Global and diffuse radiation estimated from METEOSAT data at Bergen, Norway.(PDF 272Ko) (2000) Skartveit A. and Olseth J.A., Geophysical Institute, University of Bergen. Final report for SATELLIGHT. 2 years (1996-1997) of hourly observations of global irradiance at Bergen, Norway, show a negligible mean bias deviation compared to data derived from METEOSAT by the Heliosat procedure. There is, however, a slight tendency that satellite data exceed ground truth under overcast sky, while the opposite is true under approximately cloudfree sky. These minor deviations in global irradiance propagate, via a diffuse fraction model, into the Heliosat diffuse irradiances which at any solar elevation show mean bias deviations relative to ground truth amounting to some 5-10% of the average observed global irradiance. Contribution to validation and dissemination of information provided by the Satellight server over the Central European Territory. (1999) Kittler R., Darula S. and Sloboda M., Institute of Construction and Architecture, Slovak Academy of Science. Report for contract L01317. In Bratislava, Slovakia, the comparison of ground measured and Satellight data in availability diagrams has shown a quite good agreement of results especially when year-round data are tested and compared. This fact is very important considering their utilisation for solar energy purposes and energy trade-offs calculations or long term energy conscious design purposes. In other words the longer time period or averages are used for comparisons the relatively greater is the chance of a good agreement and thus the validity of Satellight data for locally undetectable or unavailable information. As already realized by the Satellight authors, a better agreement is reached during sunny or quasi-sunny conditions. Therefore care should be taken when using Satellight data for studies of local and short dynamic changes in the occurrence of illuminance levels, or the occurrence of specific or extreme sky types the effect of which are far from average or typical conditions. There is also a relatively good correlation between monthly availability and monthly mean sunshine duration. The difference between the July 1996 and 1997 global irradiance availability indicated by Satellight, is explained by the difference in monthly sunshine duration: 0.52 in July 1996 and 0.41 in July 1997. Bereitstellung von Tageslicht und Solarstrahlungsdaten aus METEOSAT Satellitendaten: Das europäische Projekt SATELLIGHT. (1998) Beyer H.G., Hammer A., Heinemann D., Reise Ch., Tagungsbericht 11. Int. Sonnenforum, Köln. The satellight model of turbidity variations in Europe. (1998) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Report for the sixth SATELLIGHT meeting in Freiburg, Germany, September 1998. Daylight availability in Freiburg and Nantes, two sites close in latitude. (1998) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Report for the sixth SATELLIGHT meeting in Freiburg, Germany, September 1998. SATELLIGHT: A WWW Server which provides High Quality Daylight and Solar Radiation Data for Western and Central Europe. (1998) Fontoynont M., Dumortier D., Heinemann D., Hammer A., Olseth J., Skartveit A., Ineichen P., Reise Ch., Page J., Roche L., Beyer H.G., Wald L., Proc. 9th Conf. on Satellite Meteorology and Oceanography, Paris. Radiation Derivation from Meteosat Counts (PDF 220Ko) (1998) Ineichen P., Group of Applied Physics, University of Geneva. Report for the sixth SATELLIGHT meeting in Freiburg, Germany, September 1998. The advantage of deriving in an independent way the different radiation components from the Meteosat counts is that the former applied model does not influence the bias and dispersion. This working paper presents the evaluation of such models and their performances are compared to the heliosat version used in the satellight program. Both mathematics and statistic comparison are done. It appears that depending on the final application of the evaluated radiation, one should use direct model or cumulated models. The bias, the root mean square difference and the frequency analysis show that, apart from the time and space determination of the satellite counts that should be improved, work has to be done to better understand the climate and geographical dependency of the models. High latitude global and diffuse radiation estimated from METEOSAT data. (1998) Olseth J.A. and Skartveit A., European Conference on Applied Climatology, ECAC 98, Vienna, Austria October 19-23, 1998. For snow-free ground, hourly observations of global irradiance at 9 Scandinavian ground stations (58 - 64°N) show a negligible mean bias deviation compared to data derived from METEOSAT. The satellite data nicely reproduce the spatial variation between the ground truth stations. Moreover, if time specific hourly data are required at a specific snow-free location, the satellite data for that location are probably more accurate than data from a ground station more than