A solar cell unit, comprising a solar cell with a light receiving surface, and a transparent optical element frictionally connected to the receiving surface. The optical element having a portion of surface formed substantially convex such that sunlight striking the receiving surface is bundled by the convex receiving surface. The light receiving surface is surrounded by a shoulder-shaped ledge that has a first rim surface and a second rim surface. A first alignment mark is provided in association with the first rim surface and a second alignment mark is provided in association with the second rim surface to position the optical element in regard to the receiving surface of the solar cell via the two alignment marks. The first alignment mark being spaced apart from the second alignment mark in order to guide the incident sunlight totally or at least largely to the receiving surface.