Multispectral imaging is a powerful technique which allows to retrieve a large amount of spectroradiometric information and can be advantageously exploited in solar energy field. In particular, in Concentrated Photovoltaic (CPV) systems the angular acceptance is usually limited to few degrees and thus the modules has to be moved in such a way to be always aligned to the sun direction. In that, the indication of the tracking error the is an important parameter to assess the electronics and mechanical design of the sun tracker. Another fundamental parameter is given by the direct normal irradiance, which is usually measured by means of a pyroeliometer. Here we present the design guidelines, the realization steps and the characterization of a multi-spectral camera which has been tailored to be used a accuracy measurement device for sun trackers, capable of single-wavelength and wide band spectroradiometric measurements. Usually the sun-tracking accuracy measurement is carried out by position sensitive devices attached to the moving structure, which cannot be considered reliable as radiometric detectors. As sun intensity changes, the response of wide band detector changes accordingly, but it is not possible to make any type of correction due to modification of the spectral power density, which occurs as the cloud index or air mass ratio changes. Thanks to multispectral imaging it is possible to grab a set of images of the sun during the tracking and calculate with high precision both the angular shift of the structure with respect to the reference direction and the direct normal irradiance under a wide range of climatic conditions.
Measurement of Sun-Tracking Accuracy and Solar Irradiance through Multispectral Imaging
VINCENZI, Donato;BARICORDI, Stefano;STEFANCICH, Marco;PARRETTA, Antonio;MARTINELLI, Giuliano
2010
Abstract
Multispectral imaging is a powerful technique which allows to retrieve a large amount of spectroradiometric information and can be advantageously exploited in solar energy field. In particular, in Concentrated Photovoltaic (CPV) systems the angular acceptance is usually limited to few degrees and thus the modules has to be moved in such a way to be always aligned to the sun direction. In that, the indication of the tracking error the is an important parameter to assess the electronics and mechanical design of the sun tracker. Another fundamental parameter is given by the direct normal irradiance, which is usually measured by means of a pyroeliometer. Here we present the design guidelines, the realization steps and the characterization of a multi-spectral camera which has been tailored to be used a accuracy measurement device for sun trackers, capable of single-wavelength and wide band spectroradiometric measurements. Usually the sun-tracking accuracy measurement is carried out by position sensitive devices attached to the moving structure, which cannot be considered reliable as radiometric detectors. As sun intensity changes, the response of wide band detector changes accordingly, but it is not possible to make any type of correction due to modification of the spectral power density, which occurs as the cloud index or air mass ratio changes. Thanks to multispectral imaging it is possible to grab a set of images of the sun during the tracking and calculate with high precision both the angular shift of the structure with respect to the reference direction and the direct normal irradiance under a wide range of climatic conditions.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