some 30 km away. However, snow cover reduces the agreement between surface observations and satellite derived data. The overall average and even the hour to hour variation of diffuse irradiance at the two stations Bergen and Gävle is nicely reproduced by the satellite data. An hourly diffuse fraction model with correction for variability and surface albedo. (1998) Skartveit A., Olseth J.A. and Tuft M.E., Solar Energy, 63, N°3, pp 173-183. The paper presents an improved version of a previously published model for the diffuse fraction of hourly global irradiance. In addition to hourly solar elevation and clearness index, an hour-to-hour variability index and regional surface albedo are included among the input parameters. Moreover, to prevent excessively high normal incidence beam irradiances at very low solar elevations, the model does not allow a solar elevation dependent maximum beam transmittance to be exceeded. This new model is tuned to 32 years of data from Bergen. Moreover, a test against independent data from 4 European stations showed that the model performs better than the models of Erbs et al. (1982), Maxwell (1987), and Perez et al. (1992). Global and diffuse radiation estimated from METEOSAT data at some Nordic stations (PDF 480Ko) (1998) Skartveit A and Olseth J.A., Proc. XXI Nordisk Meteorologmrte, Reykjavik, Iceland 24-28 June 1998, pp 119-124. Test of four new versions of the heliosat method used to produce global horizontal irradiances, results in six sites. (1997) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Report for the fifth SATELLIGHT meeting in Sophia Antipolis, November 1997. Test of various routes to derive global and diffuse horizontal illuminance/irradiance from Meteosat images - Five sites in Europe. (1997) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Report for the fourth SATELLIGHT meeting in Oldenburg, Germany, June 1997. Evaluation of luminous efficacy models according to sky types and atmospheric conditions. (1997) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Proc. Lux Europa '97, Amsterdam. Test of the heliosat methods used to produce half hour averaged irradiances from Meteosat images. (1997) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Report for the third SATELLIGHT meeting in Les Marécottes, Switzerland, January 1997. Day to day performance of the heliosat versions in Vaulx-en-Velin and in Lisbon, in June 1994. (1997) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Report for the third SATELLIGHT meeting in Les Marécottes, Switzerland, January 1997. Satellight: A European Programme Dedicated to Serving Daylight Data Computed from Meteosat Images. (1997) Fontoynont M., Dumortier D., Heinemann D., Hammer A., Olseth J., Skartveit A., Ineichen P., Reise Ch., Page J., Roche L., Beyer H.G., Wald L., Santos A., Proc. Lux Europa 1997, The 8th European Lighting Conference, Amsterdam. Clear sky diffuse irradiance: validation of two models against measured data. (1997) Hammer A., Heinemann D., Westerhellweg A., Department of Physics, Carl Von Ossietzky Universität Oldenburg, Germany. Report for the fifth SATELLIGHT meeting in Sophia Antipolis, France, November 1997. Global and diffuse radiation from Meteosat images - an overview about methods for data derivation. (1997) Hammer A., Heinemann D., Department of Physics, Carl Von Ossietzky Universität Oldenburg, Germany. Report for the third SATELLIGHT meeting in Les Marécottes, Switzerland, January 1997. Radiation and Illuminance Components from Meteosat Images (PDF 372Ko) (1997) Ineichen P., Group of Applied Physics, University of Geneva. Report for the fourth SATELLIGHT meeting in Oldenburg, Germany, June 1997. We investigate in the present working paper the relationship between satellite count, global irradiance and other solar and illumination resource components, bringing a particular attention to low solar elevation situations (below 20ƒ) which are very important in northern latitudes. We developed a model that directly relates an elevation dependent clearness index to the cloud index. This methodology presents a definite advantage because it can be generalized to address the clearness index of other solar radiation components, besides global irradiance, such as direct irradiance, diffuse illuminance, etc. The correlations described in this paper were developed on the data from Geneva. Their precision, on an hourly basis, are respectively 34%, 41% and 68% for the global, diffuse and beam components (93, 53 and 97 W/m2). Notes on Heliosat v2a,v2b and v3: Comparison with Geneva's data (PDF 132Ko) (1997) Ineichen P., Group of Applied Physics, University of Geneva. Report for the third SATELLIGHT meeting in Les Marécottes, Switzerland, January 1997. These notes present the behavior of 3 heliosat versions when applied on the data from Geneva. Model versus measurements scatter plots and parameter dependence are given in this working paper. We pointed out some systematic dispersion for a high