Context and challenges Radiance is the density of power received on a plane from a given direction. Irradiance is the angular integral of radiances on the portion of sky vault seen by the plane. Distribution of radiances is not uniform. The radiance is a function of the azimut and elevation for an observer. It is the greatest in the direction of the sun and decreases towards the horizon; it varies very rapidly in the vicinity of the sun direction. Several systems converting solar radiation into energy exhibit limited angular aperture and comprise a device for tracking the sun, such as thermodynamical concentrating systems or concentrated photovoltaic systems. Pyrheliometers that measure the beam irradiance have similar characteristics. The irradiance received by such systems is presently not well modelled. A more accurate description and modelling of the radiances should yield a better assessment of the solar radiation available for energy conversion. It will be a first step towards the modelling of radiances for all skies. Scientific objectives The objectives of the thesis are firstly to define a method for the fast simulation of the distribution of radiances on the sky vault as a function of the optical state of the clear atmosphere, and then to develop and validate a model of this distribution. Emphasis is put on the beam and circumsolar radiation. Methodology The student will get acquainted with atmosphere optics via literature analysis and with the libRadtran radiative transfer model. Several simulations will be performed with libRadtran in order to define the order of magnitude of the influence of each input on the output. This will be done by taking into account the statistical distribution observed worldwide for each input. The student will analyse the results and will design and implement a method for a fast simulation of radiances as a function of the optical state of the clear atmosphere. The resulting distribution will be analysed and compared to measurements made by other institutes, such as école nationale des travaux publics de létat (ENTPE) or LENS (Laboratory for Energy and Nano Science) of Masdar Institute of Science and Technology, and to existing models. The assessment protocol will be defined; measurements will be collected and scrutinized before their use. Analyses of results will yield proposals for improvements of existing models or new models. A validation of the new model will be performed against measurements, especially those made by pyrheliometers for measuring beam radiation. Eventually, the student will develop a model accepting any angular aperture as input to simulate irradiance received by any concentrating system defined by an aperture angle and a sun-tracking device. The climate of interest is desert. The student will analyse the possibility of extending the models to other climates. Expected results The research will yield a numerical tool predicting the distribution of radiances on sky vault and the beam irradiance as a function of the optical state of the clear atmosphere. This tool will be further used to simulate radiances that could be concentrated for energy production by systems of parabol or trough type, or Fresnel lens.
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