 132-133:291-298. https://doi.org/10.1016/j.atmosres.2013.05.020S291298132-13