diffuse fraction, and low backscatter angles for the global component and for all the versions of heliosat. If this result is corroborated with other data sets, the cloud index derivation (geometric and albedo corrections) can be improved. Concerning the diffuse component, a parameter dependence study on the measurements shows systematic biases with the cloud index stability, the backscatter angle, the humidity, etc. This leads to the conclusion that a direct model to derive the diffuse component could give good results. Sky luminance distribution from Meteosat images (PDF 288Ko) (1997) Ineichen P., Group of Applied Physics, University of Geneva. Report for the third SATELLIGHT meeting in Les Marécottes, Switzerland, January 1997. This working paper describes the method used for the evaluation of the sky luminance distribution on the basis of Meteosat information. The single pixel model will provide a model that cannot take into account the cloud distribution in the sky vault and the output data will therefore be symmetrical to the sun azimuth. The use of the surrounding pixels, the multiple pixel method, takes into account the clouds' position, but it needs higher resolution input data and IR data to evaluate the altitude of the clouds. The two methods are investigated, with all the possible input parameters, and the sky luminance zones are integrated to obtain vertical illuminances. The use of the modified CIE model with modeled input parameters gives a negligible bias and a dispersion of 61% for any direction in the sky vault. The model overestimates the luminance in a south direction and underestimates in the north direction. One can partly attributes these results to the intrinsic properties of the CIE model. When integrating the luminance distribution over the sky vault in the four vertical directions, one obtains illuminance with a bias of 1800 [lux] (negative in the north direction and positive in the south direction) with a precision of 45% to 50%. Half of these bias and dispersion are due to the integration process. High latitude global and diffuse radiation estimated from Heliosat-versions 7, 8, 9, and 10 (PDF 1.2Mo) (1997) Olseth J.A. and Skartveit A., Report for the fifth SATELLIGHT meeting in Sophia Antipolis, November 1997. We compare some high latitude hourly ground observations with global radiation estimated from the geostationary satellite Meteosat with different Heliosat versions. In addition to looking at the mean bias errors, our note focuses on how well frequency distributions of hourly global irradiance at the surface are reproduced by corresponding data retrieved from Meteosat data. Among the tested versions Heliosat Version 8 fitted our data best at snow-free conditions. Besides, the diffuse fraction model which was developed during the project improved the satellite derived diffuse irradiances significantly. High latitude global and diffuse radiation estimated from Heliosat (PDF 1.7Mo) (1997) Olseth J.A. and Skartveit A., First draft, May 1997. Report for the fourth SATELLIGHT meeting, Oldenburg, Germany, June 1997. Horizontal and vertical illuminance / irradiance from 4 IDMP stations (PDF 3.3Mo) (1997) Olseth J.A. and Skartveit A., First draft, June 1997. Report for the fourth SATELLIGHT meeting, Oldenburg June 1997. Spatial distribution of photo-synthetically active radiation over complex topography. (1997) Olseth J.A. and Skartveit A., Agricultural and Forest Meteorology, 86, pp 205-214. The paper presents a technique for spatially continuous mapping of local screening effects on diffuse and direct beam fluxes of short-wave radiation (0.3 - 3 _m) or Photo-synthetically Active Radiation (PAR: 0.4 - 0.7 _m). The method requires a digitized topographical map, and radiation data either from a site with an unobscured horizon or from radiative transfer calculations requiring minimum input data. Within one selected complex topography, screen-ing/reflection effects yield substantial local spatial variations in the PAR field. These variations depend on albedo and cloudiness, and they are (on a percentage basis) most pronounced at high latitudes. High latitude global radiation estimated from 5 versions of Heliosat. (1997) Olseth J.A. and Skartveit A., Report for the third SATELLIGHT meeting, Les Marécottes, Switzerland, January 1997. Comparing satellite remote sensing and ground network measurements for the production of site/time specific irradiance data. (1997) Perez R., Seals R. and Zelenka A., Solar Energy, 60, N°2, pp 89-96. In this article, we compare the accuracy of satellite-derived time/site specific hourly irradiances, with that of irradiances obtained via extrapolation and/or interpolation of nearby ground measuring stations. The results show that, for hourly data, the satellite becomes more accurate than a local ground station if the distance from the station exceeds 34 km, down from a previously reported 50 km range for daily irradiances. Heliosat v7…v10 versus IDMP & 1000 Roofs: comparison of horizontal global and diffuse irradiance data. (1997) Reise C., Fh-ISE, Freiburg, Germany. Report for the fifth SATELLIGHT meeting in Sophia Antipolis, France, November 1997. Heliosat v3n versus 1000 roofs & IDMP: comparison of horizontal global and diffuse irradiance data. (1997) Reise C., Fh-ISE, Freiburg, Germany. Report for the fourth SATELLIGHT meeting in Oldenburg, Germany, June 1997. 