We introduce and discuss the design of lowconcentrating optics for trackless PV modules, to be coupled to high-performance silicon cells, to leverage their economical competitiveness. Aiming at high compatibility with standard installation infrastructures and high energy rating, the leading design rules are the minimization of the aspect ratio of the concentrator and the maximization of the optical collection efficiency for sunlight, whilst accounting for the daily and yearly evolution in the relative orientation of the PV module and the sun. A ray-tracing numerical simulator was used for the design. The result is a prismatic 2D concentrator unit, which features a geometrical gain G = 2 and more than 82% in yearly averaged effective optical performance ratio, if supposed operated in Southern Europe environment, comprising the contribution given by diffused light. The optimized aspect ratio of concentrating optics measures ~ 0.27. The prismatic shape of the concentrator can be slightly tuned, to address different orientation in the installation, without impairing the optical performance. The maximization of the effective optical performance ratio contributes to lower the Levelized Cost of Electricity for this solution, what supports the market sustainability of the present approach to trackless LCPV.