System for measuring the intensity of solar radiation consisting of a polyhedral solar sensor comprising: - a plurality of sensors (13a to 13m) each suitable for detecting the intensity of the solar radiation reaching it, - a support shaped to house said sensors (13a to 13m) in such a way that: a first group of sensors (13a to 13f) is arranged with a sensor on each face of a polyhedron with a first sensor which is arranged in an upper central face oriented upwards of said support, second sensors (13b to 13f) being arranged on lateral faces of said oriented polyhedron inclined upwards with a same elevation angle and angularly equidistant in the azimuthal plane; a second group of sensors (13g to 13m) in which the sensors are arranged angularly equidistant from each other in the azimuthal plane, - an integrated processor electrically and / or electronically connected to said plurality of sensors (13a to 13m) to receive from each of said sensors data pertaining to the intensity of the solar radiation detected by it and to process said data to determine at least the intensity of global solar radiation, the intensity of direct solar radiation and the intensity of diffused solar radiation, said solar radiation measurement system being characterized in that each of said sensors (13a to 13m) is arranged to measure separately in at least three different bands, the sensors of said second group of sensors (13g to 13m) being arranged vertically, said processor being configured for processing said data according to a predictive neural network scheme in which said sensors (13a to 13m) constitute input nodes of said neural network, said neural network being guided by an analytical algorithm suitable for scaling the measurements of said sensors (13a to 13m) based on coefficients defined by a geometric projection model of the point light source that is the sun on the faces of the polyhedral solar sensor itself, and said processor being configured for determining the intensity of the solar radiation reflected by the ground based on the value of the diffused solar radiation and based on the intensity of the radiation detected by said second group of sensors (13g to 13m) by comparing the differences in the intensity detected by a same sensor in said at least three different bands. - a plurality of sensors (13a to 13m) each suitable for detecting the intensity of the solar radiation reaching it, - a support shaped to house said sensors (13a to 13m) in such a way that: a first group of sensors (13a to 13f) is arranged with a sensor on each face of a polyhedron with a first sensor which is arranged in an upper central face oriented upwards of said support, second sensors (13b to 13f) being arranged on lateral faces of said oriented polyhedron inclined upwards with a same elevation angle and angularly equidistant in the azimuthal plane; a second group of sensors (13g to 13m) in which the sensors are arranged angularly equidistant from each other in the azimuthal plane, - an integrated processor electrically and / or electronically connected to said plurality of sensors (13a to 13m) to receive from each of said sensors data pertaining to the intensity of the solar radiation detected by it and to process said data to determine at least the intensity of global solar radiation, the intensity of direct solar radiation and the intensity of diffused solar radiation,