1000 Roofs data versus satellite data: first results. (1997) Reise C., Fh-ISE, Freiburg, Germany. Report for the third SATELLIGHT meeting in Les Marécottes, Switzerland, January 1997. Satellite derived and ground truth horizontal and vertical illuminance/irradiance from the IDMP stations at Geneva and Gävle (PDF 1.0Mo) (1997) Skartveit A and Olseth J.A., Report for the fifth SATELLIGHT meeting in Sophia Antipolis, November 1997. This note deals with observed and modelled relationships between irradiance and illuminance measured on horizontal and vertical surfaces at the four IDMP stations Gävle, Geneva, Lyon and Lisboa. Although satellite derived horizontal and vertical illuminances do not match ground truth data perfectly on an hour by hour basis, their frequency distribution is close to the distribution of illuminances derived from ground truth horizontal irradiances and even to the distribution of ground truth illuminances. Test of a luminous efficacy model on illuminance/irradiance data from 4 European IDMP stations (PDF 300Ko) (1997) Skartveit A and Olseth J.A., Report for the third SATELLIGHT-meeting, Les Marécottes, January 1997. Horizontal and vertical illuminance/irradiance from the IDMP station in Geneva (PDF 1.1Mo) (1997) Skartveit A and Olseth J.A., Report for the third SATELLIGHT meeting in Les Marécottes, January 1997. Spatial distribution of daylight - CIE standard Overcast Sky and Clear Sky. (1996) CIE Standard S003. Comparison between half hour averaged irradiances measured in Vaulx-en-Velin and half hour estimates from Meteosat images. (1996) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Report for the second SATELLIGHT meeting in Bergen, Norway, June 1996. Day to day performance of the Bourges and Kasten Heliosat procedures in Vaulx-en-Velin, and half hour estimates from Meteosat images. (1996) Dumortier D., Ecole Nationale des Travaux Publics de l'Etat, Vaulx-en-Velin, France. Report for the second SATELLIGHT meeting in Bergen, Norway, June 1996. Use of Meteosat data to produce sky luminance maps (PDF 204Ko) (1996) Ineichen P., Group of Applied Physics, University of Geneva. Report for the second SATELLIGHT meeting in Bergen, Norway, June 1996. One of the objectives of the Satellight program is to provide sky luminance patterns from the Meteosat satellite images. Sky luminance distribution models have been developed in the last years on the basis of horizontal diffuse illuminance. Their precision depends on the input data and these models cannot take into account the statistical cloud distribution in the sky vault. This could be possible on the basis of satellite images. This working paper points out the importance of the measurements used to derive the model, the influence of the number of sky zones (145 for the measurements, 13 for the majority of the applications) and the applicability of existent models on the 13 zones. It also describes a first attempt to derive the sky voult luminance distribution directly based on a satellite count. The conclusion is that the development of such a model will need higher resolution Meteosat images over at least a year and its precision and validation can only be assessed by a large-scale evaluation on data from other sites. The Linke turbidity factor based on improved values of the integral Rayleigh optical thickness. (1996) Kasten F., Solar Energy, 56, 3, pp 239-244. Spectral data on extraterrestrial solar radiation, Rayleigh scattering, ozone absorption and absorption by the uniformly mixed gases are critically evaluated and used for computing the integral Rayleigh optical thickness of the clean and dry atmosphere for a given relative optical air mass or solar elevation angle. The results are compared to the corresponding values calculated with the help of the three parameterization formulae. Based on the comparison, the formula of Louche et al. slightly adjusted to the new values may be recommended for general use. Equations are given for converting the earlier into the new values of the integral Rayleigh optical thickness and the Linke turbidity factors based on these new expressions. Both the earlier and the new algorithms yield identical values of the direct solar irradiance. Modelling the spatial distribution of solar resources and its dependency on latitude, topography, albedo and cloudiness. (1996) Olseth J.A. and Skartveit A., Abstract Volume, European Conference on Applied Climatology, Norrköping, Sweden, 7-10 May 1996, pp 89-90. The spatial distribution of solar irradiation is important in e.g. botany, hydrology, solar