NOVELTY - A solar concentrator comprises solar cell(s) comprising a front surface (21); and an optical system concentrating solar radiation towards the solar cell, and comprising an optical stepped lens having a front surface for receiving the solar radiation and an opposite rear surface (22) facing the front surface of the solar cell.    USE - A solar concentrator.    ADVANTAGE - The concentrator has stepped profile, and minimizes the effects of possible roundness.    DETAILED DESCRIPTION - A solar concentrator comprises:    (A) solar cell(s) comprising a front surface (21); and    (B) an optical system concentrating solar radiation towards the solar cell, and comprising an optical stepped lens having a front surface for receiving the solar radiation and an opposite rear surface (22) facing the front surface of the solar cell.    The rear surface has a stepped profile defining stepped structures (24) in a cross-sectional plane of the lens; and formed by a slope facet and a draft each having different inclinations. The slope facet extends for a first length in the cross-sectional plane and the draft facet extends for a second length in the cross-sectional plane. The front surface of the lens comprises lenticular converging elements having a first and a second peripheral edge. The lenticular element (23) lies opposite to a corresponding stepped structure and is configured so that a first ray incident on the first edge of the lenticular element along a first incident direction lying in the cross-sectional plane passes through the lens while being refracted to impinge on the slope facet of the respective stepped structure at a first intercept point, and a second ray parallel to the first ray and incident on the second edge of the lenticular element passes through the lens while being refracted to impinge on the slope facet of the corresponding stepped structure at a second intercept point. The slope portion in the cross-sectional plane extends within the first length and defines a focalization region of the stepped structure. An INDEPENDENT CLAIM is included for optical lens.    DESCRIPTION OF DRAWING(S) - The drawing is a cross-sectional schematic view of a refractive Fresnel lens.    Impinging radiation (20)    Front surface (21)    Rear surface (22)    Lenticular element (23)    Stepped structures (24)