energy utilization, and even remote sensing of solar irradiation. The density of radiometric stations is, however, limited for economical reasons, and some technique for spatially continuous mapping of solar irradiation is therefore needed. The required spatial dis-tribution is governed mainly by: (1) solar elevation, (2) atmospheric composition (clouds in particular), (3) orienta-tion of the irradiated surface, (4) surface albedo, (5) screening/reflection effects from the surrounding terrain. As regards the factors (1) and (2), several techniques for estimating solar radiation at locations between network sites have been developed and evaluated. This paper addresses the contributions from factors (3)-(5) to the small scale spatial distribution of sunshine duration and beam/diffuse solar irradiation in a complex topography. The factors (3) and (4) are quantified by a procedure reported by Skartveit and Olseth (1986), while factor (5) is quantified by means of data from a Fortran code requiring digitized topographical maps as input (Olseth et al., 1995 & Olseth and Skartveit, 1995). Our scheme requires a digitized topographical map, and radiation data either from a site with free horizon or from radiative transfer calculations requiring minimum input data.Within one selected complex topography (a 10 x 10 km area surrounding Bergen; 60o24'N, 5o19'E) screening/reflection effects yield substantial local spatial variations in the solar radiation field, amounting to a factor of more than two within the selected area. Calculations for the same selected topography placed at the equator and at 65oN, show that these variations depend on albedo and cloudiness, and they are (on a percentage basis) most pronounced at high latitudes. On an annual basis, the variations within the selected topography are more than two times larger under cloudless sky at 65oN than at the equator. Moreover, we find that elevated hillsides significantly affect diffuse irradiation, and not only beam irradiation as often assumed for computational reasons. Thus, within our topography at 65oN, screening/reflection effects from elevated hillsides yield spatial variations in annual diffuse irradiation amounting to ±23% of the free horizon global irradiation. Retrospective quality control of solar radiation data (PDF 880Ko) (1996) Olseth J.A., Skartveit A and Skaar E., Report for the second SATELLIGHT meeting in Bergen, Norway, June 1996. Quality control of solar radiation data includes measures take prior to sensor deployment in the field (sensor calibration/characterization), real time automatic quality control tests during measurements, and retrospective analysis. Some quality control criteria may rely on redundancy in the observed data, like for instance the requirement that global irradiance equals the sum of diffuse plus beam irradiance. In the absence of such redundancy, some retrospective quality control is possible by identification of data which may be adequately tested against reliable models. The present note focuses on some aspects of retrospective quality control applied to solar radiation from Norway. High latitude global radiation estimated from METEOSAT. (1996) Olseth J.A. and Skartveit A., Report for the second SATELLIGHT meeting in Bergen, Norway, June 1996. Algorithms for the Satellight programme. (1996) Page J., Technical Report for the second SATELLIGHT meeting in Bergen, Norway, June 1996. Solar radiation calculations at low solar elevations. (1996) Skartveit A and Olseth J.A., Note from DNMI before the Third SATELLIGHT-meeting, Les Marécottes, Switzerland, January 1997. Unless special care is taken at low solar elevations large errors on slope irradiances/illuminances can occur. The present note focus on how to handle Meteosat data at low solar elevations. Illuminance/irradiance at a high latitude IDMP station (PDF 324Ko) (1996) Skartveit A and Olseth J.A., Report for the second SATELLIGHT meeting in Bergen, Norway, June 1996. An attempt to estimate the diffuse component of solar radiation on horizontal plane from satellite images. (1995) Diabate L., Wald L., AJST series, Vol.11, N°1. Mesure, analyse et modélisation du gisement lumineux. Application à l'évaluation des performances de l'éclairage naturel des bâtiments. (1995) Dumortier D., PhD Thesis, Université de Savoie, France, 350 pages. Spatially continuous mapping of solar resources in a complex high latitude topography. (1995) Olseth J.A., Skartveit A. and Han Zou, Solar Energy, 55, pp 475-485. The annual number of hours with low sun is highest at 60-70° latitude, making the scope for horizon screening effects particularly wide there. The present paper presents a technique for spatially continuous mapping of local screening effects. The method requires a digital topographical map, and radiation data from a site with free horizon. Screening effects are found to introduce local spatial variations in the solar radiation field, amounting to a factor of more than two within a 10 x 10 km area around Bergen (60°24'N, 5°19'E). A Review of Satellite Methods to Derive Surface Solar Irradiance. (1995) Pinker R. T., Frouin R., Li Z., Remote Sensing of the Environment, 51, pp 108-124. Satellite-Derived Radiation Data for PV System Studies - An Appraisal. (1994) Beyer H.G., Heinemann D., Perez R., Reise Ch., Seals R, Proc. 12th CEC PV Solar Energy Conference, Amsterdam. Sky luminance data validation, comparison of 7 models with 4 data banks. (1994) Ineichen P., Molinaux B. and Perez R., Solar Energy, 52, N°4. A comparison of sky luminance models with measured data from Garston. (1994) Littlefair P.J., United Kingdom, Solar Energy, 53, N°4, pp 315-322. Luminous efficacy models and their application for calculation of photo-synthetically active radiation. (1994) Skartveit A. and Olseth J.A., Solar Energy, 52, pp 391-399. From a spectral radiative transfer model, an algorithm is developed for the conversion of illuminance to different measures of Photo-synthetically Active Radiation PAR (in Wm-2 or in mEm-2s-1). This illuminance to PAR conversion may even be used in combination with a luminous efficacy model and thus form a photosynthetic efficacy model. In this work, two luminous efficacy models are chosen, one empirical and one derived from the above radiative transfer model. Observed PAR energy flux and PAR photon flux from 7 Nordic stations (56-70°N) and illuminance from one U.S. station (43°N) are, together with observed all-wave solar irradiance from all stations, used for verification. Observed and modeled luminous efficacies agree on the average within 1% at high solar elevation under cloudless sky, while it is indicated that the illuminance, PAR energy flux, and PAR photon flux radiometers are mutually inconsistent by some 6-16%. Even differences in cosine response between radiometer types are apparent at low solar elevation under cloudless sky. In the present climates, the global radiation efficacy is 10-12% higher under an average cloudless atmosphere than it is outside the atmosphere. By introducing an average cloud deck in this cloudless atmosphere, a further efficacy increase slightly exceeding these 10-12% is observed. However, observations indicate that the cloud transmittance algorithm used in the radiative transfer model significantly overestimates the global radiation efficacy increase caused by horizontally inhomogeneous cloud decks. Solar Irradiance Estimation from Geostationary Satellite Data: I. Statistical Models. (1993) Noia M., Ratto C. F., Festa R., II. Physical Models, Solar Energy, 51, pp 449-465. Modeling daylight illuminance and photosynthetic active irradiance. (1993) Olseth J.A. and Skartveit A., Harmony With Nature - Ises , Solar World Congress 1993, Budapest, Vol. 2, pp 143-148. From a spectral radiative transfer model, an algorithm is developed for the conversion of illuminance to different measures of Photo-synthetically Active Radiation PAR). This illuminance to PAR conversion may even be used in combination with a luminous efficacy model and thus form a photosynthetic efficacy model. In this work two luminous efficacy models are chosen, one empirical and one derived from the above radiative transfer model. Observed global illuminance, PAR energy flux, PAR photon flux, and all-wave solar irradiance from 7 Nordic and one U.S. station (43-70°N) are used for verification. All weather model for sky luminance distribution, preliminary configuration and validation. (1993) Perez R., Seals R. and Michalsky J., Solar Energy, 50, N°3, pp. 235-245. Climatic data handbook for Europe. (1992) Bourges B. Editor, Kluwer Academic Publishers, 281 pages. Models for estimating solar irradiation and illumination - Energy Conservation in Buildings. (1990) Olseth J.A. and Skartveit A., Proc. NORTH SUN 90 International Solar Energy Conference, Reading, pp 193-198. There is an increasing demand for detailed data on irradiance and illuminance on hourly basis both for horizontal and for sloping surfaces. This paper describes models for estimating these detailed data from long-term global irradiation and also presents examples of how these models are used to produce the required detailed data for the Norwegian solar energy community. Modeling daylight availability and irradiance components from direct and global irradiance. (1990) Perez R., Ineichen P., Seals R., Michalsky J. and Stewart R., Solar Energy Conference, 44, N°5, pp 271-289. This paper presents the latest versions of several models developed by the authors to predict short time-step solar energy and daylight availability quantities needed by energy system modelers or building designers. The modeled quantities are global, direct and diffuse daylight illuminance, diffuse irradiance and illuminance impinging on tilted surfaces of arbitrary orientation, sky zenith luminance and sky luminance angular distribution. All models share a common operating structure and a common set of input data: hourly (or higher frequency), direct (or diffuse) and global irradiance plus surface dew point temperature. Key experimental observations leading to model development are briefly reviewed. Comprehensive validation results are presented. Model accuracy assessed in terms of root mean square and mean bias errors, is analyzed both as a function of insolation conditions and site climatic environment. Revised optical air mass tables and approximation formula. (1989) Kasten F. and Young A.T., Applied Optics, 28, pp 4735-4738. Observed and modelled hourly luminous efficacies under arbitrary cloudiness. (1989) Olseth J.A. and Skartveit A., Solar Energy, 42, pp 221-233. The luminous efficacy of solar irradiance under cloudless sky is evaluated by a spectral radiative transfer model. Based on model runs with input data from Bergen, Norway, the beam and diffuse luminous efficacies are parameterized for the cloudless case in terms of solar elevation and day number of the year. The luminous efficacy under an unbroken cloud cover is evaluated by a combination of the cloudless model and an overcast radiative transfer model, and then parameterized in terms of solar elevation and clearness index. Based on a physical argument an overall model is finally presented, yielding the luminous efficacy at arbitrary cloud conditions by a tuned interpolation between the efficacies for the overcast and the cloudless case. This model yields deviations from observations that are small relative to the luminous efficacy variations caused by variations in solar elevation and cloudiness. Hourly illuminance modelled from global irradiance, Daylight and Solar Radiation Measurements. (1989) Olseth J.A. and Skartveit A., Proc. CIE-WMO International Symposium, Berlin, pp 272-281. A simulation of daylight availability in buildings requires daylight data that are most often not available, at least this is the case in Norway. The possibility of estimating daylight illuminance from prescribed luminous efficacies and observed (or even estimated) global irradiance is therefore a tempting one, since irradiance data are far more abundant than illuminance data. In this paper, a model for estimating illuminance from irradiance data is described. Measurements of the luminous efficacy of daylight. (1988) Littlefair P.J., Lighting Research & Technology, 20 (4) pp 177-188. A model for the diffuse fraction of hourly global radiation. (1987) Skartveit A. and Olseth J.A., Solar Energy, 38, pp 271-274. Hourly values of diffuse and global irradiance are often required in cases where, at best, only global irradiance is available. For use in the evaluation of the climatological potential for solar energy utilization in Norway, an analytical model is proposed expressing the hourly diffuse fraction of global irradiance in terms of hourly solar elevation and clearness index. This model, developed for average snow-free close to sea level conditions in Norway fairly well fits the average picture of an extensive independent data base. Simple solar spectral model for direct and diffuse irradiance on horizontal and tilted planes at the earth's surface for cloudless atmospheres. (1986) Bird R.E. and Riordan C., J. Climate Appl. Meteor., 25, 87. Modeling slope irradiance at high latitudes. (1986) Skartveit A. and Olseth J.A., Solar Energy, 36, pp 333-344. Irradiance on slopes is often required in cases where it is not directly measured and, consequently, has to be modelled from alternative data. In this paper three models for the derivation of hourly slope irradiance from hourly horizontal beam and diffuse sky irradiances are tested against 5 years of recorded slope irradiances at Bergen (60o24'N, 5o19'E). The test demonstrated the importance of accounting for sky radiance anisotropy both at overcast and cloudless weather. Moreover, a stepwise procedure for the derivation of long-term mean slope irradiance from various kinds of input data is outlined. Testing against observations demonstrated that, except for steeply south-facing slopes at low mid-winter sun, long-term slope irradiance is derived with reasonably accuracy from mean cloudiness. Moreover, observed horizontal irradiances, wheter global or beam and diffuse, as input data yield satisfactory accuracy throughout the year on all slopes. The luminous efficacy of daylight: a review. (1985) Littlefair P.J., Lighting Research & Technology, 17 (4) pp 162-182. Luminance distribution of intermediate sky. (1985) Nakamura H., Oki M. and Hayashi Y., Journal of Light and Visual Environment, 9, N°1, pp 6-13. A short-wave parameterization revised to improve cloud absorption. (1984) Stephens G.L., Ackerman S. and E.A. Smith, J. Atmos. Sci., 41, 687. Study of shortwave radiation on non-horizontal surfaces. (1979) Hay J.E., Report N°79-12, Atmospheric Environment Service, Downsview, Ontario. Correlation equation for hourly diffuse radiation on a horizontal surface. (1977) Skartveit A. and Olseth J.A., Solar Energy, 19, pp 357-359.